Aim. To characterize the morphological parameters of the knee joint in medial osteoarthritis (OA), accounting for joint line obliquity (JLO) as assessed by a method proposed by the author (mJLO).

Materials and methods. A total of 100 standard weight-bearing anteroposterior knee radiographs from 70 patients with medial knee OA were analyzed. The following radiographic parameters were evaluated: anatomical lateral distal femoral angle (aLDFA), anatomical medial proximal tibial angle (aMPTA), femorotibial angle (FTA), joint line convergence angle (JLCA), joint line obliquity (JLO), and mJLO. Values of mJLO <177° were defined as apex distal (AD), 177–183° as apex neutral (AN), and >183° as apex proximal (AP). Statistical significance was set at p ≤ 0.05.

Results. AD was identified in 72 cases (72.0 %), AN in 25 (25.0 %), and AP in 3 (3.0 %). The mean mJLO values were: AD 172.13 ± 4.15°, AN 178.92 ± 1.53°, and AP 187.33 ± 2.52° (p < 0.00001). The corresponding values for other parameters were: FTA: AD – 175.90 ± 5.08°, AN – 179.58 ± 5.68°, AP – 185.00 ± 3.00° (p = 0.003); aLDFA: AD – 83.33 ± 2.75°, AN – 85.82 ± 2.37°, AP – 86.33 ± 3.06° (p = 0.0003); aMPTA: AD – 82.80 ± 3.28°, AN – 87.10 ± 2.50°, AP – 95.00 ± 2.65° (p < 0.00001); JLCA: AD – 4.41 ± 1.39°, AN – 3.72 ± 0.99°, AP – 3.50 ± 1.32° (p = 0.08); JLO: AD – 0.83 ± 3.52°, AN – 3.50 ± 4.15°, AP – 4.00 ± 1.00° (p = 0.009). Higher mJLO values (characteristic of the AP phenotype) positively correlated with increased FTA (τ = +0.21, p = 0.002), aLDFA (τ = +0.53, p < 0.0000001), and aMPTA (τ = +0.56, p < 0.0000001), while negatively correlating with JLCA (τ = -0.18, p = 0.007). The likelihood of the AD phenotype was significantly increased in patients with aLDFA 79–83° (OR = 3.86; 95 % CI: 1.51–11.10; p = 0.004), aMPTA ≤84° (OR = 15.35; 95 % CI: 5.05–61.75; p < 0.001), JLCA ≥4.1° (OR = 4.04; 95 % CI: 1.52–12.47; p = 0.004), and JLO <0° (OR = 3.69; 95 % CI: 1.31–12.62; p = 0.01). Conversely, the AN phenotype was more probable in patients with aLDFA ≥84° (OR = 5.56, CI (2.06–17.31), p = 0.0005), aMPTA 85–90° (OR = 4.13, CI (1.65-10.90), p = 0.002), aMPTA ≥91° (OR = 5.30, CI (1.46–20.93), p = 0.01), JLCA 2,1–4,0° (OR = 3.42, CI (1.32–9.90), p = 0.01), JLO >0° (OR = 3.03, CI (1.07–10.41), p = 0.04).

Conclusions. Morphological parameters of the knee joint in medial osteoarthritis patients significantly differ based on mJLO values.