Biomechanical but Not Strength or Performance Measures Differentiate Male Athletes Who Experience ACL Reinjury on Return to Level 1 Sports

Abstract

Background: Performance measures such as strength, jump height/length, and change of direction (CoD) time during anterior cruciate ligament (ACL) rehabilitation have been used to determine readiness to return to play and identify those who may be at risk of rerupture. However, athletes may reach these criteria despite ongoing biomechanical deficits when performing these tests. Combining return-to-play criteria with an assessment of movement through 3-dimensional (3D) biomechanics in male field sports athletes to identify risk factors for ACL rerupture has not been explored previously.

Purpose: To prospectively examine differences in strength, jump, and CoD performance and movement using 3D biomechanics in a cohort of male athletes playing level 1 sports (ie, multidirectional field sports that involve landing, pivoting, or CoD) between those who reinjured the reconstructed ACL (RI group) and those with no reinjury (NRI group) after 2 years of follow-up and to examine the ability of these differences to predict reinjury.

Study design: Cohort study; Level of evidence, 2.

Methods: After primary ACL reconstruction (ACLR), 1045 male athletes were recruited and underwent testing 9 months after surgery including isokinetic strength, jump, and CoD performance measures as well as patient-reported outcomes and 3D biomechanical analyses. Participants were followed up after 2 years regarding ACL reinjury status. Differences were determined between the RI and NRI groups in patient-reported outcomes, performance measures, and 3D biomechanics on the ACLR side and symmetry between limbs. The ability of these measures to predict ACL reinjury was determined through logistic regression.

Results: No differences were identified in strength and performance measures on the ACLR side or in symmetry. Biomechanical analysis indicated differences on the ACLR side primarily in the sagittal plane for the double-leg drop jump (effect size, 0.59-0.64) and greater asymmetry primarily in the frontal plane during unplanned CoD (effect size, 0.61-0.69) in the RI group. While these biomechanical test results were different between groups, multivariate regression modeling demonstrated limited ability (area under the curve, 0.67 and 0.75, respectively) to prospectively predict ACL reinjury.

Conclusion: Commonly reported return-to-play strength, jump, and timed CoD performance measures did not differ between the RI and NRI groups. Differences in movement based on biomechanical measures during double-leg drop jump and unplanned CoD were identified, although they had limited ability to predict reinjury. Targeting these variables during rehabilitation may reduce reinjury risk in male athletes returning to level 1 sports after ACLR.

Registration: NCT02771548 (ClinicalTrials.gov identifier).

Keywords: anterior cruciate ligament reconstruction; biomechanics; reinjury; return to play.

Figures

Figure 1.

Flow diagram of matching process between the reinjury and no-reinjury groups. 3D, 3-dimensional; ACL, anterior cruciate ligament; ACLR, ACL reconstruction; RTP, return to play.

Figure 2.

Biomechanical differences on the anterior cruciate ligament reconstruction side during the double-leg drop jump in the reinjury group as compared with the no-reinjury group illustrate longer ground contact times, greater knee flexion, and lower center of mass (COM) to the ankle.

Figure 3.

Difference in knee flexion angle on the anterior cruciate ligament (ACL) reconstruction side between the reinjury (RI) and no-reinjury (NRI) groups during the double-leg drop jump. Top panel illustrates mean and SD clouds for RI (red) and NRI (black) limbs. Middle panel illustrates SPM{t}, the t statistic as a function of time describing the difference between the groups. The dotted red line of the SPM curve indicates P < .05 and that a significant difference exists between groups. The bottom panel illustrates effect size as a function of time, describing magnitude of the effect. The dotted black line and shaded portion indicate an average Cohen d >.0.5, with orange indicating a medium effect size and a significant difference throughout that phase. There was less knee flexion in the RI group (9%−22%) with a medium effect size (0.64). fle, flexion; SPM, statistical parametric mapping.

Figure 4.

Biomechanical variables with greater asymmetry during unplanned change of direction in the reinjury group as compared with the no-reinjury group illustrate greater asymmetry of trunk-side flexion, distance from center of mass (COM) to the knee and ankle in the frontal plane, pelvic tilt, and pelvic drop.