Quadriceps Strength and Kinesiophobia Predict Long-Term Function After ACL Reconstruction: A Cross-Sectional Pilot Study

Background: Many patients live with long-term deficits in knee function after an anterior cruciate ligament reconstruction (ACLR). However, research is inconclusive as to which physical performance measure is most strongly related to long-term patient-reported outcomes after ACLR. Hypothesis: Quadriceps strength would be most strongly associated with patient-reported long-term outcomes after ACLR. Study Design: Cross-sectional study. Level of Evidence: Level 3. Methods: A total of 40 patients (29 female) consented and participated an average of 10.9 years post-ACLR (range, 5-20 years). Patients completed the Lower Extremity Functional Scale (LEFS), the International Knee Documentation Committee (IKDC) Scale, Knee injury and Osteoarthritis Outcome Score Quality of Life (KOOS QoL) and Sport (KOOS Sport) subscales, and the Tampa Scale of Kinesiophobia (TSK-17). Each patient subsequently performed maximal isometric quadriceps contraction, a 60-second single-leg step-down test, and the single-leg single hop and triple hop for distance tests. Multivariate linear and logistic regression models determined how performance testing was associated with each patient-reported outcome when controlling for time since surgery, age, and TSK-17. Results: When controlling for time since surgery, age at the time of consent, and TSK-17 score, maximal isometric quadriceps strength normalized to body weight was the sole physical performance measure associated with IKDC (P < 0.001), KOOS Sport (P = 0.006), KOOS QoL (P = 0.001), and LEFS scores (P < 0.001). Single-leg step-down, single hop, and triple hop did not enter any of the linear regression models (P > 0.20). Additionally, TSK-17 was associated with all patient-reported outcomes (P ≤ 0.01) while time since surgery was not associated with any outcomes (P > 0.05). Conclusion: Isometric quadriceps strength and kinesiophobia are significantly associated with long-term patient-reported outcomes after ACLR. Clinical Relevance: These results suggest that training to improve quadriceps strength and addressing kinesiophobia in the late stages of recovery from ACLR may improve long-term self-reported function.