Accuracy verification of the photostereometric system KKN/1B developed for intraoperative measurement of knee movement immediately after total knee arthroplasty.

The function and integrity of the knee joint following total knee arthroplasty (TKA) is determined at first by the design and implantation of the prosthesis, and later by the tension of soft tissues surrounding it. Accurate post-TKA motion data obtained intraoperatively could be used not only to optimize implantation techniques from a kinematic standpoint, but also to improve prosthetic design. We therefore developed a system specifically geared to photostereometric measurement of 6 d.o.f. knee motion. A total of eight LEDs are mounted on the prosthetic components in two sets of four by means of connecting measuring-bows. The positions of the LEDs are detected in three-dimensions by two sets of three linear CCD cameras, located bilaterally relative to the knee. The position and orientation of the femoral component relative to the tibial one are estimated from the positions of all LEDs in the sense of least-squares. Based upon results of various accuracy validation experiments performed after precise camera calibration, static overall accuracy and spatial resolution were considered to lie within 0.52 and 0.11 mm, respectively, at any point on the femoral articular surface.