Children with spinal muscular atrophy (SMA) face several orthopedic challenges including scoliosis, joint flexion contractures, subluxations and dislocations of the hip, and bone fractures.1,2 By far the most common orthopedic problem in SMA patients is a progressive, neuromuscular scoliosis.2 In fact, the rate of scoliosis in non-ambulatory children with SMA approaches 100%, and most ambulatory patients with SMA Type 1 or SMA Type 2 have some degree of scoliosis. Spinal scoliosis is also related to kyphosis and pelvic obliquity. The ensuing loss of stability when seated has a substantial, negative impact on daily activities.3 Spinal abnormalities further compound respiratory issues brought on by weakness of the intracostal muscles, which puts patients at great risk for restrictive pulmonary disease and various respiratory comorbidities.4
In general, nonsurgical treatment of scoliosis is attempted before moving to surgical interventions. Nonsurgical treatment for scoliosis associated with SMA includes orthoses to slow the progression of scoliosis and wheelchair seating systems designed to promote sitting posture and accommodate pelvic obliquity. Despite nonsurgical interventions for scoliosis, non-ambulatory children with SMA II generally acquire an additional 8° of curvature each year.5 When the curvature of the spine becomes too great, surgical management of scoliosis is becomes necessary.Â
Surgical management of SMA-associated scoliosis hinges on the skeletal maturity of the patient. Management differs whether the patient is younger or older than 10 years of age. In the skeletally immature child (<age 10), orthopedic surgery can be technically challenging. Surgeons tend to prefer growing rod constructs without arthrodesis (fusion). These include distraction-based systems such as Vertical Expandable Prosthetic Titanium Ribs (VEPTR) or MAGnetic Expansion Control (MAGEC) rods, or guided growth systems such as modern Luque trolley and SHILLA devices. Surgical treatment of scoliosis can be effective over the long term long-term; over an 11.6 year study period, the predicted forced vital capacity of the untreated patient would have declined at a rate of 5.31% per year, yet with surgery that rate of decline was only 1.77% per year.6 On the other hand, the use of these devices is associated with various complications including infection, anchor displacement, premature arthrodesis, and laminar fracture. Revision surgery is often required.
When possible, scoliosis surgery should be reserved for patients who have reached skeletal maturity (>age 10). Patients whose scoliosis cannot be controlled with bracing, and/or patients with curves greater than 40° are typically candidates for orthopedic scoliosis surgery. Non-ambulatory patients with a Cobb angle >20° are also candidates for surgery.7,8 The typical procedure for non-ambulatory patients involves a posterior spinal fusion (fusion of the entire thoracic and lumbar spine including the pelvis) with segmental instrumentation. Importantly, ambulatory patients should be spared from fusion at the level of the pelvis since arthrodesis at this level could hasten the use of a wheelchair. The risk of complication and clinical deterioration after surgery must be discussed with patients and their families. Implant failure, pseudo-arthrosis, infection, and thromboembolic phenomenon are possible complications.
References
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2. Fujak A, Raab W, Schuh A, Kress A, Forst R, Forst J. Operative Treatment of Scoliosis in Proximal Spinal Muscular Atrophy: Results of 41 Patients. Arch Orthop Trauma Surg. 2012;132(12):1697-1706. doi:10.1007/s00402-012-1610-8Â
3. Bridwell KH, Baldus C, Iffrig TM, Lenke LG, Blanke K. Process Measures and Patient/Parent Evaluation of Surgical Management of Spinal Deformities in Patients with Progressive Flaccid Neuromuscular Scoliosis (Duchenne’s Muscular Dystrophy and Spinal Muscular Atrophy). Spine (Phila Pa 1976). 1999;24(13):1300-1309.Â
4. Evans GA, Drennan JC, Russman BS. Functional Classification and Orthopaedic Management of Spinal Muscular Atrophy. J Bone Joint Surg Br. 1981;63b(4):516-522.Â
5. Fujak A, Raab W, Schuh A, Richter S, Forst R, Forst J. Natural Course of Scoliosis in Proximal Spinal Muscular Atrophy Type Ii and Iiia: Descriptive Clinical Study with Retrospective Data Collection of 126 Patients. BMC Musculoskeletal Disorders. 2013;14:283-283. doi:10.1186/1471-2474-14-283Â
6. Chua K, Tan CY, Chen Z, et al. Long-Term Follow-up of Pulmonary Function and Scoliosis in Patients with Duchenne’s Muscular Dystrophy and Spinal Muscular Atrophy. J Pediatr Orthop. 2016;36(1):63-69. doi:10.1097/bpo.0000000000000396Â
7. Haaker G, Fujak A. Proximal Spinal Muscular Atrophy: Current Orthopedic Perspective. The Application of Clinical Genetics. 2013;6(11):113-120. doi:10.2147/TACG.S53615Â
8. Fujak A, Ingenhorst A, Heuser K, Forst R, Forst J. Treatment of Scoliosis in Intermediate Spinal Muscular Atrophy (Sma Type Ii) in Childhood. Ortop Traumatol Rehabil. 2005;7(2):175-179.Â