Energy Absorption In The Single Leg Vertical And Horizontal Hops In Adolescents Post-acl Reconstruction

Single leg tasks, such as the single leg horizontal hop (SLHH) and single leg vertical hop (SLVH) are used to assess performance and return to sport (RTS) readiness in clinical populations. Research on the landing of the SLVH has shown equal contributions from the hip, knee and ankle while the SLHH relies mostly on the knee. Differences between the tasks have not been examined in children. PURPOSE: To examine the difference in intralimb contributions to energy absorption during landing of SLHH and SLVH post-anterior cruciate ligament reconstruction (ACLR). METHODS: 9 athletes (3 female; median age 16.1 years, IRQ 1.5, range 14.9-18.4) after ACLR (median 8.3 months post-surgery, IQR 4.1, range 6.1-13.6) completed the SLVH and SLHH while kinematics and kinetics were collected. Height/distance and energy absorption (power integral) at the hip, knee and ankle were averaged across trials during landing. The percent contribution of each joint to total energy absorption was calculated. Performance, total energy absorption, and percent energy absorption at each joint were compared across tasks and between limbs. RESULTS: SLHH and SLVH distance were shorter for ACLR compared to contralateral limbs, but significant for SLVH only (1.45 vs. 1.55, 0.31 vs. 0.34, p=0.02). Total energy absorption was lower on the ACLR side for both tasks (3.3 vs. 4.1, 3.2 vs. 3.9, p≤0.004). Distribution of energy absorption differed between tasks with SLVH having greater ankle contribution (p<0.0001) and lower contributions of the hip (p=0.0002) and knee (p=0.0008). A lower percentage of energy was absorbed by the ACLR compared with contralateral knees in both tasks (p≤0.04, Fig. 1). This was compensated by a trend toward increased energy absorption at the hip in ACLR limbs (significant for the SLHH, p=0.03). CONCLUSION: Intralimb contributions to energy absorption differ between the SLVH and SLHH and there is lower energy absorption and offloading of ACLR compared with contralateral limbs in both tasks.