Biomechanical evaluation of current patella fracture fixation techniques

Objective: To compare the mechanical effectiveness of three different techniques for stabilization of transverse fractures of the patella. Design: Cadaveric knees were used to model acute fractures of the patella. To test three treatment techniques in pairs of knees, specimen pairs were assigned randomly to a set of predetermined treatment pairs so as to provide equal numbers of paired and unpaired data sets. Results then were analyzed using a two-way analysis of variance. Setting: The treatment techniques used are widely applicable in the clinical setting for the treatment of transverse fractures of the patella. No specialized equipment or training is required for the general or subspecialized orthopaedic surgeon. Patients/Participants: None. Interventions: Fractures were created in eighteen knees (nine pairs) and repaired by one of three techniques: (a) modified tension band (AO technique); (b) two parallel 4.5-millimeter interfragmentary lag screws; or (c) a new technique using four-millimeter cannulated lag screws with a tension band wired through the screws. Main Outcome Measures: In mechanical testing, the amount of interfragmentary separation in simulated knee extension and the maximum load to failure at 45 decrees of flexion were measured. Results: Fractures stabilized with a modified tension band were found to displace significantly more than those fixed with screws alone or screws plus a tension band in simulated knee extensions (p < 0.05). The fractures fixed with the cannulated screws plus the tension band failed at higher loads (mean = 732 newtons) than those stabilized with screws alone (mean = 554 newtons, p = 0.06) or those with a modified tension band (mean = 395 newtons, p < 0.05). Conclusions: Combining interfragmentary screw fixation with the tension band principle appears to provide improved stability over the modified tension band or screws alone for transverse patella fractures. Cannulated screws allow for simple, reliable addition of a tension band to screw fixation.