In patients with knee osteoarthritis (OA), high pain levels and low pressure pain thresholds at baseline predicted worse pain outcomes after total knee replacement (TKR) surgery, but did not predict outcomes after nonsurgical interventions, according to a study published in the European Journal of Pain.
Researchers analyzed 12-month follow-up results from 2 randomized clinical trials (Clincaltrials.gov identifiers: NCT01410409 and NCT01535001). They used patients’ self-reports as a measure of absolute pain intensity, along with pressure pain thresholds as a measure of pain sensitization, to determine potential predictors of therapeutic outcome after TKR and nonsurgical intervention, associations between pain intensity and pressure pain thresholds, and any sex distinctions.
The first randomized clinical trial examined TKR with nonsurgical care vs nonsurgical care alone, whereas the second trial examined nonsurgical care alone vs usual care (2 informational leaflets). Each trial enrolled 100 participants, who were randomly assigned evenly between treatment groups. Pain intensity, pressure pain thresholds, and painful site counts were evaluated at baseline and at 12 months.
Pain improved across all study groups, with lower sensitization among all patients. Patients from both cohorts reporting the lowest pressure pain thresholds and highest pain levels at the start of the studies experienced the greatest relative improvements in intensity and sensitization over the course of 12 months. However, these individuals also experienced the greatest absolute intensities and sensitizations after 12 months.
The TKR group in the first trial demonstrated the largest improvements in absolute pain, and low initial pressure pain thresholds predicted high pain intensity after surgery. Compared with participants who underwent nonsurgical treatment, participants who received TKRs reported significantly fewer painful sites at 12 months (P =.017). The nonsurgical group in the second trial saw greater improvements in pain compared with those in the usual care group, but low pressure pain thresholds did not accurately predict treatment outcomes.
Participants with the highest pain and lowest pressure pain thresholds at baseline still retained the lowest pressure pain thresholds at 12 months. This was true for participants in both studies, for the affected side (P <.001) as well as the contralateral side (P <.001). Women exhibited considerably lower pressure pain thresholds at baseline (mean difference, 368 to 393 KPa) and at 12 months (mean difference, 332 to 371 KPa; P <001).
Study limitations included the potential for improvement in the nonsurgical paradigms; uncertainty regarding the ability to generalize findings to all patients with knee OA; the use of only pressure pain thresholds for sensory testing, as opposed to additional modalities; and static pressure pain threshold measurements that only assess 1 specific local site.
This secondary analysis indicated that TKR with nonsurgical follow-up is the most efficient therapy for those with painful knee OA, followed by nonsurgical treatment alone, in terms of improvements in pain intensity, sensitization, and site counts.
The trials were partially funded by grants from the Danish Rheumatism Association, the Health Science Foundation of North Denmark Region, Obel Family Foundation, Foot Science International, Spar Nord Foundation, the Bevica Foundation, the Association of Danish Physiotherapists Research Fund, Medical Specialist Heinrich Kopps Grant, and the Danish Medical Association Research Fund.
Arendt-Nielsen L, Simonsen O, Laursen MB, et al. Pain and sensitization after total knee replacement or nonsurgical treatment in patients with knee osteoarthritis: Identifying potential predictors of outcome at 12 months [published online February 15, 2018]. Eur J Pain. doi:10.1002/ejp.1193