Surgical Treatment of Hip Instability in Patients With Lower Lumbar Level Myelomeningocele: Is Muscle Transfer Required?

BACKGROUND: Treatment of hip instability in patients with lower lumbar level myelomeningocele is clinically challenging. Muscle transfer procedures, release of contractures, and intertrochanteric varus-rotation osteotomies have been described to restore weak or absent abductor strength as well as relocation of the hip. However, controlled trials evaluating hip instability in lower lumbar myelomeningocele are limited in the current literature. QUESTIONS/PURPOSES: The purposes of this study were to compare the (1) radiographic evidence for joint stability; (2) clinical outcomes (including abductor strength, ambulatory ability, and residual use of orthoses); and (3) complications between patients undergoing combined periarticular contracture releases and bony procedures with and without external oblique abdominal muscle transfers.
METHODS: Between 2004 and 2013, 14 pediatric patients (16 hips) were treated for hip instability secondary to myelomeningocele using releases with or without muscle transfer. From those, 13 patients (15 hips) with a mean age of 6 years who had L3 to L5 level involvement were evaluated retrospectively. The patients were separated into two groups. Nine hips (in eight patients) were treated by performing a combination of external oblique abdominal muscle transfer to the greater trochanter, periarticular release of contractures, and bony procedures. These were compared with six hips (five patients) treated by performing a combination of periarticular release of contractures and bony procedures without external oblique abdominal muscle transfer. This study compared the results between two surgeons, one of whom always performed these muscle transfers in this setting and the other who never performed muscle transfer during the study period. The patients were clinically followed up at a mean of 41 months (range, 14-122 months); none of the patients was lost to followup. Radiographic evaluation criteria included Reimer's migration index, acetabular index, femoral neck-shaft angle, pelvic obliquity, and the presence of scoliosis. Clinical evaluation included muscle strength examination, periarticular contractures, necessity for using orthoses as walking aids, and Hoffer criteria of mobility. All complications were also noted from a chart review.
RESULTS: There were no differences between the two groups regarding postoperative femoral head localization, reflecting the presence or absence of residual subluxation, according to Reimer's index (Reimer's index = 32%; range, 10%-40%, in the muscle transfer group compared with 27%; range, 15%-43%, in the no-transfer group at latest followup; p = 0.723). Postoperatively, abductor strength improved in the group treated with external oblique transfer compared with the group treated without muscle transfer (median improvement of 2 versus 0, p = 0.02), but this improvement neither resulted in a clinically important difference in Hoffer criteria of mobility (no change was detected in either group) nor decreased the need for use of an orthosis (no change was detected in either group). With the numbers available, there was no difference with respect to complications between the two groups (two complications versus one).
CONCLUSIONS: External oblique abdominal muscle transfer did not provide a clinically important improvement in functional recovery when compared with patients with L3 to L5 myelomeningocele and hip instability who were treated without it. We therefore do not recommend a routine muscle transfer procedure during the operative management of hip instability in patients with lower lumbar level myelomeningocele. LEVEL OF EVIDENCE: Level III, therapeutic study.