Saw Cut Accuracy in Knee Arthroplastyâ€'An Experimental Case-Control Study

Introduction: Navigated TKA (Total Knee Arthroplasty) has heightened awareness of mal-alignment in conventional TKA, as well as providing an accurate means of measuring alignment intra-operatively. Debate as to the importance and significance of alignment versus knee balance continues. Aim: To assess cutting error, and examine the hypothesises: • ‘Slotted osteotomies are more accurate than non-slotted’ • ‘Second pass of the saw blade improves the accuracy of osteotomies’ Method: Three pairs of fresh frozen human knees were prepared, exposed, and positioned as for primary TKA. Standard cutting guides were used in conjunction with a clinical navigation system, and the error (difference between the achieved resection, and the planned resection) in each osteotomy was measured. A second, tidying, pass of the saw blade was made and the error re-measured. Cutting guides were used with a slotted and un-slotted technique in left and right knees respectively. A single experienced surgeon performed all 96 osteotomies. Results: Slotted tibial osteotomies are significantly more accurate in the sagittal (p=0.01) and coronal (p=0.04) planes. Second pass osteotomies reduce variability in femoral (p=0.07) and tibial (p=0.17) osteotomies. Discussion: The bone cutting process is prone to high levels of random error that can result in implant malalignment, and thus predispose to aseptic loosening. Navigated TKA gives the operating surgeon the opportunity to check each osteotomy, and correct any error where necessary. In conventional TKA the use of dual pass, slotted osteotomies should provide improved accuracy.