Impact of sagittal and coronal pelvic tilt on hip subluxation in non-ambulatory flaccid neuromuscular scoliosis patients following spinal correction.

Purpose: To evaluate the actual change in clinical hip pain and hip migration after operation for non-ambulatory flaccid neuromuscular (NM) scoliosis and investigate whether there is an association between hip migration and coronal/sagittal pelvic tilt (CO-PT/SA-PT).

Patients And Methods: This retrospective, single-center, observational study evaluated a total of 134 patients with non-ambulatory flaccid neuromuscular scoliosis who underwent surgery performed by a single surgeon between 2003 and 2020, with at least 2 years of follow-up period. Operation procedures were conducted in two stages, beginning with L5-S1 anterior release followed by posterior fixation. Radiologic parameters were measured at preoperative, immediate postoperative, and last follow-up periods with clinical hip pain and clinical hip dislocation events.

Results: The significant improvements occurred in various parameters after correction surgery for NM scoliosis, containing Cobb's angle of major curve and CO-PT. However, Reimer's hip migration percentage (RMP) was increased on both side of hip (High side, 0.23 ± 0.16 to 0.28 ± 0.21; Low side, 0.20 ± 0.14 to 0.23 ± 0.18). Hip pain and dislocation events were also increased (Visual analog scale score, 2.5 ± 2.3 to 3.6 ± 2.6, P value < 0.05; dislocation, 6-12). Logistic regression analysis of the interactions between ΔRMP(High) and the change of sagittal pelvic tilt (ΔSA-PT) after correction reveals a significant negative association. (95% CI 1.003-1.045, P value = 0.0226).

Conclusions: In cases of non-ambulatory flaccid NM scoliosis, clinical hip pain, and subluxation continued to deteriorate even after correction of CO-PT. There was a relationship between the decrease in SA-PT, and an increase in hip migration percentage on high side, indicating the aggravation of hip subluxation.