Summary

In a skeletally immature population MRI imaging was used to evaluate effects of transphyseal ACL reconstruction on physeal bar formation.

Abstract

Introduction

Transphyseal paediatric anterior cruciate ligament (ACL) reconstruction presents a risk of angular limb deformity and limb length discrepancy in the growing child. The exact pathogenesis of these growth-related complications remains poorly understood. It is thought that physeal bar formation adjacent to ACL graft tunnels is one possible cause. Other causes include metabolic stimulation of growth plate and physeal tethering due to graft tension.

Many previous studies on the effects of transphyseal ACL in paediatric populations review older children who are beyond skeletal maturity at time of surgery. This may underestimate the effect of transphyseal tunnel placement on the growing physis. In addition, a recently validated knee MRI bone age atlas improves our ability to distinguish between normal physiological physeal closure and iatrogenic growth plate injury.

This study evaluates the incidence of iatrogenic physeal bar formation in a paediatric population undergoing transphyseal ACL reconstruction using a previously validated high-resolution MRI protocol.

Methods

A prospective series of paediatric patients undergoing transphyseal ACL reconstruction (using hamstring autograft with double suspensory fixation) at a single institute was conducted from 2015-2021. High resolution 3T MRIs were performed at 12 months post-surgery. A validated knee bone age MRI atlas was then used to exclude patients with evidence of physiological physeal closure indicative of skeletal maturity at the 12 month post-surgery follow up. Patients with partial phsyiological physeal closure were included as long as greater than two-thirds of the physis was open and the area of closure was not within 1.5cm of the tunnels. 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

114 patients met the inclusion criteria for age. Following bone age screening of 12 month post-surgery MRI scans, 73 patients were excluded as they exhibited evidence of complete physiological closure of either the tibial or femoral physes. Of the remaining 41 patients (31 male; 10 female), all had open fibular physes, 12 had partial closure of the tibial physes, and 5 had partial closure of both the tibial and femoral physes. Mean age at time of surgery was 14.2 years (9.8-16.7). Mean tibial tunnel size 8.2 mm (SD 0.81 mm) and femoral tunnel size 7.9 mm (SD 0.88 mm). Two cases of physeal bar formation in the proximal tibia were found in two males (ages at surgery 14.2 and 14.7) both of whom had otherwise completely open physes. No leg length discrepancy was observed for these two patients at a 12 month long leg alignment scan. No cases of physeal bar formation were identified in the femur.

Conclusion

High resolution 3T MRI scan taken 12 months after transphyseal ACL reconstruction in a genuine paediatric population demonstrated two tibial physeal bar formations (6.6% incidence) and no femoral physeal bars. Neither of the two cases exhibited angular deformity or limb length discrepancy after 12 months. Central physiological closure of the tibial physis was commonly seen in this age group and may be easily confused with physeal bar formation.