Publications by authors named "Roger Zauel"

28 Publications

  • Page 1 of 1

Quantifying shoulder activity after rotator cuff repair: Technique and preliminary results.

J Orthop Res 2021 Jun 30. Epub 2021 Jun 30.

Henry Ford Health System, Detroit, Michigan, USA.

Repair tissue healing after rotator cuff repair remains a significant clinical problem, and excessive shoulder activity after surgical repair is believed to contribute to re-tears. In contrast, small animal studies have demonstrated that complete removal of activity impairs tendon healing and have advocated for an "appropriate" level of activity, but in humans the appropriate amount of shoulder activity to enhance healing is not known. As an initial step toward understanding the relationship between postoperative shoulder activity and repair tissue healing, the objectives of this study were to assess the precision, accuracy, and feasibility of a wrist-worn triaxial accelerometer for measuring shoulder activity. Following assessments of precision (±0.002 g) and accuracy (±0.006 g), feasibility was assessed by measuring 1 week of shoulder activity in 14 rotator cuff repair patients and 8 control subjects. Shoulder activity was reported in terms of volume (mean acceleration, activity count, mean activity index, active time) and intensity (intensity gradient). Patients had significantly less volume (p ≤ .03) and intensity (p = .01) than controls. Time post-surgery was significantly associated with the volume (p ≤ .05 for mean acceleration, activity count, and mean activity index) and intensity (p = .03) of shoulder activity, but not active time (p = .08). These findings indicate this approach has the accuracy and precision necessary to continuously monitor shoulder activity with a wrist-worn sensor. The preliminary data demonstrate the ability to discriminate between healthy control subjects and patients recovering from rotator cuff repair and provide support for using a wearable sensor to monitor changes over time in shoulder activity.
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http://dx.doi.org/10.1002/jor.25122DOI Listing
June 2021

Assessment of Intravertebral Mechanical Strains and Cancellous Bone Texture Under Load Using a Clinically Available Digital Tomosynthesis Modality.

J Biomech Eng 2021 10;143(10)

Bone & Joint Center, Henry Ford Hospital, Integrative Biosciences Center (iBio), 6135 Woodward, Detroit, MI 48202.

Vertebral fractures are the most common osteoporotic fractures, but clinical means for assessment of vertebral bone integrity are limited in accuracy, as they typically use surrogate measures that are indirectly related to mechanics. The objective of this study was to examine the extent to which intravertebral strain distributions and changes in cancellous bone texture generated by a load of physiological magnitude can be characterized using a clinically available imaging modality. We hypothesized that digital tomosynthesis-based digital volume correlation (DTS-DVC) and image texture-based metrics of cancellous bone microstructure can detect development of mechanical strains under load. Isolated cadaveric T11 vertebrae and L2-L4 vertebral segments were DTS imaged in a nonloaded state and under physiological load levels. Axial strain, maximum principal strain, maximum compressive and tensile principal strains, and von Mises equivalent strain were calculated using the DVC technique. The change in textural parameters (line fraction deviation, anisotropy, and fractal parameters) under load was calculated within the cancellous centrum. The effect of load on measured strains and texture variables was tested using mixed model analysis of variance, and relationships of strain and texture variables with donor age, bone density parameters, and bone size were examined using regression models. Magnitudes and heterogeneity of intravertebral strain measures correlated with applied loading and were significantly different from background noise. Image texture parameters were found to change with applied loading, but these changes were not observed in the second experiment testing L2-L4 segments. DTS-DVC-derived strains correlated with age more strongly than did bone mineral density (BMD) for T11.
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http://dx.doi.org/10.1115/1.4051280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8299817PMC
October 2021

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography.

J Vis Exp 2021 03 12(169). Epub 2021 Mar 12.

Bone and Joint Center, Department of Orthopaedic Surgery, Henry Ford Health System;

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, multiple ligaments, and approximately 20 muscles. Unfortunately, shoulder pathologies (e.g., rotator cuff tears, joint dislocations, arthritis) are common, resulting in substantial pain, disability, and decreased quality of life. The specific etiology for many of these pathologic conditions is not fully understood, but it is generally accepted that shoulder pathology is often associated with altered joint motion. Unfortunately, measuring shoulder motion with the necessary level of accuracy to investigate motion-based hypotheses is not trivial. However, radiographic-based motion measurement techniques have provided the advancement necessary to investigate motion-based hypotheses and provide a mechanistic understanding of shoulder function. Thus, the purpose of this article is to describe the approaches for measuring shoulder motion using a custom biplanar videoradiography system. The specific objectives of this article are to describe the protocols to acquire biplanar videoradiographic images of the shoulder complex, acquire CT scans, develop 3D bone models, locate anatomical landmarks, track the position and orientation of the humerus, scapula, and torso from the biplanar radiographic images, and calculate the kinematic outcome measures. In addition, the article will describe special considerations unique to the shoulder when measuring joint kinematics using this approach.
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http://dx.doi.org/10.3791/62210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8109214PMC
March 2021

Vertebral stiffness measured via tomosynthesis-based digital volume correlation is strongly correlated with reference values from micro-CT-based DVC.

Med Eng Phys 2020 10 1;84:169-173. Epub 2020 Sep 1.

Bone and Joint Center, Henry Ford Hospital, Integrative Biosciences Center (iBio), 6135 Woodward, Detroit, MI 48202, United States. Electronic address:

Digital tomosynthesis (DTS) is a clinically available modality that allows imaging of a patient's spine in supine and standing positions. The purpose of this study was to establish the extent to which vertebral displacement and stiffness derived from DTS-based digital volume correlation (DTS-DVC) are correlated with those from a reference method, i.e., microcomputed tomography-based DVC (μCT-DVC). T11 vertebral bodies from 11 cadaveric donors were DTS imaged twice in a nonloaded state and once under a fixed load level approximating upper body weight. The same vertebrae were µCT imaged in nonloaded and loaded states (40 μm voxel size). Vertebral displacements were calculated at each voxel using DVC with pairs of nonloaded and loaded images, from which endplate-to-endplate axial displacement (D) and vertebral stiffness (S) were calculated. Both D and S demonstrated strong positive correlations between DTS-DVC and μCT-DVC, with correlations being stronger when vertebral displacement was calculated using the median (R=0.80; p<0.0002 and R=0.93; p<0.0001, respectively) rather than average displacement (R=0.63; p<0.004 and R=0.69; p<0.002, respectively). In conclusion, the demonstrated relationship of DTS-DVC with the μCT standard supports further development of a biomechanics-based clinical assessment of vertebral bone quality using the DTS-DVC technique.
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http://dx.doi.org/10.1016/j.medengphy.2020.08.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7522399PMC
October 2020

Instantaneous helical axis estimation of glenohumeral kinematics: The impact of rotator cuff pathology.

J Biomech 2020 08 2;109:109924. Epub 2020 Jul 2.

Bone and Joint Center, Department of Orthopaedic Surgery, Henry Ford Health System, 6135 Woodward Avenue, Detroit, MI 48202, USA.

The rotator cuff is theorized to contribute to force couples required to produce glenohumeral kinematics. Impairment in these force couples would theoretically result in impaired ball-and-socket kinematics. Although less frequently used than traditional kinematic descriptors (e.g., Euler angles, joint translations), helical axes are capable of identifying alterations in ball-and-socket kinematics by quantifying the variability (i.e., dispersion) in axis orientation and position during motion. Consequently, assessing glenohumeral helical dispersion may provide indirect evidence of rotator cuff function. The purpose of this exploratory study was to determine the extent to which rotator cuff pathology is associated with alterations in ball-and-socket kinematics. Fifty-one participants were classified into one of five groups based on an assessment of the supraspinatus using diagnostic imaging: asymptomatic healthy, asymptomatic tendinosis, asymptomatic partial-thickness tear, asymptomatic full-thickness tear, symptomatic full-thickness tear. Glenohumeral kinematics were quantified during coronal plane abduction using a biplane x-ray system and described using instantaneous helical axes. The degree to which glenohumeral motion coincided with ball-and-socket kinematics was described using the angular and positional dispersion about the optimal helical axis and pivot, respectively. No statistically significant difference was observed between groups in angular dispersion. However, symptomatic individuals with a full-thickness supraspinatus tear had significantly more positional dispersion than asymptomatic individuals with a healthy supraspinatus or tendinosis. These findings suggest that symptomatic individuals with a full-thickness supraspinatus tear exhibit impaired ball-and-socket kinematics, which is believed to be associated with a disruption of the glenohumeral force couples.
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http://dx.doi.org/10.1016/j.jbiomech.2020.109924DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7443981PMC
August 2020

Digital tomosynthesis based digital volume correlation: A clinically viable noninvasive method for direct measurement of intravertebral displacements using images of the human spine under physiological load.

Med Phys 2019 Oct 31;46(10):4553-4562. Epub 2019 Aug 31.

Bone and Joint Center, Henry Ford Hospital, Detroit, MI, USA.

Purpose: We have developed a clinically viable method for measurement of direct, patient-specific intravertebral displacements using a novel digital tomosynthesis based digital volume correlation technique. These displacements may be used to calculate vertebral stiffness under loads induced by a patient's body weight; this is particularly significant because, among biomechanical variables, stiffness is the strongest correlate of bone strength. In this proof of concept study, we assessed the feasibility of the method through a preliminary evaluation of the accuracy and precision of the method, identification of a range of physiological load levels for which displacements are measurable, assessment of the relationship of measured displacements with microcomputed tomography based standards, and demonstration of the in vivo application of the technique.

Methods: Five cadaveric T11 vertebrae were allocated to three groups in order to study (a) the optimization of digital volume correlation algorithm input parameters, (b) accuracy and precision of the method and the ability to measure displacements at a range of physiological load levels, and (c) the correlation between displacements measured using tomosynthesis based digital volume correlation vs. high resolution microcomputed tomography based digital volume correlation and large scale finite element models. Tomosynthesis images of one patient (Female, 60 yr old) were used to calculate displacement maps, and in turn stiffness, using images acquired in both standing and standing-with-weight (8 kg) configurations.

Results: We found that displacements were accurate (2.28 µm total error) and measurable at physiological load levels (above 267 N) with a linear response to applied load. Calculated stiffness among three tested vertebral bodies was within an acceptable range relative to reported values for vertebral stiffness (5651-13260 N/mm). Displacements were in good qualitative and quantitative agreement with both microcomputed tomography based finite element (r  = 0.762, P < 0.001) and digital volume correlation (r  = 0.799, P < 0.001) solutions. For one patient tested twice, once standing and once holding weights, results demonstrated excellent qualitative reproducibility of displacement distributions with superior endplate displacements increasing by 22% with added weight.

Conclusions: The results of this work collectively suggest the feasibility of the method for in vivo measurement of intravertebral displacements and stiffness in humans. These findings suggest that digital volume correlation using digital tomosynthesis imaging may be useful in understanding the mechanical response of bone to disease and may further enhance our ability to assess fracture risk and treatment efficacy for the spine.
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http://dx.doi.org/10.1002/mp.13750DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6822382PMC
October 2019

Effects of asymptomatic rotator cuff pathology on in vivo shoulder motion and clinical outcomes.

J Shoulder Elbow Surg 2017 Jun 25;26(6):1064-1072. Epub 2017 Jan 25.

Bone and Joint Center, Henry Ford Health System, Detroit, MI, USA.

Background: The incidence of asymptomatic rotator cuff tears has been reported to range from 15% to 39%, but the influence of asymptomatic rotator cuff pathology on shoulder function is not well understood. This study assessed the effects of asymptomatic rotator cuff pathology on shoulder kinematics, strength, and patient-reported outcomes.

Methods: A clinical ultrasound examination was performed in 46 asymptomatic volunteers (age: 60.3 ± 7.5 years) with normal shoulder function to document the condition of their rotator cuff. The ultrasound imaging identified the participants as healthy (n = 14) or pathologic (n = 32). Shoulder motion was measured with a biplane x-ray imaging system, strength was assessed with a Biodex (Biodex Medical Systems, Inc., Shirley, NY, USA), and patient-reported outcomes were assessed using the Western Ontario Rotator Cuff Index and visual analog scale pain scores.

Results: Compared with healthy volunteers, those with rotator cuff pathology had significantly less abduction (P = .050) and elevation (P = .041) strength, their humerus was positioned more inferiorly on the glenoid (P = .018), and the glenohumeral contact path length was longer (P = .007). No significant differences were detected in the Western Ontario Rotator Cuff Index, visual analog scale, range of motion, or acromiohumeral distance.

Conclusions: The differences observed between the healthy volunteers and those with asymptomatic rotator cuff pathology lend insight into the changes in joint mechanics, shoulder strength, and conventional clinical outcomes associated with the early stages of rotator cuff pathology. Furthermore, these findings suggest a plausible mechanical progression of kinematic and strength changes associated with the development of rotator cuff pathology.
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http://dx.doi.org/10.1016/j.jse.2016.11.048DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5438772PMC
June 2017

Effects of Rotator Cuff Pathology and Physical Therapy on In Vivo Shoulder Motion and Clinical Outcomes in Patients With a Symptomatic Full-Thickness Rotator Cuff Tear.

Orthop J Sports Med 2016 Sep 26;4(9):2325967116666506. Epub 2016 Sep 26.

Bone and Joint Center, Henry Ford Health System, Detroit, Michigan, USA.

Background: Physical therapy (PT) is often prescribed for patients with rotator cuff tears. The extent to which PT influences strength, range of motion (ROM), and patient-reported outcomes has been studied extensively, but the effect of PT on in vivo joint kinematics is not well understood.

Purpose: To assess the influence of symptomatic rotator cuff pathology and the effects of PT on shoulder motion, strength, and patient-reported outcomes.

Study Design: Controlled laboratory study.

Methods: Twenty-five patients with a symptomatic rotator cuff tear and 25 age-matched asymptomatic control subjects were recruited. Shoulder motion was measured using a biplane radiography imaging system, strength was assessed with a Biodex dynamometer, and patient-reported outcomes were assessed using the Western Ontario Rotator Cuff Index and visual analog scale (VAS) pain scores. Data were acquired from the patients before and after 8 weeks of physical therapy. Data were acquired at 1 time point for the control subjects.

Results: Compared with the control subjects, patients with a symptomatic rotator cuff tear had significantly worse pain/function scores ( < .01); less ROM ( < .01); lower abduction (ABD), external rotation (ER), and internal rotation (IR) strength ( < .01); less scapulothoracic posterior tilt ( = .05); and lower glenohumeral joint elevation ( < .01). Physical therapy resulted in improved pain/function scores ( < .01), increased ROM ( < .02), increased scapulothoracic posterior tilt ( = .05), increased glenohumeral joint elevation ( = .01), and decreased acromiohumeral distance (AHD) ( = .02).

Conclusion: Compared with age-matched controls, patients had worse pain/function scores, less ROM, and lower ABD, ER, and IR strength. Patients also had less scapulothoracic anteroposterior tilt, less glenohumeral joint elevation, and an altered glenohumeral joint contact path. PT resulted in improved pain/function scores, increased ROM, greater posterior scapulothoracic tilt, increased glenohumeral joint elevation, an increased range of superoinferior joint contact, and a lower mean AHD. Of these differences, PT only returned scapulothoracic tilt to control levels.

Clinical Relevance: This study documents the effects of PT on shoulder motion and conventional clinical outcomes. It is expected that understanding how changes in joint motion are associated with conventional clinical outcomes will lead to improved nonoperative interventions for patients with rotator cuff tears.
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http://dx.doi.org/10.1177/2325967116666506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5040201PMC
September 2016

Measuring Three-Dimensional Thorax Motion Via Biplane Radiographic Imaging: Technique and Preliminary Results.

J Biomech Eng 2016 Jan;138(1)

Measures of scapulothoracic motion are dependent on accurate imaging of the scapula and thorax. Advanced radiographic techniques can provide accurate measures of scapular motion, but the limited 3D imaging volume of these techniques often precludes measurement of thorax motion. To overcome this, a thorax coordinate system was defined based on the position of rib pairs and then compared to a conventional sternum/spine-based thorax coordinate system. Alignment of the rib-based coordinate system was dependent on the rib pairs used, with the rib3:rib4 pairing aligned to within 4.4 ± 2.1 deg of the conventional thorax coordinate system.
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http://dx.doi.org/10.1115/1.4032058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4844245PMC
January 2016

Digital tomosynthesis and high resolution computed tomography as clinical tools for vertebral endplate topography measurements: Comparison with microcomputed tomography.

Bone 2015 Dec 26;81:300-305. Epub 2015 Jul 26.

Bone and Joint Center, Henry Ford Hospital, Detroit, MI, United States.

Endplate morphology is understood to play an important role in the mechanical behavior of vertebral bone as well as degenerative processes in spinal tissues; however, the utility of clinical imaging modalities in assessment of the vertebral endplate has been limited. The objective of this study was to evaluate the ability of two clinical imaging modalities (digital tomosynthesis, DTS; high resolution computed tomography, HRCT) to assess endplate topography by correlating the measurements to a microcomputed tomography (μCT) standard. DTS, HRCT, and μCT images of 117 cadaveric thoracolumbar vertebrae (T10-L1; 23 male, 19 female; ages 36-100 years) were segmented, and inferior and superior endplate surface topographical distribution parameters were calculated. Both DTS and HRCT showed statistically significant correlations with μCT approaching a moderate level of correlation at the superior endplate for all measured parameters (R(2)Adj=0.19-0.57), including averages, variability, and higher order statistical moments. Correlation of average depths at the inferior endplate was comparable to the superior case for both DTS and HRCT (R(2)Adj=0.14-0.51), while correlations became weak or nonsignificant for higher moments of the topography distribution. DTS was able to capture variations in the endplate topography to a slightly better extent than HRCT, and taken together with the higher speed and lower radiation cost of DTS than HRCT, DTS appears preferable for endplate measurements.
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http://dx.doi.org/10.1016/j.bone.2015.07.033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4640984PMC
December 2015

Associations between in-vivo glenohumeral joint motion and morphology.

J Biomech 2015 Sep 6;48(12):3252-7. Epub 2015 Jul 6.

Department of Orthopaedic Surgery, Bone & Joint Center, Henry Ford Health System, United States.

Joint morphology has a significant influence on joint motion and may contribute to the development of rotator cuff pathology, but the relationships between glenohumeral joint (GHJ) morphology and in-vivo GHJ motion are not well understood. The objectives of this study were to assess measures of joint morphology and their relationship with in-vivo joint motion in two populations: shoulders with intact rotator cuffs (n=48) and shoulders with rotator cuff pathology (n=36, including 5 symptomatic tears, 9 asymptomatic tears and 22 repaired tears). GHJ morphology was measured from CT-based three-dimensional models of the humerus and scapula. In-vivo GHJ motion was measured during shoulder abduction using biplane x-ray imaging. Associations between GHJ morphology and motion were assessed with univariate and best subsets regression. The only morphological difference identified between the populations was the critical shoulder angle (intact: 34.5 ± 4.7°, pathologic: 36.9 ± 5.0°, p=0.03), which is consistent with previous research. In intact shoulders, the superior/inferior (S/I) position of the humerus on the glenoid during shoulder abduction was significantly associated with the glenoid's S/I radius of curvature (p<0.01), conformity index (p<0.01), and stability angle (p<0.01). Furthermore, the S/I position of the humerus on the glenoid was negatively associated with the critical shoulder angle (p=0.04), which contradicts previous research. No significant associations between GHJ morphology and GHJ motion were detected in shoulders with rotator cuff tears. It is unknown if rotator cuff pathology compromises the relationships between GHJ morphology and motion, or if the absence of this relationship is a pre-existing condition that increases the likelihood of pathology.
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http://dx.doi.org/10.1016/j.jbiomech.2015.06.030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4592808PMC
September 2015

Differences in glenohumeral joint morphology between patients with anterior shoulder instability and healthy, uninjured volunteers.

J Shoulder Elbow Surg 2015 Jul 7;24(7):1014-20. Epub 2015 May 7.

Bone and Joint Center, Henry Ford Hospital, Detroit, MI, USA.

Background: Traumatic glenohumeral joint (GHJ) dislocations are common, resulting in significant shoulder disability and pain. Previous research indicates that bony morphology is associated with an increased risk of injury in other joints (eg, the knee), but the extent to which bony morphology is associated with traumatic GHJ dislocation is unknown. This study assessed GHJ morphology in patients with anterior GHJ instability and in a control population of healthy volunteers.

Methods: Bilateral computed tomography scans were used to measure GHJ morphology in both shoulders of 11 patients with instability and 11 control subjects. Specific outcome measures included the glenoid radius of curvature (ROC) in the anterior/posterior (A/P) and superior/inferior (S/I) directions, humeral head ROC, A/P and S/I conformity index, and A/P and S/I stability angle.

Results: Compared with the control subjects, the glenoid of the instability the injured shoulder in patients with instability was flatter (ie, higher ROC) in the A/P (P = .001) and S/I (P = .01) directions and this finding was also true for uninjured, contralateral shoulder (A/P: P = .01, S/I: P = .03). No differences in GHJ morphology were detected between the instability patients' injured and contralateral shoulders (P > .07). Similarly, no differences in GHJ morphology were detected between the control subjects' dominant and nondominant shoulders (P > .51).

Conclusions: There are significant differences in GHJ morphology between healthy control subjects and both shoulders (injured and uninjured, contralateral) of patients diagnosed with anterior instability after GHJ dislocation. These findings are important clinically because they suggest that glenoid morphology may influence the risk of GHJ dislocation.
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http://dx.doi.org/10.1016/j.jse.2015.03.024DOI Listing
July 2015

Directional tortuosity as a predictor of modulus damage for vertebral cancellous bone.

J Biomech Eng 2015 Jan;137(1)

There are many methods used to estimate the undamaged effective (apparent) moduli of cancellous bone as a function of bone volume fraction (BV/TV), mean intercept length(MIL), and other image based average microstructural measures. The MIL and BV/TV are both only functions of the cancellous microstructure and, therefore, cannot directly account for damage induced changes in the intrinsic trabecular hard tissue mechanical properties. Using a nonlinear finite element (FE) approximation for the degradation of effective modulus as a function of applied effective compressive strain, we demonstrate that a measurement of the directional tortuosity of undamaged trabecular hard tissue strongly predicts directional effective modulus (r2>0.90) and directional effective modulus degradation (r2>0.65). This novel measure of cancellous bone directional tortuosity has the potential for development into an anisotropic approach for calculating effective mechanical properties as a function of trabecular level material damage applicable to understanding how tissue microstructure and intrinsic hard tissue moduli interact to determine cancellous bone quality.
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http://dx.doi.org/10.1115/1.4029177DOI Listing
January 2015

Accuracy and feasibility of dual fluoroscopy and model-based tracking to quantify in vivo hip kinematics during clinical exams.

J Appl Biomech 2014 Jun 25;30(3):461-70. Epub 2014 Feb 25.

Department of Orthopaedics and the Department of Bioengineering, University of Utah, Salt Lake City, UT.

Accurate measurements of in-vivo hip kinematics may elucidate the mechanisms responsible for impaired function and chondrolabral damage in hips with femoroacetabular impingement (FAI). The objectives of this study were to quantify the accuracy and demonstrate the feasibility of using dual fluoroscopy to measure in-vivo hip kinematics during clinical exams used in the assessment of FAI. Steel beads were implanted into the pelvis and femur of two cadavers. Specimens were imaged under dual fluoroscopy during the impingement exam, FABER test, and rotational profile. Bead locations measured with model-based tracking were compared with those measured using dynamic radiostereometric analysis. Error was quantified by bias and precision, defined as the average and standard deviation of the differences between tracking methods, respectively. A normal male volunteer was also imaged during clinical exams. Bias and precision along a single axis did not exceed 0.17 and 0.21 mm, respectively. Comparing kinematics, positional error was less than 0.48 mm and rotational error was less than 0.58°. For the volunteer, kinematics were reported as joint angles and bone-bone distance. These results demonstrate that dual fluoroscopy and model-based tracking can accurately measure hip kinematics in living subjects during clinical exams of the hip.
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http://dx.doi.org/10.1123/jab.2013-0112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4143504PMC
June 2014

Variability of trabecular microstructure is age-, gender-, race- and anatomic site-dependent and affects stiffness and stress distribution properties of human vertebral cancellous bone.

Bone 2011 Oct 19;49(4):886-94. Epub 2011 Jul 19.

Section of Biomechanics, Bone and Joint Center, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202, USA.

Cancellous bone microstructure is an important determinant of the mechanical integrity of vertebrae. The numerous microstructural parameters that have been studied extensively are generally represented as a single value obtained as an average over a sample. The range of the intra-sample variability of cancellous microstructure and its effect on the mechanical properties of bone are less well-understood. The objectives of this study were to investigate the extent to which human cancellous bone microstructure within a vertebra i) is related to bone modulus and stress distribution properties and ii) changes along with age, gender and locations thoracic 12 (T12) vs lumbar 1 (L1). Vertebrae were collected from 15 male (66±15 years) and 25 female (54±16 years) cadavers. Three dimensional finite element models were constructed using microcomputed tomography images of cylindrical specimens. Linear finite element models were used to estimate apparent modulus and stress in the cylinders during uniaxial compression. The intra-specimen mean, standard deviation (SD) and coefficient of variation (CV) of microstructural variables were calculated. Mixed model statistical analysis of the results demonstrated that increases in the intra-specimen variability of the microstructure contribute to increases in the variability of trabecular stresses and decreases in bone stiffness. These effects were independent from the contribution from intra-specimen average of the microstructure. Further, the effects of microstructural variability on bone stiffness and stress variability were not accounted for by connectivity and anisotropy. Microstructural variability properties (SD, CV) generally increased with age, were greater in females than in males and in T12 than in L1. Significant interactions were found between age, gender, vertebra and race. These interactions suggest that microstructural variability properties varied with age differently between genders, races and vertebral levels. The current results collectively demonstrate that microstructural variability has a significant effect on mechanical properties and tissue stress of human vertebral cancellous bone. Considering microstructural variability could improve the understanding of bone fragility and improve assessment of vertebral fracture risk.
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http://dx.doi.org/10.1016/j.bone.2011.07.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3170516PMC
October 2011

Damage initiation sites in osteoporotic and normal human cancellous bone.

Bone 2011 Mar 23;48(3):663-6. Epub 2010 Nov 23.

Lawrence J. Ellison Musculoskeletal Research Center, Department of Orthopaedic Surgery, University of California, Davis, Sacramento, CA, USA.

Using a finite element (FE) method called biomechanical stereology, Wang et al. previously reported increased microcrack formation and propagation in bone samples from patients with a history of osteoporotic fracture as compared to normal subjects. In this study, we re-analyzed the data from Wang's report to determine the microscopic differences between bone tissue from osteoporotic patients and normal subjects that caused these different patterns of bone tissue damage between the groups. The morphological features examined were the number of "voids" (or osteocyte lacunae) visible and the distance of the lacunae from the initiation of the microcracks. We found that bone samples from patients with a history of osteoporotic fracture contained significantly more lacunae than normal control specimens. We also found a significant correlation (r² = 0.483, p = 0.001) between the number of lacunae visible in the image and the number of microcracks formed. These results help to explain the differences in total microcrack number between the osteoporotic and normal subjects reported in our previous work.
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http://dx.doi.org/10.1016/j.bone.2010.11.009DOI Listing
March 2011

Stiffness of the endplate boundary layer and endplate surface topography are associated with brittleness of human whole vertebral bodies.

Bone 2010 Oct 12;47(4):783-9. Epub 2010 Jul 12.

Bone and Joint Research Center, Department of Orthopaedics, Henry Ford Hospital, 2799 W. Grand Blvd., Detroit, MI 48202, USA.

Stress magnitude and variability as estimated from large scale finite element (FE) analyses have been associated with compressive strength of human vertebral cancellous cores but these relationships have not been explored for whole vertebral bodies. In this study, the objectives were to investigate the relationship of FE-calculated stress distribution parameters with experimentally determined strength, stiffness, and displacement based ductility measures in human whole vertebral bodies, investigate the effect of endplate loading conditions on vertebral stiffness, strength, and ductility and test the hypothesis that endplate topography affects vertebral ductility and stress distributions. Eighteen vertebral bodies (T6-L3 levels; 4 female and 5 male cadavers, aged 40-98 years) were scanned using a flat-panel CT system and followed with axial compression testing with Wood's metal as filler material to maintain flat boundaries between load plates and specimens. FE models were constructed using reconstructed CT images and filler material was added digitally. Two different FE models with different filler material modulus simulating Wood's metal and intervertebral disc (W-layer and D-layer models) were used. Element material modulus to cancellous bone was based on image gray value. Average, standard deviation, and coefficient of variation of von Mises stress in vertebral bone for W-layer and D-layer models and also the ratios of FE parameters from the two models (W/D) were calculated. Inferior and superior endplate surface topographical distribution parameters were calculated. Experimental stiffness, maximum load and work to fracture had the highest correlation with FE-calculated stiffness while experimental ductility measures had highest correlations with FE-calculated average von Mises stress and W-layer to D-layer stiffness ratio. Endplate topography of the vertebra was also associated with its structural ductility and the distribution parameter that best explained this association was kurtosis of inferior endplate topography. Our results indicate that endplate topography variations may provide insight into the mechanisms responsible for vertebral fractures.
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http://dx.doi.org/10.1016/j.bone.2010.07.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3710658PMC
October 2010

In Vivo Measurement of Glenohumeral Joint Contact Patterns.

EURASIP J Adv Signal Process 2010 Jan;2010

Department of Orthopaedic Surgery, Bone and Joint Center, Henry Ford Hospital, 2799 W. Grand Blvd., E&R 2015, Detroit, MI 48202, USA.

The objectives of this study were to describe a technique for measuring in-vivo glenohumeral joint contact patterns during dynamic activities and to demonstrate application of this technique. The experimental technique calculated joint contact patterns by combining CT-based 3D bone models with joint motion data that were accurately measured from biplane x-ray images. Joint contact patterns were calculated for the repaired and contralateral shoulders of 20 patients who had undergone rotator cuff repair. Significant differences in joint contact patterns were detected due to abduction angle and shoulder condition (i.e., repaired versus contralateral). Abduction angle had a significant effect on the superior/inferior contact center position, with the average joint contact center of the repaired shoulder 12.1% higher on the glenoid than the contralateral shoulder. This technique provides clinically relevant information by calculating in-vivo joint contact patterns during dynamic conditions and overcomes many limitations associated with conventional techniques for quantifying joint mechanics.
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http://dx.doi.org/10.1155/2010/162136DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3086287PMC
January 2010

Glenoid inclination: in vivo measures in rotator cuff tear patients and associations with superior glenohumeral joint translation.

J Shoulder Elbow Surg 2009 Mar-Apr;18(2):231-6. Epub 2008 Dec 5.

Department of Orthopaedic Surgery, Bone and Joint Center, Henry Ford Hospital, Detroit, MI, USA.

Glenoid inclination has been associated with rotator cuff tears and superior humeral translation, but the relationship between glenoid inclination and superior humeral translation has not been assessed in vivo. This study compared glenoid inclination between repaired and contralateral shoulders in 21 unilateral rotator cuff repair patients. As a secondary analysis, we assessed the relationship between glenoid inclination and in vivo superior humeral translation. Glenoid inclination was measured from patient-specific, computed tomography-based bone models. Glenohumeral joint motion was measured from biplane radiographs collected during coronal-plane abductions. Glenoid inclination was significantly lower for the rotator cuff tear shoulders (90.7 degrees ) than the asymptomatic, contralateral shoulders (92.3 degrees , P = .04). No significant correlation existed between increased glenoid inclination and superior-inferior translation of the uninjured shoulder (P > .30). This study failed to support the theory that glenoid inclination is responsible for superior humeral translation and the development of subacromial impingement.
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http://dx.doi.org/10.1016/j.jse.2008.08.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2669899PMC
June 2009

Accuracy of biplane x-ray imaging combined with model-based tracking for measuring in-vivo patellofemoral joint motion.

J Orthop Surg Res 2008 Sep 4;3:38. Epub 2008 Sep 4.

Henry Ford Health Systems, Department of Orthopaedics, Bone and Joint Center, E&R 2015, 2799 W Grand Blvd, Detroit, MI 48202, USA.

Background: Accurately measuring in-vivo motion of the knee's patellofemoral (PF) joint is challenging. Conventional measurement techniques have largely been unable to accurately measure three-dimensional, in-vivo motion of the patella during dynamic activities. The purpose of this study was to assess the accuracy of a new model-based technique for measuring PF joint motion.

Methods: To assess the accuracy of this technique, we implanted tantalum beads into the femur and patella of three cadaveric knee specimens and then recorded dynamic biplane radiographic images while manually flexing and extending the specimen. The position of the femur and patella were measured from the biplane images using both the model-based tracking system and a validated dynamic radiostereometric analysis (RSA) technique. Model-based tracking was compared to dynamic RSA by computing measures of bias, precision, and overall dynamic accuracy of four clinically-relevant kinematic parameters (patellar shift, flexion, tilt, and rotation).

Results: The model-based tracking technique results were in excellent agreement with the RSA technique. Overall dynamic accuracy indicated errors of less than 0.395 mm for patellar shift, 0.875 degrees for flexion, 0.863 degrees for tilt, and 0.877 degrees for rotation.

Conclusion: This model-based tracking technique is a non-invasive method for accurately measuring dynamic PF joint motion under in-vivo conditions. The technique is sufficiently accurate in measuring clinically relevant changes in PF joint motion following conservative or surgical treatment.
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http://dx.doi.org/10.1186/1749-799X-3-38DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2538511PMC
September 2008

Postfailure modulus strongly affects microcracking and mechanical property change in human iliac cancellous bone: a study using a 2D nonlinear finite element method.

J Biomech 2008 Aug 30;41(12):2654-8. Epub 2008 Jul 30.

Lawrence J. Ellison Musculoskeletal Research Center, University of California Davis Medical Center, Room 2000, Research Facility I, 4635 Second Avenue, Sacramento, CA 95817, USA.

A two-dimensional (2D) finite element (FE) method was used to estimate the ability of bone tissue to sustain damage as a function of postfailure modulus. Briefly, 2D nonlinear compact-tension FE models were created from quantitative back-scattered electron images taken of human iliac crest bone specimens. The effects of different postfailure moduli on predicted microcrack propagation were examined. The 2D FE models were used as surrogates for real bone tissues. The crack number was larger in models with higher postfailure modulus, while mean crack length and area were smaller in these models. The rate of stiffness reduction was greater in the models with lower postfailure modulus. Hence, the current results supported the hypothesis that hard tissue postfailure properties have strong effects on bone microdamage morphology and the rate of change in apparent mechanical properties.
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http://dx.doi.org/10.1016/j.jbiomech.2008.06.011DOI Listing
August 2008

Validation of three-dimensional model-based tibio-femoral tracking during running.

Med Eng Phys 2009 Jan 23;31(1):10-6. Epub 2008 Apr 23.

University of Pittsburgh, Department of Orthopaedic Surgery, Orthopaedic Research Laboratories, 3820 South Water Street, Pittsburgh, PA 15203, USA.

The purpose of this study was to determine the accuracy of a radiographic model-based tracking technique that measures the three-dimensional in vivo motion of the tibio-femoral joint during running. Tantalum beads were implanted into the femur and tibia of three subjects and computed tomography (CT) scans were acquired after bead implantation. The subjects ran 2.5m/s on a treadmill positioned within a biplane radiographic system while images were acquired at 250 frames per second. Three-dimensional implanted bead locations were determined and used as a "gold standard" to measure the accuracy of the model-based tracking. The model-based tracking technique optimized the correlation between the radiographs acquired via the biplane X-ray system and digitally reconstructed radiographs created from the volume-rendered CT model. Accuracy was defined in terms of measurement system bias, precision and root-mean-squared (rms) error. Results were reported in terms of individual bone tracking and in terms of clinically relevant tibio-femoral joint translations and rotations (joint kinematics). Accuracy for joint kinematics was as follows: model-based tracking measured static joint orientation with a precision of 0.2 degrees or better, and static joint position with a precision of 0.2mm or better. Model-based tracking precision for dynamic joint rotation was 0.9+/-0.3 degrees , 0.6+/-0.3 degrees , and 0.3+/-0.1 degrees for flexion-extension, external-internal rotation, and ab-adduction, respectively. Model-based tracking precision when measuring dynamic joint translation was 0.3+/-0.1mm, 0.4+/-0.2mm, and 0.7+/-0.2mm in the medial-lateral, proximal-distal, and anterior-posterior direction, respectively. The combination of high-speed biplane radiography and volumetric model-based tracking achieves excellent accuracy during in vivo, dynamic knee motion without the necessity for invasive bead implantation.
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http://dx.doi.org/10.1016/j.medengphy.2008.03.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2668117PMC
January 2009

Cancellous bone lamellae strongly affect microcrack propagation and apparent mechanical properties: separation of patients with osteoporotic fracture from normal controls using a 2D nonlinear finite element method (biomechanical stereology).

Bone 2008 Jun 15;42(6):1184-92. Epub 2008 Feb 15.

Lawrence J. Ellison Musculoskeletal Research Center, University of California, Davis, Medical Center, Room 2000, Research Facility I, 4635 Second Avenue, Sacramento, CA 95817, USA.

Biomechanical stereology is proposed as a two-dimensional (2D) finite element (FE) method to estimate the ability of bone tissue to sustain damage and to separate patients with osteoporotic fracture from normal controls. Briefly, 2D nonlinear compact tension FE models were created from quantitative back scattered electron images taken of iliac crest bone specimens collected from the individuals with or without osteoporotic fracture history. The effects of bone mineral microstructure on predicted bone fracture toughness and microcrack propagation were examined. The 2D FE models were used as surrogates for the real bone tissues. The calculated microcrack propagation results and bone mechanical properties were examined as surrogates for measurements from mechanical testing of actual specimens. The results for the 2D FE simulation separated patients with osteoporotic fracture from normal controls even though only the variability in tissue mineral microstructure was used to build the models. The models were deliberately created to ignore all differences in mean mineralization. Hence, the current results support the following hypotheses: (1) that material heterogeneity is important to the separation of patients with osteoporotic fracture from normal controls; and (2) that 2D nonlinear finite element modeling can produce surrogate mechanical parameters that separate patients with fracture from normal controls.
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http://dx.doi.org/10.1016/j.bone.2008.01.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684698PMC
June 2008

Measuring dynamic in-vivo glenohumeral joint kinematics: technique and preliminary results.

J Biomech 2008 9;41(3):711-4. Epub 2007 Nov 9.

Henry Ford Hospital, Department of Orthopaedics, Bone and Joint Center; E&R 2015, 2799 W. Grand Blvd., Detroit, MI 48202, USA.

Rotator cuff tears are a common injury that affect a significant percentage of the population over age 60. Although it is widely believed that the rotator cuff's primary function is to stabilize the humerus against the glenoid during shoulder motion, accurately measuring the three-dimensional (3D) motion of the shoulder's glenohumeral joint under in-vivo conditions has been a challenging endeavor. In particular, conventional motion measurement techniques have frequently been limited to static or two-dimensional (2D) analyses, and have suffered from limited or unknown in-vivo accuracy. We have recently developed and validated a new model-based tracking technique that is capable of accurately measuring the 3D position and orientation of the scapula and humerus from biplane X-ray images. Herein we demonstrate the in-vivo application of this technique for accurately measuring glenohumeral joint translations during shoulder motion in the repaired and contralateral shoulders of patients following rotator cuff repair. Five male subjects were tested at 3-4 months following arthroscopic rotator cuff repair. Superior-inferior humeral translation was measured during elevation, and anterior-posterior humeral translation was measured during external rotation in both the repaired and contralateral shoulders. The data failed to detect statistically significant differences between the repaired and contralateral shoulders in superior-inferior translation (p=0.74) or anterior-posterior translation (p=0.77). The measurement technique overcomes the limitations of conventional motion measurement techniques by providing accurate, 3D, in-vivo measures of glenohumeral joint motion during dynamic activities. On-going research is using this technique to assess the effects of conservative and surgical treatment of rotator cuff tears.
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http://dx.doi.org/10.1016/j.jbiomech.2007.09.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2288548PMC
June 2008

The effect of regional variations of the trabecular bone properties on the compressive strength of human vertebral bodies.

Ann Biomed Eng 2007 Nov 10;35(11):1907-13. Epub 2007 Aug 10.

Bone and Joint Center, Department of Orthopaedics and Rehabilitation, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202, USA.

Cancellous centrum is a major component of the vertebral body and significantly contributes to its structural strength and fracture risk. We hypothesized that the variability of cancellous bone properties in the centrum is associated with vertebral strength. Microcomputed tomography (micro-CT)-based gray level density (GLD), bone volume fraction (BV/TV), and finite element modulus (E) were examined for different regions of the trabecular centrum and correlated with vertebral body strength determined experimentally. Two sets of images in the cancellous centrum were digitally prepared from micro-CT images of eight human vertebral bodies (T10-L5). One set included a cubic volume (1 per vertebral centrum, n = 8) in which the largest amount of cancellous material from the centrum was included but all the shell materials were excluded. The other set included cylindrical volumes (6 per vertebral centrum, n = 48) from the anterior (4 regions: front, center, left, and right of the midline of vertebra) and the posterior (2 regions: left and right) regions of the centrum. Significant positive correlations of vertebral strength with GLD (r (2) = 0.57, p = 0.03) and E (r (2) = 0.63, p = 0.02) of the whole centrum and with GLD (r (2) = 0.65, p = 0.02), BV/TV (r (2) = 0.72, p = 0.01) and E (r (2) = 0.85, p = 0.001) of the central region of the vertebral centrum were found. Vertebral strength decreased with increasing coefficient of variation of GLD, BV/TV, and E calculated from subregions of the vertebral centrum. The values of GLD, BV/TV, and E in centrum were significantly smaller for the anterior region than for the posterior region. Overall, these findings supported the significant role of regional variability of centrum properties in determining the whole vertebral strength.
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http://dx.doi.org/10.1007/s10439-007-9363-1DOI Listing
November 2007

In vivo measurement of subacromial space width during shoulder elevation: technique and preliminary results in patients following unilateral rotator cuff repair.

Clin Biomech (Bristol, Avon) 2007 Aug 8;22(7):767-73. Epub 2007 Jun 8.

Henry Ford Hospital, Department of Orthopaedic Surgery, Bone and Joint Center, 2799 W. Grand Blvd., E&R 2015 Detroit, MI 48202, United States.

Background: The shoulder's subacromial space is of significant clinical interest due to its association with rotator cuff disease. Previous studies have estimated the subacromial space width to be 2-17 mm, but no study has measured in vivo subacromial space width during shoulder motion. The purpose of this study was to measure the in vivo subacromial space width during shoulder elevation in patients following rotator cuff repair.

Methods: Biplane X-ray images were collected during shoulder elevation of 11 patients who had undergone rotator cuff repair. Glenohumeral joint motion was measured from the biplane X-ray images for each subject's repaired and asymptomatic, contralateral shoulders. The joint motion data were combined with subject-specific CT models to measure the subacromial space width during shoulder motion.

Findings: Subacromial space width decreased with shoulder elevation, ranging from 2.3 to 7.4 mm in the repaired shoulder and 1.2-7.1 mm in the contralateral shoulder. Subacromial space width in the repaired shoulder was only 0.5 mm less than the contralateral shoulder when averaged over 10-60 degrees of glenohumeral elevation.

Interpretation: The results indicate that the humerus in the repaired shoulder is positioned more cranially on the glenoid than in the contralateral shoulder. It is unclear if these subtle differences in subacromial space width are due to the surgical procedure or post-operative stiffness, or if subacromial impingement contributed to the development of the rotator cuff tear. Future research will ascertain if these results represent a transient response to the surgery or a more fundamental difference in rotator cuff function between repaired and contralateral shoulders.
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http://dx.doi.org/10.1016/j.clinbiomech.2007.04.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2033432PMC
August 2007

Validation of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics.

J Biomech Eng 2006 Aug;128(4):604-9

Henry Ford Health Systems, Department of Orthopaedics and Rehabilitation, Bone and Joint Center, E&R 2015, 2799 W. Grand Blvd., Detroit, MI 48202, USA.

Shoulder motion is complex and significant research efforts have focused on measuring glenohumeral joint motion. Unfortunately, conventional motion measurement techniques are unable to measure glenohumeral joint kinematics during dynamic shoulder motion to clinically significant levels of accuracy. The purpose of this study was to validate the accuracy of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics. We have developed a model-based tracking technique for accurately measuring in vivo joint motion from biplane radiographic images that tracks the position of bones based on their three-dimensional shape and texture. To validate this technique, we implanted tantalum beads into the humerus and scapula of both shoulders from three cadaver specimens and then recorded biplane radiographic images of the shoulder while manually moving each specimen's arm. The position of the humerus and scapula were measured using the model-based tracking system and with a previously validated dynamic radiostereometric analysis (RSA) technique. Accuracy was reported in terms of measurement bias, measurement precision, and overall dynamic accuracy by comparing the model-based tracking results to the dynamic RSA results. The model-based tracking technique produced results that were in excellent agreement with the RSA technique. Measurement bias ranged from -0.126 to 0.199 mm for the scapula and ranged from -0.022 to 0.079 mm for the humerus. Dynamic measurement precision was better than 0.130 mm for the scapula and 0.095 mm for the humerus. Overall dynamic accuracy indicated that rms errors in any one direction were less than 0.385 mm for the scapula and less than 0.374 mm for the humerus. These errors correspond to rotational inaccuracies of approximately 0.25 deg for the scapula and 0.47 deg for the humerus. This new model-based tracking approach represents a non-invasive technique for accurately measuring dynamic glenohumeral joint motion under in vivo conditions. The model-based technique achieves accuracy levels that far surpass all previously reported non-invasive techniques for measuring in vivo glenohumeral joint motion. This technique is supported by a rigorous validation study that provides a realistic simulation of in vivo conditions and we fully expect to achieve these levels of accuracy with in vivo human testing. Future research will use this technique to analyze shoulder motion under a variety of testing conditions and to investigate the effects of conservative and surgical treatment of rotator cuff tears on dynamic joint stability.
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http://dx.doi.org/10.1115/1.2206199DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3072582PMC
August 2006

3-D computational modeling of media flow through scaffolds in a perfusion bioreactor.

J Biomech 2005 Mar;38(3):543-9

Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 315 Ferst Dr. NW, Atlanta, GA 30332, USA.

Media perfusion bioreactor systems have been developed to improve mass transport throughout three-dimensional (3-D) tissue-engineered constructs cultured in vitro. In addition to enhancing the exchange of nutrients and wastes, these systems simultaneously deliver flow-mediated shear stresses to cells seeded within the constructs. Local shear stresses are a function of media flow rate and dynamic viscosity, bioreactor configuration, and porous scaffold microarchitecture. We have used the Lattice-Boltzmann method to simulate the flow conditions within perfused cell-seeded cylindrical scaffolds. Microcomputed tomography imaging was used to define the scaffold microarchitecture for the simulations, which produce a 3-D fluid velocity field throughout the scaffold porosity. Shear stresses were estimated at various media flow rates by multiplying the symmetric part of the gradient of the velocity field by the dynamic viscosity of the cell culture media. The shear stress algorithm was validated by modeling flow between infinite parallel plates and comparing the calculated shear stress distribution to the analytical solution. Relating the simulation results to perfusion experiments, an average surface shear stress of 5x10(-5)Pa was found to correspond to increased cell proliferation, while higher shear stresses were associated with upregulation of bone marker genes. This modeling approach can be used to compare results obtained for different perfusion bioreactor systems or different scaffold microarchitectures and may allow specific shear stresses to be determined that optimize the amount, type, or distribution of in vitro tissue growth.
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http://dx.doi.org/10.1016/j.jbiomech.2004.04.011DOI Listing
March 2005
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