Is the association between physical activity and fatigue mediated by physical function or depressive symptoms in symptomatic knee osteoarthritis? The Multicenter Osteoarthritis Study

Objectives: To examine whether physical activity (PA) was associated with fatigue, and quantify the extent of potential mediation through depressive symptoms or physical function (PF) on the relationship between PA and fatigue in symptomatic knee osteoarthritis (KOA).Method: This longitudinal study used data from the Multicenter Osteoarthritis Study (n = 484), comprising subjects aged ≥ 50 years. Baseline PA was quantified via an ankle-worn accelerometer. The outcome was fatigue, measured using a 0-10 rating scale at 2 year follow-up. Mediators included gait speed as a measure of PF and depressive symptoms at 2 year follow-up. Mediation analysis was carried out after adjustment for baseline confounders. Stratified analysis by baseline fatigue status [no/low (< 4) and high (≥ 4) fatigue] was performed.Results: A significant direct association was found between PA and fatigue at 2 years [unstandardized coefficient (B) = -0.054; 95% confidence interval (CI) -0.107, -0.002, p = 0.041]. The PA-fatigue relationship was not mediated by gait speed (B = -0.006; 95% CI -0.018, 0.001) or depressive symptoms (B = 0.009; 95% CI 0.009, 0.028). In the subgroup with high baseline fatigue, direct associations were found between PA and fatigue (gait speed model:, B = -0.107; 95% CI -0.212, -0.002, p = 0.046; depressive symptoms model: B = -0.110; 95% CI -0.120, -0.020, p = 0.017); but in the no/low baseline fatigue group, no significant association was found between PA and fatigue.Conclusion: In the symptomatic KOA population, higher baseline PA was directly associated with reduced fatigue 2 years later, especially in those with high baseline fatigue. However, this relationship was not mediated by depressive symptoms or PF.

Muscle strength, pain and disability in patients with osteoarthritis

OBJECTIVE

Reduced muscle strength is regarded as a risk factor for pain and disability in osteoarthritis (OA). Currently, various indices for muscle strength are used when assessing determinants of pain and disability. The goal of the present study was to evaluate these indices of muscle strength.

DESIGN

Isometric muscle strength was measured for 16 muscle actions around the knees and hips in 52 patients with OA of the hip and 70 patients with OA of the knee. Various indices of muscle strength were derived from these measurements, applying five alternative approaches. These approaches ranged from a single overall index to a set of 16 separate indices. The internal consistency of these indices was determined (Cronbach's alpha), and it was determined to what extent they could reveal the association between reduced muscle strength on the one hand and pain and disability on the other hand.

RESULTS

Internal consistency was satisfactory for all indices (Cronbach's alpha >0.74). As expected, reduced muscle strength was associated with increased disability, but no clear relationship could be established between muscle weakness and pain. The strength of these associations did not depend on the approach used to derive the indices for muscle strength.

CONCLUSIONS

The indices did not show major differences with regard to internal consistency or the extent to which the association with pain and disability could be revealed. For reasons of parsimony, approaches resulting in few indices appear to be most useful. However, muscle strength was found to be significantly reduced around affected joints, compared with muscle strength around unaffected joints. Therefore, the most suitable approach for reducing muscle strength data into indices is one that results in as few indices as possible, but with separate indices for muscle strength around affected and unaffected joints.

Coping, pain, and disability in osteoarthritis: a longitudinal study

OBJECTIVE

To establish the role of coping styles as prospective determinants of pain and disability in patients with osteoarthritis (OA) of the knee or hip.

METHODS

Data from 71 patients with OA of the hip and 119 patients with OA of the knee were used. Using regression analysis, relationships were established between the use of active and passive coping styles and the level of pain and disability 36 weeks later.

RESULTS

In patients with knee OA, the passive coping style of resting was found to predict a higher level of disability 36 weeks later after controlling for the baseline level of disability. In the same manner in patients with knee OA, the active coping style of transforming pain was found to predict higher levels of pain 36 weeks later. In patients with hip OA, no significant relationship between coping styles and pain and disability was found.

CONCLUSION

The role of resting as a prospective determinant of disability, as reported in patients with other chronic disorders, could also be established for knee OA, but not hip OA. Transforming pain was found to be a risk factor for pain in knee OA.

Responsiveness of observational and self-report methods for assessing disability in mobility in patients with osteoarthritis

OBJECTIVE

To establish the responsiveness of observational and self-report methods for the assessment of disability in mobility in patients with osteoarthritis (OA).

METHODS

Data from 186 patients with hip OA or knee OA were used. Data from 1 observational method and 4 self-report methods for the assessment of disability in mobility were collected at week 0 and again 12 weeks later. Using correlations and factor analysis, the relationships among changes in these 5 methods were established.

RESULTS

Intercorrelations between change scores of the self-report methods ranged from 0.12 to 0.34. Correlations between the observational method and the self-report methods ranged from 0.14 to 0.26. In the factor analysis, both the self-report methods and the observational method loaded on the same factor.

CONCLUSION

In a longitudinal design, no evidence for differential responsiveness of observational and self-report methods was obtained. Because of the advantages of questionnaires (they are easier to use, less time-consuming, and less of a burden to subjects), this implies that the use of self-report methods is to be preferred over observational methods.

Range of joint motion and disability in patients with osteoarthritis of the knee or hip

OBJECTIVE

To establish the relationships between the range of joint motion (ROM) and disability in patients with osteoarthritis (OA) of the knee or hip. Two related issues were addressed: (1) the inter-relationships between ROMs of joint actions, and (2) the relationship between ROM and disability.

METHODS

Data on 198 patients with OA of the knee or hip were used. The ROM was assessed bilaterally for the hip and knee, using a goniometer. Disability was assessed using a self-reporting method (questionnaire) and an observational method. Correlation and factor analysis were used to establish the inter-relationships between the ROMs of joint actions. Correlation and multiple regression analyses were carried out to establish the relationships between ROM and disability.

RESULTS

Close inter-relationships were found between the ROMs of the same joint action of the lateral and contralateral joints; inter-relationships between ROMs of different joint actions were substantially weaker. Low ROMs were associated with high levels of disability, both self-reported and observed. Some 25% of the variation in disability levels could be accounted for by differences in ROM. In both knee and hip OA patients, flexion of the knee and extension and external rotation of the hip were found to be most closely associated with disability.

CONCLUSION

Restricted joint mobility, especially in flexion of the knee and extension and external rotation of the hip, appears to be an important determinant of disability in patients with OA.

Internal consistency and validity of an observational method for assessing disability in mobility in patients with osteoarthritis

OBJECTIVE

To establish the internal consistency and validity of an observational method for assessing disability in mobility in patients with osteoarthritis (OA).

METHODS

Data were obtained from 198 patients with OA of the hip or knee. Results of the observational method were compared with results of self-report methods (questionnaires) on disability in mobility.

RESULTS

Both Cronbach's alpha and Mokken Scale Analysis indicate that the method is internally consistent. Using factor analysis, observed and self-reported disability in mobility were found to be closely associated and could not be differentiated.

CONCLUSIONS

The observational method is internally consistent and indeed measures disability in mobility (high convergent validity), but observations and self-report seem to yield largely equivalent information (low divergent validity). This raises questions regarding the simultaneous use of both observational and self-report methods in the assessment of disability in mobility in OA patients.