The influence of sequential debridement in total knee arthroplasty on the flexion axis of the knee using computer‐aided navigation

The effects of osteophyte debridement, bony cuts, and soft tissue releases on the functional flexion axis of the knee can be assessed by evaluating 3D kinematics following each step of a total knee arthroplasty. Using a navigated knee system with dedicated software, the functional flexion axis (helical axis) can be determined after each step. Five paired fresh‐frozen cadaveric knees were used with a CT scan performed on each specimen identifying implanted fiducial markers. Kinematics data were recorded during each step of sequential osseous cuts and soft tissue releases for both an unloaded and loaded limb by each of three surgeons. The functional helical (flexion/extension) axis was identified for all specimens. The internal/external rotation angle (θ) of the helical axis differed from the transepicondylar axis by −8.3° to +6.7° for the unloaded condition. θ ranged from −7.2° to +7.4° with distraction. Soft tissue releases had no effect on θ; until a bony cut of the articular surface, which increased θ from −0.3° to +9.7°. Implantation of cruciate retaining prosthetic components subsequently reduced the θ range −7.3° to +4.0°. Thus, soft tissue releases had minimal effect on θ of the helical axis except for resection of the proximal tibia. Implantation of the CR prosthesis reduced è close to that of the intact knee. In a minority of knees, the helical axis did not coincide exactly with the transepicondylar axis. Interspecimen and left/right variability of θ were significant, although interinvestigator variability and an applied distraction force were insignificant.