KASS CONVERSION-SWITCHING FROM ANTERIOR TO POSTERIOR SURGERY

Abstract

Purpose: To identify patients in whom anterior scoliosis correction was not possible and to determine pre-operative factors that may predict such an outcome.

Methods: From 1999–2005, 257 patients were listed for anterior correction with the Kaneda Anterior Spine System (KASS). Of these 246 were completed successfully. However in 11 cases it was not possible to complete the procedure.

We performed a retrospective review of case notes and X-rays. A control group of 22 patients, in whom anterior surgery was completed, matched to age, sex and type of curve, was used.

Results: Two reasons for abandoning anterior instrumentation were identified; loss of cord signal (7) and failure to achieve adequate correction after anterior release and reduction (4).

Of the seven patients with lost signal three were syndromic and four were associated with syrinx. In all seven, loss of signal occurred on clamping of segmental vessels. All seven had no residual neurological deficit post-operatively and had uncomplicated posterior correction the following week.

All four patients in whom inadequate correction was achieved after anterior release and repositioning had idiopathic curves. Of these two were thoracic and two were thoracolumbar. Mean pre-operative Cobb angle was 67 (range 59–85) compared to a mean of 56 (range 42–68) in the control group. Mean pre-operative stiffness index was 91% (range 85%–100%) compared to a mean stiffness index of 65% (range 53–80) in the control population.

Conclusion: Whilst a successful outcome is achieved in a majority of KASS instrumentations we have identified two reasons why anterior surgery has to be abandoned. Whilst one often cannot pre-operatively anticipate intra-operative loss of cord signal, we found that in cases with an underlying syrinx there is a particular risk of this occurrence. Our experience has shown particularly stiff curves (Stiffness index ≥ 85%) may not be suitable for stand-alone anterior surgery.