Diagnostic Value of Knee Arthrometry in the Prediction of ACL Strain During Landing

OBJECTIVES: Excessive knee joint laxity may decrease overall joint stability and increase the risk of anterior cruciate ligament (ACL) injury during high risk activities. Despite the frequent clinical use of knee arthrometry, as an accurate and valid method for evaluation of knee laxity, no data exists to correlate instrumented laxity measures and ACL strain during dynamic high-risk activities. The purpose of this study was to evaluate relationships between instrumented anterior knee laxity measurements and ACL strain during simulated bi-pedal landing (as an identified high-risk injurious task). We hypothesized that a strong correlation would be observed between ACL strain and arthrometry displacement, and that specimens with greater anterior knee laxity would demonstrate increased peak ACL strain during landing. METHODS: 20 cadaveric lower limbs (46±6 years, 10 female and 10 male) were tested using a CompuKT knee arthrometer to measure anterior knee joint laxity. Each specimen was tested under four continuous cycles of A-P shear force (±134 N) applied to the tibial tubercle. To quantify ACL strain, a DVRT displacement transducer was arthroscopically placed on the ACL (AM-bundle), and specimens were retested. Subsequently, bi-pedal landing from 30 cm was simulated on a subset of 14 specimens (45±5 years, 6 female and 8 male) using a novel custom-designed drop-stand. Paired sample t-tests, and a general linear model were used to evaluate changes in joint laxity and ACL strain. RESULTS: During simulated drawer tests, 134 N of applied anterior drawer load produced an average 3.1±1.1 mm peak anterior tibial translation and 4.9±4.3% peak ACL strain. Anterior drawer load was a significant determinant of anterior tibial translation (p<0.0005) and peak ACL strain (p=0.02). A strong correlation (r=0.78, P<0.0005) was observed between anterior tibial translation and ACL strain during simulated drawer tests. Cadaveric simulations of landing produced an average 4070±732 N axial impact load representing the generated ground reaction force during landing following a jump. Simulated landing significantly increased peak anterior tibial translation to 10.4±3.5 mm and peak ACL strain to 6.8+2.8 % (p<0.0005) compared to pre-landing conditions. Impact-induced anterior tibial translation was a significant factor in peak ACL strain (p=0.001). Strong correlations were observed between peak ACL strain during landing and anterior tibial translation quantified by knee arthrometry (Figure 1). CONCLUSION: This work represents the first cadaveric study to establish a strong correlation between arthrometrically measured anterior knee joint laxity and peak ACL strain during dynamic landing (as a high-risk injurious condition). Experimental findings support the tested hypothesis, as a strong correlation between arthrometry displacement collected during laxity tests and concurrent calculated ACL strain was demonstrated. Instrumented measures of anterior knee laxity were predictive of peak ACL strain during landing, while specimens with greater knee laxity demonstrated higher levels of peak ACL strain during landing. Considering ACL strain as an established quantifiable measure of ACL injury risk, current findings highlight the importance of instrumented anterior knee laxity assessments as a potential indicator of ACL injury risk in addition to its clinical utility in the evaluation of ACL integrity.