Radiographic Pseudoscoliosis in Healthy Male Subjects Following Voluntary Lateral Translation (Side Glide) of the Thoracic Spine

Abstract

Harrison DE, Betz JW, Cailliet R, Colloca CJ, Harrison DD, Haas JW, Janik TJ. Radiographic pseudoscoliosis in healthy male subjects following voluntary lateral translation (side glide) of the thoracic spine. Objective To determine projected Cobb angles associated with trunk list (side shift) posture, hypothesizing that the side shift “scoliotic” curvature would be similar to true scoliotic curvature in the early stages. Design Anteroposterior (AP) radiographs of volunteers in neutral, in left, and right lateral translations of the thoracic cage (trunk list) were digitized. Setting Computer laboratory. Participants Fifteen healthy male volunteers. Interventions Not applicable. Main Outcome Measures Cobb and Risser-Ferguson angles determined from digitizing vertebral body corners from T12 to L5 on 51 AP lumbar radiographs. Results Using the horizontal displacement of T12 from S1, subjects could translate an average of 54.0mm to the left and 52.5mm to the right. The average digitized Cobb T12-L5 angle produced for the 30 translated postures was 16°. Angles ranged from 2.6° to 27.0°. Risser-Ferguson angles averaged 10° between T12 and L5. Statistical correlations were found between Cobb L1-5 and translation to the left ( P=.015), Cobb T12-L5 and translation to the right ( P=.024), Risser-Ferguson angle and translation to the left ( P=.021), and the lumbosacral angle to the right and trunk translation to the right ( P=.027). Conclusions During lateral translation of the thorax (trunk list), coupled lumbar lateral flexion resulted in the appearance of a pseudoscoliosis on AP radiographs. For this trunk list posture, Cobb angles are considerable (16°) and increase as the magnitude of trunk translation increases. Differentiating true structural scoliosis from this pseudoscoliosis would be clinically important. The small coupled axial rotation in trunk list is in contrast to the considerable degree of axial rotation observed in structural idiopathic scoliosis.