Effect of Surgical Technique on Growth-Plate Violation in Simulated Adolescent ACL Reconstruction

OBJECTIVES: Increases in rates of participation and intensity of youth sports have led to elevated incidences of anterior cruciate ligament (ACL) injury and ACL reconstruction in adolescents. When applied to the skeletally immature patient, traditional reconstruction techniques lead to violations of the growth plates that carry with them the potential for disturbed growth and deformity. The purpose of this study was to compare the volume and location of the femoral growth plate violations that follow from the use of anteromedial (AM) and transtibial (TT) techniques. Growth plate disturbances were quantified by performing simulated reconstructions on computer models created from magnetic resonance (MR) images of adolescent knees. METHODS: MR scans were made of the right knees of 17 adolescent participants (10 M; 7 F; mean age 11.4 ± 2.0 y) positioned in both extension and in flexion. These scans were used to construct three dimensional computer models using Simpleware imaging software. An orthopedic surgeon, who was blinded to the location of the femoral physis in the models, specified the locations of simulated AM and TT tunnels. Tunnels with lengths of 20 mm, 25 mm, and 30 mm were placed for each subject with simulated drill diameters of 7 mm, 8 mm, and 9 mm (Figure 1). Normalized measures of both violation volume and the laterality of the violation were computed using routines custom written in MATLAB. RESULTS: For the AM approach, the mean normalized violation volumes for the 7 mm, 8 mm, and 9 mm drills were 4.14%, 5.02%, 6.01%, respectively, and 3.84%, 4.70%, 5.65% for the TT approach. The mean lateral positions of the violation for the AM approach, normalized by physis width for 7 mm, 8 mm, and 9 mm drills were 0.579, 0.590, 0.600, respectively, and 0.293, 0.290, 0.286 for the TT approach (with 0.000 corresponding to the femoral midline and 1.000 to the lateral cortex). Tunnels created using an AM approach disrupted a significantly larger percentage of the physis (p = 0.007) and produced a violation that was significantly more lateral (p < 0.001) when compared to the TT approach. Sixteen out of 153 (9 conditions x 17 subjects) simulated reconstructions for the AM approach and ten (out of 153) for the TT approach produced growth-plate violations greater than 8%. CONCLUSION: Use of an AM approach produced growth plate violations that were larger and more lateral than the violations generated using a TT technique. It has been suggested that more lateral violations are more likely to result in growth limitation and valgus deformity. In addition, violations accounting for more than 8% of the total physeal volume have been identified as posing a greater risk of growth disturbance. In the present study, younger subjects in general had larger physis violations, and violations of 8% or greater tended to occur when using a larger diameter drill to create a longer tunnel, regardless of the approach. Caution should be taken when using larger diameter drills and tunnel lengths 25mm or greater, especially in younger subjects for whom growth-plate violations may be greater than 8% for the AM approach.