The Whitecloud Awards honour the best clinical and scientific papers at IMAST. This year’s winners, Jacob Buchowski and Vishal Sarwahi, talk to Spinal News International about their award-winning papers.
Jacob Buckowski, assistant professor, Orthopaedic and Neurological Surgery, Washington University Orthopedics, Missouri, USA, won the Whitecloud Award for the best clinical paper at IMAST 2011. In his paper, preoperative vitamin D status in adults undergoing spinal fusion surgery, he found an “alarmingly” high rate of vitamin D abnormality among 262 patients undergoing spinal fusion. He and his co-authors concluded: “While certain previously identified risk factors were confirmed, validated indices of spine-related disability were higher in the presence of hypovitaminosis D”.
Why did you and your co-authors decide to investigate preoperative vitamin D status in adults undergoing spinal fusion surgery?
Although osteoporosis is probably the best-known sequelae of vitamin D deficiency, the adverse effects of vitamin D deficiency on bone and cartilage extend well beyond diminished bone mineral density. Hypovitaminosis D can promote pathologically distinct osteomalacia, which is, fundamentally, reduced bone quality as opposed to the reduced quantity observed in osteoporosis. With this in mind, we thought vitamin D deficiency may hinder surgical spinal fusion and potentially, by decreasing the quality of bone, predispose a patient to screw pullout and instrumentation failure.
The global epidemic of hypovitaminosis D is exceptionally well-documented: over a billion individuals may have 25-hydroxyvitamin D levels below 30ng/mL. As such, the 27% prevalence of deficiency (levels below 20ng/mL) in our study population was not particularly surprising. However, we feel that this prevalence is greatly underestimated among spine surgeons and that bringing it to light is crucial.
Going forward, should all patients with spinal deformities be assessed for vitamin D deficiency or just those who are at high risk of deficiency?
Given vitamin D’s central role in establishing optimal bone health, we recommend preoperative 25-hydroxyvitamin D screening for all spine patients undergoing spinal fusion, regardless of whether or not they have an underlying spinal deformity. It must be said, however, that spinal deformity patients were actually statistically less likely to be deficient in our population, but this may be attributed to their comparatively higher rate of prior vitamin D supplementation. In addition, the price of this laboratory test is not negligible, so at institutions where systematic screening is not economically feasible, attention should be focused on those patients at high risk (eg, patients without prior vitamin D or multivitamin supplementation). Future clinical outcomes studies will hopefully elucidate whether systematic screening is cost-effective.
You conclude that patients with hypovitaminosis D should receive vitamin D augmentation. What dose would you recommend? Are there any studies that show the benefit of vitamin supplementation in this patient population?
Currently, vitamin D-deficient patients at our centre are prescribed 50,000IU of vitamin D2 (ergocalciferol) per week for eight weeks. This regimen has proven to be effective in correcting serum vitamin D levels.
As with screening, the issue of who should be supplemented is convoluted. We are not aware of any high-powered study that has shown superior postoperative outcomes for vitamin D-supplemented spinal fusion patients versus controls. However, it is generally well accepted that vitamin D deficiency predisposes to vertebral compression fractures and that fracture prophylaxis via repletion is effective; this is pertinent, considering the biomechanical stress imparted by modern instrumentation constructs. Furthermore, the incidence of fixation loss (ie, screw pullout) is elevated in the setting of suboptimal bone density.
What other studies do you think should be done in this area?
In the immediate future, retrospective/longitudinal clinical outcome studies are most needed. These types of investigations can be performed relatively quickly and should shed light on whether deficiency predisposes to complications and poor outcomes. Prospective, randomised, controlled trials would naturally follow. From a basic science standpoint,
developing a vitamin D-deficient animal model for spinal fusion is another important objective. Steps towards this end are currently being taken at our institution.
Vishal Sarwahi, associate professor, Orthopaedic Surgery, Albert Einstein College of Medicine, New York, USA, won the Whitecloud best science paper award for his paper on monitoring spinal cord blood flow, using laser doppler, to identify pre-injury state during surgery. He and his co-authors found that real-time spinal cord blood flow measurement corresponded well with changes in motor evoked potentials (MEPs). They concluded: “In the presence of cord compression, the laser doppler can detect spinal cord injury earlier than MEPs. This pre-injury, hyperaemic state can provide the operating surgeon with an opportunity to intervene before complete cord injury occurs.”
Why did you and your co-authors decide to investigate spinal cord blood flow to identify pre-injury state during surgery?
Iatrogenic spinal cord injury is a devastating complication of spine surgery. The greatest challenge in dealing with complex spine deformity is to correct the deformity without risking the spinal cord. The current preference is intraoperative spinal cord monitoring. Although this method is highly reliable, it still cannot detect spinal cord perturbations pre-injury. Most intraoperative spinal cord injuries, whether due to manipulation or compression, can be attributed to vascular or ischaemic aetiologies. So it appeared logical that measuring spinal cord blood flow in real time should detect the presence of spinal cord injury. It also appeared plausible that the use of laser doppler to measure spinal cord blood flow in real time may detect impending or actual spinal cord injury before changes were detected on MEPs.
Why is identifying spinal cord injury earlier than is done presently with MEPs important?
Let us look at the history. In the 1970s, Stagnara described the wake-up test. This involved waking the patient up during surgery and asking him or her to move their legs. It quickly became the gold standard. The wake-up test was done just before wound closure, which was a few hours after the instrumentation and correction manoeuvres were started. However if you are worried about spinal cord injury, you want to know as soon as it happens. By the time you realised that an injury had occurred, with the wake-up test, precious time had been lost.
In the 1990s, spinal cord monitoring became a reality; real-time monitoring of sensory pathways was capable of picking up the majority of injuries. However, the wake-up test was still necessary, as the motor pathways were not monitored. In the last few years, multimodality, spinal cord monitoring has evolved, which allows for real-time monitoring of the motor pathways as well. The surgeon can now know within minutes that an injury has occurred. However, as they say, prevention is better than cure. The ability to prevent an injury from happening is the ultimate safeguard. This is what real-time spinal cord blood flow monitoring promises to be. This groundbreaking finding means that surgeons can be alerted about an impending spinal cord injury several minutes before it actually happens.
Are there any plans to measure spinal cord blood flow in human patients?
We have an institutional review board submission in the works to get approval for such a study. We plan to do it for all spinal surgeries that require monitoring. We also plan to collaborate with other spine centres to collect a broad set of data for various spine pathologies.
If spinal cord blood flow is found to be a way of identifying spinal cord injury at an earlier stage, what is the potential impact of this in terms of the safety of complex spine surgery?
Use of laser doppler intraoperatively has the potential of making complex spine surgery much safer. Advances in spine surgery have allowed surgeons to treat complex cases. As more complex spine surgeries are increasingly performed, it is crucial to continue making surgeries safer. Spinal cord ischaemia is a reversible state as against infarction, and thus detection at a pre-injury state alerts the surgeon of an impending injury and provides an opportunity to halt its progression. In addition monitoring of spinal cord blood flow post-injury can help prognosticate recovery, something that MEPs and somato sensory evoked potential are incapable of. This can potentially decrease the incidence of neurological injury during complex procedures. Every injury prevented, after all, is one less paraplegia. This changes the whole paradigm.