Topographical pressure pain sensitivity maps of the shoulder region in individuals with subacromial pain syndrome

Highlights

• The topographical map proposed revealed an excellent intra-rater reliability.

• There is no alteration in mechanical sensitivity in individuals with SAPS.

• The shoulder area showed a heterogeneous distribution in mechanical sensitivity.

• Women exhibited higher mechanical sensitivity compared to men.

• Results would not support the presence of central sensitization in SAPS.

Abstract

Background

Topographical pain maps (TPM) are useful tools to assess deep tissue sensitivity in musculoskeletal pain conditions. There is evidence suggesting bilateral sensitivity in subacromial pain syndrome (SAPS), although it is not widely accepted. No previous study has investigated TPM of the shoulder in SAPS.

Objective

To investigate whether differences for TPM of the shoulder are evident among patients with unilateral SAPS and controls.

Methods

Pressure pain thresholds (PPTs) were assessed 3 times at each point and there was a 20 s rest period between each one. The TPM were calculated using 29 pre-determined points on both shoulders in all groups by inverse distance weighted interpolation of PPT data. Multivariate Analysis of Covariance was applied to detect differences in PPTs between groups, sides, points (gender as covariate).

Results

The results revealed significant differences between points and genders (both, P < 0.001), but not between groups (P = 0.243) and sides (P = 0.812). Heterogeneous distribution of mechanical pain sensitivity was found in both groups as the PPTs were lower on the root spine of the scapula and the posterior border of the acromion (points 5–8, P < 0.05), glenohumeral joint (points 17–20, P < 0.01) and the anterior deltoid muscle (points 21–25, P < 0.001) compared to the average of the other sites on the shoulder. Women exhibited bilateral lower PPTs in all points than men in both groups (all, P < 0.01).

Conclusions

This study revealed no differences for mechanical pain sensitivity in patients with SAPS experiencing lower levels of pain compared with matched controls, but showed heterogeneous distribution of PPTs in the shoulder.

Introduction

Upper extremity musculoskeletal disorders are usually associated with high social and financial costs showing a prevalence of 36.8% of all the cases in the general population (Huissted et al., 2008). Shoulder pain is one of the most common complaints, comprising 16% of all musculoskeletal symptoms (Urwin et al., 1998, Pope et al., 2001), and subacromial pain syndrome (SAPS) is the most frequent condition for shoulder pain (Lewis, 2011, Tekavec et al., 2012). The etiology of SAPS is not yet understood, but there is evidence showing inflammation and degeneration of the bursa and rotator cuff tendons on the sub-acromial space (Lewis, 2011, Diercks et al., 2014). Furthermore, alterations in kinematics (Ludewig and Cook, 2000, Timmons et al., 2012), muscle activity/performance (Camargo et al., 2008, Phadke et al., 2009) and the presence of active trigger points (TrPs) (Hidalgo-Lozano et al., 2010, Alburquerque-Sendín et al., 2013) have also been reported.

Several studies have demonstrated the impact of shoulder pain on upper extremity function and health-related quality of life (Camargo et al., 2007, Camargo et al., 2009). There is evidence suggesting the presence of unilateral regional shoulder mechanical hyperalgesia in these patients (Alburquerque-Sendín et al., 2013), whereas multiregional and bilateral shoulder pain hyperalgesia has been also documented (Hidalgo-Lozano et al., 2010, Paul et al., 2012). Both peripheral (Alburquerque-Sendín et al., 2013) and central (Hidalgo-Lozano et al., 2010, Paul et al., 2012) sensitization mechanisms are suggested in playing a role in SAPS.

Peripheral sensitization is mainly caused by endogenous substances related to trauma and inflammation processes that may elicit primary hyperalgesia over the injured area (Curatolo et al., 2006). Central sensitization refers to persistent changes in the central nervous system following prolonged peripheral nociception (Arendt-Nielsen and Graven-Nielsen, 2008). Both peripheral (Alburquerque-Sendín et al., 2013) and central (Hidalgo-Lozano et al., 2010, Paul et al., 2012, Sanchis et al., 2015) sensitizations have already been identified in individuals with SAPS. It is suggested that both mechanisms can contribute to the development and maintenance of chronic pain (Graven-Nielsen and Arendt-Nielsen, 2010).

A number of studies have proposed the utility of topographical pain sensitivity maps as an exploratory method allowing spatial assessment of sensitization mechanisms in several chronic pain disorders, e.g., lateral epicondylalgia (Ruiz_Ruiz et al., 2011), carpal tunnel syndrome (Fernández-de-las-Peñas et al., 2010b), headaches (Fernández-de-las-Peñas et al., 2008, Cuadrado et al., 2010), migraine (Fernández-de-las-Peñas et al., 2009, Fernández-de-las-Peñas et al., 2010a), shoulder pain (Ge et al., 2008) or work-related musculoskeletal disorders (Binderup et al., 2011). These studies revealed that mechanical sensitivity depicted by assessing pressure pain thresholds (PPTs) is not uniformly distributed around the same muscle (Fernández-de-las-Peñas et al., 2008, Ge et al., 2008) or around an anatomical area, e.g., the elbow (Ruiz_Ruiz et al., 2011), the hand (Fernández-de-las-Peñas et al., 2010b) or the head (Cuadrado et al., 2010). Furthermore, increased mechanical sensitivity can also occur on the non-affected side as a sign of central sensitization (Ge et al., 2008). Although bilateral hyperalgesia has already been identified in unilateral shoulder pain (Hidalgo-Lozano et al., 2010, Paul et al., 2012, Coronado et al., 2014; Sanchis et al., 2015), results are still conflicting which increases the interest of research in this area.

To the best of the authors' knowledge, no previous study has used topographical pain maps to investigate mechanical sensitivity around the shoulder girdle in individuals with SAPS. Therefore, the aim of the current study was to investigate whether differences for topographical pain sensitivity maps of the shoulder area are evident between patients with unilateral SAPS and healthy people. We hypothesized the presence of heterogeneous topographical pressure pain sensitivity maps of the shoulder area and the presence of regional shoulder pain hyperalgesia in subjects with SAPS compared with controls highlighting different levels of mechanical sensitivity on the shoulder in this patient population.