Characterization of knee alignment in children with mucopolysaccharidosis types I and II and outcome of treatment with guided growth

PURPOSE To describe knee alignment in children of different ages with severe mucopolysaccharidosis (MPS) I and II and the outcome of treatment with guided growth in a patient subgroup. METHODS This is a retrospective observational study of 58 knees in 29 children with severe MPS I and II. Long-leg standing radiographs were evaluated to determine mechanical axis deviation, mechanical lateral distal femoral angle and medial proximal tibial angle at different ages throughout childhood. The change in deformity in individual children over time is reported. 20 knees in 10 patients were treated with guided growth using eight-plates. Radiographic measurements were recorded at the time of plate insertion, at plate removal and at 1 year following removal. RESULTS At 8 years of age, all MPS I children and three-quarters of MPS II children had valgus knee alignment. There was deformity progression in two-thirds of MPS I knees and half of MPS II knees. Guided growth corrected the deformities. There was recurrence in most cases 1 year after plate removal. CONCLUSIONS Knee deformity is common in children with severe MPS I and II. Guided growth can be considered where there is significant and/or or progressive deformity with the aim of halting progression and correcting existing deformity and thus minimizing the risk of gross deformity. Patients should be aware of the high rate of recurrence and the need for repeat surgery.