Transphyseal ACL reconstruction resulted in a low incidence of tibial physeal bars at 1-year follow-up

Introduction
Transphyseal anterior cruciate ligament reconstruction (ACLR) is associated with a risk of angular limb deformity and limb length discrepancy particularly when there is a significant period of growth remaining.
Previous studies on the effects of transphyseal ACLR have used inconsistent methodology to estimate bone age, and therefore subjects may have underestimated the effect on the physis.
This study sought to evaluate the incidence of iatrogenic physeal bar formation following ACLR using high-resolution MRI and a validated bone age atlas.

Methods
A prospective series of patients undergoing transphyseal ACLR at a single institute, with high resolution 3T MRIs at 12 months, were included. MRI-validated knee bone age atlas was then used to exclude patients with evidence of physiological physeal closure. The remaining skeletally immature MRI scans were appraised by two independent reviewers for the presence of physeal bar formation adjacent to transphyseal ACL tunnels.

Results
From 142 patients undergoing transphyseal ACLR with post-operative MRI, 94 patients were found to exhibit evidence of complete closure of either the tibial or femoral physis and were excluded. 48 patients (38 male – mean age 14.1; 10 female – mean age 13.9) meeting inclusion criteria were included. Mean tibial tunnel diameter was 8.2 mm (SD ± 0.81) and mean femoral tunnel diameter was 7.9 mm (SD ± 0.88). There were two cases (4.2% of total) of physeal bar formation in the proximal tibia in males (aged 14.2 and 14.7 years) with otherwise open physes. No leg length discrepancy was observed for these patients at a 12 months. No cases of femoral physeal bar formation were identified in our cohort.

Conclusion
High resolution 3T MRI scan performed 12 months after transphyseal ACL reconstruction demonstrated 4.2% incidence of tibial physeal bars and no femoral physeal bars. Neither of the cases physeal bar cases exhibited angular deformity or limb length discrepancy. Central physiological closure of the tibial physis was commonly seen in this age group and may be easily confused with physeal bar formation.