Scoliosis almost invariably begins in the first decade of life in SMA type II and in a substantial proportion of children with SMA type III. The curves progress over time, sometimes quite rapidly during transition to increased wheelchair use or in conjunction with a growth spurt. In non-ambulatory patients, spinal bracing may improve sitting stability, as long as care is taken not to compromise abdominal movement in those with intercostal muscle weakness.
However, continuous use of such bracing should be limited if possible in order to maintain trunk strength and mobility. Periodic pulmonary function studies help to establish a profile for the individual patient, allowing design of the most appropriate care plan surrounding respiratory care in the post-surgical period. Since worsening is inevitable in most children, once the curve reaches 40 degrees a decision to intervene may be warranted. When very young patients develop scoliosis, bracing can sometimes help to defer surgery for variable periods of time, and "growth rods" or other means of accommodating growth may be indicated.
Proximal muscle weakness predisposes patients to progressive subluxation and dislocation of the hip. Subsequent hip degeneration can result in significant chronic pain. In non-ambulatory patients, it is important to prevent the hips from dislocating for reasons of comfort, good sitting balance, and maintenance of pelvic alignment.
To achieve an optimal result, operative intervention may be required in some cases. Patients who have type III SMA and are still able to walk present a difficult management problem. These patients are also prone to subluxation of the hip due to significant proximal muscle weakness. However, because surgical intervention with proximal femoral varus osteotomy may result in additional weakening of the abductor muscles, the physician should be cautious in recommending such surgical procedures in an ambulatory patient.