Impedance force control for lateral milling of bone in total knee arthroplasty

Robotic knee surgery performs bone cutting without relying on mechanical jigs during bone preparation of TKA (total knee arthroplasty). The inaccuracy induced by loose jig fixation and slot width tolerance can, subsequently, be avoided. Mill is usually used as the bone cutter in most of the current knee surgical robots, in which all bones are milled out. This might not be desired. In some cases, the cut bone may be used by the surgeon for adjustment of soft tissue balance and/or varus/valgus for some patients. Therefore the existent bone cutting method may not be adequate. Different scenarios of bone cutting in order to preserve the cut-off bones to be in pieces should be developed. In the proposed cutting process, the side edge instead of the bottom edge of the mill is used to move and cut the bone along the designated boundary of the cutting plane. Thus cut-off bone is in the form of pieces rather than blurs or chips. However, this cutting process will give rise to large and non-uniform cut forces on the cutter. As a result, the cutter is under large bending and the cutting trajectory may be deviated or, even worse, the cutter may be broken. To overcome the problem, the paper proposed an adaptive impedance force control strategy to maintain the stability and accuracy of bone cutting process.