Conditioned Pain Modulation Is Not Impaired in Individuals with Frozen Shoulder: A Case-Control Study.

Marta Aguilar-Rodríguez,Mercè Balasch I Bernat,Mira Meeus,Lirios Dueñas,Filip Struyf,Enrique Lluch

doi:10.3390/ijerph182312330

Abstract

Frozen shoulder (FS) is a poorly understood condition resulting in substantial shoulder pain and mobility deficits. The mechanisms behind FS are not yet fully understood, but, similar to other persistent pain states, central pain mechanisms may contribute to ongoing symptoms in this population. The objective of this research was to investigate conditioned pain modulation (CPM) in people with FS compared with pain-free individuals. A total of 64 individuals with FS and 64 healthy volunteers participated in this cross-sectional study. CPM was assessed by using the pressure pain threshold (PPT) and an occlusion cuff (tourniquet test) as the test and conditioning stimulus, respectively. The absolute and percentage of change in PPT (CPM effect) as well as pain profiles (pro-nociceptive vs. anti-nociceptive) of individuals with FS and healthy controls were calculated. No significant differences in the absolute change in the PPT or CPM effect were found in people with FS compared to pain-free controls. Moreover, no between-group differences in the percentage of subjects with pro-nociceptive and anti-nociceptive pain profiles were observed. These results suggest that endogenous pain inhibition is normally functioning in people with FS. Altered central pain-processing mechanisms may thus not be a characteristic of this population.

Highlights

Frozen shoulder (FS), known as adhesive capsulitis, is one of the most common yet challenging conditions for clinicians and physiotherapists
This study investigated the efficiency of inhibitory endogenous pain mechanisms in subjects with FS by using the conditioned pain modulation (CPM) paradigm
The results showed that subjects with FS do not present altered CPM efficacy compared to healthy controls, as no significant differences in the absolute change or the CPM effect were found

Summary

Introduction

Frozen shoulder (FS), known as adhesive capsulitis, is one of the most common yet challenging conditions for clinicians and physiotherapists. It is a poorly understood condition resulting in substantial shoulder pain and mobility deficits. FS has been widely studied, its epidemiology, etiology, diagnosis, and assessment are still poorly understood [4,5]. The pathophysiology of FS is characterized by an immune and inflammatory response and subsequent fibrosis of the anterior joint capsule and related structures (e.g., rotator cuff interval) [6,7]. The local inflammatory genesis of FS has been widely demonstrated both in animal [8] and human studies [9].

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