The shoulder is the most mobile joint of the body, and as such, is often injured. Undiagnosed and inadequately treated shoulder injuries contribute to rampant shoulder dysfunction later in life. Adhesive capsulitis or “frozen shoulder” is the most common repercussion, but impingement syndromes due to cumulative rotator cuff degeneration and AC arthritis can also limit mobility. Shoulder health later in life depends on proper treatment of acutes, to prevent adhesions and degeneration, and limit the development of disabling complications. It is often useful to order a radiographic image of the injured area. If a diagnosis is not clear, or if the injury indicates it, further imaging may be ordered.
The most common etiology for acute onset shoulder pain is trauma. The most frequent injuries are AC separation, glenohumeral dislocation, rotator cuff injuries, bicipital tendon injuries, bursitis, and fractures of the clavicle and humerus. Only 15% of shoulder pain is referred. If there is no traumatic mechanism one should certainly rule out MI, pneumonia, gall bladder disease and perforated peptic ulcers. For many shoulder injuries a diagnosis may be made clinically, however the use of imaging to confirm or refine a diagnosis, detect unexpected damages, or rule out a worst case scenario, is always an option.
The differentials for which emergent imaging is strongly indicated include suspected fractures, posterior or direct mechanism shoulder dislocations, and tendon or ligamentous ruptures. There are different imaging needs to assess for MI, pneumonia, gall bladder disease and ulcers, not covered here. Imaging by CT or MRI is routinely used before and after surgeries, and may be used to assess joint effusion, osteonecrosis, and osteomyelitis.
It is important to note that systemic conditions might present with a shoulder injury. A few conditions affecting the shoulders include Ankylosing Spondylitis, Rheumatoid Arthritis, Acromegaly, Marfan Syndrome, Hyperparathyroidism, and Calcium Pyrophosphate Dihydrate Deposition Disease (CPPD). Rheumatoid Arthritis predisposes the patient to rupture of rotator cuff tendons, and can cause complete resorption of the humeral head. Anklyosing Spondylitis patients may have erosions of the lateral humeral head and distal clavicle and an elevated humeral head due to rotator cuff tears. The specifics for all these conditions are not included, however I hope that you will think broadly when presented with an acute shoulder. The differential to follow is focused on local injuries, however these injuries may reflect the outcome of broader processes at work.
Differential for Acute, Non-Referred Shoulder Pain:
Acromioclavicular joint injury
Glenohumeral dislocation and subluxation
Rotator cuff injuries
Bicipital tendon injuries
Fractures of the clavicle, humerus and scapula
Acromioclavicular joint injury
Injury of the AC joint is called shoulder "separation" ( not to be confused with “dislocation” considered in the next section), and accounts for approximately 12% of the dislocations associated with the shoulder girdle. AC separation usually occurs traumatically, due to foosh or a downward blow to the acromion process at the point of the shoulder. Injuries are graded I-VI, with Grade I being a partial tear of the AC ligament without deformity. Grade II involves a complete AC tear with a minor step deformity, but the joint is held in place by a coracoclavicular ligament that is partly or completely intact. At Grade III the coracoclavicular ligament is also ruptured, and there is a step deformity caused by minimal displacement and prominence of the lateral aspect of the clavicle on the involved side. Grade III separations will have pain on palpation and with AC distraction and compression, horizontal adduction with overpressure.
Grades IV-VI disruptions have severe instability and pain in all directions, requiring immediate referral for imaging (CT or MRI) and surgery. In severe AC disruptions the sternoclavicular ligament may also be disrupted, and one out of four are retrosternal, meaning that the end of the bone has penetrated tissue inside the thorax. This is potentially life threatening as the fractured clavicle can compress or puncture the trachea, lung, or large vessels of the throat. In a youth, suspect a Salter-harris type 1 epiphyseal fracture. Any of these merits an immediate visit to the ER with expert transport.
The patient may need surgical fixation for sprains of Grades II and III, or they may heal without surgery, depending on the degree of the sprain, and the general health and vitality of the individual. Ligaments are slow to heal and require concerted treatment for full recovery. If you choose to conservatively treat a Grade I-III sprain, check in with the patient frequently. If it is not much improved at 3 weeks contact a surgeon to discuss the case. At four weeks a surgery referral is mandatory if the patient is not much improved. Surgical repair is best done by 6 weeks after the injury.
Any injury to the AC joint may result in arthritic changes resulting in grinding or popping when reaching overhead or across the chest. Arthritis can also occur without traumatic injuries, for example some 35% of CPPD patients have calcifications of the AC cartilage.
The optimal image to seek to visualize the AC joint is an AP projection with a 15 degree celphalad tilt, with and without 10-15lb weights in the patient’s hands. Bilateral images allow for comparison of the normal joint spaces on the unaffected side to the displaced joints on the affected side.
Glenohumeral dislocations and subluxations
Most shoulder dislocations can be diagnosed clinically based on history and the appearance and ROM of the glenohumeral joint. Of all shoulder girdle dislocations, 85% occur at the GH joint, 12% at the AC, 2% at the SC, and 1% are scapulothoracic. For indirect (tractioning) mechanisms of dislocation (tug of war, racquet sports, kayaking) bony involvement is less likely, and the direction of dislocation is usually anterior. In cases of nontraumatic anterior dislocation, reduction based on clinical evaluation may be indicated, without the need for prior imaging. Reduction of an uncomplicated GH dislocation will immediately and drastically relieve the pain. Delay in seeking imaging may cause more damage to compressed and overstretched tissues. Overstretching injury can also be caused by subluxation (partial dislocation that has self-reduced). Careful monitoring of distal circulation, sensation and motion after the reduction will reveal if there has been injury to the neurovascular bundle, which would be an indication to seek a CT or MRI.
Pseudosubluxation of the humerus is not a dislocation at all, but rather the displacement of the humeral head from its usual location due to the widening of the humeral space. It is usually caused by hemarthrosis or lipohemarthrosis after a trauma to the shoulder.
The Hill-Sachs and Bankart fractures that are mentioned as complications of anterior shoulder dislocations are common but not usually severe. The Hill-Sachs fracture is an impaction fracture of the posterolateral aspect of the humeral head where the bone has contacted the edge of the glenoid fossa. It occurs in up to 60% of cases, and MRI is best for assessing it. The Bankart fracture is the trauma incurred at the anterio-inferior glenoid rim secondary to the same traumatic collision. Even if these fractures are suspected, immediate reduction of the shoulder may be preferable to delay, to reduce the cumulative damages from increasing muscle spasms while the joint remains dislocated.
For a person of average conditioning (and with the shoulder externally rotated and abducted) it only takes 12 pounds of traction to pull the humeral head out of the glenoid fossa. When a person has the rotator cuff laxity consistent with prior dislocations, it may take considerably less force than that. For example, a person may roll over in bed and wake to discover that their shoulder is “out”. People who have “loose shoulders” usually can reduce their own shoulders, and will benefit from physical therapy to tone the rotator cuff. If their shoulders are still loose after a period of concerted PT, a CT or MRI is indicated to evaluate the need for and possible efficacy of reconstructive surgery.
Posterior dislocations account for 2-5% of all glenohumeral dislocations, and are generally caused by direct mechanisms such as collision, but also may be caused by electrical shocks or epileptic convulsions. Inferior dislocations are even less common, and require considerable lever arm force on the humerus to occur. Any dislocation due to a direct mechanism, and any posterior or inferior dislocation, should be evaluated with imaging before reduction is attempted unless urgent care is hours to days away. Posterior dislocations are more likely (than anterior) to be associated with fractures and bone chips because the posterior edge of the glenoid fossa obstructs dislocation more than the anterior edge. Even a subluxation in the posterior direction may result in complications including compression or disruption of the neurovascular bundle, or further injury to bursae and other soft tissue by bone fragments and edges. These injuries predispose the patient toward osteochondritis dessicans and osteonecrosis of the humeral head. Other complications of glenohumeral dislocations include tears in the glenoid labrum, and increasing laxity of the joint.
It is important to be aware that a patient with a dislocated shoulder will probably not be able to rest their affected humerus against their rib cage. Forcing the dislocated limb into a classic sling and swath arrangement can cause a great deal more harm. The general rule is to splint the limb into the antalgic position that the patient naturally assumes. A sling may be appropriate, then padding must be secured under the slinged arm such that the arm is well supported and the humeral head is not pressed into the glenoid rim. Proper transport is less uncomfortable and may help spare the blood vessels that supply the humeral head, reducing complications such as avascular necrosis. It is furthermore worth mentioning that anti-inflammatory medications that may cause increased bleeding (ibuprofen, aspirin) should be avoided in dislocations until after imaging and any emergent treatments.
The “Y” view is the radiographic image that allows visualization of the humerus between the acromion and the coracoid, aiding in the specific diagnosis of glenohumeral dislocation. This view is also known as the Grashey view. An AP view will illustrate posterior (aka infracoracoid) dislocation.
Regardless of the type of dislocation, it is incumbent on the responsible physician to followup in 1-2 days, and again in 1-2 weeks, to be certain that recovery is progressing and to order followup imaging as needed.
SLAP lesions and other labrum injuries
SLAP stands for superior labrum anterior and posterior, and it refers to a tear in the glenoid labrum that extends in both directions mentioned. It is most often seen in athletes who throw, but also after some shoulder traumas including glenohumeral dislocations. MRI is the optimal imaging choice to visualize labral avulsions, clefts, or the absence of a labrum. Subtle SLAP lesions can be difficult to diagnose even on MRI. Magnetic resonance arthrography (MRA) increases the sensitivity for detecting these abnormalities.
Rotator cuff injuries
Rotator cuff injuries are ubiquitous. According to Dr Frangos, 34% of asymptomatic people of all ages have rotator cuff tears, as do 54% of patients over 60 and 50% of patients without preceding trauma. Damages accumulate with age. The supraspinatus, infraspinatus, teres major and subscapularis may be injured by foosh, trauma, and overuse through work or play. Sports involving throwing (pitching), swimming, reaching overhead (lifting weights, racquet sports, kayaking), or pushing downward (skiing) may cause minor damages. The tendons can become worn, or calcified, or inflamed. Repeated low grade trauma and chronic inflammation may result in a “snap” during a strenuous motion. Weakness and pain when lying on the affected side or reaching overhead are classic signs. Pain is often referred to the outer deltoid. The damages are graded: I is minor pain and weakness, II is pain and moderate disability, III is pain with severe disability. Old rotator cuff injuries may not have pain anymore, but the weakness will persist. It is difficult to assess these injuries when the pain is present.
The supraspinatous is the most commonly injured, and it is easily identified as the muscle which lifts the arm above shoulder height, where the deltoid no longer functions. If the patient leans the torso toward the injured shoulder and then can lift the arm above shoulder height, it is an indication of supraspinatus involvement. Radiography is usually not helpful, unless there is calcification of the ligament. The part of the supraspinatus that is most commonly injured is the relatively hypovascular area 1-2cm from the insertion on the greater tuberosity.
Impingement syndrome is a chronic process that can begin in the 20’s. Entrapment of the tendons of the supraspinatus and biceps, and the subacromial subdeltoid bursa between the coracoacromial arch and the humeral head causes degeneration of the rotator cuff tendons. Up to 95% of rotator cuff tears may be related to chronic impingement. The diagnosis of impingement is made clinically.
Chronic rotator cuff tears can sometimes be diagnosed on radiograph by the narrowing of the distance between the undersurface of the acromion and the humeral head. Radiograph can also detect calcific tendonitis involving nodular deposition on rotator cuff tendons. Specialized tests may assist in pinpointing the specific areas of damage. Codman’s arm drop, Gerber’s Lift off test, Appley’s scratch test, the empty Can test, and others should be employed to direct the investigation.
The best imaging for visualizing rotator cuff injuries is the MRI, though CT is also good. The positioning depends on the specific muscle or tendon that is implicated, though frequently the entire cuff will be imaged as more than one component may be damaged and they are not easy to separate out by physical exam. The most commonly used images are on the oblique sagittal and oblique coronal planes, as well as axial images. A typical MRI appearance of rotator cuff damage is seen as an increased T2 signal within the tendon. Normal tendons have little fluid in them. Muscle atrophy can also be appreciated by fatty infiltration on T1 weighted images as well as decreased bulk.
Inflammation or degeneration of the tendon of the long head of the biceps is common. This tendon runs in the bicipital groove and if the transverse ligament is lax or ruptured, the tendon may sublux causing pain or popping with internal or external rotation, resulting in inflammation. If the tendon does not slide back into its groove it remains quite painful. Repetitive lifting and overhead reaching are implicated in inflammation, as is increasing age. The tendon may also rupture, resulting in a “Popeye” bunching of the biceps muscle on the distal humerus. Up to 10% of chronically inflamed bicipital tendons rupture. These ruptures are not usually repaired, unless the patient is a professional athlete. The long head portion of the biceps eventually grows to the short head portion, resulting in a minimal loss of supination strength but no loss of elbow flexion. Diagnosis of all these variations is clinical, and treatment is unlikely to require surgery. Speeds and Yergason’s tests may help guide diagnosis. Imaging is most commonly not indicated. If the patient is still suffering from pain, tenderness, or weakness after three months, refer.
In the shoulder, bursitis is most frequently caused by calcifications on tendons running through the area. Most commonly affected is the subdeltoid bursa, which is aggravated by the supraspinatous tendon. The bursa may be painful when it is compressed under the acromion by passive abduction of the arm to 60 degrees. Subacromial bursa calcifications are also common. Aside from visualizing calcifications, radiography is not helpful. Usually bursitis responds to conservative treatment within 3-6 weeks, and if it does not, followup with CT or MRI may be indicated.
Fractures of the clavicle, humerus and scapula
The clavicle is one of the most frequently fractured bones in the body, and 80% of clavicular fractures occur in the middle of the bone. It can be fractured during the birth process and remains fragile throughout childhood. Some 15% of clavicle fractures are at the lateral end, and only 5% occur at the medial end of the bone. These fractures may be identified by physical exam, and simple radiography may be sufficient to confirm the extent of the damage and allow treatment.
The humerus is much more difficult to fracture, but becomes weaker with age. Among elders the surgical neck of the humerus is a frequent fracture. Fractures of the surgical neck are usually comminuted and involve both the greater and lesser tuberosities. Fractures of the proximal humeral shaft are comminuted approximately 10% of the time. For a suspected comminuted fracture, CT is the imaging of choice because it allows for the location of bone fragments. Any fracture proximal to the anatomical neck causes an increased risk of avascular necrosis of the humeral head.
Fractures of the scapula are very rare but if they happen it is usually the neck or body of the bone. There are reports of stress fractures of the scapula induced by doing pushups.
The shoulder is a complex joint with a broad variety of possible injuries and dysfunctions. There is no simple rule that can be followed to make diagnostic decisions. Each case needs to be evaluated carefully. Sometimes imaging is necessary, and sometimes it is not. It is up to the clinician to apply what they know, and refer when appropriate. No amount of imaging can replace a full understanding of the joint and of the patient.
Radiology Secrets Plus, 3rd Ed, E. Scott Pretorius, MD, and Jeffrey A Solomon, MD, MBA, 2011
Radiology Study Guide, by Yochum, Haag and Rowe, Williams & Wilkins publishers, 1988.
Shoulder Injuries Edited by Terry R Malone, Volume 1 Number 2 June 1988
*2009 and 2010 lectures by NCNM’s Dr Frangos and Dr Thom
*WFR trainings through WMA and SOLO