Rheumatoid Arthritis (RA) is a chronic, systemic inflammatory disease that primarily affects the diarthrodial joints, leading to significant joint damage and deformity. The disease typically presents as a symmetrical, destructive polyarthritis, involving both small and large synovial joints and is often accompanied by systemic symptoms and a variety of extra-articular features. A hallmark of RA is the presence of circulating Rheumatoid Factor (RF), an immunoglobulin antibody [1]. RA is a globally prevalent disease, affecting all ethnic groups, with an estimated worldwide prevalence ranging from 0.3% to 1.5%. In Iraq, the prevalence is approximately 1% and RA occurs 2.5 times more frequently in females than in males [2-4]. While Sacroiliac (SI) joint involvement is more commonly associated with seronegative spondyloarthropathies such as ankylosing spondylitis, psoriatic arthritis and Reiter's syndrome, it can also occur in RA. Diagnosing early inflammatory changes in the SI joint can be challenging, as the symptoms often mimic mechanical low back pain [5]. Sacroiliitis, inflammation of the SI joint, can be identified clinically through stress tests such as compressing or separating the iliac crests or applying pressure over the sacrum while the patient is prone, which elicits pain in the SI joints. Although sacroiliac joint involvement is relatively uncommon in RA, when it occurs, the erosive changes can be aggressive [6]. Asymptomatic sacroiliac joint changes, particularly on the iliac side, are more common in long-standing RA.

The SI joint is a synovial joint located between the sacrum and the iliac bones. It is supported by strong ligaments, limiting its movement and allowing it to primarily transmit the weight of the body from the vertebral column to the pelvis. Radiologically, the SI joint is visualized through specific projections that reveal any anatomical changes such as erosions or joint space narrowing [9, 10]. In RA, radiographs may show juxta-articular osteopenia, irregular joint margins and erosion or narrowing of the joint space, which occur in about 10-15% of cases [12]. The aim of this study was to determine the prevalence of sacroiliac joint involvement in Iraqi patients with seropositive RA and evaluate the correlation between sacroiliac joint involvement and clinical as well as laboratory features of RA.

Patients and Methods

This study was conducted on 97 consecutive seropositive Rheumatoid Arthritis (RA) patients (78 females and 19 males) and 78 control patients with Osteoarthritis (OA) of the knee joints (51 females and 27 males) attending the rheumatology unit at Baghdad Teaching Hospital, Medical City, between October 2002 and March 2003. The study included both inpatients and outpatients.

Patients were excluded from the study if they had a history of fever, tested negative for rheumatoid factor, or had a positive agglutination test for brucellosis.

Clinical Assessment

Data collected from RA patients included:

• Duration of disease
• Disease pattern
• Presence of backache
• Rheumatoid nodules
• Joint deformities
• Functional class based on disease severity
• Duration of morning stiffness

RA patients were classified into functional classes based on their ability to perform daily activities [13]:

Class I:    Fully able to perform all activities of daily living (self-care, vocational and avocational)

Class II:  Able to perform self-care and vocational activities but limited in avocational activities

Class III: Able to perform self-care activities but limited in vocational and avocational activities

Class IV: Limited in the ability to perform usual self-care, vocational and avocational activities

Additionally, all patients underwent an eye examination for uveitis and a Sacroiliac (SI) joint stress test.

Laboratory Assessment

Laboratory tests performed included:

• Hemoglobin (Hb) levels

• Erythrocyte Sedimentation Rate (ESR)

• Latex agglutination test for rheumatoid factor

• Rose Bengal test

Radiological Assessment

Radiological examinations were performed for all RA patients, including:

• Posteroanterior (PA) view of both hands to detect erosions

• X-ray of the pelvis in a prone position to visualize the SI joints. These radiographs were conducted at the radiology department of Baghdad Teaching Hospital and were interpreted by a radiologist

For the control group (patients with OA), clinical examination included an assessment for backache and an SI joint stress test. Laboratory tests included Hb levels, ESR and the Rose Bengal test. X-rays of the pelvis were also performed.

Statistical Analysis

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 10.1. Data were presented in terms of frequency, percentage, mean and Standard Deviation (SD). Simple linear correlation was used to assess the relationship between two quantitative variables. A p-value of less than 0.05 was considered statistically significant.

This study included 97 Rheumatoid Arthritis (RA) patients who fulfilled the American Rheumatism Association (ARA) 1987 revised criteria. Their ages ranged from 20 to 70 years and the demographic characteristics, disease duration, presence of backache and rheumatoid nodules are summarized in Table 1.

Out of the 97 RA patients, there were 78 females and 19 males, giving a female-to-male ratio of 4:1. The mean age of the RA patients was 45.5 years (range: 20-70 years) and the mean disease duration was 7.5 years. Among these patients, 51 (52.6%) reported backache, 16 (16.5%) had rheumatoid nodules and 32 (33%) exhibited joint deformities.

Table 1: Demographic Features, Rheumatoid Nodules, and Backache in Rheumatoid Patients

Table 2: Disease Pattern, Functional Class, and Duration of Morning Stiffness in RA Patients

The pattern of disease was predominantly polyarticular in 93 patients (95.9%), while 4 patients (4.1%) had oligoarticular involvement. The functional classification of patients revealed that 80 (82.5%) were in Class I, 8 (8.2%) in Class II, 4 (4.1%) in Class III and 5 (5.3%) in Class IV. The duration of morning stiffness was less than 60 minutes in 33 patients (34%), more than 60 minutes in 47 patients (48.5%) and 17 patients (17.5%) reported no morning stiffness (Table 2).

The most commonly affected joints were the hands (29.8%), wrists (25.5%) and knees (12.3%). Other joints affected included the feet, elbows, ankles and hips (Table 3).

The control group, consisting of 78 osteoarthritis (OA) patients (51 females, 27 males), had a mean age of 47.3 years (range: 34-60 years). Backache was present in 30 patients (38.5%) and morning stiffness in 12 patients (15.4%). The ESR levels in the control group ranged from 12-41 mm/hr with a mean of 25 mm/hr (Table 4).

Table 3: Joint Deformities in RA Patients

Table 4: Demographic Features, Backache, and Morning Stiffness in OA Patients

Sacroiliac joint (SIJ) involvement was observed in 3 RA patients (3.1%) based on clinical and radiological findings. One patient exhibited juxta-articular osteopenia with irregular joint margins, while two patients showed only juxta-articular osteopenia on X-ray. No SIJ involvement was observed in the control group.

There was a positive correlation between SIJ involvement and age (p=0.035) as well as disease duration (p=0.001), but no significant correlation was found with ESR levels (p=0.455) despite elevated ESR in patients with SIJ involvement (Table 5).

SIJ involvement showed a significant correlation with joint deformities (p=0.034) and rheumatoid nodules (p=0.001), but not with backache, hand erosions, or disease pattern (Table 6).

No correlation was found between SIJ involvement and functional class or duration of morning stiffness (Table 7).

Sacroiliac (SI) joint inflammation can occur in Rheumatoid Arthritis (RA), though its diagnosis is challenging in the early stages as symptoms often mimic those of mechanical low back pain, making clinical distinction difficult [5,11]. In this study, we observed that SI joint involvement in RA is uncommon, with a prevalence of 3.1%. This is consistent with the findings of Chopra et al. [14], who also reported that sacroiliac joint involvement is rare in RA.

RA is well known as a chronic disease that predominantly affects women and this was confirmed in the present study, where the female-to-male ratio was 4:1. This gender disparity likely reflects the outpatient population seen in clinics, as RA disproportionately affects women. The disease pattern was mostly polyarticular, which aligns with typical RA presentations.

Although SI joint changes in RA are rare, they are often less severe than those seen in seronegative spondyloarthropathies. It has been reported that up to 30% of patients with long-standing RA may exhibit sacroiliac changes, particularly when more advanced imaging techniques, such as Computed Tomography (CT), are used [7,15]. In this study, diagnosis of SI joint involvement was based on clinical findings, such as the sacroiliac stress test and radiological examination, which identified unilateral juxta-articular osteopenia and irregularity of the joint margins in affected patients.

Table 5: Correlation of SIJ Involvement with Age, Disease Duration, and ESR Level

Table 6: Correlation of SIJ Involvement with Backache, Joint Deformities, and Rheumatoid Nodules

Table 7: Correlation of Duration of Disease and Functional Class with SIJ Involvement

We found a positive correlation between SI joint involvement and both age and disease duration, suggesting that as RA progresses and patients age, the likelihood of SI joint involvement increases. This finding contrasts with Rantapää-Dahlqvist et al. [16], who reported no correlation between SI joint inflammation and age or disease duration. However, our results are comparable to those of Devacatho et al. [6], who found that sacroiliac involvement is more likely in patients with more advanced RA affecting other parts of the body.

Interestingly, there was no significant association between elevated ESR levels and SI joint involvement, nor was there a correlation with the functional class of patients. This is in line with the findings of Rantapää-Dahlqvist et al. [16], who also found no significant link between high ESR levels and SI joint inflammation. Despite elevated ESR levels in patients with SI joint involvement, the lack of correlation suggests that other factors may play a more significant role in sacroiliac changes.

A notable finding in this study was the positive correlation between SI joint involvement and joint deformities as well as the presence of rheumatoid nodules. To our knowledge, this correlation has not been reported in previous studies. However, the lack of correlation with Hemoglobin (HB) levels further highlights that sacroiliac changes are independent of systemic anemia, which is often seen in advanced RA. Additionally, we found no correlation between SI joint involvement and backache, supporting the notion that sacroiliac changes in RA are often asymptomatic, particularly in patients with long-standing disease [8,11].

All three patients with sacroiliac involvement also exhibited hand erosions. This finding suggests that destructive changes in RA are often more pronounced in peripheral joints than in the SI joints. This aligns with prior research indicating that peripheral joints are more severely affected by the erosive process of RA [7,17].

• Sacroiliac joint involvement can occur in RA, but it is rare, with a prevalence of 3.1% in this study

• There was a positive correlation between SI joint involvement and patient age, duration of disease, joint deformity and the presence of rheumatoid nodules

• No correlation was found between SI joint involvement and backache, functional class, or hemoglobin levels

• While SI joint involvement was associated with elevated ESR levels and hand erosions, these associations were not statistically significant

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