SPINE Volume 30, Number 23, pp 2701–2705 ©2005, Lippincott Williams & Wilkins, Inc. Reduction of Vertebral Blood Flow by Segmental Vessel Occlusion: An Intraoperative Study Using Laser Doppler Flowmetry Axel Hempﬁng, MD,* Marc Dreimann, MD,* Stefan Krebs, MD,* Oliver Meier, MD,* Hubert No ¨tzli, MD,† and Peter Metz-Stavenhagen, MD* Study Design. During anterior spinal surgery, verte- bral perfusion was assessed by laser Doppler ﬂowmetry. Blood ﬂow changes were assessed after unilateral ligation and contralateral compression of the segmental vessels. Objective. To assess the inﬂuence of unilateral and bilateral segmental vessel occlusion on vertebral blood ﬂow. Summary of Background Data. During anterior spinal surgery, segmental vessels are frequently being ligated. The reduced blood supply to the vertebrae may impair intervertebral fusion, and the decreased spinal cord per- fusion may lead to ischemic myelopathy. To our knowl- edge, this is the ﬁrst in vivo study to investigate vertebral blood ﬂow. Methods. There were 10 patients who underwent an- terior release for adult idiopathic scoliosis (n = 6), Scheuermann disease (n = 3), and posttraumatic kypho- sis (n = 1). A high-power laser Doppler ﬂowmeter was used to assess vertebral blood ﬂow. Measurements were performed in 19 thoracic and 4 lumbar vertebrae (n = 23) after unilateral segmental vessel ligation and additional temporary digital compression of the contralateral vessels. Results. Initial mean blood ﬂow was 49.1  27.6 arbi- trary units, and all signals were pulsatile. The blood ﬂow decreased by a mean of 8% after unilateral ligation of the segmental vessels. With additional compression of the contralateral vessels, the signal heights decreased signif- icantly by 54% (mean 18.3  7.8 arbitrary units, P = 0.00003), and a loss of the pulsatile pattern was observed in 75% of the vertebrae. On release of digital compres- sion, the signal height as well as the pulsatility promptly returned. Conclusions. Unilateral ligation of segmental vessels led only to a slight decrease of the vertebral blood ﬂow. Future studies may show whether sparing the segmental vessels during anterior fusion enhances bone graft incor- poration, thus decreasing the rate of pseudarthrosis. Ac- cording to clinical data, the risk of neurologic injury through unilateral ligation is negligible. Bilateral segmen- tal vessel occlusion markedly reduced vertebral blood ﬂow. Therefore, when treating patients with a higher neu- rologic risk or in revision cases, the surgeon should al- ways consider sparing the segmental vessels. Key words: anterior spinal surgery, segmental vessels, vertebral blood ﬂow, pseudarthrosis, paraplegia. Spine 2005;30:2701–2705 The segmental arteries of the thoracic and upper lum- bar spinal column occur from the aorta. At the inter- vertebral foramen, they divide into several nutritional branches to the vertebrae, building a rich anastomotic network between ipsilateral and contralateral arteries. They also provide blood supply to the spinal canal, where “medullary feeders” reinforce the anterior spi- nal artery. 1,2 During anterior spinal surgery, segmen- tal vessels are frequently ligated to expose vertebrae and discs. It has been suspected that this procedure can lead to a reduction of the blood supply to the vertebrae as well as the spinal canal. There is an ongoing discus- sion whether segmental vessels should be preserved not to impair incorporation of intervertebral bone grafts, especially since the advent of thoracoscopic procedures. A recent study in goats has collected fur- ther evidence in this direction, pointing out a reduced stiffness of the anterior fusion mass in those animals in which the vessels had been ligated. 3 Regarding perfu- sion of the spinal canal, the risk of ischemic myelopa- thy after segmental vessel ligation is very low. 4–6 Nev- ertheless, pure ischemic myelopathy after segmental vessel ligation has been suspected. 4,7–10 To our knowledge, there has been no in vivo study assessing vertebral blood ﬂow during anterior spinal sur- gery to date. The purpose of this study was to assess the inﬂuence of segmental vessel occlusion on vertebral blood ﬂow by laser Doppler ﬂowmetry (LDF). This new high energy laser system has been a reliable method for the measurement of intraosseous perfusion. 11–13 Materials and Methods There were 10 patients, including 9 females and 1 male, with a mean age of 31 years (range 14 –54) who underwent ante- rior release for idiopathic scoliosis (n = 6, additional ventral derotation spondylodesis n = 2), Scheuermann disease (n = 3), and posttraumatic kyphosis (n = 1). None of the patients had histories of former spinal surgery. All patients had un- dergone a standard open approach to the thoracic and/or lumbar spine. Following human subject regulations at our institution, the segmental vessels were dissected, and the From the *German Scoliosis Center, Werner Wicker Clinic, Bad Wil- dungen, Germany, and †Clinic for Orthopaedic Surgery, Ziegler Spital, Bern, Switzerland. Acknowledgment date: August 17, 2004. First revision date: Novem- ber 17, 2004. Acceptance date: December 20, 2004. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No beneﬁts in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Axel Hempﬁng, MD, German Scoliosis Center, Center for Spine Surgery, Werner-Wicker Klinik, 34125 Bad Wildungen-Reinhardshausen, D-34125 Germany; E-mail: axel@hempﬁng.de 2701