Secondary deformity following paediatric tibial lengthening with circular fixators

To evaluate the incidence, magnitude, and risk factors for secondary angular deformity after tibial lengthening with a circular external fixator in skeletally immature patients. We hypothesized that younger age and low bone healing index would predispose to late valgus drift.

A retrospective review was conducted on 98 children who underwent tibial lengthening using a circular external fixator, with a minimum follow-up of one year. Radiographic assessment included full-length standing AP radiographs and lateral tibial views obtained preoperatively, at fixator removal, six months post-removal, and at final follow-up. Measured parameters included the mechanical Medial Proximal Tibial Angle, Center of Rotation of Angulation, and Posterior Proximal Tibial Angle. Risk factors for secondary deformity were analyzed using independent T test, Chi-Square test, Pearson test and multivariate logistic regression.

A valgus deformity greater than 3° developed in 36 patients (37%), primarily within the first six months after frame removal. Younger age at surgery (p = 0.017) and a bone healing index ≤ 40 days/cm (OR 2.3; p = 0.049) were significantly associated with valgus drift. A progressive valgus shift in CORA correlated with a shorter consolidation index (p = 0.021). Sagittal alignment showed a small but significant early decrease.

Secondary valgus deformity is a common and under-recognized complication following tibial lengthening with a circular external fixator in skeletally immature patients. Younger age at surgery and low bone healing index are the principal risk factors for this late angular drift. Furthermore, they question the efficacy of intentional frontal overcorrection to reliably prevent secondary deformity and suggest that additional corrective strategies may be required.