Radiographic joint space in rheumatoid acromioclavicular joints: a 15 year prospective follow-up study in 74 patients
J. T. Lehtinen,
M. U. K. Lehto1,
K. Kaarela1,
H. J. Kautiainen1,
E. A. Belt1 and
M. J. Kauppi1
Department of Surgery, Tampere University Hospital and
1 Rheumatism Foundation Hospital, Heinola, Finland
Correspondence to:
M. U. K. Lehto, Rheumatism Foundation Hospital, Department of Orthopaedics, FIN-18120 Heinola, Finland.
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Abstract
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Objective. To evaluate radiographically the acromioclavicular joint space in patients with long-term rheumatoid arthritis (RA).
Methods. A cohort of 74 patients with RA was followed prospectively for 15 yr. At the end point, 148 shoulders were radiographed with a standard method. The acromioclavicular (AC) joint space was examined from the radiographs with a method developed previously for population studies; the joint space was measured at its superior and inferior border, and the average of the two measurements, the integral space, calculated.
Results. Mean AC joint space in RA patients was 4.9 (S.D. 3.7), range 020.5 mm; 6.2 mm (S.D. 5.1) in men and 4.5 mm (S.D. 3.0) in women. An AC joint space wider than 7 mm in men was found in 11 (31%) out of 36 joints and wider than 6 mm in women in 17 (15%) out of 112 joints. Joint space widening was associated (r=0.87, 95% CI 0.820.90) with increasing destruction (Larsen grading) of the joint and it seems to be an inevitable consequence of AC joint affection in RA. Joint space widening is more progressive on the caudal side because of the nature of the erosive destruction. Degeneration with joint space narrowing was observed in 8 (11%) patients (11 joints, 7%; three bilateral).
Conclusions. The largest value of the joint space may be used when evaluating rheumatoid AC joint space. In RA patients, a joint space of >7 mm in men and >5 mm in women is a sign of destructive AC joint affection.
KEY WORDS: Rheumatoid arthritis, Acromioclavicular joint, Joint space, Radiography, Larsen method
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Introduction
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Rheumatoid erosions occur frequently in the acromioclavicular (AC) joint, leading to osteolysis of the distal end of the clavicle and increasing joint space widening [14]. Larsen grading for AC joints is partly based on the joint space widening as illustrated by Petersson [3, 5]. Joint space narrowing is a well-known sign of osteoarthrosis and degeneration of the AC joint [68]. However, narrowing has been described in rheumatoid AC joints as well [1, 2, 912].
Oppenheimer [13] and Zanca [10] have proposed that the normal AC joint space in an adult is 13 mm wide. Petersson and Redlund-Johnell [8] have developed a standard method for population studies to measure AC joint space. By measuring normal AC joints, they came to the conclusion that a joint space wider than 7 mm in men and 6 mm in women is abnormal. Recently, an ultrasound study of AC joints suggested that the joint space is 4.1 mm on average in patients with chronic arthritis [12].
To our knowledge, rheumatoid AC joint space measurements from radiographs have not been previously published. Reported widening and narrowing have been based on visual evaluation of radiographs [1, 2, 3, 911]. The aim of the present study was to analyse the AC joint space width in a cohort of 74 patients with rheumatoid arthritis (RA) followed up for 15 yr.
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Patients and methods
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During 197375, a total of 121 patients with recent (<6 months) RA were studied at the Rheumatism Foundation Hospital in Heinola. The selection criteria, data collection strategy and details of the patients have been described elsewhere [14, 15]. At the 3 yr follow-up, 102 patients had rheumatoid factor (RF)-positive and erosive RA. After the 3 yr check-up, 24 had died, and four failed to attend the 15 yr follow-up. Thus, 74 patients (18 males and 56 females) are the subjects of the present study. The age at onset ranged from 17 to 66 yr, mean 42 (S.D. 12). The patients were treated with anti-rheumatic drugs and no surgical procedures were performed on the AC joints.
Radiographs of the 148 shoulders were taken at the 15 yr check-up (mean 15 yr, S.D. 1). The standard positioning was as follows: patient laying supine, slightly turned (20°) to imaged side (a support under the other shoulder) and the arm in external rotation, palm facing upwards. The same radiographer confirmed exact positioning and took the radiographs with a standard technique: the straight antero-posterior projection (distance 0.95 m) was used with exposure factors of 48 kV and -63 mAs. The size of the film (Kodak Lanex Regular) was 18x24 cm.
The AC joints were classified according to the six Larsen grades from 0 to 5 [3, 5]. The joint space was measured with a ruler at its superior and inferior border, and the average of the two measurements, the integral space, calculated. The numbers of joints fulfilling the reported pathological criteria, >7 mm in men and >6 mm in women, were calculated [8]. The degenerative changes (cartilage degeneration) were assessed according to the three grades illustrated by Petersson [7].
The 15 yr Larsen score of 0100 was determined, and was calculated as the sum of the Larsen grades of wrists, 10 metacarpophalangeal and eight metatarsophalangeal joints [15]. The occupations of the patients were registered at the onset of the disease. MannWhitney U-test, Spearman and Pearson correlation coefficients were used in statistical analysis.
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Results
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There was no systematic rightleft difference in either sex (r=0.80); therefore, the measurements of the two sides were pooled. The mean integral AC joint space was 4.9 (S.D. 3.7, minimum 0.0, maximum 20.5). The results of the measurements from different measuring sites for both men and women, separately for right and left, are presented in Table 1
. Cranial and caudal values differed in 120 joints (Fig. 1
). In destructive cases, the caudal space appeared more widened; the largest difference was 17 mm. The cranial space was 4 mm wider in the two largest cases (Fig. 1
). The Pearson correlation coefficient between right and left largest values was 0.79 (95% CI 0.690.87). The right and left largest values for both men and women are shown in Fig. 2
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FIG. 1. Distribution of cranial and caudal joint space values from 148 rheumatoid AC joints. The black line indicates the equal cranial and caudal values. Most of the measured values diverge from the line; therefore, the largest values demonstrate the joint space in destructed AC joints better.
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FIG. 2. Distribution of right and left largest AC joint space values from 74 RA patients (18 men, 56 women). Pearson's correlation between right and left values was 0.79 (95% CI 0.690.87).
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In men, an integral joint space wider than 7 mm was found in 11 (31%) out of 36 joints and in women an integral joint space wider than 6 mm was found in 17 (15%) out of 112 joints.
The distribution of the AC joints (n=148) according to the Larsen grading and the mean integral joint spaces and the mean largest values for each group are shown in Table 2
. Both the integral joint space (r=0.87, 95% CI 0.820.90) and the largest joint space value (r=0.86, 95% CI 0.810.90) correlated with the joint destruction (Larsen grading). A correlation (r=0.97) was seen between the integral and the largest joint space values.
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TABLE 2. Radiographic assessment of 148 rheumatoid acromioclavicular joints according to the Larsen grading and mean joint spaces for each group
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In 17 joints, the joint space was
1.5 mm, 10 of these had degenerative features. In addition, severe cartilage degeneration was observed in one joint with a joint space of 2 mm. The degeneration of cartilage was classified as grade II or III in these 11 joints (bilateral in three cases). In both sides, there was a highly significant (MannWhitney U-test, P<0.001) reduction of the joint space with these degenerative joints. The mean Larsen score of the patients with degenerative AC joints (n=8) was 19 (S.D. 9). This was significantly lower (MannWhitney U-test with exact P value 0.004) than the 45 (S.D. 26) in the remaining group (n=66). Mean age at onset of the disease of these patients with degenerative AC joints was higher (47 yr) than in the remaining group (41 yr); however, this difference was not statistically significant.
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Discussion
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The results of the present study confirm the visually observed joint space widening in rheumatoid AC joints [1, 3]. The mean AC joint space of patients with RA was noticeably wider compared to the suggested normal variation of 13 mm [10, 13]. Petersson and Redlund-Johnell [8] used the same standard technique as us in their series of normal population and reported that the average AC width is 3.1 mm, and pathological when exceeding 7 mm in men and 6 mm in women. The pathological limits were exceeded in 31% of AC joints in men (>7 mm) and in 15% of the joints in women (>6 mm) with long-lasting RA in this study. All the joints graded as Larsen 3 or more fulfilled these criteria. Based on our results, we suggest that a joint space of >5 mm would be pathological in women. With this criterion, 29% (n=32) of the AC joints in women showed pathological features. This limit is reasonable, since it was fulfilled only with joints classified at least as Larsen grade 2, indicating definite rheumatoid involvement. In addition, 5 mm falls outside 2 S.D. of the normal, 4.7 mm, according to Petersson and Redlund-Johnell [8].
Alasaarela et al. [12] measured 33 AC joint spaces by ultrasound in patients with chronic arthritis. The average joint space was 4.1 mm, which is 0.8 mm less than our average. This parallels well with our results, since the image is slightly magnified in radiographs because of the filmfocus distance. However, the mean disease duration was shorter (11.7 yr) in their series, and seronegative as well as other arthritic diseases were included in their material.
An interesting finding in this study was the difference in width in cranial and caudal measuring sites. In normal AC joints, cranial space is noticeably wider than caudal [8], whereas in the rheumatoid AC joints it is the opposite. This can be explained by the nature of the erosive process in rheumatoid AC joints. The erosions occur most often on the inferior joint margin of the clavicle [4]. The destructive process continues more prominently in the inferior part of the clavicle [1]. The joint space increases with Larsen grading and we suggest that the joint space widening in rheumatoid AC joints is a part of the destructive process and finally a consequence of remarkable bone resorption (Fig. 3
). Since the destructive process affects different parts of the joint, the integral space can be misleading. The largest value describes the rheumatoid AC joint space more accurately, taking into account the erosive destruction.

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FIG. 3. Severely destroyed rheumatoid AC joint (Larsen 5) of a female patient. Integral joint space is 12.5 mm.
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Degeneration of the AC joint is quite common and may sometimes develop rather early [6, 8]. As described in the literature [1, 2, 912], we also found AC joint space narrowing in several AC joints in RA patients. Degeneration of the AC joint was observed in 8 (11%) out of 74 RA patients (three bilateral; Fig. 4
) and the joint space values in 10 of these 11 joints fell outside 2 S.D. of the normal [8]. These patients were manual labourers, their average age was higher and RA was less erosive (Larsen scores were lower) than in the remaining RA patients. Thus, their AC joint degeneration may have started before RA, or only slightly erosive disease may have enabled them to work longer.

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FIG. 4. Degenerative and hypertrophic features of the AC joint (Larsen 0) in a male RA patient. Integral joint space is 0.5 mm.
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We conclude that rheumatoid inflammation in AC joints frequently causes joint space widening, which should be noticed when examining radiographs from painful rheumatoid shoulders. The joint space widening is seldom uniform due to the erosive destruction; therefore, the largest measured value is more practical and may be used instead of the integral space. In RA patients, an AC joint space of >7 mm in men and >5 mm in women is a definite sign of destructive joint affection. However, degeneration with joint space narrowing may be seen in RA patients as well (Fig. 4
).
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Acknowledgments
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This study was supported by a research grant from the Medical Research Fund of Tampere University Hospital.
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Submitted 10 February 1999;
revised version accepted 14 May 1999.