Are joint line changes after primary navigated total knee arthroplasty predictable?

Background: Navigation systems have been successful in reducing the outlier of leg alignment after total knee arthroplasty (TKA). Less is known about the restoration of the anatomical joint line with computer-assisted knee replacement. The aim of this study was to determine whether joint line changes <3 or ≥3 mm are predictable with several pre- and intraoperative parameters.

Methods: The study included a total of 180 cases of primary computer-assisted TKA performed using the gap-balancing/tibia-first technique. The final shift of the joint line was calculated using computer verification of proximal tibial and distal femoral cuts. In consideration of the clinical relevance of a 3-mm joint line shift, patients were stratified into two groups: Group I, with joint line change <3 mm, and Group II, with joint line change ≥3 mm. Between groups, variables such as demographics, Kellgren & Lawrence degree of osteoarthritis, preoperative flexion contracture, pre-/intraoperative mechanical leg alignment, flexion/extension gaps, and implant design/sizes were compared statistically.

Results: The absolute joint line shift averaged 1.6 ± 1.3 mm (range 0-6 mm). A joint line shift ≥3 mm was observed in 28 cases (15 %). A statistically significant difference between groups was not identified for any of the parameters. Shift of the joint line did not correlate with the analyzed variables.

Conclusions: Joint line was adequately restored when computer navigation was carefully applied as a measuring tool for primary TKA. Knee joint deformity, leg alignment, gap balance, and implant type did not aid in predicting the joint line shift.