The NOAR Damaged Joint Count (NOAR-DJC): a clinical measure for assessing articular damage in patients with early inflammatory polyarthritis including rheumatoid arthritis

D. K. Bunn1, L. Shepstone2, L. M. Galpin1, N. J. Wiles3 and D. P. M. Symmons4

1 Norfolk Arthritis Register, Norfolk and Norwich University Hospital, 2 School of Medicine, Health Policy and Practice, University of East Anglia, Norwich, 3 Division of Psychiatry, University of Bristol, Bristol and 4 ARC Epidemiology Unit, University of Manchester, Manchester, UK.

Correspondence to: D. Bunn, Norfolk Arthritis Register, Norfolk and Norwich University Hospital, Colney Lane, Norwich, Norfolk NR4 7UY, UK. E-mail: diane{at}fs1.ser.man.ac.uk


    Abstract
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Objectives. To evaluate the reliability and validity of the Norfolk Arthritis Register Damaged Joint Count (NOAR-DJC) in patients with early inflammatory polyarthritis (IP).

Methods. The NOAR-DJC examines deformity in 51 joints. Deformity is defined as inability to adopt the anatomical position, reduction in range of movement by at least one-third, and/or surgical alteration of the joint. Reliability was investigated by assessing intra- and inter-observer agreement in 40 and 32 patients, respectively. Validity was assessed by correlating the NOAR-DJC with the eroded joint count (criterion validity), the Health Assessment Questionnaire (HAQ) (convergent construct validity) and tender and swollen joint counts (divergent construct validity) and by discriminating between those who did and did not satisfy criteria for rheumatoid arthritis (discriminant validity).

Results. The intraclass correlation coefficient for the intra- and inter-rater studies were 0.88 [95% confidence interval (CI) 0.79, 0.94, P<0.00001] and 0.74 (95% CI 0.53, 0.86, P<0.00001), respectively. Correlations with eroded joint counts and HAQ scores after 5 yr follow-up were rs = 0.42 (95% CI 0.35, 0.49, P<0.01) and rs = 0.45 (95% CI 0.4, 0.5, P<0.01), respectively. Correlations with tender and swollen joint counts were weak (rs = 0.28 and rs = 0.33).

Conclusion. The NOAR-DJC is a quick, reliable and valid tool for assessing articular damage in patients with early IP.

KEY WORDS: Inflammatory polyarthritis, NOAR, Damaged Joint Count, Clinical assessment


    Introduction
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Joint damage is an important adverse outcome of inflammatory polyarthritis (IP) and its subset rheumatoid arthritis (RA). Clinically, the damage may be manifest as permanent deformity or loss of movement in the joint. Damage may also be documented on X-ray. However, X-ray studies in IP and RA are usually confined to the hands and feet. There is a need for a valid and reliable clinical assessment of joint damage that includes joints in addition to the hands and feet, and which can be repeated at frequent intervals to monitor progress without causing concern about radiation dose. Such a measure is of particular value in longitudinal observational studies but, if sufficiently sensitive to change, could also be of value in clinical trials.

There have been a number of attempts to develop a simple and reliable clinical measure of joint damage (Table 1). The idea of clinically assessing joint damage was included by the American Rheumatism Association (ARA) in their Dictionary of the Rheumatic Diseases in 1982 [1]. However, this did not include a formal description of an index. The first clinical index of deformity was described by Spiegel and Spiegel in 1987—the Joint Alignment and Motion Scale (JAM) [2]—and this was followed by the Escola Paulista Medicina Range of Motion Scale (EPM-ROM) in 1990 [3] (although the EPM-ROM looks at movements rather than individual joints). Since then, the Deformity Index (DI) was introduced in 1999 as an amalgam of the JAM and EPM-ROM scales, but it has not been formally validated in this combined format [4]. More recently, three further measures have been published: the Mechanical Joint Score (MJS) [5]; the Rheumatoid Arthritis Articular Damage Score (RAAD) [6] and the Number of Deformed Joints Score (NDJ) [7]. All these measures have been validated on groups of hospital patients with established RA and, with the exception of the NDJ (which uses a simple binary scoring system of normal/abnormal), they all incorporate a grading system to identify the extent of damage in each joint assessed. The NDJ assesses 48 joints [excluding the distal interphalangeal joints (DIPs) but including the temporomandibular, sternoclavicular and acromioclavicular joints]. It provides no definition of malalignment and has been evaluated in established RA.


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TABLE 1. Published clinical measures of articular damage

 
The Norfolk Arthritis Register (NOAR) is a longitudinal observational study of patients with early IP recruited from primary and secondary care [8]. Joint damage is assessed annually using the NOAR–Damaged Joint Count (NOAR-DJC). The NOAR-DJC uses a simple binary scoring system looking at deformity, restrictions in range of movement (ROM) and surgical alteration in 51 synovial joints (Fig. 1). This is the first measure to be evaluated across the spectrum of early IP.



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FIG. 1. The 51 joints assessed for deformity, tenderness and swelling by NOAR, shown using the recording mannikin.

 
When developing any new clinical measure, there are three methodological criteria which need to be addressed: feasibility, reliability and validity. Feasibility looks at whether the measure is practical to perform in the circumstances in which it is required. Reliability refers to the reproducibility of the measure and validity addresses the question of whether the instrument actually measures what it is intended to. Tugwell and Bombardier describe five types of validity that should be addressed when developing a new measure in rheumatology: face, content, construct, criterion and discriminant [9].

The aim of this study was to assess the reliability and validity of the NOAR-DJC in patients with early IP.


    Patients and methods
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
All patients studied were recruited from NOAR, which has been described in detail elsewhere [8]. In brief, adults (≥16 yr) presenting to their general practitioner or hospital doctor with a history of at least two swollen joints lasting for ≥4 weeks are invited to participate in the study. Patients are assessed within a month of referral by research nurses, who interview the patients, examine their joints for tenderness and swelling and administer the Health Assessment Questionnaire (HAQ) [10]. The 1987 ARA criteria for RA are applied at each visit [11]. After registration, patients are visited at years 1, 2, 3 and 5 and the following data are recorded.

Health Assessment Questionnaire
This is a validated self-administered questionnaire used to assess function in rheumatology patients [10]. An overall score between 0 (no disability) and 3 (severe disability) is obtained. NOAR patients complete a HAQ at each follow-up.

Tender and swollen joint counts
These were conducted on all patients at each visit until the fifth anniversary visit, when 641 (66%) of the 965 patients seen had this examination.

All the joints shown in Fig. 1, except the hips, are examined for tenderness and swelling. The hips are only examined for tenderness. Tenderness is elicited by squeezing the joint at rest, the pressure being sufficient to cause whitening of the examiner's nail beds. In the case of the hips, pain on motion constitutes tenderness. Joint swelling is defined as soft tissue swelling. It is detected by manual palpation and/or visual estimation [12].

Assessing joint damage
The NOAR-DJC is conducted on every patient visited at years 1, 2, 3 and 5. It assesses the presence or absence of deformity in 51 joints [neck, shoulders, elbows, wrists, metacarpophalangeal joints (MCPs), proximal interphalangeal joints (PIPs), DIPs, hips, knees, hindfoot/ankles, metatarsophalangeal joints (MTPs) (Fig. 1)] using a simple binary score of normal/abnormal. The DIPs are included because the NOAR-DJC was intended for use in patients with early IP, some of whom go on to develop psoriatic arthritis. Tendon involvement is not included. The hindfoot and ankle are recorded as a single joint area. A joint is recorded as being deformed if any one of the following criteria applies: inability to adopt the anatomical position; reduction in ROM by one-third (unassisted movements); and surgical alteration to the joint.

Table 2 describes the manner in which the deformity examination is conducted. The results are recorded on a mannikin (Fig. 1). The NOAR-DJC will pick up, and does not discriminate between, damage caused by osteoarthritis and damage caused by IP. The examination takes less than 5 min.


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TABLE 2. NOAR guidelines for the assessment of deformity

 
The nurses examine the joints in a standardized way and regularly attend training sessions that incorporate inter-observer assessments.

X-rays
Within a longitudinal observational study it would be unethical to expose patients with early disease who were unlikely to have radiological changes to radiation. Therefore, only those patients who satisfied the ARA criteria for RA and those in whom a finding of radiological damage would lead to them fulfilling the criteria were invited to attend for an X-ray of the hands and feet at the first follow-up. An X-ray examination formed part of the fifth annual follow-up for all patients (where consent was given) after 1995. The differing protocols for X-ray examination at the first and fifth anniversaries may mean that the prevalence of X-ray damage may be higher at the first anniversary than at the fifth.

A posteroanterior view of the hands and feet is obtained and the films are read by two experienced rheumatologists with arbitration by a third in the case of disagreement. Larsen's method is used to score the following joints: wrists, MCPs, PIPs and MTPs 2–5 [13]. With this method, each joint is given a score between 0 and 5. A score of 2 or more for an individual joint indicates erosive damage.

Reliability study
The reliability of the NOAR-DJC was examined in two ways. Firstly, the intraclass correlation coefficient (ICC) was calculated for the total scores in both the intra- and inter-observer study as an estimate of rater agreement. Secondly, levels of agreement were examined using the kappa statistic, a measure of agreement for categorical data between one or more observers [14], in 11 individual joint areas (neck, shoulders, elbows, wrists, MCPs, PIPs, DIPs, hips, knees, hindfoot/ankles, MTPs). For the intra-observer study, 40 patients were examined on two separate occasions (within 3 months, mean time interval 1.58 months), by one of the research nurses (DKB). For the inter-observer study, 32 patients were examined by two Research Nurses (DKB and LMG) within 30 min of each other. For both studies, consecutive patients (any anniversary) were invited to take part as their routine assessment fell due.

Validity study
The validity of the NOAR-DJC was investigated by correlating deformed joint counts with tender and swollen joint counts, the number of eroded joints and HAQ scores. X-rays were only included in this study if they had been taken within 3 months of the clinical examination. Discriminant validity looked at whether the NOAR-DJC was able to discriminate between those who had met the ARA criteria by the fifth anniversary visit from those who had not.

The validation studies used data collected at the first and fifth anniversary visits for all patients notified to NOAR between 1 January 1990 and 31 December 1994 whose data had been entered onto the NOAR database by 31 December 1999. These anniversaries were chosen because they are the only ones at which X-rays were performed. Data were not normally distributed and therefore non-parametric tests were used. The frequency data for each anniversary were compared using the Wilcoxon signed rank sum test. All correlations used Spearman's rank correlation coefficient. Correlations between the NOAR-DJC and those of disease activity (tenderness and swelling) and HAQ scores used all 51 joints. The correlations between the NOAR-DJC and eroded joint count used only the 30 joints common to both assessments (i.e. wrists, MCPs, PIPs and MTPs 2–5). Discriminant validity was analysed using the Mann–Whitney U test. Finally, the change in the NOAR-DJC between 1 and 5 yr was correlated with the change in the eroded joint count and HAQ scores. All analyses were conducted using, SPSS versions 9.0 and 11.5 for Windows [15, 16].

Approval was obtained from the local research ethics committee for both the NOAR study and this study in particular.


    Results
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Reliability studies
The characteristics of the patients used for the intra-and inter-observer studies are shown in Table 3. In both groups, a greater proportion were female; the average age was 61 yr and the mean symptom duration was 5.4 and 6.9 yr, respectively. The inter-observer group had slightly more cases who satisfied the 1987 ARA criteria for RA (53%) compared with the intra-observer group (45%).


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TABLE 3. Characteristics of study population in the reliability studies

 
The ICC for the total score for the NOAR-DJC was slightly higher for the intra-observer study [0.88, 95% confidence interval (CI) 0.79, 0.94, P<0.001] than for the inter-observer study (0.74, 95% CI 0.53, 0.86, P<0.001). Both results suggest good levels of agreement for the total score. The 11 individual joint areas were analysed using the kappa statistic (Table 4). According to the interpretation of kappa proposed by Landis and Koch [14], the levels of agreement are all ‘moderate’ and above ({kappa}>0.4) in the intra-observer study, with four joint areas showing ‘substantial agreement’ ({kappa}>0.61–0.8) and a further four joint areas demonstrating ‘near perfect’ agreement ({kappa}>0.81). In the inter-observer study, the level of agreement obtained between the two observers was ‘fair’ ({kappa}>0.21–0.4) for the wrists and DIPs; ‘moderate’ for the neck, elbows, hips and MTPs ({kappa}>0.41–0.6); ‘substantial’ for the MCPs, PIPs, knees ({kappa}>0.61–0.8); and ‘almost perfect’ for the shoulders ({kappa}>0.81). It was not possible to calculate a value for kappa for the ankles, as one of the observers found them to be normal in all 32 cases. As expected, intra-rater agreement was better than inter-rater agreement for the majority of joint areas.


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TABLE 4. Results of intra- and inter-observer reliability studies II: joint areas

 
Validity studies
By 31 December 1999, 1157 and 965 patients had been visited and assessed at the first and fifth anniversary visits, respectively (Table 5). At first anniversary 522 (45%) had X-rays within 3 months of the clinical examination. At the fifth anniversary 641 (66%) had a tender and swollen joint count and 497 (52%) had an X-ray examination within 3 months of the clinical assessment (Table 6).


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TABLE 5. Clinical characteristics of the NOAR patients studied at first and fifth anniversaries

 

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TABLE 6. Prevalence of deformed, tender, swollen and eroded joints at first and fifth anniversaries

 
The mean age at onset at the time of the fifth anniversary was slightly higher than at the first anniversary (Table 5). This is because younger patients were more likely to be lost to follow-up. The mean duration of disease at presentation was 10.3 months. As the ARA criteria were applied cumulatively, the increase seen at the fifth anniversary is to be expected. There was also a small increase in the number of patients who were ever rheumatoid factor-positive.

There was a small but significant increase (Wilcoxon signed rank sum test, Z = –4.491, P<0.0001) in the number of cases with deformed joints at the fifth anniversary. There was also an increase in the number of deformed joints per case, with 23.5% having six or more deformed joints at the fifth anniversary compared with 17% at the first anniversary (Table 6). Additionally, the number of cases reporting any disability rose between the first and fifth anniversaries (Wilcoxon signed rank sum test, Z = –10.380, P<0.0001) and there was also an increase in level of disability (Table 7). In contrast, the number of patients with any tender or swollen joints decreased significantly (Wilcoxon signed rank sum test, Z = –6.855 and Z = –7.044, respectively, P<0.0001) between the first and fifth anniversaries and there was also a decrease in the number of tender and swollen joints per case.


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TABLE 7. Frequency of HAQ scores obtained at first and fifth anniversaries

 
The correlations between the NOAR-DJC and the tender and swollen joint counts were weak at both the first and the fifth anniversary (Table 8). The results were almost identical if the DIPs were excluded (data not shown). Correlation between the NOAR-DJC and the eroded joint count was weak at the first anniversary (rs = 0.19, P<0.01) but stronger at the fifth anniversary (rs = 0.42, P<0.01). These analyses do not include the DIPs. At both anniversaries the strongest correlation was with the HAQ score (rs = 0.39, P<0.01 and rs = 0.45, P<0.01, respectively). The correlations were very similar in the subgroup of patients with RA (Table 9). The change in the NOAR-DJC between the first and fifth anniversaries correlated weakly with the change in the HAQ score (rs = 0.24, P = 0.0001) but not with the change in eroded joint count (rs = 0.10, not significant).


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TABLE 8. Correlations between deformity, tender, swollen and eroded joint counts and HAQ scores at first and fifth anniversaries for IP group

 

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TABLE 9. Correlations between deformity, tender, swollen and eroded joint counts and HAQ scores at first and fifth anniversaries for RA group

 
There was a greater number of cases with deformed joints in the group of patients who had met the ARA criteria cumulatively at the fifth anniversary (452, 64%) compared with those who had not (83, 32%), Mann–Whitney U, Z = –9.622, P<0.0001.


    Discussion
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
The NOAR-DJC is the first instrument measuring joint damage to be validated in patients in the early stages of IP and including cases which represent the full profile of disease manifestations: those with mild IP as well as RA, in primary and secondary care. Therefore, direct comparisons with other published measures of joint damage have their limitations, because of the differing profiles of the groups used to validate these measures (RA patients attending hospital with much longer disease duration) compared with the NOAR cohort.

Reliability
The period of 3 months between observations for the intra-observer study was chosen to coincide with routine NOAR practice of requesting X-rays within 3 months of the clinical assessment, the assumption being that no discernible damage could occur during this interval. We explored the levels of agreement obtained within and between observers for the total joint count as well as for each joint area. An ICC of 0.88 and 0.74 for the total scores in both the intra- and inter-observer studies, respectively, demonstrated good levels of agreement. The NDJ (the only other study to use the ICC) also displayed a high level of agreement [7]. When looking at individual joint areas, the results in the intra-observer study were all ‘moderate’ and above, with nine out of the 11 areas showing ‘substantial’ agreement. As expected, the levels of agreement in the inter-observer study were lower. Two joint areas (the wrists and DIPs) were in the ‘fair’ category. This indicates that further training is needed for these areas, as well as the hindfoot. The results for the remaining joint groups were in the ‘moderate’ category and above. The RAAD score is the only other measure for which levels of inter-observer agreement within both individual joints and joint areas using kappa have been assessed [6]. As with our results, the majority of their observations was in the ‘moderate’ category and above. We therefore conclude that the reliability of the NOAR-DJC is at least as good as other damaged joint counts.

Validity
The NOAR-DJC was examined using all five types of validity proposed by Tugwell and Bombardier (face, content, criterion, construct and discriminant) [9]. Face validity asks the question: does the measure appear sensible and reasonable for assessing joint damage in this way? As there have been several published indices for clinical assessment of joint damage, it would appear reasonable that joint damage can be assessed in this way.

Content validity looks at the appropriateness of the joints, examinations and scoring system. The 51 joints used in the NOAR–DJC represent a comprehensive assessment of the possible joints likely to be involved in early IP (including the DIPs). It could be argued that including the DIPs means that the NOAR-DJC is biased by detecting Heberden's nodes. However, Heberden's nodes alone would not lead to the joint being scored as abnormal—the joint would have to exhibit deviation or loss of movement by one-third. Omitting the DIPs meant that the proportion of patients with no deformed joints rose only from 45.9% to 47.8% at the first anniversary and 44.6% to 46% at the fifth anniversary. There may be a case for separating out the ankle and true hindfoot. Each published index has used a different number and combination of joints. Further work is required to establish the number and pattern of joints which yields the most reliable results, a process which has been undertaken in tender and swollen joint counts [17]. The examinations used to detect deformity are comparable between the different published indices. However, the scoring systems differ substantially, with all the other measures except one (the NDJ) [7] using graded scoring systems (Table 1). It has been established in tender and swollen joint counts that grading is a source of error and that binary scoring systems are more reliable [18]. This has not yet been investigated in clinical measures of joint deformity but it is likely that a joint count will be more reliable than a scale. However, it does mean that the NOAR-DJC gives a measure of the extent rather than the severity of joint damage. This may make it a more useful tool in the early rather than the later years of IP.

Criterion validity compares the measure under investigation with a gold standard. Although there is no true gold standard with which to compare clinical joint damage, the eroded joint count on X-rays of the hands and feet was substituted. A minor degree of X-ray damage may have no clinical consequences. The expectation was that we should be able to demonstrate a reasonable correlation between clinical deformity and radiographic evidence which would become stronger with increasing disease duration. It is not suggested that the NOAR-DJC should replace X-rays but that it provides reliable additional information, especially for monitoring progress between serial X-rays. Correlations improved between 1 and 5 yr from 0.19 to 0.42. The correlation coefficient of 0.42 at the fifth anniversary is weaker than those obtained for other indices using patients with established RA in secondary care, in whom a range of between 0.74 and 0.83 [6, 7] has been obtained. However, our results were obtained from a large group of patients that included those with undifferentiated IP as well as RA, from both primary and secondary care, with early disease.

Finally, in circumstances where there is no true gold standard available, it is acceptable to devise a construct whereby the relationship between the new measure and those of similar measures is investigated. In case the NOAR-DJC is simply a surrogate measure of tenderness and swelling, because both can cause some reduction in movement, we compared the NOAR–DJC with tender and swollen joint counts, testing divergent construct validity. As we expected, these correlations were weak at both anniversaries, in common with other studies [2, 5, 6]. These results indicate that tenderness, swelling and deformity are distinct from each other. Also, whereas the number of swollen and tender joints decreased between 1 and 5 yr, the number of deformed joints increased, a finding also reported by Callahan et al. in their study looking at changes in disease activity and damage in the first 5 yr of RA [19].

By comparing the NOAR-DJC with HAQ scores, we addressed the issue of convergent construct validity: expecting that as they both measure aspects of disease damage, the correlations will reflect this. We did not expect the correlation to be higher as physical function is determined by pain, muscle strength and psychological factors as well as joint damage. Our results of 0.39 and 0.45 at the first and fifth anniversaries, respectively, would support this. Again, these findings are consistent with those from other studies, in which correlations of between 0.38 and 0.56 were obtained [5–7].

By being able to discriminate between two groups: those who met the ARA criteria and those who did not, the NOAR-DJC was able to show discriminant validity also.

Longitudinal studies
We examined the correlation between the change in the NOAR-DJC scores between the first and fifth anniversaries and the change in the number of eroded joints and HAQ scores for the same period. The correlations with X-ray data demonstrated no relationship, although there was a weak relationship between the change in NOAR-DJC and HAQ scores. A previous analysis within the NOAR cohort, using generalized estimating equations for repeated measures data, demonstrated that the NOAR-DJC was associated with having an HAQ score of ≥1 across the first 5 yr of follow-up [20]. The NDJ score showed moderate correlation between the change in deformity score and the change in X-ray score over 2 yr (r = 0.32, P = 0.04) [7], whereas the change in MJS did not correlate with change in HAQ scores over 5 yr (r = 0.102, P = 0.6) [5]. Both the NDJ and MJS were assessed in patients with established RA.

In conclusion, the NOAR-DJC has been shown to be both valid and reliable. It is also feasible to perform, taking no more than 5 min, and can be conducted anywhere by assessors following a short training period. These results can be generalized to patients with any form of early IP (<5 yr of disease) presenting in primary or secondary care.


    Acknowledgments
 
The work of the Norfolk Arthritis Register is funded by the Arthritis Research Campaign. This analysis was funded in part by Action Arthritis. We acknowledge the ongoing support of the general practitioners in the former Norwich Health Authority, the rheumatologists at the Norfolk and Norwich University Hospital, and the NOAR research nurses.

The authors have declared no conflicts of interest.


    References
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 

  1. American Rheumatism Association. Dictionary of the rheumatic diseases. Volume 1: signs and symptoms. New York: Contact Associates International, 1982.
  2. Spiegel TM, Spiegel JS, Paulus HE. The Joint Alignment and Motion Scale: a simple measure of joint deformity in patients with rheumatoid arthritis. J Rheumatol 1987;14:887–92.[ISI][Medline]
  3. Ferraz MB, De Oliveira LM, Araujo PMP, Atra E, Walter SD. EPM-ROM Scale: an evaluative instrument to be used in rheumatoid arthritis trials. Clin Exp Rheumatol 1990;8:491–4.[ISI][Medline]
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  5. Johnson AH, Hassell AB, Jones PW, Mattey DL, Saklatvala J, Dawes PT. The mechanical joint score (MJS): a new clinical index of joint damage and function in rheumatoid arthritis. Rheumatol 2002;41:189–95.[Abstract/Free Full Text]
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Submitted 4 January 2004; revised version accepted 13 July 2004.



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