The straw that broke the monkey's back

Citation: Togawa D, Kovacic JJ, Bauer TW, Reinhardt MK, Brodke DS, Lieberman IH. Radiographic and histologic findings of vertebral augmentation using polymethylmethacrylate in the primate spine: percutaneous vertebroplasty versus kyphoplasty. Spine. 2006 Jan 1; 31(1):E4-10.

Summary of Experiment: Compression fractures are a common and very painful complication of osteoporosis and some traumatic injuries. The two procedures most commonly used to stabilize this type of fracture in people are vertebroplasty and kyphoplasty.

Six elderly female baboons were used to test the efficacy and rate of complications of these two procedures (two vertebrae each). Necrosis, foreign body reaction and leaking in those vertebrae were compared to holes that were created but not stabilized (two vertebrae) and one unaltered vertebrae. Analgesics and IV fluids were administered after surgery. Animals were checked twice per day for “abnormalities.” Three animals were killed “according to AVMA guidelines” 24 hours post surgery, and the other three at six months.

My Notes:

• The efficacy and rate of leaking complications of both procedures among people receiving these same two procedures were tested in a 2002 study, which was not cited. My search revealed nearly 100 papers that compare some aspect of these two procedures in human subjects.


• They fail to mention that baboons aren’t bipedal. The fact that the animals don’t walk upright and would be less susceptible to either compression fractures or vertical compression/stress during recovery has apparently been overlooked.


• These baboons did not have osteoporosis.


• Despite the fact that the entire spine was removed after the animals were killed, they forgot to remove of the vertebroplasty bones for examination.

Quote from the article:

“Unfortunately… bone mineral density of the baboons was much greater than that of human osteoporotic patients so that we were not able to expand the bone tamps to the same degree as is often achievable in humans. This fact may have artificially increased the risk of cement leak in both procedures. Some of the findings in the current study may not be supported in the patients with osteoporotic vertebral compression fractures because of these limitations. Moreover, the baboon vertebrae are morphologically different to human vertebrae (taller height in proportion than human vertebrae), so it is difficult to simulate human osteoporotic vertebral compression fracture. Future studies should attempt to induce more significant osteoporosis in other models using diet, pharmacologic, and surgical (i.e., oophorectomy) means.”

Why is the fact that they didn't have osteoporosis unfortunate?

So the authors admit it’s a crappy model, and everyone knows that there is a sea of human research data, but these people want to do more experiments on monkeys anyway?

Author Affiliations:
Cleveland Clinic Spine Institute, Cleveland, OH
Departments of Orthopaedic Surgery and Anatomic Pathology, Cleveland
Clinic Foundation, Cleveland, OH
Department of Orthopaedic Surgery, University of Utah, Salt Lake City, UT.

Funding acknowledged: Funds from “Kyphon Inc.” This competing interest was declared.