Background/Purpose:

To correlate cartilage thickness as measured by ultrasound (US) with joint space narrowing as measured by conventional radiography in the metacarpophalangeal (MCP) joints of patients with rheumatoid arthritis.

Methods:

In this pilot study we examined 120 MCP joints of 15 patients with rheumatoid arthritis (RA). The cartilage layer of the metacarpal heads and proximal phalangeal bases of digits 2-5 were assessed bilaterally using a 15 Mhz linear transducer (GE Logic E9) from a dorsal longitudinal view in midline, with joints in 90° flexion. Cartilage thickness was measured in mm with an integrated caliper on static images. Joint space narrowing (JSN) was evaluated using the van der Heijde modified Sharp scoring method (vdHS) performed on conventional posterior-anterior radiographs of both hands. Cartilage thickness was correlated with x-ray findings using Spearman correlation, while differences of JSN within groups of different cartilage thickness (using tertiles) were evaluated by Kruskal-Wallis test.

Results:

Mean disease duration was 9.3+6.2 years, mean CDAI 8.3+7.4; 63% of the patients were rheumatoid factor positive. US measurement of metacarpal cartilage thickness was 0,38+/-0,17 mm and correlated with total JSN of MCP 2-5 (r=0.54, p<0.001) as well as with the total vdHS (r=0.53, p<0.001). No correlation was found between phalangeal cartilage thickness and JSN. Metacarpal cartilage thickness correlated better with JSN than the sum score of metacarpal and phalangeal cartilage thickness (r=0.54 p<0.01 vs. 0.47 p<0.05). Moderate correlation was found between the left and right hand with regard to metacarpal cartilage thickness (r=0.56, p<0.05). Correlation was slightly higher between metacarpal cartilage thickness of the left hand and JSN (r=0.57 vs. 0.53; p<0.05). Significant differences of total vdHS, total JSN and JSN sum score for the MCP joints (JSN.mcp) were found between tertiles of metacarpal cartilage thickness using Kruskal-Wallis Test (Figure 1). No correlation between cartilage thickness and disease activity, functional disability, or disease duration was seen.

Conclusion:

JSN by radiography indeed represents cartilage thickness at least in MCP joints. When radiographic scoring is not available, US measurement of cartilage thickness of the metacarpal head might be a feasible alternative to depict cartilage damage in patients with rheumatoid arthritis. Phalangeal cartilage thickness has no added value beyond the measurement of metacarpal cartilage thickness.

Figure 1.Differences of JSN between groups of different cartilage thickness using tertiles.

Tertile I: mean cartilage size 0.0189 (±0.003) mm; Tertile II: mean cartilage size: 0.035 (±0.005) mm; Tertile III: mean cartilage size: 0.058 (±0.009) mm