Clinical characteristics of an anatomical hand index measured in patients with rheumatoid arthritis as a potential outcome measure

J. Highton, V. Markham, T. C. A. Doyle1 and P. L. Davidson2

Departments of Medicine, 1 Radiology and 2 Preventive and Social Medicine, University of Otago Medical School, Dunedin, New Zealand.

Correspondence to: J. Highton, Department of Medicine, Dunedin School of Medicine, University of Otago, P. O. Box 913, Dunedin, New Zealand. E-mail: john.highton{at}stonebow.otago.ac.nz


    Abstract
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Objectives. To determine the clinical characteristics of an anatomical hand index previously reported as a potential measure of joint deformity and outcome in patients with rheumatoid arthritis.

Methods. The hand index (open hand span – closed hand span/lateral height of the hand) was measured in a cross-sectional study of 145 out-patients with rheumatoid arthritis with disease durations 0–55 yr. Subsets of patients were restudied at mean follow-ups of approximately 9 months and 4 yr.

Results. The hand index fell gradually with disease duration. Correlations were demonstrated with the Sharp index (r = – 0.39, P = 0.000) and to a lesser extent with disease activity score (r = – 0.28, P = 0.001). At 260 ± 115 days the hand index worsened by 0.09 units (P = 0.09, NS). At 51.6 ± 5.4 months the index showed a fall from 1.96 ± 0.73 to 1.61 ± 0.65 (P = 0.000). During the same interval the Sharp index increased from 60 ± 68 to 80 ± 71 (P = 0.000).

Conclusions. Measurement of simple hand dimensions can demonstrate worsening of hand deformity with time in patients with rheumatoid arthritis. We suggest that more sophisticated analysis of digital hand images, as used in our original study, might yield additional information and increase the sensitivity of an anatomical hand index as an outcome measure in rheumatoid arthritis.

KEY WORDS: Rheumatoid arthritis, Outcome assessment


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The impacts of rheumatoid arthritis include systemic features such as fatigue, weight loss and increased mortality [1] as well as destructive synovitis most evident in the hands and feet. Rheumatologists assess some systemic features through direct tests such as haemoglobin, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and others indirectly such as with questionnaire-based instruments for fatigue [2–5]. Joint impacts such as tenderness [6] and swollen and tender joint counts can be combined with other core set variables [7] to give composite assessments of joint disease activity such as ACR 20 and disease activity score (DAS) [8, 9]. Disability is commonly measured using the Health Assessment Questionnaire (HAQ) [10, 11] and wider disease impacts with SF 36 [12]. Many of these instruments are indirect and include graded responses to questions or arbitrary judgements such as global scores.

One of the fundamental variables for assessing the progress of rheumatoid arthritis is measurement of damage. The gold standard for this has become plain X-rays [13]. The methodology for scoring X-ray changes has been highly developed with refinement of the original methodology [14–18]. The disadvantage of using X-rays is that only erosions and loss of joint space are assessed. Magnetic resonance imaging (MRI) gathers data from a wider range of tissues either as a direct measurement such as volume of erosion [19] or in a scoring system [20]. However, further study is required because although baseline MRI is able to predict outcome in patients with early arthritis [21], it is less clear that it gives distinct advantages over X-ray scoring for follow-up measurements [22].

Ideally it would be useful to have a means of assessing damage due to rheumatoid arthritis simple enough to be performed in the clinic. Other desirable attributes would be the use of direct measurement rather than scores, and the incorporation of information on more aspects of damage such as muscle wasting and deformity. The joint alignment and motion (JAM) scale [23] and the mechanical joint score [24] can both be performed in the clinic and show strong correlation with radiological damage and measures of function, but use scores rather than direct measurements.

If asked where to start assessing the impact of rheumatoid arthritis most clinicians would first turn to the hands where many damaging aspects of the disease are visually evident. It seemed to us that much of this information could be captured in a photographic image. Digital imaging and transfer of this information to computers provides the potential to analyse the contained information. In 1996 we used digital images to measure standard anthropometric hand dimensions and compared these in patients with rheumatoid arthritis and normal controls [25]. This approach by no means attained the ideal of using all the information in the image but we were able to detect significant differences between patients and normal subjects. In this paper we describe studies aimed at determining if such simple hand measurements would change with time and advancement of rheumatoid disease.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Hand index
In 1996 we compared 13 standard anthropometric hand dimensions in patients with rheumatoid arthritis and normal subjects. From these we selected the three dimensions that showed the greatest difference between patients and controls, and also showed the least variation when measured at intervals. The chosen dimensions were incorporated into a hand index where hand index = open hand span – closed hand span/lateral height of the hand. In patients with rheumatoid arthritis closed hand span increases, open hand span decreases and lateral height of the hand increases resulting in a fall in the hand index. Consequently the mean hand index in normals was 3.76 ± 0.6 vs 1.51 ± 0.9 in patients [25].

Laser-aligned hand measurement system
In the 1996 study we used digital images of hands photographed within a frame of known dimensions. However, there was some difficulty in accurately defining the highest point for measurement of lateral height of the hand at the metacarpophalangeal (MCP) joint. We therefore developed a system using laser pointers mounted on digital callipers in a rigid frame so that bright laser light could be used to facilitate picking the highest point of the hand at the level of the MCP joints [26]. In this study the laser-aligned method was used to make hand measurements from the patient's dominant hand for calculation of the hand index.

Cross-sectional study
Ethical permission for the study was obtained from the Otago Ethics Committee. Patients with rheumatoid arthritis were informed of the study as they attended out-patients. Consenting patients were entered into the study (n = 145). Basic information recorded included age, sex, ACR diagnostic criteria [27], disease duration, rheumatoid factor (RF) status, DAS [28] and modified HAQ (mHAQ) [29]. New X-rays of the hands and feet were arranged if recent films were not available. Radiological status was assessed using the Sharp index measured by a single experienced observer [18, 30].

Longitudinal studies
Paired follow-up measurements were made in a subset of 96 patients at a mean interval of approximately 9 months which we anticipated might be just long enough to show a change in the Sharp index (mean interval 260 days ± S.D. 115 days or 37 weeks).

A further set of paired measurements was made in a subset of 80 patients at 51.6 ± 5.4 months. The original cohort was contacted where possible. In 15 cases the patients were deceased. We were unable to contact 25. A further 25 declined further involvement due to health, work, distance and other considerations.

Statistics
Results were analysed using the SPSS statistical package. Data are displayed in the form of box plots indicating median, 25th and 75th centiles and whiskers indicating 5th and 95th centiles. Multiple regression analysis was used to look for correlations between different variables. Paired follow-up results were analysed using two-tailed Student's t-test. Missing data were handled by pair-wise exclusion for each analysis.


    Results
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Cross-sectional study
Measurements of the hand index were made using the laser-aligned system in 145 consenting patients. Patient characteristics are shown in Table 1. Measurement of the hand index showed a slow decline as disease duration increased (Fig. 1). Measurements of the hand index correlated with disease duration (R = –0.20, P = 0.02), and the Sharp index (r = –0.39, P = 0.000) as might be expected of a measure of structural damage. However, there was also a correlation with DAS (r = –0.28, P = 0.001). In comparison, the Sharp index increased with disease duration at an average of 3.65 units per year in this group of patients. It showed a stronger correlation with disease duration (R = 0.42, P = 0.000) and no correlation with disease activity. In this group of patients neither of these measures of structural damage showed any correlation with disability measured as mHAQ which correlated more strongly with DAS (r = 0.58, P = 0.000).


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TABLE 1. Patient characteristics

 


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FIG. 1. Changes in the anatomic hand index of joint deformity, with length of disease duration in years, in comparison with changes in the Sharp Index of radiological joint damage, MHAQ of function and inflammatory disease activity score (DAS).

 
Paired measurements at 9 months and at 4 yr
In paired measurements in 96 patients at 260 ± 115 days the hand index showed a mean decline of 0.09 units (P = 0.09, NS). The change in the Sharp index of 1.55 units was also not significant. Disease activity decreased (mean change 0.21, P = 0.05) and MHAQ fell by 0.02 (P = 0.69) (Fig. 2).



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FIG. 2. Measurements in the original subjects and subsets at different time intervals. Box plots of measurements taken at T = 0, visit 1; T = 260 ± 115 days, visit 2 and T = 51.6 ± 5.4 months, visit 3. Box plots show median, 25th and 75th centiles and whiskers indicate 5th and 95th centiles.

 
At an interval of 51.6 ± 5.4 months we contacted the original cohort as described. We were able to obtain follow-up measurements in 80 patients. Paired measurements showed a change in hand index from 1.96 ± 0.73 to 1.61 ± 0.65 (P = 0.000). During this interval the Sharp Index increased from 60 ± 68 units to 80 ± 71 (P = 0.000). Disease activity fell from 2.6 ± 1.0 to 1.82 ± 0.69 (P = 0.000) but there was no significant change in mHAQ (0.47 ± 0.48 vs 0.38 ± 0.38, P = 0.07).


    Discussion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The concepts involved in this study began with an attempt to use information contained in digital images of hands of patients with rheumatoid arthritis in order to measure deformity due to the disease. The aim of the original study in 1996 was to establish if such clinically accessible information might be sufficient to document differences between patients with rheumatoid arthritis and normal subjects. The methods derived from that study and applied in the present investigation are simple but have the advantage of being direct measurements rather than estimated scores. At the simplest level the measurements necessary for the hand index used in this study can be made in around 5 min with a ruler and callipers, though a laser-aligned method was used in this study [26].

The cross-sectional part of the present study was undertaken in 145 out-patients with rheumatoid arthritis. As a group they had reasonably controlled disease as judged by a mean DAS of 2.6. In keeping with this the Sharp index progressed on average at 3.65 units per year of disease duration. It might therefore be expected that any change in the hand index would also be relatively slow. This proved to be the case. We showed no difference in paired measurements in the same patients at a mean interval of around 9 months. The minimum interval required for change has therefore not been established but is likely to be at least 1 yr. At a longer interval of approximately 4 yr a significant change was demonstrated. Some of the clinical features of the subset of patients studied at 4 yr such as the presence of more rheumatoid nodules suggest that this may have been a subset with more severe disease. Despite this the results at least clearly show that measurements as simple as those in the hand index can demonstrate change with progression of rheumatoid arthritis.

In the cross-sectional part of this study we also noted a correlation between the hand index and radiological damage measured by the Sharp index as might be expected if the hand index reflects damage. However, there was also some correlation with disease activity. Although we selected hand measurements that showed the least variation from day to day in our original study [25] there is clearly an element of function in such measurements as open and closed hand span that would be affected by pain and stiffness due to joint inflammation. Our data therefore suggest that the hand index is not as ‘clean’ a measure of damage as the Sharp index.

What then is the use of the hand index? In its present form it is quick and easy to measure and it can be performed with only a ruler and callipers if necessary. As such it could be used to follow the progress of rheumatoid arthritis where X-rays are not readily available. It could also be applied to the assessment of other conditions that cause damage to the hand such as scleroderma or hand injuries. We have now shown that measuring even very simple dimensions from hands that can be taken from digital images or by direct measurement can show changes in the progress of rheumatoid arthritis. It would now seem appropriate to go back to digital images of patient's hands and see what additional data can be utilized. Additional information should increase the responsiveness of an improved anatomical hand index to measuring the progress of rheumatoid arthritis.


    Acknowledgments
 
The authors would like to acknowledge receipt of a Limited Clinical Research Grant from the Health Research Council of New Zealand and the support of the Arthritis Foundation of New Zealand and the HS and JC Anderson Trust. Dr Peter Herbison provided invaluable statistical advice and analysis.

The authors have declared no conflicts of interest.


    References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Submitted 21 October 2004; revised version accepted 11 January 2005.



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