Summary

Injury to the anterolateral structures was identified to be the most important risk factor for grade 3 pivot shift in acute ACL-injured knees when previously described osseous and soft-tissue parameters were comprehensively accounted for in an adequately powered study.

Abstract

Introduction

Pre-operative high-grade pivot shift (PS) has been reported to be associated with higher rates of anterior cruciate ligament (ACL) failure, persistent instability and inferior patient reported outcomes. The aetiology of a high-grade PS is multifactorial and numerous factors have been suggested to be responsible. However, the literature is conflicting. In part, this is due to numerous underpowered studies that also fail to account for known risk factors. The aim of this study was to determine risk factors for high-grade pivot shift with a particular emphasis on addressing the limitations of previous studies, therefore including a comprehensive evaluation of both soft-tissue and osseous parameters in an adequately powered study.

Methods

A prospective evaluation of consecutive patients undergoing acute ACL reconstruction (within 10 days of injury) was undertaken. An a priori sample size calculation was performed in order to ensure recruitment of an adequate number of patients. At the time of surgery, the pivot shift test was performed in a standardized manner and graded (International Knee Documentation Criteria). Details regarding patient and injury characteristics were recorded, as were details of injuries to soft-tissues structures including the menisci, anterolateral structures (ALS), medial collateral ligament (other multi-ligament injuries excluded) and articular cartilage. Osseous parameters (tibial slope and condylar ratios) were evaluated using established magnetic resonance imaging (MRI) protocols.

A multivariate logistic regression with Penalized Maximum Likelihood was used to identified risk factors associated with grade 3 pivot shift. Factors initially considered were those selected as statistically significant at the 25% threshold, or of previously reported clinical interest. A stepwise descending strategy was applied from the initial full model to determine the most parsimonious one.

Results

200 consecutive patients with a mean age of 28.3 +/- 9.8 years were included in the study. 67.5% of patients were male. 35 (17.5%) of patients had a high grade (grade 3) pivot shift and 165 (82.5%) had a low-grade pivot shift (grades 1 and 2). Univariate analyses demonstrated that injury to the ALS was the only significant risk factor for high grade pivot shift. This finding remained true when factors reaching the 25% threshold or of previously reported clinical interest were included in multivariate analysis (OR 13.49; 95% CI, 1.80-1725.53). Although previous studies have suggested that there are other important risk factors for high grade pivot shift, this did not hold true in the current study.

Conclusions

This comprehensive evaluation of soft-tissue and osseous factors has identified that injury to the ALS is the most important risk factor for grade 3 pivot shift in acute ACL-injured knees.