An in vitro biomechanical evaluation of bone cements used in percutaneous vertebroplasty

The purpose of this study was to determine the strength and stiffness of osteoporotic vertebral bodies (VBs) subjected to compression fractures and subsequently treated with bipedicular injections of various polymethylmethacrylate cements. Ten spines were harvested from nonembalmed female cadavers (age 68.6 +/- 13.7 years) and evaluated for bone mineral density using the dual energy X-ray absorptiometry method (t-score = -2.3 +/- 2.4). The 50 VBs (L1-L5) were disarticulated, compressed in a materials testing machine to determine initial strength and stiffness, and then assigned to one of six groups. Two of these groups (n = 8, n = 9) concerned experimental cements, the results of which are not reported here. The 33 vertebral bodies in the remaining four groups were left untreated or were repaired using a transpedicular injection of one of three commercially available polymethylmethacrylate cements. These four groups were: a) no treatment (no cement, n = 8); b) Simplex P (n = 9); c) Cranioplastic (n = 8); and d) Osteobond (n = 8). The VBs were then compressed again according to the initial protocol, and posttreatment strength and stiffness were measured. Results suggested that bipedicular injection of Simplex P and Osteobond restored VB stiffness to initial values, whereas VBs injected with Cranioplastic were significantly less stiff than in their initial state. VBs injected with cement (regardless of type) were significantly stronger than they were initially.