Optimizing the vertical position of the brace thoracic pad: Apical rib or apical vertebra?

INTRODUCTION: The vertical position of the thoracic pad is a subject of controversy in brace design. Traditional recommendations dictate a maximal force applied at the level of the apical rib, about 2 levels below the apical vertebra. We sought to evaluate the optimal vertical position of the brace thoracic pad using fulcrum bending radiographs.

HYPOTHESIS: A lateral force applied at the apical vertebra of a thoracic curve is more efficient at correcting coronal deformity than a force placed the apical rib.

PATIENTS AND METHODS: In this prospective study, we recruited patients presenting with adolescent idiopathic scoliosis (AIS) and Risser stage 0-2 over a period of 12 months. Patients with a history of spine or thoracic surgery were excluded. Two fulcrum bending radiographs were performed for each patient: one with the center of the fulcrum placed under the most lateral part of the apical rib and another with the fulcrum centered below the apical vertebra. Cobb angles were measured on each fulcrum radiograph and compared using a paired t test.

RESULTS: Fifty-two patients were included, with a mean age of 12.4 years and mean thoracic Cobb angle of 39.4˚. Placing a fulcrum under the apical vertebra reduced the Cobb angle to a mean of 11.5˚, which was significantly lower than a fulcrum placed under the apical rib (14.3˚, p=0.001). This corresponded to a 20% relative loss in the absolute correction angle when placing the fulcrum under the apical rib. The difference between the 2 Cobb angles was not significantly correlated to patient age (p=0.896) or curve apex (p=0.813).

DISCUSSION: This is the first clinical study addressing the vertical position of the thoracic pad in braces for AIS. A lateral force applied at the level of the apical vertebra was significantly more efficient at reducing thoracic curve deformities than one applied at the apical rib. Our results provide clinical support to finite element studies that refute traditional recommendations of brace design, advocating for a revision of these guidelines to optimize non-operative treatment of AIS.

LEVEL OF EVIDENCE: II, prospective comparative study.