INTRODUCTION

During the routine assessment and treatment of ‘neck pain’ the physician treating spinal disorders will be presented with extrinsic pathology that generates pain in similar patterns to that of cervical spine disorders. Therefore, the history, physical examination, and diagnostic work-up should all point to the same etiologic agent of the patient’s chief complaint. As clinicians, our best treatment rationale is based upon an accurate diagnosis. The more understanding that other factors may contribute to, or cause pain about the cervical region, the better it should be for patient care.

Spinal pain itself is complex in nature. To add another dimension to the diagnostic dilemma, the shoulder itself is among the most complex of all the body’s joints (Fig. 49.1). The shoulder is composed of four joints: the glenohumeral (GH), the acromioclavicular (AC), the sternoclavicular (SC), and the scapulothoracic (ST). It entails anywhere from 22 to 26 individual muscles and/or muscle slips, which are utilized for a combination of stability, power, and control of elevation and rotation. The shoulder is unique in that it is highly mobile, with an estimated 16 to 17 thousand positions in which the upper extremity may be placed, while necessarily exhibiting a concurrent lack of bony stability. The arm can move through approximately 180 degrees in elevation, 150 degrees of internal and external rotation, and flexion and extension or anterior and posterior rotation in the horizontal plane of approximately 170 degrees.¹ The very interaction of the musculature both as agonist and antagonist must be coordinated for even the simplest motions in order for there to be an effective movement. An understanding of the anatomy and biomechanics of the shoulder is essential for clinicians who treat spinal disorders, as well as for other orthopedic practitioners.

Fig. 49.1 (A and B) The shoulder is composed of four joints: the glenohumeral (GH), the acromioclavicular (AC), the sternoclavicular (SC), and the scapulothoracic (ST).

ANATOMY

The shoulder joint is unique, as multiplanar mobility of the joint is dominant over static stability. This generous amount of mobility can lead to a multitude of intrinsic ailments about the shoulder and, in fact, a majority of shoulder problems stem from this relative lack of bony stability. All of the 26 or so muscles about the shoulder play a role in ensuring appropriate motion of the joint complex but, as a nonweight-bearing joint, there is tolerance of some loss of individual muscle and/or tendon function that still allows for adequate usage in activities of daily life.

Glenohumeral joint

The glenohumeral joint is what the layman and many in the healthcare field think of as the ‘shoulder joint.’ Although this joint is considered a ball (humerus) and socket (glenoid) joint, the socket covers only one-quarter of the humeral head.^3–5 This ratio was initially calculated by the following simple formula, known as the glenohumeral index:

Maximum diameter of the glenoid:maximum diameter of humeral head

Saha recalculated the ratio to 0.6 in the transverse plane and 0.75 in the sagittal plane.⁶ Maki and Gruen further refined the ratio to 0.58 and 0.86 in a presentation to the Orthopedic Research Council in 1976.

Three different types of glenohumeral articulations have been identified, and in each case the humeral head is classified as being smaller, equal to, or larger than the radius of curvature of the glenoid.^6,7 This difference is believed to impact a variety of shoulder instability patterns. A smaller glenoid surface diameter is necessarily a smaller effective contact surface for the humeral head and is thus a more unstable configuration.^6,8,9 In the coronal plane, the articular surface of the glenoid comprises an arc of approximately 75 degrees, whereas the articular surface of the humeral head is roughly 120 degrees, or one-third of a sphere.

The glenoid labrum increases coverage about the humeral head by nearly 100%, and doubles the depth.¹⁰ The glenoid labrum is composed of dense fibrous connective tissue, and serves not only to increase the surface area and depth of the glenoid, but also to increase the structure’s load-bearing ability.¹¹ The labrum is a structure which appears to be fibrocartilagenous in structure when examined superiorly but, as one approaches the inferior surface, is almost capsular in appearance. There are wide variations in labral anatomy among individuals, and there is no correlation between labral depth and glenoid size. Two aspects of labral anatomy that are fairly consistent are that the most stable, largest portion is the anterior and inferior area, and that the labrum itself acts to physically double the depth of the socket for the humeral head.

The glenohumeral joint allows for three distinctly different types of motion: spinning, sliding, and rolling. Spinning is when the contact point on the glenoid remains the same, but the contact point of the humeral head is changing. Sliding occurs when the contact point on the glenoid is changing, but that of the humerus remains the same. This generally occurs in unstable joints, and in extremes of motion in normal joints. The third type of motion, rolling, is when the contact points on both the glenoid and humeral head change.¹²

Anatomically, the proximal humerus is separated into four parts: the articular surface, the greater tuberosity, the lesser tuberosity, and the diaphyseal shaft. In relation to the shaft, there is a 45-degree medial angulation to the humeral head, and a 30-degree retroversion relative to the transcondylar axis of the distal humerus. The intertubercular groove lies between the greater and lesser tuberosities, and it is here that the tendon of the long head of the biceps lays.¹³ This tendon is held in place not only by the coracohumeral ligament, but also by the transverse humeral ligament. During shoulder abduction, the humeral head slides on this tendon. If the biceps tendon should rupture, anterior translation of the humeral head is subsequently increased.¹⁴

Utilizing an elegant approach, Johnson noted in 1937 that in order for the upper limb to maximally elevate, the humerus must externally rotate.¹⁵ Initially, research pointed to a physical obstruction caused by the coracoacromial arch to the greater tuberosity of the humeral head. By 1976, it was realized that this movement provides for loosening of the inferior ligaments of the glenohumeral joint while simultaneously allowing for optimal articulation with the glenoid.¹⁶ Thus, full arm elevation combined with external rotation is a position of greater stability than full elevation alone. This is due to a combination of relative laxity and stability of the three glenohumeral ligaments, intrinsic muscular forces, and negative intracapsular pressure.¹⁷

The ligamentous restraints of the glenohumeral joint are the inferior glenohumeral ligament (IGHL), the middle glenohumeral ligament (MGHL), and the superior glenohumeral ligament (SGHL) (Fig. 49.2). These glenohumeral ligaments, which insert onto the glenoid labrum and humeral neck, have often been described as ‘capsular thickenings.’¹⁵ This ‘capsular-ligamentous’ complex is the major static stabilizer of the shoulder, and although all of the ligaments are necessary for proper function, the IGHL is the most essential component of this complex. Studies have shown that the shoulder joint capsule possesses greater elasticity and twice the strength of that of similar structures within the elbow.¹⁹ The superior, middle, and inferior glenohumeral ligaments are considered the anterior glenohumeral ligaments.

Fig. 49.2 The ligamentous restraints of the glenohumeral joint are the inferior glenohumeral ligament (IGHL), the middle glenohumeral ligament (MGHL), and the superior glenohumeral ligament (SGHL).

The coracohumeral ligament, which runs laterally from the coracoid process to insert upon the superior–anterior aspect of the humeral head, is the most consistent of the ligaments of the shoulder capsule.²⁰ In addition to providing an anterior stabilizing force to the biceps tendon, it also renders stability to the shoulder, particularly when the arm is in the dependent position.²¹

The superior glenohumeral ligament lies beneath the coracohumeral ligament, and has been found to contribute little to the stability of the glenohumeral joint. It also is a relatively constant structure, and arises from the tubercle of the glenoid, inserting upon the lesser tuberosity of the proximal humerus. The long head of the biceps tendon originates posteriorly to the SGHL. In concert with the superior tilt of the glenoid, the SGHL provides passive resistance to inferior subluxation and dislocation of the humerus.²²

The middle glenohumeral ligament exists underneath the subscapularis muscle, and its presence is the most variable of the glenohumeral ligaments.²⁰ Its origin is at the supraglenoid tubercle at the superior glenoid and anterior superior labrum, and inserts with the subscapularis muscle at the lesser tuberosity of the humerus. This ligament provides the majority of resistance to anterior humeral head displacement.^20,23 It may measure up to 2 cm wide, and as much as 4 mm in thickness.²⁴

The thickest of the glenohumeral ligaments is the inferior glenohumeral, which originates from most of the anterior glenoid labrum, and inserts on the inferior margin of the humeral head articular surface. The IGHL is the main static stabilizer in the abducted arm, and it reinforces the inferior capsule.^25,26

A fundamental knowledge of the anatomy of the IGHL is instrumental in understanding the pathophysiology behind recurrent anterior humeral dislocation. When the humeral head dislocates in an anterior direction, the associated detached bone–labral complex essentially renders the IGHL an incompetent structure. The IGHL is composed of an anterior and posterior band with an axillary pouch in between.²⁷ The anterior band serves as the major stabilizer of the glenohumeral joint when the arm is in abduction and external rotation.²⁵ In this position, the anterior band appears to fan out, while the posterior band becomes cordlike. With the arm in internal rotation, the anterior band becomes cordlike, while the posterior band spreads into a fan shape to support the joint.

BIOMECHANICS

The relative motion between the scapulothoracic articulation and the glenohumeral joint during shoulder abduction is termed the scapulothoracic rhythm.^17,29–31 Over the entire arc of abduction, the glenohumeral joint moves more than the scapulothoracic joint; however, this difference is large at the beginning of abduction, and minimal at the end range of motion. Glenohumeral motion is much greater than scapulothoracic motion for the first 30 degrees of abduction; this ratio has been reported as ranging from 4:1 to 7:1.^16,32 Over the subsequent 30–180 degrees of shoulder abduction there is less asymmetry between glenohumeral motion and scapulothoracic motion, and the ratio is then closer to 5:4.

The arc of full arm elevation involves anterior rotation of the scapula by about 6 degrees, with subsequent posterior rotation of the scapula on the order of 16 degrees until the arm is at its final resting position. That is, 10 degrees posterior to it’s starting position.³³ In addition to these movements, there is also a simultaneous forward tilt of the scapula by 20 degrees.^10,34

Passive stability about the shoulder girdle is afforded by a united structure consisting of the joint articulation itself, the capsuloligamentous restraints, glenoid labrum, and resting muscle tension, as well as negative intra-articular pressure within the shoulder joint.

The articulation of the humeral head with the glenoid portion of the scapula was found by Saha⁶ to be posteriorly oriented by an average of 7 degrees in relation to the body of the scapula. This apparently minor retroversion is thought to be an important element of the static restraint system. It has been clinically correlated that those individuals with less retroversion have a greater tendency towards recurrent anterior dislocation at the glenohumeral joint. While there is agreement that there is a wide array of the amount of retroversion within individuals, there is still no consensus with regards to the clinical relevance, or in research with regards to these variations and their part in instability of the joint.

Within the glenohumeral joint there is a small but measurable amount of negative pressure, on the order of −4 mmHg. This also is thought to be a small but important contributor to static stability of the joint. It is believed that any compromise of the capsule or even some fraying of the undersurface of the supraspinatus may result in the loss of this stabilizer. While this work has relied on cadaver examination, it is still not known the extent of loss that may occur in living tissue, as the entire human body is believed to be under negative pressure.

Resting muscle tension appears to account for much of the stability about the shoulder girdle. The base of the shoulder girdle is the scapula, and three groups of muscles concordantly maintain its stability: the posterior, intrinsic, and extrinsic groups.³⁵ The scapulohumeral stabilizers comprise the posterior group of muscles, consisting of the trapezius, levator scapulae, rhomboids, and serratus muscles. This group helps to provide a stable base of rotation for glenohumeral motion, and maintains the glenoid in a position of maximal congruency with the humeral head, thus maintaining the proper length–tension relationship of the glenohumeral musculature.^36,37 The intrinsic groups of muscles are the glenohumeral stabilizers and include the rotator cuff musculature: the supraspinatus, infraspinatus, teres minor, and subscapularis. Dynamic stability about the shoulder is dependent upon muscular forces generated by these muscles and those surrounding the scapulothoracic joint.³⁸ The deltoid is the primary muscle of the extrinsic group, with biceps and triceps being secondary extrinsic muscles. These muscles comprise the primary positioners of the humerus and forearm.³⁸

Pink and Perry have made an excellent point to acknowledge that while these restraints are static in nature, they are also plastic. They have the ability to deform by stretching from different sources, whether intrinsic or extrinsic. Once deformation has occurred there may be further clinical sequelae that need to be addressed.

Inman and associates first described the concept of a ‘force couple’ in 1944.¹³ They described the dynamics of multiple forces passing across and through the shoulder during active motion to allow for any desired arm position. For example, their theory noted that if the deltoid were to pull the humerus superiorly, then the subscapularis, infraspinatus, and teres minor would act as a single functional unit to counteract any shearing forces that the deltoid placed upon the glenohumeral joint. This would then allow the humeral head to maintain itself in a congruent alignment to the glenoid by simultaneously depressing the humeral head and allowing the head to rotate about the glenoid.

In addition to causing direct joint compression, the rotator cuff musculature provides dynamic stability in another manner. It allows finely tuned asymmetric contractions to maintain the humeral head in the glenoid during active motions that may otherwise cause subluxation or shoulder instability.

STRENGTH

Up to 26 muscles have been described as encompassing the shoulder girdle. However, as the cross-sectional area, overall length, and bony attachment sights of each muscle vary, strength about the shoulder is not symmetrical. Rather, there are contrasting relative strength differences dependent upon the particular plane of motion within which movement takes place. These relative strengths in descending order are as follows: adduction, extension, flexion, abduction, internal rotation, and external rotation.

The maximal force a muscle can produce is proportional to the number and size of muscle fibers it contains. This is indirectly measured by the muscle’s cross-sectional mass. Lever length, or muscle–joint orientation, is composed of both the actual length of the muscle as well as how distant its attachment sites are from the joint proper. This determinant is variable, as it is dependent on joint position. The greater the perpendicular distance between a muscle’s line of pull and the fulcrum of motion, the more effective is the muscle’s force. This is related to Inman’s ‘force-couple’ concept previously discussed.

Muscle activity level as measured by electromyogram (EMG) is a concept related to muscle endurance. This is usually expressed as a percentage of maximum muscle test (MMT) by generally accepted muscle strength testing positions. Some authors prefer to use the terms percentage of maximum muscle activity (MMA), or percentage of maximal voluntary contraction (MVC), also determined by manual strength testing. In general, when a muscle is firing at less than an MMT (MMA or MVC) of 25–40% it can be used for an extended period of time without fatiguing. Conversely, when a muscle is utilized at an MMT of greater than 50% it will fatigue relatively quickly.

For discussion, we can think in terms of a general arrangement of the shoulder musculature. Muscles that link the axial skeleton to the scapula, such as the rhomboids major and minor, levator scapulae, serratus anterior, and trapezius, are muscles which act as stabilizers, of the shoulder. The muscles that serve to link the axial skeleton to the humerus, namely the pectoralis major and latissimus dorsi, yield power to the extremity in internal rotation, adduction, and extension. The four muscles of the rotator cuff along with the teres major and deltoid, control elevation and rotation, as well as serve to link the scapula with the humerus. The muscles that provide the power of elevation, the upper pectorals and middle trapezius, link the scapula and clavicle to the humerus.

To effectively elevate the upper extremity, four muscles need to act in a coordinated fashion. The deltoid and supraspinatus muscles act to elevate the humerus while the trapezius and serratus anterior muscles act to stabilize the scapula. If there is a deficiency of any two of these muscles, functional elevation of the upper extremity becomes impossible.

Precise control of shoulder motion is allowed by the muscle action as described by Inman’s concept of the ‘force-couple.’ This coupling of forces about a joint is based on the theory that with greater generation of compressive force there tends to be less shear and, therefore, less nonrotational motion about a joint. It is easier to understand if we think of those forces directed toward the center of the joint as compression forces, and those that run parallel to the joint surface as shear forces. At the glenohumeral joint, maximum shear forces are generated when the extremity is held at 60 degrees of abduction, and maximum compression forces are with the extremity at 90 degrees of abduction. Pure compression allows the joint to support approximately 10 times the weight of the arm, or approximately the weight of the entire body. Thus, the primary role of the rotator cuff is to minimize glenohumeral shearing force, as rotational control is secondary.

NERVE SUPPLY

Innervation of the shoulder complex (Fig. 49.3) is mainly via the C5 through C7 nerve roots, via the brachial plexus. Because of its proximity to many bony structures, the great mobility about the shoulder and neck, and superficial location, the brachial plexus is particularly susceptible to traumatic injury.³⁹ The branches that come off of the lateral cord of the brachial plexus, the lateral pectoral nerve and musculocutaneous nerve, are those that are most essential to shoulder function. The musculocutaneous nerve passes through the coracobrachialis muscle, several centimeters below its insertion when leaving the axilla.⁴⁰

Fig. 49.3 Innervation of the shoulder complex is mainly via the C5 through C7 nerve roots, via the brachial plexus.

The upper and lower subscapular nerves are also important branches off the posterior cord of the brachial plexus with regards to innervation of the subscapularis muscle. Also from the posterior cord arises the thoracodorsal nerve (also known as the middle subscapular nerve), which supplies the latissimus dorsi, and travels along the lateral border of the scapula.⁴⁰

The axillary nerve, after obtaining its contributions from the C5 and C6 nerve roots, travels along the inferior portion of the subscapularis muscle, and is a large terminal branch of the posterior cord of the brachial plexus. It winds around the surgical neck of the humerus to supply the teres minor and deltoid muscles, and terminates as the upper lateral brachial cutaneous nerve and supplies skin sensation over the inferior half of the deltoid and adjacent areas of the arm.³⁸ This intimate association with the humeral neck places the axillary nerve in a potentially compromising position, as it is susceptible to injury from trauma to the area or from surgical procedures about the shoulder.⁴¹

The long thoracic nerve is made up of contributions from the ventral branches of the C5, C6, and C7 nerve roots. It then travels along the medial wall of the axilla and supplies the serratus anterior.

The suprascapular nerve, after receiving its innervation from the C5 and C6 nerve roots from the upper trunk of the brachial plexus, travels along the superior border of the scapula in the suprascapular notch, eventually supplying the supraspinatus and infraspinatus muscles. The transverse scapular ligament is a potential entrapment site and may compress the suprascapular nerve as it crosses through the scapular notch.⁴⁰

The innervation of the glenohumeral joint is mainly from the axillary nerve, suprascapular nerve, and the lateral pectoral nerves.⁴²

VASCULAR SUPPLY

The arterial supply of the entire upper limb comes from the subclavian artery, which becomes the axillary artery after crossing the first rib, and continues into the arm as the brachial artery (Fig. 49.4).⁴³ The axillary artery extends between the first rib and the lower border of the teres major muscle, and gives off branches to the thoracic wall and its covering muscles, as well as to the shoulder and upper part of the arm. There are six named branches off of the axillary artery.⁴³

Fig. 49.4 The arterial supply of the entire upper limb comes from the subclavian artery, which becomes the axillary artery after crossing the first rib, and continues into the arm as the brachial artery.

Venous drainage is mainly by the axillary vein, which is joined by the cephalic vein, lying between the deltoid and pectoralis major muscles, and two brachial veins. The upper end of the cephalic vein is the only superficial vessel of any size in the shoulder region.⁴³

Many anatomic variations may be found at the cervicothoracic junction, some which can compress neurovascular structures to generate a variety of thoracic outlet syndromes (TOSs).³⁹ There are three distinctly different pathophysiologic types of thoracic outlet syndrome.⁴⁴ The most common type of TOS may also be referred to as costoclavicular syndrome, and presents without neurologic or vascular anomalies, but with symptoms of pain and/or paresthesias in the arms. The symptomatology is felt to be a direct result of brachial plexus compression between the clavicle and a normal first rib.³⁹ A second type of TOS is neurologic TOS, in which weakness and sensory deficits stem from stretch and/or compression of the lower trunk of the brachial plexus. Some anatomic variations that may be responsible for the neurologic TOS are an accessory cervical rib with or without an associated fibrous band, an enlarged cervical transverse process, an abnormal first rib, hypertrophy of the anterior scalene muscle (termed scalenus anticus syndrome), and hyperabduction syndrome.⁴ The third type of TOS is vascular, and consists of narrowing of the subclavian artery as it angles over the first rib in patients with a well-developed cervical rib. In this case there are often signs of vascular compromise such as intermittent blanching of the fingers or entire hand, and rarely, frank ischemia, and gangrene. Neurologic symptoms should be absent in this purely vascular type of TOS.³⁹

Rarely, Doppler ultrasound and duplex scanning can indicate that subclavian artery compression by the scalene muscles is the etiology of early fatigue, arm heaviness, and hand coldness in the upper extremity of well-conditioned athletes.^45,46 When the shoulder is positioned in abduction and external rotation, these findings can be elicited in many asymptomatic individuals, as well as overhead athletes; therefore, this test is not considered specific. This is the basis behind ‘Adson’s maneuver,’ in which the examiner externally rotates and extends the patient’s test arm while palpating the radial pulse. The patient then extends and rotates the neck towards the test arm and takes a deep breath. Absence or diminishing radial pulse is felt to indicate vascular TOS caused by compression of the subclavian artery by the scalene muscles. As mentioned above, this test is non-specific and is thought to have a greater than 50% incidence of false positivity.^47–49

Occasionally, symptoms may result from a subclavian artery aneurysm with thrombosis. In this case, embolization to the hand with severe ischemia may result.⁴⁶ Compression of the axillary, posterior humeral circumflex, suprascapular, or subscapular arteries may all result in similar, localized symptoms.⁴⁶

ASSESSMENT

As difficult as it is to master the biomechanics of the shoulder, to perform and understand the findings of the examination may be only slightly easier. Even some of the most accomplished leaders in the field have confided that, at times, they still have diagnostic difficulty based upon history and physical examination of the shoulder alone. The physical complexity of the joints under what can be a vast soft tissue covering, coupled with the wide ranges of motion that may be achieved, make both the sensitivity and specificity of any single examination finding somewhat questionable. Even with a relatively lengthy examination, many of the previously accepted assumptions have come under more scrutiny. The improvement in diagnostic imaging as used as an adjuvant for shoulder maladies, along with the ability of enhanced surgical techniques, have led many authors and clinicians to question previously accepted standards.

The assessment should include an adequate history to evaluate for an underlying etiologic agent such as trauma, repetitive motion, metabolic illness, rheumatoid history (familial and personal), nicotine or other pharmaceuticals, change in or additions to a workout regimen, overall intensity of shoulder usage, and older versus younger populations. In athletes, sports-specific questions such as sport, position, training techniques, dominant versus nondominant side, and expectations of future usage are all pertinent areas to query.

A detailed history of the pain complaint should also be elicited including: relative intensity, positional differences (including the effect of direct weight bearing), radiation, aggravating and alleviating factors, associated symptoms, and of course, the location of the pain. Not all patients have the ability to see a physician in a timely fashion, so the presentation may be either acute or chronic. In the senior author’s practice he has noted that the more acute the process, the more closely the above descriptors correlate with the origin of the pain.

With acute injuries, pain is usually associated with a decrement in range of motion. In addition, to avoid pain, the patient will position the affected arm in a dependent posture at the side. Motion of the glenohumeral joint can be affected within a few days or less and, especially in the older population, a secondary adhesive capsulitis may develop relatively easily.

Some patients may present with a visible or palpable deformity or, more rarely, localized edema or an effusion may be present. These are typically the residua from a traumatic event such as a fall or other direct trauma. The correlation of history and physical findings in this instance is typically quite high. Treatment rationale can therefore follow established protocols with expected success rates dependent upon extent of injury, provider skill, medication delivery, other underlying medical processes, and patient commitment.

It is the patient that presents with a chronic history of shoulder pain of more than a few months that typically represents the greater diagnostic challenge. As the pain persists, other areas in continuity with or near the shoulder may become symptomatic areas. Chronic shoulder symptoms may include pain, instability, stiffness, weakness, a sense of ‘catching,’ crepitus, deformity, paresthesias or dysethesias, or any combination of the above. This multitude of symptoms may or may not be reported in combination with neck, elbow, or arm pain, which may confuse the diagnosis, as the work-up is no longer as simple as that of the acutely involved patient.

The classic teaching of mid-deltoid pain for conditions such as inflammation or tears of the rotator cuff, degenerative arthritis, calcific tendinitis, labral tearing, avascular necrosis of the humeral head, localized bursitis, or adhesive capsulitis usually allows for a direct approach to treatment. Making the correct diagnosis becomes more challenging, however, when the pain is either within this region or described beyond the local area without the above ‘classic’ findings on examination, plain radiographs, or magnetic resonance imaging (MRI) scans.

Several authors have reported an approximately 5% incidence of pain referable to the cervical spine in patients presenting with shoulder pain.^50–54 Slipman et al. reported of a case of extrinsically induced pain that included symptoms that all pointed to an intrinsic cause of pain. Despite diagnostic work-up for both shoulder and cervical spine etiologies, all signs pointed to an intrinsic pathology, but arthroscopic findings were minimal and postoperatively there was no change in symptoms. Repeat diagnostic studies of the cervical spine were performed and there was no change from the initial findings. A diagnostic selective nerve root block was then performed, providing complete relief of pain and immediate return of full range of motion.⁵⁵ This case helps to illustrate that even though the entire work-up may point toward one etiology, when evaluating nonacute presentations of pain, perseverance may be needed to correctly diagnose and adequately treat the condition, and a referal for ‘chronic pain management’ may be premature.

In those patients with chronic shoulder symptoms, the history may be less helpful for several reasons. The duration of symptoms may lead to some forgetfulness on the part of the patient, blurring memory of some of the initial symptoms and treatment as well as other associated medical maladies at the onset. As noted above, loss of range of motion of the shoulder girdle, primarily at the glenohumeral joint, typically happens since the arm tends to be held in a pain-free, dependent position, mainly at one’s side. This lack of glenohumeral mobility demands an alteration of the basic biomechanics of the shoulder. The patient will have to substitute another aspect of the shoulder complex to allow overhead or other reaching motions. Typically, a greater contribution from the scapulothoracic joint is needed to achieve the elevation required to perform even simple activities of daily living.⁵⁶

This alteration in the pattern of movement of the shoulder will therefore require an increase in contribution from the joints adjacent to the shoulder girdle proper. Whether there is a substitution pattern of the adjacent musculature, or if greater motion of the elbow is required to place the upper limb in a desired position, an increase in stress to these regions will lead to associated symptoms such as an epicondylitis of the elbow as the problem progresses.

Most of us were taught that pain radiating to or from the paracervical region or below the elbow is not consistent with primary shoulder pathology. While this is typical in acute conditions, the senior author has not found this to be true after just a few months, if symptoms are left untreated. In his practice, many patients with ongoing symptoms of at least a few months report both upper limb paresthesias, primarily in an ulnar nerve distribution, as well as radiating pain either across the scapula or about the upper trapezius to the paraspinal musculature. Some patients report concomitant headaches with, more rarely, photophobia.

The history is taken in the same way, with attention to onset, and previous treatments and studies, with a particular interest with regards to changes in the pattern or severity of the pain. We are always interested in not only which particular treatments have been rendered, but also how well they seem to have worked. In particular, we find it necessary to ask where about the shoulder an injection may have been given and not simply if one has been performed. Was the injection to the subacromial space, acromioclavicular joint, or to the glenohumeral joint? The patient may have undergone a trigger point injection or an injection to the long head of the biceps sheath. Dependent upon the previous injection site, one might consider another injection. This would depend upon further physical examination findings in combination with recent radiological tests.

Abnormalities seen on radiographic evaluation, as well as bone or soft tissue masses found clinically, need to be evaluated in a methodical and well-organized fashion.⁵⁷ Both benign and malignant tumors may be found in and about the shoulder complex. The goals in treatment of malignant tumors are, in order of priority, preservation of life, limb, and function.⁵⁷ Benign tumors found about the shoulder include osteoid osteoma, osteoblastoma, osteochondroma, enchondroma, giant cell tumors, chondroblastoma, eosinophilic granuloma, and synovial osteochondromatosis⁵⁷. Malignant tumors include osteosarcoma, chondrosarcoma, Ewing’s sarcoma, and myeloma.⁵⁷ In addition to malignant and benign tumors, there may also be various tumor-like conditions associated with the shoulder, such as aneurysmal bone cyst, simple bone cyst, fibrous dysplasia, and Paget’s disease of the bone.⁵⁷

We always ask not just if physical therapy has been advised or how long they may have been in therapy but what precisely was the composition of that therapy. We find it helpful to go over all of the therapeutic exercises since, even in the most restricted cases, the ability to place the arm in a multitude of positions can lead to enhanced pain. This pain most often appears to be caused by repeated tensile forces about the long head of the biceps tendon. This tendon can act to function as a humeral head depressor, creating increased anterior shoulder pain with motion. Typically, we prefer to protect the anterior structures of the shoulder by only stretching those of the posterior cuff and capsule. Resistive exercises are performed in planes that also are protective of these anterior structures, principally by limiting the ranges of motion of the involved limb. All motions should be pain-free during the workout and none need to be performed with the involved hand above shoulder height in a non-thrower. Typically, a simple program consisting of just four to six exercises is initiated with progression determined by amount of pain, overall range of motion, strength, and patient requirements.

The assessment itself then turns to the physical examination. While no human is perfectly symmetrical, we do look for side-to-side differences in muscle mass, height and angulation of the shoulder, and motion of the scapula and arm during both passive and active range of motion. Watching the scapula itself is a superb way to evaluate for subtle pathologic findings. We observe not only the rotation of the scapula (rhythm) but its positional changes on the torso, such as how much it may move laterally, and its stability upon the torso.⁵⁸ Glenohumeral impingement testing as well as compression testing of the acromioclavicular joint is performed. Manual muscle testing of all shoulder related and upper extremity musculature is performed bilaterally as well. Resistive testing to enhance subtle scapular instability may also be performed. Assessment of distal pulses, sensation, muscle stretch reflexes, and distal extremity muscle bulk is performed. Palpation of not only the bony prominences but also of the bicipital groove, posterior cuff structures, trapezius, latissimus dorsi, and parascapular muscles is also performed to assess for tender spots or myofascial trigger points to conclude the initial examination. Assessment for other etiologies may need to be performed either at the end of the shoulder evaluation or on an ensuing visit to ascertain for extrinsic causes of pain including spinal, peripheral nerve, or vascular etiologies.

Many times, radiating pain that has a dysesthetic quality emanates from a non-neurogenic cause. When assessing the scapula, weakness of the supporting musculature will allow the scapula to wing away from the thoracic cage, thus creating scapular instability. The rhomboids, upper trapezius, any of the four rotator cuff muscles, or paraspinal muscles may have been weakened from the initial injury. As noted earlier, when a muscle is chronically firing at 40% or more of MMT, fatigue will become a factor. Myofascial trigger points have been described in the literature since the mid-1800s.⁵⁹ Trigger points presumably appear in these fatigued muscles and on cursory look may mimic either cervical or thoracic radicular symptoms. These symptoms may include, but are not limited to, paracervical radiating pain, radiating pain through the scapular body, and radiating pain about the thorax either anteriorly or posteriorly. As described by Simmons et al., both observation and hands-on experience are needed to help delineate these etiologies.⁶⁰ Symptoms may be exacerbated by manual muscle testing as well. Observation of the scapula during resistive testing such as infraspinatus strength testing or a wall push-up may help in making the diagnosis.

Observing both active and passive range of motion of the shoulder contributes to the determination of intrinsic or extrinsic etiologies as well. Patients may be able to have near-symmetrical active range of motion by utilizing muscular substitution patterns. However, they are rarely able to reproduce such a full range when the arm is passively moved as the scapula is stabilized. Most patients do have either a decrement in abduction–internal rotation or abduction–external rotation and many may have positive impingement signs. It is rare that extrinsic causes of pain would yield any significant difference in side-to-side comparison.

Motor strength testing of the shoulder girdle and rotator cuff is very useful in the overall examination of the shoulder, but not in differentiating the etiology of symptoms. Typically, intrinsic shoulder pathology will lead to weakness in one or more of the muscles of the cuff, such as the supraspinatus or infraspinatus. When the parascapular musculature is weakened, there may be good to excellent strength within the rotator cuff itself, but there may be early fatigue or enhancement of scapular instability during resistive maneuvers. Direct palpation may yield areas over the rhomboids consistent with myofascial trigger points as well. In cases of chronic cervical spine disease, especially at the C5 and C6 levels, a similar result may be noted due to the effects of neurogenic damage affecting the shoulder girdle musculature, with resultant weakness.

Evaluation of muscle stretch reflexes may help indicate a neurogenic cause of pain. However, while a Tinel’s sign may reveal irritation of a peripheral nerve, it has not helped in our practice in the differential diagnosis of shoulder pathology. As noted earlier, a more extensive neurovascular examination may be warranted if the initial examination does not point to a defined etiologic agent or previous work-up has failed.

Diagnostic imaging is beneficial to evaluate for both intrinsic agents of pain such as arthritic causes, calcific and degenerative tendinopathies, tumors, fractures, dislocations, separations, avascular necrosis, soft tissue injuries such as cuff tears or labral injuries, as well as to assess for foreign and loose bodies. Plain radiographs may be obtained in three orthogonal planes with views dependent upon the type and extent of injury, patient mobility, and physician preference. If further imaging is sought, the MRI is the test of choice and may be performed with an intra-articular contrast agent to better evaluate the integrity of the labral lining or postoperative changes that would be difficult to differentiate by MRI alone.

Electrodiagnostic studies play an important role in evaluation of the painful shoulder. It has been shown that sensory loss, such as an axillary patch for axillary nerve injuries, is unreliable in the diagnosis of axillary nerve injury.⁶¹ Electrodiagnostic testing can delineate neuromuscular involvement, including severity, and help with prognostication. Appropriately timed studies are important in defining the degree of nerve compromise.⁶² Electrodiagnostic testing usually is not performed until wallerian degeneration has taken place, approximately 3 weeks after injury, unless there is suspicion of nerve transection, which can be identified within 1 day of the event. The most common nerve injury associated with shoulder pathology is axillary nerve injury. Axillary nerve injury is most commonly associated with traumatic anterior shoulder dislocation, resulting in a neuropraxia or axonotmesis caused by traction.^61,63 Spontaneous recovery of axillary nerve function has been documented up to 7 months after injury.⁶⁴

The shoulder examination may not be straightforward, even when performed by the most experienced of clinicians (Fig. 49.5) One must always be aware of extrinsic etiologies of pain in this region. The cervical spine is a primary extrinsic cause of pain and not all patients will present with ‘classic’ symptoms. A solid fund of knowledge in combination with an appropriately detailed diagnostic work-up is crucial to completely address a patient’s need for treatment and future prevention of both clinical symptoms and recurrence of pathology.

Fig. 49.5 Algorithmic approach to patient presenting with shoulder injury.