Comparison of functional outcome and revision-free survivorship of proximal femoral megaprosthesis in paediatric patients with open versus closed triradiate physes

Aims: A high rate of hip subluxation has previously been reported after implantation of a proximal femoral megaprosthesis in children. The primary aim of this retrospective study was to compare the incidence of acetabular dysplasia and hip subluxation, and the functional outcome and revision-free survival between children with open and closed triradiate physes at the time of implantation of their prostheses. Methods: All patients were aged < 18 years and had a reconstruction with a non-extendable proximal femoral megaprosthesis. Extra-articular resections involving the acetabulum were excluded. Patients were classified into two groups: Group A with an open and Group B with a closed triradiate physis at the time of limb salvage surgery. A total of 36 patients were included; 15 in Group A and 21 in Group B. Their mean age at the time of surgery was nine years (2 to 13; SD 3.14) in Group A and 14 years (12 to 17; SD 1.57) in Group B, with a median follow-up duration of 103 months (IQR 54 to 110) and 58 months (IQR 38 to 106), respectively. Modes of failure and functional outcome were described using the modified Henderson classification and Musculoskeletal Tumor Society score, respectively. The two groups were compared using the Mann-Whitney U and chi-squared tests. The five-year revision-free survival was estimated using Kaplan-Meier and compared between groups using the log-rank test. Results: Limb length inequality, hip subluxation, and acetabular dysplasia were significantly higher in Group A (p < 0.001, p = 0.032, and p = 0.007, respectively). There were no significant differences in functional outcome, revision-free survival, or time-to-resurfacing between groups (p = 0.076, p = 0.469, and p = 0.587, respectively). Conclusion: Functional outcome and revision-free survival of proximal femoral megaprosthesis in children with an open triradiate physis are no different from those with closed physes, despite the high rate of acetabular dysplasia and hip subluxation.