How well do observed functional limitations explain the variance in Roland Morris scores in patients with chronic non-specific low back pain undergoing physiotherapy?

Self-rated activity limitations in patients with non-specific chronic low back pain (cLBP) do not correlate well with performance in traditional tests of impairment (e.g. back strength, ROM, etc.). Tests using more "functional activities" have therefore been recommended as alternative "objective" outcome measures. We examined the relationship between a battery of such tests and self-reported activity limitations, before and in response to physiotherapy, and the influence of psychological factors on the relationship.

37 patients with cLBP took part (45 ± 12 years; 23 female, 14 male); 32 completed 9 weeks' physiotherapy. Before and after therapy, the patients completed the Roland Morris (RM) disability questionnaire and questionnaires to assess fear avoidance beliefs, catastrophising and psychological disturbance. They also performed eight simple functional tests (stair climb, prolonged flexion, stand to floor, lift test, sock test, roll-up test, pick-up test, fingertip-to-floor test).

Baseline RM scores were significantly (p < 0.05) correlated with all but one of the functional test scores (ranging from r = -0.34 (half-flexion) to 0.56 (pick-up test), and with a functional test index score for all tests together (r = 0.60, p < 0.0001). The correlation between the change-scores (after treatment) for RM and for the functional test index was 0.55 (p = 0.001). Psychological factors explained 7-23 % variance in RM scores (baseline, post-therapy, and change scores), beyond that which was explained by the functional tests. Effect sizes for patients with a self-rated "good global outcome" were 1.23 for RM and 0.75 for the functional test index; for those with a "poor outcome", they were -0.08 and 0.23, respectively.

Moderately high correlations (for both absolute and change scores) were observed between the subjective and observed measures of activity limitation. This indicates that to some extent they are assessing the same underlying construct, but it also suggests that each is delivering a certain amount of unique information. Psychological factors explained some of the discrepancy between the two types of measure. Both were responsive to therapy, and their change scores reflected well the patients' global outcome ratings. The two methods of assessing activity limitations should serve to complement one another in the assessment of treatment outcome.