Biomechanical and fracture characteristics of different filling and fixation methods applied to various proximal tibial metaphyseal defect sizes in an ovine model.

BACKGROUND

Ideal treatment method based on the size of the defect in local aggressive bone tumors is yet to be described. We evaluated the mechanical behavior of different fixation methods for various defect sizes located in the proximal tibia.

METHODS

Ninety-one sheep tibiae were distributed in five groups. Each study group was further divided into three subgroups, forming 25%, 50%, and 75% metaphyseal defects. The five groups were divided as follows: 1) control group where tibiae remained intact (n = 7); 2) isolated defect created, without filling (n = 21); 3) filling with cement (n = 21); 4) application of two subchondral cortical screws in addition to cement (n = 21); and 5) application of plate-screw fixation in addition to cement (n = 21). A loading test simulating the axial load applied by the distal femur to the tibia plateau was performed. The maximum failure load was compared between groups according to the defect size and fixation method.

FINDINGS: In 25% defects, group 5 had significantly higher failure load than other groups. However, in 50% and 75% defects, additional fixation did not increase the failure load. Also, additional screw fixation did not increase failure load in all defect sizes. There was a significant positive correlation between fracture morphology and defect size, fixation method, and failure load.

INTERPRETATION: Additional plate-screw fixation would increase the stability in defects ≤25%. In defects ≥50%, additional fixation does not increase stability. Screw fixation in addition to cementing does not increase stability in all defect sizes.