Summary

This 3D model simulation study defines safe drilling zones and orientations for Lateral Extra-articular Procedures in epiphyseal ACL reconstruction, in patients with open growth plates. It identifies the spatial position of the anterolateral ligament relative to the physis, quantifies physeal damage and prevents epiphyseal ACL tunnel collision.

Abstract

Purpose

Lateral Extra-articular Procedures (LEAP) are increasingly being used during Anterior Cruciate Ligament (ACL) reconstruction in patients with open growth plates. These procedures have shown a reduction in graft failure among high-risk patients. To date, only few cadaveric studies have reported the anatomic position of the anterolateral ligament (ALL) relative to the physis. This comprehensive study identifies the relative ALL's position, quantifies physeal damage, and defines safe zones and orientations for LEAP to avoid physeal injury and prevent epiphyseal ACL tunnel collision in a three-dimensional (3D) model simulation.

Methods

Magnetic resonance images (MRI) of patients aged 10-17 were analyzed to create 3D models of the distal femur and distal femoral physis (DFP) using developed software. In each model, the femoral footprints of the ACL and ALL were identified based on cadaveric and imaging studies. ALL drillings were simulated with 4-mm drills and 20 mm depth, starting from ALL-femoral insertion at all possible angles within a 90° cone. ACL tunnels were simulated with 8-mm drills, starting from ACL-femoral insertion with Anterolateral (AL) and Direct Lateral (DL) directions—the most common approaches for epiphyseal ACL reconstruction. Safe zones for drilling or fixation anchoring for LEAP were defined as directions where neither the DFP, ACL tunnel, nor articular surface were breached. Physeal injury was quantified as a percentage of total physeal volume. Statistical analysis was performed using Student’s t-test, one-way ANOVA, Mann-Whitney, and Kruskal-Wallis tests, significance at p<0.05.

Results

A total of 52 knees with open growth plates were obtained, with a mean age of 13.1 years [SD 2], 44.2% women. In 42% of cases, the ALL footprints were located beneath the lateral border of the DFP, while the rest were positioned between the borders. The median distance from the center of the ALL to the DFP was 1.74 mm [IQR 2.13], decreasing with age (p < 0.01), without differences regarding sex. Maximum DFP damage occurred with more horizontal drilling (10° cephalic, 5° posterior), resulting in 1.67% [SD 0.78] physeal injury, with no significant differences by sex or age. The optimal directions for safe zones in drilling or fixation anchoring during LEAP were 18° anterior and 21° distal from the ALL footprints in DL epiphyseal reconstruction approaches, with a posterior shift observed with age (p = 0.006). For AL approaches, the optimal directions were 17° posterior and 18° distal, with a greater angular area compared to DL epiphyseal approaches (p = 0.009). No other significant age-related or gender-specific variations were observed.

Conclusions

This 3D model simulation study identifies the ALL's position relative to the physis, quantifies physeal damage, and defines safe zones and orientations for LEAP drilling and fixation anchoring. The ALL was located between or beneath the lateral border of the DFP, decreasing their distance with age. Maximum DFP damage occurred with more horizontal drilling (10° cephalic, 5° posterior). This study establishes definitive safe zones for tunnel orientations for AL and DL epiphyseal reconstruction approaches, with wider angular area with AL approaches—while avoiding physeal damage and preventing epiphyseal ACL tunnel collision.