Intrinsic shoulder pain

Patients with intrinsic shoulder injury will present with pain, stiffness, weakness, and instability of the shoulder joint. Pain is most commonly at the anterolateral shoulder and is reproducible with specific shoulder movements. Postoperative intrinsic shoulder pain is most commonly due to patient positioning. Surgical positioning in the supine or lateral decubitus position may lead to neurological, vascular, or ligamentous compromise. The supine patient should have arms abducted no more than 90 degrees to limit brachial plexus stress or musculoskeletal injury. Ligamentous injury, labral or rotator cuff tear, or complete shoulder subluxation may occur because of trauma during positioning. Any patient moved from the supine to prone position is at risk for traumatic shoulder injury. Additionally, the particular placement of arm boards or arm board malfunction may contribute to intrinsic shoulder injury if not properly secured to the operating room table. Ligament injury presents as shoulder weakness, anterolateral shoulder pain, and a popping sensation when the shoulder is moved.^[1] Complete shoulder subluxation will result in multidirectional instability of the shoulder, excessive range of motion, and crepitus over the shoulder joint. Symptoms are often vague and non-specific. If intrinsic musculoskeletal injury is suspected, specialty consultation should be sought.

Positioning in lateral decubitus position may cause compression of the shoulder structures and entrapment of the axillary neurovascular bundle. At the thoracic outlet, the subclavian vasculature and the brachial plexus exit the chest and enter the arm. The thoracic outlet is an anatomically small space confined by the clavicle, first rib, and scalene tendon. Subtle variations in the anatomy of the passage may cause compression and irritation of the nerves and vessels. Entrapment of the axillary neurovascular bundle at the thoracic outlet commonly presents as numbness, paresthesia, and pain radiating from the hand to the shoulder. A weak radial pulse may be palpated that diminishes with change in arm position.^[2] Acute thoracic outlet syndrome may be due to venous obstruction (blue, swollen, painful arm) or arterial obstruction (pain, pallor, diminished pulse).^[3] If acute thoracic outlet syndrome is suspected, urgent surgical consultation is recommended.

Extrinsic shoulder pain

Extrinsic shoulder pain is poorly localized to the shoulder joint and not exacerbated with shoulder movement. Range of motion is typically normal. The differential diagnosis of referred pain to the shoulder is robust, but a few causes are frequently observed after surgery.

Subdiaphragmatic gas: Laparoscopic surgery may cause extrinsic shoulder pain and has been reported to occur in up to 63% of laparoscopic cases.^[4] The pain is often reported in the Post-Anesthesia Care Unit (PACU) and may peak at 24 hours after the surgery.^[5] The pain is typically self-limited and resolves by 72 hours.^[6] Carbon dioxide retention in the subdiaphragmatic region causes irritation of the phrenic nerve.^[7] Additionally, the rapid overstretching of the diaphragm and peritoneum during insufflation may cause trauma to muscle fibers, blood vessels, and nerves, resulting in referred shoulder pain through the phrenic nerve.^[4] Left shoulder pain is more common than right shoulder pain, since the liver protects against gas accumulation under the right hemi-diaphragm.^[8] Specific neurons within the ventroposterolateral nucleus of the thalamus have been shown to have a dual response to both phrenic sensory stimulation and tactile stimulation of the shoulder, providing a mechanism for referred diaphragmatic pain.^[9]

Subdiaphragmatic gas pain management: Although self-limited, this complication may be associated with significant patient discomfort and attempts have been made to decrease the incidence with attention to surgical technique. Decreased shoulder pain has been associated with low flow, low pressure pneumoperitoneum, as well as gasless exposure by mechanical lifting to allow surgical visualization.^[10] The ability to decrease the incidence of postoperative shoulder pain is procedure specific. For laparoscopic cholecystectomy (performed in reverse Trendelenburg position), only low flow, low pressure pneumoperitoneum has been demonstrated to decrease the incidence and severity of shoulder pain.^[11] Conversely, for gynecological laparoscopy (performed in Trendelenburg position), active gas drainage and pulmonary recruitment maneuvers are beneficial.^[12] Attempts to relieve shoulder pain by local anesthetic infiltration of the diaphragm and aspiration of the pneumoperitoneum at the conclusion of surgery have been moderately successful. Postoperative phrenic nerve block has proven efficacious, but confers only transient pain relief.^[13] Pain relief of post laparoscopic shoulder pain is most commonly achieved with non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen, or opioids. Typically, pain may be controlled with oral analgesics and home discharge, if desired, need not be delayed.

Visceral injury: Shoulder pain may also occur because of irritation, ischemia, compression, or rupture of visceral organs. Referred shoulder pain has been reported following esophageal, gastric, or intestinal rupture; surgery to the liver, biliary tree, or spleen; adrenal or pancreatic hematoma; and cholecystitis.^[2] Pneumoperitoneum or hemoperitoneum secondary to viscus or vasculature injury may occur following trauma, endoscopy, laparotomy, lower extremity vascular access, or any surgical procedure involving the abdomen. In addition to shoulder pain, patients with pneumoperitoneum or hemoperitoneum may display hypotension and peritonitis. Shoulder pain after esophagoscopy should raise concern for esophageal rupture and may be accompanied by chest pain, throat pain, and fever. This is a surgical emergency and consultation should be sought.

Thoracotomy: Ipsilateral shoulder tip pain has been described following thoracotomy, and may occur in up to 50% of cases.^[14] Pain is typically independent of movement, poorly localized, aching in quality, and described as moderate to severe.^[15,16] Ipsilateral post-thoracotomy shoulder pain is not relieved with epidural analgesia.^[15] Referred shoulder pain can be differentiated from incisional pain by dosing an epidural catheter. With a properly functioning catheter, incisional pain will be relieved; however, referred ipsilateral shoulder pain will persist. Classic ipsilateral post-thoracotomy shoulder pain will gradually decline over the first 4 to 6 postoperative hours, rarely extending until postoperative day 1.^[15,17] Many hypotheses exist about the etiology of ipsilateral shoulder pain including excessive surgical retraction, brachial plexus positioning injury, transaction of a major bronchus, or pleural irritation secondary to thoracostomy tube. The phrenic nerve clearly plays a role in referred pain transmission as preoperative phrenic nerve infiltration with local anesthetic has been shown to reduce ipsilateral shoulder pain by nearly 50%.^[18] Additionally, postoperative phrenic nerve blockade by an interscalene brachial plexus block has been shown to provide immediate pain relief lasting 6 to 10 hours.^[16] The cornerstone of postoperative ipsilateral shoulder pain treatment is conservative management with NSAIDs or acetaminophen.^[15] A postoperative interscalene brachial plexus block may be considered for pain relief; however, care must be taken in selecting patients, as blockage of the phrenic nerve and ipsilateral diaphragm may cause respiratory compromise. Ipsilateral shoulder pain does not respond well to intravenous opioids and care must be taken to avoid overmedication and respiratory depression in patients with compromised pulmonary function.^[18]

Other referred pain: Other sources of extrinsic pain include neurological, vascular, pulmonary, and cardiac disease. Referred pain to the shoulder may arise from the neck, thymus, and spleen. Particularly important in the postoperative patient are pulmonary and cardiac insult.

The administration of anesthesia depresses airway reflexes and places the patient at risk for pulmonary aspiration of gastric contents. Aspiration occurs in approximately 1 in 8,000 general anesthetics in healthy patients and may occur in the presence of endotracheal intubation.^[19] Aspiration pneumonia may present in the postoperative period with hypoxia, cough, bronchospasm, and pleuritic shoulder pain. Diagnosis can be confirmed by chest X-ray. Management includes supplemental oxygen and advanced airway management.

Classically, acute myocardial infarction may present as nausea, diaphoresis, shortness of breath, substernal chest pain, and referred left-sided shoulder, jaw, or neck pain. In the postoperative setting, associated chest and referred pain may be masked by systemic opioids and anesthetic recovery. Myocardial ischemia in the PACU typically presents as tachycardia and hypotension. Myocardial ischemia should be considered in postoperative patients with risk factors for cardiac disease displaying tachycardia, hypotension, and shoulder pain.