Discordance between radiographic findings, pain, and superficial temperature in knee osteoarthritis

Introduction
Knee pain is an imprecise marker of radiographic evidence of osteoarthritis (OA). These patients are more likely to develop central sensitisation to pain, a risk factor for chronic pain.

Objectives
The aim of this study was to examine the associations among radiographic evidence of OA, self-reported pain, pressure pain thresholds (PPT), and superficial knee temperature in indivi­duals with knee OA.

Material and methods
This cross-sectional study enrolled 25 patients with knee OA with clinic and radiographic diagnosis of bilateral OA (Kellgren-Lawrence grading scale 1–4 in X-ray images), but symptoms of pain and discomfort in only one of the knees, with pain perception in the symptomatic knee equal to or above 4 in a visual analogue scale. Volunteers underwent an evaluation including demographic data, superficial knee temperature (infrared thermography, mean superficial temperature of the region of the knee) and PPT (digital algometry at longus adductor, vastus lateralis, vastus medialis and tibialis anterior muscles, patellar tendon, and centre of the patella).

Results
Comparisons between symptomatic and asymptomatic knees revealed no differences regarding Kellgren-Lawrence classification, knee superficial temperature, or PPT. Significant weak and moderate associations were found between radiographic classification of OA and PPT of both knees in almost all sites evaluated. Nonetheless, superficial temperature of the knee was not associated with PPT or Kellgren-Lawrence grading scale.

Conclusions
Patients with bilateral knee OA presented no differences in symptomatic and asymptomatic knees regarding radiographic evidence, knee temperature, and PPT, indicating that central sensitisation may be present in them. Radiographic classification of OA was significantly associated with PPT in both knees.