Hemilaminectomy Versus Mini-Hemilaminectomy in Canine Intervertebral Disk Extrusion

In a recent study, mini-hemilaminectomy decompressed the spinal cord to a greater extent than hemilaminectomy in dogs with thoracolumbar intervertebral disk (IVD) extrusion. The prospective study was conducted by researchers in Sweden and published in Frontiers in Veterinary Science.

Surgical spinal cord decompression is performed in dogs with neurologic deficits caused by IVD extrusion. Hemilaminectomy and mini-hemilaminectomy are two of the techniques used to gain access to the vertebral canal to remove extruded disk material.

Hemilaminectomy is the removal of half of the vertebral arch, including the lamina, pedicle, and articular process. In mini-hemilaminectomy, the pedicle is removed but the articular process is spared. A dorsal or dorsolateral approach is typically used for hemilaminectomy. A mini-hemilaminectomy can be performed via a lateral approach, which the researchers used for the dogs in this study.

The investigators compared the degree of spinal cord compression before and after hemilaminectomy or mini-hemilaminectomy in 30 dogs (15 in each group) with acute thoracolumbar IVD extrusion. All dogs were client-owned pets randomly assigned to either the hemilaminectomy or the mini-hemilaminectomy group. Exclusion criteria were evidence of IVD extrusion, neurologic deficits, or pain lasting longer than 3 weeks; elevated serum creatinine level; and myelography.

The researchers evaluated spinal cord compression by measuring the cross-sectional diameter of the spinal cord with computed tomography (CT) before and after administration of intravenous contrast material. CT images were obtained before and within 1 week after decompression in all dogs. For dogs in both groups, the procedures included removal of all visible disk material, fenestration of the affected disk, and placement of a fat graft over the laminectomy site.

Before decompression, the mean spinal cord cross-sectional diameter was not significantly different between the two groups. In both groups, the mean spinal cord diameter significantly increased after the operation, indicating that both procedures reduced spinal cord compression. However, the reduction in compression—the difference in compression before and after the procedure—was significantly greater after mini-hemilaminectomy than after hemilaminectomy.

The result is “surprising,” write the authors, “given that one would expect that a larger laminectomy defect would lead to at least equal amount of decompression.” They suggest that the lateral approach used for mini-hemilaminectomy could provide better access to the ventral spinal canal and allow more extruded disk material to be removed. A lateral approach also makes fenestration easier and reduces the trauma to surrounding tissues, they write.

The authors note that the study design did not allow for blinding of the CT reviewer or anonymization of the CT images. Another limitation was the variation in timing of the postoperative CT acquisitions, although the mean time to postoperative CT was similar in the two groups.

The authors conclude that if further studies confirm their results, mini-hemilaminectomy could become preferred over hemilaminectomy because of the advantages of the lateral approach and the potential for greater spinal cord decompression.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.