Background/Purpose: Pain catastrophizing and widespread pain (WP) —constructs reflecting cognitive processes during the pain experience—predict disability, pain chronicity/severity, and lower quality of life in a range of conditions. Gaps remain in our understanding of the extent to which each is a stable (trait) or dynamic (state) variable. We assess a) the stability of pain catastrophizing and WP from before to after TKR and b) whether changes in these measures could be explained by changes in pain.

Methods: We used data from a prospective study of TKR recipients ages 40+. Questionnaires included a body pain diagram to assess WP, the Pain Catastrophizing Scale (PCS; 0-52, 52=worst), and WOMAC Pain (0-100, 100=worst). To calculate WP score, we summed the number of body regions, excluding the index knee, in which a subject attested to pain in the past week (maximum=7).

We divided subjects into 3 WP groups (0 vs. 1-2 vs. ≥3 pain regions) and into low and high PCS groups (≤16 vs. >16) at baseline and 12 months post-TKR. We assessed changes in group membership from baseline to 12 months. To assess whether changes in PCS and WP were associated with knee pain relief, we created 4 groups by amount of WOMAC pain improvement: <10, 10-29, 30-49, ³50. Changes in PCS score and WP were compared across these groups using ANOVA.

Results: 176 subjects completed the scales at baseline and 12 months; 64% were female, mean age was 66, and baseline median WOMAC pain was 40.

The number of subjects in the high PCS score group diminished from 45 (26%) pre- to 23 (13%) post-TKR. Mean PCS score diminished from 11 (SD: 10) to 6 (SD: 8). The number of subjects in each WP group was similar pre- and 12 months post-TKR. However, 73 subjects (41%) changed group and were similarly likely to worsen (55%) and to improve (45%). As Figure 1 depicts, most changes in PCS group were in the direction of improvement while, for WP group, similar proportions worsened and improved.

Improvements in PCS score were associated with WOMAC pain reductions. The group with most pain relief (≥50 points) had a greater mean improvement in PCS score (11 (SD:12)) than the group with least pain relief (4 (SD: 12)) (p = 0.02). We did not find a statistically significant association between change in WP and change in WOMAC.

Conclusion: 71% of those with baseline high PCS improved sufficiently to join the low PCS group after TKR. PCS score improvements were associated with pain relief, suggesting that the present measure of catastrophizing reflects state-like aspects that diminish along with pain. In contrast, WP scores were as likely to increase as to decrease after TKR, regardless of knee pain relief. The findings urge caution in interpreting PCS and WP as trait measures in MSK pain research.

Figure 1. Percent of subjects changing PCS or WP group membership from baseline to 12 months