Assessment of trunk balance in thoracic scoliosis

Study Design. A retrospective radiographic review was undertaken in patients with idiopathic thoracic scoliosis. Objectives. To determine if a mathematical relationship exists between the 2 methods used to assess trunk balance (lateral trunk shift [LTS] and thoracic apical vertebral translation [AVT]), and to determine if one of these measurements can satisfactorily predict the value of the other. Summary of Background Data. No previous reports exist, to our knowledge, comparing these 2 methods used to asess trunk balance. Methods. Coronal balance (CB), LTS, thoracic AVT, and curve magnitude were measured from standing preoperative posteroanterior radiographs of 91 patients with Lenke 1A/1B curves. The data were analyzed to determine if predictive relationships existed between LTS and thoracic AVT alone or between LTS and the sum of CB and thoracic AVT. Results. A statistically significant relationship was shown between LTS and the sum of thoracic AVT and CB, In general, the LTS can be estimated by taking two thirds of the sum of thoracic AVT and CB (in centimeters) and subtracting 0.8. This relationship weakened as CB improved. The relationship between LTS and AVT was not statistically significant when CB was excluded. Conclusions. In patients with thoracic idiopathic scoliosis, if the CB and thoracic AVT values are known, then the LTS can be reliably estimated. The use of correct terminology for describing trunk balance and CB is important if valid comparisons of spinal deformity literature are desired.