Poster 359: Muscle Performance and Drop Jump Mechanics Associate with Second Injury in a Matched Cohort of Athletes Who Passed Functional Return-to-Sport Criteria after ACL Reconstruction

Objectives: In young athletes who undergo an anterior cruciate ligament reconstruction (ACLR), up to one-third will suffer a second injury. Sport and activity level, quadriceps strength, ability to single-leg hop, biomechanical movement patterns, and time to return-to-sport (RTS) clearance are among the known risk factors associated with ACL reinjury. Passing a battery of RTS testing has shown to reduce second injury rate by up to 84%. However, the feasibility of validated RTS batteries in most orthopedic clinics is poor, though recent steps have been made toward investigating more clinic-friendly testing methods. The purpose of this study is to compare muscle performance and drop vertical jump mechanics in a matched cohort of young athletes who, after passing a clinic-based RTS battery after primary ACLR, returned to sport with or without sustaining a second injury. Methods: This is a secondary analysis of 22 young athletes (age 16.2 ± 2.4 years, BMI 24.6 ± 4.7 kg/m2, 16 male, 6 female) selected from part of a prospective cohort study with 69 athletes. All 69 athletes from the original trial underwent RTS testing 5-15 months after primary ACLR, had no prior history of injury or surgery to either knee and were planning to return to >50 hours/year of cutting and pivoting sports. 53 of these athletes passed a clinic-based RTS battery of >90% limb symmetry during isometric quadriceps strength using a Klau crane scale at 90° knee flexion, 1-rep max knee extension (from 90° to 0°), and 4 single-leg hop tests (single, crossover, triple for distance, 6-meter timed), as well as >90% on the Global Rating Scale and International Knee Documentation Committee (IKDC) 2000 Subjective Knee Form. These athletes then underwent formal lab testing within 14 days of passing clinic testing. Lab testing included isometric quadriceps strength (90° knee flexion) and isokinetic concentric quadriceps and hamstring strength (60°/sec) using an electromechanical dynamometer (Biodex System 4 Pro, Shirley, NY). Additionally, biomechanical testing was performed with an 8-camera Qualisys system (240 Hz; Goteborg, Sweden) and 2 embedded Bertec force plates (2160 Hz; Columbus, OH) to measure knee joint angles and external moments normalized to body mass and height during 5 bilateral drop vertical jumps (BDVJ) and 5 unilateral drop vertical jumps (UDVJ). All athletes were followed for 1 year after passing clinic-based RTS testing for reinjury and RTS outcomes. Nine athletes who returned to t