Epidemiology
Anterior shoulder instability can arise from primarily three different etiologies: trauma, congenital laxity, and acquired laxity. Determining the difference between instability and laxity is essential. Matsen proposed most patients with recurrent instability fall into one of two groups. The acronym TUBS describes a traumatic unidirectional event, usually with a Bankart lesion and commonly warranting surgery . AMBRII describes an atraumatic, multidirectional instability, commonly bilateral condition which is usually addressed with rehabilitation ; however, if surgery is performed an inferior shift and rotator interval closure are important. It is critical to realize that these classifications may overlap, and an individual who is congenitally “loose” could still sustain a traumatic event resulting in a unidirectional problem.
A traumatic episode could result in injury to static and dynamic stabilizers including the glenohumeral capsule and ligaments, the glenoid labrum, the bone of the glenoid or humeral head, or the rotator cuff. Most often there is a combination of these various lesions. Congenital laxity could include local anomalies such as glenoid dysplasia or more systemic abnormalities such as Ehlers-Danlos syndrome. Neer introduced the category of acquired laxity as a gradual stretching or elongation of the capsule secondary to repetitive microtrauma from particular sports such as gymnastics or swimming. ,
Acute traumatic anterior dislocation
Approximately 1% to 2% of the population will experience a glenohumeral dislocation in their lifetime. Anterior glenohumeral dislocations account for almost 85% of all shoulder dislocations and has been reported as high as 89% to 98%. A population-based cohort study from the United Kingdom following 17,000 patients over 20 years (1995 to 2015) found that approximately 72% of shoulder dislocations occurred in men, and the highest incidence (80.5 per 100,000 person-years) was found in young males, aged 16 to 20 years. For females, the highest incidence occurred in women aged 61 to 70 years old. Similarly, a 2010 study from the United States showed an overall incidence of 23.9 per 100,000 person-years, with the incidence in males 2.6 times higher than in females. It is believed the true incidence could be even greater because many dislocations may spontaneously reduce and not present to an emergency department. In all, only 20% of anterior shoulder dislocations occur in individuals older than 60 years. Contact athletes are at an especially higher risk for shoulder dislocation. American football athletes have shown shoulder dislocation incidence up to 0.51 per 1000 athlete-exposures, and the prevalence of shoulder dislocation during one season of rugby has been shown to be approximately 15%. Thus anterior shoulder instability occurs most commonly in young, active males who participate in contact sports.
Recurrent anterior instability
Numerous factors contribute to the likelihood of recurrent anterior instability of the shoulder, with younger age the most significant risk factor ( Box 30.1 ). Male sex and activity level with those involved in contact sports are also at higher risk. All of these variables should be taken into account and weighed in the formulation of the treatment plan.
Young age
Male sex
Athletic participation, especially contact sports
Severity of original trauma
Previous dislocation events
Ligamentous laxity
Large Hill-Sachs defect
Glenoid fracture or bone loss
Effect of age
The age of the patient at the time of the initial dislocation has a major influence on the incidence of recurrent instability. , Several authors have reported that patients younger than 20 years at the time of the initial dislocation have up to a 90% chance of recurrent instability. In patients older than 40 years, the incidence drops sharply to 10% to 15%. , The majority of all recurrences occur within the first 2 years of the first traumatic dislocation. ,
Hovelius et al. reported in a prospective Swedish study a lower incidence of recurrence in each age group: 33% in those younger than 20 years, 25% between ages 20 and 30 years, and 10% between ages 30 and 40 years. However, his 25-year follow-up presented the natural history of the nonoperatively treated primary anterior shoulder dislocations in patients younger than 40 years and observed that more than 50% of those patients had a repeat episode of shoulder instability. Furthermore, in the same cohort evaluated at 25 years after injury, more than 50% of the patients had developed glenohumeral arthritis from recurrent instability.
Effect of trauma, sports, sex, and dominance
Rowe , has pointed out that the recurrence rate varies inversely with the severity of the original trauma; in other words, the more easily the dislocation occurred initially, the more easily it recurs. The recurrence rate in athletes is thought to be higher than in nonathletes and higher in men than women. Dominance of the affected shoulder does not seem to have a major effect on the recurrence rate, although it may have implications in the treatment algorithm and discussion with the patient.
Buss et al. reported that out of 30 athletes, 37% had an additional recurrence episode when trying to return to sport that same season. Presenting on a cohort of West Point intercollegiate contact athletes, only 27% with an instability episode successfully returned to play and completed the season without recurrence. In contrast, 64% of those who returned to in-season play had subsequent recurrent instability. The same authors in 2017 reported of those intercollegiate athletes treated nonoperatively after an anterior shoulder instability event, only 40% had a successful return to their sport without a recurrence the following season. Owens documented at one collegiate institution that football players and wrestlers had the highest incidence of anterior instability.
Effect of fractures
In chronic anterior instability, bone lesions of the glenoid or the humerus have been identified on plain films in up to 95% of patients. The humeral head Hill-Sachs impaction rate was reported in 73.1% of patients in their study. Sugaya et al. showed that in patients with recurrent anterior shoulder instability, 50% had a glenoid fracture (bony Bankart lesion), 40% did not have a glenoid osseous fragment but did have erosion or compression of the glenoid rim, and 10% had normal glenoid bony configuration. Of those with a glenoid fracture, 2% had a large bony fragment (27% of the glenoid fossa, on average), 54% had a medium-sized bony fragment (11% of the glenoid fossa, on average), and 44% had a small bony fragment (3% of the glenoid fossa, on average). A different study by Dickens et al. showed that, on average, there was a statistically significant glenoid bone loss after a single anterior instability event equivalent to 6.8% of the glenoid width. This bone loss increased to 22.8% in the setting of recurrent instability. The percentage of glenoid bone loss has been shown to be an important factor in management of anterior shoulder instability. Historically, “critical” glenoid bone loss of 20% to 25% has been shown to negatively affect outcomes after primary arthroscopic labral repair. However, more recently, it has been shown that when glenoid bone loss is as low as 13.5%, there are poor clinical outcomes after primary arthroscopic anterior labral repair, suggesting that the traditional amount of “critical” glenoid bone loss should be reconsidered. To date, although many studies have shown good clinical outcomes after open Bankart repair, no studies have evaluated “critical” glenoid bone loss in open repair. Surgical treatment of anterior shoulder instability is discussed further in Chapter 31, Chapter 32, Chapter 33 .
The incidence of recurrent instability is lower when a first-time shoulder dislocation is associated with a greater tuberosity fracture. , , , This may be due to a variety of factors: increased trauma and hemorrhage from the fracture may lead to greater stimulation to repair and form scar tissue, and these fractures also tend to occur in older patients. Hovelius reported that these fractures were three times as common in patients older than 30 years, at 23% versus 8%, than in patients younger than 30 years.
History
The history is perhaps the most important aspect for the patient presenting with anterior instability for guiding treatment. Patient demographics obtained should include age, hand dominance, and sports participation including position and time of the season the dislocation occurred. In addition, the patient’s future goals with regard to sports, work, and recreational activities should be discussed. If sensory disturbances and/or motor weakness persist following reduction, further neurologic evaluation should be initiated. Persistent swelling or temperature-related symptoms should trigger the need for a vascular workup.
Acute traumatic anterior dislocation
The history should document the mechanism of the injury, including the position of the arm, the amount of force applied, and the point of force application. , The position of the arm during the first dislocation can be highly variable. Injury with the arm in abduction, extension, and external rotation favors an anterior dislocation. Depending on the position of the arm at the time of the event, the chances of recurrence can be predicted. Di Giacomo et al. demonstrated with three-dimensional (3D) computed tomography (CT) scans that dislocations at abduction angles greater than 60 degrees result in Hill-Sachs lesions more parallel to the anterior glenoid in positions of function and thus have a greater chance for recurrent instability. Electric shock, seizures, or a fall on the flexed and adducted arm are commonly associated with posterior dislocation. If the instability is recurrent, the history should document the initial injury, the position or action that results in instability, how long the shoulder had initially remained dislocated, whether radiographs are available with the shoulder dislocated, and what means were necessary to reduce the shoulder. The history also solicits evidence of neurologic, vascular, or rotator cuff problems after previous episodes of shoulder instability. Previous treatment of the recurrent instability and the effectiveness of this treatment should be documented.
Recurrent anterior instability
Following initial dislocation, the shoulder may regain full range of motion, strength, and functional stability, or recurrent instability may occur. Although intermediate forms of recurrent instability do occur, the great majority of recurrently unstable shoulders may be thought of as being either atraumatic (AMBRII) or traumatic (TUBS) in origin.
Atraumatic
Most patients with atraumatic instability are younger than 30 years. Secondary to the instability occurring in the midrange positions of the shoulder, atraumatic instability typically causes discomfort and dysfunction in ordinary activities of daily living. Commonly, such patients have the greatest difficulty sleeping, lifting overhead, and throwing.
The onset in the atraumatic population is usually insidious, but it can also occur after a minor injury or period of disuse. The symptomatic translations can range from a sensation of a minor slip in the joint to complete dislocation of the humeral head from the glenoid. The displacement characteristically reduces spontaneously, after which the patient is usually able to return to previous activities without much pain or problem. As the condition progresses, the patient can subjectively notice the shoulder has become “looser” and sense apprehension that it may slip out and clunk back in with increasing ease in an increasing number of activities. The shoulder can become uncomfortable, even with the arm at rest. Patients report they can make the shoulder pop out voluntarily and that at times the shoulder feels as though it needs to be “popped out” or released secondary to a feeling of pressure. Patients may admit they had a habit of dislocating the joint but that they can now no longer control the stability of the joint. The surgeon must determine whether habitual dislocation remains a feature of the patient’s problem because surgery to cure voluntary instability is clearly difficult.
There are other important factors to obtain in addition to the history and the circumstances surrounding the onset of the problem, as well as every position of the shoulder in which the patient experiences instability. Determining whether the opposite shoulder is symptomatic is important to note because many patients in this population have bilateral shoulder difficulties. A family history might reveal other family members similarly affected, in addition to possible connective tissue disorders known to predispose for atraumatic instability, such as Ehlers-Danlos or Marfan syndromes.
Traumatic
In characteristic anterior traumatic instability, the usual mechanism of injury involves the application of a large extension–external rotation force to the arm elevated near the coronal plane (abduction, extension, external rotation). In this position, the anterior inferior glenohumeral ligament is under maximal tension and is the primary static restraint resisting anterior humeral translation. Injury in this position classically results in a Bankart lesion with the capsulolabral complex detaching from the glenoid ( Fig. 30.1 ). This mechanism of injury can occur in a multitude of sports (e.g., a fall while snow skiing, while executing a high-speed cut in water skiing, in an arm tackle during football, or with a block of a volleyball or basketball shot). In addition, this can occur in the workplace in relatively violent industrial accidents in which a posteriorly directed force is applied to the hand while the arm is abducted and externally rotated. Of note, the mechanism of injury could occur in other positions as well, such as when a boxer misses an opponent and sustains an anterior dislocation.
An initial traumatic dislocation often requires assistance in reduction rather than a spontaneous reduction, as is usually the case in atraumatic instability. However, some patients are able to self-reduce the shoulder, even if fully dislocated. A traumatic dislocation is usually associated with severe pain, and the patient will not be able to continue with sports or recreational activities at the time of injury. Radiographs from previous emergency department visits may be available to show the shoulder in its dislocated position. Axillary or other neuropathies may have accompanied the glenohumeral dislocation and should be documented. Any of these findings individually or in combination support the diagnosis of traumatic as opposed to atraumatic instability.
Traumatic instability can occur without a complete dislocation. In this situation, the injury produces a traumatic lesion, but it is insufficient to allow the humeral head to completely escape from the glenoid. The shoulder may still be unstable as a result of the injury where apprehension or subluxation could be experienced when the arm is placed near the position of injury. Such patients have no history of the need for reduction and have no radiographs with the shoulder in the dislocated position. Thus the diagnosis rests to an even greater extent on obtaining a careful history that focuses on the position and forces involved in the initial episode.
Characteristically, a shoulder with recurrent traumatic instability is comfortable when troublesome positions are avoided. However, the apprehension or fear of instability can prevent the patient from returning effectively to work or sports. Recurrent subluxation or dislocation can occur when the shoulder is unexpectedly forced into the abducted, externally rotated position or during sleep when the patient’s active guard is less effective. Lastly, the patient might have a history of increasing ease of dislocation as the remaining stabilizing factors are progressively compromised.
Physical exam
The ability to examine the patient will be less tolerated in the acute anterior dislocation setting than the more chronic or recurrent instability individual. Therefore the detailed history and imaging will be more relied upon in the acute setting. The physical exam should always start with a thorough assessment of the cervical spine and progress to the shoulder. An appropriate scapular examination is also critical because scapula dyskinesia or dysfunction is often misinterpreted for instability. Although common examination maneuvers for anterior instability lack sensitivity and specificity, a systematic and thorough approach to the shoulder for assessment of all structures can still be extremely effective and help to confirm the diagnosis and determine other injuries that may coexist.
Acute traumatic anterior dislocation
An acute anterior shoulder dislocation is usually very painful, and muscles are in spasm in an attempt to stabilize the joint. The humeral head may be palpable anteriorly. The posterior and lateral aspect of the shoulder shows a hollow beneath the acromion. The arm is held in slight abduction, and passive and active motions are limited by pain. Secondary to the possible association of nerve injuries and, to a lesser extent, vascular injuries, an essential part of the physical examination of an anteriorly dislocated shoulder is assessment of the neurovascular status of the upper extremity and charting of the findings prior to a reduction attempt. The particular situation will determine if a radiograph should be taken prior to reduction attempt. For example, if the patient is already in a controlled environment such as the emergency department or clinic, radiographs can be obtained expeditiously prior to a reduction attempt. However, if the patient is outside this environment and radiographs cannot be obtained quickly, a reduction should be attempted after a neurovascular exam and prior to radiographs if an acute shoulder dislocation is suspected.
Vascular injury
Several reports of arterial and neurologic injury with shoulder dislocation reinforce the importance of a thorough neurovascular evaluation. , Vascular damage most often occurs in elderly patients with stiffer, more fragile vessels. The injury may be to the axillary artery or vein or to branches of the axillary artery: the thoracoacromial, subscapular, circumflex and, rarely, the long thoracic. Injury can occur at the time of either dislocation or reduction. Vascular damage may be obvious or subtle. Findings can include worsening pain, expanding hematoma, pulse deficit, peripheral cyanosis, peripheral coolness and pallor, neurologic dysfunction, and shock. Doppler or an arteriogram should confirm the diagnosis and locate the site of injury if there is any suspicion of vascular injury.
Nerve injury
The reported incidence of nerve injuries in clinical series of acute dislocations is substantial, often as high as 33%. , , The axillary nerve is most commonly associated with involvement in up to one-third of first-time anterior dislocations. , , , , The dislocated humeral head displaces the subscapularis and the overlying axillary nerve anteroinferiorly and creates traction and direct pressure on the nerve. , The injury may be a neurapraxia (no structural damage, recovery in approximately 6 weeks), an axonotmesis (disruption of the axons, preservation of the nerve sheath, axonal regrowth at 1 inch per month), or a neurotmesis (complete nerve disruption, guarded prognosis for recovery). The likelihood of an axillary nerve injury increases with the age of the patient, the duration of the dislocation, and the amount of trauma that initiated the dislocation. , Other frequently injured nerves are the radial, musculocutaneous, median, and ulnar, but the entire brachial plexus can be involved. The diagnosis of nerve injury is considered in any patient with neurologic symptoms or signs such as weakness or numbness after a dislocation. A nerve injury can also be manifested as delayed recovery of active shoulder motion after glenohumeral dislocation. Blom and Dahlbäck demonstrated that axillary neuropathy can exist without numbness in the usual sensory distribution of the axillary nerve. Electromyography provides an objective evaluation of neurologic function, provided that 3 or 4 weeks have passed between the injury and the evaluation. Most axillary nerve injuries resulting from anterior dislocation are traction neuropraxias and will resolve completely. However, if recovery has not occurred in 3 months, the prognosis is not as good. ,
Recurrent anterior instability
When performing the following maneuvers, it is important to first examine the opposite shoulder to establish a baseline for comparison. The examiner should also ask the patient to demonstrate the positions that create instability or apprehension prior to manipulating the affected shoulder.
Laxity tests
Laxity tests seek to define the amount of translation or rotation that an examiner can elicit in the relaxed shoulder. This translation is determined both by the position of the shoulder and by the properties of the ligaments and capsule. When interpreting the significance of the degree of translation on laxity tests, it is important to use the contralateral shoulder as an example of what is “normal” for the patient. Glenohumeral translation can be defined as movement of the center of the humeral head with respect to the face of the glenoid ( Fig. 30.2 ).
In the past, laxity was often confused with instability; treatments were directed at managing laxity rather than at enabling the humeral head to stay centered in the glenoid. Shoulders without clear evidence of instability were tightened because they were lax and painful; the results were not consistent. For this reason, it is important to recognize that normal shoulders are lax and that laxity is often not increased in unstable shoulders. Many normally stable shoulders, such as those of gymnasts, demonstrate substantial translation on laxity tests even though they are asymptomatic.
In performing the tests described next, it is important for the examiner to note not only the amount of laxity, but also any additional findings associated with the translation or rotation, such as the patient’s subjective response to the test.
In the sulcus test , the patient sits upright with the arm relaxed at the side in a neutral position. The examiner centers the head with a mild compressive load and then pulls the arm downward at the distal humerus while watching the lateral edge of the acromion ( Figs. 30.3 and 30.4 ). The inferior sulcus can be graded in centimeters depending on the distance of the hollow from the lateral acromion to the humeral head. Grade 1 is 1 cm, grade 2 is 2 cm, and grade 3 is 3 cm or more. Repeating this maneuver with the arm in external rotation at the side and demonstrating the same amount of sulcus could represent injury or incompetence to the rotator interval ( Fig. 30.5 ). The presence of an inferior sulcus remaining in external rotation is important to determine if surgical stabilization is performed with the need for a 6 o’clock anchor and axillary pouch capsulorraphy critical.
In the anterior load-and-shift test , the amount of passive anterior humeral head translation on the glenoid is tested. The patient is supine with the injured shoulder at edge of the bed. The forearm is grasped by the examiner at the flexed elbow, stabilizing the humeral head in the socket, while the other hand grasps the proximal arm and produces an anterior force ( Fig. 30.6 ). This is performed at 0, 45, and 90 degrees of abduction. A 3-point grading scale can be used to assess the amount of anterior translation. Grade 1 is translation to but not over the glenoid rim. Grade 2 is translation over the glenoid rim but spontaneous reduction of the humeral head. Grade 3 is humeral head translation over the glenoid rim, where spontaneous reduction does not occur. A positive finding with this test suggests injury to the anterior band of the inferior glenohumeral ligament and deficiency of the anterior labrum.
In the drawer test, the patient is seated with the forearm resting on the lap and the shoulder relaxed. The examiner stands behind the patient. One of the examiner’s hands stabilizes the upper shoulder (scapula and clavicle), while the other grasps the proximal end of the humerus. These tests are performed with a minimal compressive load (just enough to center the head in the glenoid) and a substantial compressive load (to gain a feeling for the effectiveness of the glenoid concavity). Starting from the centered position with a minimal compressive load, the humerus is first pushed forward with more compression to determine the amount of anterior displacement relative to the scapula (glenoid) ( Fig. 30.7 ). The anterior translation of a normal shoulder reaches a firm end point with no clunking, no pain, and no apprehension. Laxity with this test suggests injury to the middle glenohumeral ligament. A clunk or snap on anterior subluxation or reduction can suggest a labral tear or Bankart lesion.
The Gagey test is used for assessment of the anterior inferior glenohumeral ligament. The patient is seated in an upright position while the examiner stabilizes the upper shoulder with one hand and brings the arm up into abduction with the other hand ( Fig. 30.8 ). The amount of abduction is measured and compared with the contralateral side. Greater than 15 degrees of increase on the injured side or greater than 105 degrees is positive. Gagey reported 85% of anesthetized patients with shoulder instability had greater than 105 degrees of abduction. The end point is also firmer in a normal shoulder versus a softer end point with instability.
The magnitude of translation on standard tests of glenohumeral laxity does not necessarily distinguish stable from unstable shoulders. However, an experienced examiner can detect diminished resistance to anterior translation on either the drawer test or the anterior load-and-shift test when the humeral head is compressed into the glenoid fossa, indicating a loss of the anterior glenoid lip. Comparison exam of the opposite shoulder can be helpful in detecting these differences. These maneuvers can also elicit grinding as the humeral head slides over the bony edge of the glenoid from which the detached capsulolabral complex labrum has been avulsed or elicit catching as the head passes over a torn soft tissue.
Provocative stability tests
Provocative stability tests examine the ability of the shoulder to resist challenges to stability in positions in which the ligaments are normally under tension. A key element of these tests is noting if the maneuver reproduces the symptoms of pain or concern/apprehension to the patient. Again, it is important that the examiner ask the patient to demonstrate the positions that create instability or apprehension prior to manipulating the affected shoulder, as some of these test maneuvers may cause redislocation.
In the apprehension and relocation test the patient is supine with the shoulder at the edge of the table. The patient’s arm is held in 90 degrees of abduction and external rotation with the elbow flexed to 90 degrees. The examiner rotates the arm into increasing external rotation ( Fig. 30.9 ). A sense of apprehension if the shoulder is going to subluxate or dislocate and increased discomfort is a positive finding. In the same position of apprehension, a posterior-directed force to the anterior humerus should provide a sense of stability with decreased apprehension and discomfort ( Fig. 30.10 ).
In the fulcrum test the patient lies supine at the edge of the examination table with the arm abducted to 90 degrees. The examiner places one hand posterior to the shoulder under the glenohumeral joint to act as a fulcrum. The patient’s arm is gently and progressively extended and externally rotated over this fulcrum ( Fig. 30.11 ). Maintaining gentle passive external rotation for a minute can fatigue the subscapularis and challenge the capsular contribution to anterior stability of the shoulder. Normally, no apprehension or translation occurs because the anterior ligaments are intact and can resist anterior translation. A patient with anterior instability usually becomes apprehensive as this maneuver is carried out, suggesting deficiency in the anterior stabilizing structures.
In summary, although the laxity and provocative stability tests are specific tests used in the assessment of the patient with anterior instability, a systematic approach to the cervical spine and shoulder needs to be carried out routinely. Strength of the deltoid and the rotator cuff should be determined. In patients older than 35 years, the possibility of rotator cuff tear increases and must be evaluated. Finally, it is critical to perform a thorough neurovascular examination determining the integrity of the axillary nerve and other branches of the brachial plexus, as well as to rule out possible vascular compromise.
Imaging
Acute traumatic anterior dislocation
When a shoulder is dislocated, radiographs are used to determine the direction of the dislocation, the existence of associated fractures (displaced or not), and possible barriers to reduction. Dorgan and McLaughlin have pointed out that reliance on anteroposterior (AP) and transthoracic radiographs could lead an orthopedist into a “diagnostic trap.” The glenohumeral joint is most reliably imaged with three standardized views referred to the plane of the scapula. The complete series of three views oriented to the scapula provides much more information than does the commonly obtained view in the plane of the body ( Fig. 30.12 ).
The first is an AP view in the plane of the scapula ( Fig. 30.13 ). In 1923, Grashey recognized that to take a true AP radiograph of the shoulder joint, the direction of the x-ray beam must be perpendicular to the plane of the scapula. This view is most easily accomplished by placing the scapula flat on the cassette (a position that the patient can help achieve) and passing the x-ray beam at right angles to this plane and centering it on the coracoid process ( Fig. 30.14 ). The beam is generally approximately 30 degrees medial from the neutral arm position and aimed medial to lateral. This view can be taken with the arm in a sling and the body rotated to the desired position ( Fig. 30.15 ). In a normal shoulder, this view reveals clear separation of the humeral subchondral bone from that of the glenoid. In an injured shoulder, it often reveals the pathology ( Fig. 30.16 ).
The second is a scapular lateral view ( Fig. 30.17 ). This view is taken at right angles to the AP view in the plane of the scapula. , , The radiographic beam is passed in a medial to lateral direction parallel to the body of the scapula while the cassette is held perpendicular to the beam at the anterolateral aspect of the shoulder ( Fig. 30.18 ). Like the AP view, it can be obtained by positioning the body without moving the dislocated shoulder, which can remain in a sling ( Fig. 30.19 ). In this view, the contour of the scapula projects as the letter Y, and the view is often referred to as a scapular Y view. The downward stem of the Y is projected by the body of the scapula; the upper forks are projected by the coracoid process anteriorly and by the spine and acromion posteriorly ( Figs. 30.20 and 30.21 ). The glenoid is located at the junction of the stem and the two arms of the Y. In a normal shoulder, the humeral head is in the middle of the arms of the Y, centered in the glenoid fossa. In an anterior dislocation, the humeral head is viewed anterior to the glenoid (see Fig. 30.20 ).
The third is an axillary view ( Fig. 30.22 ). First described by Lawrence in 1915, the view is obtained by placing the cassette on the superior aspect of the shoulder. This requires the humerus to be abducted sufficiently to allow the radiographic beam to pass between it and the thorax. Sufficient abduction can usually be achieved by gentle positioning of the dislocated shoulder or by modifications of the technique, which are discussed later. The axillary radiograph is critical in evaluation of a dislocated shoulder. It not only unambiguously reveals the direction and magnitude of head displacement relative to the glenoid but can also demonstrate the presence and size of head compression fractures, fractures of the glenoid, and fractures of the humeral tuberosities ( Figs. 30.23 through 30.27 ).
West point view
Modifications to the axillary lateral view have been described. Rokous et al. described the West Point axillary view. This is our preferred axillary view in patients with recurrent instability. In this technique, the patient is placed prone on the x-ray table with the involved shoulder on a pad raised 7.5 cm from the top of the table. The head and neck are turned away from the involved side. With the cassette held against the superior aspect of the shoulder, the x-ray beam is centered on the axilla, 25 degrees downward from the horizontal and 25 degrees medial. The resulting radiograph is a tangential view of the anteroinferior rim of the glenoid ( Fig. 30.28 ).
Rockwood has pointed out that in a situation in which the patient cannot abduct the arm sufficiently, a curved cassette or a rolled cardboard cassette can be placed in the axilla and the radiographic beam passed from a superior position ( Fig. 30.29 ). Bloom and Obata modified the axillary technique so that the arm does not have to be abducted ( Fig. 30.30 ) and referred to the modification as the Velpeau axillary lateral view. While wearing a sling or Velpeau dressing, the patient leans backward 30 degrees over the cassette on the table. The x-ray tube is placed above the shoulder, and the beam is projected vertically down through the shoulder onto the cassette. An additional modification to the classic axillary view is the trauma axillary lateral radiograph ( Fig. 30.31 ). An understanding of these modification techniques is important because in the trauma setting it is often difficult to obtain an appropriate axillary view. In addition, the experience and expertise of the radiology technologist can vary.
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