Surgical Treatment of Spinal Cord Injury: A Description of Methods and Devices

Milan Radojicic, MD

A number of pathophysiologic mechanisms have been shown to accompany spinal cord injury, including calcium influx, glutamate excitotoxicity, myelin breakdown products and the formation of an astrogliotic scar. However, despite decades of research, no adequate explanation has been proposed to account for the ongoing cystic degeneration in spinal cord injury, known as syringomyelia, that is associated with ongoing clinical decline in SCI patients. Some recent work has suggested that altered CSF hydrodynamics may responsible for initiating syrinx formation in humans1, 2. Moreover, Radojicic, working with an animal model of chronic SCI, has recently demonstrated a pattern of histologic changes consistent with this hypothesis3.

SCI patients frequently develop meningeal fibrosis and cord tethering at the site of injury. Some have proposed a surgical intervention for patients with chronic post-traumatic myelomalacic myelopathy, known as an expansive duraplasty, and has achieved some success4. I propose a pre-emptive expansive duraplasty for patients with acute spinal cord injury within a short period following their injury. This will allow 1.) expansion of the spinal cord due to edema 2.) prevent subsequent scar formation and promote favorable CSF hydrodynamics. The following is a protocol to test this treatment regimen.

1.) Expansive Duraplasty Protocol

a.) First, the rats will be deeply anesthetized with a Ketamine/Xylazine anesthetic as described in the original protocol (the dose will be 60 mg/kg Ketamine and 10 mg/kg of Xylazine i.p.). A deep level of anesthesia will be verified by ensuring that there is no withdrawal reflex to a pinch to the hind limbs, by testing the lack of the ocular reflex and for the lack of response to auditory stimuli as described in the protocol. If it is found that the animal has not reached a sufficiently deep level of anesthesia, an extra half dosage of anesthetic mix will be administered and the anesthesia level will be reassessed after an additional fifteen minutes. Our laboratory has many years of experience with the Ketamine/Xylazine anesthetic mixture. We are able to achieve extremely reliable deep anesthesia with this mixture with virtually no anesthesia-related mortality.
b.) After a deep level of anesthetia is achieved, a laminectomy will be performed at the T9-T10 level, as described in the original protocol. A 1x1cm patch of the dorsal fat pad will be harvested from the animal at the time of dissection for later use in the duraplasty. Thereafter, a moderate contusion injury will be achieved with the Infinite Horizon device, according to standard protocol.
c.) Utilizing standard microsurgical techniques and an operating microscope at high magnification, a two paramedian 1 cm longitudinal durotomy will be performed using a No. 11 blade at the epicenter of the injury along the dorsal vein, within one hour of the contusion injury. Care will be taken to preserve the dorsal vein. A blunt dissector will be used to separate the dura from the pia-arachnoid, thereby a new surgical plane. Care will be taken to avoid unnecessary mechanical manipulation of the spinal cord itself. I propose a series of washes for the injured spinal cord in slightly hypertonic aCSF. This is the first time this intervention has been suggested, but I believe the washes will reduce edema and remove debris and inflammatory mediators.
d.) Using fine-tipped forceps, the edges of the durotomy will be tented up. The aforementioned 1x1 cm patch of dorsal fat pad will be utilized as a duraplasty material and sutured using 10-0 nylon in a continuous fashion, achieving a watertight dural closure. Autologous duraplasty material is being utilized to minimize any potential inflammatory reactions.
e.) The duraplasty will be observed at high power to ensure watertight closure. Thereafter, a thin coating of fibrin glue will be applied to promote dural closure and prevent excessive connective tissue ingrowth at the site of the duraplasty.
f.) The muscles will be closed in layers and the skin will be stapled using standard protocol.
g.) Post-operative care will be achieved using standard protocol.

Milan Radojicic, MD will be performing the microsurgical "early" expansive duraplasty.

Cadaveric dura, biosynthetic dura, goretex, ePFTE and autologous grafting material can be used as duraplasty material. I have proposed a novel biosynthetic dural substitute product, one seeded with selected growth factors for healing and regeneration, inhibitors of scar formation and antibiotics will be necessary. Moreover, a biosynthetic material could be seeded with meningeal cells to acts as a true dural substitute. We will be developing this intellectual property.


Reference List

1. Klekamp,J., Volkel,K., Bartels,C.J., & Samii,M. Disturbances of cerebrospinal fluid flow attributable to arachnoid scarring cause interstitial edema of the cat spinal cord. Neurosurgery 48, 174-185 (2001).
2. Klekamp,J. The pathophysiology of syringomyelia - historical overview and current concept. Acta Neurochir. (Wien. ) 144, 649-664 (2002).
3. Radojicic,M., Nistor,G., & Keirstead,H. A Novel Pathogenic Mechanism in Spinal Cord Injury. (In submission)(2005).
4. Lee,T.T. et al. Progressive posttraumatic myelomalacic myelopathy: treatment with untethering and expansive duraplasty. J. Neurosurg. 86, 624-628 (1997).