Abstract
Introduction: Pre-operative templates for total knee arthroplasty are routinely provided by the manufacturers. These often provide a representation of the required size of prosthesis and of the bone cuts. A common deficiency is that the actual cuts made by the jigs are angulated to allow for factors such as distal femoral angulation and back-slope on the tibia. The templates that were provided do not take into account this built in angulation and can lead to bone cuts which appear different to the cuts determined by the template. This factor is taken into account by the surgeon intra-operatively but leaves a situation where estimation is replacing pre-operative planning.
Method and Results: New universal templates have been produced as an adjunct those provided to take into account this angulation. A mathematical proof of the exact difference between various angle templates and right-angle templates yield significant variation in thickness of bone cuts. Using an average of 80mm width of the femur, a difference of 7.0mm in bone cuts is obtained with a five degree template compared with a right-angle template. A tibial anterior-posterior distance of 50mm yields a 2.62mm difference in bone cuts with a back slope of three degrees when compared with that predicted by a right-angle template.
Conclusions: The use of right-angle templates in total knee arthroplasty for sizing should be supplemented with angled templates to allow an accurate assessment of bone cuts to be made.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
