Relationships of Functional Tests Following ACL Reconstruction: Exploratory Factor Analyses of the Lower Extremity Assessment Protocol

Context: After ACL reconstruction (ACLR), deficits are often assessed using a variety of functional tests, which can be time consuming. It is unknown whether these tests provide redundant or unique information. Objective: To explore relationships between components of a battery of functional tests, the Lower Extremity Assessment Protocol (LEAP) was created to aid in developing the most informative, concise battery of tests for evaluating ACLR patients. Design: Descriptive, cross-sectional. Setting: Laboratory. Participants: 76 ACLR patients (6.86 +/- 3.07 months postoperative) and 54 healthy participants. Intervention: Isokinetic knee flexion and extension at 90 and 180 degrees/second, maximal voluntary isometric contraction for knee extension and flexion, single leg balance, 4 hopping tasks (single, triple, crossover, and 6-meter timed hop), and a bilateral drop vertical jump that was scored with the Landing Error Scoring System (LESS). Main Outcome Measures: Peak torque, average torque, average power, total work, fatigue indices, center of pressure area and velocity, hop distance and time, and LESS score. A series of factor analyses were conducted to assess grouping of functional tests on the LEAP for each limb in the ACLR and healthy groups and limb symmetry indices (LSI) for both groups. Correlations were run between measures that loaded on retained factors. Results: Isokinetic and isometric strength tests for knee flexion and extension, hopping, balance, and fatigue index were identified as unique factors for all limbs. The LESS score loaded with various factors across the different limbs. The healthy group LSI analysis produced more factors than the ACLR LSI analysis. Individual measures within each factor had moderate to strong correlations. Isokinetic and isometric strength, hopping, balance, and fatigue index provided unique information. Conclusions: Within each category of measures, not all tests may need to be included for a comprehensive functional assessment of ACLR patients due to the high amount of shared variance between them.