Paper # 128: Inconsistent Manual Techniques Make Qualitative and Quantitative Analyses of the Pivot Shift Test Difficult in Both ACL-Deficient and Intact Knees

Abstract

Recent attempts have been made to quantify the results of the pivot shift test. The purpose of this study was to compare clinical grade of the pivot shift with instrumented measures collected simultaneously during the test, as well as to the results of a robotic knee test (RKT). Two complete cadaveric lower bodies (pelvis and bilateral lower extremities) were prepared for testing. All knees were evaluated arthroscopically by a single surgeon. One specimen was noted to be ACL-deficient with moderate arthritic changes, and the other specimen was found to have all ligaments intact with moderate arthritic changes to the medial femoral condyle. Five board-certified orthopaedic surgeons that were blinded to the side and nature of the injury bilaterally performed the following battery of clinical tests on both cadaveric specimens: Lachman, anterior drawer, posterior drawer, pivot shift, dial test at 30° of flexion, and varus and valgus stress tests at both 0° and 30° of flexion. Each surgeon verbally graded laxity during each test, and upon completion of all of the tests, each surgeon gave his impression of diagnosis. The surgeons were blinded to each other's clinical exam results and diagnoses. In addition, electromagnetic sensors were rigidly fixed to each femur and tibia, and the electromagnetic system was used to quantify the amount of anterior tibial translation (ATT), internal rotation (IR), and valgus rotation (VL) during the pivot shift tests. The cadavers were also evaluated using a non-invasive RKT system. The RKT bilaterally cycled the knees into anterior and posterior translation (ATT, PTT), internal and external rotation (IR, ER), and varus and valgus rotation (VR, VL). Three cycles of each motion were performed, and both the amount of torque applied and the rate at which the torque was applied were controlled by the system. Following 3 preconditioning cycles, 3 additional test cycles were performed and the 3-dimensional position and orientation data were collected with an electromagnetic motion analysis system in order to determine 3-dimensional joint kinematics. The amount of ATT and IR that occurred during the pivot shift phenomenon were coupled in order to determine the relative magnitude of medial and lateral compartment translation. Kinematic data collected during the manual and robotic exams were compared with the clinical grade of laxity and diagnoses given by each of the surgeons. When asked to perform the pivot shift test, 4/5 surgeons performed the test consistent with the technique described by Slocum et al, in which the test is initiated with the knee internally rotated in full extension in order to examine for the reduction event of an already subluxated tibia. One surgeon performed the test consistent with the technique described by Losee et al, in which the test is initiated in flexion and is performed to examine for the presence of the subluxation event. All surgeons were in agreement that the intact knee demonstrated negative pivot shift results. On the contrary, while all surgeons responded that the ACL-deficient knee demonstrated a positive pivot shift test, the grades of test ranged from 1 to 2+, with only 2 surgeons agreeing on the grade of laxity. The grade of laxity did not appear to be related to ATT (8.1±0.8 mm), lateral compartment translation (10.3±1.3 mm), IR (5.3°±4.7°), or VL (3.5°±2.9°). The RKT results demonstrated that the maximum amount of ATT was 10.3 mm, maximum IR was 4.2°, and maximum VL was 8.5°. Furthermore, using similar calculations as to what was used during the pivot shift, the amount of lateral compartment translation was determined to 11.3 mm. Clearly the surgeon does not use his ability to kinematically move the tibia pathologically with respect to the femur to determine the pivot grade. No absolute kinematic measures, either individually or combined, correlated with the surgeon's clinical grade of pivot shift. This suggests that the surgeon's clinical grade of pivot shift may not be based upon kinematics alone but may include information related to force, speed and acceleration between the tibia and femur. Furthermore, under clinical situations the amount, the speed, and the acceleration of force application are not controlled between patients or surgeons, thus, contributing to the inconsistencies of the pivot shift grading system currently available.