Publications by authors named "Kurt Manal"

55 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
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8481340PMC
March 2021

The cross-sectional relationships between age, standing static balance, and standing dynamic balance reactions in typically developing children.

Gait Posture 2019 09 3;73:20-25. Epub 2019 Jul 3.

Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE, United States. Electronic address:

Background: Static balance performance is a common metric for evaluating the development of postural control in children. Less is known about the potentially independent development of dynamic balance performance.

Research Question: How does age relate to static (i.e. postural sway) and dynamic (i.e. stepping thresholds) standing balance performance, and what is the relationship between postural sway and stepping thresholds?

Methods: Twenty-six typically developing children (12 males, 14 females; 5-12 years of age) were recruited for this cross-sectional study. Static balance performance was quantified as the total path length during a postural sway assessment using a force platform with conditions of eyes open and eyes closed. Dynamic balance performance was quantified using a single-stepping threshold assessment, whereby participants attempted to prevent a step in response to treadmill-induced perturbations in the anterior and posterior directions. Relationships between age and body-size scaled measures of static and dynamic balance performance were assessed using Spearman rank correlations.

Results: There was a weak correlation between age and postural sway (|r| < 0.10, p >  0.68), but a moderate-to-strong correlation between age and single-stepping thresholds (r > 0.68, p < 0.001). A weak correlation was found between postural sway and single-stepping thresholds (|r| < 0.20, p >  0.39).

Significance: Dynamic, but not static standing balance performance, may improve with typical development between the ages of 5 and 12 years. Static and dynamic balance should be considered as unique constructs when assessed in children.
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http://dx.doi.org/10.1016/j.gaitpost.2019.07.128DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6707867PMC
September 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

Changes in gait mechanics and muscle activity with wedge height in an orthopaedic boot.

Gait Posture 2019 05 25;70:59-64. Epub 2019 Feb 25.

University of Delaware, Department of Physical Therapy, 540 South College Ave, Newark, DE, USA. Electronic address:

Background: Orthopaedic boots with wedging are commonly used in the treatment of individuals with Achilles tendon rupture to immobilize the foot in plantar flexion and approximate tendon ends.

Research Question: To describe changes in muscle activity of the triceps surae and gait mechanics with the use of wedges in an orthopaedic boot immediately and after an accommodation period.

Methods: Muscle activity of the triceps surae and gait parameters (vertical ground reaction force, knee extension power, gait speed) were collected using surface electromyography and motion capture in 12 healthy individuals. Participants walked in an instrumented orthopaedic boot with 0, 3, and 5 wedges tested in random order. Participants were provided a one hour accommodation period where time spent walking was collected. This was followed by a repeat assessment of triceps surae activity and gait.

Results: Peak and integrated EMG in the medial gastrocnemius (p = 0.001, p < 0.001) and soleus (p = 0.010, p < 0.001) significantly decreased with increasing number of wedges. Peak and integrated EMG had a slight but non-significant decrease with increasing number of wedges in the lateral gastrocnemius (p = 0.151, p = 0.077). Vertical ground reaction force decreased (p = 0.019) and peak knee extension power increased (p = 0.003) with increasing number of wedges. There were no statistically significant differences in gait speed with wedges (p = 0.450). There were no significant changes in EMG or gait parameters from pre- to post-accommodation period.

Significance: A combination of factors yield decreased triceps surae activity in individuals wearing an orthopaedic boot with wedges - decreasing loading on the immobilized limb and shifting power generation proximally.
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http://dx.doi.org/10.1016/j.gaitpost.2019.02.027DOI Listing
May 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

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

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

Biomechanical analysis of gait termination in 11-17year old youth at preferred and fast walking speeds.

Hum Mov Sci 2016 Oct 15;49:178-85. Epub 2016 Jul 15.

Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, United States. Electronic address:

In populations where walking and/or stopping can be difficult, such as in children with cerebral palsy, the ability to quickly stop walking may be beyond the child's capabilities. Gait termination may be improved with physical therapy. However, without a greater understanding of the mechanical requirements of this skill, treatment planning is difficult. The purpose of this study was to understand how healthy children successfully terminate gait in one step when walking quickly, which can be challenging even for healthy children. Lower extremity kinematic and kinetic data were collected from 15 youth as they performed walking, planned, and unplanned stopping tasks. Each stopping task was performed as the subject walked at his/her preferred speed and a fast speed. The most significant changes in mechanics between speed conditions (preferred and fast) of the same stopping task were greater knee flexion angles (unplanned: +16.49±0.54°, p=0.00; planned: +15.75±1.1°, p=0.00) and knee extension moments (unplanned: +0.67±0.02N/kgm, p=0.00; planned: +0.57±0.23N/kgm, p=0.00) at faster speeds. The extra range of motion in the joints and extra muscle strength required to maintain the stopping position suggests that stretching and strengthening the muscles surrounding the joints of the lower extremity, particularly the knee, may be a useful intervention.
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http://dx.doi.org/10.1016/j.humov.2016.07.001DOI Listing
October 2016

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

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

Site-Specific Transmission of a Floor-Based, High-Frequency, Low-Magnitude Vibration Stimulus in Children With Spastic Cerebral Palsy.

Arch Phys Med Rehabil 2016 Feb 21;97(2):218-23. Epub 2015 Sep 21.

Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE. Electronic address:

Objective: To determine the degree to which a high-frequency, low-magnitude vibration signal emitted by a floor-based platform transmits to the distal tibia and distal femur of children with spastic cerebral palsy (CP) during standing.

Design: Cross-sectional study.

Setting: University research laboratory.

Participants: Children with spastic CP who could stand independently (n=18) and typically developing children (n=10) (age range, 4-12y) participated in the study (N=28).

Interventions: Not applicable.

Main Outcome Measures: The vibration signal at the high-frequency, low-magnitude vibration platform (approximately 33Hz and 0.3g), distal tibia, and distal femur was measured using accelerometers. The degree of plantar flexor spasticity was assessed using the Modified Ashworth Scale.

Results: The high-frequency, low-magnitude vibration signal was greater (P<.001) at the distal tibia than at the platform in children with CP (.36±.06g vs .29±.05g) and controls (.40±.09g vs .24±.07g). Although the vibration signal was also higher at the distal femur (.35±.09g, P<.001) than at the platform in controls, it was lower in children with CP (.20±.07g, P<.001). The degree of spasticity was negatively related to the vibration signal transmitted to the distal tibia (Spearman ρ=-.547) and distal femur (Spearman ρ=-.566) in children with CP (both P<.05).

Conclusions: A high-frequency, low-magnitude vibration signal from a floor-based platform was amplified at the distal tibia, attenuated at the distal femur, and inversely related to the degree of muscle spasticity in children with spastic CP. Whether this transmission pattern affects the adaptation of the bones of children with CP to high-frequency, low-magnitude vibration requires further investigation.
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http://dx.doi.org/10.1016/j.apmr.2015.08.434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4996345PMC
February 2016

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

Clinically-relevant measures associated with altered contact forces in patients with anterior cruciate ligament deficiency.

Clin Biomech (Bristol, Avon) 2014 May 3;29(5):531-6. Epub 2014 Apr 3.

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

Background: Knee joint contact forces are altered after anterior cruciate ligament injury during walking and may be related to clinically-relevant measures of impairments or self-reported function. The purpose of this study was to investigate the association of several clinically-relevant measures with altered knee contact forces in patients with anterior cruciate ligament injury.

Methods: Data for this study represent a cross-sectional observational analysis of thirty-seven (23 M, 14 F) patients with complete unilateral anterior cruciate ligament injury. Gait analysis with electromyography was used to obtain estimates of tibiofemoral joint contact force using an electromyography-driven musculoskeletal model. Multivariable linear regression was used to identify measures associated with tibiofemoral joint contact force.

Findings: Involved knee extensor muscle strength and patient-reported knee function on the Global Rating Scale of perceived function were significantly associated with peak tibiofemoral contact force for the involved limb. Patients who were stronger and who perceived higher knee function walked with greater contact forces on their involved knees. After controlling for walking speed, involved extensor strength explained 8.9% of the variance in involved peak tibiofemoral contact force and score on the Global Rating Scale explained an additional 9.4% of the variance.

Interpretation: Improvements in involved quadriceps strength and overall function as measured by patient self-report may be important for increasing involved limb contact forces, thereby restoring loading symmetry in these patients who demonstrate decreased involved limb loading after injury. These results highlight the potential value of studying the recovery of strength, self-reported function and joint loading symmetry in patients with anterior cruciate ligament injury.
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http://dx.doi.org/10.1016/j.clinbiomech.2014.03.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4074918PMC
May 2014

Subject-specific measures of Achilles tendon moment arm using ultrasound and video-based motion capture.

Physiol Rep 2013 Nov 7;1(6):e00139. Epub 2013 Nov 7.

Department of Mechanical Engineering, Delaware Rehabilitation Institute Newark, Delaware, 19716 ; Department of Mechanical Engineering, University of Delaware Newark, Delaware, 19716.

THE ACHILLES TENDON (AT) MOMENT ARM IS AN IMPORTANT BIOMECHANICAL PARAMETER MOST COMMONLY ESTIMATED USING ONE OF TWO METHODS: (A) center of rotation and (B) tendon excursion. Conflicting findings regarding magnitude and whether it changes with contraction intensity have been reported when using these methods. In this study, we present an alternate method of measuring the AT moment arm by combining ultrasound and video-based motion capture. Moment arms for 10 healthy male subjects were measured at five different joint angles in 10° increments ranging from 20° of dorsiflexion (DF) to 20° of plantar flexion (PF). Moment arms were measured at rest and also during maximum voluntary contraction (MVC). For both conditions, the AT moment arm increased in magnitude as the ankle moved from DF to PF. In 20° of DF, the moment arm at rest averaged 34.6 ± 1.8 mm and increased to a maximum value of 36.9 ± 1.9 mm when plantar flexed to 10°. Moment arms during MVC ranged from 35.7 ± 1.8 mm to 38.1 ± 2.6 mm. The moment arms we obtained were much more consistent with literature values derived using ultrasound and tendon excursion compared to center of rotation or in vitro methods. This is noteworthy as the hybrid method is easy to implement and as it is less costly and timing consuming than other methods, including tendon excursion, it is well suited for large-scale studies involving many subjects.
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http://dx.doi.org/10.1002/phy2.139DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3871454PMC
November 2013

Characteristics of human knee muscle coordination during isometric contractions in a standing posture: the effect of limb task.

J Electromyogr Kinesiol 2013 Dec 19;23(6):1398-405. Epub 2013 Jun 19.

University of Delaware, Delaware Rehabilitation Institute, 126 Spencer, 130 Academy Street, Newark, DE 19711, USA.

Different functional roles for the hands have been demonstrated, however leg control is not as well understood. The purpose of the present study was to evaluate bilateral knee neuromuscular control to determine if the limb receiving greater attention would have more well-tuned control compared to an unattended limb. Surface electrodes were placed on seven muscles of each limb, before standing on two force platforms. Visual feedback was given of the forces and moments of the "focus limb," but not the "unattended limb." Static isometric forces were matched with their focus limb, requiring their unattended limb to push in the opposite direction, using a combination of forward-backward-medial-lateral shear forces while muscle activity was collected bilaterally. There was a significant main effect for limb task (p = 0.02), with the medial hamstrings being more specific (p = 0.001) while performing the unattended limb and the lateral hamstring being more well-tuned (p = 0.007) while performing the focus limb task. The focus limb's medial and lateral gastrocnemius were principally active in the forwards direction, but only the unattended limb's lateral gastrocnemius was active in the backwards direction. Findings suggest unique neuromuscular control strategies are used for the legs depending on limb task.
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http://dx.doi.org/10.1016/j.jelekin.2013.05.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4315617PMC
December 2013

Compensatory muscle activation caused by tendon lengthening post-Achilles tendon rupture.

Knee Surg Sports Traumatol Arthrosc 2015 Mar 23;23(3):868-74. Epub 2013 Apr 23.

University of Delaware, 126 Spencer Lab, Newark, DE, 19716-3140, USA,

Purpose: The purpose of this study was to establish a relationship between the lengthening of the Achilles tendon post-rupture and surgical repair to muscle activation patterns during walking in order to serve as a reference for post-surgical assessment.

Method: The Achilles tendon lengths were collected from 4 patients with an Achilles tendon rupture 6 and 12 months post-surgery along with 5 healthy controls via ultrasound. EMG was collected from the triceps surae muscles and tibialis anterior during overground walking.

Results: Achilles lengths at 6 and 12 months post-surgery were significantly longer (p < 0.05) on the involved side compared to the uninvolved side, but there were no side-to-side differences in the healthy controls. The integrated EMG (iEMG) of the involved side was significantly higher than the uninvolved side in the lateral gastrocnemius at 6 months and for the medial gastrocnemius at 12 months in the patients with Achilles tendon rupture; no side-to-side difference was found in the healthy controls. The triceps surae muscles' activations were fair to moderately correlated to the Achilles lengths (0.38 < r < 0.52).

Conclusions: The increased Achilles tendon length and iEMG from the triceps surae muscles indicate that loss of function is primarily caused by anatomical changes in the tendon and the appearance of muscle weakness is due to a lack of force transmission capability. This study indicates that when aiming for full return of function and strength, an important treatment goal appears to be to minimize tendon elongation.
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http://dx.doi.org/10.1007/s00167-013-2512-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3778146PMC
March 2015

Minimum detectable change for knee joint contact force estimates using an EMG-driven model.

Gait Posture 2013 Sep 16;38(4):1051-3. Epub 2013 Apr 16.

Biomechanics and Movement Science Program, University of Delaware, Newark, DE, United States; Delaware Rehabilitation Institute, University of Delaware, Newark, DE, United States.

Unlabelled: Adequate test-retest reliability of model estimates is a necessary precursor to examining treatment effects or longitudinal changes in individuals.

Purpose: The purpose of this study was to establish thresholds for minimal detectable change (MDC) for joint contact forces obtained using a patient specific EMG-driven musculoskeletal model of the knee.

Design: A sample of young, active individuals was selected for this study, and subjects were tested on 2 separate days. Three-dimensional motion analysis with electromyography (EMG) was used to obtain data from each subject during gait for model input. An EMG-driven modeling approach was used to estimate joint contact forces at each session.

Results: MDC's for contact force variables ranged from 0.30 to 0.66 BW. The lowest MDC was for peak medial compartment force (0.30 BW) and the highest was for peak tibiofemoral contact force (0.66 BW). Test-retest reliability coefficients were also reported for comparison with previous work.

Conclusions: Using the present model, changes in joint contact forces between baseline and subsequent measurements that are greater than these MDCs are greater than typical day-to-day variation and can be identified as real change.
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http://dx.doi.org/10.1016/j.gaitpost.2013.03.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3795951PMC
September 2013

An electromyogram-driven musculoskeletal model of the knee to predict in vivo joint contact forces during normal and novel gait patterns.

J Biomech Eng 2013 Feb;135(2):021014

Delaware Rehabilitation Institute, Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA.

Computational models that predict internal joint forces have the potential to enhance our understanding of normal and pathological movement. Validation studies of modeling results are necessary if such models are to be adopted by clinicians to complement patient treatment and rehabilitation. The purposes of this paper are: (1) to describe an electromyogram (EMG)-driven modeling approach to predict knee joint contact forces, and (2) to evaluate the accuracy of model predictions for two distinctly different gait patterns (normal walking and medial thrust gait) against known values for a patient with a force recording knee prosthesis. Blinded model predictions and revised model estimates for knee joint contact forces are reported for our entry in the 2012 Grand Challenge to predict in vivo knee loads. The EMG-driven model correctly predicted that medial compartment contact force for the medial thrust gait increased despite the decrease in knee adduction moment. Model accuracy was high: the difference in peak loading was less than 0.01 bodyweight (BW) with an R(2 )= 0.92. The model also predicted lateral loading for the normal walking trial with good accuracy exhibiting a peak loading difference of 0.04 BW and an R(2 )= 0.44. Overall, the EMG-driven model captured the general shape and timing of the contact force profiles and with accurate input data the model estimated joint contact forces with sufficient accuracy to enhance the interpretation of joint loading beyond what is possible from data obtained from standard motion capture studies.
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http://dx.doi.org/10.1115/1.4023457DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3705826PMC
February 2013

A Real-time EMG-driven Musculoskeletal Model of the Ankle.

Multibody Syst Dyn 2012 Aug 23;28(1-2):169-180. Epub 2011 Nov 23.

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

The real-time estimation of muscle forces could be a very valuable tool for rehabilitation. By seeing how much muscle force is being produced during rehabilitation, therapists know whether they are working within safe limits in their therapies and patients know if they are producing enough force to expect improvement. This is especially true for rehabilitation of Achilles tendon ruptures where, out of fear of overloading and causing a re-rupture, minimal therapy is typically done for eight weeks post-surgery despite animal studies that show that low-level loading is beneficial. To address this need, we have developed a biomechanical model that allows for the real-time estimation of forces in the triceps surae muscle and Achilles tendon. Forces are estimated using a Hill-type muscle model. To account for differences in neuromuscular control of each subject, the model used EMGs as input. To make this clinically useful, joint angles were measured using electrogoniometers. A dynamometer was used to measure joint moments during the model calibration stage, but was not required during real-time studies. The model accounts for the force-length and force-velocity properties of muscles, and other parameters such as tendon slack length and optimal fiber length. Additional parameters, such as pennation angle and moment arm of each muscle in the model, vary as functions of joint angle. In this paper, the model is presented and it application is demonstrated in two subjects: one with a healthy Achilles tendon and a second six months post Achilles tendon rupture and repair.
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http://dx.doi.org/10.1007/s11044-011-9285-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3571695PMC
August 2012

Sex differences in soleus strength may predispose middle age women to falls.

J Strength Cond Res 2013 Sep;27(9):2596-602

Department of Athletic Training, Daemen College, Amherst, NY, USA.

This study investigated middle age healthy adults to elucidate if plantar flexion (PF) strength differences exist because of the triceps surae or the soleus when comparing between sexes. A random population sample was stratified by sex and included 25 healthy (12 women and 13 men) subjects who volunteered for participation. Dorsiflexion range of motion was measured using a biplane goniometer. Self-reported function was assessed using the Foot and Ankle Ability Measure. Ankle PF strength was assessed using the Biodex System 3. To determine triceps surae vs. soleus strength, testing positions included (1) full ankle dorsiflexion with the knee in full extension and (2) full ankle dorsiflexion with 90° of knee flexion. Results indicated that women were significantly weaker than men in absolute PF strength for both triceps surae and soleus testing positions. Furthermore, even with normalizing PF strength to body mass PF strength deficits persisted. Additionally, when the contribution of the soleus was accounted for in the full knee extended position (triceps surae), normalized strength differences no longer existed between sexes. Therefore, these results indicate that what appeared as triceps surae complex strength deficits in middle age women compared with men was actually soleus weakness. This may suggest that middle age women are predisposed to increased falls at an early age than previously reported. Additionally, this may indicate that the soleus muscle should be a focus of strength training for women during middle age.
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http://dx.doi.org/10.1519/JSC.0b013e31827f522cDOI Listing
September 2013

Altered loading in the injured knee after ACL rupture.

J Orthop Res 2013 Mar 23;31(3):458-64. Epub 2012 Oct 23.

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

Articular loading is an important factor in the joint degenerative process for individuals with anterior cruciate ligament (ACL) rupture. Evaluation of loading for a population that exhibits neuromuscular compensation for injury requires an approach which can incorporate individual muscle activation strategies in its estimation of muscle forces. The purpose of this study was to evaluate knee joint contact forces for patients with ACL deficiency using an EMG-driven modeling approach to estimate muscle forces. Thirty athletes with acute, unilateral ACL rupture underwent gait analysis after resolving range of motion, effusion, pain, and obvious gait impairments. Electromyography was recorded bilaterally from 14 lower extremity muscles and input to a musculoskeletal model for estimation of muscle forces and joint contact forces. Gait mechanics were consistent with previous reports for individuals with ACL-deficiency. Our major finding was that joint loading was altered in the injured limb after acute ACL injury; patients walked with decreased contact force on their injured knee compared to their uninjured knee. Both medial and lateral compartment forces were reduced without a significant change in the distribution of tibiofemoral load between compartments. This is the first study to estimate medial and lateral compartment contact forces in patients with acute ACL rupture using an approach which is sensitive to individual muscle activation patterns. Further work is needed to determine whether this early decreased loading of the injured limb is involved in the development of osteoarthritis in these patients.
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http://dx.doi.org/10.1002/jor.22249DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3553294PMC
March 2013

Are mechanics different between male and female runners with patellofemoral pain?

Med Sci Sports Exerc 2012 Nov;44(11):2165-71

Division of Physical Therapy, Ohio University, Athens, OH, USA.

Introduction: Patellofemoral pain (PFP) has often been attributed to abnormal hip and knee mechanics in females. To date, there have been few investigations of the hip and knee mechanics of males with PFP. The purpose of this study was to compare the lower extremity mechanics and alignment of male runners with PFP with healthy male runners and female runners with PFP. We hypothesized that males with PFP would move with greater varus knee mechanics compared with male controls and compared with females with PFP. Furthermore, it was hypothesized that males with PFP would demonstrate greater varus alignment.

Methods: A gait and single-leg squat analysis was conducted on each group (18 runners per group). Measurement of each runner's tibial mechanical axis was also recorded. Motion data were processed using Visual 3D (C-Motion, Bethesda, MD). ANOVAs were used to analyze the data.

Results: Males with PFP ran and squatted in greater peak knee adduction and demonstrated greater peak knee external adduction moment compared with healthy male controls. In addition, males with PFP ran and squatted with less peak hip adduction and greater peak knee adduction compared with females with PFP. The static measure of mechanical axis of the tibial was not different between groups. However, a post hoc analysis revealed that males with PFP ran with greater peak tibial segmental adduction.

Conclusion: Males with PFP demonstrated different mechanics during running and during a single-leg squat compared with females with PFP and with healthy males. Based upon the results of this study, therapies for PFP may need to be sex specific.
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http://dx.doi.org/10.1249/MSS.0b013e3182629215DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3475738PMC
November 2012

Kinematic and kinetic analysis of planned and unplanned gait termination in children.

Gait Posture 2013 Feb 24;37(2):178-82. Epub 2012 Jul 24.

Department of Exercise Sciences, Brigham Young University, Provo, UT 84602-2213, United States.

Gait termination is a task which requires people to alter momentum and stabilize the body. To date, many of the kinematic and kinetic characteristics of gait termination have not been reported, making it difficult for clinicians to design interventions to improve the ability to terminate gait quickly and efficiently. Therefore, the purpose of this study was to describe the lower body mechanics of healthy children as they performed walking trials, planned stopping trials, and unplanned stopping trials. Kinematic and kinetic data were collected from 15 healthy children between the ages of 11 and 17 years (14.3±2.1 years). The timing and magnitude of peak sagittal plane joint angles and moments were compared across the three conditions for the leg that led the stop step. Most differences were found when comparing unplanned stopping to both walking and planned stopping. During unplanned stopping, most subjects used either a hip/knee extension strategy or hip/knee flexion strategy to stabilize and perform the stopping task. The magnitudes of the peak hip extension moment and peak knee flexion angle were significantly greater, while the peak plantarflexion moment was significantly smaller during unplanned stopping than walking and planned stopping. The peak plantarflexion moment occurred significantly earlier during the stop stance phase of planned and unplanned stopping than during walking. This suggests that the ability to create sufficient joint moments in a short period of time is essential to be able to stop quickly and safely. Therefore, possible treatments/interventions should focus on ensuring that patients have appropriate strength, power, and range of motion.
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http://dx.doi.org/10.1016/j.gaitpost.2012.06.030DOI Listing
February 2013

The effect of isolated gastrocnemius contracture and gastrocnemius recession on lower extremity kinematics and kinetics during stance.

Clin Biomech (Bristol, Avon) 2012 Nov 20;27(9):917-23. Epub 2012 Jul 20.

Department of Athletic Training, Daemen College, Amherst, NY, USA.

Background: Isolated gastrocnemius contracture limits ankle dorsiflexion with full knee extension and is potentially problematic during mid-stance of gait when 10° of dorsiflexion and full knee extension are needed. It is during this time that patients with isolated gastrocnemius contracture may demonstrate altered kinematics and/or kinetics. When conservative management fails to resolve painful foot pathologies associated with non-spastic isolated gastrocnemius contracture, gastrocnemius recession surgery has been suggested to resolve contracture and improve function and strength. However, there are no published reports on lower extremity kinematics/kinetics in the non-spastic isolated gastrocnemius contracture population. Assessment of alterations in gait mechanics is necessary to examine the effects of this potential surgical intervention.

Methods: Lower extremity kinematics and kinetics were assessed in 6 patients clinically diagnosed with isolated gastrocnemius contracture pre- and post-surgical recession compared with 33 healthy control participants.

Findings: Pre-operatively, patients with isolated gastrocnemius contracture demonstrated significantly increased peak knee flexion angles and knee flexion moments during mid-stance. There were no differences in peak ankle dorsiflexion angle or peak plantar flexion moment. Gastrocnemius recession did not alter gait kinematics/kinetics following surgery. Joint kinematic strategies utilized to compensate for isolated gastrocnemius contracture varied minimally between participants with IGC; most employed a flexed knee strategy, while one participant utilized a reduced ankle dorsiflexion strategy.

Interpretation: Select post-surgical gait mechanics were unaltered; however, gait mechanics were not similar between non-spastic isolated gastrocnemius contracture patients and healthy control participants. Surgical intervention for patients with isolated gastrocnemius contracture does not appear to create any negative gait adaptations; however, patients may benefit from gait retraining post-recession as maladaptive gait patterns persist post operatively.
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http://dx.doi.org/10.1016/j.clinbiomech.2012.06.010DOI Listing
November 2012

Deficits in heel-rise height and achilles tendon elongation occur in patients recovering from an Achilles tendon rupture.

Am J Sports Med 2012 Jul 16;40(7):1564-71. Epub 2012 May 16.

University of Delaware, Newark, Delaware, USA.

Background: Whether an Achilles tendon rupture is treated surgically or not, complications such as muscle weakness, decrease in heel-rise height, and gait abnormalities persist after injury.

Purpose: The purpose of this study was to evaluate if side-to-side differences in maximal heel-rise height can be explained by differences in Achilles tendon length.

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

Method: Eight patients (mean [SD] age of 46 [13] years) with acute Achilles tendon rupture and 10 healthy subjects (mean [SD] age of 28 [8] years) were included in the study. Heel-rise height, Achilles tendon length, and patient-reported outcome were measured 3, 6, and 12 months after injury. Achilles tendon length was evaluated using motion analysis and ultrasound imaging.

Results: The Achilles tendon length test-retest reliability (intraclass correlation coefficient = 0.97) was excellent. For the healthy subjects, there were no side-to-side differences in tendon length and heel-rise height. Patients with Achilles tendon ruptures had significant differences between the injured and uninjured side for both tendon length (mean [SD] difference, 2.6-3.1 [1.2-1.4] cm, P = .017-.028) and heel-rise height (mean [SD] difference, -4.1 to -6.1 [1.7-1.8] cm, P = .012-.028). There were significant negative correlations (r = -0.943, P = .002, and r = -0.738, P = .037) between the side-to-side difference in heel-rise height and Achilles tendon length at the 6- and 12-month evaluations, respectively.

Conclusion: The side-to-side difference found in maximal heel-rise height can be explained by a difference in Achilles tendon length in patients recovering from an Achilles tendon rupture. Minimizing tendon elongation appears to be an important treatment goal when aiming for full return of function.
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http://dx.doi.org/10.1177/0363546512447926DOI Listing
July 2012

Gait and neuromuscular asymmetries after acute anterior cruciate ligament rupture.

Med Sci Sports Exerc 2012 Aug;44(8):1490-6

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

Unlabelled: The decreased internal knee extensor moment is a significant gait asymmetry among patients with anterior cruciate ligament (ACL) deficiency, yet the muscular strategy driving this altered moment for the injured limb is unclear.

Purpose: This study aimed to determine whether patients with ACL deficiency and characteristic knee instability would demonstrate normal extensor and increased flexor muscle force to generate a decreased internal extensor moment (i.e., use a hamstring facilitation strategy).

Methods: Gait analysis was performed on 31 athletes with acute ACL rupture who exhibited characteristic knee instability after injury. Peak internal knee extensor moment was calculated using inverse dynamics, and muscle forces were estimated using an electromyography-driven modeling approach. Comparisons were made between the injured and contralateral limbs.

Results: As expected, patients demonstrated decreased peak knee flexion (P = 0.028) and internal knee extensor moment (P = 0.0004) for their injured limb but exhibited neither an isolated decrease in extensor force (quadriceps avoidance) nor an isolated increase in flexor force (hamstring facilitation) at peak knee moment. Instead, they exhibited decreased muscle force from both flexor (P = 0.0001) and extensor (P = 0.0103) groups. This strategy of decreased muscle force may be explained in part by muscle weakness that frequently accompanies ACL injury or by apprehension, low confidence, and fear of further injury.

Conclusions: This is the first study to estimate muscle forces in the ACL-deficient knee using an electromyography-driven approach. These results affirm the existence of neuromuscular asymmetries in the individuals with ACL deficiency and characteristic knee instability.
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http://dx.doi.org/10.1249/MSS.0b013e31824d2783DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3399054PMC
August 2012
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