Proximal tibial fracture stability with intramedullary nail fixation using oblique interlocking screws

Objectives: The purpose of this study was to evaluate the mechanical stability of oblique interlocking screws in supplementing intramedullary nail fixation of high proximal tibial fractures. Design: In vitro experimental testing. Setting: Orthopaedic biomechanics laboratory, Sunnybrook and Women's College Health Sciences Center. Participants: Ten paired fresh-frozen human cadaver tibiae. Intervention: One tibia of each pair was randomized to be instrumented with an intramedullary nail (M/DN; Zimmer, Warsaw, Indiana), while the other was stabilized with a 13-hole stainless steel lateral tibial head plate (Synthes AO/ASIF). Specimens were tested in varus-valgus (v/v), flexion-extension (f/e) and torsion, before and after a 2-cm gap osteotomy was performed in the proximal segment. Testing of the nailed tibiae was performed with and without oblique proximal screws. Bone density was physically determined by removing a core of trabecular bone from the distal end of each tibia following testing. Main Outcome Measurement: Biomechanical construct stability. Results: The addition of the proximally placed oblique screws increased the stability of the nail construct in v/v by 50% (6.8 mm, P < 0.05), in f/e by 47% (7.2 mm, P < 0.05), and in torsion by 18% (3.0degrees, P < 0.05). There was no significant difference observed between the stability of the intramedullary nail construct with oblique screws and the plated construct. Trabecular bone density had a significant effect in reducing stability (P < 0.05) in nail and plate fixation. Conclusion: The addition of oblique interlocking screws significantly improves the stability of a nailed proximal tibia fracture and provides comparable stability to a plate osteosynthesis.