Peak Knee Extension Moment Research Articles

Landing biomechanics in anterior cruciate ligament reconstructed females who pass or fail a functional test battery

BackgroundA functional test battery (FTB) has been proposed to determine return to full activity following anterior cruciate ligament reconstruction (ACLR). However, there is little biomechanical evidence of FTB usefulness. The purpose of this study was to compare knee joint landing and cutting biomechanics between ACLR patients who passed (ACLR-Pass), failed (ACLR-Fail), and healthy females (Healthy) before and after exercise. MethodsThirty females were included: 10 ACLR-Pass, eight ACLR-Fail and 12 Healthy. Participants performed a FTB consisting of The 2000 International Knee Documentation Committee Subjective Knee Evaluation Form, the Knee Outcome Survey Activities of Daily Living Scale, and quadricep strength and single-leg hop tests. Double-leg jump landing (DLJL) and single-leg jump cutting (SLJC) biomechanics were assessed before and after exercise. ResultsSignificant main effects of exercise were found during DLJL: lesser knee flexion angle at initial contact after exercise (before exercise: 15.8 ± 5.0, after exercise: 14.2 ± 5.4, P = 0.01, ηp 2 = 0.25); and during SLJC: smaller peak knee extension moment (before exercise: −0.33 ± 0.1, after exercise: −0.31 ± 0.1, P = 0.02, ηp 2 = 0.18). While there was a significant group by time interaction effect with lesser peak knee flexion angle after exercise, this interaction effect was likely driven by a reduction in peak knee flexion in only the Healthy group. ConclusionsHealthy females exhibited a reduction in peak knee flexion during SLJC after exercise. However, there were no differences in ACLR knee biomechanics during DLJL and SLJC performed before and after exercise.

Does Chronic Ankle Instability Influence Knee Biomechanics of Females during Inverted Surface Landings?

The primary purpose of the study was to determine whether atypical knee biomechanics are exhibited during landing on an inverted surface. A seven-camera motion analysis system and two force plates were used to collect lower extremity biomechanics from two groups of female participants: 21 subjects with chronic ankle instability (CAI) and 21 with pair-matched controls. Subjects performed ten landings onto inverted and flat platforms on the CAI/matched and non-test limbs, respectively. Knee and ankle joint angles, joint angular displacements, joint moments and eccentric work were calculated during the landing phase and/or at the initial contact. Paired t-tests were used to compare between-group differences (p<0.05). We observed that CAI group displayed a significantly increased knee flexion angle, knee flexion displacement, peak knee extension moment and internal rotation moment, and eccentric work in the sagittal plane, possibly due to altered ankle biomechanics. Participants with CAI employed some compensatory strategy to improve their ankle and postural stability during landing onto the tilted surface. The increased knee extension and internal rotation moments of CAI participants could potentially result in a greater ACL loading. In future studies, it may be worthwhile to measure or estimate the ACL loading to confirm whether CAI could relate to the mechanism of ACL injury.

Effect of dual task on gait asymmetry in patients after anterior cruciate ligament reconstruction

Individuals who received anterior cruciate ligament (ACL) reconstruction surgeries demonstrated lower extremity movement asymmetries. The purpose of this study was to determine if psychological impairment was a contributor to lower extremity movement asymmetries in walking for individuals who received ACL reconstruction surgeries. Three-dimensional videographic and force plate data were collected for 25 males after unilateral ACL reconstruction performing walking without (single-task condition) and with the concurrent cognitive task (dual-task condition). Both uninjured and injured legs had significantly smaller peak knee flexion angle and peak knee extension moment during loading response and mid-stance phases in dual-task condition compared to single task condition (P ≤ 0.012). Walking condition and leg had significant interaction effects on peak hip adduction angle during mid-stance phase (P = 0.042) and peak hip abduction moment during loading response phase (P = 0.048). The inter-leg difference of peak hip adduction angle during mid-stance (P = 0.038) and terminal stance (P = 0.036) phases, and peak hip abduction moment during loading response phase (P = 0.024) were significantly decreased in dual-task condition compared to single-task condition. Psychological factors have significant effects on post-operative movements of both injured and uninjured knees of individuals who received ACL reconstruction surgery. Although physical factors may be primary contributors to the post-operative lower extremity movement asymmetries, psychological factors also contribute to the post-operative hip movement asymmetries.

Real-time biofeedback can increase and decrease vertical ground reaction force, knee flexion excursion, and knee extension moment during walking in individuals with anterior cruciate ligament reconstruction

Individuals with anterior cruciate ligament reconstruction (ACLR) often exhibit a “stiffened knee strategy” or an excessively extended knee during gait, characterized by lesser knee flexion excursion and peak internal knee extension moment (KEM). The purpose of this study was to determine the effect of real-time biofeedback (RTBF) cuing an acute change in peak vertical ground reaction force (vGRF) during the first 50% of the stance phase of walking gait on: (1) root mean square error (RMSE) between actual vGRF and RTBF target vGRF; (2) perceived difficulty; and (3) knee biomechanics. Acquisition and short-term recall of these outcomes were evaluated. Thirty individuals with unilateral ACLR completed 4 separate walking sessions on a force-measuring treadmill that consisted of a control (no RTBF) and 3 experimental loading conditions using RTBF including: (1) 5% vGRF increase (high-loading), (2) 5% vGRF decrease (low-loading) and (3) symmetric vGRF between limbs. Bilateral biomechanical outcomes were analyzed during the first 50% of the stance phase, and included KEM, knee flexion excursion, peak vGRF, and instantaneous vGRF loading rate (vGRF-LR) for each loading condition. Peak vGRF significantly increased and decreased during high-loading and low-loading, respectively compared to control loading. Instantaneous vGRF-LR, peak KEM and knee flexion excursion significantly increased during the high-loading condition compared to low-loading. Perceived difficultly and RMSE were lower during the symmetrical loading condition compared to the low-loading condition. Cuing an increase in peak vGRF may be beneficial for increasing KEM, knee flexion excursion, peak vGRF, and vGRF-LR in individuals with ACLR. Clinical Trials Number: NCT03035994.

Wide step width reduces knee abduction moment of obese adults during stair negotiation

PurposeAn increased likelihood of developing obesity-related knee osteoarthritis may be associated with increased peak internal knee abduction moments (KAbM). Increases in step width (SW) may act to reduce this moment. The purpose of this study was to determine the effects of increased SW on knee biomechanics during stair negotiation of healthy-weight and obese participants. MethodsParticipants (24: 10 obese and 14 healthy-weight) used stairs and walked over level ground while walking at their preferred speed in two different SW conditions – preferred and wide (200% preferred). A 2 × 2 (group × condition) mixed model analysis of variance was performed to analyze differences between groups and conditions (p < 0.05). ResultsIncreased SW increased the loading-response peak knee extension moment during descent and level gait, decreased loading-response KAbMs, knee extension and abduction range of motion (ROM) during ascent, and knee adduction ROM during descent. Increased SW increased loading-response peak mediolateral ground reaction force (GRF), increased peak knee abduction angle during ascent, and decreased peak knee adduction angle during descent and level gait. Obese participants experienced disproportionate changes in loading-response mediolateral GRF, KAbM and peak adduction angle during level walking, and peak knee abduction angle and ROM during ascent. ConclusionIncreased SW successfully decreased loading-response peak KAbM. Implications of this finding are that increased SW may decrease medial compartment knee joint loading, decreasing pain and reducing joint deterioration. Increased SW influenced obese and healthy-weight participants differently and should be investigated further.

Limb asymmetry during recovery from anterior cruciate ligament reconstruction.

There is limited literature that follows a population of Anterior Cruciate Ligament Reconstruction (ACLR) patients through recovery. Our aim was to examine differences in movement and loading patterns across time and between limbs over four visits during 12 months post-ACLR. We hypothesized that kinematic and kinetic data during a stop-jump would have time- and limb-dependent differences through 12 months post-surgery. Twenty-three ACLR athletes performed five vertical stop-jumps at 4, 5, 6, and 12 months post-op with motion capture and force plate data collection. The peak knee flexion (PKF) was different between the 4 and 12, 5 and 6, and the 5 and 12 month visits with earlier months exhibiting higher PKF. The peak vertical ground reaction force (vGRF) was lower at 4 than at 5 and 6 months. The peak posterior ground reaction force (pGRF) was lower at 4 months than all other visits. Frontal knee and sagittal hip range of motion (ROM) were different between 12 months and each previous visit. Asymmetries were present in peak vGRF, peak knee extension moment and impulse up to 12 months. The loading rate and peak pGRF demonstrated between limb differences up to 6 months; limb stiffness demonstrated differences up to 5 months post-ACLR. PKF was only asymmetric at the 4 month visit. While some variables improved in the 12 months post-ACLR, limb asymmetries in peak knee extension moment, peak vGRF and impulse persisted up to 12 months. Additionally, frontal plane knee and sagittal hip ROM had not normalized at 12 months. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1887-1893, 2018.

Slow gait speed after bilateral total knee arthroplasty is associated with suboptimal improvement of knee biomechanics

The aim of this study was to investigate gait speed changes 2years after bilateral total knee arthroplasty (TKA) and identify kinetic and kinematic factors associated with such changes by comparing patients with age- and sex-matched controls. The study group included 34 female patients with end-stage knee osteoarthritis (OA) who underwent bilateral TKA and 42 age- and sex-matched controls without knee pain or OA. Standard TKA was performed on all arthritic patients with placement of posterior stabilized fixed-bearing implants. Kinetic and kinematic parameters were evaluated using a commercial optoelectric gait analysis system. Gait speed, kinetic and kinematic changes and determinants of speed were assessed via principal component analysis and multiple regression analysis. The average gait speed of an arthritic patient was 90.2±18.4cm/s and improved to 96.0±12.3cm/s after TKA (p=0.032). However, the speed remained slower than that of controls (111.2±8.2cm/s, p<0.001). With regard to kinetics, the peak knee extension moment (KEM) generated by the quadriceps was unchanged after TKA and weaker than that of controls (p<0.001). The proportions of KEM contributing to the total sagittal moment were also smaller in the pre-/post-operative groups than in the control group (13-14% vs. 19%). On the other hand, the ankle plantar flexion moment (APFM) was increased after TKA (p=0.007) and its proportion of the total sagittal moment was greater than in controls (46% vs. 42%). With regard to kinematics, knee range of motion (ROM) improved after TKA (p=0.025), but was smaller than that of controls (p<0.001). In controls, gait speed was determined principally by hip and knee joint moments. However, in the TKA group, speed was determined by the knee ROM and APFM. Despite showing improvement, the gait speed of TKA patients remained slower than that of controls. Slow gait speed after bilateral TKA was associated with suboptimal improvement of knee biomechanics. Quadriceps strengthening exercises and the achievement of greater ROM during gait are advised for the further improvement of gait speed. Retrospective cohort study, Level III.

The Ability of Sagittal Plane Kinematic Variables to Predict Loading in Different Populations of Runners

It is known that sagittal plane kinematics are able to predict loading in runners. This may be of use to clinicians who don’t have access to force measurement devices. However, running biomechanics differ between genders and age groups. Thus it may be that models used to predict loading in demographically distinct groups of runners need to be specific to age and gender. PURPOSE: To determine if kinematic predictors of kinetic variables during running apply across genders and age groups. METHODS: Sagittal plane kinematics and kinetics were assessed in young male (YM: n=13, age=23.1 ± 2.3 yrs, mass=77.0 ± 12.1 kg, height=1.79 ± 0.08 m, velocity=3.32 ± 0.48 m/s) and middle-aged female runners (MF: n=28, age=47.3 ± 7.0 yrs, mass=63.7 ± 7.8 kg, height=1.66 ± .07 m, velocity=2.55 ± 0.37 m/s) using a 5 camera motion analysis system (Qualysis, Goteborg, Sweden) running on an instrumented treadmill (Treadmetrix, Park City, Utah) at their preferred running pace. Kinematics (knee flexion at initial contact, foot angle at initial contact, step position, peak knee flexion and COM excursion) were the independent variables; kinetics (average vertical loading rate, braking impulse, knee power absorption and peak knee extension moment and peak vertical ground reaction force) were the dependent variables. Linear regression models were developed to predict loading in both groups (α=0.05). RESULTS: In both YM and MF, sagittal plane kinematics were useful in predicting peak knee moment (YM: R2=0.56, p=.002; MF: R2=0.47,p=.0002), knee power absorption (YM: R2=0.78, p=.0002; MF: R2=0.55, p<.0001), braking impulse (YM: R2=0.66, p=0.01; MF: R2=0.67, p<.0001), and peak vertical ground reaction force (YM: R2=0.31, p=0.03; MF: R2=0.23, p=0.02). Peak knee flexion appeared in the most models (peak knee moment, knee power absorption and braking impulse for both men and women), and thus may be the most useful single kinematic variable to assess loading across age groups and genders. In all models, greater knee flexion was associated with increased magnitude of loading. Average vertical loading rate could not be predicted using the chosen kinematics in either group. CONCLUSIONS: When equipment for kinetic assessment is not available, sagittal plane gait analysis may be a useful tool for clinicians to estimate loading in runners.

Does shoe heel design influence ground reaction forces and knee moments during maximum lunges in elite and intermediate badminton players?

BackgroundLunge is one frequently executed movement in badminton and involves a unique sagittal footstrike angle of more than 40 degrees at initial ground contact compared with other manoeuvres. This study examined if the shoe heel curvature design of a badminton shoe would influence shoe-ground kinematics, ground reaction forces, and knee moments during lunge.MethodsEleven elite and fifteen intermediate players performed five left-forward maximum lunge trials with Rounded Heel Shoe (RHS), Flattened Heel Shoe (FHS), and Standard Heel Shoes (SHS). Shoe-ground kinematics, ground reaction forces, and knee moments were measured by using synchronized force platform and motion analysis system. A 2 (Group) x 3 (Shoe) ANOVA with repeated measures was performed to determine the effects of different shoes and different playing levels, as well as the interaction of two factors on all variables.ResultsShoe effect indicated that players demonstrated lower maximum vertical loading rate in RHS than the other two shoes (P < 0.05). Group effect revealed that elite players exhibited larger footstrike angle, faster approaching speed, lower peak horizontal force and horizontal loading rates but higher vertical loading rates and larger peak knee flexion and extension moments (P < 0.05). Analysis of Interactions of Group x Shoe for maximum and mean vertical loading rates (P < 0.05) indicated that elite players exhibited lower left maximum and mean vertical loading rates in RHS compared to FHS (P < 0.01), while the intermediate group did not show any Shoe effect on vertical loading rates.ConclusionsThese findings indicate that shoe heel curvature would play some role in altering ground reaction force impact during badminton lunge. The differences in impact loads and knee moments between elite and intermediate players may be useful in optimizing footwear design and training strategy to minimize the potential risks for impact related injuries in badminton.

Effect of total-contact orthosis on medial longitudinal arch and lower extremities in flexible flatfoot subjects during walking.

Total-contact orthosis (TCO) is one kind of foot orthosis (FO) that is used to adjust biomechanics in flexible flatfoot. To determine the effects of a TCO on the MLA moment, MLA deformation angle and lower limb biomechanics. Cross-sectional study. Seven-flatfoot and thirteen-normal foot subjects were recruited by footprint and radiographs. The biomechanics of subjects with normal foot (NF), flatfoot with shoe only (FWOT) and flatfoot with TCO (FWT) were collected in a 3D motion analysis laboratory and force plates. The MLA and lower limb biomechanics in each condition during specific sub-phases of stance were analyzed. The NF had larger MLA eversion moment after shod walking ( p = 0.001). The FWT condition compared with the FWOT condition had a significantly larger peak MLA upward moment ( p = 0.035) during pre-swing, larger peak knee external rotation angle ( p = 0.040) during mid stance, smaller peak knee extension moment during terminal stance ( p = 0.035) and a larger ground reaction force in the anterior-posterior direction during early stance ( p < 0.05). Our study found positive effects from the customized TCOs which included an increased TCO angle that led to a decreased peak MLA moment in the frontal plane in flexible flatfoot subjects during walking. Clinical relevance Lower limb biomechanics is different from normal in subjects with flexible flatfoot. The design of a TCO affects MLA, ankle and knee biomechanics and may be used to clinically correct biomechanical changes in flexible flatfoot.

LANDING WITH LESS HIP FLEXION IS ASSOCIATED WITH INCREASED RISK OF ACL INJURIES IN YOUNG FEMALE TEAM SPORTS PLAYERS

BackgroundStiff landings with less knee flexion and high vertical ground reaction force have shown to be associated with increased risk of ACL injuries (Leppänen et al. 2016). The association between...

Association of Quadriceps Strength and Psychosocial Factors With Single-Leg Hop Performance in Patients With Meniscectomy.

Background:Clinicians use the single-leg hop test to assess readiness for return to sports after knee injury. Few studies have reported the results of single-leg hop testing after meniscectomy. Additionally, the contributions of impairments in quadriceps strength and psychosocial factors to single-leg hop performance are unknown.Purpose:To compare single-leg hop performance (distance and landing mechanics) between limbs and to examine the association of single-leg hop performance with quadriceps strength and psychosocial factors in patients with meniscectomy.Study Design:Descriptive laboratory study.Methods:A total of 22 subjects who underwent meniscectomy for traumatic meniscal tears received either standard rehabilitation alone or with additional quadriceps strengthening. Testing was conducted immediately postrehabilitation and at 1 year postsurgery. A single-leg hop test was performed bilaterally, and hop distance was used to create a hop symmetry index. Landing mechanics (peak knee flexion angle, knee extension moment, and peak vertical ground-reaction force) were analyzed with a motion-capture system and a force plate. An isokinetic dynamometer (60 deg/s) assessed knee extensor peak torque and rate of torque development (RTD0-200ms and RTD0–peak torque). Questionnaires assessed fear of reinjury (Tampa Scale for Kinesiophobia [TSK-11]) and self-efficacy (Knee Activity Self-Efficacy [KASE]).Results:Rehabilitation groups did not significantly differ in single-leg hop performance; therefore, groups were combined for further analyses. The mean hop symmetry index was 88.6% and 98.9% at postrehabilitation and 1 year postsurgery, respectively. Compared with the nonsurgical limb, the surgical limb showed decreased peak knee flexion angle at postrehabilitation and decreased knee extension moment at 1 year postsurgery. The hop symmetry index was positively associated with peak torque, RTD0-200ms, and the KASE score at postrehabilitation. Moreover, at postrehabilitation, the peak knee flexion angle was positively associated with peak torque and RTD0-200ms, and the knee extension moment was positively associated with RTD0-200ms. At 1 year postsurgery, peak knee flexion angle and knee extension moment were both positively associated with peak torque, RTD0-200ms, and RTD0–peak torque.Conclusion:Although the hop symmetry index could be considered satisfactory for returning to sports, asymmetries in landing mechanics still exist in the first year postmeniscectomy. Greater quadriceps strength was associated with greater single-leg hop distance and better landing mechanics at both postrehabilitation and 1 year postsurgery. Knee activity self-efficacy was the only psychosocial factor associated with single-leg hop performance and isolated to a positive association with single-leg hop distance at postrehabilitation.Clinical Relevance:Rate of development is not typically measured in the clinic but can be an additional quadriceps measure to monitor for single-leg hop performance. Quadriceps strength and psychosocial factors appear to have separate influence on single-leg hop performance after meniscectomy, which has implications for developing appropriate interventions for optimal single-leg hop performance.

Erratum to: Knee contact forces and lower extremity support moments during running in young individuals post-partial meniscectomy.

While partial meniscectomy results in a compromised tibiofemoral joint, little is known regarding tibiofemoral joint loading during running in individuals who are post-partial meniscectomy. It was hypothesized that individuals post-partial meniscectomy would run with a greater hip support moment, yielding reduced peak knee extension moments and reduced tibiofemoral joint contact forces. 3-D Treadmill running mechanics were evaluated in 23 athletic individuals post-partial meniscectomy (37.5 ± 19.0 months post-partial meniscectomy) and 23 matched controls. Bilateral hip, knee and ankle contributions to the total support moment and the peak knee extension moment were calculated. A musculoskeletal model estimated peak and impulse tibiofemoral joint contact forces. Knee function was quantified with the Knee injury and Osteoarthritis Outcome Score (KOOS). During running, the partial meniscectomy group had a greater hip support moment (p = 0.002) and a reduced knee support moment (p < 0.001) relative to the total support moment. This movement pattern was associated with a 14.5 % reduction (p = 0.019) in the peak knee extension moment. Despite these differences, there were no significant group differences in peak or impulse tibiofemoral joint contact forces. Lower KOOS Quality of Life scores were associated with greater hip support moment (p = 0.004, r = −0.58), reduced knee support moment (p = 0.006, r = 0.55) and reduced peak knee extension moment (p = 0.01, r = 0.52). Disordered running mechanics are present long term post-partial meniscectomy. A coordination strategy that shifts a proportion of the total support moment away from the knee to the hip reduces the peak knee extension moment, but does not equate to reduced tibiofemoral joint contact forces during running in individuals post-partial meniscectomy. III.

Lower Extremity Movement Differences Persist After Anterior Cruciate Ligament Reconstruction and When Returning to Sports.

To examine how landing mechanics change in patients after anterior cruciate ligament reconstruction (ACL-R) between 6 months and 12 months after surgery. Case-series. Laboratory. Fifteen adolescent patients after ACL-R participated. Lower extremity three-dimensional motion analysis was conducted during a bilateral stop jump task in patients at 6 and 12 months after ACL-R. Joint kinematic and kinetic data, in addition to ground reaction forces, were collected at each time point. During the stop jump landing, the peak joint moments and the initial and peak joint motion at the ankle, knee, and hip were examined. The peak vertical ground reaction force was also examined. Interactions were observed for both the peak knee (P = 0.03) and hip extension moment (P = 0.07). However, only the hip extension moment was symmetrical level at 12 months. Statistically significant (P < 0.05) side-to-side differences existed for the ankle angle at initial contact, peak plantarflexion moment, peak hip flexion angle, and peak impact vertical ground reaction force independent of time. The findings of this study suggest that sagittal plane moments at the knee and hip demonstrate an increase in symmetry between 6 months and 1 year after ACL-R surgery, however, symmetry of the knee extension moment is not established by 12 months after surgery. The lack of change in the variables across time was unexpected. As a result, it is inappropriate to expect a change in landing mechanics solely as a result of time alone after discharge from rehabilitation.

Comparison of Lower Extremity Kinematics and Kinetics during Downhill and Valley-shape Combined Slope Walking

Objective: The purpose of this study was to determine the knee and ankle joint kinematics and kinetics by comparing downhill walking with valley-shape combined slope walking. Method: Eighteen healthy men participated in this study. A three-dimensional motion capture system equipped with eight infrared cameras and a synchronized force plate, which was embedded in the sloped walkway, was used. Obtained kinematic and kinetic parameters were compared using paired two-tailed Student's t-tests at a significance level of 0.05. Results: The knee flexion angle after the mid-stance phase, the mean peak knee flexion angle in the early swing phase, and the ankle mean peak dorsiflexion angle were greater during downhill walking compared with valley-shape combined slope walking (p < 0.001). Both the mean peak vertical ground reaction force (GRF) in the early stance phase and late stance phase during downhill walking were smaller than those values during valley-shape combined slope walking. (p = 0.007 and p < 0.001, respectively). The mean peak anterior GRF, appearing right after toe-off during downhill walking, was also smaller than that of valley-shape combined slope walking (p = 0.002). The mean peak knee extension moment and ankle plantar flexion moment in late stance phase during downhill walking were significantly smaller than those of valley-shape combined slope walking (p = 0.002 and p = 0.015, respectively). Conclusion: These results suggest that gait strategy was modified during valley-shape combined slope walking when compared with continuous downhill walking in order to gain the propulsion for lifting the body up the incline for foot clearance.

The influence of passive-dynamic ankle-foot orthosis bending axis location on gait performance in individuals with lower-limb impairments

BackgroundPassive-dynamic ankle-foot orthoses are commonly prescribed to augment impaired ankle muscle function, however their design and prescription are largely qualitative. One design includes a footplate and cuff, and flexible strut connecting the two. During gait, deflection occurs along the strut, with the greatest deflection at a central bending axis. The vertical location of the axis can affect lower extremity biomechanics. The goal of this study was to investigate the influence of bending axis location on gait performance. MethodsFor thirteen participants with unilateral ankle muscle weakness, an additive manufacturing framework was used to fabricate passive-dynamic ankle-foot orthosis struts with central and off-center bending axes. Participants walked overground while electromyographic, kinetic and kinematic data were collected for three different bending axes: proximal (high), central (middle) and distal (low), and the participants indicated their order of bending axis preference after testing. Gait measures and preference effect sizes were examined during six regions of the gait cycle. FindingsA few differences between bending axes were observed: in the first double-leg support peak plantarflexion angle, peak dorsiflexion moment and positive hip work, in the early single-leg support peak knee extension moment and positive ankle and knee work, and in the late single-leg support gastrocnemius activity and vertical ground reaction force impulse. In addition, preference was strongly related to various gait measures. InterpretationDespite the observed statistical differences, altering bending axis location did not produce large and consistent changes in gait performance. Thus, individual preference and comfort may be more important factors guiding prescription.

Knee Biomechanics of Replaced and Non-replaced Limbs during Level Walking Following Total Knee Arthroplasty

Previously we showed that total knee arthroplasty (TKA) patients still showed deficiencies in replaced limbs in a stair ascent test compared to healthy subjects. These differences were mainly reflected in the reduced peak frontal plane ankle moments but elevated peak frontal plane hip moments at a similar preferred ascent speed. However, peak knee sagittal- and frontal-plane moments were similar. PURPOSE: To compare knee biomechanics of replaced and non-replaced limbs of TKA participants and control limbs of age and body mass index (BMI) matched healthy controls in level walking. METHODS: A total of 13 TKA (65.6 yrs, 28.3 BMI & 24.5 months from TKA surgery) and 15 healthy (62.3 yrs & 27.1 BMI) participants performed functional tests and five level walking trials at a preferred speed. A one-way ANOVA was used to detect difference between replaced, non-replaced limbs and healthy controls (p<0.05). RESULTS: TKA participants had a slower level walking speed (1.18m/s) than healthy controls (1.40m/s, p<0.001); they also had slower stair ascent and descent times on an 11-step staircase but similar timed-up-and-go times compared to healthy controls. The push-off peak vertical ground reaction force (GRF) was reduced in replaced limbs [1.04±0.05 body weight (BW)] compared to control limbs (1.10±0.05 BW). The peak knee extension moment during loading response was decreased in both replaced (0.54±0.23 Nm/kg) and non-replaced (0.54±0.35 Nm/kg) limbs compared to control limbs (0.83±0.27 Nm/kg). The loading response peak internal abduction moment was also reduced in replaced limbs (-0.35±0.13 Nm/kg) compared to control limbs (-0.54±0.18 Nm/kg). CONCLUSIONS: After rehabilitation and recovery, the TKA patients still demonstrated slower walking speeds. The reduced speeds were accompanied by decreased peak GRF, peak sagittal-, and frontal-plane knee moments in replaced limbs, and reduced peak sagittal-plane moment in non-replaced limbs of TKA patients. The results are in contrast to the stair ascent results showing similar peak knee moments between the replaced, non-replaced and control limbs. The differences may be related to different roles or strategies played by knee, hip and ankle muscles in level walking and stair ascent, suggesting that both tests are necessary in order to detect deficits of TKA patients.

Knee and Ankle Biomechanics during Level Walking Both Prior to and Following a Stroke

One of the side effects to gait following a stroke is foot drop syndrome. This presents movement challenges at the ankle, which necessitate compensations at other lower extremity joints. The knee joint angle patterns during stance and swing are often altered, though at faster walking speeds knee joint angles tend to be more similar to normal able bodied individuals. Comparisons between able bodied individuals, though beneficial, lack the strengths of a longitudinal study. The inability of predicting a stroke make these types of studies nearly impossible, especially on a large scale. PURPOSE: To compare level walking biomechanics of one participant prior to and following a stroke. METHODS: 3D kinematics and kinetics of the ankle and knee were analyzed during the stance phase of level walking for one participant (age: 64) at a self-selected walking speed prior to and 5 months post-stroke. A faster walking condition was added in post-stroke testing. RESULTS: Pre-stroke walking speed (1.37 m/s) was faster than post-stroke preferred walking speed (1.19 m/s) but similar to post-stroke fast walking speed (1.38 m/s). The ankle joint changed from dorsiflexion to plantarflexion post-stroke at heel strike [pre (4.0±1.2 deg), post-slow (-8.34±1.9 deg), post-fast (-5.11±1.4 deg)] and knee flexion at foot strike became more flexed following the stroke [pre (0.22±0.7 deg), post-slow (-13.02±0.06 deg), post-fast (-16.7±1.28 deg)]. In addition, the peak ankle plantarflexion moments were reduced following the stroke [pre (-1.49±0.4 Nm/kg), post-slow (-1.02±0.06 Nm/kg), post-fast (-1.03±0.05 Nm/kg)]. The peak knee extension moment was only greater in the post-fast condition (1.32 Nm/kg) compared with pre-stroke (1.05 Nm/kg). CONCLUSION: During the fast condition, the participant appears to be more similar to the pre-stroke condition at the ankle, but not at the knee. Similar ankle moments between fast and preferred walking post stroke, paired with the large increase in the post-fast knee extension moment show greater reliance on the knee joint while walking fast. This data is consistent in showing that the subject had to compensate at the knee during the post-slow and post-fast testing. The longitudinal nature of this study help confirm findings of deficits in other studies that compare to healthy able bodied individuals.

Knee contact forces and lower extremity support moments during running in young individuals post-partial meniscectomy.

While partial meniscectomy results in a compromisedtibiofemoral joint, little is known regarding tibiofemoral joint loading during running in individuals who are post-partial meniscectomy. It was hypothesized that individuals post-partial meniscectomy would run with a greater hip support moment, yielding reduced peak knee extension moments and reduced tibiofemoral joint contact forces. 3-D Treadmill running mechanics were evaluated in 23 athletic individuals post-partial meniscectomy (37.5±19.0months post-partial meniscectomy) and 23 matched controls. Bilateral hip, knee and ankle contributions to the total support moment and the peak knee extension moment were calculated. A musculoskeletal model estimated peak and impulse tibiofemoral joint contact forces. Knee function was quantified with the Knee injury and Osteoarthritis Outcome Score (KOOS). During running, the partial meniscectomy group had a greater hip support moment (p=0.002) and a reduced knee support moment (p<0.001) relative to the total support moment. This movement pattern was associated with a 14.5% reduction (p=0.019) in the peak knee extension moment. Despite these differences, there were no significant group differences in peak or impulse tibiofemoral joint contact forces. Lower KOOS Quality of Life scores were associated with greater hip support moment (p=0.004, r=-0.58), reduced knee support moment (p=0.006, r=0.55) and reduced peak knee extension moment (p=0.01, r=0.52). Disordered running mechanics are present long term post-partial meniscectomy. A coordination strategy that shifts a proportion of the total support moment away from the knee to the hip reduces the peak knee extension moment, but does not equate to reduced tibiofemoral joint contact forces during running in individuals post-partial meniscectomy. III.

Effects of Prophylactic Knee Bracing on Lower Limb Kinematics, Kinetics, and Energetics During Double-Leg Drop Landing at 2 Heights

Background: Anterior cruciate ligament (ACL) injuries commonly occur during landing maneuvers. Prophylactic knee braces were introduced to reduce the risk of ACL injuries, but their effectiveness is debated. Hypotheses: We hypothesized that bracing would improve biomechanical factors previously related to the risk of ACL injuries, such as increased hip and knee flexion angles at initial contact and at peak vertical ground-reaction force (GRF), increased ankle plantar flexion angles at initial contact, decreased peak GRFs, and decreased peak knee extension moment. We also hypothesized that bracing would increase the negative power and work of the hip joint and would decrease the negative power and work of the knee and ankle joints. Study Design: Controlled laboratory study. Methods: Three-dimensional motion and force plate data were collected from 8 female and 7 male recreational athletes performing double-leg drop landings from 0.30 m and 0.60 m with and without a prophylactic knee brace. GRFs, joint angles, moments, power, and work were calculated for each athlete with and without a knee brace. Results: Prophylactic knee bracing increased the hip flexion angle at peak GRF by 5.56° (P < .001), knee flexion angle at peak GRF by 4.75° (P = .001), and peak hip extension moment by 0.44 N·m/kg (P < .001). Bracing also increased the peak hip negative power by 4.89 W/kg (P = .002) and hip negative work by 0.14 J/kg (P = .001) but did not result in significant differences in the energetics of the knee and ankle. No differences in peak GRFs and peak knee extension moment were observed with bracing. Conclusion: The application of a prophylactic knee brace resulted in improvements in important biomechanical factors associated with the risk of ACL injuries. Clinical Relevance: Prophylactic knee braces may help reduce the risk of noncontact knee injuries in recreational and professional athletes while playing sports. Further studies should investigate different types of prophylactic knee braces in conjunction with existing training interventions so that the sports medicine community can better assess the effectiveness of prophylactic knee bracing.