Abstract:

BACKGROUND: Static compressure effect between the fracture fragments was generated by fixation itself (tension band wire and screw), but dynamic compression effects were generated during flexion. Mechanical strength and stability of patellar fracture fixation have obvious advantages. However, there are lacks of quantitative comparative studies on static and dynamic compression effects of these fixation methods.
OBJECTIVE: To observe strength changes and clinical significance of static and dynamic compression using four fixation techniques.
METHODS: Standardized transverse patellar fracture models were created with fresh cow patellas. The patellas were randomly divided into four groups: fixation was accomplished with modified tension band wiring (wire group); modified tension band with braided cable (cable group); interfragmentary screws (screw group); cannulated screw tension band with wire (cannulated screw group). Before fracture fixation, Fuji pressure-sensitive film was laid among fracture fragments to measure the pressure among fracture fragments after fixation, i.e., static and dynamic compression. Model of each group was measured as follows: (1) after fixation, the fixation was removed, and the Fuji pressure-sensitive film was taken out; (2) after fixation, material testing machine was used. Samples underwent a three-point bending test with a 5 000 N load, simulating dynamic compression during knee flexion. Subsequently, Fuji pressure-sensitive film was taken out. Each Fuji pressure-sensitive film was tested using prescale FPD-8010E software. Thus, average pressure among broken bone ends was obtained, and statistical analysis was performed. Static and dynamic compression among broken bone ends was compared in each group.
RESULTS AND CONCLUSION: Average static compression was significantly lower in the wire group than in the cable group, screw group and cannulated screw group (P < 0.05). Under 5 000 N load of dynamic compression, similar compression among broken bone ends was visible among wire group and cable group, screw group and cannulated screw group (P > 0.05). Dynamic compression was higher than static compression in the wire group (P < 0.05). Results verified that compared with modified tension band wire fixation technique, cable or screw could evidently increase static compression among broken bone ends, but simultaneously weaken dynamic compression among broken bone ends.

Key words: biomechanics, patella, fractures, bone, fixed