Femoral neck osteosynthesis using interfragmentary compression or position screw in synthetic bones. What are the mechanical differences?

ABSTRACT

PURPOSE: We aim to compare interfragmentary compression with the position osteosynthesis in the fixation of different femoral neck fractures (FN) in synthetic bones subjected to vertical load. METHODS: Forty-two synthetic femurs were subjected to neck fractures and separated into 3 groups according to the Pauwels classification Pauwels I had 6 units (PI); Pauwels II, 24 units, with and without comminution (PII); and Pauwels III, 12 units, with and without comminution (PIII). After, they were fixed with 2 different ways three 7, 0 mm cannulated lag screws (CSs) versus three 6, 5 mm solid fully threaded screws (SSs). Screws positioning was oriented by the Pauwels classification inverted triangle or crossed screws. All specimens were submitted to vertical loading until failure. RESULTS: The average force was 79.4 ± 22.6 Kgf. The greatest one was recorded in model 1 (135.6 Kgf), and the lowest in model 41 (39.6 Kgf). CSs and SSs had similar resistance until failure (p = 0.2). PI showed heightened resistance and PIII showed a worse response (p < 0,01). CSs had better performance in PIII (p = 0.048). Comminution and screws orientation caused no difference on peak force (p = 0.918 and p = 0.340, respectively). CONCLUSIONS: In synthetic bones, the resistance of a femoral neck fracture osteosynthesis using a 7, 0 mm cannulated lag screw or 6, 5 mm solid fully threaded screw are similar. There was no loss of efficiency with comminution in the femoral neck. Osteosynthesis resistance decreased with the verticalization of the fracture line and, in the more vertical ones, interfragmentary compression with CSs was more resistant than positional osteosynthesis with SSs.