Time-course changes in lower limb strength, vertical jump metrics and their relationship with patient reported outcomes following anterior cruciate ligament reconstruction

Abstract

Purpose: To (1) investigate how lower limb strength, vertical jump metrics, and patient reported outcome measures (PROMs) change in the initial 3- to 12-months of recovery following ACLR; and (2) explore which strength and vertical jump metrics best differentiate between lower and higher Knee Osteoarthritis Outcome Score (KOOS) and Anterior Cruciate Ligament Return to Sport After Injury (ACL-RSI) scores. Methods: Thirty recreationally active athletes undergoing unilateral primary ACLR underwent field-based assessments of knee flexion and extension strength, hip adduction and abduction strength, and double and single leg countermovement (CMJ) and drop vertical jump (DVJ) kinetics at 3-, 6-, 9- and 12-months following surgery. The KOOS and ACL-RSI were also completed. Mixed models were used to investigate how measures of lower limb strength, vertical jump metrics and PROMs change across the first 12-months of rehabilitation. Mixed model decision trees were used to determine which strength and vertical jump measures best discriminated between lower and higher PROMs. Results: Vertical jump height and reactive strength index (RSI) improved significantly over time (p < 0.001), with reductions in contraction and contact times (p < 0.05). Isometric knee extension and eccentric knee flexion strength increased significantly (p < 0.001), as did KOOS and ACL-RSI scores (p < 0.001). Surgically reconstructed limbs displayed deficits in most vertical jump and strength measures compared to the uninjured contralateral limb, although deficits reduced over time with between limb asymmetry deceasing in 70% of these variables (p range: 0.05 to <0.001). Single leg CMJ jump height < 8.4 cm best discriminated between lower and higher ACL-RSI scores (r2 = 0.67, d = 0.8), whilst knee extension peak force asymmetry < 38.3% best discriminated between lower and higher KOOS scores (r2 = −0.78, d = 0.9) across the time-course of rehabilitation. Conclusion: Most measures of lower limb strength and vertical jump metrics change in both the ACLR and uninjured contralateral limbs across the first 12-months of recovery following primary ACLR. A strong relationship was found between measures of lower limb strength and vertical jump performance with PROMs. Level of Evidence: Level II, lower quality prospective cohort study.