Early Objective Clinical Testing Predicts Jump Landing Mechanics Following an ACL Reconstruction: Impact for the Clinician and Return to Play Testing

OBJECTIVES: Currently, objective functional assessments are performed at the time of return to play following an anterior cruciate ligament (ACL) reconstruction. While informative, by that time the majority of organized rehabilitation has been completed, leaving little time for clinicians to address remaining impairments. Further, few objective tests have been compared to faulty movement mechanics. Identifying objective clinical tests that can be administered early during recovery from an ACL reconstruction which predict long term joint mechanics would provide sufficient time to address the underlying deficits prior to return to play testing. Thus, the purpose of this study was to determine if objective clinical tests (60 second single leg step down test and quadriceps strength) administered 3 months after surgery predicted jump landing mechanics of the knee (knee extension moment, average loading rate, vertical impact peak) at 6 months following an ACL reconstruction. METHODS: 29 subjects completed objective clinical testing at 3 months post operatively that included the 60 second single leg step down test and an assessment of isometric knee strength. To perform the 60 second single leg step down test, subjects performed a single leg squat by touching their heel on a scale with less than 10% of their bodyweight as many times as they could for 60 seconds while standing on an 8-inch box. Isometric knee extension strength was assessed with a hand held dynamometer secured to a table. The subject performed 4 isometric maximum isometric contractions for 5 seconds. At 6 months, performed a instrumented drop vertical landing jumping. Three trials were taken and the data were analyzed using custom Labview and Visual 3D code. The average loading rate was defined as the linear portion of the vertical ground reaction curve between 20-80% of foot contact to initial impact peak. Associations between quadriceps strength and the timed single leg step down test to knee extensor moment, average loading rate, and vertical impact peak were then made with Pearson correlation coefficients. RESULTS: 29 subjects (15 male and 14 female, Ages 20.2 ± 4.7 yrs, 24 bone patellar bone vs 5 hamstring autografts, H 1.75 ± 0.12 m, M 72.2 ± 12.1 kg) completed the study. The mean quadriceps strength was 23.3 ± 10.2 N, timed single leg step down test 20 ± 11 step downs, knee extensor moment 1.32 ± 0.54 Nm/kg, loading rate was 64.5 ± 23.6 %bodyweight/sec, and vertical impact peak 0.97 ± 0.36 %bodyweight. We found significant positive associations between 3 month quadriceps strength and knee extensor moment (r=0.442, p=0.016), average vertical loading rate (r=0.426, p=0.021), and vertical impact peak (r=0.619, p=0.000) (Figure 1). We found no significant associations between 3 month single leg step down performance and landing mechanics. CONCLUSION: We show the ability of a early, quick, clinically-feasible method of assessing quadriceps strength to predict joint mechanics during a drop vertical jump 6 months after ACL reconstruction. This assessment can be used to screen individuals at much earlier time point who need additional focused treatment to improve their outcomes prior to return to play testing. Further, they can give the orthopedic surgeon additional data to educate the patient and family about the need to not return to higher level activities too early and reinforces the need to be compliant with rehabilitation in order to maximize results at the time individuals begin return to sport drills.