Three-dimensional measurement technique to assess implant position and orientation after total knee arthroplasty

The performance of implant placement technologies are often evaluated based on their achieved post-operative implant alignment. Therefore accurate assessment techniques are necessary to compare pre-operatively planned implant positions with the corresponding post-operatively placed implant positions in total knee arthroplasty. This paper describes a CT based 3D measurement method for evaluation of implant positioning accuracy comparing post-operative implant position to the corresponding pre-operative planned implant position using 3D virtual models. TKAs were carried out on three phantoms and processed three times to investigate the accuracy of the method. The measurements were then assessed against measurements taken through an optical scan. The results indicate that an average measurement error less than 1 ° and 0.5mm can be obtained except in the proximal-distal direction where the error was up to 1.34mm. The accuracy of this 3D measurement technique is sufficiently reliable to enable reporting on implant position and orientation in the same coordinate system as pre-operatively defined independently of the planning system or the surgical implant placement technology (patient-specific guides, robotics, and navigation).