Anatomic Landmarks Utilized for Physeal-Sparing, Anatomic Anterior Cruciate Ligament Reconstruction: An MRI-Based Study (SS-68)

Abstract

<h3>Introduction</h3> ACL injury and reconstruction are becoming more common in the skeletally immature. Damage to the femoral physes and concomitant growth disturbance is a fear for the surgeon, patient, and family. The use of an all-epiphyseal technique on the femoral side is gaining popularity, but is technically difficult, requires intraoperative X-ray, leads to variable femoral tunnel locations and is non-anatomic as currently described. The purpose of the study was to develop an easily reproducible, anatomic reconstructive technique using intra- and extra-articular landmarks, which can reliably produce a femoral tunnel of adequate length and diameter, while at the same time avoiding the femoral physis. <h3>Methods</h3> 188 MRI studies were evaluated for children aged 6 to 17. Multiple anatomic landmarks were examined to determine optimal landmarks for ACL reconstruction (reproducibility, physeal safety, ease of identification, etc.). The extra-articular landmarks were the femoral origin of the popliteus tendon and the lateral epicondyle. The intra-articular landmark was the central portion of the femoral ACL origin. Using multi-plane computer software, points were plotted at the three landmarks in all three planes. Lines, depicting potential femoral tunnels were then drawn connecting the ACL origin to the popliteal insertion and the lateral epicondyle. Distances were then calculated for lengths of these tunnels, the shortest distance from the physis to these tunnels, the width of the femoral notch, and the width and height of the femoral condyles. Statistical analysis was then performed, comparing distances between age groups and sexes. 3D MRI Physeal-reconstruction employed, confirmed that the chosen landmarks spared the physes after tunnel placement. <h3>Results</h3> Tunnel lengths from the ACL origin to the popliteus insertion, tunnel lengths from the ACL origin to the lateral epicondyle, total femoral widths, and notch widths significantly differed across all age groups and sexes (p<0.001), as did condylar heights (p<0.03). Average distance to the femoral physis from the tunnel, which was from the ACL origin to the popliteus were 12 mm, independent of sex or age (p<0.94), and the shortest distance was 8 mm. This tunnel length averaged 30.1 mm in males and 27.4 mm in females (p<0.001), with an average of 25.6 mm in 6-year-olds and 30.2 mm in 17-year-olds. Average distance to the femoral physis from the tunnel, which was from the ACL origin to the lateral epicondyle were 8.8 mm in males and 8.9 mm in females (p<0.55), and this tunnel's average length was 34.3 mm in males and 31.6 mm in females (p<0.001). <h3>Conclusion</h3> Advantages to sparing the femoral physis when drilling the femoral ACL tunnel are obvious, however the biomechanical advantages of anatomic ACL reconstruction are still being studied. A combination of the two techniques may be the preferred technique for skeletally immature patients in the future. Drilling from the ACL origin to the popliteal insertion will produce an average tunnel length of 27-30 mm for graft incorporation and safely allow at least an 8-10 mm diameter tunnel in a patient 6 to 17 years old. Using the easily identifiable landmarks discussed in this paper will allow safe, reproducible anatomic ACL reconstructions without the need for tedious x-ray utilization intra-operatively.