Medial Malleolar Screw Length to Achieve Thread Purchase in the Dense Bone of the Tibial Epiphyseal Scar Location Based on CT Model.

Medial malleolar ankle fractures are one of the most common surgically treated fractures of the ankle joint. Current AO guidelines for medial malleolar fractures recommend 2 partially threaded cancellous screws across the fracture line. For these screws to cross the fracture line, the threads must purchase the distal tibial metaphysis, which is an area of decreased bone density especially in elderly osteoporotic bone. The epiphyseal scar of the tibia is the densest portion of distal metaphysis of the tibia, and it has been determined that bone density decreases significantly further proximal through the tibia. One hundred eighty-three individual weightbearing coronal CT scans were assessed to measure the location of the epiphyseal scar and propose an ideal screw length to purchase this area and remain within the distal most portion of the tibia. In following with this criteria it was determined that a 34 mm ⅓ thread pattern screw and a 38 mm ½ thread pattern screw would suffice for 92.6% and 75.3% of males, respectively. It was determined that a 30 mm ⅓ thread pattern screw and a 32 mm ½ thread pattern screw would suffice for 93.4% and 85.3% of females, respectively. This study proposes optimal screw lengths in a theoretical area of increased bone density that may decrease complications in patients with compromised bone quality.