Publications by authors named "Oliver Kessler"

27 Publications

  • Page 1 of 1

Function and strain of the anterolateral ligament part II: reconstruction.

Knee Surg Sports Traumatol Arthrosc 2020 Jul 25. Epub 2020 Jul 25.

Institute of Orthopaedic Research and Biomechanics, Trauma Research Centre, University of Ulm, Medical Centre, Helmholtzstraße 14, 89081, Ulm, Germany.

Purpose: Anterolateral rotatory instability (ALRI) may result from isolated ruptures of the anterior cruciate ligament (ACL) or combined lesions with the anterolateral ligament (ALL). Biomechanical studies have demonstrated that the ALL contributes to the overall rotational stability of the knee. The purpose of this study was to investigate the biomechanical function of anatomic ALL reconstruction (ALL) in the setting of a combined ACL and ALL injury and reconstruction. The hypothesis was that combined ACL reconstruction (ACL) and ALL (ACL/ALL) significantly reduces internal rotation and shows load sharing between both reconstructions compared with isolated ACL.

Methods: Eight fresh-frozen cadaveric knees were evaluated using a six degrees of freedom knee simulator. Continuous passive motion and external loads were tested. Kinematic differences between ACL and combined ACL/ALL were compared. Additionally, ACL graft tension and ALL graft strain were measured continuously throughout the testing protocol.

Results: Combined anatomic ACL/ALL significantly improved the internal rotatory stability compared with isolated ACL at 30°-90° under an internal rotation moment. During a static pivot-shift test, additional ALL showed no significant reduction of ap-translation. ALL resulted in an increase in ACL graft tension during continuous passive motion and with additional internal rotation moment.

Conclusion: In the case of a combined ACL and ALL deficiency, concurrent ACL and ALL significantly improved the rotatory stability of the knee compared with solely reconstructing the ACL at flexion angles ≥ 30°. Nevertheless, additional ALL with fixation at 60° and with low tension could not restore extension-near rotatory stability. For that reason, ALL with fixation at 60° flexion cannot be recommended in clinical application.
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http://dx.doi.org/10.1007/s00167-020-06137-8DOI Listing
July 2020

AGRASS Questionnaire: Assessment of Risk Management in Health Care.

Rev Saude Publica 2020 10;54:21. Epub 2020 Feb 10.

Agência Nacional de Vigilância Sanitária. Gerência Geral de Tecnologia em Serviços de Saúde. Brasília, DF, Brasil.

Objective: This study aims to assess the development and the validity analysis of the Assessment of Risk Management in Health Care Questionnaire (AGRASS).

Methods: This is a validation study of a measurement instrument following the stages: 1) Development of conceptual model and items; 2) Formal multidisciplinary assessment; 3) Nominal group for validity analysis with national specialists; 4) Development of software and national pilot study in 62 Brazilian hospitals 5) Delphi for validity analysis with the users of the questionnaire. In stages 3 and 5, the items were judged based on face validity, content validity, and utility and viability, by a 1-7 Likert scale (cut-off point: median < 6). Accuracy and reliability of the questionnaire were analyzed with the Confirmatory Factor Analysis and the Cronbach's alpha.

Results: The initial version of the instrument (98 items) was adapted during stages 1 to 3 for the final version with 40 items, which were considered relevant, of adequate content, useful, and viable. The instrument has 2 dimensions and 9 subdimensions, and the items have closed-ended questions (yes or no). The software for the automatic collection and analysis generates indicators, tables, and automatic graphs for the assessed institution and aggregated data. The adjustment indices confirmed a bi-dimensional model composed of structure and process (X2/gl = 1.070, RMSEA ≤ 0.05 = 0.847, TLI = 0.972), with high reliability for the AGRASS Questionnaire (α = 0.94) and process dimension (α = 0.93), and adequate for the structural dimension (α = 0.70).

Conclusions: The AGRASS Questionnaire is a potentially useful instrument for the surveillance and monitoring of the risk management and patient safety in health services.
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http://dx.doi.org/10.11606/s1518-8787.2020054001335DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7006914PMC
April 2020

Meniscal Replacement With a Silk Fibroin Scaffold Reduces Contact Stresses in the Human Knee.

J Orthop Res 2019 12 26;37(12):2583-2592. Epub 2019 Aug 26.

Institute of Orthopaedic Research and Biomechanics, Centre for Trauma Research Ulm, Ulm University Medical Centre, Helmholtzstraße 14, 89081, Ulm, Germany.

The aim of the current study was to verify if a previously developed silk fibroin scaffold for meniscal replacement is able to restore the physiological distribution of contact pressure (CP) over the articulating surfaces in the human knee joint, thereby reducing peak loads occurring after partial meniscectomy. The pressure distribution on the medial tibial articular surface of seven human cadaveric knee joints was analysed under continuous flexion-extension movements and under physiological loads up to 2,500 N at different flexion angles. Contact area (CA), maximum tibiofemoral CP, maximum pressure under the meniscus and the pressure distribution were analysed for the intact meniscus, after partial meniscectomy as well as after partial medial meniscal replacement using the silk fibroin scaffold. Implantation of the silk fibroin scaffold considerably improved tibiofemoral contact mechanics after partial medial meniscectomy. While the reduced CA after meniscectomy was not fully restored by the silk fibroin scaffold, clinically relevant peak pressures on the articular cartilage surface occurring after partial meniscectomy were significantly reduced. Nevertheless, at high flexion angles static testing demonstrated that normal pressure distribution comparable to the intact meniscus could not be fully achieved. The current study demonstrates that the silk fibroin implant possesses attributes that significantly improve tibiofemoral CPs within the knee joint following partial meniscectomy. However, the failure to fully recapitulate the CAs and pressures observed in the intact meniscus, particularly at high flexion angles, indicates that the implant's biomechanical properties may require further improvement to completely restore tibiofemoral contact mechanics. © 2019 The Authors. Journal of Orthopaedic Research published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2583-2592, 2019.
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http://dx.doi.org/10.1002/jor.24437DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8647912PMC
December 2019

The challenge of implant integration in partial meniscal replacement: an experimental study on a silk fibroin scaffold in sheep.

Knee Surg Sports Traumatol Arthrosc 2019 Feb 27;27(2):369-380. Epub 2018 Sep 27.

Institute of Orthopaedic Research and Biomechanics, Centre for Trauma Research Ulm, Ulm University Medical Centre, Helmholtzstraße 14, 89081, Ulm, Germany.

Purpose: To restore meniscal function after excessive tissue damage, a silk fibroin implant for partial meniscal replacement was developed and investigated in an earlier sheep model. After 6 months implantation, it showed promising results in terms of chondroprotection and biocompatibility. To improve surgical fixation, the material was subjected to optimisation and a fibre mesh was integrated into the porous matrix. The aim of the study was the evaluation of this second generation of silk fibroin implants in a sheep model.

Methods: Nine adult merino sheep received subtotal meniscal replacement using the silk fibroin scaffold. In nine additional animals, the defect was left untreated. Sham surgery was performed in another group of nine animals. After 6 months of implantation macroscopic, biomechanical and histological evaluations of the scaffold, meniscus, and articular cartilage were conducted.

Results: Macroscopic evaluation revealed no signs of inflammation of the operated knee joint and most implants were located in the defect. However, there was no solid connection to the remaining peripheral meniscal rim and three devices showed a radial rupture at the middle zone. The equilibrium modulus of the scaffold increased after 6 months implantation time as identified by biomechanical testing (before implantation 0.6 ± 0.3 MPa; after implantation: 0.8 ± 0.3 MPa). Macroscopically and histologically visible softening and fibrillation of the articular cartilage in the meniscectomy- and implant group were confirmed biomechanically by indentation testing of the tibial cartilage.

Conclusions: In the current study, biocompatibility of the silk fibroin scaffold was reconfirmed. The initial mechanical properties of the silk fibroin implant resembled native meniscal tissue. However, stiffness of the scaffold increased considerably after implantation. This might have prevented integration of the device and chondroprotection of the underlying cartilage. Furthermore, the increased stiffness of the material is likely responsible for the partial destruction of some implants. Clinically, we learn that an inappropriate replacement device might lead to similar cartilage damage as seen after meniscectomy. Given the poor acceptance of the clinically available partial meniscal replacement devices, it can be speculated that development of a total meniscal replacement device might be the less challenging option.
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http://dx.doi.org/10.1007/s00167-018-5160-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6394547PMC
February 2019

Biomechanical, structural and biological characterisation of a new silk fibroin scaffold for meniscal repair.

J Mech Behav Biomed Mater 2018 10 30;86:314-324. Epub 2018 Jun 30.

Institute of Orthopaedic Research and Biomechanics, Centre for Trauma Research Ulm, Ulm University Medical Centre, Helmholtzstr. 14, 89081 Ulm, Germany.

Meniscal injury is typically treated surgically via partial meniscectomy, which has been shown to cause cartilage degeneration in the long-term. Consequently, research has focused on meniscal prevention and replacement. However, none of the materials or implants developed for meniscal replacement have yet achieved widespread acceptance or demonstrated conclusive chondroprotective efficacy. A redesigned silk fibroin scaffold, which already displayed promising results regarding biocompatibility and cartilage protection in a previous study, was characterised in terms of its biomechanical, structural and biological functionality to serve as a potential material for permanent partial meniscal replacement. Therefore, different quasi-static but also dynamic compression tests were performed. However, the determined compressive stiffness (0.56 ± 0.31 MPa and 0.30 ± 0.12 MPa in relaxation and creep configuration, respectively) was higher in comparison to the native meniscal tissue, which could potentially disturb permanent integration into the host tissue. Nevertheless, µ-CT analysis met the postulated requirements for partial meniscal replacement materials in terms of the microstructural parameters, like mean pore size (215.6 ± 10.9 µm) and total porosity (80.1 ± 4.3%). Additionally, the biocompatibility was reconfirmed during cell culture experiments. The current study provides comprehensive mechanical and biological data for the characterisation of this potential replacement material. Although some further optimisation of the silk fibroin scaffold may be advantageous, the silk fibroin scaffold showed sufficient biomechanical competence to support loads already in the early postoperative phase.
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http://dx.doi.org/10.1016/j.jmbbm.2018.06.041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6079190PMC
October 2018

Correction to: In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model.

Knee Surg Sports Traumatol Arthrosc 2018 07;26(7):2216

Institute of Orthopaedic Research and Biomechanics, Centre of Musculoskeletal Research, University of Ulm, Helmholtzstraße 14, 89081, Ulm, Germany.

The author would like to correct the errors in the publication of the original article. The corrected details are given below for your reading.
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http://dx.doi.org/10.1007/s00167-018-4878-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6828356PMC
July 2018

Function and strain of the anterolateral ligament part I: biomechanical analysis.

Knee Surg Sports Traumatol Arthrosc 2017 Apr 3;25(4):1132-1139. Epub 2017 Mar 3.

Institute of Orthopedic Research and Biomechanics, Trauma Research Center, University of Ulm-Medical Center, Helmholtzstraße 14, 89081, Ulm, Germany.

Purpose: Because reconstruction of the anterior cruciate ligament (ACL) in a double-bundle technique did not solve the problem of persistent rotatory laxity after surgery, new potential answers to this issue are of great interest. One of these is an extraarticular stabilization based on the rediscovery of the anterolateral ligament (ALL). Knowledge about its biomechanical function and benchmark data for an optimal reconstruction remain lacking. Therefore, the purpose of this study was to assess the function of the ALL under passive motion, anterior tibial translation and tibial rotational moments.

Methods: Continuous passive motion (0°-120° flexion), ap-translation and static pivot shift tests were performed on eight cadaveric knees. The knees were measured in intact, ACL-resected (ACL) and ACL + ALL-resected (ALL) conditions. Ap-translation and static pivot shift under 134 N anterior shear load were determined at 0°, 30°, 60° and 90° flexion. Strain of the ALL was recorded in intact and ACL conditions.

Results: During continuous passive motion under unloaded conditions, no significant difference in internal rotation between ACL and ALL was observed. With an additional internal tibial torque of 1-4 Nm, internal rotation increased significantly between 60° and 120° after resection of the ALL (p ≤ 0.05). Anterior tibial translation was significantly higher at 30° in ALL (p = 0.01) and for a simulated pivot shift at 60° and 90° in ACL (p ≤ 0.01). The ALL was not strained under unloaded passive motion. Adding different internal tibial torques led to strain starting at 60° flexion (1 N m internal torque) and 15° flexion (4 N m internal torque) in intact ligaments. In ACL, significantly greater ALL strains under lower flexion angles were seen for each condition (p ≤ 0.05).

Conclusions: This study demonstrated the ALL to be without function under passive motion and with no influence on tibial rotation. On application of extrinsic loads, the ALL had a low but significant stabilizing effect against anterior tibial shear load at low flexion angles. For this reason, it can be concluded that the ALL is supporting the ACL against internal tibial loads to a minor degree. A relationship between the ALL and the pivot shift cannot be concluded. With these results ALL-reconstruction cannot be recommended at the moment without further biomechanical investigations.
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http://dx.doi.org/10.1007/s00167-017-4472-3DOI Listing
April 2017

Strong correlation between the morphology of the proximal femur and the geometry of the distal femoral trochlea.

Knee Surg Sports Traumatol Arthrosc 2014 Dec 2;22(12):2900-10. Epub 2014 Oct 2.

Department of Mechanical Engineering, Centre for Orthopaedic Biomechanics, University of Bath, Bath, BA2 7AY, UK,

Purpose: Previous investigations suggested that the geometry of the proximal femur may be related to osteoarthritis of the tibiofemoral joint and various patellofemoral joint conditions. This study aims to investigate the correlation between proximal and distal femoral geometry. Such a correlation could aid our understanding of patient complications after total knee arthroplasty (TKA) and be of benefit for further development of kinematic approaches in TKA.

Methods: CT scans of 60 subjects (30 males, 30 females) were used to identify anatomical landmarks to calculate anatomical parameters of the femur, including the femoral neck anteversion angle, neck-shaft angle (NSA), mediolateral offset (ML-offset), condylar twist angle (CTA), trochlear sulcus angle (TSA) and medial/lateral trochlear inclination angles (MTIA/LTIA). Correlation analyses were carried out to assess the relationship between these parameters, and the effect of gender was investigated.

Results: The CTA, TSA and LTIA showed no correlation with any proximal parameter. The MTIA was correlated with all three proximal parameters, mostly with the NSA and ML-offset. Per 5° increase in NSA, the MTIA was 2.1° lower (p < 0.01), and for every 5 mm increase in ML-offset, there was a 2.6° increase in MTIA (p < 0.01). These results were strongest and statistically significant in females and not in males and were independent of length and weight.

Conclusions: Proximal femoral geometry is distinctively linked with trochlear morphology. In order to improve knowledge on the physiological kinematics of the knee joint and to improve the concept of kinematic knee replacement, the proximal femur seems to be a factor of clinical importance.

Level Of Evidence: III.
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http://dx.doi.org/10.1007/s00167-014-3343-4DOI Listing
December 2014

In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model.

Knee Surg Sports Traumatol Arthrosc 2015 Aug 26;23(8):2218-2229. Epub 2014 Apr 26.

Institute of Orthopaedic Research and Biomechanics, Centre of Musculoskeletal Research, University of Ulm, Helmholtzstraße 14, 89081, Ulm, Germany.

Purpose: Due to the negative effects of meniscectomy, there is a need for an adequate material to replace damaged meniscal tissue. To date, no material tested has been able to replace the meniscus sufficiently. Therefore, a new silk fibroin scaffold was investigated in an in vivo sheep model.

Methods: Partial meniscectomy was carried out to the medial meniscus of 28 sheep, and a scaffold was implanted in 19 menisci (3-month scaffold group, n = 9; 6-month scaffold group, n = 10). In 9 sheep, the defect remained empty (partial meniscectomy group). Sham operation was performed in 9 animals.

Results: The silk scaffold was able to withstand the loads experienced during the implantation period. It caused no inflammatory reaction in the joint 6 months postoperatively, and there were no significant differences in cartilage degeneration between the scaffold and sham groups. The compressive properties of the scaffold approached those of meniscal tissue. However, the scaffolds were not always stably fixed in the defect, leading to gapping between implant and host tissue or to total loss of the implant in 3 of 9 cases in each scaffold group. Hence, the fixation technique needs to be improved to achieve a better integration into the host tissue, and the long-term performance of the scaffolds should be further investigated.

Conclusion: These first in vivo results on a new silk fibroin scaffold provide the basis for further meniscal implant development. Whilst more data are required, there is preliminary evidence of chondroprotective properties, and the compressive properties and biocompatibility are promising.
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http://dx.doi.org/10.1007/s00167-014-3009-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4661201PMC
August 2015

Clinical risk management in hospitals: strategy, central coordination and dialogue as key enablers.

J Eval Clin Pract 2013 Apr 13;19(2):363-9. Epub 2012 Mar 13.

ETH Zurich, Center for Organizational and Occupational Sciences, Zurich, Switzerland.

Objective: The study aims to identify key enablers fostering clinical risk management (CRM) in hospitals to guide health care in this vital area of patient safety.

Method: A cross-sectional survey was conducted at the national level in 324 Swiss hospitals in 2007-2008 to assess the relationship between key elements and systematic CRM. Therefore, a comprehensive monitoring instrument for CRM was used for the first time. Organizational factors (e.g. strategy, coordination, resources) and structural conditions (e.g. hospital size) were tested as key elements. CRM was assessed by evaluating its maturity (i.e. the level of CRM development) by 12 theoretically derived indices joining together essential aspects of CRM at the hospital level and the service level. Chi-square measures were used to analyse the relationships between organizational factors or structural conditions and maturity of CRM.

Results: Participation in this voluntary survey was good, with CRM experts of 138 out of 324 hospitals responding (response rate 43%). Three key enablers for CRM were identified: implementing a function for central CRM coordination, assuring dialogue with and between the different hospital services, and developing strategic CRM objectives.

Conclusions: This study offers, for the first time, an assessment of the maturity of hospitals' CRM and identifies key enablers related to CRM. This is a feasible first step in guiding hospitals to shape their CRM and presents a basis for future studies, for example, linking CRM to outcome data.
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http://dx.doi.org/10.1111/j.1365-2753.2012.01836.xDOI Listing
April 2013

Assessing hospitals' clinical risk management: Development of a monitoring instrument.

BMC Health Serv Res 2010 Dec 13;10:337. Epub 2010 Dec 13.

ETH Zurich, Center for Organizational and Occupational Sciences, Switzerland.

Background: Clinical risk management (CRM) plays a crucial role in enabling hospitals to identify, contain, and manage risks related to patient safety. So far, no instruments are available to measure and monitor the level of implementation of CRM. Therefore, our objective was to develop an instrument for assessing CRM in hospitals.

Methods: The instrument was developed based on a literature review, which identified key elements of CRM. These elements were then discussed with a panel of patient safety experts. A theoretical model was used to describe the level to which CRM elements have been implemented within the organization. Interviews with CRM practitioners and a pilot evaluation were conducted to revise the instrument. The first nationwide application of the instrument (138 participating Swiss hospitals) was complemented by in-depth interviews with 25 CRM practitioners in selected hospitals, for validation purposes.

Results: The monitoring instrument consists of 28 main questions organized in three sections: 1) Implementation and organizational integration of CRM, 2) Strategic objectives and operational implementation of CRM at hospital level, and 3) Overview of CRM in different services. The instrument is available in four languages (English, German, French, and Italian). It allows hospitals to gather comprehensive and systematic data on their CRM practice and to identify areas for further improvement.

Conclusions: We have developed an instrument for assessing development stages of CRM in hospitals that should be feasible for a continuous monitoring of developments in this important area of patient safety.
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http://dx.doi.org/10.1186/1472-6963-10-337DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3022874PMC
December 2010

A useful radiologic method for preoperative joint-line determination in revision total knee arthroplasty.

Clin Orthop Relat Res 2010 May 5;468(5):1279-83. Epub 2009 Nov 5.

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

Unlabelled: Intraoperative joint-line determination during revision TKA is difficult and no method exists to plan the position preoperatively. Two questions need to be answered: to which extent does the joint line differ from its anatomic position after revision TKA if it has only been determined intraoperatively, and can the joint line be calculated preoperatively based on the transepicondylar width. Of 22 consecutive patients with complete preoperative (before and after primary TKA) and postoperative (after revision TKA) radiograph documentation, the joint-line position was measured on plane radiographs using the medial epicondyle as a reference. On another set of 45 consecutive patients with no knee disorders other than meniscal lesions, the transepicondylar axis width (TEAW) and the perpendicular distance from the medial and lateral epicondyles to the joint line were measured twice by two independent observers on plane AP radiographs of the knee. Significant joint-line alterations were observed after primary and revision TKA, implicating that a method for preoperative planning is needed. Because a linear correlation between the TEAW and the perpendicular distance from the epicondyles to the joint-line tangent was found, the ratio is useful to calculate the true joint-line position from the TEAW before revision TKA.

Level Of Evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
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http://dx.doi.org/10.1007/s11999-009-1114-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2853645PMC
May 2010

A prospective randomized assessment of earlier functional recovery in THA patients treated by minimally invasive direct anterior approach: a gait analysis study.

Clin Biomech (Bristol, Avon) 2009 Dec 21;24(10):812-8. Epub 2009 Aug 21.

Department for Orthopaedic Surgery/Experimental Orthopaedics, Medical University Innsbruck, Salurnerstr. 15, A-6020 Innsbruck, Austria.

Background: Total hip replacement using a minimally invasive surgical approach is claimed to enable recovering of motor function more quickly. The purpose of this prospective As per the stylesheet, kindly provide section headings for abstract.and randomized study was to test this claim by evaluating early patient functional outcomes by gait analysis.

Methods: Seventeen patients were operated on using a traditional anterolateral approach (AL), 16 using a minimally invasive direct anterior approach (DA). Gait analysis was performed the day before surgery, and at 6 and 12 weeks after surgery. Time-distance and kinematics analyses were performed by a recently proposed anatomically-based gait analysis protocol. A static double-leg stance and five walking trials at self-selected speeds were recorded on a 9-m walkway.

Findings: At 6 weeks follow-up, but in the DA group only, a statistically significant improvement with respect to preoperative status was observed for the percentage of single support and for the stride time. Between 6- and 12-week follow-up, the DA group showed a significant improvement in cadence, stride time and length, walking speed, hip flexion at foot contact, maximum hip flexion in swing, and hip total range of motion in the sagittal and the coronal planes. Between 6 and 12 weeks, the AL group showed significant improvements in opposite foot contact and step time, and in flexion at foot contact, maximum flexion in swing, and range of flexion at the hip joint.

Interpretation: Minimally invasive DA patients improved in a larger number of gait parameters than patients receiving the traditional AL approach. The majority of improvements occurred between the 6- and 12-week follow-ups.
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http://dx.doi.org/10.1016/j.clinbiomech.2009.07.010DOI Listing
December 2009

The effect of femoral component malrotation on patellar biomechanics.

J Biomech 2008 Dec 18;41(16):3332-9. Epub 2008 Nov 18.

Scientific Affairs, Stryker Europe, Thalwil, Switzerland.

Patellofemoral complications are among the important reasons for revision knee arthroplasty. Femoral component malposition has been implicated in patellofemoral maltracking, which is associated with anterior knee pain, subluxation, fracture, wear, and aseptic loosening. Rotating-platform mobile bearings compensate for malrotation between the tibial and femoral components and may, therefore, reduce any associated patellofemoral maltracking. To test this hypothesis, we developed a dynamic model of quadriceps-driven open-kinetic-chain extension in a knee implanted with arthroplasty components. The model was validated using tibiofemoral and patellofemoral kinematics and forces measured in cadaver knees. Knee kinematics and patellofemoral forces were measured after simulating malrotation (+/-3 degrees ) of the femoral component. Rotational alignment of the femoral component affected tibial rotation near full extension and tibial adduction at higher flexion angles. External rotation of the femoral component increased patellofemoral lateral tilt, lateral shift, and lateral shear forces. Up to 21 degrees of bearing rotation relative to the tibia was noted in the rotating-bearing condition. However, the rotating bearing had minimal effect in reducing the patellofemoral maltracking or shear induced by femoral component rotation. The rotating platform does not appear to be forgiving of malalignment of the extensor mechanism resulting from femoral component malrotation. These results support the value of improving existing methodologies for accurate femoral component alignment in total knee arthroplasty.
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http://dx.doi.org/10.1016/j.jbiomech.2008.09.032DOI Listing
December 2008

Changes in knee kinematics reflect the articular geometry after arthroplasty.

Clin Orthop Relat Res 2008 Oct 13;466(10):2491-9. Epub 2008 Aug 13.

Department of Bioengineering, Imperial College London, London, UK.

We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. TKA caused loss of the screw-home; the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63 degrees to 11 degrees extension. The range of internal-external rotation was shifted externally from 30 degrees to 20 degrees extension. There was a small tibial posterior translation from 40 degrees to 90 degrees flexion. The varus-valgus alignment and laxity did not change after TKA. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, the data confirmed our hypothesis for rotations but not for translations. It is not known whether the standard navigated position provides the best match to physiologic kinematics.
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http://dx.doi.org/10.1007/s11999-008-0440-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2584306PMC
October 2008

Bony impingement affects range of motion after total hip arthroplasty: A subject-specific approach.

J Orthop Res 2008 Apr;26(4):443-52

Scientific Affairs, Stryker Europe, Thalwil, Switzerland.

Hip range of motion after total hip arthroplasty has been shown to be dependent on prosthetic design and component placement. We hypothesized that bony anatomy would significantly affect range of motion. Computer models of a current generation hip arthroplasty design were virtually implanted in a model of pelvis and femur in various orientations ranging from 35 degrees to 55 degrees cup abduction, 0 degrees to 30 degrees cup anteversion, and 0 degrees to 30 degrees femoral anteversion. Four head sizes ranging from 22.2 to 32 mm and two neck sizes ranging from 10-mm and 12-mm diameter were tested. Range of motion was recorded as maximum flexion-extension, abduction-adduction, and axial rotation of the femur before any contact between prosthetic components or bone was detected. Bony impingement preceded component impingement in about 44% of all conditions tested, ranging from 66% in adduction to 22% in extension. Range of motion increased as head size increased. However, increasing head size also increased the propensity for bony impingement, which tended to reduce the beneficial effect of increased head size on range of motion. Reducing neck diameter had a greater effect on prosthetic impingement (mean, 3.5 degrees increase in range of motion) compared to bone impingement (mean, 1.9 degrees ). This model allowed for a clinically relevant assessment of range of motion after total hip arthroplasty and may also be used with patient-specific geometry [such as that obtained from preoperative computed tomography (CT) scans] for more accurate preoperative planning.
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http://dx.doi.org/10.1002/jor.20541DOI Listing
April 2008

The clinical consequences of flexion gap asymmetry in total knee arthroplasty.

J Arthroplasty 2007 Feb;22(2):235-40

Department of Orthopedic Surgery, University of Zurich, Balgrist, Switzerland.

This study was carried out to compare femoral component rotation of 18 knees from 18 patients who suffered from lateral flexion instability after total knee arthroplasty (Western Ontario and McMaster University Osteoarthritis [WOMAC], 6.4 points; International Knee Society [IKS] score, 119 points) with 10 asymptomatic controls (WOMAC, 0.1 points; IKS score, 182 points) after total knee arthroplasty. The symptomatic patients showed increased lateral joint laxity as determined by fluoroscopic stress radiography. Femoral component rotation was determined by computed tomography scans. The femoral component rotation was more internally rotated in symptomatic patients (5.5 degrees ) than in controls (1.0 degrees ) (P = .04). Varus laxity in flexion was higher in symptomatic patients (11.0 degrees ) than in controls (7.0 degrees ) (P < .001). Increased lateral flexion laxity is associated with increased internal femoral component rotation and a less favorable clinical outcome.
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http://dx.doi.org/10.1016/j.arth.2006.04.024DOI Listing
February 2007

Sagittal curvature of total knee replacements predicts in vivo kinematics.

Clin Biomech (Bristol, Avon) 2007 Jan 9;22(1):52-8. Epub 2006 Oct 9.

Scientific Affairs, Stryker Europe, Thalwil, Switzerland.

Background: It is known that in vivo kinematics after total knee replacement is influenced by the design of the implant. The goal of this study was to show that the sagittal curvature of two different knee prostheses differing in geometric design predicts their in vivo motion behavior.

Methods: Three-dimensional tibio-femoral displacements of two prosthesis designs (single radius vs. dual radius) were measured during knee extension under weight bearing conditions by in vivo video fluoroscopy. Finite helical axes were computed to represent the tibio-femoral motions. Angular deviation alpha and the spatial localization deviation delta were used to characterize the motions. Angular deviation is the angle between each incremental finite helical axis and the medio-lateral axis of the femoral component of the prosthesis. The spatial localization deviation is the distance between each finite helical axis and the center of the femoral component of the prosthesis. Statistical comparisons were performed using the median and the interquartile range of the angular deviation and the spatial localization deviation.

Findings: The single-radius design showed finite helical axes concentrated at a single axis near to the medio-lateral axis of the femoral component. The angular and spatial localization deviation of the dual radius design were larger compared to the single radius design, exhibiting finite helical axes varying between two axes.

Interpretation: Video fluoroscopy in combination with finite helical axis analysis proved to be suitable methods to evaluate the in vivo kinematical behavior of total knee arthroplasty, which can be useful for implant designers. Knowledge of in vivo kinematics can also provide surgeons with more background information about the total knee arthroplasty models they implant.
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http://dx.doi.org/10.1016/j.clinbiomech.2006.07.011DOI Listing
January 2007

Reliability of the transepicondylar axis as an anatomical landmark in total knee arthroplasty.

J Arthroplasty 2006 Sep;21(6):878-82

Innsbruck Medical University, Department of Orthopaedic Surgery, Thalwil, Switzerland.

Femoral component malalignment after total knee arthroplasty is known to cause clinical symptoms, such as anterior knee pain. For intraoperative referencing, several anatomical landmarks are used by surgeons. One frequently used landmark is the transepicondylar axis, yet the accuracy and reproducibility of defining this axis have not been established. In 6 human cadavers, 4 different experienced orthopedic surgeons performed selections of the most prominent points of the medial and lateral epicondyle. Each individual position was digitized and recorded by an accurate optical navigation system. In addition, the most prominent points of the medial and lateral epicondyle were defined on a computed tomography image. After transforming the cadaver points in the computed tomography coordinate system, distances to the epicondyles were measured. The overall distribution of selected points was located in an area of 278 mm2 upon the medial epicondyle and 298 mm2 of the lateral.
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http://dx.doi.org/10.1016/j.arth.2005.10.020DOI Listing
September 2006

Malrotation in total knee arthroplasty: effect on tibial cortex strain captured by laser-based strain acquisition.

Clin Biomech (Bristol, Avon) 2006 Jul 22;21(6):603-9. Epub 2006 Mar 22.

STRYKER Europe, Department for Scientific Affairs, Florastrasse 13, 8800 Thalwil, Switzerland.

Background: Malrotation of the tibial and femoral components has been recognized to be a clinical complication affecting the performance and durability of total knee arthroplasty. This study used a novel strain acquisition technique to determine the effect of tibio-femoral component malrotation on tibial torque and strain distribution of the proximal tibial cortex with a cemented fixed-bearing posterior-stabilized knee.

Methods: Using electronic speckle pattern interferometry, strain on the proximal tibia of human cadaveric knees was obtained in response to 1500N axial loading for neutrally aligned tibial and femoral components, and for 10 degrees internal and external malrotation between the tibial and femoral components. Local strain gage measurements were combined with full-field optical strain measurements to quantify effects on tibial cortex strain and strain distributions caused by the 10 degrees malrotations. In addition, tibial torque was measured for incremental degrees of tibio-femoral malrotation.

Findings: Tibio-femoral malrotations as small as 2 degrees caused tibial torque in excess of 4 Nm. At 10 degrees malrotation, tibial torque significantly increased to over 8 Nm (P<0.001) as compared to neutrally aligned components. Local strain gage results significantly increased from 500 muepsilon to 632 muepsilon compressive strain in response to 10 degrees external malrotation, and to 1000 muepsilon compressive strain in response to 10 degrees internal malrotation. Full-field optical strain reports yielded the highest strain of 2153 muepsilon for 10 degrees internal malrotation 30 mm below the joint line.

Interpretation: Laser-based strain measurement technology provides novel capabilities to capture cortex strain fields. The sensitivity of cortex strain and torsion to small amounts of tibio-femoral malrotation may explain factors contributing to aseptic implant loosening of the tibial component.
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http://dx.doi.org/10.1016/j.clinbiomech.2006.01.011DOI Listing
July 2006

The frontal pelvic plane provides a valid reference system for implantation of the acetabular cup: spatial orientation of the pelvis in different positions.

Acta Orthop 2005 Dec;76(6):848-53

Department of Orthopaedic Surgery, Innsbruck Medical University, Austria.

Background: The frontal pelvic plane has traditionally served as the reference plane for implantation of the acetabular cup during total hip arthroplasty, with referencing performed with the patient supine on the operating table. During daily activities in an upright position, the frontal pelvic plane changes from a horizontal to a vertical orientation. If this change in orientation is accompanied by a substantial change in pelvic inclination angle, it would mean that the use of the frontal pelvic plane as a reference plane for implantation of the acetabular cup would not be valid for proper alignment of the cup. To evaluate this possibility, we measured the change of inclination of the pelvis from the supine to the standing position.

Subjects And Methods: We evaluated 120 patients, first positioned in a standing position and then supine on a table. Three pelvic landmarks were digitized percutaneously, and the spatial coordinates were calculated with regard to pelvic orientation in the horizontal and the vertical plane.

Results: We found a mean inclination of 6.7 degrees in the standing position and 5.6 degrees in the supine position. Patients who were more than 60 years of age who did not have coxarthrosis had a greater inclination angle (8.7 degrees ) while standing. Pelvic orientation was stable with regard to the supine and standing positions. These results were independent of sex, level of arthrosis, or status after implantation of a total hip replacement.

Interpretation: The frontal pelvic plane is a valid reference plane for implantation of the acetabular cup.
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http://dx.doi.org/10.1080/17453670510045471DOI Listing
December 2005

A mobile-bearing knee prosthesis can reduce strain at the proximal tibia.

Clin Orthop Relat Res 2006 Jun;447:105-11

Biomechanics Laboratory, Legacy Research & Technology Center, Portland, OR 97232, USA.

Mobile and fixed-bearing knee prostheses are likely to generate distinct strain gradients in the proximal tibia. The resulting strain distribution in the proximal tibia governs bone remodeling and affects implant integration and stability. We determined the effects of fixed and mobile-bearing total knee prostheses on strain distribution at the proximal tibia. This mobile-bearing prosthesis was evaluated in cadaveric specimens under axial and torsional loading. Strain on the proximal tibial cortex was measured with rosette strain gages and an optical full-field strain acquisition system. Tibial torsion in response to combined axial and torsional loading was documented. There was no difference in cortex strain between the fixed and the mobile-bearing prostheses under 1.5 kN axial loading. Superimposing 10 degrees tibial internal rotation induced 22% less compressive strain in the mobile-bearing prosthesis compared with the fixed-bearing prosthesis. Under 10 degrees tibial external rotation, the mobile-bearing prosthesis induced 33% less compressive strain than the fixed-bearing prosthesis. Optically acquired strain fields showed peak compressive strain at the anteromedial aspect 30 mm below the joint line. The mobile-bearing prosthesis reduced torque in the proximal tibia during knee rotation by 68-73% compared with the fixed-bearing prosthesis. Our data suggest that the particular mobile-bearing prosthesis tested potentially reduces elevated strain levels in the proximal tibia.
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http://dx.doi.org/10.1097/01.blo.0000203463.27937.97DOI Listing
June 2006

Navigation improves accuracy of rotational alignment in total knee arthroplasty.

Clin Orthop Relat Res 2004 Sep(426):180-6

Department of Orthopaedics, University of Innsbruck, Innsbruck, Austria.

Successful total knee arthroplasty is dependent on the correct alignment of implanted prostheses. Major clinical problems can be related to poor femoral component positioning, including sagittal plane and rotational malalignment. A prospective randomized study was designed to test whether an optical navigation system for total knee arthroplasty achieved greater implantation precision than a nonnavigated technique. The primary variable was rotation of the femoral component in the transverse plane, measured from postoperative radiographs and computed tomography images. Sixty-four patients were included in the study. All patients received the Duracon total knee prosthesis. The patients were randomly divided into two groups: Group C patients had conventional total knee arthroplasty without navigation; Group N patients had total knee arthroplasty using a computer-assisted knee navigation system. Analysis showed that patients in Group N had significantly better rotational alignment and flexion angle of the femoral component than patients in Group C. In addition, superior postoperative alignment of the mechanical axis, posterior tibial slope, and rotational alignment was achieved for patients in Group N. The use of a navigation system provides improved alignment accuracy, and can help to avoid femoral malrotation and errors in axial alignment.
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http://dx.doi.org/10.1097/01.blo.0000136835.40566.d9DOI Listing
September 2004

Reduced variability of acetabular cup positioning with use of an imageless navigation system.

Clin Orthop Relat Res 2004 Sep(426):159-63

Department of Orthopaedic Surgery, Medical University of Innsbruck, Austria.

Positioning the acetabular component is one of the most important steps in total hip arthroplasty; malpositioned components can result in dislocations, impingement, limited range of motion, and increased polyethylene wear. Conventional surgery makes use of specialized alignment guides provided by the manufacturers of the implants. The use of mechanical guides has been shown to result in large variations of cup inclination and version. We investigated acetabular cup alignment with the nonimage-based hip navigation system compared with a conventional mechanically guided procedure in 12 human cadavers. Postoperative cup position relative to the pelvic reference plane was assessed in both groups with the use of a three-dimensional digitizing arm. In the navigated group, a median inclination of 45.5 degrees and a median anteversion of 21.9 degrees (goals, 45 degrees and 20 degrees) were reached. In the control group, the median inclination was 41.8 degrees and the median anteversion was 24.6 degrees. The ninetieth percentile showed a much wider range for the control group (36.1 degrees-51.8 degrees inclination, 15 degrees-33.5 degrees anteversion) than for the navigated group (43.9 degrees-48.2 degrees inclination, 18.3 degrees-25.4 degrees anteversion). This cadaver study shows that computer-assisted cup positioning using a nonimage-based hip navigation system allowed for more consistent placement of the acetabular component.
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http://dx.doi.org/10.1097/01.blo.0000141902.30946.6dDOI Listing
September 2004

Malformation of the acetabular fossa as a cause of intrapelvic injury in total hip arthroplasty: a report of 2 cases.

J Arthroplasty 2004 Jan;19(1):129-31

Department of Orthopaedic Surgery, University of Innsbruck, Anichstrasse 35, A-6020, Austria.

We report 2 cases of bone defects of the acetabulum. The first case was a patient who underwent a total hip arthroplasty. An intraoperative bleeding occurred because of an injury of an intrapelvic artery. Preoperative radiographs did not show this bone defect. A similar abnormality of the acetabulum was found in a series of 30 pelves that were dissected for a cadaver study. In this case, the bone defect was located in the center of the right acetabulum.
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http://dx.doi.org/10.1016/s0883-5403(03)00401-7DOI Listing
January 2004

Fluoroscopically assisted stress radiography for varus-valgus stability assessment in flexion after total knee arthroplasty.

J Arthroplasty 2003 Jun;18(4):513-5

Orthopedic Department University Hospital Zürich, Switzerland.

A radiographic technique to quantify varus and valgus joint laxity in flexion after total knee arthroplasty (TKA) was evaluated by means of inter-rater assessment in 12 patients. The test was shown to have good reliability. The simple method helps to detect instability in knee flexion that might be overlooked in a conventional clinical examination.
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http://dx.doi.org/10.1016/s0883-5403(03)00060-3DOI Listing
June 2003

Avoidance of medial cortical fracture in high tibial osteotomy: improved technique.

Clin Orthop Relat Res 2002 Feb(395):180-5

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

A new technique in oblique incomplete high tibial osteotomy that permits an increase of valgus correction while preventing fracture of the medial cortex was investigated. Closing wedge or opening wedge osteotomy was done on 23 tibias from cadavers before loading in an Instron testing machine. In seven specimens (Group 1), lateral oblique wedge osteotomy was done. In seven other specimens (Group 2), one medial oblique cut was made. In both groups, the osteotomy terminated 10 mm from the cortex and approximately 2 cm below the plateau. In nine specimens (Group 3), the osteotomy terminated in a 5-mm diameter hole, drilled in an anteroposterior direction, with its center positioned 10 mm from the medial cortex and 2 cm below the articular surface. The maximum angle of opening or closing before fracture of the cortex took place was recorded. In Groups 1 and 2, similar maximum correction angles were observed, 6.7 degrees versus 6.5 degrees, respectively. In Group 3, the stress relieving hole allowed the correction angle to be increased to 10 degrees. An oblique high tibial valgus closing wedge osteotomy with an apical drill hole allows a significant increase of the correction angle compared with the same osteotomy without a drill hole. Medial open wedge osteotomy offers no advantage over lateral closed wedge osteotomy in the maximum obtainable correction angle without failure of the cortex.
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http://dx.doi.org/10.1097/00003086-200202000-00020DOI Listing
February 2002
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