Single-leg Backward Hopping Imposes Greater Knee Demands Compared To Forward Hopping In ACLR Patients

Practitioners commonly use single-leg forward hopping distances to evaluate knee function in patients following anterior cruciate ligament (ACL) injuries. However, symmetric forward hopping distances cannot ensure symmetric bilateral strength and movement patterns. Recently, single-leg backward hopping was found to impose greater mechanical demands on the knee compared to forward hopping, suggesting the potential of using single-leg backward hopping to better assess knee strength and mechanics in patients who underwent ACL reconstructions (ACLR). PURPOSE: To quantify knee mechanics during single-leg forward and backward hopping in ACLR patients in comparison to healthy controls. METHODS: Fifteen female participants were recruited with 8 unilateral ACLR patients (33.8 ± 22.1 months after ACLR, age 20.2 ± 1.5 yr, height 1.6 ± 0.1 m, and mass 69.2 ± 14.3 kg) and 7 healthy controls (age 19.6 ± 1.3 yr, height 1.7 ± 0.0 m, and mass 67.1 ± 16.0 kg). Participants performed single-leg forward and backward hopping for distance on each leg with motion and force data collected. The hopping distance, peak knee flexion angle, knee extension moment, and knee power were calculated during the jumping phase. Results were reported for each leg in ACLR patients and the average of both legs in healthy controls. RESULTS: Single-leg backward hopping demonstrated greater peak knee flexion angle, knee extension moment, and knee power than forward hopping, regardless of legs and groups (Table 1). The decreasing order of knee mechanical variables were healthy controls, uninvolved knee, and involved knee in single-leg backward hopping. The uninvolved knee showed greater knee mechanical variables than the involved knee in both forward and backward hopping. CONCLUSION: Single-leg backward hopping imposes greater knee demands than forward hopping in ACLR patients and healthy controls, indicating a more challenging task to assess knee function in individuals following ACL injuries.