Publications by authors named "Thomas S Buchanan"

76 Publications

An Efficient One-Step Moment Balancing Algorithm for Computing Medial and Lateral Knee Compartment Contact Forces.

J Biomech Eng 2021 Sep 22. Epub 2021 Sep 22.

Biomechanics and Movement Science, University of Delaware, Newark, DE, USA; Department of Biomedical Engineering, University of Delaware, Newark, DE, USA; Department of Mechanical Engineering, University of Delaware, Newark, DE, USA.

The knee adduction moment is associated with the progression of knee osteoarthritis (OA). The adduction moment reflects the net effect of muscles, passive tissues and bone-on-bone contact forces. Medial compartment OA is more common than lateral and therefore our ability to correctly partition bone-on-bones forces across the medial and lateral compartments is key to understanding mechanical factors associated with the onset and progression of knee OA. We have used frontal plane moment balancing to resolve medial and lateral compartment forces. In this technical brief we present an alternate and more efficient methodology, the 1-step approach, linking the sagittal and frontal planes in the determination of muscle forces. Muscle forces are the dominant contributors to knee joint loading and therefore our ability to predict compartmental contact is dependent on our ability to predict muscle forces. The 1-step approach introduces a penalty function limiting total compressive force from acting in the lateral compartment whenever the internal moment is net abduction (i.e., external knee adduction). Total compressive force in the lateral compartment implies greater lateral loading compared to medial, and this is inconsistent with what we know about the knee adduction moment and medial-to-lateral force distribution during gait. An EMG-driven musculoskeletal model with modified hamstrings EMG was implemented to demonstrate the 1-step methodology and compare results with frontal plane moment balancing. The 1-step approach is a more efficient methodology that can be used in place of frontal plane moment balancing.
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http://dx.doi.org/10.1115/1.4052494DOI Listing
September 2021

Knee cartilage T relaxation times 3 months after ACL reconstruction are associated with knee gait variables linked to knee osteoarthritis.

J Orthop Res 2021 Mar 30. Epub 2021 Mar 30.

Department of Mechanical Engineering, University of Delaware, Newark, Delaware, USA.

Osteoarthritis development after ACL reconstruction (ACLR) is not well understood. Investigators have examined associations between knee biomechanical alterations and quantitative MRI (qMRI) variables, reflective of cartilage health, 12-60 months following ACLR; however, none have done so early after surgery. As part of an exploratory study, 45 individuals (age, 23 ± 7 years) underwent motion analysis during walking and qMRI 3 months after ACLR. For each limb, peak knee adduction moment (pKAM) and peak knee flexion moment (pKFM) were determined using inverse dynamics and peak medial compartment force was calculated using a neuromusculoskeletal model. T relaxation times in the medial compartment and linear regressions were used to determine the associations between gait variables and deep and superficial cartilage T relaxation times in six regions. pKAM was positively associated with deep layer T relaxation times within the femoral central and posterior regions when examined in the involved limb and from an interlimb difference perspective (involved limb - uninvolved limb). After adjusting for age, the association between interlimb difference of pKAM and interlimb difference of deep layer T relaxation times in the tibial central region became significant (p = .043). Interlimb difference of pKFM was negatively associated with interlimb difference of deep layer T relaxation times within the femoral central and posterior regions. These associations suggest that degenerative pathways leading to osteoarthritis may be detectable as early as 3 months after reconstruction. Preventative therapeutic techniques may need to be employed early in the rehabilitation process to prevent cartilage degradation.
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http://dx.doi.org/10.1002/jor.25043DOI Listing
March 2021

Patients Walking Faster After Anterior Cruciate Ligament Reconstruction Have More Gait Asymmetry.

Int J Sports Phys Ther 2021 Feb 1;16(1):169-176. Epub 2021 Feb 1.

University of Delaware.

Background: Gait asymmetries after anterior cruciate ligament reconstruction (ACLR) may lead to radiographic knee osteoarthritis. Slower walking speeds have been associated with biomarkers suggesting cartilage breakdown. The relationship between walking speed and gait symmetry after ACLR is unknown.

Hypothesis/purpose: To determine the relationship between self-selected walking speeds and gait symmetry in athletes after primary, unilateral ACLR.

Study Design: Secondary analysis of a clinical trial.

Methods: Athletes 24±8 weeks after primary ACLR walked at self-selected speeds as kinematics, kinetics, and electromyography data were collected. An EMG-driven musculoskeletal model was used to calculate peak medial compartment contact force (pMCCF). Variables of interest were peak knee flexion moment (pKFM) and angle (pKFA), knee flexion and extension (KEE) excursions, peak knee adduction moment (pKAM), and pMCCF. Univariate correlations were run for walking speed and each variable in the ACLR knee, contralateral knee, and interlimb difference (ILD).

Results: Weak to moderate positive correlations were observed for walking speed and all variables of interest in the contralateral knee (Pearson's r=.301-.505, p≤0.01). In the ACLR knee, weak positive correlations were observed for only pKFM (r=.280, p=0.02) and pKFA (r=.263, p=0.03). Weak negative correlations were found for ILDs in pKFM (r=-0.248, p=0.04), KEE (r=-.260, p=0.03), pKAM (r=-.323, p<0.01), and pMCCF (r=-.286, p=0.02).

Conclusion: Those who walk faster after ACLR have more asymmetries, which are associated with the development of early OA. This data suggests that interventions that solely increase walking speed may accentuate gait symmetry in athletes early after ACLR. Gait-specific, unilateral, neuromuscular interventions for the ACLR knee may be needed to target gait asymmetries after ACLR.

Level Of Evidence: III.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7872452PMC
February 2021

Quadriceps Strength Symmetry Does Not Modify Gait Mechanics After Anterior Cruciate Ligament Reconstruction, Rehabilitation, and Return-to-Sport Training.

Am J Sports Med 2021 02 29;49(2):417-425. Epub 2020 Dec 29.

Biomechanics and Movement Science Program, University of Delaware, Newark, Delaware, USA.

Background: After anterior cruciate ligament (ACL) reconstruction (ACLR), biomechanical asymmetries during gait are highly prevalent, persistent, and linked to posttraumatic knee osteoarthritis. Quadriceps strength is an important clinical measure associated with preoperative gait asymmetries and postoperative function and is a primary criterion for return-to-sport clearance. Evidence relating symmetry in quadriceps strength with gait biomechanics is limited to preoperative and early rehabilitation time points before return-to-sport training.

Purpose/hypothesis: The purpose was to determine the relationship between symmetry in isometric quadriceps strength and gait biomechanics after return-to-sport training in athletes after ACLR. We hypothesized that as quadriceps strength symmetry increases, athletes will demonstrate more symmetric knee joint biomechanics, including tibiofemoral joint loading during gait.

Study Design: Cross-sectional study; Level of evidence, 3.

Methods: Of 79 athletes enrolled in the ACL-SPORTS Trial, 76 were participants in this study after completing postoperative rehabilitation and 10 return-to-sport training sessions (mean ± SD, 7.1 ± 2.0 months after ACLR). All participants completed biomechanical walking gait analysis and isometric quadriceps strength assessment using an electromechanical dynamometer. Quadriceps strength was calculated using a limb symmetry index (involved limb value / uninvolved limb value × 100). The biomechanical variables of interest included peak knee flexion angle, peak knee internal extension moment, sagittal plane knee excursion at weight acceptance and midstance, quadriceps muscle force at peak knee flexion angle, and peak medial compartment contact force. Spearman rank correlation (ρ) coefficients were used to determine the relationship between limb symmetry indexes in quadriceps strength and each biomechanical variable; alpha was set to .05.

Results: Of the 76 participants, 27 (35%) demonstrated asymmetries in quadriceps strength, defined by quadriceps strength symmetry <90% (n = 23) or >110% (n = 4) (range, 56.9%-131.7%). For the biomechanical variables of interest, 67% demonstrated asymmetry in peak knee flexion angle; 68% and 83% in knee excursion during weight acceptance and midstance, respectively; 74% in internal peak knee extension moment; 57% in medial compartment contact force; and 74% in quadriceps muscle force. There were no significant correlations between quadriceps strength index and limb symmetry indexes for any biomechanical variable after return-to-sport training ( > .129).

Conclusion: Among those who completed return-to-sport training after ACLR, subsequent quadriceps strength symmetry was not correlated with the persistent asymmetries in gait biomechanics. After a threshold of quadriceps strength is reached, restoring strength alone may not ameliorate gait asymmetries, and current clinical interventions and return-to-sport training may not adequately target gait.
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http://dx.doi.org/10.1177/0363546520980079DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7863565PMC
February 2021

Sex and mechanism of injury influence knee joint loading symmetry during gait 6 months after ACLR.

J Orthop Res 2021 05 13;39(5):1123-1132. Epub 2020 Aug 13.

Department of Physical Therapy, University of Delaware, Newark, Delaware.

Early-onset knee osteoarthritis (OA) is associated with gait asymmetries after anterior cruciate ligament reconstruction (ACLR). Women have higher risks of sustaining non-contact injuries, and are more likely to present with aberrant movement patterns associated with the mechanism of injury (MOI). We hypothesized that sex and MOI would influence gait after ACLR. Seventy participants, grouped by sex and MOI, completed biomechanical testing during over-ground walking when they had full knee range of motion, trace or less knee effusion, greater than 80% quadriceps strength limb symmetry index, ability to hop on each leg without pain, and initiated running. Bilateral knee kinetics, kinematics, and joint contact forces were compared using mixed-model analysis of variance (α = .05). There was a three-way interaction effect of sex × MOI × limb for peak medial compartment contact force (P = .002), our primary outcome measure previously associated with OA development. Men with non-contact injuries walked with asymmetry characterized by underloading of the involved limb. Men with contact injuries walked with the most symmetrical loading. In women, no clear pattern emerged based on MOI. Targeting, and possibly prioritizing interventions for athletes who present with gait asymmetries after ACLR based on sex and MOI, may be necessary to optimize outcomes. Statement of Clinical Significance: Sex and MOI may influence walking mechanics, and could be considered in future interventions to target gait symmetry, as a response to interventions may vary based on differences in sex and MOI.
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http://dx.doi.org/10.1002/jor.24822DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7864984PMC
May 2021

Validating Wearable Sensors Using Self-Reported Instability among Patients with Knee Osteoarthritis.

PM R 2021 02 12;13(2):119-127. Epub 2020 Aug 12.

Delaware Rehabilitation Institute, University of Delaware, Newark, DE.

Background: Self-perceived instability among patients with knee osteoarthritis (OA) is defined as giving way, buckling, or shifting of the knee during activities, especially walking. Although instability is a leading cause of mobility decline with knee OA, methods for quantifying the symptom, determining the mechanisms, and establishing effective interventions remain unclear. Recently, data outputs (ie, linear acceleration and its time-derivative, jerk) from wearable sensors are showing strong associations with self-perceived instability among patients with other knee pathologies and may offer insight into OA-related instability.

Objective: To examine discriminant and convergent validity of using data outputs from wearable sensors to quantify self-reported instability among patients with knee OA.

Design: Secondary analysis of a cross-sectional study.

Setting: Primary recruitment from an institutional outpatient physical therapy clinic and collection completed in an institutional research laboratory.

Patients: Thirty-nine total participants. The OA group included 26 participants with radiographic evidence of moderate to severe knee OA in the medial compartment; knee pain >3 out of 10, and a walking speed of ≥1.0 m/s. The control group included 13 participants with no history of knee OA. Participants with current or history of low back, hip, or foot/ankle injury; knee replacement; skeletal realignment surgery; or comorbidities that limit walking, pregnancy, and inability to walk without an assistive device were excluded.

Interventions: N/A MAIN OUTCOME MEASURES: Data output from wearable sensors at the tibia.

Results: Midstance acceleration (P = .01) and jerk (P = .04) were significantly greater for those with than without knee OA. Acceleration was significantly associated with self-reported instability (Spearman's rho = -0.63, P < .01).

Conclusions: Data from wearable sensors are a valid measurement for exploring the mechanisms and risks of instability among patients with knee OA.
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http://dx.doi.org/10.1002/pmrj.12393DOI Listing
February 2021

Operative and nonoperative management of anterior cruciate ligament injury: Differences in gait biomechanics at 5 years.

J Orthop Res 2020 12 20;38(12):2675-2684. Epub 2020 Mar 20.

Biomechanics and Movement Science Program, University of Delaware, Newark, Delaware.

Gait biomechanics after anterior cruciate ligament (ACL) injury are associated with functional outcomes and the development of posttraumatic knee osteoarthritis. However, biomechanical outcomes between patients treated nonoperatively compared with operatively are not well understood. The primary purpose of this study was to compare knee joint contact forces, angles, and moments during loading response of gait between individuals treated with operative compared with nonoperative management at 5 years after ACL injury. Forty athletes treated operatively and 17 athletes treated nonoperatively completed gait analysis at 5 years after ACL reconstruction or completion of nonoperative rehabilitation. Medial compartment joint contact forces were estimated using a previously validated, patient-specific electromyography-driven musculoskeletal model. Knee joint contact forces, angles, and moments were compared between the operative and nonoperative group using mixed model 2 × 2 analyses of variance. Peak medial compartment contact forces were larger in the involved limb of the nonoperative group (Op: 2.37 ± 0.47 BW, Non-Op: 3.03 ± 0.53 BW; effect size: 1.36). Peak external knee adduction moment was also larger in the involved limb of the nonoperative group (Op: 0.25 ± 0.08 Nm/kg·m, Non-Op: 0.32 ± 0.09 Nm/kg·m; effect size: 0.89). No differences in radiographic tibiofemoral osteoarthritis were present between the operative and nonoperative groups. Overall, participants treated nonoperatively walked with greater measures of medial compartment joint loading than those treated operatively, while sagittal plane group differences were not present. Statement of clinical relevance: The differences in medial knee joint loading at 5 years after operative and nonoperative management of ACL injury may have implications on the development of posttraumatic knee osteoarthritis.
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http://dx.doi.org/10.1002/jor.24652DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7808330PMC
December 2020

ACL injury and reconstruction affect control of ground reaction forces produced during a novel task that simulates cutting movements.

J Orthop Res 2020 08 3;38(8):1746-1752. Epub 2020 Feb 3.

Biomechanics and Movement Science Program, College of Engineering, University of Delaware, Newark, Delaware.

After anterior cruciate ligament (ACL) injury and reconstruction, biomechanical and neuromuscular control deficits persist and 25% of those who have experienced an ACL injury will experience a second ACL rupture in the first year after returning to sports. There remains a need for improved rehabilitation and the ability to detect an individual's risk of secondary ACL rupture. Nonlinear analysis metrics, such as the largest Lyapunov exponent (LyE) can provide new biomechanical insight in this population by identifying how movement patterns evolve over time. The purpose of this study was to determine how ACL injury, ACL reconstruction (ACLR), and participation in high-performance athletics affect control strategies, evaluated through nonlinear analysis, produced during a novel task that simulates forces generated during cutting movements. Uninjured recreational athletes, those with ACL injury who have not undergone reconstruction (ACLD [ACL deficient]), those who have undergone ACL reconstruction, and high-performance athletes completed a task that simulates cutting forces. The LyE calculated from forces generated during this novel task was greater (ie, force control was diminished) in the involved limb of ACLD and ACLR groups when compared with healthy uninjured controls and high-performance athletes. These data suggest that those who have experienced an ACL injury and subsequent reconstructive surgery exhibit poor force control when compared with both uninjured controls and high-performance athletes. Clinical significance: significantly larger LyE values after ACL injury and reconstruction when compared with healthy athletes suggest a continuing deficit in force control not addressed by current rehabilitation protocols and evaluation metrics that could contribute to secondary ACL rupture.
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http://dx.doi.org/10.1002/jor.24604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7477805PMC
August 2020

Slower Walking Speed Is Related to Early Femoral Trochlear Cartilage Degradation After ACL Reconstruction.

J Orthop Res 2020 03 18;38(3):645-652. Epub 2019 Nov 18.

Department of Mechanical Engineering, University of Delaware, Newark, Delaware.

Post-traumatic patellofemoral osteoarthritis (OA) is prevalent after anterior cruciate ligament reconstruction (ACLR) and early cartilage degradation may be especially common in the femoral trochlear cartilage. Determining the presence of and factors associated with early femoral trochlear cartilage degradation, a precursor to OA, is a critical preliminary step in identifying those at risk for patellofemoral OA development and designing interventions to combat the disease. Early cartilage degradation can be detected using quantitative magnetic resonance imaging measures, such as tissue T relaxation time. The purposes of this study were to (i) compare involved (ACLR) versus uninvolved (contralateral) femoral trochlear cartilage T relaxation times 6 months after ACLR, and (ii) determine the relationship between walking speed and walking mechanics 3 months after ACLR and femoral trochlear cartilage T relaxation times 6 months after ACLR. Twenty-six individuals (age 23 ± 7 years) after primary, unilateral ACLR participated in detailed motion analyses 3.3 ± 0.6 months after ACLR and quantitative magnetic resonance imaging 6.3 ± 0.5 months after ACLR. There were no limb differences in femoral trochlear cartilage T relaxation times. Slower walking speed was related to higher (worse) femoral trochlear cartilage T relaxation times in the involved limb (Pearson's r: -0.583, p = 0.002) and greater interlimb differences in trochlear T relaxation times (Pearson's r: -0.349, p = 0.080). Walking mechanics were weakly related to trochlear T relaxation times. Statement of clinical significance: Slower walking speed was by far the strongest predictor of worse femoral trochlear cartilage health, suggesting slow walking speed may be an early clinical indicator of future patellofemoral OA after ACLR. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:645-652, 2020.
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http://dx.doi.org/10.1002/jor.24503DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7028512PMC
March 2020

Partial medial meniscectomy leads to altered walking mechanics two years after anterior cruciate ligament reconstruction: Meniscal repair does not.

Gait Posture 2019 10 27;74:87-93. Epub 2019 Aug 27.

University of Delaware, Newark, DE, USA.

Background: Partial meniscectomy dramatically increases the risk for post-traumatic, tibiofemoral osteoarthritis after anterior cruciate ligament reconstruction (ACLR). Concomitant medial meniscus surgery influences walking biomechanics (e.g., medial tibiofemoral joint loading) early after ACLR; whether medial meniscus surgery continues to influence walking biomechanics two years after ACLR is unknown.

Research Question: Does medial meniscus treatment at the time of ACLR influence walking biomechanics two years after surgery?

Methods: This is a secondary analysis of prospectively collected data from a clinical trial (NCT01773317). Fifty-six athletes (age 24 ± 8 years) with operative reports, two-year biomechanical analyses, and no second injury prior to two-year testing participated after primary ACLR. Participants were classified by concomitant medial meniscal status: no medial meniscus involvement (n = 36), partial medial meniscectomy (n = 9), and medial meniscus repair (n = 11). Participants underwent biomechanical analyses during over-ground walking including surface electromyography; a validated musculoskeletal model estimated medial compartment tibiofemoral contact forces. Gait variables were analyzed using 3 × 2 ANOVAs with group (medial meniscus treatment) and limb (involved versus uninvolved) comparisons.

Results: There was a main effect of group (p = .039) for peak knee flexion angle (PKFA). Participants after partial medial meniscectomy walked with clinically meaningfully smaller PKFAs in both the involved and uninvolved limbs compared to the no medial meniscus involvement group (group mean difference [95%CI]; involved: -4.9°[-8.7°, -1.0°], p = .015; uninvolved: -3.9°[-7.6°, -0.3°], p = .035) and medial meniscus repair group (involved: -5.2°[-9.9°, -0.6°], p = .029; uninvolved: -4.7°[-9.0°, -0.3°], p = .038). The partial medial meniscectomy group walked with higher involved versus uninvolved limb medial tibiofemoral contact forces (0.45 body weights, 95% CI: -0.01, 0.91 BW, p = 0.053) and truncated sagittal plane knee excursions, which were not present in the other two groups.

Significance: Aberrant gait biomechanics may concentrate high forces in the antero-medial tibiofemoral cartilage among patients two years after ACLR plus partial medial meniscectomy, perhaps explaining the higher osteoarthritis rates and offering an opportunity for targeted interventions.

Level Of Evidence: Level III.
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http://dx.doi.org/10.1016/j.gaitpost.2019.08.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6790293PMC
October 2019

Gait Mechanics in Women of the ACL-SPORTS Randomized Control Trial: Interlimb Symmetry Improves Over Time Regardless of Treatment Group.

J Orthop Res 2019 08 20;37(8):1743-1753. Epub 2019 May 20.

Biomechanics and Movement Science Program, University of Delaware, Newark, Delaware.

Women after anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) are more likely than men to exhibit asymmetric movement patterns, which are associated with post-traumatic osteoarthritis. We developed the ACL specialized post-operative return-to-sports (ACL-SPORTS) randomized control trial to test the effect of strength, agility, plyometric, and secondary prevention (SAPP) training with and without perturbation training (SAPP + PERT) on gait mechanics in women after ACLR. We hypothesized that movement symmetry would improve over time across both groups but more so among the SAPP + PERT group. Thirty-nine female athletes 3-9 months after primary ACLR were randomized to SAPP or SAPP + PERT training. Biomechanical testing during overground walking occurred before (Pre-training) and after (Post-training) training and one and 2 years post-operatively. Hip and knee kinematic and kinetic variables were compared using repeated measures analysis of variance with Bonferroni corrections for post hoc comparisons (α = 0.05). There was a time by limb interaction effect (p = 0.028) for peak knee flexion angle (PKFA), the primary outcome which powered the study, characterized by smaller PKFA in the involved compared to uninvolved limbs across treatment groups at Pre-training, Post-training, and 1 year, but not 2 years. Similar findings occurred across sagittal plane knee excursions and kinetics and hip extension excursion at midstance. There were no meaningful interactions involving group. Neither SAPP nor SAPP + PERT training improved walking mechanics, which persisted 1 but not 2 years after ACLR. Statement of clinical significance: Asymmetrical movement patterns persisted long after participants achieved symmetrical strength and functional performance, suggesting more time is needed to recover fully after ACLR. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1743-1753, 2019.
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http://dx.doi.org/10.1002/jor.24314DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6824924PMC
August 2019

Self-reported walking difficulty and knee osteoarthritis influences limb dynamics and muscle co-contraction during gait.

Hum Mov Sci 2019 Apr 15;64:409-419. Epub 2018 Nov 15.

540 S. College Ave, University of Delaware, Delaware Rehabilitation Institute, Newark, DE, USA. Electronic address:

Knee osteoarthritis (OA) gait is characterized by simultaneous flexor and extensor use, or co-contraction. Co-contraction can stabilize and redirect joint forces. However, co-contraction can push and pull on the femur and tibia that exacerbate OA symptoms and make walking difficult. Such movements are quantifiable by limb dynamics (i.e., linear acceleration and jerk); thus, this study examines limb dynamics and its relationship with co-contraction and OA related walking difficulty. Three groups of age-and-sex-matched subjects with and without OA and walking difficulty (N = 13 per group) walked with electromyography (EMG) on the knee extensors and flexors and inertial measurement units (IMUs) at the femur and tibia. We calculated co-contraction from antagonistic EMG signals and linear acceleration and its derivative jerk from IMUs. We determined group differences using one-way ANOVAs, nonparametric equivalence, and effect sizes, and main and interaction effects of walking difficulty with regression modeling. Medium effect sizes and differences for femoral acceleration (d = 0.64; P = .02) and jerk (d = 0.51; P = .01) were observed between with and without knee OA. Medium to large effect sizes (r = 0.33 to 0.51 and d = 0.81 to 0.97) and differences (P = .01 to 0.05) for tibial acceleration and jerk were obsevered between with and without walking difficulty. Walking difficulty moderated the relationship between tibial jerk and co-contraction (p < .05). Tibial jerk differences were observed based on walking difficulty. The significant interaction effect suggested that walking difficulty explained the relationship between limb dynamics and co-contraction. Perhaps co-contraction levels used by those with knee OA and no walking difficulty are optimal as compared to those with walking difficulty.
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http://dx.doi.org/10.1016/j.humov.2018.11.002DOI Listing
April 2019

High muscle co-contraction does not result in high joint forces during gait in anterior cruciate ligament deficient knees.

J Orthop Res 2019 01 9;37(1):104-112. Epub 2018 Oct 9.

Biomechanics and Movement Science, University of Delaware, 540 South College Avenue, Newark 19713, Delaware.

The mechanism of knee osteoarthritis development after anterior cruciate ligament injuries is poorly understood. The objective of this study was to evaluate knee gait variables, muscle co-contraction indices and knee joint loading in young subjects with anterior cruciate ligament deficiency (ACLD, n = 36), versus control subjects (n = 12). A validated, electromyography-informed model was used to estimate joint loading. For the involved limb of ACLD subjects versus control, muscle co-contraction indices were higher for the medial (p = 0.018, effect size = 0.93) and lateral (p = 0.028, effect size = 0.83) agonist-antagonist muscle pairs. Despite higher muscle co-contraction, medial compartment contact force was lower for the involved limb, compared to both the uninvolved limb (mean difference = 0.39 body weight, p = 0.009, effect size = 0.70) as well as the control limb (mean difference = 0.57 body weight, p = 0.007, effect size = 1.14). Similar observations were made for total contact force. For involved versus uninvolved limb, the ACLD group demonstrated lower vertical ground reaction force (mean difference = 0.08 body weight, p = 0.010, effect size = 0.70) and knee flexion moment (mean difference = 1.32% body weight * height, p = 0.003, effect size = 0.76), during weight acceptance. These results indicate that high muscle co-contraction does not always result in high knee joint loading, which is thought to be associated with knee osteoarthritis. Long-term follow-up is required to evaluate how gait alterations progress in non-osteoarthritic versus osteoarthritic subjects. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.
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http://dx.doi.org/10.1002/jor.24141DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6393175PMC
January 2019

A Novel and Safe Approach to Simulate Cutting Movements Using Ground Reaction Forces.

Sensors (Basel) 2018 Aug 11;18(8). Epub 2018 Aug 11.

Biomechanics and Movement Science Program, College of Engineering, University of Delaware, Newark, DE 19716, USA.

Control of shear ground reaction forces (sGRF) is important in performing running and cutting tasks as poor sGRF control has implications for those with knee injuries, such as anterior cruciate ligament (ACL) ruptures. The goal of this study was to develop a novel and safe task to evaluate control or accurate modulation of shear ground reaction forces related to those generated during cutting. Our approach utilized a force control task using real-time visual feedback of a subject's force production and evaluated control capabilities through accuracy and divergence measurements. Ten healthy recreational athletes completed the force control task while force control via accuracy measures and divergence calculations was investigated. Participants were able to accurately control sGRF in multiple directions based on error measurements. Forces generated during the task were equal to or greater than those measured during a number of functional activities. We found no significant difference in the divergence of the force profiles using the Lyapunov Exponent of the sGRF trajectories. Participants using our approach produced high accuracy and low divergence force profiles and functional force magnitudes. Moving forward, we will utilize this task in at-risk populations who are unable to complete a cutting maneuver in early stages of rehabilitation, such as ACL deficient and newly reconstructed individuals, allowing insight into force control not obtainable otherwise.
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http://dx.doi.org/10.3390/s18082631DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6111832PMC
August 2018

Gait Mechanics After ACL Reconstruction Differ According to Medial Meniscal Treatment.

J Bone Joint Surg Am 2018 Jul;100(14):1209-1216

University of Delaware, Newark, Delaware.

Background: Knee osteoarthritis risk is high after anterior cruciate ligament reconstruction (ACLR) and arthroscopic meniscal surgery, and higher among individuals who undergo both. Although osteoarthritis development is multifactorial, altered walking mechanics may influence osteoarthritis progression. The purpose of this study was to compare gait mechanics after ACLR among participants who had undergone no medial meniscal surgery, partial medial meniscectomy, or medial meniscal repair.

Methods: This was a secondary analysis of data collected prospectively as part of a clinical trial. Sixty-one athletes (mean age of 21.4 ± 8.2 years) who had undergone primary ACLR participated in the study when they achieved impairment resolution (5.3 ± 1.7 months postoperatively), including minimal to no effusion, full knee range of motion, and ≥80% quadriceps-strength symmetry. Participants were classified by concomitant medial meniscal treatment: no involvement or nonsurgical management of a small, stable tear; partial meniscectomy; or meniscal repair. Participants underwent comprehensive walking analyses. Joint contact forces were estimated using a previously validated, electromyography-driven musculoskeletal model. Variables were analyzed using a mixed-model analysis of variance with group and limb comparisons (α = 0.05); group comparisons of interlimb differences in measurements (surgical minus contralateral limb) were performed to determine significant interactions.

Results: The participants in the partial meniscectomy group walked with a higher peak knee adduction moment (pKAM) in the surgical versus the contralateral limb as compared with those in the meniscal repair group and those with no medial meniscal surgery (group difference for partial versus repair: 0.10 N-m/kg-m, p = 0.020; and for partial versus none: 0.06 N-m/kg-m, p = 0.037). Participants in the repair group walked with a smaller percentage of medial to total tibiofemoral loading in the surgical limb compared with both of the other groups (group difference for repair versus partial: -12%, p = 0.001; and for repair versus none: -7%, p = 0.011). The participants in the repair group loaded the medial compartment of the surgical versus the contralateral limb 0.5 times body weight less than did the participants in the partial meniscectomy group.

Conclusions: Participants in the partial meniscectomy group walked with higher pKAM and shifted loading toward the medial compartment of the surgical limb, while participants in the repair group did the opposite, walking with lower pKAM and unloading the surgical limb relative to the contralateral limb. These findings may partially explain the conflicting evidence regarding pKAM after ACLR and the elevated risk for osteoarthritis (whether from overloading or underloading) after ACLR with concomitant medial meniscectomy or repair.

Level Of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
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http://dx.doi.org/10.2106/JBJS.17.01014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6636792PMC
July 2018

Gait mechanics and tibiofemoral loading in men of the ACL-SPORTS randomized control trial.

J Orthop Res 2018 09 24;36(9):2364-2372. Epub 2018 Apr 24.

Biomechanics and Movement Science, University of Delaware, Newark, Delaware.

The risk for post-traumatic osteoarthritis is elevated after anterior cruciate ligament reconstruction (ACLR), and may be especially high among individuals with aberrant walking mechanics, such as medial tibiofemoral joint underloading 6 months postoperatively. Rehabilitation training programs have been proposed as one strategy to address aberrant gait mechanics. We developed the anterior cruciate ligament specialized post-operative return-to-sports (ACL-SPORTS) randomized control trial to test the effect of 10 post-operative training sessions consisting of strength, agility, plyometric, and secondary prevention exercises (SAPP) or SAPP plus perturbation (SAPP + PERT) training on gait mechanics after ACLR. A total of 40 male athletes (age 23 ± 7 years) after primary ACLR were randomized to SAPP or SAPP + PERT training and tested at three distinct, post-operative time points: 1) after impairment resolution (Pre-training); 2) following 10 training sessions (Post-training); and 3) 2 years after ACLR. Knee kinematic and kinetic variables as well as muscle and joint contact forces were calculated via inverse dynamics and a validated electromyography-informed musculoskeletal model. There were no significant improvements from Pre-training to Post-training in either intervention group. Smaller peak knee flexion angles, extension moments, extensor muscle forces, medial compartment contact forces, and tibiofemoral contact forces were present across group and time, however the magnitude of interlimb differences were generally smaller and likely not meaningful 2 years postoperatively. Neither SAPP nor SAPP + PERT training appears effective at altering gait mechanics in men in the short-term; however, meaningful gait asymmetries mostly resolved between post-training and 2 years after ACLR regardless of intervention group. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2364-2372, 2018.
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http://dx.doi.org/10.1002/jor.23895DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6157011PMC
September 2018

Influences of knee osteoarthritis and walking difficulty on knee kinematics and kinetics.

Gait Posture 2018 03 2;61:439-444. Epub 2018 Feb 2.

Delaware Rehabilitation Institute, University of Delaware,(1) 540 South College Ave, Newark, DE 19713, United States. Electronic address:

Background: Self-reported walking difficulty is a problem among patients with knee osteoarthritis (OA), however, these patients have never been studied as a subgroup population.

Objective: The purpose of this study is to examine known knee OA gait mechanics among those with knee OA, with (Diff) and without (NoDiff) self-reported walking difficulty, as compared to age- and sex-matched controls without knee OA.

Methods: A total of 39 subjects in three groups of 13 individuals walked at a controlled gait speed during instrumented gait analysis. Gait mechanics were compared between a priori determined groups using the independent t-test.

Results: The results of the study found that among those with knee OA, knee excursion angles were not significantly different between the Diff and NoDiff groups. Whereas, external knee moments were significantly different between the Diff and NoDiff groups but not between the NoDiff and the control groups. The lack of difference between the NoDiff and control groups were especially interesting because of the moderate to severe OA in the NoDiff group. Therefore, the findings of this study suggest the importance of considering self-reported walking difficulty among those with knee OA. Perhaps patients with knee OA-related walking difficulties use alternative gait parameters that may need to be clinically addressed. Strengths of the study included a matched design and controlled walking speed, whereas limitations were the small sample size and cross-sectional design.

Conclusions: Given the relationships found among self-reported walking difficulty, OA presence, and gait parameters, addressing gait parameters specifically related to walking difficulty may be indicated in this sub-group knee OA population.
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http://dx.doi.org/10.1016/j.gaitpost.2018.01.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6311109PMC
March 2018

Dynamic structure of lower limb joint angles during walking post-stroke.

J Biomech 2018 02 15;68:1-5. Epub 2017 Dec 15.

Department of Biomechanics, University of Nebraska at Omaha, Omaha, NE, United States. Electronic address:

Background: Variability in joint kinematics is necessary for adaptability and response to everyday perturbations; however, intrinsic neuromotor changes secondary to stroke often cause abnormal movement patterns. How these abnormal movement patterns relate to joint kinematic variability and its influence on post-stroke walking impairments is not well understood.

Objective: The purpose of this study was to evaluate the movement variability at the individual joint level in the paretic and non-paretic limbs of individuals post-stroke.

Methods: Seven individuals with hemiparesis post-stroke walked on a treadmill for two minutes at their self-selected speed and the average speed of the six-minute walk test while kinematics were recorded using motion-capture. Variability in hip, knee, and ankle flexion/extension angles during walking were quantified with the Lyapunov exponent (LyE). Interlimb differences were evaluated.

Results: The paretic side LyE was higher than the non-paretic side at both self-selected speed (Hip: 50%; Knee: 74%), and the average speed of the 6-min walk test (Hip: 15%; Knee: 93%).

Conclusion: Differences in joint kinematic variability between limbs of persons post-stroke supports further study of the source of non-paretic limb deviations as well as the clinical implications of joint kinematic variability in persons post-stroke. The development of bilaterally-targeted post-stroke gait interventions to address variability in both limbs may promote improved outcomes.
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http://dx.doi.org/10.1016/j.jbiomech.2017.12.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5858158PMC
February 2018

Semitendinosus Tendon for ACL Reconstruction: Regrowth and Mechanical Property Recovery.

Orthop J Sports Med 2017 Jun 27;5(6):2325967117712944. Epub 2017 Jun 27.

Delaware Rehabilitation Institute, University of Delaware, Newark, Delaware, USA.

Background: Semitendinosus/gracilis (STG) tendon autograft has been used effectively for restoring knee stability after anterior cruciate ligament (ACL) rupture. Though ACL reconstruction with STG autograft is an effective surgical technique for return to sports, short-term hamstring strength asymmetries exist after surgery. Although imaging evidence has demonstrated regrowth and reorganization of the semitendinosus (ST) tendon, no studies show whether the regrowth is associated with residual muscle function. Continuous shear wave elastography (cSWE) using an external actuator and high-frame rate ultrasound is a promising technique for evaluating the mechanical properties of regrown tendons in vivo.

Purpose: To demonstrate recovery of the mechanical properties of the hamstring tendons after ACL reconstruction using an STG tendon autograft.

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

Methods: Thirteen patients underwent an STG autograft reconstruction after ACL rupture. Regrowth of the ST tendon was confirmed via b-mode ultrasound between 6 and 24 months postreconstruction. The shear elastic () and viscosity moduli () of the ST tendons were ascertained through cSWE using an external actuator and high-frame rate ultrasound.

Results: Significant differences in both shear elastic (129.4 vs 73.0 kPa) and viscous moduli (192.6 vs 114.3 Pa·s) existed bilaterally for uninvolved and involved limbs, respectively. Additionally, a positive correlation between time postoperative and shear elasticity was observed ( = 0.60). More than 12 months were required for patients to regain a large percentage of the tendon's mechanical properties compared with the contralateral side (, 80.6% at >12 months vs 39.9%; , 78.7% at >12 months vs 46.0%).

Conclusion: The imaging and elastography data demonstrate tendon regrowth and recovery of functional biomechanical properties with time. The elastic modulus of the recovered tendon indicates the ability to transmit muscle force across the joint and recovery of semitendinosus function after its use for an ACL graft.
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http://dx.doi.org/10.1177/2325967117712944DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5490845PMC
June 2017

The Advantages of Normalizing Electromyography to Ballistic Rather than Isometric or Isokinetic Tasks.

J Appl Biomech 2017 Jul 26;33(3):189-196. Epub 2017 Jun 26.

1 University of Delaware.

Isometric tasks have been a standard for electromyography (EMG) normalization stemming from anatomic and physiologic stability observed during contraction. Ballistic dynamic tasks have the benefit of eliciting maximum EMG signals for normalization, despite having the potential for greater signal variability. It is the purpose of this study to compare maximum voluntary isometric contraction (MVIC) to nonisometric tasks with increasing degrees of extrinsic variability, ie, joint range of motion, velocity, rate of contraction, etc., to determine if the ballistic tasks, which elicit larger peak EMG signals, are more reliable than the constrained MVIC. Fifteen subjects performed MVIC, isokinetic, maximum countermovement jump, and sprint tasks while EMG was collected from 9 muscles in the quadriceps, hamstrings, and lower leg. The results revealed the unconstrained ballistic tasks were more reliable compared to the constrained MVIC and isokinetic tasks for all triceps surae muscles. The EMG from sprinting was more reliable than the constrained cases for both the hamstrings and vasti. The most reliable EMG signals occurred when the body was permitted its natural, unconstrained motion. These results suggest that EMG is best normalized using ballistic tasks to provide the greatest within-subject reliability, which beneficially yield maximum EMG values.
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http://dx.doi.org/10.1123/jab.2016-0146DOI Listing
July 2017

Gait mechanics and second ACL rupture: Implications for delaying return-to-sport.

J Orthop Res 2017 09 18;35(9):1894-1901. Epub 2016 Nov 18.

Biomechanics and Movement Science, University of Delaware, Newark, Delaware.

Second anterior cruciate ligament rupture is a common and devastating injury among young women who return to sport after ACL reconstruction, but it is inadequately understood. The purpose of this study was to compare gait biomechanics and return-to-sport time frames in a matched cohort of young female athletes who, after primary ACLR, returned to sport without re-injury or sustained a second ACL injury. Approximately 6 months after primary reconstruction, 14 young women (age 16 ± 2 years) involved in jumping, cutting, and pivoting sports underwent motion analysis testing after physical therapy and impairment resolution. Following objective return-to-sport clearance, seven athletes sustained a second ACL rupture within 20 months of surgery (13.4 ± 4.9 months). We matched them by age, sex, and sport-level to seven athletes who returned to sports without re-injury. Data were analyzed using a previously validated, EMG-informed, patient-specific musculoskeletal model. Compared to athletes without re-injury, athletes who sustained a second ACL injury received surgery sooner (p = 0.023), had post-operative impairments resolved earlier (p = 0.022), reached criterion-based return-to-sport benchmarks earlier (p = 0.024), had higher body mass index (p = 0.039), and walked with lower peak knee flexor muscle forces bilaterally (p = 0.021). Athletes who sustained a second injury also tended to walk with larger (p = 0.089) and more symmetrical peak knee flexion angles and less co-contraction, all indicative of a more normal gait pattern. Statement of Clinical Significance: Delayed return-to-sport clearance even in the absence of gait or clinical impairments following primary ACL reconstruction may be necessary to mitigate second ACL injury risk in young women. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1894-1901, 2017.
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http://dx.doi.org/10.1002/jor.23476DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5423861PMC
September 2017

Predictors of knee joint loading after anterior cruciate ligament reconstruction.

J Orthop Res 2017 03 17;35(3):651-656. Epub 2016 Oct 17.

University of Delaware, Newark, Delaware.

Anterior cruciate ligament (ACL) injury results in altered knee joint mechanics which frequently continue even after ACL reconstruction. The persistence of altered mechanical loading of the knee is of concern due to its likely role in the development of post-traumatic osteoarthritis (OA). Joint contact forces are associated with post-traumatic OA development, but evaluation of factors influencing the magnitude of contact forces after ACL injury is needed to advance current strategies aimed at preventing post-traumatic OA. Therefore, the purpose of this study was to identify predictive factors of knee joint contact forces after ACL reconstruction. Thirty athletes completed standard gait analysis with surface electromyography 6 months after ACL reconstruction. An electromyographic-driven musculoskeletal model was used to estimate joint contact forces. External knee adduction moment was a significant predictor of medial compartment contact forces in both limbs, while vertical ground reaction force and co-contraction only contributed significantly in the uninvolved limb. The large influence of the knee adduction moment on joint contact forces provides mechanistic clues to understanding the mechanical pathway of post-traumatic OA after ACL injury. Statement of Clinical Significance: This study provides critical information in improving the understanding of mechanisms influencing the development of post-traumatic OA after ACL injury. Further work is needed to identify additional driving factors of joint loading in the ACL-injured limb and develop treatment strategies to avert the deleterious consequences of post-traumatic OA. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:651-656, 2017.
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http://dx.doi.org/10.1002/jor.23408DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6309880PMC
March 2017

Gait mechanics in those with/without medial compartment knee osteoarthritis 5 years after anterior cruciate ligament reconstruction.

J Orthop Res 2017 03 27;35(3):625-633. Epub 2016 Apr 27.

Departmentof Biomedical Engineering, University of Delaware, 540 South College Avenue, Newark, Delaware, 19713.

The objective of the study was to evaluate differences in gait mechanics 5 years after unilateral anterior cruciate ligament reconstruction surgery, for non-osteoarthritic (n = 24) versus osteoarthritic (n = 9) subjects. For the involved knee, the osteoarthritic group demonstrated significantly lower peak knee flexion angles (non-osteoarthritic = 24.3 ± 4.6°, osteoarthritic = 19.1 ± 2.9°, p = 0.01) and peak knee flexion moments (non-osteoarthritic = 5.3 ± 1.2% Body Weight × Height, osteoarthritic = 4.4 ± 1.2% Body Weight × Height, p = 0.05). Differences in peak knee adduction moment approached significance, with a higher magnitude for the osteoarthritic group (non-osteoarthritic = 2.4 ± 0.8% Body Weight × Height, osteoarthritic = 2.9 ± 0.5% Body Weight × Height, p = 0.09). Peak medial compartment joint load was evaluated using electromyography-informed neuromusculoskeletal modeling. Peak medial compartment joint load in the involved knee for the two groups was not different (non-osteoarthritic = 2.4 ± 0.4 Body Weight, osteoarthritic = 2.3 ± 0.6 Body Weight). The results suggest that subjects with dissimilar peak knee moments can have similar peak medial compartment joint load magnitudes. There was no evidence of inter-limb asymmetry for either group. Given the presence of inter-group differences (non-osteoarthritic vs. osteoarthritic) for the involved knee, but an absence of inter-limb asymmetry in either group, it may be necessary to evaluate how symmetry is achieved, over time, and to differentiate between good versus bad inter-limb symmetry, when evaluating knee gait parameters. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:625-633, 2017.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065735PMC
http://dx.doi.org/10.1002/jor.23261DOI Listing
March 2017

Fetal Rat Gubernaculum Mesenchymal Cells Adopt Myogenic and Myofibroblast-Like Phenotypes.

J Urol 2016 07 31;196(1):270-8. Epub 2015 Dec 31.

Pediatric Urology Research Laboratory, Nemours Biomedical Research/Alfred I. duPont Hospital for Children, Wilmington, Delaware. Electronic address:

Purpose: Gubernaculum-cremaster complex development is hormonally regulated and abnormal in a cryptorchid rat model. Using cell tracking techniques and imaging we studied myogenic phenotypes and fates in the fetal rat gubernaculum-cremaster complex.

Materials And Methods: Embryonic day 17 gubernaculum-cremaster complexes were labeled with CellTracker™ or the DNA synthesis marker EdU (5-ethynyl-2'-deoxyuridine), or immobilized in Matrigel® and grown in culture. Embryonic day 17 to 21 gubernaculum-cremaster complex sections and cells were imaged using wide field and deconvolution immunofluorescence microscopy, and muscle and/or myofibroblast specific antibodies. Deconvolved image stacks were used to create a 3-dimensional model of embryonic day 21 gubernaculum-cremaster complex muscle.

Results: PAX7 (paired box 7) positive and myogenin positive muscle precursors were visible in a desmin-rich myogenic zone between muscle layers that elongated and became thicker during development. Gubernaculum-cremaster complex inner mesenchymal cells expressed desmin and αSMA (α smooth muscle actin) at lower levels than in the myogenic zone. After pulse labeling with CellTracker or EdU mesenchymal cells became incorporated into differentiated muscle. Conversely, mesenchymal cells migrated beyond Matrigel immobilized gubernaculum-cremaster complexes, expressed PAX7 and fused to form striated myotubes. Mesenchymal gubernaculum-cremaster complex cell lines proliferated more than 40 passages and showed contractile behavior but did not form striated muscle. Our 3-dimensional gubernaculum-cremaster complex model had 2 orthogonal ventral layers and an arcing inner layer of muscle.

Conclusions: Our data suggest that mesenchymal cells in the peripheral myogenic zone of the fetal gubernaculum-cremaster complex contribute to formation of a distinctively patterned cremaster muscle. Nonmyogenic, desmin and αSMA positive gubernaculum-cremaster complex mesenchymal cells proliferate and have a myofibroblast-like phenotype in culture. Intrinsic mechanical properties of these divergent cell types may facilitate perinatal inversion of the gubernaculum-cremaster complex.
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http://dx.doi.org/10.1016/j.juro.2015.12.081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4914458PMC
July 2016

Decreased Knee Joint Loading Associated With Early Knee Osteoarthritis After Anterior Cruciate Ligament Injury.

Am J Sports Med 2016 Jan 22;44(1):143-51. Epub 2015 Oct 22.

University of Delaware, Newark, Delaware, USA.

Background: Anterior cruciate ligament (ACL) injury predisposes individuals to early-onset knee joint osteoarthritis (OA). Abnormal joint loading is apparent after ACL injury and reconstruction. The relationship between altered joint biomechanics and the development of knee OA is unknown.

Hypothesis: Altered knee joint kinetics and medial compartment contact forces initially after injury and reconstruction are associated with radiographic knee OA 5 years after reconstruction.

Study Design: Case-control study; Level of evidence, 3.

Methods: Individuals with acute, unilateral ACL injury completed gait analysis before (baseline) and after (posttraining) preoperative rehabilitation and at 6 months, 1 year, and 2 years after reconstruction. Surface electromyographic and knee biomechanical data served as inputs to an electromyographically driven musculoskeletal model to estimate knee joint contact forces. Patients completed radiographic testing 5 years after reconstruction. Differences in knee joint kinetics and contact forces were compared between patients with and those without radiographic knee OA.

Results: Patients with OA walked with greater frontal plane interlimb differences than those without OA (nonOA) at baseline (peak knee adduction moment difference: 0.00 ± 0.08 N·m/kg·m [nonOA] vs -0.15 ± 0.09 N·m/kg·m [OA], P = .014; peak knee adduction moment impulse difference: -0.001 ± 0.032 N·m·s/kg·m [nonOA] vs -0.048 ± 0.031 N·m·s/kg·m [OA], P = .042). The involved limb knee adduction moment impulse of the group with osteoarthritis was also lower than that of the group without osteoarthritis at baseline (0.087 ± 0.023 N·m·s/kg·m [nonOA] vs 0.049 ± 0.018 N·m·s/kg·m [OA], P = .023). Significant group differences were absent at posttraining but reemerged 6 months after reconstruction (peak knee adduction moment difference: 0.02 ± 0.04 N·m/kg·m [nonOA] vs -0.06 ± 0.11 N·m/kg·m [OA], P = .043). In addition, the OA group walked with lower peak medial compartment contact forces of the involved limb than did the group without OA at 6 months (2.89 ± 0.52 body weight [nonOA] vs 2.10 ± 0.69 body weight [OA], P = .036).

Conclusion: Patients who had radiographic knee OA 5 years after ACL reconstruction walked with lower knee adduction moments and medial compartment joint contact forces than did those patients without OA early after injury and reconstruction.
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http://dx.doi.org/10.1177/0363546515608475DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4703470PMC
January 2016

Viscoelastic properties of healthy achilles tendon are independent of isometric plantar flexion strength and cross-sectional area.

J Orthop Res 2015 Jun 27;33(6):926-31. Epub 2015 Apr 27.

Delaware Rehabilitation Institute, University of Delaware, Newark, Delaware.

Changes in tendon viscoelastic properties are observed after injuries and during healing as a product of altered composition and structure. Continuous Shear Wave Elastography is a new technique measuring viscoelastic properties of soft tissues using external shear waves. Tendon has not been studied with this technique, therefore, the aims of this study were to establish the range of shear and viscosity moduli in healthy Achilles tendons, determine bilateral differences of these parameters and explore correlations of viscoelasticity to plantar flexion strength and tendon area. Continuous Shear Wave Elastography was performed over the free portion of both Achilles tendons from 29 subjects. Isometric plantar flexion strength and cross sectional area were measured. The average shear and viscous moduli was 83.2 kPa and 141.0 Pa-s, respectively. No correlations existed between the shear or viscous modulus and area or strength. This indicates that viscoelastic properties can be considered novel, independent biomarkers. The shear and viscosity moduli were bilaterally equivalent (p = 0.013, 0.017) which allows determining pathologies through side-to-side deviations. The average bilateral coefficient of variation was 7.2% and 9.4% for shear and viscosity modulus, respectively. The viscoelastic properties of the Achilles tendon may provide an unbiased, non-subjective rating system of tendon recovery and optimizing treatment strategies.
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http://dx.doi.org/10.1002/jor.22878DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4683615PMC
June 2015

Continuous Shear Wave Elastography: A New Method to Measure Viscoelastic Properties of Tendons in Vivo.

Ultrasound Med Biol 2015 Jun 19;41(6):1518-29. Epub 2015 Mar 19.

Biomedical Engineering Program, University of Delaware, Newark, Delaware, USA.

Viscoelastic mechanical properties are frequently altered after tendon injuries and during recovery. Therefore, non-invasive measurements of shear viscoelastic properties may help evaluate tendon recovery and compare the effectiveness of different therapies. The objectives of this study were to describe an elastography method for measuring localized viscoelastic properties of tendons and to discuss the initial results in healthy and injured human Achilles and semitendinosus tendons. The technique used an external actuator to generate the shear waves in the tendon at different frequencies and plane wave imaging to measure shear wave displacements. For each of the excitation frequencies, maps of direction-specific wave speeds were calculated using local frequency estimation. Maps of viscoelastic properties were obtained using a pixel-wise curve fit of wave speed and frequency. The method was validated by comparing measurements of wave speed in agarose gels with those obtained using magnetic resonance elastography. Measurements in human healthy Achilles tendons revealed a pronounced increase in wave speed as a function of frequency, which highlights the importance of tendon viscoelasticity. Additionally, the viscoelastic properties of the Achilles tendon were larger than those reported for other tissues. Measurements in a tendinopathic Achilles tendon indicated that it is feasible to quantify local viscoelastic properties. Similarly, measurement in the semitendinosus tendon revealed substantial differences in viscoelastic properties between the healthy and contralateral tendons. Consequently, this technique has the potential to evaluate localized changes in tendon viscoelastic properties caused by injury and during recovery in a clinical setting.
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http://dx.doi.org/10.1016/j.ultrasmedbio.2015.02.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4426016PMC
June 2015

Knee contact force asymmetries in patients who failed return-to-sport readiness criteria 6 months after anterior cruciate ligament reconstruction.

Am J Sports Med 2014 Dec 15;42(12):2917-25. Epub 2014 Oct 15.

Delaware Rehabilitation Institute, University of Delaware, Newark, Delaware, USA Department of Physical Therapy, University of Delaware, Newark, Delaware, USA.

Background: After anterior cruciate ligament (ACL) injury, contact forces are decreased in the injured knee when compared with the uninjured knee. The persistence of contact force asymmetries after ACL reconstruction may increase the risk of reinjury and may play an important role in the development of knee osteoarthritis in these patients. Functional performance may also be useful in identifying patients who demonstrate potentially harmful joint contact force asymmetries after ACL reconstruction.

Hypothesis: Knee joint contact force asymmetries would be present during gait after ACL reconstruction, and performance on a specific set of validated return-to-sport (RTS) readiness criteria would discriminate between those who demonstrated contact force asymmetries and those who did not.

Study Design: Descriptive laboratory study.

Methods: A total of 29 patients with ACL ruptures participated in gait analysis and RTS readiness testing 6 months after reconstruction. Muscle and joint contact forces were estimated using an electromyography (EMG)-driven musculoskeletal model of the knee. The magnitude of typical limb asymmetry in uninjured controls was used to define limits of meaningful limb asymmetry in patients after ACL reconstruction. The RTS testing included isometric quadriceps strength testing, 4 unilateral hop tests, and 2 self-report questionnaires. Paired t tests were used to assess limb symmetry for peak medial and tibiofemoral contact forces in all patients, and a mixed-design analysis of variance was used to analyze the effect of passing or failing RTS testing on contact force asymmetry.

Results: Among all patients, neither statistically significant nor meaningful contact force asymmetries were identified. However, patients who failed RTS testing exhibited meaningful contact force asymmetries, with tibiofemoral contact force being significantly lower for the involved knee. Conversely, patients who passed RTS testing exhibited neither significant nor meaningful contact force asymmetries.

Conclusion: Joint contact force asymmetries during gait are present in some patients 6 months after ACL reconstruction. Patients who demonstrated poor functional performance on RTS readiness testing exhibited significant and meaningful contact force asymmetries.

Clinical Relevance: When assessing all patients together, variability in the functional status obscured significant and meaningful differences in contact force asymmetry in patients 6 months after ACL reconstruction. These specific RTS readiness criteria appear to differentiate between those who demonstrate joint contact force symmetry after ACL reconstruction and those who do not.
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http://dx.doi.org/10.1177/0363546514552184DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4314107PMC
December 2014

Differences in Plantar Flexor Fascicle Length and Pennation Angle between Healthy and Poststroke Individuals and Implications for Poststroke Plantar Flexor Force Contributions.

Stroke Res Treat 2014 23;2014:919486. Epub 2014 Jul 23.

Biomechanics and Movement Science Program, University of Delaware, Newark, DE 19716, USA ; Delaware Rehabilitation Institute, University of Delaware, Newark, DE 19713, USA.

Poststroke plantar flexor muscle weakness has been attributed to muscle atrophy and impaired activation, which cannot collectively explain the limitations in force-generating capability of the entire muscle group. It is of interest whether changes in poststroke plantar flexor muscle fascicle length and pennation angle influence the individual force-generating capability and whether plantar flexor weakness is due to uniform changes in individual muscle force contributions. Fascicle lengths and pennation angles for the soleus, medial, and lateral gastrocnemius were measured using ultrasound and compared between ten hemiparetic poststroke subjects and ten healthy controls. Physiological cross-sectional areas and force contributions to poststroke plantar flexor torque were estimated for each muscle. No statistical differences were observed for any muscle fascicle lengths or for the lateral gastrocnemius and soleus pennation angles between paretic, nonparetic, and healthy limbs. There was a significant decrease (P < 0.05) in the paretic medial gastrocnemius pennation angle compared to both nonparetic and healthy limbs. Physiological cross-sectional areas and force contributions were smaller on the paretic side. Additionally, bilateral muscle contributions to plantar flexor torque remained the same. While the architecture of each individual plantar flexor muscle is affected differently after stroke, the relative contribution of each muscle remains the same.
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http://dx.doi.org/10.1155/2014/919486DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4134812PMC
August 2014

Poststroke muscle architectural parameters of the tibialis anterior and the potential implications for rehabilitation of foot drop.

Stroke Res Treat 2014 16;2014:948475. Epub 2014 Jul 16.

Biomechanics and Movement Science Program, University of Delaware, Newark, DE 19716, USA ; Delaware Rehabilitation Institute, University of Delaware, Newark, DE 19713, USA ; Department of Biomedical Engineering, University of Delaware, Newark, DE 19716, USA.

Poststroke dorsiflexor weakness and paretic limb foot drop increase the risk of stumbling and falling and decrease overall functional mobility. It is of interest whether dorsiflexor muscle weakness is primarily neurological in origin or whether morphological differences also contribute to the impairment. Ten poststroke hemiparetic individuals were imaged bilaterally using noninvasive medical imaging techniques. Magnetic resonance imaging was used to identify changes in tibialis anterior muscle volume and muscle belly length. Ultrasonography was used to measure fascicle length and pennation angle in a neutral position. We found no clinically meaningful bilateral differences in any architectural parameter across all subjects, which indicates that these subjects have the muscular capacity to dorsiflex their foot. Therefore, poststroke dorsiflexor weakness is primarily neural in origin and likely due to muscle activation failure or increased spasticity of the plantar flexors. The current finding suggests that electrical stimulation methods or additional neuromuscular retraining may be more beneficial than targeting muscle strength (i.e., increasing muscle mass).
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http://dx.doi.org/10.1155/2014/948475DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4124652PMC
August 2014
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