Publications by authors named "Tobias Götschi"

40 Publications

Shear-stress sensing by PIEZO1 regulates tendon stiffness in rodents and influences jumping performance in humans.

Nat Biomed Eng 2021 May 24. Epub 2021 May 24.

University Hospital Balgrist, University of Zurich, Zurich, Switzerland.

Athletic performance relies on tendons, which enable movement by transferring forces from muscles to the skeleton. Yet, how load-bearing structures in tendons sense and adapt to physical demands is not understood. Here, by performing calcium (Ca) imaging in mechanically loaded tendon explants from rats and in primary tendon cells from rats and humans, we show that tenocytes detect mechanical forces through the mechanosensitive ion channel PIEZO1, which senses shear stresses induced by collagen-fibre sliding. Through tenocyte-targeted loss-of-function and gain-of-function experiments in rodents, we show that reduced PIEZO1 activity decreased tendon stiffness and that elevated PIEZO1 mechanosignalling increased tendon stiffness and strength, seemingly through upregulated collagen cross-linking. We also show that humans carrying the PIEZO1 E756del gain-of-function mutation display a 13.2% average increase in normalized jumping height, presumably due to a higher rate of force generation or to the release of a larger amount of stored elastic energy. Further understanding of the PIEZO1-mediated mechanoregulation of tendon stiffness should aid research on musculoskeletal medicine and on sports performance.
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http://dx.doi.org/10.1038/s41551-021-00716-xDOI Listing
May 2021

Augmented reality in the operating room: a clinical feasibility study.

BMC Musculoskelet Disord 2021 May 18;22(1):451. Epub 2021 May 18.

Spine Division, University Hospital Balgrist, University of Zürich, Forchstrasse 340, 8008, Zurich, Switzerland.

Background: Augmented Reality (AR) is a rapidly emerging technology finding growing acceptance and application in different fields of surgery. Various studies have been performed evaluating the precision and accuracy of AR guided navigation. This study investigates the feasibility of a commercially available AR head mounted device during orthopedic surgery.

Methods: Thirteen orthopedic surgeons from a Swiss university clinic performed 25 orthopedic surgical procedures wearing a holographic AR headset (HoloLens, Microsoft, Redmond, WA, USA) providing complementary three-dimensional, patient specific anatomic information. The surgeon's experience of using the device during surgery was recorded using a standardized 58-item questionnaire grading different aspects on a 100-point scale with anchor statements.

Results: Surgeons were generally satisfied with image quality (85 ± 17 points) and accuracy of the virtual objects (84 ± 19 point). Wearing the AR device was rated as fairly comfortable (79 ± 13 points). Functionality of voice commands (68 ± 20 points) and gestures (66 ± 20 points) provided less favorable results. The greatest potential in the use of the AR device was found for surgical correction of deformities (87 ± 15 points). Overall, surgeons were satisfied with the application of this novel technology (78 ± 20 points) and future access to it was demanded (75 ± 22 points).

Conclusion: AR is a rapidly evolving technology with large potential in different surgical settings, offering the opportunity to provide a compact, low cost alternative requiring a minimum of infrastructure compared to conventional navigation systems. While surgeons where generally satisfied with image quality of the here tested head mounted AR device, some technical and ergonomic shortcomings were pointed out. This study serves as a proof of concept for the use of an AR head mounted device in a real-world sterile setting in orthopedic surgery.
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http://dx.doi.org/10.1186/s12891-021-04339-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8132365PMC
May 2021

Augmented Reality Navigated Sacral-Alar-Iliac Screw Insertion.

Int J Spine Surg 2021 Feb 18;15(1):161-168. Epub 2021 Feb 18.

Department of Orthopedics, University Hospital Balgrist, University of Zürich, Zürich, Switzerland.

Background: Sacral-alar-iliac (SAI) screws are increasingly used for lumbo-pelvic fixation procedures. Insertion of SAI screws is technically challenging, and surgeons often rely on costly and time-consuming navigation systems. We investigated the accuracy and precision of an augmented reality (AR)-based and commercially available head-mounted device requiring minimal infrastructure.

Methods: A pelvic sawbone model served to drill pilot holes of 80 SAI screw trajectories by 2 surgeons, randomly either freehand (FH) without any kind of navigation or with AR navigation. The number of primary pilot hole perforations, simulated screw perforation, minimal axis/outer cortical wall distance, true sagittal cranio-caudal inclination angle (tSCCIA), true axial medio-lateral angle, and maximal screw length (MSL) were measured and compared to predefined optimal values.

Results: In total, 1/40 (2.5%) of AR-navigated screw hole trajectories showed a perforation before passing the inferior gluteal line compared to 24/40 (60%) of FH screw hole trajectories ( < .05). The differences between FH- and AR-guided holes compared to optimal values were significant for tSCCIA with -10.8° ± 11.77° and MSL -65.29 ± 15 mm vs 55.04 ± 6.76 mm ( = .001).

Conclusions: In this study, the additional anatomical information provided by the AR headset and the superimposed operative plan improved the precision of drilling pilot holes for SAI screws in a laboratory setting compared to the conventional FH technique. Further technical development and validation studies are currently being performed to investigate potential clinical benefits of the AR-based navigation approach described here.

Level Of Evidence: 4.
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http://dx.doi.org/10.14444/8021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7931709PMC
February 2021

The quantitative influence of current treatment options on patellofemoral stability in patients with trochlear dysplasia and symptomatic patellofemoral instability - a finite element simulation.

Clin Biomech (Bristol, Avon) 2021 Apr 27;84:105340. Epub 2021 Mar 27.

Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.

Background: Trochlear dysplasia is highly associated with patellofemoral instability. The goal of conservative and surgical treatment is to stabilize the patella while minimizing adverse effects. However, there is no literature investigating the quantitative influence of different treatment options on patellofemoral stability in knees with trochlear dysplasia. We created and exploited a range of finite element models to address this gap in knowledge.

Methods: MRI data of 5 knees with trochlear dysplasia and symptomatic patellofemoral instability were adapted into this previously established model. Vastus medialis obliquus strengthening as well as double-bundle medial patellofemoral ligament reconstruction and the combination of medial patellofemoral ligament reconstruction and trochleoplasty were simulated. The force necessary to dislocate the patella by 10 mm and fully dislocate the patella was calculated in different flexion angles.

Findings: Our model predicts a significant increase of patellofemoral stability at the investigated flexion angles (0°-45°) for a dislocation of 10 mm and a full dislocation after medial patellofemoral ligament reconstruction and the combination of medial patellofemoral ligament reconstruction and trochleoplasty compared to trochleodysplastic (P = 0.01) and healthy knees (P = 0.01-0.02). Vastus medialis obliquus strengthening has a negligible effect on patellofemoral stability.

Interpretations: This is the first objective quantitative biomechanical evidence supporting the place of medial patellofemoral ligament reconstruction and medial patellofemoral ligament reconstruction combined with trochleoplasty in patients with symptomatic patellofemoral instability and trochlear dysplasia type B. Vastus medialis obliquus strengthening has a negligible effect on patellar stability at a low total quadriceps load of 175 N.
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http://dx.doi.org/10.1016/j.clinbiomech.2021.105340DOI Listing
April 2021

Region- and degeneration dependent stiffness distribution in intervertebral discs derived by shear wave elastography.

J Biomech 2021 May 24;121:110395. Epub 2021 Mar 24.

Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland.

Information on the local stiffness characteristics of the intervertebral disc (IVD) is crucial for the understanding of its structure-function properties in health and disease and may improve numerical modeling. Previous studies have attempted to map local tissue stiffness by sectioning the disc and performing mechanical testing on these discrete tissue units, which is technically challenging and may bias the results. Shear wave elastography (SWE) represents a nondestructive alternative that can provide spatially continuous elasticity estimates. We investigated the feasibility of SWE for human intervertebral disc elasticity mapping in a laboratory setting. To this end, global spinal segment mechanical behavior was determined in 6 loading directions and served as ground truth data for the validation of the approach. Subsequently, the cranial spinal vertebra was removed and shear wave elastographic scans of the IVD were acquired. SWE-measurements were reconstructed into three-dimensional elastographic maps, discretized into distinct IVD regions and correlated with global segment mechanical parameters. SWE-derived Young's modulus estimates were compared among different regions and as a function of their state of degeneration. We found annulus shear wave speed to be moderately correlated with segment mechanical behavior irrespective of the loading direction whereas shear wave speed in the nucleus pulposus showed a very weak association (mean (SD) absolute Pearson correlation coefficients: 0.51 (0.14) and 0.17 (0.12), respectively). Young's modulus mapping of the intervertebral disc revealed stiffness to be highest in the ventral annulus with a stiffness decrease both circumferentially towards the dorsal aspect as well as towards the center of the disc. SWE hence provides a valid alternative to disc sectioning and piecewise mechanical testing.
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http://dx.doi.org/10.1016/j.jbiomech.2021.110395DOI Listing
May 2021

Similar scapular morphology in patients with dynamic and static posterior shoulder instability.

JSES Int 2021 Mar 15;5(2):181-189. Epub 2021 Jan 15.

Department of Orthopaedic Surgery, University of Zürich, Balgrist University Hospital, Zürich, Switzerland.

Background: There is evidence that specific variants of scapular morphology are associated with dynamic and static posterior shoulder instability. To this date, observations regarding glenoid and/or acromial variants were analyzed independently, with two-dimensional imaging or without comparison with a healthy control group. Therefore, the purpose of this study was to analyze and describe the three-dimensional (3D) shape of the scapula in healthy and in shoulders with static or dynamic posterior instability using 3D surface models and 3D measurement methods.

Methods: In this study, 30 patients with unidirectional posterior instability and 20 patients with static posterior humeral head subluxation (static posterior instability, Walch B1) were analyzed. Both cohorts were compared with a control group of 40 patients with stable, centered shoulders and without any clinical symptoms. 3D surface models were obtained through segmentation of computed tomography images and 3D measurements were performed for glenoid (version and inclination) and acromion (tilt, coverage, height).

Results: Overall, the scapulae of patients with dynamic and static instability differed only marginally among themselves. Compared with the control group, the glenoid was 2.5° ( = .032), respectively, 5.7° ( = .001) more retroverted and 2.9° ( = .025), respectively, 3.7° ( = .014) more downward tilted in dynamic, respectively, static instability. The acromial roof of dynamic instability was significantly higher and on average 6.2° ( = .007) less posterior covering with an increased posterior acromial height of +4.8mm ( = .001). The acromial roof of static instability was on average 4.8° ( = .041) more externally rotated (axial tilt), 7.3° ( = .004) flatter (sagittal tilt), 8.3° ( = .001) less posterior covered with an increased posterior acromial height of +5.8 mm (0.001).

Conclusion: The scapula of shoulders with dynamic and static posterior instability is characterized by an increased glenoid retroversion and an acromion that is shorter posterolaterally, higher, and more horizontal in the sagittal plane. All these deviations from the normal scapula values were more pronounced in static posterior instability.
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http://dx.doi.org/10.1016/j.jseint.2020.11.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7910728PMC
March 2021

Three-Dimensional Mapping of Shear Wave Velocity in Human Tendon: A Proof of Concept Study.

Sensors (Basel) 2021 Feb 27;21(5). Epub 2021 Feb 27.

Sports Medical Research Group, Department of Orthopaedics, Balgrist University Hospital, University of Zurich, 8008 Zurich, Switzerland.

Ultrasound-based shear wave elastography (SWE) provides the means to quantify tissue mechanical properties in vivo and has proven valuable in detecting degenerative processes in tendons. Its current mode of use is for two-dimensional rendering measurements, which are highly position-dependent. We therefore propose an approach to create a volumetric reconstruction of the mechano-acoustic properties of a structure of interest based on optically tracking the ultrasound probe during free-hand measurement sweeps. In the current work, we aimed (1) to assess the technical feasibility of the three-dimensional mapping of unidirectional shear wave velocity (SWV), (2) to evaluate the possible artefacts associated with hand-held image acquisition, (3) to investigate the reproducibility of the proposed technique, and (4) to study the potential of this method in detecting local adaptations in a longitudinal study setting. Operative and technical feasibility as well as potential artefacts associated with hand-held image acquisition were studied on a synthetic phantom containing discrete targets of known mechanical properties. Measurement reproducibility was assessed based on inter-day and inter-reader scans of the patellar, Achilles, and supraspinatus tendon of ten healthy volunteers and was compared to traditional two-dimensional image acquisition. The potential of this method in detecting local adaptations was studied by testing the effect of short-term voluntary isometric loading history on SWV along the tendon long axis. The suggested approach was technically feasible and reproducible, with a moderate to very good reliability and a standard error of measurement in the range of 0.300-0.591 m/s for the three assessed tendons at the two test-retest modalities. We found a consistent variation in SWV along the longitudinal axis of each tendon, and isometric loading resulted in regional increases in SWV in the patellar and Achilles tendons. The proposed method outperforms traditional two-dimensional measurement with regards to reproducibility and may prove valuable in the objective assessment of pathological tendon changes.
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http://dx.doi.org/10.3390/s21051655DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7957754PMC
February 2021

Inter-rater variability of three-dimensional fracture reduction planning according to the educational background.

J Orthop Surg Res 2021 Feb 25;16(1):159. Epub 2021 Feb 25.

Research in Orthopedic Computer Science (ROCS), Balgrist University Hospital, University of Zurich, Balgrist CAMPUS, Zurich, Switzerland.

Background: Computer-assisted three-dimensional (3D) planning is increasingly delegated to biomedical engineers. So far, the described fracture reduction approaches rely strongly on the performance of the users. The goal of our study was to analyze the influence of the two different professional backgrounds (technical and medical) and skill levels regarding the reliability of the proposed planning method. Finally, a new fragment displacement measurement method was introduced due to the lack of consistent methods in the literature.

Methods: 3D bone models of 20 distal radius fractures were presented to nine raters with different educational backgrounds (medical and technical) and various levels of experience in 3D operation planning (0 to 10 years) and clinical experience (1.5 to 24 years). Each rater was asked to perform the fracture reduction on 3D planning software.

Results: No difference was demonstrated in reduction accuracy regarding rotational (p = 1.000) and translational (p = 0.263) misalignment of the fragments between biomedical engineers and senior orthopedic residents. However, a significantly more accurate planning was performed in these two groups compared with junior orthopedic residents with less clinical experience and no 3D planning experience (p < 0.05).

Conclusion: Experience in 3D operation planning and clinical experience are relevant factors to plan an intra-articular fragment reduction of the distal radius. However, no difference was observed regarding the educational background (medical vs. technical) between biomedical engineers and senior orthopedic residents. Therefore, our results support the further development of computer-assisted surgery planning by biomedical engineers. Additionally, the introduced fragment displacement measure proves to be a feasible and reliable method.

Level Of Evidence: Diagnostic Level II.
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http://dx.doi.org/10.1186/s13018-021-02312-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7905543PMC
February 2021

No difference in long-term outcome between open and arthroscopic rotator cuff repair: a prospective, randomized study.

JSES Int 2020 Dec 18;4(4):818-825. Epub 2020 Sep 18.

Department of Orthopaedics, Balgrist University Hospital, Zürich, Switzerland.

Background: Arthroscopic rotator cuff repair techniques have almost replaced open repairs. Short- and mid-term studies have shown comparable outcomes, with no clear superiority of either procedure. The aim of this study was to compare the long-term clinical and imaging outcomes following arthroscopic or open rotator cuff repair.

Methods: Forty patients with magnetic resonance imaging (MRI)-documented, symptomatic supraspinatus or supraspinatus and infraspinatus tears were randomized to undergo arthroscopic or open rotator cuff repair. Clinical and radiographic follow-up was obtained at 6 weeks, 3 months, 1 year, 2 years, and >10 years postoperatively. Clinical assessment included measurement of active range of motion, visual analog scale score for pain, functional scoring according to the Constant-Murley score (CS), and assessment of the Subjective Shoulder Value. Imaging included conventional radiography and MRI for the assessment of cuff integrity and alteration of the deltoid muscle.

Results: We enrolled 20 patients with a mean age of 60 years (range, 50-71 years; standard deviation [SD], 6 years) in the arthroscopic surgery group and 20 patients with a mean age of 55 years (range, 39-67 years; SD, 8 years) in the open surgery group. More than 10 years' follow-up was available for 13 patients in the arthroscopic surgery group and 11 patients in the open surgery group, with mean follow-up periods of 13.8 years (range, 11.9-15.2 years; SD, 1.1 years) and 13.1 years (range, 11.7-15 years; SD, 1.1 years), respectively. No statistically significant differences in clinical outcomes were identified between the 2 groups: The median absolute CS was 79 points (range, 14-84 points) in the arthroscopic surgery group and 84 points (range, 56-90 points) in the open surgery group ( = .177). The median relative CS was 94% (range, 20%-99%) and 96% (range, 65%-111%), respectively ( = .429). The median Subjective Shoulder Value was 93% (range, 20%-100%) and 93% (range, 10%-100%), respectively ( = .976). MRI evaluation showed a retear rate of 30% equally distributed between the 2 groups. Neither fatty infiltration of the deltoid muscle, deltoid muscle volume, nor the deltoid origin were different between the 2 groups.

Conclusion: In a small cohort of patients, we could not document any difference in clinical and radiographic outcomes at long-term follow-up between arthroscopic and open rotator cuff repair. The postulated harm to the deltoid muscle with the open technique could not be confirmed.
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http://dx.doi.org/10.1016/j.jseint.2020.08.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7738583PMC
December 2020

Biomechanical and Clinical Evaluation of the Optimal Arm Position After Rotator Cuff Surgery With an Adjustable Abduction Brace.

Orthopedics 2021 Jan 15;44(1):e1-e6. Epub 2020 Dec 15.

Abduction braces are used with the intention of relieving tension on the supraspinatus, thereby protecting an operative repair. It is not known, however, whether patients wearing a brace do deposit the weight of the arm on the brace effectively or actively stabilize the arm despite the brace. It is further unknown what position of the arm is most effective to relax the shoulder and is considered most comfortable. Twenty-two patients who had undergone an arthroscopic supraspinatus repair were postoperatively fitted with a standard abduction brace equipped with a torque sensor to measure the weight of the arm on the brace on the first and second postoperative days. The most comfortable arm position, tear size, and degenerative muscular changes on magnetic resonance imaging were assessed. Most patients (15 vs 5) preferred a low angle of abduction with the brace in the scapular rather than the true frontal plane irrespective of tear location or size. While loads applied to the brace were slightly higher at high abduction angles (70° and 90°) under regional anesthesia (day 1), they were significantly higher at low abduction angles (30° and 50°) with the arm fully awake (day 2). The most comfortable brace position-which is at low angles of abduction (30° to 50°) in the scapular plane-is associated with the highest load transfer to the brace in the unanesthetized arm. The authors therefore conclude that if an abduction brace is used, it should be fitted in the scapular plane with an abduction angle between 30° and 50°. [Orthopedics. 2021;44(1):e1-e6.].
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http://dx.doi.org/10.3928/01477447-20201210-01DOI Listing
January 2021

Os Acromiale in Reverse Total Shoulder Arthroplasty: A Cohort Study.

Orthop J Sports Med 2020 Nov 24;8(11):2325967120965131. Epub 2020 Nov 24.

Department of Orthopedics, Balgrist University Hospital, University of Zürich, Zürich, Switzerland.

Background: Increased passive deltoid tension after reverse total shoulder arthroplasty (RTSA) potentially leads to displacement or tilting of a preexisting os acromiale.

Purpose: To analyze patients with an os acromiale who underwent RTSA and compare their outcomes and complications with a matched control group without an os acromiale.

Study Design: Cohort study; Level of evidence, 3.

Methods: In this study, 45 shoulders in 42 patients with an os acromiale (cases) were matched to 133 patients without os acromiale (controls) who underwent RTSA between 2005 and 2016. The mean follow-up was 52 ± 32 months. Matching criteria included sex, type of surgery, duration of follow-up, and age. The Constant score (CS), Subjective Shoulder Value (SSV), and radiological outcomes were assessed postoperatively at 1-year, 2-year, and final follow-up visits.

Results: The mean CS, SSV, and range of motion improved from preoperative levels to the final follow-up in both groups ( < .01). Patients with an os acromiale had a relative CS of 70 ± 23 versus 76 ± 21 points ( = .15) and an SSV of 70 ± 30 versus 73 ± 24 ( = .52) compared with controls at the final follow-up visit. Patients with an os acromiale had significantly decreased active flexion of 104° ± 33° versus 114° ± 33° ( = .03) at 1 year and active abduction of 103° ± 37° versus 121° ± 38° at 2 years postoperatively ( = .02). A postoperatively painful os acromiale was found in 12 cases (27%) and spontaneously resolved in 8 cases after a mean of 33 months (range, 12-47 months; = .04).

Conclusion: RTSA reliably restores patient satisfaction despite the presence of an os acromiale, with a slightly impaired range of motion. Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients, but this resolves spontaneously over time in the majority of patients.
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http://dx.doi.org/10.1177/2325967120965131DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7705793PMC
November 2020

Treatment of hindfoot and ankle infections with Ilizarov external fixator or spacer, followed by secondary arthrodesis.

J Orthop Res 2020 Dec 6. Epub 2020 Dec 6.

Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich, Switzerland.

An established treatment strategy in surgical site infection after hindfoot and ankle surgery is a two-stage procedure with debridement and placement of a cement spacer, followed by antibiotic treatment and secondary arthrodesis. However, there is little evidence to favor this treatment over a one-stage procedure with debridement, followed by primary arthrodesis with an Ilizarov external fixator and antibiotic treatment. We compared the infection control and clinical and radiological outcome of a two-stage and a one-stage procedure. In this study, 7 patients with a two-stage revision and 11 patients with a one-stage revision between 2005 and 2015 were included. The primary outcome was infection control (absence of the Musculoskeletal Infection Society PJI criteria) 2 years after the ankle or hindfoot arthrodesis. Secondary outcome measures were the AOFAS hindfoot score and radiological consolidation rate. Infection control was 85% (6 out of 7 patients) in the two-stage group and 81% (9 out of 11 patients) in the one-stage group (p = 1.0). One patient (14%) of the two-stage and two patients (18%) in the one-stage group needed below-knee amputation. In the two-stage group, the mean postoperative AOFAS score was 74.8 (SD: ±11.3) versus 71.7 (SD: ±17.8) in the one-stage group. Radiological consolidation could be achieved in 71% in the spacer group (n = 5) and in 72% in the Ilizarov external fixator group (n = 9). Infection control, AOFAS score, and radiologic consolidation of hindfoot and ankle arthrodesis were comparable in both groups of patients with complicated postsurgical hindfoot or ankle infections.
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http://dx.doi.org/10.1002/jor.24938DOI Listing
December 2020

Hand or foot train-of-four tests and surgical site muscle relaxation assessed with multiple motor evoked potentials: A prospective observational study.

Eur J Anaesthesiol 2020 Nov 27. Epub 2020 Nov 27.

From the Department of Orthopaedics (MB, TG, RS, JMS, MF), Department of Anaesthesiology, Intensive Care and Pain Medicine (JA, MB) and Spinal Cord Injury Center, Balgrist University Hospital, University of Zurich, Zurich, Switzerland (MS, BH).

Background: Intra-operative muscle relaxation is often required in orthopaedic surgery and the hand train-of-four (TOF) test is usually used for its quantification. However, even though full muscle relaxation is claimed by anaesthesiologists based on a TOF count of zero, surgeons observe residual muscle activity.

Objective: The aim of the study was to assess if hand or foot TOF adequately represents intra-operative muscle relaxation compared with multiple motor evoked potentials.

Design: Prospective observational study.

Setting: A single-centre study performed between February 2016 and December 2018 at the Balgrist University Hospital, Zurich, Switzerland.

Patients: Twenty patients scheduled for elective lumbar spinal fusion were prospectively enrolled in this study after giving written informed consent.

Interventions: To assess neuromuscular blockade (NMB) with the intermediate duration nondepolarising neuromuscular blocking agent rocuronium, hand TOF (adductor pollicis) and foot TOF (flexor hallucis brevis) monitoring, and muscle motor evoked potentials (MMEPs) from the upper and lower extremities were assessed prior to surgery under general anaesthesia. Following baseline measurements, muscle relaxation was performed with rocuronium until the spinal surgeon observed sufficient relaxation for surgical intervention. At this timepoint, NMB was assessed by TOF and MMEP.

Main Outcome Measures: The primary outcome was to determine the different effect of rocuronium on muscle relaxation comparing hand and foot TOF with the paraspinal musculature assessed by MMEP.

Results: Hand TOF was more resistant to NMB and had a shorter recovery time than foot TOF. When comparing MMEPs, muscle relaxation occurred first in the hip abductors, and the paraspinal and deltoid muscles. The most resistant muscle to NMB was the abductor digiti minimi. Direct comparison showed that repetitive MMEPs simultaneously recorded from various muscles at the upper and lower extremities and from paraspinal muscles reflect muscle relaxation similar to TOF testing.

Conclusion: Hand TOF is superior to foot TOF in assessing muscle relaxation during spinal surgery. Hand TOF adequately represents the degree of muscle relaxation not only for the paraspinal muscles but also for all orthopaedic surgical sites where NMB is crucial for good surgical conditions.

Trial Registration: clinicalTrials.gov (NCT03318718).
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http://dx.doi.org/10.1097/EJA.0000000000001398DOI Listing
November 2020

Patellofemoral instability in trochleodysplastic knee joints and the quantitative influence of simulated trochleoplasty - A finite element simulation.

Clin Biomech (Bristol, Avon) 2021 01 9;81:105216. Epub 2020 Nov 9.

Department of Orthopedics, Balgrist University Hospital, Zurich, Switzerland.

Background: Patellofemoral instability is a debilitating condition mainly affecting young patients and has been correlated with trochlear dysplasia. It can occur when the patella is insufficiently guided through its range of motion. Currently, there is no literature describing patellofemoral stability in trochleodysplastic knees and the effect of isolated trochleoplasty on patellofemoral stability.

Methods: The effect of isolated trochleoplasty in trochleodysplastic knees of patients with symptomatic patellofemoral instability was investigated using a quasi-static finite element model. MRI data of five healthy knees were segmented, meshed and a finite element analysis was performed in order to validate the model. A second validation was performed by comparing simulated patellofemoral kinematics to in-vivo values obtained from upright- weight bearing CT scans. Subsequently, five trochleodysplastic knees were modelled before and after simulated trochleoplasty. The force necessary to dislocate the patella by 10 mm and to fully dislocate the patella was calculated in various knee flexion angles between 0 and 45°.

Findings: The developed models successfully predicted outcome values within the range of reference values from literature. Lateral stability was significantly lower in trochleodysplastic knees compared to healthy knees. Trochleoplasty was determined to significantly increase the force necessary to dislocate the patella in trochleodysplastic knees to comparable values as in healthy knees.

Interpretation: This is the first study to investigate lateral patellofemoral stability in patients with symptomatic patellofemoral instability and dysplasia of the trochlear groove. We confirm that patellofemoral stability is significantly lower in trochleodysplastic knees than in healthy knees. Trochleoplasty increases patellofemoral stability to levels similar to healthy.
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http://dx.doi.org/10.1016/j.clinbiomech.2020.105216DOI Listing
January 2021

Biomechanics of Ankle Ligament Reconstruction: A Cadaveric Study to Compare Stability of Reconstruction Techniques Using 1 or 2 Fibular Tunnels.

Orthop J Sports Med 2020 Oct 22;8(10):2325967120959284. Epub 2020 Oct 22.

Investigation performed at Universitätsklinik Balgrist, Zürich, Switzerland.

Background: Anatomic lateral ankle ligament reconstruction has been proposed for patients with chronic ankle instability. A reliable approach is a reconstruction technique using an allograft and 2 fibular tunnels. A recently introduced approach that entails 1-fibular tunnel reconstruction might reduce the risk of intraoperative complications and ultimately improve patient outcome.

Hypothesis: We hypothesized that both reconstruction techniques show similar ankle stability (joint laxity and stiffness) and are similar to the intact joint condition.

Study Design: Controlled laboratory study.

Methods: A total of 10 Thiel-conserved cadaveric ankles were divided into 2 groups and tested in 3 stages-intact, transected, and reconstructed lateral ankle ligaments-using either the 1- or the 2-fibular tunnel technique. To quantify stability in each stage, anterior drawer and talar tilt tests were performed in 0°, 10°, and 20° of plantarflexion (anterior drawer test) or dorsiflexion (talar tilt test). Bone displacements were measured using motion capture, from which laxity and stiffness were calculated together with applied forces. Finally, reconstructed ligaments were tested to failure in neutral position with a maximal applicable torque in inversion. A mixed linear model was used to describe and compare the outcomes.

Results: When ankle stability of intact and reconstructed ligaments was compared, no significant difference was found between reconstruction techniques for any flexion angle. Also, no significant difference was found when the maximal applicable torque of the 1-tunnel technique (9.1 ± 4.4 N·m) was compared with the 2-tunnel technique (8.9 ± 4.8 N·m).

Conclusion: Lateral ankle ligament reconstruction with an allograft using 1 fibular tunnel demonstrated similar biomechanical stability to the 2-tunnel approach.

Clinical Relevance: Demonstrating similar stability in a cadaveric study and given the potential to reduce intraoperative complications, the 1-fibular tunnel approach should be considered a viable option for the surgical therapy of chronic ankle instability. Clinical randomized prospective trials are needed to determine the clinical outcome of the 1-tunnel approach.
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http://dx.doi.org/10.1177/2325967120959284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7585988PMC
October 2020

Resting TcPO2 levels decrease during liner wear in persons with a transtibial amputation.

PLoS One 2020 28;15(9):e0239930. Epub 2020 Sep 28.

Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich, Switzerland.

Background: In our clinic, a substantial number of patients present with transtibial residual limb pain of no specific somatic origin. Silicone liner induced tissue compression may reduce blood flow, possibly causing residual limb pain. Thus, as a first step we investigated if the liner itself has an effect on transcutaneous oxygen pressure (TcPO2).

Methods: Persons with unilateral transtibial amputation and residual limb pain of unknown origin were included. Medical history, including residual limb pain, was recorded, and the SF-36 administered. Resting TcPO2 levels were measured in the supine position and without a liner at 0, 10, 20 and 30 minutes using two sensors: one placed in the Transverse plane over the tip of the Tibia End (= TTE), the other placed in the Sagittal plane, distally over the Peroneal Compartment (= SPC). Measurements were repeated with specially prepared liners avoiding additional pressure due to sensor placement. Statistical analyses were performed using SPSS.

Results: Twenty persons (9 women, 11 men) with a mean age of 68.65 years (range 47-86 years) participated. The transtibial amputation occurred on average 43 months prior to study entry (range 3-119 months). With liner wear, both sensors measured TcPO2 levels that were significantly lower than those measured without a liner (TTE: p < 0.001; SPC: p = 0.002) after 10, 20 and 30 minutes. No significant differences were found between TcPO2 levels over time between the sensors. There were no significant associations between TcPO2 levels and pain, smoking status, age, duration of daily liner use, mobility level, and revision history.

Conclusion: Resting TcPO2 levels decreased significantly while wearing a liner alone, without a prosthetic socket. Further studies are required to investigate the effect of liner wear on exercise TcPO2 levels.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0239930PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7521692PMC
November 2020

The "Balgrist Score" for evaluation of Charcot foot: a predictive value for duration of off-loading treatment.

Skeletal Radiol 2021 Feb 23;50(2):311-320. Epub 2020 Jul 23.

Faculty of Medicine, University of Zurich, Zurich, Switzerland.

Objective: To develop a new magnetic resonance imaging(MRI) scoring system for evaluation of active Charcot foot and to correlate the score with a duration of off-loading treatment ≥ 90 days.

Methods: An outpatient clinic database was searched retrospectively for MRIs of patients with active Charcot foot who completed off-loading treatment. Images were assessed by two radiologists (readers 1 and 2) and an orthopedic surgeon (reader 3). Sanders/Frykberg regions I-V were evaluated for soft tissue edema, bone marrow edema, erosions, subchondral cysts, joint destruction, fractures, and overall regional manifestation using a score according to degree of severity (0-3 points). Intraclass correlations (ICC) for interreader agreement and receiver operating characteristic analysis between MR findings and duration of off-loading-treatment were calculated.

Results: Sixty-five feet in 56 patients (34 men) with a mean age of 62.4 years (range: 44.5-85.5) were included. Region III (reader 1/reader 2: 93.6/90.8%) and region II (92.3/90.8%) were most affected. The most common findings in all regions were soft tissue edema and bone marrow edema. Mean time between MRI and cessation of off-loading-treatment was 150 days (range: 21-405). The Balgrist Score was defined in regions II and III using soft tissue edema, bone marrow edema, joint destruction, and fracture. Interreader agreement for Balgrist Score was excellent: readers 1/2: ICC 0.968 (95% CI: 0.948, 0.980); readers 1/2/3: ICC 0.856 (0.742, 0.917). A cutoff of ≥ 9.0 points in Balgrist Score (specificity 72%, sensitivity 66%) indicated a duration of off-loading treatment ≥ 90 days.

Conclusion: The Balgrist Score is a new MR scoring system for assessment of active Charcot foot with excellent interreader agreement. The Balgrist Score can help to identify patients with off-loading treatment ≥ 90 days.
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http://dx.doi.org/10.1007/s00256-020-03541-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7736011PMC
February 2021

Long-term Prognosis After Successful Nonoperative Treatment of Osteochondral Lesions of the Talus: An Observational 14-Year Follow-up Study.

Orthop J Sports Med 2020 Jun 2;8(6):2325967120924183. Epub 2020 Jun 2.

Department of Orthopedics, University Hospital Balgrist, University of Zurich, Zurich, Switzerland.

Background: Little is known about the long-term prognosis of osteochondral lesions of the talus (OLTs) after nonoperative treatment.

Purpose: To evaluate the clinical and radiological long-term results of initially successfully treated OLTs after a minimum follow-up of 10 years.

Study Design: Case series; Level of evidence, 4.

Methods: Between 1998 and 2006, 48 patients (50 ankles) with OLTs were successfully treated nonoperatively. These patients were enrolled in a retrospective long-term follow-up, for which 24 patients could not be reached or were available only by telephone. A further 2 OLTs (6%) that had been treated surgically were excluded from the analysis and documented as failures of nonoperative treatment. The final study group of 22 patients (mean age at injury, 42 years; range, 10-69 years) with 24 OLTs (mean size, 1.4 cm; range, 0.2-3.8 cm) underwent clinical and radiological evaluation after a mean follow-up of 14 years (range, 11-20 years). Ankle pain was evaluated with a visual analog scale (VAS), ankle function with the American Orthopaedic Foot and Ankle Society (AOFAS) score, and sports activity with the Tegner score. Progression of ankle osteoarthritis was analyzed based on plain ankle radiographs at the initial presentation and the final follow-up according to the Van Dijk classification.

Results: At final follow-up, the 24 cases (ie, ankles) showed a median VAS score of 0 (IQR, 0.0-2.25) and a median AOFAS score of 94.0 (IQR, 85.0-100). Pain had improved in 18 cases (75%), was unchanged in 3 cases (13%), and had increased in 3 cases (13%). The median Tegner score was 4.0 (IQR, 3.0-5.0). Persistent ankle pain had led to a decrease in sports activity in 38% of cases. At the final follow-up, 11 cases (73%) showed no progression of ankle osteoarthritis and 4 cases (27%) showed progression by 1 grade.

Conclusion: Osteochondral lesions of the talus that successfully undergo an initial nonoperative treatment period have minimal symptoms in the long term, a low failure rate, and no relevant ankle osteoarthritis progression. However, a decrease in sports activity due to sports-related ankle pain was observed in more than one-third of patients.
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http://dx.doi.org/10.1177/2325967120924183DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7268150PMC
June 2020

Meniscus sizing using three-dimensional models of the ipsilateral tibia plateau based on CT scans - an experimental study of a new sizing approach.

J Exp Orthop 2020 May 27;7(1):36. Epub 2020 May 27.

Department of Orthopaedic Surgery, University of Zurich, Balgrist University Hospital, Forchstrasse 340, 8008, Zurich, Switzerland.

Purpose: Selection of a meniscus allograft with a similar three-dimensional (3D) size is essential for good clinical results in meniscus allograft surgery. Direct meniscus sizing by MRI scan is not possible in total meniscectomy and indirect sizing by conventional radiography is often inaccurate. The purpose of this study was to develop a new indirect sizing method, based on the 3D shape of the ipsilateral tibia plateau, which is independent of the meniscus condition.

Methods: MRI and CT scans of fifty healthy knee joints were used to create 3D surface models of both menisci (MRI) and tibia plateau (CT). 3D bone models of the proximal 10 mm of the entire and half tibia plateau (with / without intercondylar area) were created in a standardized fashion. For each meniscus, the best fitting "allograft" couple out of all other 49 menisci were assessed by the surface distance of the 3D meniscus (best available allograft), of the 3D tibia plateau (3D-CT) and by the radiographic method of Pollard (2D-RX).

Results: 3D-CT sizing was significantly better by using only the half tibia plateau without the intercondylar area (p < 0.001). But neither sizing by 3D-CT, nor by 2D-RX could select the best available allograft. Compared to 2D-RX, 3D-CT sizing was significantly better for the medial, but not for the lateral meniscus.

Conclusions: Automatized, indirect meniscus sizing using the 3D bone models of the tibia plateau is feasible and more precise than the previously described 2D-RX method.. However, further technical improvement is needed to select always the best available allograft.
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http://dx.doi.org/10.1186/s40634-020-00252-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7251042PMC
May 2020

Dislocation rates of perineural catheters placed either perpendicular or parallel to the femoral nerve: A randomised controlled trial.

Eur J Anaesthesiol 2020 Sep;37(9):758-764

From the Department of Anaesthesia, Intensive Care and Pain Medicine (KK, BR, KA, JA, UE), Department of Orthopaedic Surgery, Balgrist University Hospital (SFF) and Department of Orthopaedic Surgery, University of Zurich, Institute for Biomechanics, ETH Zurich, Balgrist Campus, Zürich, Switzerland (TG).

Background: Ultrasound has increased the efficacy of femoral nerve catheters but their postoperative dislocation still remains a common problem. Although catheter placement parallel to the nerve seems to reduce dislocation rates in other nerves and plexuses, the possible advantage for femoral nerve catheter placement remains unclear.

Objective: To compare the dislocation rates of femoral catheters when placed perpendicular or parallel to the femoral nerve.

Design: Randomised controlled study.

Setting: University orthopaedic hospital. Duration of study: October 2018 to June 2019.

Patients: Eighty patients scheduled for major knee surgery with femoral catheter were enrolled and randomly allocated in two groups. Data from 78 patients could be analysed.

Interventions: The femoral nerve catheters was placed perpendicular to the nerve in Group 1 (n=40), whereas in Group 2 (n=38) parallel to it. For Group 1 the short-axis view of the nerve and an in-plane puncture was used. For Group 2 we used the short-axis view of the nerve and an out-of-plane puncture technique combined with rotation of the transducer to the long-axis view with the needle in-plane.

Main Outcome Measures: Primary outcome was the catheter dislocation rate in the first 48 h. Secondary outcomes were pain scores and sensory blockade.

Results: There was no statistically significant difference between the two techniques regarding dislocation of the catheters at 24 or 48 h (at 48 h, Group 1: 15%, Group 2: 2.6%, P = 0.109). Also pain scores, sensory blockade and rescue doses of ropivacaine did not differ between the groups. However, in Group 2 the technique took longer.

Conclusion: Rotating the ultrasound probe to the long-axis in-plane view enabled examination of the catheter position when it was placed parallel to the nerve. The parallel placement of the catheter required more time, but did not significantly improve dislocation rate, pain scores or sensory blockade.

Trial Registration: Clinicaltrials.gov identifier: NCT03693755.
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http://dx.doi.org/10.1097/EJA.0000000000001237DOI Listing
September 2020

Augmented reality-based navigation increases precision of pedicle screw insertion.

J Orthop Surg Res 2020 May 14;15(1):174. Epub 2020 May 14.

Spine Division, University Hospital Balgrist, University of Zürich, Forchstrasse 340, 8008, Zurich, Switzerland.

Background: Precise insertion of pedicle screws is important to avoid injury to closely adjacent neurovascular structures. The standard method for the insertion of pedicle screws is based on anatomical landmarks (free-hand technique). Head-mounted augmented reality (AR) devices can be used to guide instrumentation and implant placement in spinal surgery. This study evaluates the feasibility and precision of AR technology to improve precision of pedicle screw insertion compared to the current standard technique.

Methods: Two board-certified orthopedic surgeons specialized in spine surgery and two novice surgeons were each instructed to drill pilot holes for 40 pedicle screws in eighty lumbar vertebra sawbones models in an agar-based gel. One hundred and sixty pedicles were randomized into two groups: the standard free-hand technique (FH) and augmented reality technique (AR). A 3D model of the vertebral body was superimposed over the AR headset. Half of the pedicles were drilled using the FH method, and the other half using the AR method.

Results: The average minimal distance of the drill axis to the pedicle wall (MAPW) was similar in both groups for expert surgeons (FH 4.8 ± 1.0 mm vs. AR 5.0 ± 1.4 mm, p = 0.389) but for novice surgeons (FH 3.4 mm ± 1.8 mm, AR 4.2 ± 1.8 mm, p = 0.044). Expert surgeons showed 0 primary drill pedicle perforations (PDPP) in both the FH and AR groups. Novices showed 3 (7.5%) PDPP in the FH group and one perforation (2.5%) in the AR group, respectively (p > 0.005). Experts showed no statistically significant difference in average secondary screw pedicle perforations (SSPP) between the AR and the FH set 6-, 7-, and 8-mm screws (p > 0.05). Novices showed significant differences of SSPP between most groups: 6-mm screws, 18 (45%) vs. 7 (17.5%), p = 0.006; 7-mm screws, 20 (50%) vs. 10 (25%), p = 0.013; and 8-mm screws, 22 (55%) vs. 15 (37.5%), p = 0.053, in the FH and AR group, respectively. In novices, the average optimal medio-lateral convergent angle (oMLCA) was 3.23° (STD 4.90) and 0.62° (STD 4.56) for the FH and AR set screws (p = 0.017), respectively. Novices drilled with a higher precision with respect to the cranio-caudal inclination angle (CCIA) category (p = 0.04) with AR.

Conclusion: In this study, the additional anatomical information provided by the AR headset superimposed to real-world anatomy improved the precision of drilling pilot holes for pedicle screws in a laboratory setting and decreases the effect of surgeon's experience. Further technical development and validations studies are currently being performed to investigate potential clinical benefits of the herein described AR-based navigation approach.
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http://dx.doi.org/10.1186/s13018-020-01690-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7227090PMC
May 2020

Assessing the effects of intratendinous genipin injections: Mechanical augmentation and spatial distribution in an ex vivo degenerative tendon model.

PLoS One 2020 15;15(4):e0231619. Epub 2020 Apr 15.

Department of Orthopedics, Balgrist University Hospital, Zurich, Switzerland.

Background: Tendinopathy is a common musculoskeletal disorder and current treatment options show limited success. Genipin is an effective collagen crosslinker with low cytotoxicity and a promising therapeutic strategy for stabilizing an intratendinous lesion.

Purpose: This study examined the mechanical effect and delivery of intratendinous genipin injection in healthy and degenerated tendons.

Study Design: Controlled laboratory study.

Methods: Bovine superficial digital flexor tendons were randomized into four groups: Healthy control (N = 25), healthy genipin (N = 25), degenerated control (N = 45) and degenerated genipin (N = 45). Degeneration was induced by Collagenase D injection. After 24h, degenerated tendons were subsequently injected with either 0.2ml of 80mM genipin or buffer only. 24h post-treatment, samples were cyclically loaded for 500 cycles and then ramp loaded to failure. Fluorescence and absorption assays were performed to analyze genipin crosslink distribution and estimate tissue concentration after injection.

Results: Compared to controls, genipin treatment increased ultimate force by 19% in degenerated tendons (median control 530 N vs. 633 N; p = 0.0078). No significant differences in mechanical properties were observed in healthy tendons, while degenerated tendons showed a significant difference in ultimate stress (+23%, p = 0.049), stiffness (+27%, p = 0.037), work to failure (+42%, p = 0.009), and relative stress relaxation (-11%, p < 0.001) after genipin injection. Fluorescence and absorption were significantly higher in genipin treated tendons compared to control groups. A higher degree of crosslinking (+45%, p < 0.001) and a more localized distribution were observed in the treated healthy compared to degenerated tendons, with higher genipin tissue concentrations in healthy (7.9 mM) than in degenerated tissue (2.3 mM).

Conclusion: Using an ex-vivo tendinopathy model, intratendinous genipin injections recovered mechanical strength to the level of healthy tendons. Measured by genipin tissue distribution, injection is an effective method for local delivery.

Clinical Relevance: This study provides a proof of concept for the use of intratendinous genipin injection in the treatment of tendinopathy. The results demonstrate that a degenerated tendon can be mechanically augmented by a clinically viable method of local genipin delivery. This warrants further in vivo studies towards the development of a clinically applicable treatment based on genipin.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0231619PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7159246PMC
July 2020

Long-term results after internal partial forefoot amputation (resection): a retrospective analysis.

Arch Orthop Trauma Surg 2021 Apr 7;141(4):543-554. Epub 2020 Apr 7.

Division of Technical Orthopedics, Department of Orthopedic Surgery, Balgrist University Hospital, Forchstrasse 340, 8008, Zurich, Switzerland.

Introduction: Internal partial forefoot amputation (IPFA) is a treatment option for osteomyelitis and refractory and recurrent chronic ulcers of the forefoot. The aim of our study was to assess the healing rate of chronic ulcers, risk of ulcer recurrence at the same area or re-ulceration at a different area and revision rate in patients treated with IPFA.

Materials And Methods: All patients who underwent IPFA of a phalanx and/or metatarsal head and/or sesamoids at our institution because of chronic ulceration of the forefoot and/or osteomyelitis from 2004 to 2014 were included. Information about patient characteristics, ulcer healing, new ulcer occurrence, and revision surgery were collected. Kaplan-Meier survival curves were plotted for new ulcer occurrence and revision surgery.

Results: A total of 102 patients were included (108 operated feet). 55.6% of our patients had diabetes. In 44 cases, an IPFA of a phalanx was performed, in 60 cases a metatarsal head resection and in 4 cases an isolated resection of sesamoids. The mean follow-up was 40.9 months. 91.2% of ulcers healed after a mean period of 1.3 months. In 56 feet (51.9%), a new ulcer occurred: 11 feet (10.2%) had an ulcer in the same area as initially (= ulcer recurrence), in 45 feet (41.7%) the ulcer was localized elsewhere (= re-ulceration). Revision surgery was necessary in 39 feet (36.1%). Only one major amputation and five complete transmetatarsal forefoot amputations were necessary during the follow-up period. Thus, the major amputation rate was 0.9%, and the minor amputation rate on the same ray was 13.9%.

Conclusions: IPFA is a valuable treatment of chronic ulcers of the forefoot. However, new ulceration is a frequent event following this type of surgery. Our results are consistent with the reported re-ulceration rate after conservative treatment of diabetic foot ulcers. The number of major amputations is low after IPFA.

Level Of Evidence: Retrospective Case Series Study (Level IV).
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http://dx.doi.org/10.1007/s00402-020-03441-3DOI Listing
April 2021

Biomechanical Evaluation of a Novel Loop Retention Mechanism for Cortical Graft Fixation in ACL Reconstruction.

Orthop J Sports Med 2020 Feb 25;8(2):2325967120904322. Epub 2020 Feb 25.

Department of Orthopedics, Second Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.

Background: Implant fixation by means of a cortical fixation device (CFD) has become a routine procedure in anterior cruciate ligament reconstruction. There is no clear consensus whether adjustable-length CFDs are more susceptible to loop lengthening when compared with pretied fixed-length CFDs.

Purpose: To assess biomechanical performance measures of 3 types of CFDs when subjected to various loading protocols.

Study Design: Controlled laboratory study.

Methods: Three types of CFDs underwent biomechanical testing: 1 fixed length and 2 adjustable length. One of the adjustable-length devices is based on the so-called finger trap mechanism, and the other is based on a modified sling lock mechanism. A device-only test of 5000 cycles (n = 8 per group) and a tendon-device test of 1000 cycles (n = 8 per group) with lower and upper force limits of 50 and 250 N, respectively, were applied, followed by ramp-to-failure testing. Adjustable-length devices then underwent further cyclic testing with complete loop unloading (n = 5 per group) at each cycle, as well as fatigue testing (n = 3 per group) over a total of 1 million cycles. Derived mechanical parameters were compared among the devices for statistical significance using Kruskal-Wallis analysis of variance followed by post hoc Mann-Whitney testing with Bonferroni correction.

Results: All CFDs showed elongation <2 mm after 5000 cycles when tested in an isolated manner and withstood ultimate tensile forces in excess of estimated peak in vivo forces. In both device-only and tendon-device tests, differences in cyclic performance were found among the devices, favoring adjustable-length fixation devices over the fixed-length device. Completely unloading the suspension loops, however, led to excessive loop lengthening of the finger trap device, whereas the modified sling lock device remained stable throughout the test. The fixed-length device displayed superior ultimate strength over both adjustable-length devices. Both adjustable-length devices showed adequate fatigue behavior during high-cyclic testing.

Conclusion: All tested devices successfully prevented critical construct elongation when tested with constant tension and withstood ultimate loads in excess of estimated in vivo forces during the rehabilitation phase. The finger trap device gradually lengthened excessively when completely unloaded during cyclic testing.

Clinical Relevance: Critical loop lengthening may occur if adjustable-length devices based on the finger trap mechanism are repeatedly unloaded in situ.
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http://dx.doi.org/10.1177/2325967120904322DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7042561PMC
February 2020

Biomechanical comparison of the use of different surgical suture techniques for continuous loop tendon grafts preparation.

Sci Rep 2020 01 17;10(1):538. Epub 2020 Jan 17.

Department of Orthopedics, Balgrist University Hospital, University of Zurich, 8008, Zurich, Switzerland.

We introduce a new approach for a continuous loop tendon-graft preparation, benchmarking it against established graft preparation techniques widely used in conjunction with non-adjustable interference screw fixation. A four-strand bovine tendon graft was prepared using the following graft preparation techniques: standard graft using the baseball stitch technique (M-tech group); continuous loop graft using the GraftLink technique (Arthrex-tech group); continuous loop graft using the Kessler anastomosis technique (Kessler-tech group); and continuous loop graft using a Double-Z anastomosis technique (Double Z-tech group). Each group of eight specimens underwent cyclic loading followed by a load-to-failure test. The M-technique yielded a smaller graft diameter (8.4 ± 0.5 mm) compared to the statistically equivalent diameters of the three continuous loop techniques (8.9 ± 0.6 mm of Arthrex-tech group, 9.1 ± 0.4 mm of Kessler-tech group and 9.2 ± 0.6 mm of Double Z-Tech group). The continuous loop grafts formed by the Double Z-Technique showed outstanding performance among the tested techniques in terms of ultimate failure load (982 ± 121 N) and cyclic elongation (3.7 ± 1.0 mm). There was no significant difference between the four groups in cyclic stiffness. Of the assessed techniques, the Arthrex technique resulted in the lowest ultimate elongation (2.0 ± 0.7 mm), followed by the Double Z-tech (4.5 ± 1.8 mm), the M-tech (5.2 ± 3.9 mm), and the Kessler-tech (5.3 ± 2.4 mm). The Arthrex-tech group (5.98 ± 0.38 min) displayed the shortest graft preparation time, followed by the M-Tech (7.94 ± 0.58 min), Kessler-tech (9.03 ± 0.39 min) and Double Z-Tech (13.29 ± 1.14 min). Double Z-Tech can improve the construct of continuous loop tendon graft with regard to mechanical performance.
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http://dx.doi.org/10.1038/s41598-019-57332-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6969208PMC
January 2020

Diagnostic utility of perilesional muscle edema in myositis ossificans.

Skeletal Radiol 2020 Jun 7;49(6):929-936. Epub 2020 Jan 7.

Faculty of Medicine, University of Zurich, Zurich, Switzerland.

Objectives: To investigate the value of extensive perilesional muscle edema for the differentiation between myositis ossificans (MO) and malignant intramuscular soft tissue tumors on MRI.

Materials And Methods: Two blinded readers analyzed MR examinations of 90 consecutive patients with intramuscular soft tissue masses (group 1: MO, n = 20; group 2: malignant tumors, n = 70). Extent of edema around lesions was graded (0, none; 1, minimal edema; 2, moderate edema; 3, extensive edema). Edema-lesion ratio (ELR = ratio of the maximal diameter of the edema and the maximal diameter of the central lesion) was calculated. ROC analysis, Mann-Whitney U test, and Kappa test were used.

Results: A total of 70% and 60% of patients with MO had edema grade 3 (reader 1/reader 2), 30%/40% edema grade 2. For the patients with malignant tumors, it was 2.9%/1.4% (edema grade 3) and 16%/23% (edema grade 2). Interrater reliability was substantial (kappa = 0.66). Extent of edema was significantly higher for patients of group 1 (p < 0.0001, both readers). Mean ELR was 3.60 (group 1) and 1.35 (group 2), with statistically significant differences (p < 0.0001). Grade 3 edema showed a sensitivity/specificity of 70%/97.1% (reader 1) and 60%/99% (reader 2) for diagnosing MO. For ELR > 2.0, sensitivity was 90% and specificity 91% for diagnosing MO.

Conclusions: Extensive perilesional muscle edema on MRI of more than double the size of the central lesion is highly specific, but not pathognomonic for myositis ossificans in the early/intermediate stage in the differentiation to malignant intramuscular soft tissue lesions.
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http://dx.doi.org/10.1007/s00256-019-03351-5DOI Listing
June 2020

Watertightness of wound closure in lumbar spine-a comparison of different techniques.

J Spine Surg 2019 Sep;5(3):358-364

Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.

Background: Since a primary watertight dural suture after incidental durotomies has a failure rate of 5-10%, a watertight closure technique of the overlying layers (fascia, subcutis and skin) is essential. The purpose of this cadaveric study was to find the most watertight closure technique for fascia, subcutis and skin.

Methods: Different suturing techniques were tested for each layer in a sheep cadaveric model by measuring the leakage pressure. The specimens were mounted on a pressure chamber connected to a manometer and a water tube system. Subsequently, the leakage was over-sewed with a cross stitch and the experiment was repeated.

Results: Cross stitch suturing [median =180 mbar (43; 660)] performed best compared to continuous [median =16 mbar (6; 52)] (P=0.003) but not to single knot [median =118 mbar (21; 387)] (P=1.0) or locking stitch suturing [median =109 mbar (3; 149)] (P=0.93) for fascia closure. Continuous suture [median =9 mbar (3; 14)] resulted in a higher leakage pressure than single knot [median =1 mbar (1; 6)] (P=0.017) for subcutaneous closure. No significant differences were found between intracutaneous, Donati-continuous, single knot and locking stitch for skin closures (P=0.075). However, the Donati-continuous stitch closure resulted in higher pressures in tendency. Over-sewing increased median leakage pressure from 8.0 to 11.0 mbar (P=0.068) and from 4.0 to 13.0 mbar (P=0.042) for single knot and for locking stitch skin closures, respectively.

Conclusions: Cross stitches for the fascia, continuous suturing technique for the subcutis and Donati-continuous stitch for the skin resulted in the most watertight closure within this experimental setting. If leakage occurs, over-sewing might relevantly improve the watertightness of the wound.
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http://dx.doi.org/10.21037/jss.2019.08.01DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6787369PMC
September 2019

Anterior talofibular ligament lesion is associated with increased flat foot deformity but does not affect correction by lateral calcaneal lengthening.

BMC Musculoskelet Disord 2019 Oct 27;20(1):496. Epub 2019 Oct 27.

Department of Orthopedics, Balgrist University Hospital, University of Zurich, Forchstrasse 340, 8008, Zürich, Switzerland.

Background: Several risk factors for adult acquired flatfoot deformity (AAFD) have been identified in literature. To this date, little attention has been paid to the lateral ligament complex and its influence on AAFD, although its anatomic course and anatomic studies suggest a restriction to flatfoot deformity. The aim of this study was to assess the influence of the anterior talofibular ligament (ATFL) on AAFD and on radiologic outcome following common operative correction by lateral calcaneal lengthening.

Methods: We reviewed all patients that underwent lateral calcaneal lengthening for correction of AAFD between January 2008 and July 2018 at our clinic. Patients were grouped according to the preoperative MRI findings into those with an intact ATFL and those with an injured ATFL. Two independent readers assessed common radiographic flatfoot parameters on preoperative and postoperative radiographs.

Results: Sixty-four flatfoot corrections in 63 patients were included, whereby the ATFL was intact in 29 cases, and in 35 cases the ligament was injured. An ATFL lesion was overall radiologically associated with increased flatfoot deformity with a statistically significant difference between the two groups for preoperative talometatarsal-angle (p = 0.002), talocalcaneal-angle (p = 0.000) and talonavicular uncoverage-angle (p = 0.005). No difference between the two groups could be observed regarding the success of operative correction or operative consistency after lateral calcaneal lengthening.

Conclusion: The ATFL seems to influence the extent of AAFD. In patients undergoing lateral calcaneal lengthening, the integrity of the ligament seems not to influence the degree of correction or the consistency of the postoperative result.
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http://dx.doi.org/10.1186/s12891-019-2827-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6815414PMC
October 2019

Predictors for reoperation after lower limb amputation in patients with peripheral arterial disease.

Vasa 2019 Aug 7;48(5):419-424. Epub 2019 May 7.

Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich, Switzerland.

Major amputations in patients with peripheral arterial disease (PAD) carry a high risk for complications, including revision of the amputation, sometimes to a higher level. Determining a safe level for amputation with good wound healing potential depends largely on vascular measurements. This study evaluated potential predictive factors for revision of major lower extremity amputations in patients with PAD. A retrospective chart review of all major lower extremity amputations at our institution was conducted. Amputations due to trauma or tumor and below-ankle amputations were excluded. Patient demographics, level/type of amputation, level/time of revision, comorbidities and risk factors were extracted. 180 patients with PAD, mean age 66.48 (range: 31-93) years, 125 (69.4%) male were included. Most (154/180, 86.6%) underwent below-knee amputation. 71 (39.4%) patients had coronary arterial disease, 104 (57.8%) had diabetes. More than half of patients, (93/138; 51.7%) had undergone previous balloon angioplasty. 44 (30%) patients required revision surgery: 42/180 (23.3%) were revised at the same level, and in 12/180 (6.7%) a more proximal amputation was necessary. PAD stage was not associated with the level of reamputation (p = 0.4369). Significantly more patients who had previous balloon angioplasty required revision surgery (66.7% versus 45.2%, p = 0.009). 67 (37.2%) patients underwent preoperative TcPO2 measurement: 40/67 (59.7%) had TcPO2 ≥ 40 mmHg; 4/67 (6%) had TcPO2 < 10 mmHG. Three patients with TcPO2 ≥ 40 mmHg, one with 30 mmHg ≤ TcPO2 ≤ 40 mmHg and one with 10 mmHg ≤ TcPO2 ≤ 20 mmHg required re-amputation to a more proximal level. TcPO2 measurements are useful for determining level of lower limb amputation and predicting wound healing problems when an amputation level with TcPO2 < 40 mmHg is chosen. In transtibial amputations, TcPO2 ≥ 40 mmHg does not safely predict wound healing.
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http://dx.doi.org/10.1024/0301-1526/a000796DOI Listing
August 2019

Malpositioning of patient-specific instruments within the possible degrees of freedom in high-tibial osteotomy has no considerable influence on mechanical leg axis correction.

Knee Surg Sports Traumatol Arthrosc 2020 May 26;28(5):1356-1364. Epub 2019 Feb 26.

Department of Orthopedics, Balgrist University Hospital, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.

Purpose: Patient-specific instruments (PSIs) are helpful tools in high tibial osteotomy (HTO) in patients with symptomatic varus malalignment of the mechanical leg axis. However, the precision of HTO can decrease with malpositioned PSI. This study investigates the influence of malpositioned PSI on axis correction, osteotomy, and implant placement.

Methods: With a mean three-dimensional (3D) model (0.8° varus), PSI-navigated HTOs were computer simulated. Two different guide designs, one with stabilising hooks and one without, were used. By adding rotational and translational offsets of different degrees, wrong placements of PSI were simulated. After 5° valgisation of the postoperative mechanical axis, the distance between joint-plane and osteotomy screws, respectively, were measured. The same simulations were performed in a patient with varus deformity (7.4° varus).

Results: In the mean 3D model, the postoperative mechanical axis was within 3.9°-4.5° valgus with mean value of 4.1° ± 0.1° (correct axis 4.2° valgus). Surgical failure concerning osteotomy occurred in 17 of 76 HTOs. Significantly safer screw placement was observed using PSI with stabilising hooks (p = 0.012). In the case of the 3D model with 7.4° varus deformity, the postoperative mechanical axis was within 3.2°-3.9° valgus with mean value of 3.8° ± 0.2° (correct axis 3.9° valgus). Surgical failure concerning osteotomy occurred in 3 of 38 HTOs. Screws were always within the safety distance.

Conclusion: The clinical relevance of the presented study is that malpositioning of a PSI within the possible degrees of freedom does not have a relevant influence on the axis correction. The most vulnerable plane for surgical failure is the sagittal plane, wherefore the treating surgeon should verify correct guide placement to prevent surgical failure, particularly in this plane.

Level Of Evidence: III.
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http://dx.doi.org/10.1007/s00167-019-05432-3DOI Listing
May 2020