Accuracy of digital preoperative planning for total knee arthroplasty

Introduction: The accuracy of preoperative planning of the size of total knee arthroplasty (TKA) in literature is only 50%. A problem of conventional radiographic planning with prothesis templates is varying enlargement of the radiographs. Digital planning and analysis of lower leg geometry revealed improved reliability compared to conventional techniques. The aim of the study was to evaluate the accuracy of digital planning of TKA with special planning software and calibrated radiographs and its interobserver reliability. Methods: In a prospective study the sizes of 30 TKA were planned with special software by a senior and a junior surgeon independently. For calibration a 30 mm reference ball on the radiographs was used. The planning was compared with the intraoperative chosen size of the TKA. Results: The correlation of the planned femoral component with the chosen size was 87% for the senior and 77% for the junior surgeon. The planning of the tibial component revealed a correlation for the senior surgeon in 90% and for the junior surgeon in 87%. Both component was planned correctly in 77% by the senior and in 63% by the junior surgeon. In 50% the planning of both surgeons matched completely the used prosthesis sizes. The linear kappa coefficient of Cohen revealed a good agreement (0.65) and a high interobserver reliability. Discussion: Planning TKA with special planning software with digital, calibrated radiographs is more accurate compared to previous conventional planning. The senior surgeons planning of both component sizes matched in 77% the correct size. Clinical experience improves the accuracy of preoperative planning.