Laura C. Schmitt

BACKGROUND: Athletes who return to sport participation after anterior cruciate ligament reconstruction (ACLR) have a higher risk of a second anterior cruciate ligament injury (either reinjury or contralateral injury) compared with non-anterior cruciate ligament-injured athletes. HYPOTHESES: Prospective measures of neuromuscular control and postural stability after ACLR will predict relative increased risk for a second anterior cruciate ligament injury. STUDY DESIGN: Cohort study (prognosis); Level of evidence, 2. METHODS: Fifty-six athletes underwent a prospective biomechanical screening after ACLR using 3-dimensional motion analysis during a drop vertical jump maneuver and postural stability assessment before return to pivoting and cutting sports. After the initial test session, each subject was followed for 12 months for occurrence of a second anterior cruciate ligament injury. Lower extremity joint kinematics, kinetics, and postural stability were assessed and analyzed. Analysis of variance and logistic regression were used to identify predictors of a second anterior cruciate ligament injury. RESULTS: Thirteen athletes suffered a subsequent second anterior cruciate ligament injury. Transverse plane hip kinetics and frontal plane knee kinematics during landing, sagittal plane knee moments at landing, and deficits in postural stability predicted a second injury in this population (C statistic = 0.94) with excellent sensitivity (0.92) and specificity (0.88). Specific predictive parameters included an increase in total frontal plane (valgus) movement, greater asymmetry in internal knee extensor moment at initial contact, and a deficit in single-leg postural stability of the involved limb, as measured by the Biodex stability system. Hip rotation moment independently predicted second anterior cruciate ligament injury (C = 0.81) with high sensitivity (0.77) and specificity (0.81). CONCLUSION: Altered neuromuscular control of the hip and knee during a dynamic landing task and postural stability deficits after ACLR are predictors of a second anterior cruciate ligament injury after an athlete is released to return to sport.

BACKGROUND: The incidence of second anterior cruciate ligament (ACL) injuries in the first 12 months after ACL reconstruction (ACLR) and return to sport (RTS) in a young, active population has been reported to be 15 times greater than that in a previously uninjured cohort. There are no reported estimates of whether this high relative rate of injury continues beyond the first year after RTS and ACLR. HYPOTHESIS: The incidence rate of a subsequent ACL injury in the 2 years after ACLR and RTS would be less than the incidence rate reported within the first 12 months after RTS but greater than the ACL injury incidence rate in an uninjured cohort of young athletes. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Seventy-eight patients (mean age, 17.1 ± 3.1 years) who underwent ACLR and were ready to return to a pivoting/cutting sport and 47 controls (mean age, 17.2 ± 2.6 years) who also participated in pivoting/cutting sports were prospectively enrolled. Each participant was followed for injury and athlete exposure (AE) data for a 24-month period after RTS. Twenty-three ACLR and 4 control participants suffered an ACL injury during this time. Incidence rate ratios (IRRs) were calculated to compare the rates (per 1000 AEs) of ACL injury in athletes in the ACLR and control groups. For the ACLR group, similar comparisons were conducted for side of injury by sex. RESULTS: The overall incidence rate of a second ACL injury within 24 months after ACLR and RTS (1.39/1000 AEs) was nearly 6 times greater (IRR, 5.71; 95% CI, 2.0-22.7; P = .0003) than that in healthy control participants (0.24/1000 AEs). The rate of injury within 24 months of RTS for female athletes in the ACLR group was almost 5 times greater (IRR, 4.51; 95% CI, 1.5-18.2; P = .0004) than that for female controls. Although only a trend was observed, female patients within the ACLR group were twice as likely (IRR, 2.43; 95% CI, 0.8-8.6) to suffer a contralateral injury (1.13/1000 AEs) than an ipsilateral injury (0.47/1000 AEs). Overall, 29.5% of athletes suffered a second ACL injury within 24 months of RTS, with 20.5% sustaining a contralateral injury and 9.0% incurring a retear injury of the ipsilateral graft. There was a trend toward a higher proportion of female participants (23.7%) who suffered a contralateral injury compared with male participants (10.5%) (P = .18). Conversely, for ipsilateral injuries, the incidence proportion between female (8.5%) and male (10.5%) participants was similar. CONCLUSION: These data support the hypothesis that in the 24 months after ACLR and RTS, patients are at a greater risk to suffer a subsequent ACL injury compared with young athletes without a history of ACL injuries. In addition, the contralateral limb of female patients appears at greatest risk.

OBJECTIVE: Incidence rate (IR) of an ipsilateral or contralateral injury after anterior cruciate ligament reconstruction (ACLR) is unknown. The hypotheses were that the IR of anterior cruciate ligament (ACL) injury after ACLR would be greater than the IR in an uninjured cohort of athletes and would be greater in female athletes after ACLR than male athletes. DESIGN: Prospective case-control study. SETTING: Regional sports community. PARTICIPANTS: Sixty-three subjects who had ACLR and were ready to return to sport (RTS) and 39 control subjects. INDEPENDENT VARIABLES: Second ACL injury and sex. MAIN OUTCOME MEASURES: Second ACL injury and athletic exposure (AE) was tracked for 12 months after RTS. Sixteen subjects after ACLR and 1 control subject suffered a second ACL injury. Between- and within-group comparisons of second ACL injury rates (per 1000 AEs) were conducted. RESULTS: The IR of ACL injury after ACLR (1.82/1000 AE) was 15 times greater [risk ratio (RR) = 15.24; P = 0.0002) than that of control subjects (0.12/1000 AE). Female ACLR athletes demonstrated 16 times greater rate of injury (RR = 16.02; P = 0.0002) than female control subjects. Female athletes were 4 (RR = 3.65; P = 0.05) times more likely to suffer a second ACL injury and 6 times (RR = 6.21; P = 0.04) more likely to suffer a contralateral injury than male athletes. CONCLUSIONS: An increased rate of second ACL injury after ACLR exists in athletes when compared with a healthy population. Female athletes suffer contralateral ACL injuries at a higher rate than male athletes and seem to suffer contralateral ACL injuries more frequently than graft re-tears. The identification of a high-risk group within a population of ACLR athletes is a critical step to improve outcome after ACLR and RTS.

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To investigate the impact of quadriceps femoris (QF) muscle strength asymmetry at the time of return to sport on self-reported function and functional performance of individuals following anterior cruciate ligament reconstruction (ACLR). BACKGROUND: Evidence-based QF strength guidelines for return-to-sport decision making are lacking. Objective guidelines necessitate understanding the impact of QF strength deficits at the time of return to sport on function and performance. METHODS: Fifty-five individuals (mean age, 17.3 years) who were cleared for return to sport following primary ACLR (ACLR group) and 35 uninjured individuals (mean age, 17.0 years) in a control group participated in the study. QF strength (maximum voluntary isometric contraction) was assessed, and the quadriceps index (QI) was calculated [(involved strength/uninvolved strength) × 100%]. The ACLR group was further subdivided into 2 groups, based on the QI: high quadriceps (QI of 90% or greater) and low quadriceps (QI of less than 85%). The International Knee Documentation Committee Subjective Knee Evaluation Form score was used to assess self-reported function, and hop tests were used to assess functional performance. Multivariate analysis of variance and hierarchical regression analyses were performed. RESULTS: The individuals in the ACLR group were weaker, reported worse function, and performed worse on hop tests compared to those in the control group (P<.05). The low-quadriceps group demonstrated worse performance on the hop tests compared to the high-quadriceps group and the control group (P ≤.016). Hop test performance did not differ between the high-quadriceps and control groups (P ≥.14). QF strength predicted performance on the hop tests beyond graft type, presence of meniscus injury, knee pain, and knee symptoms. CONCLUSION: At the time of return to sport, individuals post-ACLR who had weaker QF (QI of less than 85%) demonstrated decreased function, whereas those with minimal QF strength deficits (QI of 90% or greater) demonstrated functional performance similar to uninjured individuals. QF strength deficits predicted hop test performance beyond the influences of graft type, presence of meniscus injury, knee pain, and knee symptoms.

PURPOSE: Evidence-based quadriceps femoris muscle (QF) strength guidelines for return to sport after anterior cruciate ligament (ACL) reconstruction are lacking. This study investigated the effect of QF strength asymmetry on knee landing biomechanics at the time of return to sport after ACL reconstruction. METHODS: Seventy-seven individuals (17.4 yr) at the time of return to sport after primary ACL reconstruction (ACLR group) and 47 uninjured control individuals (17.0 yr; CTRL group) participated. QF strength was assessed and quadriceps index was calculated (QI = [involved strength / uninvolved strength] × 100%). The ACLR group was subdivided based on QI: high quadriceps (HQ, QI ≥ 90%) and low quadriceps (LQ, QI < 85%). Knee kinematic and kinetic variables were collected during a drop vertical jump maneuver. Limb symmetry during landing and discrete variables were compared among the groups using multivariate analysis of variance and linear regression analyses. RESULTS: The LQ group demonstrated worse asymmetry in all kinetic and ground reaction force variables compared to the HQ and CTRL groups, including reduced involved limb peak knee external flexion moments (P < 0.001), reduced involved limb (P = 0.003) and increased uninvolved limb (P = 0.005) peak vertical ground reaction forces and higher uninvolved limb peak loading rates (P < 0.004). There were no differences in the landing patterns between the HQ and CTRL groups on any variable (P > 0.05). In the ACLR group, QF strength estimated limb symmetry during landing after controlling for graft type, meniscus injury, knee pain, and symptoms. CONCLUSIONS: At the time of return to sport, individuals after ACL reconstruction with weaker QF demonstrate altered landing patterns. Conversely, those with nearly symmetrical QF strength demonstrate landing patterns similar to uninjured individuals. Consideration of an objective QF strength measure may aid clinical decision making to optimize sports participation after ACL reconstruction.