Materials and methods

Patients

Details on the study population have been described previously.7 In short, 190 female patients with HOA between 50 and 70 years of age with a mean age of 61.6 years and mean disease duration of 11 years took part in a comprehensive clinical examination and data collection between 2000 and 2002. All participants had been referred to an outpatient rheumatology department within the previous 2 years and 159 patients (84%) fulfilled the American College of Rheumatology clinical classification criteria for HOA, whereas 31 patients (16.%) had clinical HOA without formally fulfilling the classification criteria.8 Radiographic OA abnormalities (Kellgren–Lawrence grade 2 or more) in at least 1 finger joint were found in 176 participants (93%).9

Joint examination

All joint assessments were performed by the same experienced clinician. The carpometacarpal (CMC) joints, metacarpophalangeal (MCP) joints, proximal interphalangeal (PIP) joints and distal interphalangeal (DIP) joints were examined for four categories of abnormalities and corresponding joint counts were computed: tenderness/pain on motion (tender joint count (TJC)), soft tissue swelling (swollen joint count (SJC)), bony enlargement (hard tissue swelling, including Heberden and Bouchard nodes) (bony joint count (BEJC)) and limited motion, defined to be less than “normal” range of motion (limited motion joint count (LMJC)). Presence of abnormal findings in individual joints was scored as 1, absence as 0. For each of the four categories of clinical abnormalities, we summed up the number of DIP joints (range 0–8), PIP joints (range 0–10) including the first interphalangeal joint (IP-1), CMC joints (range 0–2), DIP+PIP joints (range 0–18) and DIP+PIP+ CMC joints (range 0–20).

Outcome measures

The patients completed several questionnaires including Australian/Canadian Osteoarthritis Hand Index (AUSCAN), Arthritis Impact Measurement Scales 2 (AIMS2), Short Form 36 assessment (SF-36), Health Assessment Questionnaire (HAQ) and visual analogue scale for pain (VAS pain).10 11 12

Grip strength (kg) was measured by Jamar hand dynamometer as the best performance out of two attempts with each hand.13

Statistical analyses

We used SPSS V.14.0 (SPSS, Chicago, Illinois, USA) for statistical calculations. p Values equal to or below 0.05 were regarded as significant. Levels of health status were compared between patients with and without joint involvement in specific areas by Student t test. Associations between joint counts and patient-reported outcomes were examined with Pearson correlation coefficients. Correlations were considered to be mild, moderate and strong when r<0.3, r = 0.3 to 0.6 and r>0.6, respectively.

Results

Figure 1A,B shows that joint involvement was generally more extensive in the right compared to the left hand. DIP joint involvement was more frequent than PIP joint involvement and all categories of joint abnormalities were most frequently seen in the second and the fifth DIP joints. DIP joint involvement for pain, soft tissue swelling, bony enlargement and limited motion was observed in 90%, 93%, 89% and 42%, respectively. The MCP joints were as expected infrequently affected. The most frequently involved MCP joint was MCP 1 (pain) (fig 1B).

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Figure 1

Percentages of patients with hand osteoarthritis (HOA) with joints with soft tissue swelling (left in ellipses) and joints with bony enlargement (right in ellipses) (A) and with painful joints (left in ellipses) and joints with limited motion (right in ellipses) (B) in left and right hand in patients with hand osteoarthritis.

Patients with presence of joint tenderness/pain in the CMC, PIP and/or DIP joints had worse health status across all measures reflecting pain, stiffness and physical function of the hand (AUSCAN, AIMS2 hand and finger function) and VAS pain (table 1). Additionally, joint tenderness/pain was associated with numerically worse health status reflecting the physical dimensions of AIMS2, SF-36 and HAQ (data not shown) and grip strength (table 1).

The presence of other categories of abnormal joint findings was associated with worse pain and function as well, but the results were mostly not statistically significant (table 1). Presence of limited motion in DIP joints was associated with worse scores for AUSCAN pain and physical and weaker grip strength (table 1).

Table 2 shows the mean values for the various joint counts and the correlations between joint counts and the patient-reported outcomes. Joint counts of PIP and DIP joints were generally more strongly correlated to AUSCAN pain, physical and stiffness than separate joint counts of only DIP or PIP joints. Adding CMC joints to the counts did not make any difference (table 2). Correlations between TJC and AIMS2 hand and finger function and VAS pain and between TJC and grip strength were mild (r around 0.30, −0.30, 0.28, respectively).

SJC of the DIP and PIP joints were also mildly to moderately correlated to dimensions of AUSCAN with correlation coefficients around 0.30 (table 2). Correlations between joint counts and scores of general physical function, general pain and other dimensions of health (AIMS2 and SF-36) were usually low (data not shown).

We also conducted the respective analyses for counts of MCP joints. Similar associations between painful MCP joints and outcome measures were seen as for CMC, PIP and DIP joints (data not shown).

Discussion

Joint counts are important tools in the clinical assessment of joint diseases, such as RA, but have not yet been accepted as outcome measures in HOA. Our results show that counts of PIP and DIP joints with tenderness/pain are moderately correlated to disease specific outcome measures and impaired grip strength.

Associations between joint involvement and patient-reported outcomes were addressed with two different approaches. We compared levels of health status across patients with or without presence of one of four categories of abnormalities in the different joint areas and examined correlations between joint counts and health status. As expected, correlations with general health status measures such as AIMS2, SF-36 and HAQ were low and we focused on measures addressing pain, stiffness and functional aspects of the hand.

DIP joints were in general more frequently involved than the PIP joints (fig 1). However, correlations between joint counts focusing on either PIP or DIP joints were similarly correlated to measures of health status, and the strength of the correlations was generally increased if the joint counts included PIP and DIP joints (table 2).

The strongest association between joint abnormality and health status was seen for presence of joint tenderness/pain in DIP and DIP joints. This observation was consistent with both analytic approaches (tables 1 and 2). SJC was also mildly to moderately correlated to AUSCAN.

This study was performed in a cohort of patients who experience a substantial amount of pain and functional loss compared to healthy controls.7 Data from previous analyses of this cohort have demonstrated that patients with HOA experience a similar burden of disease as patients with RA with regard to pain.7 The patients were recruited through a rheumatology outpatient clinic and may overall have more severe disease than the average patient with HOA. Moreover, other studies have also found an obvious impact of hand problems on everyday life and have shown that extensiveness of joint involvement in HOA is associated with health outcome.14 15

A limitation of this study is the cross-sectional dataset. We have only focused on how joint involvement and joint counts are associated with patient-reported outcomes. The upper age limit in our cohort can represent a potential limitation and the results have to be interpreted in the context of the study population, which did not include patients over the age of 70 years. One strength of the study is the comprehensive data collection and that the joint counts were provided by the same experienced clinician.

What are the implications of our findings? The association between joint counts and patient-reported outcomes strengthen the face validity and external validity of joint counts as potential future outcome measures. Clinical research is increasingly focusing on measures that are relevant for patients and it is important from this perspective to examine how joint involvement and joint counts are associated to pain, stiffness and physical function. A previous placebo-controlled study has indicated that joints counts may be responsive in HOA.6 The current results should encourage future studies on composition and validation of outcome measures in HOA which include joints counts as a component.