The results of this study revealed significant discrepancies in VTE prophylaxis selection between the surgical specialties surveyed. Neurosurgeons appear to adhere more closely to guidance outlined by NICE than their orthopaedic counterparts. Quite why this should be the case is unclear and beyond the scope of this survey. Moreover, any attempt to explain or theorise why this discrepancy exists would be but conjecture.
We readily acknowledge that the small numbers surveyed and the disparity in number between the groups surveyed limits the extent to which these outcomes can be extrapolated. Similarly, we recognise the inherent limitations of this study and the potential bias, including underrepresentation, voluntary response and non-response bias, associated with a survey. However, the outcome of this study is in keeping with similar, though admittedly more robust, surveys including that conducted by Ploumis et al. who attempted to determine a basis for a consensus protocol on thromboprophylaxis in spinal surgery and trauma in the United States. After surveying 47 spinal surgeons (neurosurgical and orthopaedic) from the Spinal Trauma Study Group, Ploumis and colleagues could find no consensus on the preferred method of medical thromboprophylaxis or on thromboprophylaxis selections for 3 spinal trauma case scenarios . Clearly these results and conclusions are not wholly transferable--their study could find no agreement on the method of chemical thromboprophylaxis--rather, it illustrates the point that discrepancies and uncertainties persist, both in the United States and the United Kingdom and that variations can be seen between, and indeed within, surgical disciplines.
This uncertainty has been attributed, in large part, to a paucity of literature examining VTE in spinal surgery [12, 13]. Moreover, the scientific evidence that exists is based on level III studies rather than level I randomised controlled trials . In a 1997 review of thromboembolic complications and the effects of thromboprophylaxis in elective spinal surgery surgery, MG Catre reported an absence of statistically strong research examining the true incidence of thromboembolic complications in spinal surgery . Catre concluded that a well-designed, randomized controlled study to define the efficacy of thromboprophylaxis in elective spinal surgery would be needed before recommendations for thromboprophylactic regimes could be made . Despite considerable attention in the years that have followed, uncertainty prevails. The incidence of VTE in spinal surgery, the most appropriate regime and timing of thromboprophylaxis in spinal surgery remains a matter of debate.
Literature chronicling the incidence of thromboembolic complications following spinal surgery is varied. In 2001 Geerts et al. reported that the incidence of thromboembolic complications following elective spine surgery was unknown . In 2004 Giancarlo Agnelli placed the rate of clinically overt DVT and PE in elective spinal patients at 3.7% and 2.2% respectively , while Roktio et al. reported an incidence of 0.3% following reconstructive spinal surgery . Others have variously estimated the incidence at between 0.9% and 14% . Oda et al. identified venographic evidence of DVT in 15.5% of patients following posterior spinal surgery where no thromboprophylaxis (chemical or mechanical) was used , while Cheng et al., in a systematic review of anticoagulation risk in spine surgery, cite a risk of venous thromboembolism in patients not receiving chemical thromboprophylaxis of 2.3% in surgery for degenerative conditions, 5.3% for procedures to correct deformity and 6.0% for trauma patients .
In patients undergoing elective neurosurgical procedures, where the risk of DVT and PE are known to be higher , the incidence of overall DVT and proximal DVT in a double-blind, randomized, venography-based trial was identified at 26% and 12% respectively in patients receiving thrombembolic stockings. These figures fell to 19% and 7% in those treated with stockings and LMWH . The sequelae associated with thromboembolic complications appears equally varied; according to Cheng et al., fatal pulmonary embolism is rare  but Angelli et al., cite an incidence of pulmonary embolism in neurosurgical patients of between 1.5% and 5% with a mortality of 9% to 50% . In trauma patients and those with acute spinal cord injury (SCI) the risk of thromboembolic complications is greater than the elective realm--so much so that acute SCI patients have the highest risk of DVT among all hospital admissions . In patients who have suffered major trauma and spinal cord injury the incidence of calf DVT may be as high as 40-80%  and fatal PE is the third most common cause of death in this cohort of patients .
The risk of thromboembolism must therefore be weighed against the potentially catastrophic effects of bleeding, haematoma formation and neurological deficit . Because chemical anticoagulation has not gain widespread acceptance by spinal surgeons , largely driven by fear of the complications outlined above, the true incidence of bleeding complications is unclear. In an examination of the efficacy and safety of LMWH as prophylaxis against VTE in patients undergoing elective neurosurgery, Agnelli et al., found no increase in the risk of intracranial bleeding with the use of enoxaparin. Of the 307 patients who underwent neurosurgical procedures (including surgery for brain or spinal tumours, cerebral aneurysms, vertebral disc displacement and gliosis), three patients in the enoxaparin cohort and four patients in the placebo group suffered major intracranial bleeding . In contrast, the combination of LMWH and compression stockings nearly halved the rate of venous thromboembolism . These findings are in keeping results reported by Gerlach et al., who found that post-operative chemical thromboprophylaxis with LMWH (nadroparin) was not associated with an increased risk of post-operative haemorrhage . In a cohort of 1,954 patients who underwent spinal surgery over a 3-year period, 8 procedures (0.4%) were complicated by major post-operative haemorrhage following the administration of LMWH . However, other authors put the risk higher by a factor of 10 with complications of bleeding reportedly occurring in up to 4% of patients .
This uncertainty is reflected in the results of an email survey conducted by Globtzeker et al. assessing practices for thromboprophylaxis in cases of high-risk surgery for tumours and trauma. As was the case with our survey and the results elucidated by Polumis and colleagues, Glotzbecker et al. identified startling variability amongst the ninety-four orthopaedic and neurosurgical participants; 29% of those surveyed felt the risk of post-operative epidural haematoma was less than 1%, 47% selected a risk of between 1% and 5%, and 17% felt that may rise as high as 5%-10% . Regarding estimates for the most appropriate timing for thromboprophylaxis, 15% reported they would institute chemical thromboprophylaxis 24 hours after surgery, 22% stated they would commence thromboprophylaxis after 48 hours, 13% selected 72 hours, 10% chose 96 hours, and 12% reported they would commence therapy within 24 hours .
The one area where consensus and uniformity can be found is in the recognition of the need for further research examining thromboembolic complications and thromboprophylaxis in spinal surgery. Venous thromboembolism is a leading cause of medical morbidity and mortality [1–3]. In spinal surgery, more so than in perhaps any other surgical specialty, there exists a fine line between risk reduction for VTE and the potentially catastrophic implications for anticoagulation induced bleeding. Considerable attention has been focused on this topic but important gaps persist; the conclusion drawn by Glotzbecker et al. echoed that of Catre a decade earlier--the variability and inherent uncertainty regarding thromboembolic practice reflects a shortage of robust, scientific studies examining VTE in spinal surgery . While guidance exists, further prospective controlled research examining the epidemiology of VTE in spinal surgery, the risk of bleeding complications and the safety and efficacy of thromboprophylaxis regimes [4, 13–15] is required if substantive and acceptable guidelines--to which all practitioners adhere--are to be developed and put into clinical practice.