The purpose of this study was to test the hypothesis that Jaccoud arthropathy (JA) in patients with systemic lupus erythematosus (SLE) is associated with instability of the extensor digitorum (ED) tendons during flexion of the metacarpophalangeal (MCP) joints by comparing the position of the ED tendons between SLE patients with JA and control subjects on hand MRI obtained with flexed and extended MCP joints.

Thirty-two hands of SLE patients with JA (13 women and 3 men; mean age, 50.0±12.2 [SD] years; age range: 26–68years) and 24 hands of sex- and age-matched control subjects (20 women and 4 men; mean age, 50.1±13.0 [SD] years; age range: 24–68years) were included in the study. Axial spin echo T1-weighted MRI images of the second to fifth MCP joints in flexion and in extension were obtained. Two radiologists (R1 and R2) separately measured the amplitude and assessed the direction of the displacement of the ED tendons with respect to the midline at the level of each MCP joint. Statistical analysis included two-way ANOVA with random effects to assess differences in amplitude and Fisher–Freeman–Halton exact test to assess differences in direction with P-values<0.0083 and<0.0063 considered as statistically significant respectively.

Amplitude of the displacement of the ED tendons was statistically significantly greater in SLE patients with JA than in control subjects in flexion for both readers (median 58°, 95% confidence interval [CI]: 50°–65° vs. 20°, 95% CI: 16°–24°; P<0.0001 for R1 and 54°, 95% CI: 47°–61° vs. 25°, 95% CI: 22°–28°; P<0.0001 for R2) and in extension for one reader (17°, 95% CI: 15°–20° vs. 14°, 95% CI: 11°–16°; P=0.0048 for R1 and 20°, 95% CI: 15°–25° vs. 16°, 95% CI: 12°–18°; P=0.0292 for R2). Ulnar deviation of the ED tendons was statistically significantly more frequent in SLE patients with JA than in control subjects in flexion and in extension for both readers (P<0.0001).

JA is associated with instability of the ED tendons in patients with SLE best depicted when MCP joints are flexed.