Summary

This paired case-control study of transphyseal anatomic single-bundle ACL reconstruction in skeletally immature patients has shown that a relative steepening of the femoral intercondylar notch, or verticalization of Blumensaat’s line, occurs after surgery when compared to the intact knee, after an average follow-up of more than 3 years. The impact seems greater in Tanner stage 1 and 2 patients.

Abstract

Objective

The aim of this study was to characterize changes in knee α-angle (sagittal orientation of the notch roof), posterior tibial slope, leg length, lower limb alignment, following transphyseal anterior cruciate ligament (ACL) reconstruction in skeletally immature patients. α-angle, posterior tibial slope and lower limb alignment have previously been shown to affect the risk of ACL reconstruction failure.

Hypothesis

Following transphyseal ACL reconstruction in skeletally immature patients radiological sagittal orientation of the femoral notch roof (α-angle) and medial posterior tibial slope will be significantly lower in the operated knee compared to the paired control knee, and leg length and mechanical hip-knee-ankle angle will remain equivalent at a minimum of 9 months follow up.

Methods

Retrospective matched within-subject case-control study on 25 skeletally immature patients with a radiological follow-up 9 or more months after a transphyseal ACL reconstruction. Sagittal orientation of the femoral notch roof (α-angle), medial posterior tibial slope, mechanical hip-knee-ankle angle and leg length was assessed with a biplane x-ray imaging system (EOS) with the nonoperative limb used as an internal control.

Results

The mean chronological age of the cohort was 11.8 years (range 8.3-15.0). The α-angle was a mean of 3.3° (SD= 5.1) smaller on the surgical knee than on the contralateral knee at a median of 2.1 years (IQR = 0.3 – 4.0), with mean α-angles of 36.6° (SD= 6.6°) and 39.9° (SD= 5.3) respectively (p=0.002). Other radiological parameters were not significantly different between sides. A post hoc analysis showed a side-to-side difference in α-angles of -4.2° (SD = 5.4) in Tanner 1 and 2 patients
versus -0.8° (SD = 3.7) in Tanner 3 patients (p=0.002).

Conclusion

Transphyseal anatomic single-bundle ACL reconstruction in skeletally immature patients causes a relative decrease in α-angle, or verticalization of Blumensaat’s line, after a median follow-up of 2 years. The impact seems greater in Tanner 1 and 2 patients.