Hip-Dominant Landing Strategy During the Second Landing of a Drop Vertical Jump After ACL Reconstruction

Abstract

Drop vertical jump (DVJ) performance is often used to aid in the decision to return to sport after anterior cruciate ligament reconstruction (ACLR). In healthy subjects, the 2nd landing from a DVJ imposes greater demand in the sagittal plane. Deficits in sagittal plane angle and moments at the knee and hip are commonly seen in gait after an ACLR and are linked to poor return-to-sport outcomes. However, how this propagates to tasks such as the 2nd landing of a DVJ has not been well characterized. Furthermore, whether sagittal plane mechanics of the ACLR limb are restored to be similar to a matched control group during the 2nd landing of a DVJ is unknown. PURPOSE: To compare sagittal plane mechanics between the ACLR limb and a control group during the 2nd landing of a DVJ. METHODS: Twenty-two subjects (10 F, age 20.6 ± 5 y, H 1.74 ± 0.1 m, M 71.4 ± 12.5 kg) 6 months post ACLR and 12 controls (5 F, age 21 ± 3 y, H 1.7 ± 0.1 m, M 65 ± 12 kg) performed a DVJ. Three-dimensional motion analysis was conducted while subjects performed a DVJ by stepping off a 30.5 cm box, landing on two feet (1st landing), immediately transitioning into a maximal vertical jump, and landing on two feet a second time (2nd landing). Visual 3D was used to analyze sagittal plane hip and knee mechanics at initial contact. Independent sample t-tests were used to compare groups. RESULTS: The ACLR limb had significantly greater knee and hip flexion angles than the control group (Knee:-31 ± 9.4 vs -22 ± 5.1°, p=0.004, Hip: 27.2 ± 12.9 vs 17.2 ± 14.5°, p=0.04). Additionally, the ACLR limb demonstrated less knee extensor moment, but greater hip extensor moment compared to the control group (Knee: -0.22 ± 0.21 vs 0.03 ± 0.21 Nm/kg*m, p=0.002, Hip: -0.32 ± 0.2 vs -0.13 ± 0.24 Nm/kg*m, p=0.01). CONCLUSIONS: The combination of greater knee flexion angles with a reduced knee extensor moment suggests the ACLR limb is unable to control the increased sagittal plane demands of the 2nd landing. Additionally, increased hip extensor moment in the ACLR group indicates an altered landing strategy to transfer load absorption from the knee to the hip musculature. Future work should explore the relationship between altered landing strategies to hip and knee muscle strength to identify possible interventions to restore knee neuromuscular control after an ACLR.