Pain, sensitization and physical performances in patients with chronic painful knee osteoarthritis or chronic pain following total knee arthroplasty: An explorative study

Subgrouping of facilitatory or inhibitory conditioned pain modulation responses in patients with chronic knee pain. Explorative analysis from a multicentre trial

BACKGROUND

Facilitatory and inhibitory conditioned pain modulation (CPM) responses are observed in healthy volunteers and chronic pain patients, but the clinical implications for phenotyping are unknown. This study aimed to subgroup and compare chronic knee pain patients according to their CPM responses.

METHODS

This explorative, cross-sectional study included 127 patients with chronic knee pain (osteoarthritis or following total knee arthroplasty). Individual CPM responses were categorized as facilitatory (test stimuli pain intensity increased when conditioning stimuli were applied), as inhibitory (test stimuli pain intensity decreased) or as no change (defined as less than 5.3% change in pain intensity). Outcomes were clinical pain intensities, temporal summation, widespread pain, self-reported physical function, PainDETECT questionnaire and Pain Quality Assessment Scale. Data were analysed as comparisons between the inhibitory and the facilitatory groups and using multivariate linear regression models.

RESULTS

Fifty-four patients had facilitatory CPM responses, 49 had inhibitory CPM responses, and 24 showed no change in CPM response. A between-group difference was observed for self-reported physical function, with the facilitatory CPM group reporting better function (54.4 vs. 46.0, p = 0.028) and the facilitatory CPM group reported more deep pain sensations (3.2 vs. 2.0, p = 0.021). The remaining outcomes showed no between-group differences. Higher clinical pain intensity and facilitated temporal summation were associated in the facilitated CPM group but not in the inhibitory CPM group.

CONCLUSION

These explorative findings indicated that quantitative clinical and experimental differences exist between facilitatory or inhibitory CPM responses in a chronic knee pain patient population. Differences in patients' CPM responses should be further investigated to unravel possible clinical importance.

SIGNIFICANCE

Our findings confirm that conditioned pain modulation consist of inhibitory and facilitatory responders among a patient population with chronic knee pain. This explorative study indicates that patients with either facilitatory or inhibitory conditioned pain modulation could exhibit differences in pain outcomes. Subgrouping of chronic pain patients depending on individual conditioned pain modulation responses could be considered in phenotyping patients prior to inclusion in clinical trials or used for personalizing the management regime.

Associations between pain sensitization and measures of physical function in people with hand osteoarthritis: Results from the Nor-Hand study

OBJECTIVE

To examine whether pain sensitization is associated with hand and lower extremity function in people with hand osteoarthritis (OA) in the Nor-Hand study.

DESIGN

Pain sensitization was assessed by pressure pain thresholds (PPTs) and temporal summation (TS). Hand function was assessed by Australian/Canadian Osteoarthritis Hand Index (AUSCAN) (range: 0-36), grip strength and Moberg pick-up test, and lower extremity function was assessed by Western Ontario and McMaster Universities Osteoarthritis Index (range: 0-68), 30-s chair stand test, and 40-m walk test. We examined whether sex-standardized PPT and TS values were cross-sectionally associated with measures of physical function using linear regression analyses. Beta coefficients were presented per sex-specific standard deviation of PPT and TS. The mediating effect of pain was examined by causal-inference based mediation analysis.

RESULTS

In 206 participants, higher PPTs at/near the hand, indicative of less peripheral and/or central pain sensitization, were associated with greater grip strength and better self-reported hand function (beta for PPT at finger joint on AUSCAN function: -1.41, 95% CI -2.40, -0.42). Higher PPTs at/near the hand, near the knee and at trapezius were associated with lower extremity function, although not statistically significant for all outcomes. Self-reported pain severity mediated the effect of PPT on self-reported function. TS was not associated with hand or lower extremity function.

CONCLUSION

Peripheral sensitization, and possibly central sensitization, was associated with impaired function. Effects of PPTs on self-reported function were mediated by self-reported pain, whereas there might be a direct effect of sensitization or effects through other mediators on performance-based function.

Many Patients With Persistent Pain 1 Year After TKA Report Improvement by 5 to 7 Years: A Mixed-methods Study

BACKGROUND

Approximately 20% of patients report pain 12 months after TKA. No studies have investigated patients' experiences of living with persistent postsurgical pain 5 to 7 years after TKA by combining a qualitative and quantitative methodology.

QUESTION/PURPOSE

In a mixed-methods study, we explored patients' experiences of living with persistent pain up to 7 years after primary TKA. We asked: In a subgroup analysis of patients who reported persistent pain 1 year after TKA surgery, how do patients live with persistent pain at the 5- to 7-year postoperative timepoint?

METHODS

This follow-up study was part of a longitudinal study of pain, symptoms, and health-related quality of life in patients who underwent TKA for osteoarthritis. The present study targeted a subgroup of patients (22% [45 of 202]) identified in the longitudinal study who reported no improvement in pain interference with walking at 12 months after surgery. Inclusion criteria were: all 31 patients in this subgroup who attended their 5-year follow-up at the hospital and lived within a 2-hour drive from the hospital. Eight patients declined or were unable to participate due to illness or death. Hence, the final sample consisted of 23 patients (13 women and 10 men). The participants' mean age at surgery was 66 ± 10 years. There were no differences in sociodemographic baseline data between the 23 included and the 22 excluded participants. A mixed-methods approach was employed, in which the quantitative data were followed up and investigated with qualitative interviews. Instruments used were the Brief Pain Inventory preoperatively, 12 months, and 5 years after surgery, as well as a semistructured interview guide. The individual interviews were conducted at one timepoint 5 to 7 years postsurgery to capture how pain was experienced at that timepoint. The interviews were audiorecorded, transcribed, and analyzed using qualitative content analysis. Meaning units were identified, condensed, and sorted into subthemes that were interpreted and abstracted into themes, guided by the research question. With a small sample, the quantitative analysis focused on descriptive statistics and nonparametric statistics when comparing demographics of included and nonincluded patients. In addition, two multivariate mixed models for repeated measures were employed to estimate within-patient and between-patient variations as well as to assess the effect of time on the pain outcomes.

RESULTS

Pain with walking decreased from 12 months to 5 years postoperatively (estimated mean score 7 versus 4, difference of means -3 [95% CI -5 to -2]; p < 0.001). Pain with daily activity decreased from 12 months to 5 years postoperatively (estimated mean score 6 versus 3, difference of means -3 [95% CI -4 to -1]; p < 0.001). Pain intensity (average pain) decreased from 12 months to 5 years postoperatively (estimated mean score 5 versus 4, difference of means -1 [95% CI -3 to 0]; p = 0.03). The results are presented as point estimates rounded up to whole numbers. The qualitative data analysis yielded three themes: persistent limitations after TKA, regained wellness over time, and complexity in physical challenges. Intermittent pain with certain movements resulted in limitations with some activities in everyday life and seemed to persist beyond 5 years. Multiple painful body sites and presence of comorbidities seemed to interfere with regained wellness over time.

CONCLUSION

In this subgroup of patients experiencing postsurgical persistent pain 12 months after primary TKA, persistent postsurgical pain still limited certain activities for the participants, although pain seemed to be less influential in their everyday lives after 5 years to 7 years. Clinicians may use these findings to inform and guide patients with delayed improvements in pain into more realistic expectations for recovery, rehabilitation, and strategies for coping with pain and impaired function. However, it is imperative to rule out other reasons for pain in patients reporting pain 12 months and longer after surgery and to be attentive of possible changes in pain over time.

LEVEL OF EVIDENCE

Level III, therapeutic study.