Case Diagnosis- Surgical Hip Relocation with Femoral Derotational Osteotomy in Two Children With Spinal Muscle Atrophy Type 2 Treated with Nusinersen
Case Description-We present two cases of femoral derotational osteotomy for hip subluxation in children with spinal muscle atrophy type 2 currently treated with Nusinersen. Reimer’s migration index (MI) was used pre-operatively and post-operatively to quantify hip subluxation. The first patient is a 4-year-old male with significant bilateral hip subluxation with an MI of 40% bilaterally treated with 9 doses of Nusinersen. Post-operatively hips have remained fairly stable with only minimal subluxation. Post-operative migration indices are as follows: 1 month (20% right, 10% left), 3 months (20% right, 15% left), 10 months (25% right, 20% left) and 13 months (25% right, 15% left).
The second patient we present is a 5-year-old male with significant hip subluxation prior to surgical intervention treated with 11 doses of Nusinersen. His MI was 40% on the right and 70% on the left. At approximately 1 and 9 months post-operatively his hips remain fully contained in x-ray.
Discussion-Historically children with spinal muscular atrophy do not have their hips surgically relocated after subluxation because studies have shown that the hips are very likely to dislocate again in due time. With Nusinersen, the phenotype of spinal muscular atrophy has changed. Many children are able to reach previously unattainable developmental milestones such as standing and walking which is likely the results of improvements in muscle tone. It is now more important to protect the hip anatomy to maximize functionality in this changing population.
Conclusions-Surgical hip relocation is potentially promising in children with hip subluxation secondary to low tone from spinal muscle atrophy who have been treated with Nusinersen. Further follow-up is needed to determine the long-term outcomes in this population.