Does a Lower Limb Balance Test after Anterior Cruciate Ligament Reconstruction Have a Significant Correlation with Postoperative Clinical Score, Stability, and Functional Performance Test?

Background: Lower limb balance ability is reduced after anterior cruciate ligament reconstruction (ACLR). However, the recovery of balance based on functional test scores after ACLR is not known because the correlation between balance and clinical scores remains unclear. We aimed to analyze the correlation between lower limb balance assessed by functional test and clinical knee test scores after ACLR. Methods: We evaluated lower limb balance using the anterior-posterior stability index (APSI) of the Biodex Balance System (BBS). Patients underwent clinical tests to evaluate the knee, including the Tegner activity score, International Knee Documentation Committee (IKDC) subjective score, Lysholm score, and KT-2000 arthrometer measurement, hamstring per quadriceps muscle strength ratio at 60°/sec (HQ ratio), and functional performance tests (single-leg hop and single-leg vertical jump tests) 1 year after ACLR. We used a paired t-test to compare continuous preoperative and postoperative variables and Pearson's correlation coefficient to determine the relationship between BBS-APSI and clinical scores. Results: Forty-eight patients (35 men and 13 women; mean age, 28.9 ± 8.3 years) were included. The follow-up period and BBS-APSI were 12.4 ± 2.0 months and 0.9 ± 0.4, respectively. Tegner activity score, IKDC subjective score, Lysholm score, and KT-2000 arthrometer measurement improved significantly postoperatively (p < 0.001). BBS-APSI was correlated with the Tegner activity score (r = -0.335, p = 0.020), IKDC subjective score (r = -0.301, p = 0.037), Lysholm score (r = -0.323, p = 0.025), single-leg hop test results (r = -0.300, p = 0.038), and single-leg vertical jump test results (r = -0.336, p = 0.019). There was no correlation between KT-2000 arthrometer measurement and HQ ratio. Conclusions: BBS-APSI was correlated with functional performance test scores after ACLR, rendering the BBS-APSI as a useful assessment tool to evaluate postoperative functional recovery. Continuously improving balance after ACLR could be useful for functional recovery after surgery.