Hollow-Bone-Graft Dynamic Hip Screw Can Fix and Promote Bone Union after Femoral Neck Fracture: an Experimental Research

BACKGROUND Delayed bone union, nonunion or osteonecrosis often occur after femoral neck fractures in young adults. Secondary bone healing requires strong internal fixation, intramedullary pressure reduction and early functional exercise. OBJECTIVE To compare bone healing of femoral neck fractures treated with hollow-bone-graft dynamic hip screws (Hb-DHS) and standard dynamic hip screws (DHS) in an animal model. DESIGN Testing of specifically designed fixation devices in a pig animal model. INTERVENTIONS/METHODS We designed Hb-DHS and DHS devices appropriate to the femoral neck and head of experimental animals and used them in eight pigs (4-month-old, male or female, 30-40 kg/each). Under anesthesia, we induced medium neck type, Garden III type femoral neck fractures in each pig with fracture gaps of 0.5 mm and then fixed each left femur with Hb-DHS and each right femur with DHS. We assessed the animals radiographically and by postmortem visual appraisal of evidence of bone healing 8 and 16 weeks postoperatively. RESULTS There were significant differences in radiographic and general findings between the Hb-DHS and DHS groups at weeks 8 and 16 postoperatively. We found statistically significant differences between the Hb-DHS and DHS groups in bone healing scores, trabecular bone volume percentage and bone mineral density as assessed on plain radiographs and computed tomography images (P < 0.05). There were also significant differences between the Hb-DHS and DHS groups in postmortem visually assessed indicators of bone healing at both 8 and 16 weeks postoperatively. CONCLUSIONS The Hb-DHS device promotes femoral neck bone union, stimulates trabecular bone formation, increases BMD and has advantages over DHS for internal fixation of femoral neck fractures. This animal experiment will contribute to developing optimal treatment for femoral neck fractures in young adults.