Slotted cutting guides are used by orthopaedic surgeons to improve the accuracy of bone resection during total knee replacement. Accuracy of the saw cuts has an effect on patient mobility and on implant survival time. While computer navigation systems have improved the accuracy of cutting guide placement, the contribution to cutting error from blade toggle within the slots of the cutting guide persists. In this research, equations were derived to quantify angular cutting error based on the parameters affecting blade and cutting guide geometry. Analytically, the relationship between cutting plane error and blade thickness was determined to be linear. A smaller gap, due to thicker blades with minimal tooth offset, results in less cutting error. From an experimental standpoint, six commercially available cutting guides were tested for femoral plane cutting accuracy by resection of synthetic bone under the guidance of computer navigation. The results indicate an average flexion/extension error of 3.8 deg for a 0.89 mm thick blade and 2.0 deg for a 1.27 mm blade. Varus/valgus error due to twisting of the blade within the slot was less than 1.0 deg, regardless of blade thickness. To improve upon cutting accuracy, an adjustable slot cutting guide was designed and tested. From more closely matching slot width to blade thickness, the results indicate that cutting plane error can be reduced to less than 1.0 deg in both the flexion/extension and varus/valgus planes.