Changes in coronal knee-alignment parameters during the osteoarthritis process in the varus knee

Area of Science:

• Orthopedic Surgery
• Radiology
• Biomechanical Engineering

Background:

• Individualized knee alignment is increasingly important for surgeons aiming to restore constitutional alignment.
• Understanding natural knee alignment pre-disease is essential for personalized treatment approaches.

Purpose of the Study:

• To determine how the hip-knee-ankle (HKA) angle is affected by the osteoarthritis (OA) process.
• To investigate the correlation between joint line changes and OA progression.
• To hypothesize that coronal parameter changes are most significant at the proximal tibia and joint line.

Main Methods:

• Retrospective review of 100 sequential full-length X-rays from patients with a minimum 1-year follow-up.
• Inclusion criteria: age ≥50, HKA angle >1.3° varus; exclusion criteria: prior hip/knee surgery or fractures.
• Analysis of 15 alignment parameters and correlation with Kellgren-Lawrence (KL) grade using linear mixed models.

Main Results:

• Progressive KL grade correlates with increased HKA angle (p < 0.001).
• HKA changes are mainly driven by medial tibial plateau angle (MPTA) decrease (0.93°) and joint line convergence angle (JLCA) increase (0.86°).
• Medial distal femoral angle (mLDFA) changes are most pronounced in early OA (KL grade 1-2), while MPTA decreases significantly in later stages (KL grade 3). JLCA progressively increases from KL grade 3 onwards (p < 0.001).

Conclusions:

• Coronal alignment changes during OA progression can be defined by comparing sequential X-rays.
• The HKA angle increases with OA progression, with significant changes at the proximal tibia (MPTA) and joint line (JLCA).
• OA varus knee alignment changes occur in three stages: distal medial femoral condyle erosion, medial tibial plateau erosion, and progressive joint line angle increase.