Augmenting a dynamic hip screw with a calcium sulfate/hydroxyapatite biomaterial

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Bone Mechanics

Background:

• Internal fixation failure in hip fractures necessitates reoperation.
• Calcium sulfate/hydroxyapatite (CaS/HA) is a potential biomaterial for augmenting fracture fixation.
• Improving dynamic hip screw (DHS) fixation is critical for reducing reoperation rates.

Purpose of the Study:

• To evaluate if injecting 2 ml of CaS/HA enhances DHS fixation in synthetic and human trabecular bone.
• To assess the impact of CaS/HA on the mechanical stability of DHS constructs.
• To investigate the influence of bone quality and injection technique on CaS/HA efficacy.

Main Methods:

• Two-part study: synthetic bone blocks (n=74) and osteoporotic human femoral heads (n=29).
• Three subgroups: empty (no injection), cannulated screw injection, and fenestrated screw injection.
• Micro-computed tomography (µCT) imaging for bone volume fraction, insertion angle, and head diameter.
• Mechanical pullout tests measuring peak force, stiffness, and work.

Main Results:

• Fenestrated CaS/HA injection increased pullout strength in synthetic bone compared to no injection.
• Cannulated injection showed higher pullout strength in low-density synthetic blocks.
• No significant differences in pullout strength were observed in human femoral heads due to larger variations.
• Bone volume fraction correlated positively with peak force and work; insertion angle correlated with stiffness.

Conclusions:

• CaS/HA biomaterial can improve dynamic hip screw fixation, particularly in synthetic bone models.
• Effective spreading of CaS/HA around the screw threads is essential for successful clinical application.
• Further research is needed to optimize CaS/HA delivery and confirm efficacy in diverse patient populations.