Objective. To evaluate the relation of ribs to the spine in the transverse plane (TP) at the curve apex in preoperative AIS using a real-time ultrasound method and radiographs (Burwell et al 2002).

Design. With the subject in a prone position and head supported, readings of laminal rotation (LR) and rib rotation (RR) were made on the back by one of two observers (RKA, ASK) using an Aloka SSD 500 portable u/s machine with a veterinary long (172mm) 3.5 MHz linear array transducer. The maximal difference between LR and RR about the curve apex was calculated as the apical spine-minus-rib rotation difference (SRRD). The SRRD eliminates the effect of any anterior chest wall asymmetry on the ultrasound measurements and, assuming no movement of ribs in the TP at the costotransverse joints, is considered to be a measure of TP rib deformity. The radiographic Cobb angle (CA), apical Perdriolle rotation (AR), and apical vertebral translation (AVT) were measured by one observer (RGB). In an attempt to separate mechanical axial vertebral rotation from axial vertebral deformity a derivative was calculated as Perdriolle rotation minus ultrasound LR with the latter corrected for the positional effect of lying prone and termed the axial vertebral difference (AVD) The correction factor (CF) used is maximal Scoliometer angle of trunk rotation obtained in the standing forward bending position minus that in the prone position.

Subjects. Thirty-three preoperative patients with AIS were studied (thoracic curves 20, thoracolumbar curves 8, double curves 5).

Results. The mean figures in degrees or mm (AVT) are shown in the Table.

All curves combined. The LR is significantly greater than the RR (p< 0.001) and correlates with RR (r=0.358, p=0.041), SRRD (r=0.713, P< 0.001) but not with CA (p=0.088), AR (p=0.166), AVT or AVD. AR does not correlate significantly with CA.

Thoracolumbar and thoracic curves. In the thoracolumbar curves the SRRDs are significantly greater than those in the thoracic curves (p=0.031) implying more TP rib deformity in the thoracolumbar curves. In the thoracic curves the SRRDs correlate negatively with the AVDs (r= −0.470, p=0.036) suggesting that rib deformity and intravertebral deformity contribute reciprocally and together with axial spinal rotation to determine the overall spinal deformity of AIS.

Conclusions. The findings are consistent with the hypothesis that in preoperative AIS the axial RR and TP rib deformities are adaptations to rotational and lateral forces imposed by the scoliotic spine (Wever et al 1999). Might surgical stiffening of the posterior ends of the apical convex ribs – in an attempt to prevent TP convex rib deformity – constrain axial spinal rotation, vertebral translation and intravertebral deformity and limit curve progression? #Supported by AO/ASIF Research Commission Project 96-W21