INFLUENCE ON STABILITY OF DISTAL TIBIAL FRACTURES TREATED WITH INTRAMEDULLARY NAILING

Abstract

Introduction: The present study was performed to compare the mechanical properties and fixation stability of tibial nails of the newest generation used in the management of distal metaphyseal fractures. Furthermore, we tried to evaluate whether distal locking with 4 locking screws might increase load-sharing after stabilization of distal metaphyseal tibial fractures.

Methods: We used 16 Sawbones third generation large left tibiae (Sawbones Inc., Sweden) to create an unstable distal metaphyseal fracture model (AO type 43-A3). In 8 specimens the fracture was stabilized with 2 nails with 3 distal locking options (4x VersaNail™, DePuy Orthopaedics, Johnson& Johnson, Warsaw, IN; 4x T2 Tibial Nailing System™, Stryker, Kiel, Germany) and in 8 specimens with 2 nails with 4 locking options (4x Connex™, ITS Spectromed, Lassnitzhöhe, Austria; 4x Expert Tibial Nail™, Synthes, Switzerland). Each specimen was loaded cyclically with three loading sequences over a period of 40,000 cycles in each series (700N, 1,500N, 1,800N). Implant stiffnes during axial cyclic loading series in 7° valgus alignement was recorded as well as cycles until failure of the bone-implant-construct.

Results: In the second loading series, implant failure was observed in all tibial nails with 3 distal locking screws after a mean period of 57,196.7 cycles. If distal locking was performed with 4 screws, implant failure was recorded in the third and last loading series after a mean period of 87,518.3 cycles (p< 0.001). If distal locking was performed with 3 distal locking screws, implant stiffness was 1776 (±99) N/mm. If distal locking was performed with 4 locking screws, implant stiffness was 2674 (±208) N/mm (p< 0.001).

Conclusion: Distal locking with 4 screws improves implant-bone stability. Stability is influenced by the number of locking screws and not by screw diameter. In these fracture type, nails with 4 distal locking options should be used.