Steeper lateral posterior tibial slope and greater lateral‐medial slope asymmetry correlate with greater preoperative pivot‐shift in anterior cruciate ligament injury

Abstract

Abstract Purpose To investigate the association between posterior tibial slope (PTS) and preoperative pivot‐shift phenomenon in anterior cruciate ligament (ACL)‐injured knees. Methods Fifty unilateral ACL‐injured patients (mean age: 28.0 ± 11.4 years, 29 males) who underwent ACL reconstruction were retrospectively included. Patients with a history of injury to the ipsilateral knee joint, concomitant ligament injuries with ACL injury, and/or more than one year from injury to surgery, were excluded. Pivot‐shift tests were performed preoperatively under general anaesthesia using an electromagnetic measurement system, and tibial acceleration (m/s2) during the posterior reduction of the tibia was measured. Medial and lateral PTS (°) were measured respectively using high‐resolution CT images taken two weeks after surgery. Lateral‐medial slope asymmetry was calculated by subtracting medial PTS from lateral PTS (lateral‐medial PTS) and we evaluated the correlation between each PTS parameter (medial PTS, lateral PTS, and lateral‐medial slope asymmetry) and tibial acceleration during the pivot‐shift test. The level of significance was set at p < 0.05. Results Medial PTS was 4.9 ± 2.0°, and lateral PTS was 5.2 ± 1.9°. The lateral‐medial slope asymmetry was 0.3 ± 1.6° (range: ‐2.9 to 3.8). Tibial acceleration during the pivot‐shift test in the ACL‐injured knee was 1.6 ± 0.1 m/s2. Preoperative tibial acceleration was positively correlated with lateral PTS (r = 0.436, p < 0.01), and lateral‐medial slope asymmetry (r = 0.443, p < 0.01), while no significant correlation was found between preoperative tibial acceleration and medial PTS (r = 0.06, p = 0.70). Conclusion Preoperative greater tibial acceleration during the pivot‐shift test was associated with steeper lateral PTS and greater lateral‐medial slope asymmetry in ACL‐injured knees. These findings improve our understanding of anterolateral rotatory knee laxity by linking tibial bony morphology to quantitative measurement of pivot‐shift phenomenon. Surgeons should be aware that not only lateral PTS but also lateral‐medial slope asymmetry are the factors associated with preoperative pivot‐shift. Level of Evidence Level IV.

Keywords

• Anterior cruciate ligament
• Electromagnetic measurement system
• Pivot‐shift test
• Posterior tibial slope
• Quantitative measurement