Summary

Anterior Cruciate Ligament (ACL) all-epiphyseal technique aims to avoid the distal femoral physis, nevertheless other adjacent structures could be at risk. This 3D MRI model study identified two safe zones for the femoral tunnel drilling during this technique in patients with open growth plates. The anterolateral (AL) direction showed a larger safe area and longer tunnel length.

Abstract

Purpose

Damage to the distal femoral physis (DFP) should be minimized during Anterior Cruciate Ligament (ACL) reconstructions in patients with open growth plates. All-epiphyseal technique aims to avoid the DFP, nevertheless, other adjacent structures such as the articular surface, the lateral collateral ligament (LCL), the anterolateral ligament (ALL), and the popliteus tendon (PT) could be at risk. Current knowledge about safes zones and ideal tunnel orientation is limited. The objective of this study was to investigate the safe zones for femoral tunnel drilling in all-epiphyseal ACL reconstructions and its relation with at-risk structures.

Methods

Eighty magnetic resonance images (MRI) from patients aged 10 to 17 were obtained and randomly sampled from the institutional database, with a homogeneous distribution of age and sex. A de novo software was developed to obtain three-dimensional (3D) models of the distal femur and DFP. In each model, the femoral footprints of the ACL, LCL, ALL, and PT were identified, as established in cadaveric and imaging studies by previous authors. Drillings were simulated using 7-, and 8-mm drills, starting from the ACL femoral insertion at every possible angle within a 90° cone. Safe zones were defined as the direction in which neither the DFP, LCL, ALL, PT nor articular surface were violated. The segmentation, measurement, and statistical analysis were developed in MATLAB software. Statistical analysis was conducted using Student’s t-test, one-way ANOVA, and simple linear regression. Statistical significancy p<0.05.

Results

A total of 52 knees with open DFP were obtained, with a mean age of 13.1 [SD 2], 44.2% women. Two safe zones were found: an Anterolateral (AL) and a Direct Lateral (DL) direction. For both 7- and 8-mm tunnels, the AL orientation had a larger safe area and a longer drilling length than the DL (p<0.01). The mean safe area of the AL direction for the 7- and 8-mm tunnels were 408 y 384 mm2 respectively (p<0.01). The mean safe area of the DL orientation for the 7- and 8-mm tunnels were 236 y 219 mm2 respectively (p<0.01). The mean length for the AL direction was 34.2 mm y and for the DL was 27.4 mm (p<0.01). There were no statistical differences between sex or age.

Conclusions

This MRI simulation model study identified two safe zones for the femoral tunnel drilling during the all-epiphyseal ACL reconstruction technique in patients with open growth plates. The AL direction showed a larger safe area and longer tunnel length.