A comparative finite element study of novel design hook plates for fixation of patella fracture.

PURPOSE

To test the mechanical properties of novel design hook plates for fixation of the patellar fracture by finite element analysis.

METHODS

Finite element analysis was used to construct a model of transverse patellar fracture and inferior pole fracture of the patella (IPFP) based on the CT data of the knee joint of a healthy young male volunteer. For the transverse fracture, stress distribution within the winged hook plate fixation and displacement of the fracture was compared to that of tension-band wiring (TBW) fixation. For the IPFP, the stress distribution within the wingless plate and displacement of the fracture were calculated under the four different application methods. All the models were created by assuming the knee flexion in 45° during non-weight-bearing, and applying the quadriceps tension on the superior pole of the patella.

RESULTS

In the model of transverse patellar fracture: The displacement and stress incurred in the fixation of patellar fractures with winged hook plates are much less than with TBW fixation (0.05 mm vs 0.3 mm; 121 MPa vs 268 MPa). In the model of IPFP: The wingless hook plate-cable wire-screw construction resulted in the least amount of displacement, followed by the wingless hook plate-cable wire (0.18 mm vs 0.297 mm). Displacement of the inferior pole of the patella would be more obvious in the two constructions that did not combine cable wires, especially the construction with neither cable wires nor screws.

CONCLUSION

In consideration of improvement of mechanical rigidity, winged hook plate was superior to TBW technique when being used for fixation of transverse patellar fracture, while combination of cable wire should be recommended when wingless hook plate being used for fixation of IPFP.