Original article
The influence of a depressed scapular alignment on upper limb neural tissue mechanosensitivity and local pressure pain sensitivity

https://doi.org/10.1016/j.msksp.2017.03.001Get rights and content

Highlights

  • A depressed scapular position is associated with lower PPT over cervical sites.

  • A depressed scapular position is associated with greater upper limb neural tissue mechanosensitivity.

  • The findings help to appreciate the potential development of neck-arm pain due to an abnormal scapular position.

Abstract

Background

A depressed scapular alignment could lead to prolonged and repetitive stress or compression of the brachial plexus, resulting in sensitization of neural tissue. However, no study has investigated the influence of alignment of the scapulae on sensitization of upper limb neural tissue in otherwise asymptomatic people. In this case-control study, we investigate the influence of a depressed scapular alignment on mechanosensitivity of the upper limb peripheral nervous system as well as pressure pain thresholds (PPT).

Methods

Asymptomatic individuals with neutral vertical scapular alignment (n = 25) or depressed scapular alignment (n = 25) participated. We measured the upper limb neurodynamic test (ULNT1), including assessment of symptom response and elbow range of motion (ROM), and PPT measured over upper limb peripheral nerve trunks, the upper trapezius muscle and overlying cervical zygapophyseal joints.

Results

Subjects with a depressed scapular reported significantly greater pain intensity (t = 5.7, p < 0.0001) and reduced elbow extension ROM (t = −2.7, p < 0.01) during the ULNT1 compared to those with a normal scapular orientation. Regardless of the location tested, the group presenting with a depressed scapular had significantly lower PPT compared to those with a normal scapular orientation (PPT averaged across all sites: normal orientation: 3.3 ± 0.6 kg/cm2, depressed scapular: 2.1 ± 0.5 kg/cm2, p < 0.00001).

Conclusions

Despite being asymptomatic, people with a depressed scapular have greater neck and upper limb neural tissue mechanosensitivity when compared to people with a normal scapular orientation. This study offers insight into the potential development of neck-arm pain due to a depressed scapular position.

Introduction

Evidence has revealed an association between an aberrant scapular position and/or scapular motion (i.e. scapular dyskinesis) and the presence of neck pain, as recently reviewed by Cools et al. (2014). In particular, studies have identified similar alterations in scapular orientation and motion in patients with mechanical neck pain, which are seen in people with painful shoulder disorders (Falla et al., 2004, Helgadottir et al., 2010, Helgadottir et al., 2011a, Helgadottir et al., 2011b, Wegner et al., 2010, Zakharova-Luneva et al., 2012). Aberrant scapular posture and/or motion may contribute to painful neck disorders by adversely affecting mechanical stress on pain sensitive cervical structures (Behrsin and Maguire, 1986, Van Dillen et al., 2007). For instance, depression of the scapula is known to increase the strain forces throughout the brachial plexus (Byl et al., 2002, Kleinrensink et al., 1995, Kleinrensink et al., 2000) and compress the thoracic outlet structures between the clavicle and the first rib (Al-Shekhlee and Katirji, 2003, Watson et al., 2009). Indeed, studies have demonstrated that restoration of normal scapular kinematics can induce positive effects on the cervical spine, including increased range of motion (ROM) and reduced pain (Andrade et al., 2008, Azevedo et al., 2008, Ha et al., 2011, Van Dillen et al., 2007).

People with neck pain frequently report symptoms with functional use of their upper limb and upper limb activities can be an aggravating factor (McLean et al., 2011, Osborn and Jull, 2013). This may particularly be the case when a person presents with heightened nerve mechanosensitivity where upper limb movements may aggravate sensitized neural tissue. Neck pain associated with neural tissue mechanosensitivity is commonly labeled non-specific neck-arm pain (Dilley et al., 2005, Greening and Lynn, 1998), in the absence of neurological deficits. Clinically, it is characterized by pain in response to mechanical stimuli such as limb movements that cause nerve elongation, and by local tenderness on nerve trunk palpation (Tampin et al., 2012a). Although scientific interest in the identification and management of patients with neck-arm pain symptoms has increased (Moloney et al., 2013, Schmid et al., 2013, Tampin et al., 2012a, Tampin et al., 2012b, Tampin et al., 2013), little is known about the specific consequences of altered scapular orientation on arm pain symptoms. A depressed scapular alignment has been related to the presence of neck and arm pain (Sahrmann, 2011, Swift and Nichols, 1984), altered cervical proprioception (Ha et al., 2011), limited cervical ROM (e.g. cervical rotation) (Ha et al., 2011, Van Dillen et al., 2007) and decreased pressure pain threshold (PPT) over the upper trapezius muscle (Azevedo et al., 2008, Lee et al., 2015). Moreover, passive elevation of the scapula, either manually (Ha et al., 2011, Van Dillen et al., 2007) or using a taping technique (Lee and Yoo, 2012), reversed these limitations in pain and function. Theoretically, a depressed scapula may place prolonged and repetitive stress and/or compression on the brachial plexus, leading to sensitized neural tissue which may trigger the development of neck-arm pain symptoms (Sahrmann, 2011, Watson et al., 2009, Watson et al., 2010). Sensitization of neural tissue is commonly assessed with neurodynamic testing and the evaluation of PPTs over upper limb peripheral nerve trunks. However, no study has investigated whether a depressed scapular alignment is associated with sensitization of upper limb neural tissue in otherwise asymptomatic people.

This study addresses this topic by investigating the influence of a depressed scapular alignment on mechanosensitivity of the upper limb peripheral nervous system in asymptomatic people. In addition, the effect of a depressed scapular alignment on PPT was evaluated at sites over the upper trapezius, cervical spine (i.e. zygapophyseal joints) and neural tissue. It was hypothesized that people with a depressed scapula would be more sensitized to upper limb neurodynamic testing and would display lower PPT over nerve, muscle and joints indicative of higher pain sensitivity. This study stands to shed light on the potential development of neck-arm pain due to an altered scapular position.

Section snippets

Participants

College age students with neutral vertical scapular alignment (n = 25) or depressed scapular alignment (n = 25) volunteered to participate in this case-control study. Recruitment of potential volunteers was conducted at the University through poster advertisement. Volunteers who met the inclusion criteria were then evaluated as they reached the laboratory.

Subjects with a depressed scapular alignment were included if they reported no history of orthopedic or neurological conditions in the

Results

Table 1 presents the baseline characteristics of the participants. No differences were observed for age, gender, weight or body mass index. The mean age of all subjects was 19.4 ± 2.8 years, mean weight 58.8 ± 8.9 Kg, and mean height 168.6 ± 7.3 cm.

Overall, the group of subjects with a depressed scapula reported significantly greater pain intensity (t = 5.7, p < 0.0001) and reduced elbow extension range of motion (t = −2.7, p < 0.01) during the ULNT1 compared to those with a normal scapular

Discussion

This is the first study which has evaluated the influence of a depressed scapular alignment on upper limb neural tissue mechanosensitivity in a healthy population. As hypothesized, subjects with a depressed scapula displayed significantly greater upper limb neural tissue mechanosensitivity than those with a normal scapular orientation, as reflected by greater pain intensity and reduced elbow extension ROM during the ULNT1 and lower PPT measured at the median, radial and ulnar nerve trunks. In

Conclusions

Our results show that healthy young subjects with a depressed scapular position had significantly lower PPT over the cervical zygapophyseal joints and upper trapezius and greater upper limb neural tissue mechanosensitivity when compared to subjects with normal scapular position. These observations offer some insight into the potential development of neck-arm pain due to a depressed scapular alignment.

Funding

We affirm that we have no financial affiliation (including research funding) or involvement with any commercial organization that has a direct financial interest in any matter included in this manuscript.

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