The impact of bone morphology on the outcome of the pivot shift test: a cohort study

Abstract

BackgroundThe presence of a positive pivot shift after surgical repair of the ACL is considered an important indicator of a failed reconstruction. The ability to predict the result of a pivot shift test after an ACL reconstruction using variables that can be measured prior to surgery could provide an indication of which patients may be at-risk of a poor surgical outcome.The purpose of this study was to determine whether structural characteristics of the femur and tibia, measured using plain radiographs, were associated with the result of the pivot shift test in unilateral ACL reconstructed patients.MethodsSixteen patients who had undergone unilateral ACL reconstruction were divided into two groups based on the results of manual pivot shift testing: 1) Pivot group; and 2) No pivot group. All patients had standing true lateral radiographs of both knees. Structural measurements of the tibia and femur were made on both knees. In addition, two new variables were created to describe the tibiofemoral mismatch: 1) Femur Tibia Size Ratio (FTSR); and 2) Tibia to Posterior Femoral Condyle Ratio (TPFCR). These measures were compared within groups and between groups.ResultsNone of the individual structural characteristics were significantly different when compared between groups. No individual structural characteristics had a significant association with the presence of a positive pivot shift. When a between-group analysis was performed, both the FTSR (p < 0.03) and the TPFCR (p < 0.01) were significantly different between the Pivot group and the No Pivot group. A larger FTSR ratio, or a larger femur relative to the tibia, was associated with a positive pivot shift. A smaller TPFCR ratio, or a smaller tibial depth relative to the depth of the lateral posterior femoral condyle, was associated with a positive pivot shift.ConclusionsStructural characteristics in the lateral femoral condyle and lateral tibial plateau were found to be associated with the presence of a positive pivot shift. These characteristics could separate between patients in the Pivot group and the No Pivot group. Two indices, the FTSR and the TPFCR, provided better predictive value than individual characteristics in identifying patients with a knee that was structurally “at-risk” for developing a positive pivot shift.

Pivot Shift Syndrome of the Knee

“…15 The lateral femoral condylar to tibia size ratio is usually above 1.42 and more evident in some knees especially females. 8 Femoral movement over the tibia in early flexion consists of rolling and gliding at a ratio of 1:2. This progresses to a 1:4 ratio during later flexion.…”

“…7 The tibial eminence with its twin spines acts as a boney barrier to excessive tibial rotation and translation. 8 Increasing rotational torque will force the femur to ascend the tibial eminence thus producing distraction forces which are strongly opposed by the collateral ligaments, tendons, and capsule. 9 Named for their tibial origins, the ACL has two recognized bundles oriented at 40°to the long axis of the femur.…”

“…The final alignment in full extension has 10° of lateral tibial rotation under the femur 7 . The tibial eminence with its twin spines acts as a boney barrier to excessive tibial rotation and translation 8 . Increasing rotational torque will force the femur to ascend the tibial eminence thus producing distraction forces which are strongly opposed by the collateral ligaments, tendons, and capsule 9…”

The Pivot Shift: Current Experimental Methodology and Clinical Utility for Anterior Cruciate Ligament Rupture and Associated Injury

“…Branch et al examined a group of patients who had undergone ACL reconstruction and evaluated their bony morphology radiographically. A significantly higher rate of post-operative pivot shift was observed when patients had a higher femur-tibia size ratio (FRSR), when the femur was larger relative to the tibia, or a smaller tibia to posterior femoral condyle ratio (TPFCR), and when there was smaller tibial depth relative to the depth of the lateral posterior condyle [51].…”

A decreased ratio of height of lateral femoral condyle to anteroposterior diameter is a risk factor for anterior cruciate ligament rupture

“…Among the anatomical factors, the influence of the anatomic variance of the lateral compartment has recently attracted considerable research interest [5]. Some studies have shown that the spherical shape of the lateral femoral condyle has a clear relationship with the relative axial movement of tibiofemoral joint and the ACL rupture [6,7]. The purpose of this study was to describe the distal curvature of the lateral femoral condyle use ratio of height of lateral femoral condyle to anteroposterior diameter (HAPR), and to evaluate its correlation with ACL rupture.…”