10

The shoulder

Introduction

Shoulder pain is the most common musculoskeletal peripheral joint pain and the third most common site of pain reported after cervical and lumbar spine (Chen 2012). In the year 2000 the cost of treating shoulder dysfunction in the United States was estimated at $7 billion (Meislin et al 2005). In the US 200,000 rotator cuff operations are performed annually (Hettrich et al 2014).

Shoulder dysfunction is most commonly found in the elderly, in people with occupations that involve repetitive movements, in sportsmen and women practicing certain sports, such as racquet sports, swimming or sports that involve throwing, and in people with some medical conditions, such as diabetes.

Occupations that have been shown to have a high occurrence of shoulder complaints include manual handlers (Silverstein et al 1998, Roquelaure 2006), dentists (Lalumandier et al 2001, Dajpratham et al 2010, Harutunian et al 2011), people who work at computers (Brandt et al 2004, Bongers et al 2006), and musicians who play instruments with their arm/arms in a raised position (Nyman et al 2007, Leaver et al 2011).

The most regular injury in swimming is to the shoulder (Kluemper et al 2006, Ludewig & Reynolds 2009) with some studies stating that up to 76% of reported injuries in swimmers are shoulder-related (Weldon & Richardson 2001). Other sports include tennis (Pluim et al 2006), baseball (Wyland et al 2012) and, as would be predicted, contact sports such as rugby (Headey et al 2007, Usman et al 2011, Horsley & Herrington 2014) and (American) football (Dick et al 2007). Although volleyball has a lower injury rate than these sports, players also have a high rate of shoulder over-use injuries (Reeser et al 2006).

One common cause of persistent shoulder pain is adhesive capsulitis, more commonly known as frozen shoulder. It can affect 2–5% of the population (Prestgaard 2015), most often individuals of 50–70 years of age. Interestingly, it still has no precise definition (Zuckerman & Rokito 2011). Its etiology can be linked to several conditions such as diabetes mellitus, heart disease and thyroid dysfunction. It can also be linked to prolonged lack of use, stroke and, in rare occurrences, Parkinson’s disease. There is growing evidence that end-range articulation of the shoulder complex can be very effective in treating adhesive capsulitis (Vermeulen et al 2000, Kisner & Colby 2012). Yang et al (2007) also found that end-range articulation of the shoulder was more effective than mid-range articulation of the joint.

Some interesting work by Mintken and colleagues (2010) suggests that treatment to the cervical and thoracic spine can help in the treatment of persistent shoulder pain, although the authors acknowledge that further research is needed. Brantingham et al (2011) found that there is ‘fair evidence’ that manual treatment of the shoulder complex is beneficial, especially when combined with exercise rehabilitation.

Anatomy

The shoulder joint is the most complex biomechanical structure in the human body. It is formed by the union of three bones that connect the superior extremity to the axial skeleton. These are the humerus (upper arm bone), the scapula (shoulder blade) and the clavicle (collarbone), positioned in a special harmony that allows very considerable movement of the shoulder in different stages of motion (Halder et al 2000). Movement of the shoulder joint, which is the most flexible and mobile joint in the body, results from a complex dynamic relationship of bony articulations, tendonous restraints, ligament constraints and dynamic muscle forces (Terry & Chopp 2000).

From the structural point of view, ligaments of the shoulder, including the transverse humeral, coracohumeral and three glenohumeral ligaments, work primarily to maintain the joint’s range of motion, and the concave glenoid fossa of the scapula forms the socket for the joint and permits extensive rotational movement. Overall, the articular capsule arrangement is loose, affording considerable separation between the joint bones, which allows the extensive range of motion (Williams et al 1989).

The shoulder joint’s hyperactive mobility affords the upper extremity a myriad range of motions, including abduction, adduction, internal and external rotation, extension, flexion and up to 180° rotation in three different planes. In addition, the shoulder permits scapular extension, elevation, depression and retraction (Quillen et al 2004).

This extensive range of motion enables the arm of the athlete, for example, to perform a very wide range of sports activities. But the wide range of motion comes at a cost, as it leads the shoulder to an increased risk of injury (Sofu et al 2014), such as torn rotator cuff muscles, frozen shoulder, tendinitis, bursitis, fractures, strains, sprains, dislocations and separations. Furthermore, the shoulder joint lacks strong ligaments; it therefore relies heavily on muscles for stability, with its primary stabilizers including glenohumeral articulation, glenohumeral ligaments, labrum, deltoid muscle and rotator cuff (Bigliani et al 1996).

Two aspects of the range of movement of the shoulder can be measured: movement of the shoulder complex and movement of its individual parts. Table 10.1 shows the range of movement for the shoulder complex and later in the chapter we will look at the individual joints’ range of movement.

Bony anatomy

Humerus

The humerus is the longest bone in the upper limb, running from the shoulder to the elbow. It articulates with the scapula and connects the two lower arm bones: the ulna and the radius. Its upper portion is cylindrical in shape and consists of a rounded head, a constricted neck, proximal humeral shaft and two eminences, the greater and lesser tubercles (also known as tuberosities). The body of the humerus is more prismatic in the lower part. The lower portion includes two processes (capitulum and trochlea), two epicondyles (lateral and medial) and three fossae (coronoid, olecranon and radial) (Ashalatha & Deepa 2012).

The humeral head is inclined to the proximal shaft at an angle between 130° and 150° at the anatomical neck, and the retroversion is between 26° and 31° from the medial and lateral epicondylar plane (Kronberg et al 1990). The greater tubercle has three separate facets, which attach the supraspinatus, infraspinatus and teres minor tendons. The lesser tubercle is the point of insertion of the subscapularis, ending the rotator cuff (Terry & Chopp 2000).

Scapula

The scapula is a large triangular-shaped bone, which is placed on the posterolateral aspect of the thorax, partly covering ribs 2 to 7. It connects the humerus with the clavicle and forms the back of the shoulder girdle. It serves primarily as a site of muscle attachment and provides a stable environment for upper extremity movement. Four muscles of the rotator cuff – the subscapularis, supraspinatus, infraspinatus and teres minor – that act on the shoulder originate from the scapula. These muscles attach to the scapula surface and are accountable for the internal and external rotation of the shoulder joint, along with humeral abduction (Marieb & Hoehn 2007).

Clavicle

The clavicle is a long S-shaped bone that connects the trunk to the shoulder girdle and forms the anterior portion. It is the only bone in the human body that is placed horizontally. The clavicle is subcutaneous in its full extent and has a dual curve along its long axis. It has two articulations: the sternoclavicular joint and the acromioclavicular joint (Ljunggren 1979).

The clavicle serves as a barrier that protects underlying neurovascular structures, a site for the attachments of muscle, a strut between the scapula and the sternum, and a stabilizer of the shoulder complex (Rockwood Jr et al 2009). Furthermore, it helps to prevent the shoulder girdle’s inferior migration via the strong coracoclavicular ligaments (Terry & Chopp 2000).

Joint articulations

Glenohumeral joint

The glenohumeral (GH) joint is the major joint of the shoulder. It is a multi-axial ball-and-socket synovial joint, which is formed between the humeral head and the lateral scapula (the glenoid fossa). The articular surfaces are oval, although reciprocally curved, and are not portions of true spheres. Because the GH has a large humeral head and small glenoid cavity, it enables extensive mobility (Villaseñor-Ovies et al 2012).

The GH is loosely packed, and the surfaces are mismatching and asymmetrical. In any position of the joint, only 25–30% of the humeral head can be in articulation with the glenoid fossa (Bigliani et al 1996). However, in spite of this lack of articulating surface coverage, the normal shoulder specifically restrains the head of the humerus between 1 mm and 2 mm of the glenoid fossa center throughout most of the arc of motion (Terry & Chopp 2000). Full congruence and the close-packed situation are attained when the humerus rotates laterally, and is abducted (Peat 1986). Properties of the articulating surfaces are summarized in Table 10.2.

The GH joint’s static stabilizers include the joint capsule, the labrum glenoidal, the articulating surfaces, the glenohumeral ligaments and the coracohumeral ligament. Although these play an important role in stabilization, the GH joint heavily relies on the rotator cuff muscles for stability (Cooper et al 1992). The range of motion for the GH joint is summarized in Table 10.3.

Acromioclavicular joint

The acromioclavicular (AC) joint is a synovial joint between the lateral end of the clavicle and the medial edge of the acromion. It is covered by a fibrous capsule and is strengthened by the coracoacromial ligaments: the trapezoid and conoid ligaments. The average size of an AC joint in the adult is about 9 mm–19 mm (Terry & Chopp 2000). Static stabilizers of the joint include the ligaments, intra-articular disc and capsule. The AC joint is essentially important for shoulder stability, because it not only helps in transmitting forces between the clavicle and the acromion but also contributes to total arm movement (McCluskey & Todd 1994).

The AC joint also has little motion (see Table 10.4). However, the motion does not occur individually; rather it is coupled with the motion of the sternoclavicular joint, which includes depression, elevation, retraction, protraction and rotation of the clavicle around its axis. Movements of this joint can be notable when the arm is abducted about 90°: about 6° of internal rotation around a vertical axis and about 15° of elevation along the anteroposterior axis (Teece et al 2008). Within the joint is an articular disc which can vary in size among individuals, and can change in size through life. Due to use of the shoulder complex, the AC can become more mobile and the articular space can expand and develop a meniscoid (Cailliet 1991), thus leading to possible entrapment symptoms.

Acromioclavicular joint injuries usually result from an inferiorly directed force to the upper extremity of the shoulder, such as a fall directly on to the shoulder or fall on to an outstretched hand. Common separation injuries characterize degrees of injury level, first to the acromioclavicular joint and then to the coracoclavicular ligaments (Rockwood Jr et al 1991).

The SC joint’s static stabilizers include its joint capsule and supporting ligaments: costoclavicular, interclavicular and (anterior and posterior) sternoclavicular ligaments. However, due to the great incongruence in size between the smaller articular surface of the sternum and the large bulbous end of the clavicle, stability of the joint is mostly attributed to the surrounding ligamentous structures (Terry & Chopp 2000).

The SC joint allows the clavicle to move freely in nearly all planes, enabling elevation, depression, protraction as well as retraction (see Table 10.5). The axis for movements lies close to the clavicular attachment of the costoclavicular ligament (Frankel & Nordin 1980). This freedom of movement provides the shoulder with the ability to thrust forward.

Epidemiology

Shoulder pain

Shoulder pain comprises a diverse range of pathologies. It occurs as a result of problems in various regions of the body, including the GH joint, AC joint, SC joint, rotator cuff, neck and other soft tissues surrounding the shoulder. Risk factors include higher body mass index (BMI), decreased flexibility, imbalances in the rotator cuff muscle, disproportions in scapular stabilizing muscles, duration of injury, old age, use of a manual wheelchair and poor seated posture (Dyson-Hudson & Kirshblum 2003).

Shoulder pain affects about one-quarter of the population in the UK, based on risk factors and age. Murphy and Carr (2010) stated that every year in the UK about 1% of adults of 45 years or older suffer a new episode of shoulder pain. The authors estimated that the prevalence might be between 4% and 26%. Van der Windt et al (1995) state that for every 1000 patients seen in primary care, 15 are there for shoulder pain. But Chakravarty and Webley (1993) discovered in their research that only 47% of elderly patients who had shoulder pain reported their symptoms to their GP.

Ongoing pain in the shoulder can be the result of several conditions, including adhesive capsulitis, tendonitis, bursitis, and degenerative conditions such as osteoarthritis. Rotator cuff syndromes, adhesive capsulitis and osteoarthritis of the glenohumeral joint are often the cause of chronic shoulder pain representing 10%, 6%, and 2–5%, of all shoulder complaints respectively (Meislin et al 2005).

Shoulder injuries

Shoulder injury is the third most common musculoskeletal issue seen in general practice, and it is a potential source of disability and morbidity in the overall population (Chen 2012). Linsell et al (2006) suggested that the yearly prevalence and incidence of patients consulting for a shoulder problem in UK was 2.36% and 1.47% respectively. Risk factors include participation in athletic events, young or old age, and male gender. The reappearance of shoulder injury is also a major problem. A study to evaluate the recurrence of shoulder instability reported that, after a standard non-operative treatment, about 87% of young patients presented recurring injuries during a 5-year follow-up (Robinson et al 2006).

Common shoulder injuries are summarized in Table 10.6.

Shoulder examination

Medical history

During a shoulder joint examination, taking a detailed medical history of the patient is as essential as the physical examination itself. The healthcare provider should assess whether the injury or underlying condition hampers regular physical activities, sports and hobbies. The patient should be asked about pain, stiffness, instability, catching, locking, swelling or any other issues related to the shoulder. In most cases, the narrative provided by the patient will give information critical to narrowing the differential diagnosis and facilitate the shoulder examination.

Red flags

The clinician should make an immediate note of any signs of red flag conditions (see Table 10.7).

Physical examination

Physical examinations of shoulder problems should be done in a systematic manner. Burbank et al (2008) suggest that the preferred approach to a complete physical examination should include inspection, palpation, range of motion and strength tests, and special tests. The examination should also include the neck and the elbow, so that the practitioners can dismiss the chance of a shoulder pain arising from a pathological condition in any of these parts.

Palpation

When examining the shoulder, several important bony and soft-tissue structures need to be palpated to identify areas of pathology. Palpation should comprise examination of the AC and SC joints, the anterior GH joint, the cervical spine, the clavicle, the subacromial bursae, the coracoid process and the scapula. In addition, the practitioner should palpate both shoulders, since some structures, such as biceps tendon, can cause a painful sensation, even in a healthy shoulder (Woodward & Best 2000).

Range of motion

Movement of the shoulder should be evaluated in internal and external rotation, abduction and flexion. Both active and passive movements should be assessed; however, these ranges of motion should be examined separately. Active range of motion tests the power of different muscles, so start with that first. Assess the unaffected side first to determine the patient’s normal range. If the patient has a limitation in active movements, assess the passive range of motion. Passive movements test joint function and associated periarticular joint tissues (Buchanan et al 1997).

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