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

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.