Patients suffering from juvenile idiopathic arthritis (JIA) frequently have affected ankle joints, which can lead to foot deformities such as pes planovalgus (JIA-PPV). Usually, JIA-PPV is diagnosed by examining the foot in non-weightbearing or in weightbearing, static condition. However, functional limitations typically appear during dynamic use in daily activities such as walking. The aim of this study was to quantify the pathophysiology of JIA-PPV in both static and dynamic condition, i.e. in upright standing and during the stance phase of walking using three-dimensional (3d) gait analysis.
Eleven JIA patients (age = 12y) with at least one affected ankle joint and fixed pes planovalgus (≥5°) were compared to healthy controls (CG) (n = 14, age = 11y). Kinematic and kinetic data were obtained in barefoot standing and walking condition (1.1-1.3 m/s) with an 8-camera 3d motion analysis system including two force-plates and one pressure distribution plate. All participants were prepared using reflecting markers according to the Oxford Foot and Plug-in-Gait Model. Results were compared using the Mann-Whitney-U-test and Wilcoxon signed-rank test (p < 0.05).
In comparison to CG, JIA-PPV had an excessive hindfoot/tibia eversion (p < 0.001) and a forefoot/hindfoot supination (p < 0.001) in both static and walking condition. JIA-PPV showed a greater hindfoot/tibia eversion during walking (midstance) compared to standing (p = 0.021) in contrast to CG. The arch index, measured by plantar pressure distribution, indicates a reduced arch height in JIA-PPV (p = 0.007). Patients had a lower maximum dorsiflexion of hindfoot/tibia (p = 0.001) and a lower plantarflexion of forefoot/hindfoot (p = 0.028), both when standing and walking. The kinetic results showed lower maximum ankle dorsiflexion moments (p < 0.037) as well as generated ankle power (p = 0.086) in JIA-PPV.
The pathophysiology of JIA-PPV during walking indicated that excessive hindfoot eversion produces accessory symptoms such as a reduced arch height, increased forefoot supination and reduced propulsion effect of the ankle. Muscular and coordinative insufficiency caused by arthritis can lead to the observed increased hindfoot eversion from static to dynamic condition. Conventional static or passive foot examination techniques probably underestimate deformity in JIA pes planovalgus. 3d gait analysis might be helpful in early diagnosis of this condition, especially in JIA patients with affected ankle joints.