The natural history of SMA is well understood with progressive muscle weakness resulting in declines in function. Limited joint range of motion (ROM) and contractures, particularly in the lower extremities, are a common consequence of immobility which has a negative impact on function in SMA. Conventionally these have been treated with positioning, orthoses, stretching and ROM exercises. Concurrently, joint hypermobility (JH) is observed although not well-described, and its relationship to function is unknown. JH occurs at a single joint and generalized joint hypermobility (GJH) is present in all four limbs plus the axial skeleton. While JH is often evaluated with goniometry, the Beighton Score is a widely accepted measure of GJH. Disease modifying therapies have altered the natural history of SMA with new gains in motor function. However, the impact of contractures (restricted ROM) and joint hypermobility (excessive ROM) on function in treated SMA is unknown.
A critical review of existing literature was completed to determine what is known about the relationship between ROM and function in SMA.
A search of the literature using online-databases for peer-reviewed articles (PUBMED, MEDILINE, Web of Science, CINAHL and EMBASE), and a manual search of reference lists of included articles was completed.
The search revealed one report describing a negative relationship between reduced ROM of the lower limbs and gross motor function. The relationship to ambulatory function was not evaluated. Although excessive ROM was observed in knee flexion and ankle dorsiflexion, their impact on function was not specified. The remaining 13 articles reviewed included descriptions of restricted ROM without comparisons to function.
Understanding the impact of both excessive and restricted ROM on function is needed to optimize future rehabilitation strategies in treated SMA patients. Future work should evaluate the occurrence of JH in SMA and the influence on function.