Initial stability of type-2 tibial defect treatments.

Treatment of proximal tibial defects is important to the survival of tibial prosthesis after total knee replacement. The objective of this finite element study was to determine a better understanding of the stresses produced by different treatment options for moderate uncontained type-2 defects. Methods analysed were the use of metal wedges, metal blocks, cement wedges, and cement blocks for the two defect angles 15 degrees and 30 degrees. The effect of a stem extension on the stress profiles was also analysed for each defect treatment and angle to establish the necessity of these extensions and consequent bone removal on the stability of the augments. Equivalent stresses in two regions of interest (ROIs) adjacent to the augments and shear stresses along the bone-cement interface of the defect were investigated. The lowest equivalent stresses were found in the metal block augment for both defect angles and ROIs. The highest equivalent stress in the ROIs and shear stress values along the bone-cement interface of the defect were found in the cement wedge augment model for both defect angles. Stem extensions were shown to increase equivalent stresses in the bone closer to the tibial stem but to decrease equivalent stresses closer to the cortical bone. The use of a stem extension significantly increased the shear stresses in the cement in all cases except in the metal block model. It is recommended that metal block augments are used without a stem extension in small-defect (i.e. peripheral defect angle of 15 degrees) total knee replacement procedures.