Laminectomy membrane formation in dogs: is the answer still elusive?

Laminectomy membrane formation in dogs: Is the answer still elusive? Spinal disease is common in dogs and is frequently associated with devastating neurological deficits. The acute paraplegic patient is a large part of the case-load in many neurology referral centres, and is most commonly the chrondrodystrophoid dog with a Hansen type I (Hansen, 1952) thoracolumbar disc herniation. Laminectomy is usually the treatment of choice for these patients. Both dorso-lateral hemilaminectomy and dorsal laminectomy are performed although hemilaminectomy may be more effective because it is easier to remove extruded disc material Laminectomy membrane formation (also termed epidu-ral/constrictive fibrosis or scarring, postlaminectomy ste-nosis or scar) is a recognised complication of spinal surgery in both humans and dogs and can result in lack of recovery or worsening of neurological status following laminectomy. In a recent issue of The Veterinary Journal, Dr. Ronaldo da Costa and his colleagues at the Federal University of Santa Maria, Brazil, investigate a new method of potentially protecting the spinal cord from this serious pathological event and compare it with the routinely used free fat graft (da Costa et al., 2006). During post-operative healing of a laminectomy site, a haematoma fills the bone defect, followed by development of a fibrous callus which then undergoes metaplasia to cartilage and then bone (Trotter et al., 1988). Adhesion and fibrosis is part of this healing process, which can involve the dura and nerve root if no attempt is made to protect them after the laminectomy. In humans, considerable post-operative morbidity may occur due to adhesion around nerve roots (Songer et al., 1990) and the level of pain may be correlated to the amount of scar tissue observed on MRI (Ross et al., 1996). Adhesions can also lead to severe spinal cord compression, and this can lead to significant neurological dysfunction. Despite improvements in microsurgical techniques and diagnostic neuroradiological modalities, the development of epidural fibrosis after lumbar and lumbosacral surgery for disc herniation remains a common reason for failed back surgery in humans. Furthermore, epidural adhesions make re-exposure of the same operative area technically difficult and dangerous because the risk of nerve root injury and dur-al tears are greatly increased. Various synthetic and organic materials have been implanted into laminectomy defects to act as a barrier between the exposed dura mater and surrounding muscles to prevent epidural fibrosis (Gill et al., 1979; Songer et al., 1990). Generally, the results of previous studies have …