Intercondylar Notch Becomes Steeper After Transphyseal Anterior Cruciate Ligament Reconstruction in Skeletally Immature Knees.

BACKGROUND

Transphyseal anterior cruciate ligament (ACL) reconstruction can be a reliable and safe treatment for skeletally immature patients, with low reported rates of major growth disturbances. However, more subtle knee morphologic and radiologic characteristics, such as the α-angle (sagittal orientation of the notch roof) and posterior tibial slope, may theoretically be affected by this surgical technique and potentially represent risk factors for ACL graft tears. The objective of this study was to compare radiologic knee morphology characteristics between the operated knee and the paired contralateral knee in skeletally immature patients following transphyseal ACL reconstruction.

METHODS

This is a retrospective matched within-subject case-control study on 25 skeletally immature patients with a radiologic follow-up 9 or more months after a transphyseal anatomic ACL reconstruction. The α-angle, medial posterior tibial slope, mechanical hip-knee-ankle angle, and leg length were 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 to 15.0). The α-angle was a mean of 3.3 degrees (SD=5.1) smaller, or more vertical, on the surgical knee than on the contralateral knee at a median of 2.1 years [interquartile range (IQR)=0.3 to 4.0], with mean α-angles of 36.6 degrees (SD=6.6 degrees) and 39.9 degrees (SD=5.3), respectively ( P =0.002). Other radiologic parameters were not significantly different between sides. A post hoc analysis showed a median side-to-side difference in α-angles of -5.0 (IQR: -7.0 to -1.9) in males versus 0.6 (IQR: -4.3 to 3.8) in females ( P =0.009).

CONCLUSION

Transphyseal anatomic single-bundle ACL reconstruction in skeletally immature patients is associated with a relative decrease in α-angle, or verticalization of the notch roof, after a median follow-up of 2 years. A greater impact in α-angle was observed in male patients.

LEVEL OF EVIDENCE: Level III-prognostic case-control study.