Spinal Muscular Atrophy

Abstract

Spinal muscular atrophy (SMA) is a progressive neuromuscular condition characterized by hypotonia. Recent advances in the medical treatment of SMA has increased life expectancy and improved functional abilities. As a result, orthopaedic management in SMA is likely to take on a larger role in the care of children with SMA. Common orthopaedic manifestations in SMA include scoliosis, hip subluxation/dislocation, joint contractures, and insufficiency fractures. While certain strategies may be borrowed from the management of other neuromuscular conditions, like cerebral palsy, SMA has unique features that require special consideration given the extreme hypotonia encountered and the characteristic parasol chest deformity in SMA that contributes to the challenge of managing spine deformity. Similarly, while osteopenia is common in many neuromuscular conditions, osteopenia is reported to be the most severe in SMA above all other neuromuscular conditions, further adding difficulty to orthopaedic interventions. Furthermore, recently approved disease modifying agents often require intrathecal administration and thus a means of providing access to this anatomic space must be considered during posterior spine surgery. Despite these unique features,  SMA is more similar to some spastic neuromuscular conditions than previously thought. In particular, emerging evidence suggests that hip dislocation is not painless in all SMA patients and a better understanding of who is at risk for hip pain and how best to manage these patients is needed. The myriad of exciting new medical treatments will complicate the study of orthopaedic pathology in these patients and the future assessment of interventions as the “natural history” will be continually changing. Whether the incidence of spinal deformities and hip pathology and pain increase or decrease with improved motor function and extended lifespans is unknown; however it is likely that the increased functional demands of these patients will require more significant orthopaedic intervention. In light of the recently evolving expectations for life expectancy and functional abilities, this review offers an overview of the recent evidence in the orthopaedic management of SMA.