The adverse effects of joint line (JL) changes on kinematics and outcomes of total knee arthroplasty (TKA) have been studied. Some authors have quantified JL changes using intraoperative data from computer navigation, despite no studies validating these measurements to date. We designed a prospective study to determine whether intraoperative measurements of JL changes using computer navigation correlate with measurements obtained on weight-bearing radiographs postoperatively.
A total of 195 consecutive patients (195 knees) underwent computer-navigated cruciate-retaining TKA by the senior author. Twenty-four patients had missing radiographic data and were excluded from the study. The final JL change was calculated intraoperatively from the verified bony cuts and planned JL change as determined by the computer. JL position was also measured on preoperative and postoperative radiographs using an anteroposterior method.
One hundred seventy-one knees were evaluated. Using computer-navigated and radiographic measurements, the mean JL change was 1.95 ± 1.5 mm (0-8.0 mm) and 4.05 ± 2.9 mm (0-17.3 mm), respectively. One hundred fourteen (67%) vs 129 (75%) had JL elevation, 44 (26%) vs 30 (18%) had JL depression, and 13 (7%) vs 12 (7%) had no JL change, respectively. Inter-rater and intrarater reliability of radiographic measurements was excellent. We found a poor correlation between computer-navigated and radiographic measurements (r = 0.303).
There is a poor correlation between computer-aided and radiographic measurements of JL changes post-TKA. Elevation/depression of the JL needs to be considered in patients who remain symptomatic despite TKA, although the optimal method of assessment remains uncertain.