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Neck-shaft angle remodelling after derotation varus osteotomy for severe Perthes disease.

Sixteen patients with a severe form of Perthes disease who underwent containment derotation varus osteotomy (DVO) of the proximal femur were studied retrospectively for the neck-shaft angle (NSA) remodelling. Analysis of results after a mean follow-up of 7 years (minimum of 5 years and maximum of 8.7 years) showed mean preoperative, immediate postoperative and the latest follow-up neck-shaft angles (NSA) as 135 degrees, 110 degrees (none had varus less than 90 degrees) and 125 degrees, respectively. A statistically significant relationship between NSA remodelling and the immediate post-op NSA (P = 0.0035) was established. Patients with smaller postoperative NSA showed better remodelling compared with those who had higher degrees of NSA immediately after the surgery. No significant relationship was found between the degree of NSA remodelling and the patient's age at diagnosis, age at surgery, severity of Perthes or the Stulberg grading at maturity. The authors conclude that up to 90 degrees or more varization after DVO for Perthes disease can remodel with time, and the remodelling process is independent of the patient's age at diagnosis, age at surgery, or severity of Perthes or Stulberg grading at maturity.