Body Composition Is Associated With Physical Performance in Individuals With Knee Osteoarthritis.

BACKGROUND/OBJECTIVE: The purpose of this cross-sectional study was to determine associations between body composition, self-reported function, and physical performance after accounting for body mass index (BMI) in individuals with knee osteoarthritis. METHODS: Percent fat and lean mass were evaluated using dual energy x-ray absorptiometry. Self-reported function (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC] function subscale) and physical performance (20-m walk, chair stand, and stair climb) were collected on 46 adults (30% male; BMI, 29.6 ± 3.8 kg/m) with radiographically defined knee osteoarthritis (Kellgren-Lawrence grades 2-4). Linear regressions determined the unique association between WOMAC and physical performance explained individually by percent fat and lean mass ([INCREMENT]R) after accounting for BMI. RESULTS: Lower percent fat mass significantly associated with better physical performance after accounting for BMI (20-m walk: [INCREMENT]R = 0.10, p = 0.03; chair stand: [INCREMENT]R = 0.16, p = 0.01; stair climb: [INCREMENT]R = 0.11, p = 0.03). Higher percent lean mass significantly associated with better chair stand ([INCREMENT]R = 0.09, p = 0.04) but not 20-m walk or stair climb ([INCREMENT]R range, 0.04-0.07, p > 0.05). After accounting for BMI, neither percent fat nor lean mass associated with WOMAC. Body mass index did not significantly associate with WOMAC or physical performance. CONCLUSIONS: Lower percent fat and higher percent lean mass associated with better physical performance after accounting for BMI. Body composition and BMI may be used together in the future to more comprehensively understand the association between obesity and disability.

Females Decrease Vertical Ground Reaction Forces Following 4-Week Jump-Landing Feedback Intervention Without Negative Affect on Vertical Jump Performance.

CONTEXT: High vertical ground reaction force (vGRF) when initiating ground contact during jump landing is one biomechanical factor that may increase risk of anterior cruciate ligament injury. Intervention programs have been developed to decrease vGRF to reduce injury risk, yet generating high forces is still critical for performing dynamic activities such as a vertical jump task. OBJECTIVE: To evaluate if a jump-landing feedback intervention, cueing a decrease in vGRF, would impair vertical jump performance in a separate task (Vertmax). DESIGN: Randomized controlled trial. Patients (or Other Participants): Forty-eight recreationally active females (feedback: n = 31; 19.63 [1.54] y, 1.6 [0.08] cm, 58.13 [7.84] kg and control: n = 15; 19.6 [1.68] y, 1.64 [0.05] cm, 60.11 [8.36] kg) participated in this study. INTERVENTION: Peak vGRF during a jump landing and Vertmax were recorded at baseline and 4 weeks post. The feedback group participated in 12 sessions over the 4-week period consisting of feedback provided for 6 sets of 6 jumps off a 30-cm box. The control group was instructed to return to the lab 28 days following the baseline measurements. MAIN OUTCOME MEASURES: Change scores (postbaseline) were calculated for peak vGRF and Vertmax. Group differences were evaluated for peak vGRF and Vertmax using a Mann-Whitney U test (P < .05). RESULTS: There were no significant differences between groups at baseline (P > .05). The feedback group (-0.5 [0.3] N/kg) demonstrated a greater decrease in vGRF compared with the control group (0.01 [0.3] N/kg) (t(46) = -5.52, P < .001). There were no significant differences in change in Vertmax between groups (feedback = 0.9 [2.2] cm, control = 0.06 [2.1] cm; t(46) = 0.46, P = .64). CONCLUSIONS: While the feedback intervention was effective in decreasing vGRF when landing from a jump, these participants did not demonstrate changes in vertical jump performance when assessed during a different task. Practitioners should consider implementing feedback intervention programs to reduce peak vGRF, without worry of diminished vertical jump performance.

Associations among knee muscle strength, structural damage, and pain and mobility in individuals with osteoarthritis and symptomatic meniscal tear.

BACKGROUND: Sufficient lower extremity muscle strength is necessary for performing functional tasks, and individuals with knee osteoarthritis demonstrate thigh muscle weakness compared to controls. It has been suggested that lower muscle strength is associated with a variety of clinical features including pain, mobility, and functional performance, yet these relationships have not been fully explored in patients with symptomatic meniscal tear in addition to knee osteoarthritis. Our purpose was to evaluate the associations of quadriceps and hamstrings muscle strength with structural damage and clinical features in individuals with knee osteoarthritis and symptomatic meniscal tear. METHODS: We performed a cross-sectional study using baseline data from the Meniscal Tear in Osteoarthritis Research (MeTeOR) trial. We assessed structural damage using Kellgren-Lawrence grade and the magnetic resonance imaging osteoarthritis knee score (MOAKS) for cartilage damage. We used the Knee Injury and Osteoarthritis Outcomes Score (KOOS) to evaluate pain, symptoms, and activities of daily living (ADL), and the Timed Up and Go (TUG) test to assess mobility. We assessed quadriceps and hamstrings strength using a hand-held dynamometer and classified each into quartiles (Q). We used Chi square tests to evaluate the association between strength and structural damage; and separate analysis of covariance models to establish the association between pain, symptoms, ADL and mobility with strength, after adjusting for demographic characteristics (age, sex and BMI) and structural damage. RESULTS: Two hundred fifty two participants were evaluated. For quadriceps strength, subjects in the strongest quartile scored 14 and 13 points higher on the KOOS Pain and ADL subscales, respectively, and completed the TUG two seconds faster than subjects in the weakest quartile. For hamstrings strength, subjects in the strongest quartile scored 13 and 14 points higher on the KOOS pain and ADL subscales, respectively, and completed the TUG two seconds faster than subjects in the weakest quartile. Strength was not associated with structural damage. CONCLUSIONS: Greater quadriceps and hamstrings muscle strength was associated with less pain, less difficulty completing activities of daily living, and better mobility. These relationships should be evaluated longitudinally.

Greater intracortical inhibition associates with lower quadriceps voluntary activation in individuals with ACL reconstruction.

Decreased voluntary activation contributes to quadriceps weakness following anterior cruciate ligament reconstruction (ACLR). Alterations in neural excitability are likely responsible for reductions in quadriceps voluntary activation, and may be due to specific alterations in intracortical inhibition and facilitation. Therefore, we sought to determine if intracortical inhibition (SICI) and intracortical facilitation (ICF) associate with quadriceps voluntary activation in individuals with ACLR. Twenty-seven participants with a primary, unilateral ACLR were enrolled in this study. Bilateral central activation ratio (CAR) and paired-pulse transcranial magnetic stimulation were used to assess quadriceps voluntary activation, as well as SICI and ICF in the vastus medalis, respectively. Pearson Product Moment correlations were used to determine the association between CAR and (1) SICI, and (2) ICF in each limb. Lesser CAR associated with lesser SICI amplitude (r = 0.502, P = 0.008) in the ACLR limb. No associations in the contralateral limb were significant. Our results suggest greater intracortical inhibition associates with lesser voluntary activation in individuals with ACL. Implementing interventions that target intracortical inhibition may aid in restoring quadriceps voluntary activation following ACLR.

Immediate Biochemical Changes After Gait Biofeedback in Individuals With Anterior Cruciate Ligament Reconstruction.

CONTEXT: Gait biomechanics are linked to biochemical changes that contribute to the development of posttraumatic knee osteoarthritis in individuals with anterior cruciate ligament reconstruction (ACLR). It remains unknown if modifying peak loading during gait using real-time biofeedback will result in acute biochemical changes related to cartilage metabolism. OBJECTIVE: To determine if acutely manipulating peak vertical ground reaction force (vGRF) during gait influences acute changes in serum cartilage oligomeric matrix protein concentration (sCOMP) among individuals with ACLR. DESIGN: Crossover study. PATIENTS OR OTHER PARTICIPANTS: Thirty individuals with unilateral ACLR participated (70% female, age = 20.43 ± 2.91 years old, body mass index = 24.42 ± 4.25, months post-ACLR = 47.83 ± 26.97). Additionally, we identified a subgroup of participants who demonstrated an increase in sCOMP after the control or natural loading condition (sCOMPCHANGE > 0 ng/mL, n = 22, 70% female, age = 20.32 ± 3.00 years old, body mass index = 24.73 ± 4.33, months post-ACLR = 47.27 ± 29.32). MAIN OUTCOME MEASURE(S): Serum was collected both prior to and immediately after each condition to determine sCOMPchange. INTERVENTION(S): All participants attended 4 sessions that involved 20 minutes of walking on a force-measuring treadmill consisting of a control condition (natural loading) followed by random ordering of 3 loading conditions with real-time biofeedback: (1) symmetric vGRF between limbs, (2) a 5% increase in vGRF (high loading) and (3) a 5% decrease in vGRF (low loading). A general linear mixed model was used to determine differences in sCOMPCHANGE between altered loading conditions and the control group in the entire cohort and the subgroup. RESULTS: The sCOMPCHANGE was not different across loading conditions for the entire cohort (F3,29 = 1.34, P = .282). Within the subgroup, sCOMPCHANGE was less during high loading (1.95 ± 24.22 ng/mL, t21 = -3.53, P = .005) and symmetric loading (9.93 ± 21.45 ng/mL, t21 = -2.86, P = .025) compared with the control condition (25.79 ± 21.40 ng/mL). CONCLUSIONS: Increasing peak vGRF during gait decreased sCOMP in individuals with ACLR who naturally demonstrated an increase in sCOMP after 20 minutes of walking. TRIAL REGISTRY: ClinicalTrials.gov (NCT03035994).

Biomechanical effects of manipulating peak vertical ground reaction force throughout gait in individuals 6-12 months after anterior cruciate ligament reconstruction.

BACKGROUND: We aimed to determine the effect of cueing an increase or decrease in the vertical ground reaction force impact peak (peak in the first 50% of stance) on vertical ground reaction force, knee flexion angle, internal knee extension moment, and internal knee abduction moment waveforms throughout stance in individuals 6-12 months after an anterior cruciate ligament reconstruction. METHODS: Twelve individuals completed 3 conditions (High, Low, and Control) where High and Low Conditions cue a 5% body weight increase or decrease, respectively, in the vertical ground reaction force impact peak compared to usual walking. Biomechanics during High and Low Conditions were compared to the Control Condition throughout stance. FINDINGS: The High Condition resulted in: (a) increased vertical ground reaction forces at each peak and decreased during mid-stance, (b) greater knee excursion (i.e., greater knee flexion angle in early stance and a more extended knee in late stance), (c) greater internal extension moment for the majority of stance, and (d) lesser second internal knee abduction moment peak. The Low Condition resulted in: (a) vertical ground reaction forces decreased during early stance and increased during mid-stance, (b) decreased knee excursion, (c) increased internal extension moment throughout stance, and (d) decreased internal knee abduction moment peaks. INTERPRETATION: Cueing a 5% body weight increase in vertical ground reaction force impact peak resulted in a more dynamic vertical ground reaction force loading pattern, increased knee excursion, and a greater internal extension moment during stance which may be useful in restoring gait patterns following anterior cruciate ligament reconstruction.

Using TENS to Enhance Therapeutic Exercise in Individuals with Knee Osteoarthritis.

Transcutaneous electrical nerve stimulation (TENS) facilitates quadriceps voluntary activation in experimental settings. Augmenting therapeutic exercise (TE) with TENS may enhance the benefits of TE in individuals with knee osteoarthritis (KOA) and quadriceps voluntary activation failure (QVAF). PURPOSE: This study aimed to determine the effect of TENS + TE on patient-reported function, quadriceps strength, and voluntary activation, as well as physical performance compared with sham TENS + TE (Sham) and TE alone in individuals with symptomatic KOA and QVAF. METHODS: Ninety individuals participated in a double-blinded randomized controlled trial. Everyone received 10 standardized TE sessions of physical therapy. TENS + TE and Sham groups applied the respective devices during all TE sessions and throughout activities of daily living over 4 wk. The Western Ontario and McMaster University Osteoarthritis Index (WOMAC), quadriceps strength, and voluntary activation, as well as a 20-m walk test, chair-stand test, and stair-climb test were performed at baseline, after the 4-wk intervention (post 1) and at 8 wk after the start of the intervention (post 2). Mixed-effects models were used to determine between-group differences between baseline and post 1, as well as baseline and post 2. RESULTS: Improvements in WOMAC subscales, quadriceps strength, and voluntary activation, 20-m walk times, chair-stand repetitions, and stair-climb time were found at post 1 and post 2 compared with baseline for all groups (P < 0.05). WOMAC Pain and Stiffness improved in the TENS + TE group compared with TE alone at post 1 (P < 0.05); yet, no other between-group differences were found. CONCLUSIONS: TE effectively improved patient-reported function, quadriceps strength, and voluntary activation, as well as physical performance in individuals with symptomatic KOA and QVAF, but augmenting TE with TENS did not improve the benefits of TE.

Body Mass Index and Type 2 Collagen Turnover in Individuals After Anterior Cruciate Ligament Reconstruction.

CONTEXT: Individuals with an anterior cruciate ligament reconstruction (ACLR) are at an increased risk of developing posttraumatic osteoarthritis. How osteoarthritis risk factors, such as increased body mass index (BMI), may influence early changes in joint tissue metabolism is unknown. OBJECTIVE: To determine the association between BMI and type 2 cartilage turnover in individuals with an ACLR. DESIGN: Cross-sectional study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Forty-five individuals (31 women, 14 men) with unilateral ACLR at least 6 months earlier who were cleared for unrestricted physical activity. MAIN OUTCOME MEASURE(S): Body mass index (kg/m2) and type 2 collagen turnover were the primary outcomes. Body mass index was calculated from objectively measured height and mass. Serum was obtained to measure type 2 collagen turnover, quantified as the ratio of degradation (collagen type 2 cleavage product [C2C]) to synthesis (collagen type 2 C-propeptide [CP2]; C2C : CP2). Covariate measures were physical activity level before ACLR (Tegner score) and current level of disability (International Knee Documentation Committee Index score). Associations of primary outcomes were analyzed for the group as a whole and then separately for males and females. RESULTS: Overall, greater BMI was associated with greater C2C : CP2 (r = 0.32, P = .030). After controlling for covariates (Tegner and International Knee Documentation Committee Index scores), we identified a similar association between BMI and C2C : CP2 (partial r = 0.42, P = .009). Among women, greater BMI was associated with greater C2C : CP2 before (r = 0.47, P = .008) and after (partial r = 0.50, P = .008) controlling for covariates. No such association occurred in men. CONCLUSIONS: Greater BMI may influence greater type 2 collagen turnover in those with ACLR. Individuals, especially women, who maintain or reduce BMI may be less likely to demonstrate greater type 2 collagen turnover ratios after ACLR.

Association between kinesiophobia and walking gait characteristics in physically active individuals with anterior cruciate ligament reconstruction.

BACKGROUND: Individuals with anterior cruciate ligament reconstruction (ACLR) demonstrate persistent alterations in walking gait characteristics that contribute to poor long-term outcomes. Higher kinesiophobia, or fear of movement/re-injury, may result in the avoidance of movements that increase loading on the ACLR limb. RESEARCH QUESTION: Determine the association between kinesiophobia and walking gait characteristics in physically active individuals with ACLR. METHODS: We enrolled thirty participants with a history of unilateral ACLR (49.35 ±â€¯27.29 months following ACLR) into this cross-sectional study. We used the Tampa Scale for Kinesiophobia (TSK-11) to measure kinesiophobia. We collected walking gait characteristics during a 60-s walking trial, which included gait speed, peak vertical ground reaction force (vGRF), instantaneous vGRF loading rate, peak internal knee extension moment (KEM), and knee flexion excursion. We calculated lower extremity kinetic and kinematic measures on the ACLR limb, and limb symmetry indices between ACLR and contralateral limbs (LSI= [ACLR/contralateral]*100). We used linear regression models to determine the association between TSK-11 score and each walking gait characteristic. We determined the change in R2 (ΔR2) when adding TSK-11 scores into the linear regression model after accounting for demographic covariates (sex, Tegner activity score, graft type, time since reconstruction, history of concomitant meniscal procedure). RESULTS: We did not find a significant association between kinesiophobia and self-selected gait speed (ΔR2 0.038, P = 0.319). Kinesiophobia demonstrated weak, non-significant associations with kinetic and kinematic outcomes on the ACLR limb and all LSI outcomes (ΔR2 range = 0.001-0.098). SIGNIFICANCE: These data do not support that kinesiophobia is a critical factor contributing to walking gait characteristics in physically active individuals with ACLR.

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.

Lesser lower extremity mechanical loading associates with a greater increase in serum cartilage oligomeric matrix protein following walking in individuals with anterior cruciate ligament reconstruction.

BACKGROUND: Aberrant mechanical loading during gait is hypothesized to contribute to the development of posttraumatic osteoarthritis following anterior cruciate ligament reconstruction. Our purpose was to determine if peak vertical ground reaction force and instantaneous vertical ground reaction force loading rate associate with the acute change in serum cartilage oligomeric matrix protein following a 20-minute bout of walking. METHODS: We enrolled thirty individuals with a unilateral anterior cruciate ligament reconstruction. Peak vertical ground reaction force and instantaneous vertical ground reaction force loading rate were extracted from the first 50% of the stance phase of gait during a 60-second trial. Blood samples were collected immediately before and after 20 min of treadmill walking at self-selected speed. The change in serum cartilage oligomeric matrix protein from pre- to post-walking was calculated. Stepwise linear regression models were used to determine the association between each outcome of loading and the change in serum cartilage oligomeric matrix protein after accounting for sex, gait speed, time since anterior cruciate ligament reconstruction, graft type, and history of concomitant meniscal procedure (ΔR2). FINDINGS: Lesser peak vertical ground reaction force (ΔR2 = 0.208; ß = -0.561; P = 0.019) and instantaneous vertical ground reaction force loading rate (ΔR2 = 0.168; ß = -0.519; P = 0.037) on the anterior cruciate ligament reconstructed limb associated with a greater increase in serum cartilage oligomeric matrix protein following 20 min of walking. INTERPRETATION: Mechanical loading may be a future therapeutic target for altering the acute biochemical response to walking in individuals with an anterior cruciate ligament reconstruction.

Quadriceps Rate of Torque Development and Disability in Persons With Tibiofemoral Osteoarthritis.

Background Declines in the ability to rapidly generate quadriceps muscle torque may underlie disability in individuals with tibiofemoral osteoarthritis. Objective To determine whether quadriceps rate of torque development (RTD) predicts self-reported disability and physical performance outcomes in individuals with tibiofemoral osteoarthritis. Methods This controlled laboratory, cross-sectional study assessed quadriceps strength and RTD in 76 individuals (55% female; mean ± SD age, 61.83 ± 7.11 years) with symptomatic and radiographic tibiofemoral osteoarthritis. Early (0-50 milliseconds), late (100-200 milliseconds), and overall peak RTDs were quantified in the symptomatic (involved) and contralateral limbs and used to calculate bilateral average values. Disability was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function subscale and 3 physical performance tests, including the (1) 20-m fast-paced walk, (2) 30-second chair stand, and (3) timed stair climb. Separate univariate regression models were used to determine the unique associations among measures of quadriceps RTD, WOMAC function score, and physical performance outcomes after accounting for quadriceps strength (change in R2). Results Greater involved-side late RTD and greater bilateral average early RTD were associated with faster walking (change in R2 = 0.05, P = .013 and change in R2 = 0.05, P = .043, respectively). Greater bilateral average late RTD was associated with faster walking (change in R2 = 0.20, P<.001) and faster stair climb (change in R2 = 0.11, P = .001). No quadriceps RTD variable was significantly associated with WOMAC function score (change in R2 range, <0.01-0.017). Conclusion Involved-limb quadriceps RTD was weakly associated with physical performance outcomes, but not self-reported disability, in individuals with tibiofemoral osteoarthritis. Bilateral average quadriceps RTD was moderately associated with walking speed. Level of Evidence Prognosis, level 2b. J Orthop Sports Phys Ther 2018;48(9):694-703. Epub 22 May 2018. doi:10.2519/jospt.2018.7898.

Quadriceps Neuromuscular Function and Jump-Landing Sagittal-Plane Knee Biomechanics After Anterior Cruciate Ligament Reconstruction.

CONTEXT: Aberrant biomechanics may affect force attenuation at the knee during dynamic activities, potentially increasing the risk of sustaining a knee injury or hastening the development of osteoarthritis after anterior cruciate ligament reconstruction (ACLR). Impaired quadriceps neuromuscular function has been hypothesized to influence the development of aberrant biomechanics. OBJECTIVE: To determine the association between quadriceps neuromuscular function (strength, voluntary activation, and spinal-reflex and corticomotor excitability) and sagittal-plane knee biomechanics during jump landings in individuals with ACLR. DESIGN: Cross-sectional study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-eight individuals with unilateral ACLR (7 men, 21 women; age = 22.4 ± 3.7 years, height = 1.69 ± 0.10 m, mass = 69.4 ± 10.1 kg, time postsurgery = 52 ± 42 months). MAIN OUTCOME MEASURE(S): We quantified quadriceps spinal-reflex excitability via the Hoffmann reflex normalized to maximal muscle response (H : M ratio), corticomotor excitability via active motor threshold, strength as knee-extension maximal voluntary isometric contraction (MVIC), and voluntary activation using the central activation ratio (CAR). In a separate session, sagittal-plane kinetics (peak vertical ground reaction force [vGRF] and peak internal knee-extension moment) and kinematics (knee-flexion angle at initial contact, peak knee-flexion angle, and knee-flexion excursion) were collected during the loading phase of a jump-landing task. Separate bivariate associations were performed between the neuromuscular and biomechanical variables. RESULTS: In the ACLR limb, greater MVIC was associated with greater peak knee-flexion angle ( r = 0.38, P = .045) and less peak vGRF ( r = -0.41, P = .03). Greater CAR was associated with greater peak internal knee-extension moment (ρ = -0.38, P = .045), and greater H : M ratios were associated with greater peak vGRF ( r = 0.45, P = .02). CONCLUSIONS: Greater quadriceps MVIC and CAR may provide better energy attenuation during a jump-landing task. Individuals with greater peak vGRF in the ACLR limb possibly require greater spinal-reflex excitability to attenuate greater loading during dynamic movements.

Walking gait asymmetries 6 months following anterior cruciate ligament reconstruction predict 12-month patient-reported outcomes.

The study sought to determine the association between gait biomechanics (vertical ground reaction force [vGRF], vGRF loading rate [vGRF-LR]) collected 6 months following anterior cruciate ligament reconstruction (ACLR) with patient-reported outcomes at 12 months following ACLR. Walking gait biomechanics and all subsections of the Knee Injury and Osteoarthritis Outcomes Score (KOOS) were collected at 6 and 12 months following ACLR, respectively, in 25 individuals with a unilateral ACLR. Peak vGRF and peak instantaneous vGRF-LR were extracted from the first 50% of the stance phase. Limb symmetry indices (LSI) were used to normalize outcomes in the ACLR limb to that of the uninjured limb (ACLR/uninjured). Linear regression analyses were used to determine associations between biomechanical outcomes and KOOS while accounting for walking speed. Receiver operator characteristic curves were used to determine the accuracy of 6-month biomechanical outcomes for identifying individuals with acceptable patient-reported outcomes, using previously defined KOOS cut-off scores, 12 months post-ACLR. Individuals with lower peak vGRF LSI 6 months post-ACLR demonstrated worse patient-reported outcomes (KOOS Pain, Activities of Daily life, Sport and Recreation, Quality of Life) at the 12-month exam. A peak vGRF LSI ≥0.99 6 months following ACLR associated with 13.33× higher odds of reporting acceptable patient-reported outcomes 12 months post-ACLR. Lesser peak vGRF LSI during walking at 6-months post-ACLR may be a critical indicator of worse future patient-reported outcomes. Clinical significance achieving early symmetrical lower extremity loading and minimizing under-loading of the ACLR limb during walking may be a potential therapeutic target for improving patient-reported outcomes post-ACLR. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2932-2940, 2018.

Quadriceps rate of torque development and disability in individuals with anterior cruciate ligament reconstruction.

BACKGROUND: The purpose of this study was to determine associations between self-reported function (International Knee Documentation Committee Index), isometric quadriceps strength and rate of torque development in individuals with a unilateral anterior cruciate ligament reconstruction. METHODS: Forty-one individuals [31% male, BMI mean 25 (SD 4) kg/m2, months post anterior cruciate ligament reconstruction mean 49 (SD 40)] completed the self-reported function and isometric quadriceps function testing. Rate of torque development was assessed at 0-100ms (early), 100-200ms (late) ms, and peak following the onset of contraction. Associations were examined between rate of torque development, strength, and self-reported function. Linear regression was used to determine the unique amount of variance explained by the combination of rate of torque development and strength. FINDINGS: Higher rate of torque development 100-200ms is weakly associated with higher self-reported function in individuals with a unilateral anterior cruciate ligament reconstruction (r=0.274, p=0.091); however, rate of torque development 100-200ms does not predict a significant amount of variance in self-reported function after accounting for strength (ΔR2=0.003, P=0.721). INTERPRETATION: Quadriceps strength has a greater influence on self-reported function compared to rate of torque development in individuals with an anterior cruciate ligament reconstruction with time from surgery.

Biochemical markers of cartilage metabolism are associated with walking biomechanics 6-months following anterior cruciate ligament reconstruction.

The purpose of our study was to determine the association between biomechanical outcomes of walking gait (peak vertical ground reaction force [vGRF], vGRF loading rate [vGRF-LR], and knee adduction moment [KAM]) 6 months following anterior cruciate ligament reconstruction (ACLR) and biochemical markers of serum type-II collagen turnover (collagen type-II cleavage product to collagen type-II C-propeptide [C2C:CPII]), plasma degenerative enzymes (matrix metalloproteinase-3 [MMP-3]), and a pro-inflammatory cytokine (interleukin-6 [IL-6]). Biochemical markers were evaluated within the first 2 weeks (6.5 ± 3.8 days) following ACL injury and again 6 months following ACLR in eighteen participants. All peak biomechanical outcomes were extracted from the first 50% of the stance phase of walking gait during a 6-month follow-up exam. Limb symmetry indices (LSI) were used to normalize the biomechanical outcomes in the ACLR limb to that of the contralateral limb (ACLR/contralateral). Bivariate correlations were used to assess associations between biomechanical and biochemical outcomes. Greater plasma MMP-3 concentrations after ACL injury and at the 6-month follow-up exam were associated with lesser KAM LSI. Lesser KAM was associated with greater plasma IL-6 at the 6-month follow-up exam. Similarly, lesser vGRF-LR LSI was associated with greater plasma MMP-3 concentrations at the 6-month follow-up exam. Lesser peak vGRF LSI was associated with higher C2C:CPII after ACL injury, yet this association was not significant after accounting for walking speed. Therefore, lesser biomechanical loading in the ACLR limb, compared to the contralateral limb, 6 months following ACLR may be related to deleterious joint tissue metabolism that could influence future cartilage breakdown. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2288-2297, 2017.

Sagittal plane kinematics predict kinetics during walking gait in individuals with anterior cruciate ligament reconstruction.

BACKGROUND: Alterations in mechanical loading following anterior cruciate ligament reconstruction may lead to the development of knee osteoarthritis. Feedback that cues a change in knee kinematics during walking gait may influence mechanical loading, yet it remains unknown if knee kinematics predict kinetics during walking gait. Our aim was to determine if sagittal plane knee kinematics predict kinetics during walking gait in anterior cruciate ligament reconstructed individuals. METHODS: Forty-one individuals with a history of primary, unilateral anterior cruciate ligament reconstruction completed a motion capture walking gait analysis. Hierarchical linear regression analyses were used in order to determine the amount of variance in the kinetic variables of interest (peak vertical ground reaction force, instantaneous and linear vertical ground reaction force loading rate) that was individually predicted by the kinematic variables of interest (knee flexion angle at heelstrike, peak knee flexion angle, and knee flexion excursion). FINDINGS: Knee flexion excursion of the injured limb significantly predicted 11% of the variance in peak vGRF of the injured limb after accounting for gait speed and peak knee flexion angle (ΔR2=0.11, P=0.004). After accounting for gait speed and knee flexion angle at heelstrike, knee flexion excursion significantly predicted 16% of the variance in the injured limb peak vertical ground reaction force (ΔR2=0.16, P=0.001). No kinematic variable predicted vertical ground reaction force loading rate. INTERPRETATION: Altering knee flexion excursion may be useful as a future therapeutic target for modifying peak vertical ground reaction force during walking gait following anterior cruciate ligament reconstruction.

Persistent Muscle Inhibition after Anterior Cruciate Ligament Reconstruction: Role of Reflex Excitability.

PURPOSE: Persistent voluntary quadriceps activation deficits are common after anterior cruciate ligament reconstruction (ACLR), but the direct causes are unclear. The primary purpose of this study was to determine whether spinal reflex excitability deficits are present in individuals with a history of ACLR, and secondarily to determine whether spinal reflex excitability predicts which individuals possess full voluntary quadriceps activation. METHODS: One hundred and forty-seven individuals (74 healthy and 73 ACLR) participated in this cross-sectional case-control study. Quadriceps spinal reflex excitability was quantified using the Hoffmann reflex normalized to the maximal muscle response (H:M ratio). Voluntary quadriceps activation was evaluated with the burst superimposition technique and calculated via the central activation ratio (CAR). Separate 2 × 2 ANCOVA tests were used to compare between-limb and between-group differences for H:M ratio and CAR. A receiver operating characteristic curve was used to determine the accuracy of H:M ratio to predict if ACLR participants present with full voluntary activation (CAR ≥ 0.95). RESULTS: The ACLR H:M ratio was not different between limbs or compared with the healthy group (P > 0.05). Although ACLR CAR was lower bilaterally compared with the healthy group (P < 0.001), it did not differ between limbs. The H:M ratio has poor accuracy for predicting which individuals exhibit full voluntary activation (receiver operating characteristic area under the curve = 0.52, 95% CI = 0.37,0.66; odds ratio = 2.2, 95% CI = 0.8, 5.9). CONCLUSIONS: Spinal reflex excitability did not differ between limbs in individuals with ACLR or compared with healthy participants. The level of quadriceps spinal reflex excitability has poor accuracy at predicting which ACLR individuals would demonstrate full voluntary quadriceps activation.

Quadriceps Strength Predicts Self-reported Function Post-ACL Reconstruction.

INTRODUCTION/PURPOSE: Quadriceps strength is a useful clinical predictor of self-reported function after anterior cruciate ligament reconstruction (ACLR). However, it remains unknown if quadriceps strength normalized to body mass (QBM) or quadriceps strength limb symmetry index (QLSI) is the best predictor of self-reported function in individuals with ACLR. We sought to determine whether QBM and QLSI are able to predict individuals with ACLR who self-report high function (≥90% on the international knee documentation committee (IKDC) index). METHODS: Ninety-six individuals with a history of a primary unilateral ACLR were recruited for a multisite cross-sectional descriptive laboratory experiment. Bilateral isometric quadriceps strength was collected at 90° of knee flexion to calculate QBM and QLSI (ratio of the ACLR limb to the contralateral limb). Area under the curve (AUC) values were calculated using receiver operating characteristic curve analyses to determine the capacity of QBM and QLSI to predict individuals with high self-reported function on the IKDC index. RESULTS: QBM displayed high accuracy (AUC = 0.76; 95% confidence interval, 0.66-0.86) for identifying participants with an IKDC index ≥90%. A QBM cutoff score of 3.10 N·m·kg was found to maximize sensitivity (0.61) and specificity (0.84), and displayed 8.15 (3.09-21.55) times higher odds of reporting high function. QLSI displayed a moderate accuracy (AUC = 0.62, 0.50-0.73) for identifying participants with an IKDC index ≥90%. A QLSI cutoff score of 96.5% maximized sensitivity (0.55) and specificity (0.70), and represented 2.78 (1.16-6.64) times higher odds reporting high function. CONCLUSION: QBM is a stronger predictor of high self-reported function compared with QLSI in individuals with ACLR. Rehabilitation guidelines may benefit from incorporating the use of QBM measurements for the purpose of predicting participants that may maintain high self-reported function.