Background The 28-joint disease activity score (DAS28) is a particularly widely-used tool because it enables the physician to easily understand the state of RA. However, DAS28 assessment is primarily targeted to the joints of the upper extremity, being limited in the lower extremities to only the knee joints. Hip joints are weight bearing and their spherical shape tends to concentrate the load onto the weight-bearing area, where rapid joint distraction is often reported. Therefore, early diagnosis and treatment are essential. However, hip joints are located deep within the body, often making it difficult to obtain physical findings, such as swelling, thereby leading to delayed diagnosis.

Objectives In our present study, we examined the relationship between the histological severity of synovitis in the hip joint and the DAS28 score. We also evaluated whether DAS28 is useful for hip joint assessment.

Methods We studied 31 joints of 27 patients with rheumatoid arthritis of the hip who had undergone total hip arthroplasty. In all cases, the hip joint removed during the operation was histologically evaluable for synovitis. The subject population had a mean age of 66.3 years and mean disease duration of 13.4 years. As preoperative assessment, disease activity of RA was evaluated using DAS28 using C-reactive protein (DAS28-CRP) and CRP, and hip joint function was evaluated by the Japanese Orthopaedic Association (JOA) score for hip function. A perfect JOA score is 100 and the worst score is 0. In addition, the severity of synovitis was assessed employing the synovitis score for hematoxylin-eosin stained specimens as proposed by Krenn et al. and the correlations among individual parameters were tested for statistical significance.

Results In the preoperative assessment, mean DAS28-CRP was 2.94±0.79, mean CRP was 1.85±0.36 mg/dL, and the mean JOA score was 39.0±13.1 points. The DAS28-CRP correlated negatively with the JOA score (r=-0.6188, P=0.0002). The mean synovitis score was 3.97±0.32 points, and correlated positively with both DAS28-CRP and CRP (r=0.4565, P=0.0098)(r=0.4509, P=0.0109). Furthermore, the synovitis score did not correlate with the JOA score.

Conclusions We found significant negative correlations between preoperative DAS28 and JOA score in RA patients. The result suggests that DAS28 without hip joint assessment can indirectly represent the status of hip joints. In addition, the histological severity of synovitis in the hip joint showed positive correlations with both DAS28-CRP and CRP, supporting the usefulness of DAS28 as an indirect assessment tool for hip joints. In patients with highly active disease, physical findings may not be significant, but screening employing not only X-rays but also ultrasonography and magnetic resonance imaging, focusing on potential hip joint disorders, is anticipated to contribute to early diagnosis and prevention of hip joint destruction.

References

1. Krenn V et al. Synovitis score: discrimination between chronic low-grade and high-grade synovitis. Histopathology 49;358-64,2006

Disclosure of Interest None declared