A long term follow-up study of the development of hip disease in Mucopolysaccharidosis type VI

- Hip problems in Mucopolysaccharidosis type VI lead to severe disability.
- Study of hip development over time in MPS type VI by image assessment (quantitative and qualitative).
- Abnormal os ilium and acetabulum in MPS VI present very early in life. Later in life femoral head abnormalities develop.
- Hip deformities are severe in all patients, in contrast to other disease manifestations.

Hip problems in Mucopolysaccharidosis type VI (MPS VI) lead to severe disability. Lack of data on the course of hip disease in MPS VI make decisions regarding necessity, timing and type of surgical intervention difficult. We therefore studied the development of hip pathology in MPS VI patients over time.Data were collected as part of a prospective follow-up study. Standardized supine AP pelvis and frog leg lateral radiographs of both hips were performed yearly or every 2 years. Image assessment was performed quantitatively (angle measurements) and qualitatively (hip morphology). Clinical burden of hip disease was evaluated by physical examination, six minute walking test (6MWT) and a questionnaire assessing pain, wheelchair-dependency and walking distance.A total of 157 pelvic radiographs of 14 ERT treated MPS VI patients were evaluated. Age at first image ranged from 2.0 to 21.1 years. Median follow up duration was 6.8 years. In all patients, even in the youngest, the acetabulum and os ilium were dysplastic. Coverage of the femoral head by the acetabulum improved over time, but remained insufficient. While the femoral head appeared normal in the radiographs at young age, the ossification pattern became abnormal in all patients over time.In all patients the distance covered in the 6MWT was reduced (median Z scores − 3.3). Twelve patients had a waddling gait. Four patients were partially wheelchair-dependent and ten patients had limitations in their maximum walking distance.In conclusion, clinically significant hip abnormalities develop in all MPS VI patients from very early in life, starting with deformities of the os ilium and acetabulum. Femoral head abnormalities occur later, most likely due to altered mechanical forces in combination with epiphyseal abnormalities due to glycosaminoglycan storage. The final shape and angle of the femoral head differs significantly between individual MPS VI patients and is difficult to predict.