Predictability of implants size in Robotic Surgery for Total Knee and hip Replacement Arthroplasty

Abstract

Accuracy of implantation using computer assisted navigation and robotic total knee replacement arthroplasty (TKR) and total hip replacement (THR) has been proven. Templating the pre-operative radiographs has become standard. This gives an insight into the pre op planning and the sizes most likely to be used. This helps to reduce the inventory for storage of implants and cost. While the templating of radiographs has been helpful, implant sizes prediction remains less than desirable. Aim of present study was to look at the predictability of implant sizes in CT planning for robotic surgery. 30 MAKO robotic joint replacements were performed (15TKR/15THR) with pre op CT scans for implant size. For TKR, the sizes used were mean 5 in femur and tibia (SD1 and range 3-7). In tibia, size used was same as predicted. In the femur in two cases the size was reduced by one to balance the gaps. Insert thickness was increased by one size in 4 cases. For THR, the acetabular cup, femur, head diameter and offset were predicted 100%. The neck length had to be changed in some cases by up to two sizes. for balance/stability. In conclusion the CT scan pre-operative planning for MAKO robotic knee joint replacement can predict 100% times the size of tibia, within one size of femur and insert for TKR. These figures are better than published predictability of templates of plain radiographs where implant size was predicted 42% for femoral and 37% acetabular components while 87% of the femoral components and 78% of the acetabular cups were accurate within one size up and down.