The prevalence of moderate to severe radiographic sacroiliitis and the correlation with health status in elderly Swedish men – The MrOS study

The population in the present study is collected from the MrOS (Mister Osteoporosis) Sweden cohort [28]. MrOS Sweden is part of an international, multi-center, prospective, longitudinal, observational study with primary aim to identify risk factors for osteoporosis and fractures (vertebral and non-vertebral) in old men, and was additionally designed to determine how fractures affect quality of life in men [29]. The study was conducted in three Swedish cities, Uppsala (n = 999), Malmo (n = 1005) and Gothenburg (n = 1010) and was performed in accordance with the Declaration of Helsinki. The ethics committee of Lund, Sweden, approved the study and all participants gave written informed consent [28].

The MrOS Malmo Study enrolled 1005 men, aged 69–81 years, between October 2001 and December 2004. Invitations were sent by mail to 2065 men who were living in Malmo and who were randomly selected from the national population registry resulting in an attendance rate of 48.7% [30].

Based on the inclusion criteria for the MrOS study, the participants should be able to walk without the assistance of another person, had not undergone bilateral hip replacement operation, be able to provide self-reported data, be able to understand and sign an informed consent and not suffer from a medical condition that (in the judgment of the investigator) would result in imminent death [29].

Spinal radiographs and radiographs of the pelvis including both hip-joints were obtained for all the participants. For the spinal images, the participants were placed on their left side in the lateral position and the images included the vertebra from T2 to S1. An experienced radiologist (IRJ) screened and scored the anteroposterior pelvic radiographs for sacroiliitis. The cut-off for a positive x-ray was unilateral sacroiliitis grade 3, as defined by mNY criteria [3], because of the expected poor inter- and intra-observer concordance in grades 1 and 2 [4]. An additional reader (SE) reviewed the positive x-rays blinded for the primary scoring. There were no discordances between the two readers. The images where sacroiliitis was present were then reviewed by both readers for the presence of AS-related changes (syndesmophytes and bridges) and degenerative changes (spondylophytes and bridges). In consistence with previous proposals, the AS-related changes (syndesmophytes and bridges) were defined by a horizontal growth angle of <45° to the anterior vertebral side [31, 32]. The spinal discs were only qualitively evaluated since to our knowledge, there is not a widely accepted quantitative definition for radiographic disc degeneration.

Information on demographics, anthropometrics, lifestyle, physical activity, functional status, health-related quality of life and back-health were obtained from a self-administered questionnaire.

Physical Activity was assessed by the Physical Activity Scale for the Elderly (PASE) questionnaire which consists of self-reported occupational, household and leisure activities items commonly engaged in by elderly persons [33]. It is a valid method to classify healthy elderly people into levels of physical activity [34]. PASE scores may range from 0 to 400 or more. Higher scores indicate a higher level of physical activity. The instructions for use and scoring given in the PASE Administration and Scoring Manual were followed [35].

Functional status was assessed with the use of two questions (being able to 1. walk two to three blocks outside on level ground and 2. climb 10 steps unassisted and without using special aids) from the instrumental activities of daily living (IADL) questionnaire [36].

The Short Form Health Survey (SF-12) was used to measure perceived health and health-related quality of life (QoL) that describes the degree of general physical health status and mental health distress. Separate summary scores are obtained for each of the physical (physical component score, PCS12) and mental (mental component score, MCS12) domains. Both PCS12 and MCS12 can range between 0-100 (mean 50 ± 10). Higher scores indicate higher levels of health [37].

History of any back pain in the last 12 months was assessed with a direct question (yes/no). Secondly, five items from the Quebec Pain Disability Scale were used, in which participants reported on difficulties with bending down to pick up lightweight objects, putting socks on either foot, getting in or out of the front seat of a car, standing for 2 hours, or sitting for 30 minutes because of back pain.

In order to address a potential selection bias and assess the generalizability of the results of this study to the whole male population of this age group, we obtained complementary permission from the local ethics committee, to conduct an analysis of non-participants (n = 1060). Diagnoses codes (ICD10) from out-patient visits to physicians and hospitalization for cardiovascular disease (CVD), stroke, diabetes, chronic obstructive pulmonary disease (COPD), AS/SpA and rheumatoid arthritis (RA) were identified for the whole population (n = 2065) for the year of invitation to the study using the population based Regional Outpatient and Inpatient Health Care Registry [38] and a comparison between those enrolled in the study and those who did not participate was carried out.

All statistical analysis was conducted using SPSS software. In descriptive analyses, distributions of baseline characteristics, physical activity score (PASE), functional status (IADL), Quality of Life (SF-12) and pain characteristics (any pain, Quebec items) between men with and without evident radiographic sacroiliitis, were estimated using Mann Whitney U non-parametric test for continuous variables and Chi- 2 or Fisher’s exact test for categorical variables. P-values < 0.05 were considered significant.

Fourteen cases with moderate to severe (grade 3-4) radiographic sacroiliitis were identified corresponding to a prevalence of 1.4% (95% confidence interval - CI: 0.7-2.4). There were 7 with sacroiliitis grade 3 bilaterally, 4 with grade 4 bilaterally, 1 with grade 3 involvement at one SI-joint and grade 4 at the other and only 1 with unilateral grade 3 involvement (Table 1). The concordance between the two readers was 100%.

All cases with sacroiliitis had either AS-related changes, such as syndesmophytes and bridges or degenerative changes in the spine radiographs. The majority (8/14) had both types of changes, 4 only degenerative changes and 2 only AS-related changes (Table 1).

Among those, two had spinal findings resembling Diffuse Idiopathic Skeletal Hyperostosis (DISH) (Table 1). Their SI-joints demonstrated sacroiliitis grade 3 or 4. In the absence of CT images we were unable to say if they had a real ankylosis or only ossification of the anterior surface of the joint and consequently fulfilling the DISH criteria [39], therefore these cases were included in the final results.

At baseline there were no significant differences between men without and those with radiographic sacroiliitis regarding the age and anthropometric measures such as height, weight and body mass index (BMI) nor regarding ethnicity or smoking status (Table 2).

There were no statistically significant differences between the two groups with regard to physical activity, health related quality of life and back pain, although those with radiographic sacroiliitis tended to have a higher frequency of back pain, especially when sitting for more than 30 minutes (Table 3). The majority of individuals with sacroiliitis did not report major difficulties related to back problems (Table 3).

A higher frequency for visits among non-participants to the survey vs. participants with regard to registered ICD10 codes for stroke, diabetes and COPD, and a tendency towards higher rates of CVD was found. However, there were no apparent differences between the two groups with regard to the frequency of visits due to RA or AS/SpA. Only one subject among the non-participants had a visit with an ICD10 code of AS/SpA during the invitation year (Table 4).