Assessment of joint line obliquity and its related frontal deformity using long-standing radiographs

Purpose: To investigate how radiographic techniques and osteoarthritis grade influence measurements of knee joint line obliquity (KJLO) and KJLO-related frontal deformity, and to propose preferable KJLO measurement methods. Methods: Forty patients with symptomatic medial knee osteoarthritis indicated for high tibial osteotomy were assessed. Measurements were compared between single-leg and double-leg standing radiographs for KJLO measurement methods including joint line orientation angle by femoral condyles (JLOAF), joint line orientation angle by middle knee joint space (JLOAM), joint line orientation angle by tibial plateau (JLOAT), Mikulicz joint line angle (MJLA) and medial proximal tibial angle (MPTA), as well as KJLO-related frontal deformity parameters including joint line convergence angle (JLCA), knee ankle joint angle (KAJA) and hip-knee-ankle angle (HKA). Influences of bipedal distance in double-leg standing and osteoarthritis grade on the above measurements were analysed. Measurement reliability was evaluated by intraclass correlation coefficient. Results: From single-leg to double-leg standing radiographs MPTA and KAJA did not change significantly, whereas the other measurements showed significant changes: JLOAF, JLOAM and JLOAT decreased 0.88 degrees, 1.24 degrees and 1.77 degrees, MJLA and JLCA decreased 0.63 degrees and 0.85 degrees, and HKA increased 1.11 degrees (p < 0.05). Bipedal distance in double-leg standing radiographs moderately correlated with JLOAF, JLOAM and JLOAT (rp = -0.555, -0.574 and -0.549). Osteoarthritis grade moderately correlated with JLCA in single-leg and double-leg standing radiographs (rs = 0.518 and 0.471). All measurements had at least good reliability. Conclusion: In long-standing radiographs, measurements of JLOAF, JLOAM, JLOAT, MJLA, JLCA and HKA are all influenced by single-leg/double-leg standing; JLOAF, JLOAM and JLOAT are also affected by bipedal distance in double-leg standing; and JLCA is affected by osteoarthritis grade. Knee joint obliquity as assessed by MPTA measurement is independent of single-leg/double-leg standing, bipedal distance or osteoarthritis grade, and has excellent measurement reliability. We therefore propose MPTA as the preferable KJLO measurement method for clinical practice and future research. Level of evidence: III, cross-sectional study.

Automated summary

This study investigated the influence of radiographic techniques and osteoarthritis grade on measurements of knee joint line obliquity (KJLO) and KJLO-related frontal deformity. It was found that measurements of JLOAF, JLOAM, JLOAT, MJLA, JLCA, and HKA were influenced by single-leg/double-leg standing, while JLOAF, JLOAM, and JLOAT were also affected by bipedal distance in double-leg standing, and JLCA was affected by osteoarthritis grade. MPTA measurement of knee joint obliquity was not affected by standing position, bipedal distance, or osteoarthritis grade, and had excellent reliability. Thus, MPTA is proposed as the preferable KJLO measurement method for clinical practice and future research.