Case Based Learning for April 2025

Shoulder dislocation

HPI: 20 yo otherwise healthy individual presents to you with acute left upper arm pain. The patient reports that they were mountain-bike riding, lost control of their bike and crashed. They are not sure how they landed but report immediate pain and numbness in their left upper extremity post-crash. Patient is concerned since they cannot move their upper arm and report it feels numb over the lateral aspect of their shoulder. They were able to ambulate into your emergency department and deny other injuries. They deny prior UE trauma, chronic joint pains, illnesses, or systemic symptoms.

 

Question 1: Based on your knowledge of anatomy, describe some potential causes of traumatic upper arm pain.

Common causes of acute traumatic upper arm pain include humeral fracture, clavicular fracture, Acromioclavicular (AC) joint separation, glenohumeral dislocation, rotator cuff tear.

 

Question 2: What is the typical mechanism of injury for each of the above potential items? Think about the anatomy and how it might be disrupted.

Proximal Humeral Fracture: Most often are caused by a fall or direct blow to the lateral shoulder. Type of fracture is determined by the body and arm position when the direct force is applied. (i.e., outstretched vs adducted arm)

Clavicular Fracture: Often occurs with a fall onto a shoulder or being stuck over the clavicle with a heavy object.

AC separation: Typically occurs from direct trauma to the superior or lateral aspect of the shoulder with the arm adducted

Glenohumeral dislocation: An anterior shoulder dislocation is usually caused by a blow to the abducted, externally rotated, and extended arm. Examples would be fall on an outstretched arm, blocking a basketball shot, or blow to the posterior humerus.

Rotator cuff tear: Most rotator cuff tears are seen in the middle aged or older adults and are usually secondary to degeneration, impingement, and overload. They often begin as partial tears of the undersurface or articular portion of the supraspinatus tendon. Acute tears will occur after a fall and can affect any of the 4 tendons, but the supraspinatus tendon is the most injured.

 

Question 3: What physical exam findings will help you narrow your differential diagnosis?

Humeral Fracture: Patient will have swelling and tenderness over the injury site. There will be pain at rest and associated with attempted passive or active range of motion involving the injury site. There may be visible bruising or abrasions.

Clavicular Fracture: Often can see a bump or deformity at the fracture site on physical exam, especially if the person is thin. Patient will have swelling and tenderness over the injury site. There will be pain associated with attempted passive or active range of motion involving the injury site. There may be visible bruising or abrasions.

AC (acromioclavicular) separation: Tenderness directly over the AC joint, possible deformity. Passive cross-body adduction of the arm to compress the AC joint often elicits pain. Comparing right to left AC joints, will often reveal asymmetry.

Glenohumeral dislocation: Patient will resist all movement due to pain. If it is an anterior shoulder dislocation, patients will present with the arm slightly abducted and slightly externally rotated. There is a loss of the normal rounded contour when comparing bilateral shoulders. The acromion may appear more prominent.

Rotator cuff tear: With acute tears, patients typically have weakness and an inability to raise their arm overhead. Often there is tenderness over the greater tuberosity of the humerus and sometimes there is a high riding humeral head on exam. Pain is greater with active motion vs passive.

Question 4: How might your differential change if you palpated the patient’s neck and they had pain in addition to numbness across their shoulder and down their arm to their third digit?

You should consider a cervical spine injury with an acute C7 radiculopathy concerning for an acute C7 neve root impingement.

 

Physical Exam:
Cervical and Thoracic Spine: non-tender to palpation over the cervical and thoracic spine. Active range of motion of the neck without pain. No swelling, bruising or chest wall tenderness.

Upper Extremities: Right Upper Extremity normal. Sternum and bilateral clavicles are non-tender to palpation. Left Upper Extremity: Anterior shoulder tender to palpation with arm held by the patient’s side. Humeral head is prominent anteriorly. Severely limited range of motion due to pain. Normal neurologic examination in the distal extremity but decreased sensation in the lateral deltoid region. Pain and apprehension with attempting passive movement of the shoulder. Passive supination and pronation of the forearm is without pain. Radial pulses are 2+ and easily palpated. Distal capillary refill is less than two seconds. No tenderness with palpation of the elbow, forearm or wrist.

 

Question 5: What is the significance of the decreased sensation along the deltoid?

The axillary nerve has sensory innervation to a patch of skin on the lateral shoulder. Sensation changes to the lateral deltoid region can be secondary to an injury to the axillary nerve. The axillary nerve can be injured during a shoulder dislocation or humeral neck fracture.

 

Question 6: If your patient suffered one of the following fractures, what nerve may be injured and how might you test for an injury to that nerve?

1. Humeral Surgical Neck fracture:
2. Humeral Shaft fracture:
3. Medial epicondyle fracture:

Surgical neck fracture – Axillary nerve runs posterior to the humerus at this location and is at risk for injury. It has both sensory and motor components. The nerve innervates teres minor and the deltoid muscles. Test strength of abduction of the shoulder. There may be numbness or tingling on the superior anterior, lateral and posterior upper arm.

Transverse or Spiral fracture of humeral shaft – The radial nerve runs posterior to the humerus and distally it innervates the extensors of the forearm. If the radial nerve is injured at this point, patient may have a wrist drop.

Medial epicondyle fracture – The ulnar nerve runs posterior to the humerus in the ulnar groove. The ulnar nerve innervates most of the muscles of the hand as well as the skin producing paresthesia over the medial 1 ½ digits. The paresthesia or sensory changes are present before deficits in intrinsic hand function are seen.

Question 7: Would you like to order any imaging studies?

Give the traumatic nature of the injury and the physical exam findings, I would recommend an x-ray of the shoulder to assess for fracture or dislocation. Review the findings on the AP x-ray.

Interpretation: Anterior Dislocation. No evidence of proximal humeral, glenoid, clavicular fractures. No visible rib fractures.

 

Question 8: What makes the shoulder a relatively unstable joint?

The shoulder is an inherently unstable joint due to the shallow glenoid and small portion of the humeral head that articulates with the glenoid. The surrounding structures, including the labrum, ligaments, capsule and rotator cuff muscles maintain stability and motion.

 

Question 9: Your patient is in severe pain. What medication class might you provide your patient in the emergency department? Describe the prototypical mechanism of action of the class of medications.

Opioid (morphine, hydromorphone, fentanyl, oxycodone, hydrocodone, codeine).
Most opioids are mu agonists with varying activity on kappa receptors. All Opioid receptors are 7 transmembrane spanning proteins that are coupled to inhibitory G-proteins. When activated, they decrease adenyl cyclase production of the secondary messenger cyclic adenosine monophosphate. This causes a decrease in calcium influx from inhibition of voltage-gated calcium channels and results in the activation of potassium channels, which leads to hyperpolarization. The hyperpolarized state causes inhibition of neuronal signaling, which inhibits pain transmission.

 

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UP-TO-DATE SUMMARY AND RECOMMENDATIONS: Clinical anatomy and mechanism of injury – Shoulder (ie, glenohumeral) dislocations account for 50 percent of all major joint dislocations. Anterior dislocations comprise the large majority of these. Shoulder anatomy and mechanisms of dislocation should be reviewed and understood.

Anterior dislocation

Presentation and imaging – An anteriorly dislocated shoulder causes the arm to be slightly abducted and externally rotated. The patient resists all movement, and the acromion appears prominent. Proper evaluation includes a neurovascular examination, with particular attention to distal pulses and the function of the axillary nerve, which is most commonly injured. Radiographs routinely obtained include the anteroposterior (AP), scapular “Y,” and axillary views. Ultrasound is useful but may not reveal fractures.

Associated fractures – Clinically important fractures occur with approximately 25 percent of anterior shoulder dislocations. Factors associated with fracture include age over 40, first-time dislocation, and traumatic mechanism (eg, fight or fall). When all three factors are absent, a fracture is highly unlikely.

Reduction technique – No one of the many methods used to reduce anterior shoulder dislocations is proven to be superior. We suggest starting with scapular manipulation. If unsuccessful, we proceed to the external rotation technique, adding the Milch technique if needed. If these are unsuccessful, traction-countertraction or an alternative technique may be used. Each technique is described in the text, along with appropriate analgesia and monitoring and potential complications.

Immobilization – Following reduction, the patient’s injured arm is immobilized in a position of adduction and internal rotation. A collar and cuff, sling and swathe, or commercially available shoulder immobilizer are equally effective.

Posterior dislocation – A posterior shoulder dislocation causes prominence of the posterior shoulder with flattening anteriorly. The coracoid process appears prominent. The patient holds the arm in adduction and internal rotation and is unable to externally rotate. Posterior dislocations are commonly associated with tuberosity and surgical neck fractures. Signs of this dislocation on a standard anteroposterior radiograph are subtle and often missed. Clues to the diagnosis include the lightbulb sign, rim sign, and trough line sign.

Inferior dislocation – Patients with inferior shoulder dislocation hold the involved arm above their head and are unable to adduct the arm. Approximately 60 percent of patients have some neurologic dysfunction, with the axillary nerve most commonly involved. Neurologic dysfunction usually resolves spontaneously following reduction. Rotator cuff tears or greater tuberosity fractures are present in 80 percent of cases. Arterial injury occurs in approximately 3 percent of patients. Radiographs reveal the humeral head beneath the coracoid or the glenoid.

Indications for surgical referral – Anterior, posterior, and inferior shoulder dislocations that are successfully reduced, and are without signs of vascular injury, should be referred as an outpatient to an orthopedic surgeon for evaluation within about one week. Other indications for surgical referral are reviewed in the text and include the following:

Immediate, emergency consultation with orthopedic and vascular surgery should be obtained for any shoulder dislocation associated with signs suggestive of a vascular injury (most common with inferior dislocations).

Prior to any attempt at reduction, orthopedic consultation should be obtained for any shoulder dislocation with a concomitant surgical neck or humeral shaft fracture.

Orthopedic consultation should be obtained for older adults with subacute dislocations (after 7 to 10 days) because of the relatively high incidence of vascular injury and fractures that may occur with reduction attempts.

Orthopedic surgery consultation is necessary for any shoulder dislocation that is not successfully reduced.

 

Written by Paula Silha, MD, Chief Medical Officer,  ERx Group

 

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This is for informational purposes only. For medical advice or diagnosis, consult a physician.

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