Evaluation of calcium phosphate and calcium sulfate as injectable bone cements in sheep vertebrae

STUDY DESIGN: An animal study. OBJECTIVE: To compare the biomechanical and biometabolic properties between calcium phosphate (CaP), calcium sulfate (CaS), and polymethylmethacrylate (PMMA) as bone void fillers in a sheep model of lumbar vertebral defect. SUMMARY OF BACKGROUND DATA: PMMA is commonly used as a bone void filler in vertebroplasty and kyphoplasty. However, it has certain intrinsic limitations. CaP and CaS are considered as potential PMMA substitutes, but further in vivo evaluations of their biomechanical and biometabolic properties are needed before they can be recommended for clinical use in routine vertebroplasty and kyphoplasty procedures. METHODS: Bone voids were experimentally created on lumbar vertebrae L2-L5 with L6 left intact as a normal control in 24 adult female sheep. The defect vertebrae L2-L5 in each of the animals were randomized to receive no filler augmentation (controls) or augmentation with CaP, CaS, or PMMA. Animals were killed after 2, 12, and 24 weeks of the bone filler augmentation, respectively. Vertebrae L2-L6 were collected and their biomechanical strength/stiffness, osseointegration activity, and biodegradability were evaluated. RESULTS: At all 3 time points tested, the PMMA-augmented lumbar vertebra had the highest biomechanical strength and stiffness, followed by the intact vertebra L6. CaP and CaS significantly improved the strength as compared with the sham augmentation, but did not yet restore it to the normal level. Osteogenesis occurred at low levels in the empty vertebrae, in the CaP-augmented defect vertebrae at 12 and 24 weeks, and in the CaS-augmented vertebrae at 12 weeks, but at a substantially high level after 24 weeks of CaS augmentation. The filler biodegradation rate was low in the CaP-augmented vertebrae, but was substantially high in the CaS-augmented vertebrae. CONCLUSIONS: CaP and CaS are effective enough to strengthen the fractured lumbar vertebrae in a time-dependent manner, although not as good as PMMA. CaS has a much higher osseointegration capacity than CaP. Copyright © 2012 by Lippincott Williams &Wilkins.