What goes up must come down, part II: Consequences of jump strategy modification on dance leap landing biomechanics.

Knee injuries are common in jumping athletes; modifying jump strategy may impact loads placed on the body and reduce injury risk. The purpose of this study was to determine if modifying strategy in a saut de chat leap to focus on height would decrease sagittal plane knee loading. Biomechanical data were collected while 28 dancers performed saut de chat leaps with instructions to jump far (FAR) or jump high (UP). In the UP condition, there was greater vertical GRF and less braking GRF. Also in UP, lower extremity contact angle was greater (71.3 ± 2.9º FAR; 75.8 ± 3.3º UP; p = 0.0178), peak knee extensor moment was greater (2.8 ± 0.7 Nm FAR; 3.2 ± 0.8 Nm UP; p = 0.01), and peak ankle plantar flexor moment was lower (3.19 ± 0.4 Nm FAR; 2.94 ± 0.4 Nm UP; p < 0.01). A more acute LECA was related to greater braking force and braking force was related to greater knee extensor moments. Despite these relationships, we observed greater knee extensor moments in UP. While the relationship among these whole-body variables and knee joint loading exists, it may not be the primary factor driving load distribution during dance leap landings.

Inertial Sensor Angular Velocities Reflect Dynamic Knee Loading during Single Limb Loading in Individuals Following Anterior Cruciate Ligament Reconstruction.

Difficulty quantifying knee loading deficits clinically in individuals following anterior cruciate ligament reconstruction (ACLr) may underlie their persistence. Expense associated with quantifying knee moments (KMom) and power (KPow) with gold standard techniques precludes their use in the clinic. As segment and joint kinematics are used to calculate moments and power, it is possible that more accessible inertial sensor technology can be used to identify knee loading deficits. However, it is unknown if angular velocities measured with inertial sensors provide meaningful information regarding KMom/KPow during dynamic tasks post-ACLr. Twenty-one individuals 5.1 ± 1.5 months post-ACLr performed a single limb loading task, bilaterally. Data collected concurrently using a marker-based motion system and gyroscopes positioned lateral thighs/shanks. Intraclass correlation coefficients (ICC)(2,k) determined concurrent validity. To determine predictive ability of angular velocities for KMom/KPow, separate stepwise linear regressions performed using peak thigh, shank, and knee angular velocities extracted from gyroscopes. ICCs were greater than 0.947 (p < 0.001) for all variables. Thigh (r = 0.812 and r = 0.585; p < 0.001) and knee (r = 0.806 and r = 0.536; p < 0.001) angular velocities were strongly and moderately correlated to KPow and KMom, respectively. High ICCs indicated strong agreement between measurement systems. Thigh angular velocity (R² = 0.66; p < 0.001) explained 66% of variance in KPow suggesting gyroscopes provide meaningful information regarding KPow. Less expensive inertial sensors may be helpful in identifying deficits clinically.

Predictors of Frontal Plane Knee Moments During Side-Step Cutting to 45 and 110 Degrees in Men and Women: Implications for Anterior Cruciate Ligament Injury.

OBJECTIVE: To compare frontal plane knee moments, and kinematics and kinetics associated with knee valgus moments between cutting to 45 and 110 degrees, and to determine the predictive value of kinematics and ground reaction forces (GRFs) on knee valgus moments when cutting to these angles. Also, to determine whether sex differences exist in kinematics and kinetics when cutting to 45 and 110 degrees. DESIGN: Cross-sectional study. SETTING: Laboratory setting. PARTICIPANTS: Forty-five (20 females) healthy young adult soccer athletes aged 16 to 23 years. ASSESSMENT OF RISK FACTORS: Kinematic and kinetic variables were compared between randomly cued side-step cutting maneuvers to 45 and 110 degrees. Predictors of knee valgus moment were determined for each task. MAIN OUTCOME MEASURES: Kinematic variables: knee valgus angle, hip abduction, and internal rotation angles. Kinetic variables: vertical, posterior, and lateral GRFs, and knee valgus moment. RESULTS: Knee valgus moments were greater when cutting to 110 degrees compared with 45 degrees, and females exhibited greater moments than males. Vertical and lateral GRFs, hip internal rotation angle, and knee valgus angle explained 63% of the variance in knee valgus moment during cutting to 45 degrees. During cutting to 110 degrees, posterior GRF, hip internal rotation angle, and knee valgus angle explained 41% of the variance in knee valgus moment. CONCLUSIONS: Cutting tasks with larger redirection demands result in greater knee valgus moments. Similar factors, including shear GRFs, hip internal rotation, and knee valgus position contribute to knee valgus loading during cuts performed to smaller (45 degrees) and larger (110 degrees) angles. CLINICAL RELEVANCE: Reducing vertical and shear GRFs during cutting maneuvers may reduce knee valgus moments and thereby potentially reduce risk for anterior cruciate ligament injury.

Prioritizing limb loading improves symmetry during dual-tasking in individuals following anterior cruciate ligament reconstruction.

Understanding the extent to which attention prioritization interfere with limb loading in daily activities following anterior cruciate ligament reconstruction (ACLr) is important for reshaping loading behaviors. A dual-task paradigm, prioritizing limb loading symmetry (LLS) during standing or response time during an upper extremity task response time task was used to probe the effects of attention prioritization of loading. Individuals 115.6 ± 17.8 days post-ACLr (ACLr; n = 13) and matched healthy individuals (n = 13; CTRL) performed a simple response time (RT) task and 2 dual tasks prioritizing limb loading (LS-RT) and response time (RT-LS). 2 × 3 General Linear Model repeated measures analyses determined effects of group and focus condition on LLS error and response time. Significant interaction (P = 0.010) was noted in LLS error. ACLr group, exhibited greater LLS error in RT (P = 0.001) and RT-LS (P = 0.001) than LS-RT condition. ACLr group exhibited greater LLS error in the RT (P = 0.001) and RT-LS (P = 0.040) than CTRL, but not in LS-RT. A main effect of condition (P < 0.001) for response time indicated that times were slower in LS-RT compared to RT (P < 0.001) and to RT-LS (P < 0.001) for both groups. These data suggest that limb loading symmetry during standing is more automatic for controls than individuals following ACLr. Unlike controls, improving loading symmetry during standing requires additional attention in individuals in early recovery following ACLr.

Individuals following anterior cruciate ligament reconstruction practice underloading strategies during daily activity.

Underloading the surgical limb has been described in biomechanical studies across recovery time points following anterior cruciate ligament reconstruction (ACLr). This study aimed to examine the extent to which laboratory findings translate to daily activities. Limb loading was quantified during a sit-to-stand task in laboratory testing and throughout 2 days of daily activity in 15 individuals 114.8 (17.2) days post-ACLr and 15 controls. Vertical force impulse calculated from force platform (laboratory) and pressure insoles (daily) was used to quantify limb loading. Between-limb symmetry was calculated for limb loading and knee strength measures, 2 × 2 GLM repeated measures determined a significant group-by-limb interaction on daily limb loading. Surgical limb daily loading was lower compared to nonsurgical (p < .001; effect sizes [ES] = 0.63), and control matched limbs (surgical: p = .037, ES = 0.80 and nonsurgical: p = .02, ES = 0.89). No group differences were found in total daily loading (summed loading between limbs; p = .18; ES = 0.50) and time performing weight-bearing activities (p = .32; ES = 0.36). Pearson's correlation determined that between-limb symmetry in daily loading was related to sit-to-stand loading (r = .62; p = .01) and knee extensor strength symmetry (r = .6; p = .02) in the ACLr group. These data support the presence of underloading behaviors in individuals 10-14 weeks following ACLr that are consistent with previous biomechanical studies and current biomechanical data. Knee extensor weakness was related to greater underloading. Asymmetrical loading quantified in the laboratory is practiced throughout the day in individuals post-ACLr. Practice afforded by daily activities represents powerful contributors to learning of a pattern that contrasts the goal of rehabilitation exercises.

Center of pressure predicts Intra-limb compensatory patterns that shift demands away from knee extensors during squatting.

The persistence of knee extensor moments deficits following anterior cruciate ligament reconstruction (ACLr) may be attributed to difficulty quantifying inter- and intra-limb compensations clinically. Force plate derived center of pressure (CoPpos) and vertical force (vGRF) may provide valuable information regarding limb and joint loading impairments in this group. This study aimed to determine the: 1) relationship between measures CoPpos and intra-limb extensor moment distribution during a squat, and 2) utility of using CoPpos and vGRF to estimate knee extensor moment deficits post-ACLr. Twenty-four individuals, 142 ± 22.5 days post-ACLr, performed bilateral squats. Ankle (aEXT), knee (kEXT) and hip (hEXT) extensor moments were calculated using three-dimensional kinematics and GRF. Moments, CoPpos and vGRF were identified at peak kEXT. Intra-limb moment distribution was characterized using hEXT/kEXT and aEXT/kEXT ratios. Linear regressions analyzed relationships between CoPpos and hEXT/kEXT and aEXT/kEXT. Stepwise regressions determined if between-limb CoPpos ratio predicted between-limb ratios of hEXT/kEXT and aEXT/kEXT. Stepwise regression determined if between-limb CoPpos and vGRF ratios predicted between-limb kEXT ratio. Results found that CoPpos predicts intra-limb moment distribution (hEXT/kEXT and aEXT/kEXT); more anterior CoPpos related to higher moments at the hip and ankle relative to the knee. In addition, between-limb CoPpos ratio predicts between-limb ratio of hEXT/kEXT and aEXT/kEXT ratios. Together between-limb CoPpos (52%) and vGRF (18%) ratios explained 70% of the variance in between-limb kEXT ratios (R2 = 0.70, p < 0.001). These data suggest that force plate derived CoPpos and vGRF may be important for detection of knee extensor moment deficits in individuals post-ACLr.

Influence of Hamstrings on Knee Moments During Loading Response of Gait in Individuals Following ACL Reconstruction.

Biomechanical studies consistently report smaller knee extensor moments in the surgical limb during loading response (LR) of gait following ACL reconstruction (ACLr). However, this reduction in knee loading is quantified by net joint moments (NJM). As a result, in the presence of greater hamstring activity, the true contribution from the knee extensors may not be reduced. The purpose of this study is to compare hamstring activity and strength and knee joint moments between individuals post-ACLr and controls. Eighteen individuals 3 months post-ACLr and matched controls walked and net knee extensor moment peak and impulse and hamstring activity were identified during LR, as well as maximal hamstring strength. A hybrid musculoskeletal model estimated knee flexor moments from joint kinematics and hamstring electromyography. Flexor moments (SIMM) were scaled based on strength. Knee extensor moments were estimated from the sum of the net knee moment and estimated knee flexor moment; estimated extensor moment peaks and impulse were calculated during LR. Repeated measures analysis of variance compared groups and limbs. Smaller net knee extensor moment and greater hamstring activity, as well as deficits in maximal hamstring strength, were observed in the surgical limb (all p < 0.05). When accounting for the torque-producing capabilities of the knee flexors, estimated knee extensor moment peak and impulse were smaller in the surgical limb. These findings suggest that net knee moments accurately reflect smaller knee extensor loading post-ACLr. Statement of Clinical Significance: Rehabilitation programs should target increasing knee extensor loading to restore gait mechanics during early rehabilitation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:378-386, 2020.

Loading Behaviors Do Not Match Loading Abilities Postanterior Cruciate Ligament Reconstruction.

PURPOSE: Strategies that underload the surgical limb after anterior cruciate ligament reconstruction (ACLr) are observed in submaximal tasks. It is not known what underlies these strategies in early rehabilitation. The purpose of this study was to determine if underloading can be attributed to the inability to meet task demands with and without attention to limb loading or learned behavior. METHODS: Twenty individuals (110.6 [18.1] days) post-ACLr and 20 healthy individuals (CTRL) participated in this study. Participants performed standing, sit-to-stand, and squat tasks under natural, instructed, and feedback conditions. Limb-loading symmetry was calculated as the between-limb ratio of vertical ground reaction force impulse during each task. General Linear Model repeated-measures analysis, 2 (group) × 3 (condition), determined the effects of group and condition on limb-loading symmetry for each task. RESULTS: Significant interactions were observed for each task (all P < 0.001). Compared with CTRL, ACLr exhibited greater asymmetry during natural (deficits: standing, 10%, P = 0.001; sit-to-stand, 25%, P < 0.001; squat, 15%, P < 0.001) and instructed (deficits: sit-to-stand, 13%, P = 0.001; squat, 8%, P = 0.04), but not feedback conditions. The CTRL maintained symmetry across conditions and tasks. Anterior cruciate ligament reconstruction exhibited greater asymmetry in natural compared with instructed (deficits: standing, 11%, P < 0.001; sit-to-stand, 14%, P < 0.001; squat, 8%, P = 0.001) and feedback (deficits: standing, 10%, P = 0.001; sit-to-stand, 21%, P < 0.001; squat, 15%, P < 0.001) conditions. CONCLUSIONS: The presence of loading asymmetries in natural but not feedback conditions indicates that individuals 3 months post-ACLr shift loading away from surgical limb despite the ability to meet task demands which may be suggestive of nonuse behavior. Even when instructed to load symmetrically, individuals continued to exhibit some degree of asymmetry.

Subtle alterations in whole body mechanics during gait following anterior cruciate ligament reconstruction.

BACKGROUND: Clinically, normalization of gait following anterior cruciate ligament reconstruction (ACLr) is defined as the absence of observable deviations. However, biomechanical studies report altered knee mechanics during loading response (LR); a time of double limb support and weight transfer between limbs. It is conceivable that subtle adjustments in whole body mechanics, including center of mass (COM) velocity and ground reaction force (GRF) peaks and timing, are present. RESEARCH QUESTION: The purpose was to compare limb and whole body mechanics during LR of gait in the surgical and non-surgical limbs post-ACLr. METHODS: Anterior and vertical COM velocity at initial contact; knee flexion range of motion, peak knee extensor moment, peak vertical and posterior GRF, minimum vertical COM position and maximum anterior and vertical COM velocity during LR were identified for twenty individuals 112 ± 17 days post-ACLr without observable gait deficits. To assess differences in timing of COM variables, coupling angles (vector coding) were calculated for multidirectional coordination of vertical and anteroposterior COM velocities and GRFs and categorized as in-phase, anti-phase, vertical phase, or anteroposterior phase coordination. Paired t-tests compared peaks between limbs; non-parametric Wilcoxon signed-rank tests compared coordination pattern frequency. RESULTS: Less knee range of motion (5.6 °), 30% smaller knee extensor moment, 11% smaller posterior GRF, and slower anterior COM velocity at initial contact (2%) and peak during LR (1.3%; all p < 0.05) were observed in the surgical compared to the non-surgical limb. For COM velocity coordination, lesser anti-phase (7.38%) and greater in-phase coordination (2.88%) were observed in the surgical limb. For GRF coordination, less in-phase coordination (1.94%) was observed in the surgical limb. SIGNIFICANCE: Differences in coordination patterns, suggest that individuals post-ACLr make subtle adjustments in timing of whole body mechanics; particularly in COM velocity during gait. These adjustments are consistent with reduced sagittal plane loading in the surgical knee.

Effect of repeated application of rigid tape on pain and mobility deficits associated with sacroiliac joint dysfunction.

BACKGROUND: Sacroiliac joint dysfunction (SIJD) accounts for up to 30% of patients with low back pain. Rigid taping techniques are often used for conservative treatment of SIJD related symptoms; however, its effectiveness has not been systematically evaluated. OBJECTIVES: The aim of our study was to investigate the effect of rigid tape on pain, malalignment and mobility deficits associated with anterior innominate SIJD. METHODS: Two groups (n= 37; experimental and control) diagnosed with SIJD participated in a randomized, controlled trial. Tape was applied for 2 weeks in the experimental group, whereas the control group received no treatment. 2 × 2 (group × time) GLM-MANOVA assessed effects of tape on pain; innominate rotation; and hip rotation range of motion. Chi-square and McNemar tests assessed the effect of tape on Gillet and Sitting forward flexion mobility tests; the Patrick, Posterior shear and Gaenslen pain provocation tests were used to test pain. Variables were assessed before (PRE) and after (POST) two weeks. RESULTS: No group differences were observed for any variable PRE. Pain intensity, innominate rotation (p< 0.05) and number of positive mobility and pain provocation tests (p< 0.05) decreased from PRE versus POST in the experimental group. No differences were observed in the control group. CONCLUSION: Two weeks of rigid tape for anterior innominate correction successfully reduced symptoms related to SIJD.

Predictors of frontal plane knee excursion during a drop land in young female soccer players.

STUDY DESIGN: Controlled laboratory study using a cross-sectional, single testing session. OBJECTIVE: To determine the association between frontal plane knee excursion during a drop land task and measures of hip strength, and ankle and hip range of motion. BACKGROUND: Assessment of frontal plane knee excursion during a drop land task has been advocated as a means to screen for potentially injurious lower extremity movement patterns. Accordingly, an understanding of the physical characteristics associated with the magnitude of frontal plane knee excursion could assist clinicians in developing interventions and prevention strategies to minimize injury risk. METHODS AND MEASURES: Thirty-nine female high school soccer players (mean +/- SD age, 15.5 +/- 1.0 years; height, 162.2 +/- 5.3 cm; body mass, 56.8 +/- 6.7 kg) participated. Isometric hip muscle strength as well as ankle and hip range of motion measurements were obtained using standard clinical procedures and a handheld dynamometer. Frontal plane knee excursion was assessed using a 6-camera motion analysis system during a drop land task. Using 3-dimensional coordinate data, maximum frontal plane knee excursion was defined as the difference between the distances of right and left lateral knee markers at initial contact and maximum knee flexion during the deceleration phase of landing. Independent variables found to be significantly correlated with frontal plane knee excursion were then entered into a stepwise multiple regression procedure to determine the best set of predictors of this motion. RESULTS: Hip external rotation range of motion and ankle dorsiflexion range of motion were found to be negatively correlated with frontal plane knee excursion (r=-0.40, P=.005 and r=-0.27, P=.05, respectively). Together they accounted for 27% of the variance in frontal plane knee excursion (r=0.52, P=.03). No relationships between measures of hip strength and frontal plane knee excursion were found. CONCLUSIONS: Frontal plane knee excursion during a drop land task was partially attributed to available range of motion at the hip and ankle. These results suggest that range of motion of the joints proximal and distal to the knee should be considered when evaluating individuals who present with excessive frontal plane knee excursion during this task. Given that the relationship between range of motion and frontal plane knee excursion was small, other factors, including learned motor patterns, should be considered.

Detection of Knee Power Deficits Following Anterior Cruciate Ligament Reconstruction Using Wearable Sensors.

BACKGROUND: Following anterior cruciate ligament reconstruction (ACLR), individuals present with significant knee power absorption deficits during deceleration of dynamic tasks. An inability to quantify these deficits clinically may underlie their persistence. Recent studies suggest that segment angular velocities measured with wearable inertial sensors have the potential to provide valuable information about knee power during a single-limb loading (SLL) task. However, the diagnostic accuracy of these measures and procedures needs to be established before translating this information to clinical practice. OBJECTIVE: To determine the diagnostic accuracy of using inertial-sensor thigh angular velocities to detect asymmetrical knee loading during a dynamic SLL task in individuals following ACLR. METHODS: In this controlled laboratory study, 21 individuals following ACLR performed 3 trials of SLL on each limb. Sagittal plane peak knee power absorption was calculated for each limb (reconstructed and nonsurgical) during deceleration. Between-limb ratios (reconstructed/nonsurgical limb) were calculated for knee power using marker-based motion analysis, and thigh angular velocity was extracted from inertial sensors. Sensitivity and specificity of thigh angular velocity ratios in diagnosing asymmetrical knee loading (knee power deficits greater than 15%) were determined using receiver operating characteristic curve analysis. RESULTS: Thigh angular velocity ratios detected asymmetrical knee loading when performing SLL with high sensitivity (81%) and specificity (100%). CONCLUSION: These findings support the use of cost-effective wearable sensors to objectively quantify movement clinically in this population of individuals following ACLR. This study establishes procedures for the clinical quantification of dynamic knee loading deficits. J Orthop Sports Phys Ther 2018;48(11):895-902. Epub 11 Jul 2018. doi:10.2519/jospt.2018.7995.

Contributors to knee loading deficits during gait in individuals following anterior cruciate ligament reconstruction.

BACKGROUND: Altered gait mechanics following anterior cruciate ligament reconstruction (ACLr) are commonly reported in the surgical limb 2-3 months post-surgery when normalization of gait is expected clinically. Specifically, deficits in knee extensor moment during loading response of gait are found to persist long-term; however, the mechanisms by which individuals reduce sagittal plane knee loading during gait are not well understood. RESEARCH QUESTION: This study investigated between limb asymmetries in knee flexion range of motion, shank angular velocity, and ground reaction forces to determine the strongest predictor of knee extensor moment asymmetries during gait. METHODS: Thirty individuals 108 ± 17 days post-ACLr performed walking gait at a self-selected speed and peak knee extensor moment, peak vertical and posterior ground reaction force, and peak anterior shank angular velocity were identified during loading response. Paired t-tests compared limbs; Pearson's correlations determined associations between variables in surgical and non-surgical limbs; and stepwise linear regression determined the best predictor of knee extensor moment asymmetries during gait. RESULTS: Reduced vertical and posterior ground reaction forces and shank angular velocity were strongly associated with reduced knee extensor moment in both limbs (r = 0.499-0.917, p < 0.005). Less knee flexion range of motion was associated with reduced knee moment in the surgical limb (r = 0.358, p < 0.05). Additionally, asymmetries in posterior ground reaction force and knee flexion range of motion predicted asymmetries in knee extensor moment (R2 = 0.473, p < 0.001). SIGNIFICANCE: Modulation of kinetics and kinematics contribute to decreases in knee extensor moments during gait and provide direction for targeted interventions to restore gait mechanics.

Lower-limb dynamics and clinical outcomes for habitually shod runners who transition to barefoot running.

OBJECTIVES: Recent investigations have revealed lower vertical loading rates and knee energy absorption amongst experienced barefoot runners relative to those who rear-foot strike (RFS). Although this has led to an adoption of barefoot running amongst many recreational shoe runners, recent investigations indicate that the experienced barefoot pattern is not immediately realized. Therefore, the purpose this investigation was to quantify changes in lower-extremity dynamics and clinical outcomes measures for habitually shod runners who perform a transition to barefoot running. DESIGN & PARTICIPANTS: We examined lower-extremity dynamics and clinical outcomes for 26 RFS shod runners who performed an 8-10 week transition to barefoot running. SETTING: Runners were evaluated at the University of Southern California's Musculoskeletal Biomechanics Research Laboratory. MAIN OUTCOME MEASURES: Foot-strike patterns, vertical load rates, and joint energetics were evaluated before and after the transition using inverse dynamics. Clinical assessments were conducted throughout the transition by two licensed clinicians. RESULTS: Eighteen of the 26 runners successfully completed the transition: 7 maintained a RFS, 8 adopted a mid-foot strike (MFS), and 3 adopted a forefoot strike (FFS) during novice barefoot running. Following the transition, novice MFS/FFS runners often demonstrated reversions in strike-patterns and associated reductions in ankle energetics. We report no change in loading rates and knee energy absorption across transition time points. Importantly, there were no adverse events other than transient pain and soreness. CONCLUSIONS: These findings indicate that runners do not innately adopt the biomechanical characteristics thought to lower injury risk in-response to an uninstructed barefoot running transition.

Accelerations from wearable accelerometers reflect knee loading during running after anterior cruciate ligament reconstruction.

BACKGROUND: Following anterior cruciate ligament reconstruction, individuals exhibit sagittal plane knee loading deficits as they underload their injured limb during running. These between-limb biomechanical differences are difficult to clinically detect. Wearable accelerometers may aid in the development of early rehabilitation programs to improve symmetrical loading. This study aimed to identify whether segment accelerations from wearable accelerometers can predict knee loading asymmetry in an anterior cruciate ligament reconstructed population. METHODS: 14 individuals 5-months post-anterior cruciate ligament reconstruction performed self-selected speed running. Data were collected concurrently using a marker-based motion system and accelerometers positioned on participants' shanks and thighs. Stepwise linear regression was used to determine predictive value of accelerometer data on biomechanical variables. FINDING: Shank acceleration was not predictive of any biomechanical variable. Between-limb differences in thigh axial acceleration explained 30% of the variance in between-limb differences in knee power absorption (p = 0.045), suggesting that accelerometers placed on proximal joint segments may provide information regarding knee loading asymmetry. Between-limb differences in thigh axial acceleration also explained 38% of the variance in between-limb differences in ground reaction force (p = 0.002). INTERPRETATION: These relationships indicate that accelerations from wearable accelerometers may provide some useful information regarding knee loading during running in individuals following anterior cruciate ligament reconstruction.

Compensatory Strategies That Reduce Knee Extensor Demand During a Bilateral Squat Change From 3 to 5 Months Following Anterior Cruciate Ligament Reconstruction.

Background Decreased extensor moments in the surgical knee during bilateral squats can persist beyond 1 year following anterior cruciate ligament reconstruction (ACLR). This is accomplished using interlimb and intralimb compensations. Objectives This study sought to assess loading during squatting longitudinally, 3 and 5 months post ACLR, and to determine the extent to which interlimb and intralimb compensations contribute to reduced knee extensor moments. Methods In this controlled, longitudinal laboratory study, 11 individuals (4 male) underwent 3-D motion analysis of a squat at 3 and 5 months post ACLR. A repeated-measures multivariate analysis of variance (limb by time) assessed differences in peak knee and hip flexion angles, knee extensor moment, vertical ground reaction force, and hip-to-knee extensor moment ratio. Stepwise linear regression analysis was used to determine the contribution of interlimb (between-limb vertical ground reaction force ratio) and intralimb (within-surgical-limb hip-to-knee moment ratio) compensations to the between-limb knee extensor moment ratio. Results A significant effect of limb was observed for knee flexion angle, knee extensor moment, vertical ground reaction force, and hip-to-knee extensor moment ratio, while a significant effect of time was observed for knee extensor moment and hip-to-knee extensor moment ratio. At 3 months, the vertical ground reaction force ratio and hip-to-knee extensor moment ratio predicted the knee extensor moment ratio (R2 = 0.854, P<.001). At 5 months, the hip-to-knee extensor moment ratio predicted the knee extensor moment ratio (R2 = 0.584, P = .006). Conclusion Individuals used interlimb and intralimb compensations to reduce the knee extensor moment of the surgical limb at 3 months post ACLR. Similar reductions in the knee extensor moment at 5 months were accomplished with only intralimb compensations. J Orthop Sports Phys Ther 2018;48(9):713-718. Epub 12 Jun 2018. https://doi.org/10.2519/jospt.2018.7977.

National Athletic Trainers' Association Position Statement: Prevention of Anterior Cruciate Ligament Injury.

OBJECTIVE: To provide certified athletic trainers, physicians, and other health care and fitness professionals with recommendations based on current evidence regarding the prevention of noncontact and indirect-contact anterior cruciate ligament (ACL) injuries in athletes and physically active individuals. BACKGROUND: Preventing ACL injuries during sport and physical activity may dramatically decrease medical costs and long-term disability. Implementing ACL injury-prevention training programs may improve an individual's neuromuscular control and lower extremity biomechanics and thereby reduce the risk of injury. Recent evidence indicates that ACL injuries may be prevented through the use of multicomponent neuromuscular-training programs. RECOMMENDATIONS: Multicomponent injury-prevention training programs are recommended for reducing noncontact and indirect-contact ACL injuries and strongly recommended for reducing noncontact and indirect-contact knee injuries during physical activity. These programs are advocated for improving balance, lower extremity biomechanics, muscle activation, functional performance, strength, and power, as well as decreasing landing impact forces. A multicomponent injury-prevention training program should, at minimum, provide feedback on movement technique in at least 3 of the following exercise categories: strength, plyometrics, agility, balance, and flexibility. Further guidance on training dosage, intensity, and implementation recommendations is offered in this statement.

How well do anatomical reconstructions of the posterolateral corner restore varus stability to the posterior cruciate ligament-reconstructed knee?

BACKGROUND: With grade 3 posterolateral injuries of the knee, reconstructions of the lateral collateral ligament, popliteus tendon, and popliteofibular ligament are commonly performed in conjunction with a posterior cruciate ligament reconstruction to restore knee stability. HYPOTHESIS: A lateral collateral ligament reconstruction, alone or with a popliteus tendon or popliteofibular ligament reconstruction, will produce normal varus rotation patterns and restore posterior cruciate ligament graft forces to normal levels in response to an applied varus moment. STUDY DESIGN: Controlled laboratory study. METHODS: Forces in the native posterior cruciate ligament were recorded for 15 intact knees during passive extension from 120 degrees to 0 degrees with an applied 5 N .m varus moment. The posterior cruciate ligament was removed and reconstructed with a single bundle inlay graft tensioned to restore intact knee laxity at 90 degrees . Posterior cruciate ligament graft force, varus rotation, and tibial rotation were recorded before and after a grade 3 posterolateral corner injury. Testing was repeated with lateral collateral ligament, lateral collateral ligament plus popliteus tendon, and lateral collateral ligament plus popliteofibular ligament graft reconstructions; all grafts were tensioned to 30 N at 30 degrees with the tibia locked in neutral rotation. RESULTS: All 3 posterolateral graft combinations rotated the tibia into slight valgus as the knee was taken through a passive range of motion. During the varus test, popliteus tendon and popliteofibular ligament reconstructions internally rotated the tibia from 1.5 degrees (0 degrees flexion) to approximately 12 degrees (45 degrees flexion). With an applied varus moment, mean varus rotations with a lateral collateral ligament graft were significantly less than those with the intact lateral collateral ligament beyond 0 degrees flexion; mean decreases ranged from 0.8 degrees (at 5 degrees flexion) to 5.6 degrees (at 120 degrees flexion). Addition of a popliteus tendon or popliteofibular ligament graft further reduced varus rotation (compared with a lateral collateral ligament graft) beyond 25 degrees of flexion; both grafts had equal effects. A lateral collateral ligament reconstruction alone restored posterior cruciate ligament graft forces to normal levels between 0 degrees and 100 degrees of flexion; lateral collateral ligament plus popliteus tendon and lateral collateral ligament plus popliteofibular ligament reconstructions reduced posterior cruciate ligament graft forces to below-normal levels-beyond 95 degrees and 85 degrees of flexion, respectively. CONCLUSIONS: With a grade 3 posterolateral corner injury, popliteus tendon or popliteofibular ligament reconstructions are commonly performed to limit external tibial rotation; we found that they also limited varus rotation. With the graft tensioning protocols used in this study, all posterolateral graft combinations tested overconstrained varus rotation. Further studies with posterolateral reconstructions are required to better restore normal kinematics and provide more optimum load sharing between the PCL graft and posterolateral grafts. CLINICAL RELEVANCE: A lower level of posterolateral graft tension, perhaps applied at a different flexion angle, may be indicated to better restore normal varus stability. The clinical implications of overconstraining varus rotation are unknown.