Knee varus alters three-dimensional ankle alignment in standing- a study with upright computed tomography

Area of Science:

• Orthopedics
• Biomechanical Engineering
• Radiology

Background:

• Accurate assessment of lower limb alignment is crucial for knee osteoarthritis (OA) treatment.
• Traditional methods using surface imaging or radiographs have limitations in capturing 3D alignment in the upright position.
• Understanding lower limb alignment, including foot and ankle joints, is vital for effective knee OA management.

Purpose of the Study:

• To measure lower limb alignment in knee OA patients using upright computed tomography (CT) and radiography.
• To identify specific features of knee joint deformity in relation to foot and ankle alignment.
• To correlate lower limb alignment characteristics with the severity of knee OA.

Main Methods:

• 45 limbs from 25 knee OA patients were analyzed using both upright CT and radiography.
• Joint angles for the entire lower limb were calculated from standing position images.
• Knee OA severity was graded using the Kellgren-Lawrence (KL) scale based on radiographic findings.

Main Results:

• KL-I: Knee varus correlated with talocrural internal rotation (r=0.76).
• KL-II: Knee varus associated with subtalar eversion (r=0.63) and talocrural joint changes (r=-0.65).
• KL-III & IV: Increasing knee varus correlated with subtalar internal rotation (r=-0.62 and r=-0.58, respectively).

Conclusions:

• Compensatory knee joint alignment in knee OA becomes increasingly dependent on the ankle joint, rather than the subtalar joint, as OA severity progresses.
• Ankle joint alignment significantly impacts knee joint function during weight-bearing activities.
• These findings offer insights for optimizing rehabilitation strategies for knee OA patients.