A new quantitative method for pivot shift grading

The purposes of the study were to evaluate and to quantify the pivot shift phenomenon by using a small and easy to handle measuring device for pivot shift quantification.

Twenty patients (forty knees) with primary torn anterior cruciate ligaments (ACL) were tested under anesthesia, graded by the examiner and by the device according to the IKDC classification [normal (0), glide (1), clunk (2), and gross (3)]. For the grading by the device, a femoral and a tibial miniature inertial sensor measured the acceleration and the angular velocities. Three parameters were used for pivot shift identification and quantification: (1) difference between the positive and negative acceleration peak value (a(diff)), (2) the maximum jerk (j(max)), and (3) the standard deviation (SD(a)) of the acceleration. The ratio between the ACL-deficient and the intact knees was calculated in order to normalize the data.

The pivot shift phenomenon could be identified, and all three parameters showed significant higher values in the ACL-deficient knees compared to the intact knees (p < 0.05). The grading by examiner did not significantly correlate with a(diff) (p = 0.38; r = 0.21), j(max) (p = 0.36; r = -0.22), SD(a) (p = 0.65; r = 0.11), and grading by the device (p = 0.62; r = 0.12).

The present study has shown that the quantification of the pivot shift test is practicable when inertial sensors are used. The results have shown that the subjective grading of the pivot shift test does not correlate well with objective quantification.