The relationship between radiologic union and clinical outcome in thoracoscopic scoliosis surgery is not clear, as apparent non-union does not always correspond to a poor clinical result. Our aim was to evaluate CT fusion rates 2yrs after thoracoscopic surgery, and explore the relationship between fusion scores and; (i) rod diameter, (ii) graft type, (iii) fusion level, (iv) implant failure, and (v) lateral position in disc space.

Between 2000 and 2006 a cohort of 44 patients had thoracoscopic scoliosis correction. Discectomies were performed and defect was packed with either autograft (n=14) or allograft (n=30). Instrumentation consisted of either 4.5mm (n=24) or 5.5mm (n=20) single titanium anterior rod and vertebral body screws. Fusion quality and implant integrity were evaluated 2yr following surgery using low-dose CT. At each disc space, left, right and mid-sagittal CT reconstructions were generated and graded using the Sucato 4-point scale (Sucato, 2004) which is based on calculated percentage of fusion across disc space.

Fusion scores were measured for 259 disc spaces in 44 patients. Rod diameter had a strong effect on fusion score, with a mean score of 2.12±0.74 for 4.5mm Ti rod, decreasing to 1.41+0.55 for 5.5mm Ti rod, and to 1.09+0.36 for 5.5mm Ti-alloy rod. Mean fusion scores for autograft and allograft subgroups were 2.13±0.72 and 2.14±0.74 respectively. Fusion scores were highest in the middle of implant construct, dropping off by 20–30% toward the ends. Fusion scores adjacent to the rod (2.19±0.72) were significantly higher than on the contralateral side of the disc (1.24±0.85). Levels where rod fracture occurred (n=11) had lower fusion scores than those without fracture (1.09±0.67 vs 1.76±0.80). Levels where top screw pullout occurred (n=6) had lower CT fusion scores than those without (1.25±0.60 vs 1.83±0.76).

Rod diameter (larger), intervertebral level (proximal or distal), lateral position in disc (further from rod) and rod fracture or screw pullout all reduce fusion scores, while graft type does not affect scores. The assumed link between higher fusion score and better clinical outcome must be treated with caution, because rod fractures did not necessarily occur in patients with lower fusion scores. It is possible that with a stiffer rod, less bony fusion mass is required for a stable construct. We propose that moderate fusion scores secure successful clinical outcomes in thoracoscopic scoliosis surgery.

Introduction

Luk (Luk et al. Spine vol 23(21) 2303-2307 1998) has shown that in posterior surgery, the correction achieved can be predicted by fulcrum bending films. The relevance to anterior correction has been disputed, as this commonly involves shortening the spine by the removal of intervertebral discs. The aim of the study was to see whether the pre-operative bending angle reflected the degree of correction achieved.

Purpose

1. To evaluate how radiological parameters change during the first 3 years following anterior endoscopic surgery. 2. To report complications encountered in this period.

Introduction

Radiographic parameters have been shown to have a poor correlation with clinical outcome after open scoliosis procedures. However this has not been previously addressed after endoscopic surgery. The purpose of our study was to examine prospectively the relationship between curve correction and clinical outcome for endoscopic scoliosis surgery.