THORACOSCOPIC DISCECTOMY AND FUSION: SAFE AND EFFECTIVE WHEN SEGMENTAL BLOOD VESSELS ARE SPARED

Daniel J. Sucato, MD, MS;
Robert D. Welch, DVM, PhD;
Bill Pierce, BS;
Nessie Haideri, ME;
Hong Zang, MD;
Dwight Bronson, MS;
Sara Mattes MS
Texas Scottish Rite Hospital, Dallas, Texas, USA

INTRODUCTION:
Because thoracoscopy is relatively new and technically demanding, many surgeons ligate the segmental blood vessels to enhance spine exposure and limit risk of injury during discectomy and fusion. Although rare, spinal cord compromise secondary to segmental vessel ligation has been reported. This study was divided into two phases: the first, analyzed the amount of disc and endplate excision; the second, investigated the biomechanical strength of the fusion mass. Comparisons were made between segmental vessel ligation and spared groups.

METHODS:
Phase I: Ten mature goats were randomly assigned to either the segmental vessel–ligated (Group I) or the segmental vessel–spared (Group II) group. Disc and endplate excision was performed at 6 consecutive thoracic levels in each animal (N=30 per group). For group I, the segmental vessels were ligated cephalad and caudad to each disc. The animals were euthanized and the depth of disc excision was measured in the transverse (TR) and sagittal (SG) planes. The vertebral bodies were then separated through the disc space and photographic images of the inferior and superior aspects of the vertebral bodies were digitized and the area of endplate excision was calculated. The data were then analyzed using the two–sample t–test. Phase II: Ten mature goats were randomly assigned to Group I or II and 5 noncontiguous thoracic segments were fused using autologous iliac crest graft. At 4 months the animals were euthanized, the spines were harvested and the three–dimensional rotational and translational motions were analyzed at each disc level under physiologic loading conditions. The data were analyzed using a repeated measures analysis of variance and least square means for multiple comparisons.

RESULTS:
Each animal survived the operative procedure and no surgical complications occurred. There was no difference in operative time (21.8 vs 22.7 min/disc), blood loss (97 cc vs 159 cc), TR (81% vs 74%) or SG (85% vs 85%) disc excision between groups I and II. The total area of endplate excision was 70% in group I and 67% in group II (p>0.1). In Group II, a total of 3 vessels were injured and coagulated in the first 3 animals without injury in the remaining animals. Biomechanical testing demonstrated no difference in stiffness of the fused segments between the two groups in flexion/extension, lateral bending or axial rotation with a trend toward more motion in axial rotation in the segmental vessel–ligated spines.

CONCLUSIONS:
The segmental vessels in the thoracic spine can be effectively spared without injury during disc excision and fusion. Although slightly more disc area was excised with ligation of the vessels, this was not statistically significant and did not lead to improved fusion mass stiffness. Sparing the segmental vessels during thoracoscopic anterior disc excision and fusion can be safe and may be beneficial in those patients most at risk for neurologic injury from decreased spinal cord perfusion.