**1. Introduction**

The term impingement of the shoulder refers to a chronic and painful dysfunction of the shoulder causing pain at the elevation and internal rotation of the humerus. The prevalence of shoulder impingement syndrome (SIS) differs between age cohorts and was reported to range from 4.7–46.7% in terms of 1-year prevalence [1]. Similarly, McBeth [2] estimated that 20–33% of the general population were likely to report shoulder pain. Moreover,

**Citation:** Vogel, M.; Binneböse, M.; Wallis, H.; Lohmann, C.H.; Junne, F.; Berth, A.; Riediger, C. The Unhappy Shoulder: A Conceptual Review of the Psychosomatics of Shoulder Pain. *J. Clin. Med.* **2022**, *11*, 5490. https:// doi.org/10.3390/jcm11185490

Academic Editors: Markus W. Hollmann, Casandra I. Montoro Aguilar and Carmen María Galvez Sánchez

Received: 10 June 2022 Accepted: 14 September 2022 Published: 19 September 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

shoulder pain is among the leading causes of disability, and the third ranking condition of chronic pain. SIS is multifactorial and associated with a variety of disorders, e.g., diabetes, arterial hypertension, and thyroid disorders, as well as adiposity. In the general population, lesions of the rotator cuff (85%) and/or impingement syndromes [3] represent the most frequent causes of shoulder pain. SIS is a chronic, regional pain syndrome and based on the mechanical irritation of subacromial structures. The corresponding pain manifests mostly at the abduction of the limb from 70◦–120◦ (i.e., the so-called "painful arc", and clinical hallmark), at working overhead, and when lying on the affected side of the body [3]. The theory of impingement posits that mechanical conflicts between different structures of the joint would lead to shoulder pain, the second to third ranking musculoskeletal disorder [4]. Mostly, its symptomatic course develops in the fifth decade and the age peak lies between 40 and 60 years. Dependent on the precipitating factors, impingement syndromes are classified as primarily extrinsic, secondarily extrinsic, intrinsic, and inner impingement [5]. Glenohumeral osteoarthritis (secondarily extrinsic) and rotator cuff tear (intrinsic) are two common causes of shoulder pain, and the manifestation in the shoulder is the third ranking of osteoarthritis [6]. Regarding the subacromial impingement, ref. [7] a contact between the rotator cuff and the acromion causes damage to the rotator cuff, which may in turn confine the subacromial space. As a result, the mobility of the joint is compromised, even to the extent of total immobility as possibly suffered from in frozen shoulder. The structures mainly involved in the respective mechanical irritation are the supraspinatus tendon and the bursa subacromialis, causing irritation of the acromion and the coracoacromial ligamentum. Besides immobilization, conservative treatment is based on pain-relieving medication, physical therapy, as well as steroid injections. Even under such conservative therapeutic regimes, an operation (e.g., acromioplasty) takes place in 30% of the cases due to the lack of pain relief. Unfortunately, however, the operation does not always successfully [8] establish the desired relief of pain, either.

A similar paradox is known with respect to arthroplasty, especially of the knee, where 25% of patients tend to be unsatisfied with the results of the operation [9]. Among the explanations for this are the associations between osteoarthritis and psychopathology, esp. negative affect [10], personality [11], and trauma [12]. Besides negative affect, the psychologic suffering associated with chronic pain involves specific fears such as catastrophizing, which contribute to central sensitization and hyperalgesia, as well as to allodynia by means of heightened awareness directed to the sensation of pain. Negative affect is an umbrella term for anxiety and depression, and neuroticism reflects the tendency to experience aversive emotional states, especially negative affect [13]. Differently phrased, neuroticism resembles emotional lability and, thus, a source of complication when coping with illness. In addition, neuroticism generates unstable mood thus causing emotional lability, which is often expressed as a depressed or anxious mood, including worries about health-related issues. Negative affect is linked to chronic pain, e.g., of the knee [12], the back [14], and the shoulder [15]. Moreover, negative affect predicts worse outcomes and less satisfaction with therapies for chronic pain, such as arthroplasty [10], and is possibly a predisposition for posttraumatic stress disorder (PTSD), a connection described in the frame of the diathesis–stress model of PTSD [16], which may be of relevance for invasive therapies performed in people with posttraumatic symptoms. Negative affect was shown to rise in those with postoperative pain after total knee arthroplasty (TKA) and is deemed capable of inducing specific (i.e., pain-related) fears [12,17]. Moreover, as far as TKA is concerned, dissociative symptoms may qualify as negative affect in that they are possibly capable of inducing pain catastrophizing, thus ultimately increasing the perception of pain [12]. Dissociation is understood as posttraumatic symptomatology, and several dissociative symptoms [18] are required for the diagnosis of PTSD (i.e., amnesia, hypermnesia, derealization). Interestingly, with respect to chronic pain, PTSD itself conveys a heightened risk [19], possibly based on the activation of a clinical psychopathologic cascade initiated by negative affect and dissociation. Negative affect and neuroticism are also associated with a variety of physical illnesses, e.g., osteoarthritis [20], hypertension, and diabetes [21]. In addition to its associations with those disorders, negative affect may be a function of the right hemisphere [22]. Considering the lateralized manner in which peripheral pain is inherently organized, those anatomic underpinnings of peripheral pain possibly influence its associations with psychopathology.

A growing body of literature suggests psychosomatic and psychic comorbidity to modulate the subjective experience of shoulder pain, as well. Against this background, psychosomatic comorbidity complicates the adaptation to shoulder disorders, calling for complex and integrated approaches to their treatment. The present review gives an integrative overview of the respective findings that are suggestive of a link between the algofunction (i.e., the combined status regarding pain and function of the shoulder) related to frozen shoulder and psychiatric or psychosomatic syndromes, as well as the potential role of shoulder surgery as a crystallization point for posttraumatic psychopathology. Moreover, we strive to strengthen the hypothesis of the lateralization of psychosomatic correlates of pain.
