An in vitro optimized injectable calcium phosphate cement for augmenting screw fixation in osteopenic goats

This study reports the proportioning and standardized mixing procedures for preparing a hydroxylapatite cement (tetracalcium phosphate and dicalcium phosphate) of desired viscosity and mechanical strength reproducibly for application in trauma surgery. The behavior and the biomechanical properties of the resulting bone cement in screw augmentation were then evaluated in our osteopenic goat model. The use of a shaker standardized the mixing procedure. The optimal volume of Na2HPO4 used to prepare the injectable cement was 0.45 mL/g, with averaged in vitro compressive strength of 48.29 +/- 5.62 MPa. Histology showed increasing tightly-coupled bone apposition on the cement surface without fibrous encapsulation as observed in the screw-only controls with time in the osteopenic goat model. The cement increased the initial screw pull-out force (54.7%, p = 0.005) significantly and the energy required to failure (54.7%, p < 0.05) significantly, and remained higher than the screw-only controls after 3 months (9.8% and 20.2%, respectively) and 6 months (20.2% and 44.7%, respectively). These results imply potential in the prevention of interfacial micromotions and subsequent fibrous tissue formation at the implant-bone interface resulting in a decreased risk of implant failure. The optimized cement in this study may serve as a good candidate for augmenting fixation of osteoporotic bone.