EVALUATION OF A NEW TRUNK ASYMMETRY INDEX TO MEASURE CURVE PROGRESSION IN THORACOLUMBAR SCOLIOSIS.

Abstract

Aim: We present a new trunk asymmetry index for topographic measurement of patients with thoracolumbar scoliosis, which does not require full 3-dimensional reconstruction of the back shape and can be performed with a digital camera and a laptop.

Material and methods: To date, 27 patients were assessed preoperatively, and 14 of these also had post operative assessments. The midline was identified between the two lateral edges of the trunk visible on a digital photograph. This was compared with a straight line. We derived an asymmetry index for each image and compared this with the cobb angle on x-rays pre- and postoperatively.

Results: The new asymmetry index correlated well with the cobb angle up to about 50°. Curves beyond this tended to have compensatory curves. This made interpretation more complex, however, if the compensatory cobb angle was subtracted from the major cobb angle, the asymmetry index fell at the expected points. It clearly distinguishes pre-operative and post-operative images. With POTSI, (posterior trunk symmetry index) there is a significant difference between the pre- and post-operative groups and significant overlap of the two distributions.

Conclusions: Surface topography of scoliotic patients is a useful tool to assess the progression of scoliosis without X-rays, reducing radiation exposure. The proposed new index is a promising measurement for monitoring the progress of a thoracolumbar curve with much better sensitivity and specificity than existing topographic indices, without requiring the capital outlay for surface topography equipment as it can be obtained from a simple digtal photograph and laptop.