Validation of quantitative measures of rotatory knee laxity

Background: Prior attempts to quantify the pivot-shift examination have been too invasive or impractical for clinical use. A noninvasive method for quantifying rotatory knee laxity is needed. Hypothesis: Greater quantitative measurements of rotatory knee laxity (both of the involved knee as well as compared with the contralateral healthy knee) are associated with an increasing clinical pivot-shift grade. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 103 patients undergoing anatomic single-bundle anterior cruciate ligament (ACL) reconstruction at 4 international centers underwent a standardized pivot-shift test preoperatively on both knees while anesthetized. Clinical grading of the pivot shift was performed according to the International Knee Documentation Committee (IKDC) knee ligament rating system. Two different quantitative technologies were used to measure rotatory knee laxity: an inertial sensor and an image analysis were independently used to measure tibial acceleration and lateral compartment translation, respectively, during the pivot-shift test. Patients were dichotomized to "high-grade" (abnormal and severely abnormal) or "low-grade" (normal and nearly normal) rotatory knee laxity groups based on the clinical pivot-shift test result of the involved side. Tibial acceleration and lateral compartment translation of the involved knee and the side-to-side difference between the involved and contralateral knees were separately compared between the high- and low-grade rotatory knee laxity groups utilizing t tests; significance was set at P <.05. Results: Forty-three patients were in the low-grade rotatory knee laxity group, and 60 patients were in the high-grade rotatory knee laxity group. Patients in the high-grade knee laxity group had significantly higher lateral compartment translation as measured with the image analysis (involved knee: 3.8 ± 2.3 mm; side-to-side difference: 2.5 ± 2.4 mm) compared with patients in the low-grade group (involved knee: 2.0 ± 1.4 mm; side-to-side difference: 1.4 ± 1.5 mm) (both P <.01). As measured with the inertial sensor, tibial acceleration for patients in the high-grade group was significantly higher (involved knee: 7.2 ± 5.3 m/s2; side-to-side difference: 4.2 ± 5.4 m/s2) compared with patients in the low-grade group (involved knee: 4.2 ± 1.6 m/s2; side-to-side difference: 1.2 ± 1.2 m/s2) (both P <.01). Conclusion: The inertial sensor and image analysis techniques were able to detect differences between low- and high-grade pivot-shift test results. A quantitative assessment of the pivot-shift test could augment the diagnosis of an ACL injury and improve the ability to detect changes in rotatory knee laxity over time.