Aim: While ankle fractures are not thought of as osteoporotic fractures, poor bone quality presents difficulties in fracture fixation of the distal fibula. We measured the relation between bone density of the distal fibula and the insertional and stripping torques of screws used for fibular plating using two different plate configurations.

Methods: Ten paired fresh cadaveric ankles (average age: 81.7 years) were used for the study. Computed tomography scanning with phantoms of known density was used to determine the bone density along the distal fibula. A standard small fragment seven-hole one-third tubular plate was applied to the lateral surface of the fibula, with three proximal bicortical cortical screws and two distal unicortical cancellous screws. A posterior plate in which all five screws were cortical and achieved bi-cortical purchase was subsequently applied to the same bones such that the screw holes did not overlap. A torque sensor was used to measure the torque of each screw during insertion (Ti) and then stripping (Ts).

Results: Mean bone density of the distal fibula is significantly less than in the shaft (p< 0.01). There was a moderate positive correlation between torque and bone density for the lateral plates (r2=0.6 for Ti and r2=0.7 for Ts), and a weak correlation for the posterior plates (r2=0.4 for Ti and Ts). For the proximal three screws, there was no significant difference in average Ti and Ts between lateral and posterior plates. For the distal two screws, posterior plates had significantly higher values for both Ti and Ts than the lateral plates (p< 0.01).

Conclusions: The insertion and stripping torques of the screws in the distal fibula were significantly higher and less dependent on bone density with a posterior plate than with a lateral plate.