OTA 2005 Posters
Scientific Poster #72 Basic Science
Immediate Weight Bearing of Comminuted Tibial Shaft Fractures after Statically Locked Intramedullary Nailing
Purpose: Comminuted tibial shaft fractures are traditionally treated with statically locked intramedullary nailing and protected weight bearing until fracture callous is evident. The purpose of this study is to demonstrate that immediate full weight bearing following intramedullary nailing of these fractures is safe.
Methods: In part one of the study, a biomechanical model was designed to determine the fatigue strength of four different current brands of tibial nails (Synthes, Stryker, Smith & Nephew, Zimmer). A comminuted fracture model was created using two pieces of polyvinylchloride (PVC) pipe. 10-mm diameter tibial nails were inserted within the PVC pipe and secured proximally and distally with two or three locking bolts. The constructs were cycled in axial compression for 500,000 cycles or until implant failure. This simulates walking three miles a day for 16 weeks. The tests were conducted using staircase method (200N per step), and the fatigue strength was identified for each of the tibial nail designs. In part two of the study, 13 consecutive patients with tibial shaft fractures treated with intramedullary nailing and immediate full weight bearing were identified. Four patients were lost to follow-up. The remaining nine fractures (2 OTA type 42-A, 6 type 42-B, and 1 type 42-C) were followed to fracture union or reoperation. Five Stryker and four Synthes tibial nails with larger diameter interlocking bolts were used.
Results: When two interlocking bolts were placed proximally and distally, the fatigue strength was between 1400N and 1600N for the Smith & Nephew nail, 1200N to 1400N for the Synthes nail, 1100N to 1300N for the Zimmer nail, and 900N to 1100N for the Stryker nail. Adding a third interlocking bolt proximally and distally to the Smith & Nephew nail increased the fatigue strength by 13%. In all cases, implant failures occurred through the proximal or distal interlocking bolts. In the clinical study, no implant failures occurred and all but one fracture healed without additional surgery. One patient underwent exchange tibial nailing at 12 weeks due to delayed union.
Conclusion/Significance: Current tibial nail designs permit immediate full weight bearing of comminuted tibial shaft fractures with minimal risk of implant failure. This may facilitate mobilization in the early postoperative period, especially in the multiply injured patient.