Treatment of bone defect in revision total knee arthroplasty : a finite element study

Abstract

Proximal tibial and distal femoral bone defects are often encountered in revision total knee arthroplasty. The restoration of lost bone support and joint stability is the main challenge. Cement, cement with screw reinforcement, and metal augment are choices to repair bone loss. However, there is limited information on whether cement with screw reinforcement can repair large uncontained bone loss. The present study was conducted to determine whether cement with screw reinforcement increase the initial stability than cement alone, the optimal size of defect to repair, and to evaluate the stability and load sharing (cortical rim, cancellous bone) at the implant-cement interface under the tibial and femoral component in revision TKA. Five FE models of 5, 7.5, 10, 12.5 and 15 mm height wedge-shaped bone defects in medial tibia plateau, and models of 4, 6, 8, 10, 12mm height bone defects in medial distal femoral condyle were constructed and analysed. 30, 45, 60, 75, 90 and 115mm cemented and press-fit tibial extension stems are simulated separately. Cement, cement with screws reinforcement and metal augment were used to repair bone defects. The maximum vertical displacement of the implant-cement interface, and maximum shear stress of the bone-cement interface were investigated. The results found in cases associated with bone loss of 12.5 and 15mm height, metal augment is recommended. In case of 10 and 7.5mm height bone defect, cement with screw reinforcement and metal augment can be chosen. When the defect is 5mm, all the three options can be considered. The use of long stem, no matter cemented or press-fit, can increase the stability. Provided cemented stem is used, and cement with screw reinforcement is used to repair the bone defect; if the defect is between 12.5mm and 15mm, then the length of the stem should be ≥ 60mm, if the defect is between 10mm and 12.5mm, then the length of the stem should be ≥ 45mm. If the defect is <10mm, all length of long stem can be chosen. Provided press-fit stem is used, and cement with screw reinforcement is used to repair the bone defect; if the defect is between 12.5mm and 15mm, then the length of the stem should be ≥ 75mm. If the defect is between 10mm and 12.5mm, then the length of the stem should be ≥ 45mm. If the defect is <10mm, all length of long stem can be chosen. In femoral defects, when the defect is <6mm, cement, cement with screw reinforcement, metal augment can be used; when the defect is between 6mm and 10mm, cement with screw reinforcement can be used; when the defect is over 10mm, only metal augment can be used. This study demonstrates that the use of cement, cement with screws reinforcement, metal augment to repair bone defect in revision TKA affect the micromotion at the bone-cement interface. Cement with screw reinforcement decrease micromotion than cement alone when repair bone defect in revision TKA. The recommended treatment options to repair defect in distal femoral and proximal tibial defects are presented.