Development and evaluation of a modified injectable calcium phosphate cement with enhanced injectability and mechanical stability for bone defect repair

This study aimed to optimize an injectable carbonated hydroxyapatite cement for metaphyseal bone defect filling and to evaluate its biomechanical performance in distal radius fracture fixation. Six food- or pharmaceutical-grade additives, including sodium alginate, glycerol, astragalus gum, xanthan gum, citric acid, and hydroxypropyl methylcellulose (HPMC), were screened to improve injectability while maintaining setting behavior and mechanical strength. Among them, 2% HPMC provided the best overall performance, increasing injectability to approximately 95% without markedly affecting setting time or compressive strength. The optimized injectable carbonated hydroxyapatite cement (ICHA) was then tested in a standardized human cadaveric distal radius fracture-defect model using three fixation strategies: K-wire fixation alone, ICHA cement alone, and combined ICHA + K-wire fixation. Within a 10° torsion range, the ICHA and ICHA + K-wire groups showed higher torsional stiffness and maximum torque than the K-wire-only group, although peak torque occurred at smaller torsion angles. Under physiological compression, the groups showed comparable stability, whereas ICHA-containing groups showed greater resistance under higher compression. These findings suggest that 2% HPMC-modified ICHA may serve as an injectable metaphyseal void filler and structural adjunct to conventional K-wire fixation.