Evaluation of calcium phosphate bone cement in augmenting screw hole defects in the ulna: A biomechanical study

Following ulnar shortening osteotomies, plates are often removed due to discomfort or irritation. The screw holes left after plate removal act as stress risers and predispose the bone to fracture. To our knowledge, calcium phosphate cement (CPC) is yet to be investigated for its use in reinforcing screw holes. The aim of this study was to determine if filling screw holes with CPC in a synthetic anatomical ulna model will improve its immediate mechanical strength compared to leaving screw holes unfilled.

Eighteen synthetic anatomical ulna models were randomly divided into three equal groups. The control group was left unaltered, the drilled group received six 3.5 mm screw holes, and the CPC group had the six 3.5 mm screw holes filled with CPC. All bones were subjected to torsional loading until failure. Peak torque at failure, stiffness, and energy absorption were measured.

Compared to the drilled group, the CPC group had greater peak torque, stiffness, and energy absorption. Group effects on peak torque and stiffness were moderate (eta squared = 0.12 for both) but did not reach statistical significance (p = 0.37 and 0.38, respectively). A statistically significant group effect was found for energy absorption (p < 0.001); but post-hoc analysis revealed no difference between the drilled and CPC groups.

Effect sizes suggest CPC may improve mechanical performance, albeit modestly. Clinicians may consider using CPC for reinforcing screw holes after plate removal in bones like the ulna when refracture is of concern.