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: Knee extensor strength deficits occur after ACL reconstruction (ACLR). Prior studies have reported that age affects quadriceps strength after ACLR, however strength deficits in relation to age have not been assessed among adolescents. Isokinetic dynamometric strength testing is a tool frequently used to assess strength post-operatively in order to identify these deficits. Purposes: 1) To examine the effect of age on isokinetic extensor and flexor deficits among adolescents who were 5-10 months post-ACLR. We hypothesized that age would be inversely related to extensor strength deficit. 2) To determine if extensor or flexor strength deficits exist between adolescents post-ACLR with and without concomitant meniscus surgery. We hypothesized that those with concomitant meniscus surgery would demonstrate greater deficits in flexor and extensor strength. Methods: Study participants completed isokinetic testing within 5-10 months after primary quadriceps tendon ACLR, but before return to sport. The protocol consisted of assessing peak torque at 60, 180, and 300 degrees/s, through a limited range of knee extension and flexion. Our primary outcome variables were peak torque percent deficit of involved leg compared to uninvolved leg for flexion and extension. To address purpose 1, we constructed a series of multivariable regression models, where age was the independent variable, peak torque flexor/extensor deficits at each testing speed was the dependent variable, and sex and weight were covariates. To address purpose 2, we compared peak torque extensor and flexor deficits between those with and without concomitant meniscus surgery using independent samples t-tests. Results: A total of 44 completed the study protocol. There were no significant demographic differences between those with and without concomitant meniscus surgery (Table 1). The relationship between age at surgery and peak torque extensor deficits at 300d/s demonstrated a linear but non-significant association (Table 2; Figure 1). For every year increase in age, the expected deficit at 300d/s increased by approximately 3%. Patients who underwent isolated ACLR demonstrated significantly greater flexor deficits than those who underwent ACLR with concomitant meniscus surgery when tested at 180d/s and 300d/s (Table 3). Conclusion: Contrary to our first hypothesis, extensor deficits at 300d/s demonstrated an apparent association with older age. We observed a steady increase in strength deficit at 300d/s associated with increasing age. Contrary to our second hypothesis, no significant differences were found in extensor strength between those with and without meniscus surgery. Additionally, those with concomitant meniscus surgery demonstrated significantly less flexor deficit than those without meniscus surgery. [Table: see text][Table: see text][Figure: see text][Table: see text]