Evaluation of an osteoconductive resorbable calcium phosphate cement and polymethylmethacrylate for augmentation of orthopedic screws in the pelvis of canine cadavers.

OBJECTIVE: To evaluate the effect of an osteoconductive resorbable calcium phosphate cement (CPC) on the holding power of bone screws in canine pelvises and to compare the effect with that for polymethylmethacrylate (PMMA). SAMPLE POPULATION: 35 pelvises obtained from canine cadavers. PROCEDURE: Each pelvis was sectioned longitudinally. Within each pair of hemipelvises, one 4.0-mm cancellous screw was placed in the sacroiliac (SI) region and another in the iliac body. Similar regions on the contralateral-matched hemipelvis were assigned 1 of 3 augmentation techniques (CPC-augmented 4.0-mm cancellous screws, PMMA-augmented 4.0-mm cancellous screws, and CPC-augmented 3.5-mm cortical screws). Pullout force was compared between matched screws and between treatment groups prior to examination of cross sections for evaluation of cement filling and noncortical bone-to-cortical bone ratio.
RESULTS: CPC and PMMA augmentation significantly increased pullout force of 4.0-mm screws inserted in the SI region by 19.5% and 33.2%, respectively, and CPC augmentation significantly increased pullout force of 4.0-mm cancellous screws inserted in the iliac body by 21.2%. There was no difference in the mean percentage augmentation between treatment groups at either location. Cement filling was superior in noncortical bone, compared with filling for cortical bone. Noncortical bone-to-cortical bone ratio was significantly greater in the sacrum (6.1:1) than the ilium (1.3:1). CONCLUSIONS AND CLINICAL RELEVANCE: CPC and PMMA improve the ex vivo holding strength of 4.0-mm cancellous screws in the SI and iliac body regions and SI region, respectively. Cement augmentation may be more effective in areas with greater noncortical bone-to-cortical bone ratios.