Sagittal Plane Deformities in Children with SMA2 following Posterior Spinal Instrumentation

Abstract

This is a retrospective radiographic review to assess post-operative sagittal plane deformities in patients with Spinal Muscular Atrophy type 2 that had been treated with posterior spinal instrumentation. Thirty-two patients with a history of either spinal fusion (N = 20) or growing rods (N = 12) were identified with an average of 7.6 (2.1–16.6) years post-operative follow-up. Forty percent (13/32) of the patients were identified as having obvious “tucked chin” (N = 4), “tipped trunk” (N = 9), or both (N = 3). Sacral incidence was the only parameter that was statistically significant change between pre-operative or immediate post-operative measurements (66.9° vs. 55.2° p = 0.03). However, at final follow-up, the post-operative thoracic kyphosis had decreased over time in those that developed a subsequent sagittal deformity (24.2°) whereas it increased in those that did not (44.7°, p = 0.008). This decrease in thoracic kyphosis throughout the instrumented levels, resulted in a greater lordotic imbalance (30.4° vs. 5.6°, p = 0.001) throughout the instrumented levels in the group that developed the subsequent cervical or pelvic sagittal deformities. In conclusion, sagittal plane deformities commonly develop outside the instrumented levels in children with SMA type 2 following posterior spinal instrumentation and may be the result of lordotic imbalance that occurs through continued anterior growth following posterior instrumentation.

Feasibility of intrathecal therapeutic injections in spinal muscular atrophy patients via a percutaneous transsacral hiatus route: An initial neuroimaging morphometric study

“…We suspect that the loss of sacral curvature in most SMAps may be attributable to loss of ambulation, along with weakness of muscles that pull the sacrum ventrally during disease development and progression. Further exacerbation and straightening of the sacrum after surgical interventions in the thoracolumbar spine may manifest in two ways: increased “sacral inclination angle” and decreased “seated sacral femoral angle,” as discussed by Halanski et al 3 in type 2 SMAps.…”

“…1 This is frequently corrected by lumbar fusion surgery or by insertion of growing rods, 2 after which "tipped trunk" deformities may also occur, and increasing sacral angulation may cause a prominent buttock posteriorly. 3 SMA patients (SMAps) receiving nusinersen require frequent lumbar punctures (LPs) for drug administration, typically every 4 months. 1 However, LP in SMAps without imaging guidance is challenging, and fluoroscopy is often necessary to identify the appropriate level of entry and guide needle placement.…”

“…Spinal muscular atrophy (SMA) is characterized by progressive motor neuron death, resulting in muscular atrophy and eventual deformation of spinal curvature 1 . This is frequently corrected by lumbar fusion surgery or by insertion of growing rods, 2 after which “tipped trunk” deformities may also occur, and increasing sacral angulation may cause a prominent buttock posteriorly 3 …”