Unbalanced Medial-to-Lateral Knee Muscle Co-Contractions are Associated with Medial Tibiofemoral Underloading during Gait Three Months after Anterior Cruciate Ligament Reconstruction.

Altered medial/lateral knee muscle co-contraction (measure by co-contraction indices, CCI) occurs during gait early after anterior cruciate ligament reconstruction (ACLR). Changes in peak medial compartment forces (pMCF) are also observed early after ACLR and are linked to the development of knee osteoarthritis. We do not know if imbalanced co-contraction is associated with these alterations in knee load. The purpose of this study was to evaluate the association between pMCF and the CCIs of medial/lateral knee muscle pairs during walking three months after ACLR. Bilateral knee gait mechanics and electromyography (EMG) data were collected from 44 participants 3 months following surgery. CCIs of six muscle pairs and medial-to-lateral (M:L) CCIs ratios were calculated during the weight acceptance interval. Bilateral pMCFs were calculated using a subject-based neuromusculoskeletal model. Based on interlimb pMCF symmetry, participants were divided into three groups: symmetric loaders, underloaders, and overloaders. A 2 × 3 (limb × group) ANOVA was used to compare CCIs between limbs in all groups. A partial Spearman's test was performed to examine the association between CCIs ratios and pMCF. The CCIs of the vastus lateralis-lateral gastrocnemius muscle pair was higher in the involved limb of underloaders (vs. the uninvolved limb and vs. the involved limb of symmetric loaders). The ratio of M:L CCIs was significantly lower (more lateral CCIs) in the involved limb, which was associated with lower pMCF. These results suggest that individuals early after ACLR who walk with higher CCIs of lateral knee musculature (vs. medial), have medial tibiofemoral underloading.

Limb and sex-related differences in knee muscle co-contraction exist 3 months after anterior cruciate ligament reconstruction.

Interlimb and sex-based differences in gait mechanics and neuromuscular control are common after anterior cruciate ligament reconstruction (ACLR). Following ACLR, individuals typically exhibit elevated co-contraction of knee muscles, which may accelerate knee osteoarthritis (OA) onset. While directed (medial/lateral) co-contractions influence tibiofemoral loading in healthy people, it is unknown if directed co-contractions are present early after ACLR and if they differ across limbs and sexes. The purpose of this study was to compare directed co-contraction indices (CCIs) of knee muscles in both limbs between men and women after ACLR. Forty-five participants (27 men) completed overground walking at a self-selected speed 3 months after ACLR during which quadriceps, hamstrings, and gastrocnemii muscle activities were collected bilaterally using surface electromyography. CCIs of six muscle pairs were calculated during the weight acceptance interval. The CCIs of the vastus lateralis/biceps femoris muscle pair (lateral musculature) was greater in the involved limb (vs uninvolved; p = 0.02). Compared to men, women exhibited greater CCIs in the vastus medialis/lateral gastrocnemius and vastus lateralis/lateral gastrocnemius muscle pairs (p < 0.01 and p = 0.01, respectively). Limb- and sex-based differences in knee muscle co-contractions are detectable 3 months after ACLR and may be responsible for altered gait mechanics.

Bone-Patellar Tendon-Bone Autograft Harvest Prolongs Extensor Latency during Gait 2 yr after ACLR.

PURPOSE: Bone-patellar tendon-bone (BPTB) graft harvest for anterior cruciate ligament reconstruction alters patellar tendon properties, which inflict poor quadriceps neuromuscular function. BPTB autografts are associated with higher rates of posttraumatic osteoarthritis, which in turn is associated with pathological gait. The purpose of this study was to investigate the latency between the time of peak quadriceps activity and the peak knee flexion moment during gait, between those with BPTB grafts ( n = 23) and other graft types (hamstring autograft or allografts, n = 54), 5 ± 2 months and 2 yr (25 ± 3 months) after anterior cruciate ligament reconstruction. We hypothesized that longer latencies would be observed in the BPTB graft group in the involved limb. We expected latencies to shorten over time. METHODS: Knee moments and quadriceps EMG were collected during gait, and vastus medialis, vastus lateralis, rectus femoris (RF), and quadriceps latencies were calculated. Linear mixed-effects models were used to compare latencies between graft types and over the two time points. RESULTS: The main effects of graft type were observed for vastus medialis ( P = 0.005) and quadriceps ( P = 0.033) latencies with the BPTB graft group demonstrating longer latencies. No main effects of graft type were observed for vastus lateralis ( P = 0.051) and RF ( P = 0.080) latencies. Main effects of time were observed for RF latency ( P = 0.022). CONCLUSIONS: Our hypothesis that the BPTB graft group would demonstrate longer extensor latency was supported. Contrary to our second hypothesis, however, latency only improved in RF and regardless of graft type, indicating that neuromuscular deficits associated with BPTB grafts may persist 2 yr after surgery. Persistent deficits may be mediated by changes in the patellar tendon's mechanical properties. Graft-specific rehabilitation may be warranted to address the long-term neuromechanical deficits that are present after BPTB graft harvest.

Effects of rod diameter on kinematics of posterior cervical spine instrumented constructs: an ex vivo study.

OBJECTIVE: Posterior cervical spine fixation is a robust strategy for stabilizing the spine for a wide range of spinal disorders. With the evolution of spinal implant technology, posterior fixation with lateral mass screws in the subaxial spine is now common. Despite interest in variable rod diameters to meet a wide range of clinical needs such as trauma, revision, and deformity surgery, indications for use of posterior cervical spine fixation are not clear. This laboratory investigation evaluates the mechanical stability and kinematic properties of lateral mass fixation with various commercially available rod diameters. METHODS: The authors conducted an ex vivo experiment using 13 fresh-frozen human cervical spine specimens, instrumented from C3 to C6 with lateral mass screws, to evaluate the effects of titanium rod diameter on kinematic stability. Each intact spine was tested using a kinematic profiling machine with an optoelectrical camera and infrared sensors applying 1.5-Nm bending moments to the cranial vertebra (C2) simulating flexion-extension, lateral bending, and axial rotation anatomical motions. A compressive follower preload of 150 N was applied in flexion-extension prior to application of a bending moment. Instrumented spines were then tested with rod diameters of 3.5, 4.0, and 4.5 mm. The kinematic data between intact and surgical cases were studied using a nonparametric Wilcoxon signed-rank test. A multivariable, multilevel linear regression model was built to identify the relationship between segmental motion and rod diameter. RESULTS: Instrumentation resulted in significant reduction in range of motion in all three rod constructs versus intact specimens in flexion-extension, lateral bending, and axial rotation (p < 0.05). The maximum reductions in segmental ROM versus intact spines in 3.5-, 4.0-, and 4.5-mm rod constructs were 61%, 71%, and 81% in flexion-extension; 70%, 76%, and 81% in lateral bending; and 50%, 60%, and 75% in axial rotation, respectively. Segmental motion at the adjacent segments (C2-3 and C6-7) increased significantly (p < 0.05) with increasing rod diameter. The 4.5-mm rod construct had the greatest increase in motion compared to the intact spine. CONCLUSIONS: With increasing rod diameters from 3.5 to 4.0 mm, flexion-extension, lateral bending, and axial rotation across C3-6 were significantly reduced (p < 0.05). Similar trends were observed with a statistically significant reduction in motion in all anatomical planes when the rod diameter was increased to 4.5 mm. Although the increase in rod diameter resulted in a more rigid construct, it also created an increase (p < 0.05) in the kinematics of the adjacent segments (C2-3 and C6-7). Whether this increase translates into adverse long-term clinical effects in vivo requires further investigation and clinical assessment.

Identifying Gait Pathology after ACL Reconstruction Using Temporal Characteristics of Kinetics and Electromyography.

PURPOSE: Asymmetrical gait mechanics after anterior cruciate ligament reconstruction (ACLR) are associated with the development of posttraumatic knee osteoarthritis. Current measures of gait mechanics have focused heavily on peak magnitudes of knee kinematics, kinetics, and joint contact forces but have seldom considered the rate of knee loading, cumulative knee load, or the timing of motor input surrounding peaks. The purpose of this study was to introduce and describe novel metrics of gait using temporal characteristics of kinetics and EMG to identify neuromuscular deficits of the quadriceps in patients after ACLR. METHODS: Gait mechanics were assessed 6 months (n = 145) and 24 months (n = 116) after ACLR. External knee flexion rate of moment development (RMD) and knee flexion moment impulse (KFMI) leading up to the time of peak knee flexion moment (pKFM), peak RMD between initial contact to pKFM, and cumulative KFMI were calculated. Extensor latencies from the quadriceps, vastus medialis, vastus lateralis, and rectus femoris (time of pKFM - time of peak EMG activity) during the weight acceptance phase of gait were also calculated. Paired-sample t-tests (α = 0.05) were performed between limbs at both time points. RESULTS: Slower RMD, smaller KFMI, and longer extensor latencies in the involved compared with uninvolved limb were observed across all measures at 6 months (P < 0.005). At 24 months, RMDpeak was slower, and KFMI50ms, KFMI100ms, and KFMItotal were lower in the involved limb (P < 0.003), but no other asymmetries were found. CONCLUSIONS: Slower RMD, smaller KFMI, and prolonged extensor latencies may characterize neuromuscular deficits underlying aberrant gait mechanics early after ACLR. RMD, KFMI, and extensor latencies during gait should be considered in the future to quantify asymmetrical movement patterns observed after ACLR and as markers of recovery.

Patellofemoral contact forces after ACL reconstruction: A longitudinal study.

Osteoarthritis (OA) development after ACL reconstruction (ACLR) is common. Patellofemoral OA after ACLR is as prevalent as tibiofemoral OA; however, few have explored the mechanisms leading to disease development in this compartment. Biomechanical alterations may be one mechanism responsible for post-traumatic knee OA. Patellofemoral contact forces during dynamic tasks, such as running and single leg hops, have been assessed at return to sport and later time points. The results of these studies, however, contradict each other, are only cross-sectional in nature, and are limited to specific points in time within the movement pattern. The purpose of this study was to assess patellofemoral contact forces 3, 6, and 24 months after ACLR during level walking over the entirety of the movement pattern. Patellofemoral contact forces were calculated after determination of muscle forces from a validated, subject-specific, EMG-driven neuromusculoskeletal model. Statistical parametric mapping was used to compare patellofemoral contact forces between limbs and across time points. Patellofemoral underloading of the involved limb (vs. uninvolved) was present at 3 months (p < 0.001 from 7 to 30% of stance) and 6 months (p = 0.001 from 11 to 23% of stance and p = 0.025 from 27 to 32%) after ACLR but was resolved by 24 months. Both limbs' load increased from 3 to 6 months. The involved limb displayed relatively consistent loads from 6 months onward, while the uninvolved limb's decreased back down towards their 3-month values. Overall, these results suggest that early patellofemoral underloading exists after ACLR and may be leading to patellofemoral OA development.

Knee joint biomechanics during gait improve from 3 to 6 months after anterior cruciate ligament reconstruction.

Gait alterations after anterior cruciate ligament reconstruction (ACLR) are commonly reported and have been linked to posttraumatic osteoarthritis development. While knee gait alterations have been studied at several time points after ACLR, little is known about how these biomechanical variables change earlier than 6 months after surgery, nor is much known about how they differ over the entire stance phase of gait. The purpose of this study was to examine knee gait biomechanical variables over their entire movement pattern through stance at both 3 and 6 months after ACLR and to study the progression of interlimb asymmetry between the two postoperative time points. Thirty-five individuals underwent motion analysis during overground walking 3 (3.2 ± 0.5) and 6 (6.4 ± 0.7) months after ACLR. Knee biomechanical variables were compared between limbs and across time points through 100% of stance using statistical parametric mapping; this included a 2 × 2 (Limb × Time) repeated measures analysis of variance and two-tailed t-tests. Smaller knee joint angles, moments, extensor forces, and medial compartment forces were present in the involved versus uninvolved limb. Interlimb asymmetries were present at both time points but were less prevalent at 6 months. The uninvolved limb's biomechanical variables stayed relatively consistent over time, while the involved limb's trended toward that of the uninvolved limb. Statement of Clinical Significance: Interventions to correct asymmetrical gait patterns after ACLR may need to occur early after surgery and may need to focus on multiple parts of stance phase.

Knee cartilage T2 relaxation times 3 months after ACL reconstruction are associated with knee gait variables linked to knee osteoarthritis.

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. T2 relaxation times in the medial compartment and linear regressions were used to determine the associations between gait variables and deep and superficial cartilage T2 relaxation times in six regions. pKAM was positively associated with deep layer T2 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 T2 relaxation times in the tibial central region became significant (p = .043). Interlimb difference of pKFM was negatively associated with interlimb difference of deep layer T2 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.

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

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.

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

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.

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

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 T2 relaxation time. The purposes of this study were to (i) compare involved (ACLR) versus uninvolved (contralateral) femoral trochlear cartilage T2 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 T2 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 T2 relaxation times. Slower walking speed was related to higher (worse) femoral trochlear cartilage T2 relaxation times in the involved limb (Pearson's r: -0.583, p = 0.002) and greater interlimb differences in trochlear T2 relaxation times (Pearson's r: -0.349, p = 0.080). Walking mechanics were weakly related to trochlear T2 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.

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

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 ±â€¯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.

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

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.

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

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.

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

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.

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

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.

Predictors of knee joint loading after anterior cruciate ligament reconstruction.

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.

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

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.

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

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.

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

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.