Increased lateral tibial posterior slope is related to tibial tunnel widening after primary ACL reconstruction

The purpose of the study was to determine the influence of femoral and tibial bone morphology on the amount of femoral and tibial tunnel widening after primary anatomic ACL reconstruction. It was hypothesized that tibial and femoral bone morphology would be significantly correlated with tunnel widening after anatomic ACL reconstruction.

Forty-nine consecutive patients (mean age 21.8 ± 8.1 years) who underwent primary single-bundle anatomic ACL reconstruction with hamstring autograft were enrolled. Two blinded observers measured the bone morphology of tibia and femur including, medial and lateral tibial posterior slope, medial and lateral tibial plateau width, medial and lateral femoral condyle width, femoral notch width, and bicondylar width on preoperative magnetic resonance imaging (MRI) scans. Tibial and femoral tunnel width at three points (aperture, mid-section, and exit) were measured on standard anteroposterior radiograph from 1 week and 1 year postoperatively (mean 12.5 ± 2 months). Tunnel width measurements at each point were compared between 1 week and 1 year to calculate percent of tunnel widening over time. Multivariable linear regression was used to analyze correlations between bone morphology and tunnel widening.

Increase in lateral tibial posterior slope was the only independent bony morphology characteristics that was significantly correlated with an increased tibial tunnel exit widening (R = 0.58). For every degree increase in lateral tibial posterior slope, a 3.2% increase in tibial tunnel exit width was predicted (p = 0.003). Excellent inter-observer and intra-observer reliability were determined for the measurements (ICC = 0.91 and 0.88, respectively).

Increased lateral tibial posterior slope is an important preoperative anatomic factor that may predict tunnel widening at the tibial tunnel exit. In regard to clinical relevance, the results of this study suggest that lateral tibial posterior slope be measured preoperatively. In patients with increased lateral tibial posterior slope, more rigid graft fixation and a more conservative physical therapy regiment may be preferred.