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Background: Pre-operative quadriceps strength may have a positive influence on post-operative function and outcomes at time of return to sport. Little consideration has been given to quadriceps strength during the early post-operative timeframes. Twelveweek post-operative anterior cruciate ligament reconstruction (ACL-R) is considered a critical time point for progression in the rehabilitation process. There is currently limited research looking at the relationship between clinical measurements pre-operatively and at 12-weeks following ACL-R. Purpose/Hypothesis:The primary purpose of this study was to examine the differences between Y-Balance Test Lower Quarter (YBT-LQ) and isokinetic quadriceps strength tested pre-operatively and post-operatively following ACL-R (12-weeks). Study Design: Within subject, repeated measuresMethods: Thirty-nine participants (15.6±1.5 y/o) were diagnosed with an ACL tear and were undergoing rehabilitation to return to a sport requiring cutting and pivoting were included. YBT-LQ and isokinetic quadriceps strength were assessed pre-operatively and at 12-weeks after ACL-R. YBT-LQ composite scores were calculated bilaterally and isokinetic quadriceps strength was tested using the Biodex Multi-Joint Testing and Rehabilitation System. Paired T-tests were used to determine mean group differences between YBT-LQ and isokinetic quadriceps strength scores pre-operatively and at 12-weeks post-operative. A Pearson Correlation was performed to determine relationships between variables at both time points.Results: There was a significant improvement in YBT-LQ composite scores from pre-operative to 12-weeks post-operative on both the involved p<0.001) limbs. Quadriceps strength decreased significantly from pre-operative to 12-weeks on the involved limb (Pre-operative: 82.3 ftlbs ± 38.6; 12-weeks: 67.9 ftlbs±27.4, p<0.01), but no differences were found on the uninvolved limb (Pre-operative: 117.3ftlbs ± 42.0; 12-weeks: 121.7ftlbs ± 41.5, p = 0.226). Conclusions:Involved limb quadriceps strength decreases from time of pre-operative to 12-weeks following ACL-R. Level of Evidence: 3

Background: Quadriceps strength and knee extension are believed to be important in the ability to effectively load the knee after anterior cruciate ligament (ACL) reconstruction (ACL-R). Purpose: To compare quadriceps strength (QUADS), side-to-side knee extension difference (ExtDiff), and knee energy absorption contribution (EAC) in patients preoperatively, 12 weeks postoperatively, and at return to sport (RTS). A secondary aim was to determine how the factors of QUADS and ExtDiff contributed to the ability to load the knee (knee EAC) at each of the 3 time points. Study Design: Case series; Level of evidence, 4. Methods: Overall, 41 individuals (mean ± SD age, 15.95 ± 1.63 years) were enrolled in this study. QUADS, ExtDiff, and knee EAC during a double-limb squat were collected preoperatively, 12 weeks postoperatively, and at RTS. Isokinetic QUADS was collected at 60 deg/s, normalized to body mass, and averaged across 5 trials. Knee extension was measured with a goniometer, and ExtDiff was calculated for analyses. Knee EAC was measured during double-limb squat descent and was calculated as a percentage of total energy absorption for the limb. Observations were obtained from both the surgical and nonsurgical limbs at the 3 time points. A mixed regression model with random intercept to compare change over the 3 time points was used, and a model selection was conducted with Akaike information criteria. Significance was set at P < .05. Results: Surgical limb QUADS was significantly lower preoperatively (mean ± SD, 1.37 ± 0.49 N·m/kg; P = .0023) and at 12 weeks (1.11 ± 0.38 N·m/kg; P < .0001) than at RTS (1.58 ± 0.47 N·m/kg). Nonsurgical limb QUADS was also significantly lower preoperatively (2.01 ± 0.54 N·m/kg; P < .0256) and at 12 weeks (2.03 ± 0.48 N·m/kg; P < .0233) than at RTS (2.18 ± 0.54 N·m/kg). Knee EAC for the surgical limb was significantly lower at 12 weeks than at RTS (40.98% ± 13.73% vs 47.50% ± 12.04%; P < .0032), and ExtDiff was significantly greater preoperatively than at RTS (–2.68° ± 3.19° vs –0.63° ± 1.43°; P < .0001). Preoperatively, QUADS for both the surgical ( P < .0003) and nonsurgical ( P = .0023) limbs was a significant predictor of surgical limb knee EAC, explaining 33.99% of the variance. At 12 weeks, surgical limb QUADS was a significant predictor ( P < .0051) of surgical limb knee EAC, explaining 18.83% of the variance. At RTS, ExtDiff was a significant predictor ( P = .0201) of surgical limb knee EAC, explaining 12.92% of the variance. Conclusion: The ability to load the knee after ACL injury changes across the continuum of care and is related to QUADS and ExtDiff. These results provide clinicians with insight into potential contributing factors that may limit knee loading during the rehabilitation process.

Background:Female patients are more likely to suffer a second anterior cruciate ligament (ACL) injury after ACL reconstruction (ACLR) and return to sport (RTS) compared with healthy female controls. Few studies have examined the energy absorption contribution (EAC) that could lead to this subsequent injury.Hypothesis:The ACLR group would demonstrate an altered EAC between joints (hip, knee, and ankle) but no difference in quadriceps, hip abduction, or hip external rotation (ER) strength at the time of RTS.Study Design:Cross-sectional study; Level of evidence, 3.Methods:A total of 34 female participants (ACLR: n = 17; control: n = 17) were enrolled in the study and matched for age and activity level. Jump landing performance for the initial 50 milliseconds of landing of a lateral-vertical jump was assessed using a 10-camera 3-dimensional motion capture system and 2 force plates. Isokinetic quadriceps strength was measured using a Biodex machine, and hip abduction and ER isometric strength were measured using a handheld dynamometer. All values were normalized to the participant’s height and weight. A 1-way multivariate analysis of variance was used to assess between-group differences in the EAC at the hip, knee, and ankle. Two 1-way analyses of variance were used to independently examine quadriceps, hip abduction, and hip ER strength between the groups.Results:Significant differences in the EAC were found between the groups for the involved hip (P = .002), uninvolved hip (P = .005), and involved ankle (P = .023). There were no between-group differences in the EAC for the involved or uninvolved knee or the uninvolved ankle. Patients who underwent ACLR demonstrated significantly decreased quadriceps strength on the involved limb (P = .02) and decreased hip ER strength on both the involved (P = .005) and uninvolved limbs (P = .002). No significant strength differences were found between the groups for the uninvolved quadriceps or for involved or uninvolved hip abduction.Conclusion:At RTS, patients who underwent ACLR utilized a greater hip EAC bilaterally and a decreased involved ankle EAC during a lateral-vertical jump. Furthermore, quadriceps strength on the involved limb and hip ER strength of bilateral lower extremities remained decreased. This could place greater stress on the ACL graft and ultimately lead to an increased injury risk.

Limb symmetry strength measures are used for clinical decision-making considering when an athlete is ready to return to sport after anterior cruciate ligament (ACL) injuries. However, changes in bilateral muscle strength occur after ACL injury resulting in potentially altered limb symmetry calculations. Adolescent female soccer players are at increased risk of sustaining ACL injuries. Published age and sex-matched strength values in this population may be of benefit to clinicians to improve clinical decision-making. The purpose of this study was to establish normative hip and knee strength data of both the dominant and nondominant limbs in adolescent female soccer players. Sixty-four female soccer players (ages 10-18) were enrolled in this study. Subjects were divided by age into 2 groups (group 1: 10-14 years; group 2: 15-18 years). Subjects underwent Biodex isokinetic strength testing at 60˚•s 21 and 180˚•s 21 to assess quadriceps and hamstring strength. Isometric hip strength (abduction and external rotation) was measured using a hand-held dynamometer. No significant differences were found between groups on either limb in regards to quadriceps or hamstring strength. No significant differences were found between groups on either limb for hip external rotation strength. Significant differences in hip abduction strength were found between groups on the dominant (group 1: 0.21 6 0.04; group 2: 0.18 6 0.04; p 5 0.014) and nondominant (group 1: 0.21 6 0.05; group 2: 0.18 6 0.05; p 5 0.019) limbs. The results of this study shed light on normative strength values for a high-risk injury population.