2. Discuss common preoperative neural dysfunction involved with this injury

The majority of proximal humerus fractures are either non-displaced or minimally displaced and can be managed conservatively. Complicated or displaced fractures are at higher risk for associated neurovascular injury. Diagnosing neural dysfunction is often challenging because the clinical examination may be limited secondary to pain. A prospective study of 142 patients with proximal humerus fractures demonstrated electromyographic evidence of denervation in approximately 70% of patients. The most commonly injured nerve is the axillary nerve (58%) followed by the suprascapular nerve (48%). A combination of nerve injuries was frequently seen [9]. Axillary nerve injury results in deltoid muscle weakness with reduction of shoulder abduction and diminished sensation over the inferior deltoid. The suprascapular nerve, a branch of the upper trunk of the brachial plexus, provides sensory innervation to approximately 70% of the shoulder joint, including superior and posterior–superior regions, capsule, and overlying skin. It also innervates the supraspinatus and infraspinatus muscles of the rotator cuff and injury causes weakness with abduction and external shoulder rotation, respectively.

The radial nerve is at risk for injury with significantly displaced diaphyseal fractures secondary to its location in the spiral groove. Humeral shaft fractures are associated with radial nerve injury in 11.8% of cases [10]. Because the branches of the lateral and long head of the triceps arise before the nerve enters the groove, only the medial head of the triceps is affected, along with the posterior compartment of the forearm, resulting in wrist drop. Consequently, patients are unable to extend the wrist, straighten the fingers, extend the thumb, and have weakness with supination of the arm. Radial nerve injury causes loss of sensation in the lateral arm, posterior forearm, the lateral half of the dorsum of the hand, and the dorsal aspect of the lateral 3.5 digits. Distal humerus fractures may be associated with median and radial nerve injuries, depending on the direction of the displaced fragment. Posterolateral displacement is most common and is associated with damage to the anterior interosseus nerve (AIN), a branch of the median nerve. The AIN provides motor innervation to the flexor digitorum profundus muscle to the index finger, the flexor pollicis longus muscle to the thumb, and the pronator quadratus of the distal forearm. On physical exam, if the patient has damage to the AIN, they will be unable to make the “OK” (thumbs up) sign. Radial nerve injury is possible with posteromedial fragment displacement [11]. The AIN and radial nerves are most commonly damaged at the time of injury whereas ulnar nerve impairment can be largely attributed to iatrogenic causes [12].

3. Describe potential vascular complications

Severely displaced proximal humeral fractures can lead to significant vascular injury. The proximal humerus receives its blood supply from branches of the axillary artery while anterior and posterior humeral circumflex arteries originate distal to the anatomic neck and travel proximally to supply the humeral head. Avascular necrosis of the humeral head may occur with fractures at the anatomic neck. Injury to the surgical neck of the humerus, where the articular capsule attaches, can disrupt penetrating arteries, which also provide part of the vascular supply to the humeral head. A considerably displaced mid-shaft fracture can damage the profunda brachii artery, as it runs in the radial groove alongside the radial nerve, causing excessive bleeding. Brachial artery injury may occur with posterolateral displacement in distal humerus fractures.

4. Discuss common postoperative neural dysfunction involved with repair

Treatment options for proximal humerus fractures include closed reduction percutaneous pinning, intramedullary nailing (IMN), open reduction with internal fixation (ORIF), hemiarthroplasty with possible rotator cuff repair, and total shoulder arthroplasty. Although neural injury often occurs secondary to the fracture itself, surgical repair is also associated with postoperative neurologic dysfunction. Improper patient positioning, excessive traction on the nerves, and dislocation of the humeral head during open shoulder surgery have all been implicated in postoperative nerve injuries [13]. The axillary nerve is most commonly injured during proximal humerus repair secondary to its close proximity to the inferior shoulder capsule [14]. Other nerves at risk include the suprascapular nerve and the musculocutaneous nerve as it courses below the coracoid process. The reported incidence of nerve injury is 1 to 2% in patients undergoing rotator cuff surgery and 1 to 4% in patients undergoing arthroplasty [15].

Ulnar nerve dysfunction is commonly seen with distal humerus fracture repair due to its fixed anatomic position. The incidence of ulnar neuropathy following ORIF is reported to be 8 to 38%. Nerve injury may occur preoperatively during closed fracture manipulation; intraoperatively during surgical exposure, mobilization, stripping, and fracture fixation; or postoperatively from scar formation [16]. Prolonged use of a pneumatic tourniquet for distal humerus repair may contribute to postoperative neuropathy.

5. Describe positioning concerns during repair

Shoulder surgery may be performed in the sitting or lateral decubitus positions, though neither is associated with superior outcomes [17]. The sitting position optimizes chest-wall mechanics but may be associated with cardiovascular, central, and peripheral neurologic injury. Hypotension results from venous pooling in the lower extremities with decreased venous return and cardiac output. Significant hypotension may cause a decrease in cerebral blood flow, possibly leading to cerebral ischemia [18] and/or vision loss [19]. Blood pressure measurements should be performed as close to the level of the circle of Willis as possible, and non-invasive blood pressure monitoring on the lower extremity should be avoided. Maintaining higher end-tidal carbon dioxide at 40 to 42 mmHg has been shown to improve cerebral oxygenation in the sitting position [20].

Brachial plexus strain, ulnar nerve neuropathy, cutaneous nerve injuries, and postoperative blindness may occur with improper positioning. Care must be taken to position the patient in order to decrease strain on the brachial plexus. Cervical extension and contralateral rotation of the head should be avoided to prevent traction injuries. Brachial plexus strain can occur secondary to traction applied in various arm positions. Minimum overall strain was noted when the shoulder is at 90 degrees of flexion and 0 degrees of abduction [21]. Pressure on the ulnar sulcus should be prevented. Elbow flexion of >90 degrees may produce high intrinsic pressures under the cubital tunnel retinaculum compressing the ulnar nerve as it passes beneath and between the medial epicondyle and olecranon processes and should be avoided [22]. Cutaneous neurapraxias involving the lesser occipital and greater auricular nerves from compression by the headrest have also been reported [23]. When securing the head, ocular compression should be avoided to prevent postoperative blindness [24–25].

In the lateral decubitus position, compression of the axillary neurovascular structures may occur and result in brachial plexus injury or compartment syndrome in the dependent arm. Axillary roll placement under the dependent chest wall helps to relieve pressure on the neurovascular structures. All pressure points should also be carefully padded and pulses on the dependent arm checked regularly.

6. Consider possible regional anesthetic options and describe how options change depending upon the location of the fracture

If a regional anesthetic technique is considered, it is important to document pre-existing neurologic findings. Loss of shoulder mobility, ranging from clinically insignificant to adhesive capsulitis (frozen shoulder), is a common complication of proximal humerus fractures. Regional anesthetic techniques can significantly reduce postoperative pain, and interscalene blocks (ISB) have been shown to significantly increase shoulder range of motion during rehabilitation [26]. Compared with general anesthesia, patients undergoing shoulder surgery under regional anesthesia also have greater hemodynamic stability in the beach chair position and better neurobehavioral test results postoperatively [27]. Other advantages to ISB include decreased perioperative opioid use and associated side effects, avoidance of airway manipulation and general anesthesia, and reduced recovery time. The use of single-injection nerve block vs. continuous catheter technique should be determined on a case-by-case basis.

Attention must also be paid to possible side effects of the ISB. Phrenic nerve blockade has been reported with an incidence of 100% with standard volumes of local anesthetic. Although reduced local anesthetic volumes may decrease this incidence, it is not reliably avoided [28]. Due to possible phrenic nerve blockade, caution is also warranted in patients with severe coexisting respiratory disease or pulmonary hypertension as it may cause hypercarbia, hypoxia, and respiratory failure. Recurrent laryngeal nerve blockade with hoarseness is also common. Therefore, due to possible blockade of the phrenic and recurrent laryngeal nerves, bilateral ISB should never be performed. Ipsilateral Horner’s syndrome is also a common side effect of ISB. Patients should receive appropriate counseling and be reassured if these occur.

In patients with contraindications to ISB, selective suprascapular nerve block (SSNB) and axillary nerve block (AxNB) can be a useful alternative. A recent comparison of single-shot ISB to selective SSNB with AxNB showed that although onset of ISB was faster and resulted in more profound analgesia in the immediate postoperative period, selective SSNB and AxNB caused less motor blockade and allowed for equal patient satisfaction [29]. A combination of infraclavicular plexus block with SSNB for shoulder surgery on a patient with severe pre-existing respiratory compromise has also been reported [30].

Surgical correction of diaphyseal fractures presents a challenge for regional anesthesia. A distal plexus block will adequately cover pain from the fracture; however, repair may require instrumentation of the proximal humerus. A combination of ISB with distal plexus blocks has been described to block the innervation of the humerus in its entirety [31].

For procedures on the distal humerus, the regional technique should be altered to cover the lower roots and trunks of the brachial plexus. Supraclavicular, infraclavicular, and axillary block with musculocutaneous supplementation are all appropriate regional approaches for distal humeral fractures.