Change in angle of depressed medial tibial plateau following extra-articular mechanical realignment surgery in children with Blount's disease who presented late for treatment.

Introduction: The aim of this study was to determine whether any change in degree of medial tibia plateau depression after extra-articular mechanical realignment surgery was observed in children with Blount's disease who presented late for treatment in their adolescence and young adulthood.

Methods: We retrospectively reviewed the radiographic parameters of 22 patients (32 lower limbs) with Blount's disease who underwent gradual correction of deformity using a ring external fixator without surgical elevation of the depressed medial tibial plateau at a mean age of 15 (range 10-37) years. Preoperative and postoperative angles of depressed medial tibia plateau (ADMTPs) of the same patient were compared for any significant change. Normally distributed data were analysed using Student's t -test when comparing two groups or one-way analysis of variance when comparing more than two groups. Skewed data were analysed using Mann-Whitney test.

Results: After extra-articular mechanical alignment surgery, statistically significant improvements in medial tibial plateau depression were seen in the infantile ( P = 0.03) and juvenile ( P = 0.04) Blount's subgroups. Change in ADMTP was greater in patients who were operated on at age <17 years, before skeletal maturity ( P = 0.001). The improvement was likely due to ossification of unossified cartilage at the posteromedial proximal tibia and the remodelling potential of proximal tibia physis after mechanical realignment.

Conclusion: Improvement of medial tibia plateau depression is possible after mechanical realignment without surgical hemiplateau elevation in cases of infantile and juvenile Blount's disease that present late for treatment, especially when the operation is performed before 17 years of age.