Session I - Geriatrics
Alendronate Improves Screw Fixation in Osteoporotic Bone: A Clinical Study of Pertrochanteric Fractures
Purpose: Screw loosening is a common cause of fracture malunion and nonunion, particularly in osteoporotic bone. Because of this, fixation augmentation techniques such as the use of hydroxyapatite (HA)-coated screws have been recommended for treatment of fragility fractures. Another innovative approach to enhance implant fixation is bisphosphonate therapy. Animal studies have shown that alendronate (ALN) inhibits bone resorption at the bone-screw interface thereby enhancing fixation. However, no clinical data are yet available. We wanted to determine whether fixation with HA-coated screws could be further improved by postoperative ALN therapy in osteoporotic pertrochanteric fracture patients.
Methods: Sixteen consecutive patients with pertrochanteric fractures were selected. Inclusion criteria were female sex, age 65yrs, and bone mineral density (BMD) T-score <-2.5 SD. Exclusion criteria included pin insertion torque £1,000N/mm and bisphosphonate treatment during the 2-year period prior to fracture. Fractures were fixed with a pertrochanteric fixator and four HA-coated pins. Two pins were implanted in the femoral head (pin positions 1 and 2) and two in the femoral diaphysis (pin positions 3 and 4). Patients were randomized to therapy with either ALN (group A) or placebo (group B) for a 3-month postoperative period. Group A patients received an oral dose of 70 mg of ALN per week. Fixators were removed 3 months after surgery in all patients.
Results: All the fractures healed. No pin loosening or infection occurred in either group and no differences between femoral neck-shaft angle at 6 months versus immediately postoperative were observed. There was no significant difference in pin insertion torque between the two groups. The combined mean extraction torque of the pins implanted at positions 1 and 2 (cancellous bone of the femoral head) was 3181±1385N/mm in group A and 1890±813N/mm in group B (P<0.001). The combined mean extraction torque of the pins implanted at positions 3 and 4 (cortical bone of the femoral diaphysis) was 4327±1720 N/mm in group A and 3785±1181N/mm in group B (ns).
Discussion/Conclusions: This is the first clinical study to show improved fixation following postoperative ALN treatment. We observed a twofold fixation increase in the pins implanted in cancellous bone. With cortical bone, the difference in pin fixation was less marked. We believe that the effect of ALN on implant fixation could be even more pronounced with standard metal screws that have a lower osteointegrative ability than HA-coated screws. These findings also have enormous implications for other implant fixation procedures in weak bone.