Relationship of Knee Forces to Subjective Function Pre- and Post-ACL Reconstruction

Purpose Although basic objective measures (e.g., knee laxity, strength, and hop tests) have been related to subjective measures of function, associations between knee-specific objective and subjective measures have yet to be completed. The objective was to determine if knee joint contact and ligament forces differ between pre- and post-anterior cruciate ligament (ACL) reconstructed states and if these forces relate to their patient's respective subjective functional ability scores. Methods Twelve patients performed a hopping task before and after reconstruction. Magnetic resonance images and OpenSim were used to develop patient-specific models in static optimization and joint reaction analyses. Questionnaires concerning each patient's subjective functional ability were also collected and correlated with knee joint contact and ligament forces. Results No significant differences were observed between deficient and reconstructed groups with respect to knee joint contact or ligament forces. Nevertheless, there were several significant (P < 0.05) moderate to strong correlations between subjective and objective measures including Tegner activity level to contact force in both states (r = 0.67-0.76) and International Knee Documentation Committee to compressive and anterior shear forces (r = 0.64-0.66). Conclusion Knee-specific objective measures of a patient's functional capacity can represent their subjective ability, which explains this relationship to a greater extent than past anatomical and gross objective measures of function. This consolidation is imperative for improving the current rehabilitation schema as it allows for external validation of objective and subjective functional measures. With poor validation of subjective function against objective measures of function, the reinjury rate is unlikely to diminish, continuing the heavy financial burden on health care systems.