The Interplay Between Walking Speed, Economy, and Stability After Stroke.

BACKGROUND AND PURPOSE: Energy minimization is thought to underlie the naturally selected, preferred walking speed; however, people post-stroke walk slower than their most economical speed, presumably to optimize other objectives, such as stability. The purpose of this study was to examine the interplay between walking speed, economy, and stability. METHODS: Seven individuals with chronic hemiparesis walked on a treadmill at 1 of 3 randomized speeds: slow, preferred, and fast. Concurrent measurements of speed-induced changes in walking economy (ie, the energy needed to move 1 kg of bodyweight 1 ml O 2 /kg/m) and stability were made. Stability was quantified as the regularity and divergence of the mediolateral motion of the pelvic center of mass (pCoM) during walking, as well as pCoM motion relative to the base of support. RESULTS: Slower walking speeds were more stable (ie, pCoM motion was 10% ± 5% more regular and 26% ± 16% less divergent) but 12% ± 5% less economical. Conversely, faster walking speeds were 9% ± 8% more economical, but also less stable (ie, pCoM motion was 17% ± 5% more irregular). Individuals with slower walking speeds had an enhanced energetic benefit when walking faster ( rs = 0.96, P < 0.001). Individuals with greater neuromotor impairment had an enhanced stability benefit when walking slower ( rs = 0.86, P = 0.01). DISCUSSION AND CONCLUSIONS: People post-stroke appear to prefer walking speeds that are faster than their most stable speed but slower than their most economical speed. The preferred walking speed after stroke appears to balance stability and economy. To encourage faster and more economical walking, deficits in the stable control of the mediolateral motion of the pCoM may need to be addressed.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A416 ).

Markerless motion capture: What clinician-scientists need to know right now.

Markerless motion capture (mocap) could be the future of motion analysis. The purpose of this report was to describe our team of clinicians and scientists' exploration of markerless mocap (Theia 3D) and share data for others to explore (link: https://osf.io/6vh7z/?view_only=c0e00984e94a48f28c8d987a2127339d). Simultaneous mocap was performed using markerless and marker-based systems for walking, squatting, and forward hopping. Segment lengths were more variable between trials using markerless mocap compared to marker-based mocap. Sagittal plane angles were most comparable between systems at the knee joint followed by the ankle and hip. Frontal and transverse plane angles were not comparable between systems. The data collection experience using markerless mocap was simpler, faster, and user friendly. The ease of collection was in part offset by the added data transfer and processing times, and the lack of troubleshooting flexibility. If used selectively with proper understanding of limitations, markerless mocap can be exciting technology to advance the field of motion analysis.

Self-reported walking difficulty influences gait characteristics in patients with medial compartment knee osteoarthritis.

BACKGROUND: To differentiate gait strategies per knee osteoarthritis and self-reported walking difficulty during self-selected regular and fast gait speeds. We hypothesize that knee osteoarthritis gait characteristics during self-selected regular and fast gait speeds will be most accentuated by the osteoarthritis and walking difficulty group, followed by osteoarthritis and no walking difficulty, and least in the control group. METHODS: Prospective study of community-dwelling older adults (n = 39) who walk at functional speeds (≥1.0 m per second) were age and sex matched across the three groups. Gait strategies including knee excursion and moments, muscle activation and co-contraction, and limb dynamics (linear acceleration and jerk) were compared between groups during self-selected regular and fast gait speed trials. Significant group differences were defined as P < 0.05 and an effect size greater than small. FINDINGS: Based on walking difficulty, adduction moments (P-range = 0.00-0.03; effect size range,r = 0.42-0.52) and lateral quadriceps-gastrocnemius co-activations (P = 0.01;r = 0.36) were significant during regular gait speeds; and extension (P = 0.03;d = 0.59) and adduction (P-range = 0.00-0.02;d = 0.86;r = 0.40) moments were significant during fast trials. Per knee osteoarthritis presence, adduction moment(P = 0.01;r = 0.49), medial-quadriceps (P = 0.00;d = 1.04;r = 0.61), lateral-hamstrings (P = 0.04;d = 0.55), medial-gastrocnemius (P = 0.02;r = 0.40), medial quadriceps-hamstrings (P = 0.02;r = 0.38), medial quadriceps-gastrocnemius (P = 0.00;r = 0.56), and all limb dynamics (P = 0.00-0.01;d = 1.13-1.18;r = 0.35-0.47) were significant during regular gait speeds. Extension excursion (P = 0.02;d = 0.63), adduction moment (P = 0.01;d = 0.85) and medial-quadriceps (P = 0.01;r = 0.38) were significant during fast trials. INTERPRETATION: Many gait strategies during regular speeds that differ per walking difficulty and knee osteoarthritis attenuated at fast speeds. Perhaps gait training at fast speeds for those with knee osteoarthritis related walking difficulty is biomechanically and functionally beneficial.

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.

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.

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

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. In this technical brief we present an efficient one-step moment balancing algorithm linking the sagittal and frontal planes in the determination of musculotendon forces. Novel to the one-step approach is the introduction of a penalty function limiting total compressive force from acting in the lateral compartment when the internal moment is net abduction (i.e., external knee adduction). Medial and lateral knee contact forces were computed using the one-step moment balancing algorithm for 10 subjects walking at a self-selected pace and compared to values determined using a well-established two-step frontal moment balancing approach. Overall, average peak differences in magnitude and timing were small and the ensemble-averaged contact force profiles were similar between methods. The only statistical difference was slightly larger (0.2 BWs) peak medial contact force for the one-step method during the first half of stance, however these differences are small relative to peak values and would not likely alter interpretation of the data. The 1-step moment balancing method is a more efficient methodology for computing medial and lateral knee contact forces that can be used in place of two-step frontal plane moment balancing.

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

BACKGROUND: Gait asymmetries after anterior cruciate ligament reconstruction (ACLR) may lead to radiographic knee osteoarthritis. Slower walking speeds have been associated with biomarkers suggesting cartilage breakdown. The relationship between walking speed and gait symmetry after ACLR is unknown. HYPOTHESIS/PURPOSE: To determine the relationship between self-selected walking speeds and gait symmetry in athletes after primary, unilateral ACLR. STUDY DESIGN: Secondary analysis of a clinical trial. METHODS: Athletes 24±8 weeks after primary ACLR walked at self-selected speeds as kinematics, kinetics, and electromyography data were collected. An EMG-driven musculoskeletal model was used to calculate peak medial compartment contact force (pMCCF). Variables of interest were peak knee flexion moment (pKFM) and angle (pKFA), knee flexion and extension (KEE) excursions, peak knee adduction moment (pKAM), and pMCCF. Univariate correlations were run for walking speed and each variable in the ACLR knee, contralateral knee, and interlimb difference (ILD). RESULTS: Weak to moderate positive correlations were observed for walking speed and all variables of interest in the contralateral knee (Pearson's r=.301-.505, p≤0.01). In the ACLR knee, weak positive correlations were observed for only pKFM (r=.280, p=0.02) and pKFA (r=.263, p=0.03). Weak negative correlations were found for ILDs in pKFM (r=-0.248, p=0.04), KEE (r=-.260, p=0.03), pKAM (r=-.323, p<0.01), and pMCCF (r=-.286, p=0.02). CONCLUSION: Those who walk faster after ACLR have more asymmetries, which are associated with the development of early OA. This data suggests that interventions that solely increase walking speed may accentuate gait symmetry in athletes early after ACLR. Gait-specific, unilateral, neuromuscular interventions for the ACLR knee may be needed to target gait asymmetries after ACLR. LEVEL OF EVIDENCE: III.

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

BACKGROUND: After anterior cruciate ligament (ACL) reconstruction (ACLR), biomechanical asymmetries during gait are highly prevalent, persistent, and linked to posttraumatic knee osteoarthritis. Quadriceps strength is an important clinical measure associated with preoperative gait asymmetries and postoperative function and is a primary criterion for return-to-sport clearance. Evidence relating symmetry in quadriceps strength with gait biomechanics is limited to preoperative and early rehabilitation time points before return-to-sport training. PURPOSE/HYPOTHESIS: The purpose was to determine the relationship between symmetry in isometric quadriceps strength and gait biomechanics after return-to-sport training in athletes after ACLR. We hypothesized that as quadriceps strength symmetry increases, athletes will demonstrate more symmetric knee joint biomechanics, including tibiofemoral joint loading during gait. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Of 79 athletes enrolled in the ACL-SPORTS Trial, 76 were participants in this study after completing postoperative rehabilitation and 10 return-to-sport training sessions (mean ± SD, 7.1 ± 2.0 months after ACLR). All participants completed biomechanical walking gait analysis and isometric quadriceps strength assessment using an electromechanical dynamometer. Quadriceps strength was calculated using a limb symmetry index (involved limb value / uninvolved limb value × 100). The biomechanical variables of interest included peak knee flexion angle, peak knee internal extension moment, sagittal plane knee excursion at weight acceptance and midstance, quadriceps muscle force at peak knee flexion angle, and peak medial compartment contact force. Spearman rank correlation (ρ) coefficients were used to determine the relationship between limb symmetry indexes in quadriceps strength and each biomechanical variable; alpha was set to .05. RESULTS: Of the 76 participants, 27 (35%) demonstrated asymmetries in quadriceps strength, defined by quadriceps strength symmetry <90% (n = 23) or >110% (n = 4) (range, 56.9%-131.7%). For the biomechanical variables of interest, 67% demonstrated asymmetry in peak knee flexion angle; 68% and 83% in knee excursion during weight acceptance and midstance, respectively; 74% in internal peak knee extension moment; 57% in medial compartment contact force; and 74% in quadriceps muscle force. There were no significant correlations between quadriceps strength index and limb symmetry indexes for any biomechanical variable after return-to-sport training (P > .129). CONCLUSION: Among those who completed return-to-sport training after ACLR, subsequent quadriceps strength symmetry was not correlated with the persistent asymmetries in gait biomechanics. After a threshold of quadriceps strength is reached, restoring strength alone may not ameliorate gait asymmetries, and current clinical interventions and return-to-sport training may not adequately target gait.

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

BACKGROUND: Self-perceived instability among patients with knee osteoarthritis (OA) is defined as giving way, buckling, or shifting of the knee during activities, especially walking. Although instability is a leading cause of mobility decline with knee OA, methods for quantifying the symptom, determining the mechanisms, and establishing effective interventions remain unclear. Recently, data outputs (ie, linear acceleration and its time-derivative, jerk) from wearable sensors are showing strong associations with self-perceived instability among patients with other knee pathologies and may offer insight into OA-related instability. OBJECTIVE: To examine discriminant and convergent validity of using data outputs from wearable sensors to quantify self-reported instability among patients with knee OA. DESIGN: Secondary analysis of a cross-sectional study. SETTING: Primary recruitment from an institutional outpatient physical therapy clinic and collection completed in an institutional research laboratory. PATIENTS: Thirty-nine total participants. The OA group included 26 participants with radiographic evidence of moderate to severe knee OA in the medial compartment; knee pain >3 out of 10, and a walking speed of ≥1.0 m/s. The control group included 13 participants with no history of knee OA. Participants with current or history of low back, hip, or foot/ankle injury; knee replacement; skeletal realignment surgery; or comorbidities that limit walking, pregnancy, and inability to walk without an assistive device were excluded. INTERVENTIONS: N/A MAIN OUTCOME MEASURES: Data output from wearable sensors at the tibia. RESULTS: Midstance acceleration (P = .01) and jerk (P = .04) were significantly greater for those with than without knee OA. Acceleration was significantly associated with self-reported instability (Spearman's rho = -0.63, P < .01). CONCLUSIONS: Data from wearable sensors are a valid measurement for exploring the mechanisms and risks of instability among patients with knee OA.

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.

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

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

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.

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

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