Humeral Shaft Fractures

Introduction

Fractures of the humeral shaft represent 1% to 3% of all fractures and have an annual incidence of 4.5 per 100,000 patients. The distribution of fractures follows a bimodal distribution with peaks occurring in the seventh and third decades of life commonly due to ground-level falls in elderly females and high-energy trauma in young males, respectively. The nonoperative management of humeral shaft fractures has historically resulted in very high union rates and a high degree of patient satisfaction, with deformity of the humerus well accommodated by the large arc of motion at the shoulder and elbow. Wider indications for fixation and lower union rates with nonoperative management described in recent literature have expanded the role of operative management for humeral shaft fractures in recent years. Operative techniques include open reduction and plate fixation, minimally invasive plate osteosynthesis (MIPO), intramedullary nailing, and external fixation.

Relevant Anatomy

The management of humeral shaft fractures requires an in-depth understanding of humerus anatomy, the surrounding neurovascular structures, and, in particular, the relationship of the radial nerve to the humerus. The humeral shaft is defined as the region distal to the surgical neck and proximal to the medial and lateral epicondyles of the humerus. Proximally, the humerus is cylindrical; distally, it becomes triangular with posterior, anterolateral, and anteromedial surfaces. The humerus is supplied by a nutrient vessel located about the medial aspect of the distal aspect of the middle third of the humeral shaft ( Fig. 31.1 ). The deltoid tuberosity is an osseous elevation on the humerus that serves as the insertion for the three heads of the deltoid muscle ; it is a deforming force for humeral shaft fractures and serves as an important anatomic landmark for the radial nerve, which passes the posterior midline of the humerus within 0.1 cm of the distal-most aspect of the tuberosity ( Fig. 31.2 ). The spiral groove is a feature that separates the origins of the medial and lateral heads of the triceps, between which the radial nerve passes as it descends from proximal to distal through the posterior arm.

The radial nerve is of particular importance when managing humeral shaft fractures because it lies in direct contact with the posterior humerus from 17.1 to 10.9 cm proximal to the lateral epicondyle. The nerve enters the brachium anterior to the subscapularis and latissimus dorsi and descends with the profunda brachii artery through the triangular interval, defined as the anatomic space between the long head of the triceps and the humerus below the teres major. The nerve is maintained between the medial and lateral heads of the triceps as it courses adjacent to, but not within, the spiral groove of the humerus. Importantly, at this level, the nerve trifurcates into its main trunk, a branch to the medial head of the triceps, and the posterior antebrachial cutaneous nerve. All three branches travel together along the posterior humerus; if a single branch is mistaken to be “the radial nerve” in this region, injury may occur as other branches are not properly identified and protected ( Fig. 31.3 ). Distally, the nerve passes through the lateral intermuscular septum 10.2 cm proximal to the lateral epicondyle. As it passes across the lateral intermuscular septum, the nerve is focally tethered. This tether point is thought to be responsible for the high incidence of radial nerve palsy with mid to distal humeral shaft fractures; the eponymous Holstein-Lewis fracture is a distal third spiral fracture that was historically thought to put the radial nerve at particularly high risk for injury, although more recent literature has downplayed this association. In the anterior compartment, the nerve courses between the brachialis muscle, to which it provides partial innervation, and the brachioradialis muscle, before passing anterior to the lateral epicondyle into the forearm.

The ulnar nerve passes posterior to the pectoralis major and descends medial to the axillary artery in the anterior compartment of the brachium. It becomes of particular interest during the exposure of the distal humerus as it pierces the medial intermuscular septum 8 cm proximal to the medial epicondyle. In the posterior compartment, it descends anterior and medial to the medial head of the triceps until it passes posterior to the medial epicondyle to enter the cubital tunnel.

The median nerve and brachial artery are located anteromedial to the humerus throughout the brachium and travel in close proximity to one another. The median nerve travels lateral to the brachial artery in the interval between the brachialis and biceps until the level of the coracobrachialis insertion, when the nerve crosses anterior to the brachial artery and subsequently descends medial to the artery in the distal brachium and antecubital fossa.

The musculocutaneous nerve pierces the coracobrachialis muscle and then descends the length of the brachium in the interval between the biceps and brachialis, where it provides innervation to each muscle. It continues distally as the lateral antebrachial cutaneous nerve, which pierces the deep fascia lateral to the biceps tendon at the intercondylar line. The nerve is at risk of injury during a brachialis splitting anterior approach to the humerus if not properly identified and protected.

The axillary nerve passes in close proximity to the inferior glenoid before passing with the posterior humeral circumflex vessels through the quadrilateral space, defined by the long head of the triceps and the humerus medially and laterally, respectively, and the teres minor and teres major superiorly and inferiorly, respectively. The axillary nerve splits into anterior and posterior branches at the 6 o’clock position on the glenoid; the anterior branch courses laterally around the surgical neck of the humerus 4–6 cm distal to the acromion to provide innervation to the anterior and middle heads of the deltoid, while the posterior branch continues posteriorly to provide innervation to the posterior head of the deltoid and teres minor muscle. The posterior branch additionally gives off the superior lateral brachial cutaneous nerve. The axillary nerve serves as the proximal extent of the exposure of the humerus through a posterior approach.

Classification

The most widely used classification system for humeral shaft fractures is the AO/OTA (AO Foundation/Orthopaedic Trauma Association) classification. The humeral shaft is identified as bone number 1, fracture location 2, or AO/OTA 12 ( Fig. 31.4 ). As with other diaphyseal fractures, the AO/OTA system subdivides humeral shaft fractures into subtypes A for simple fractures, B for wedge fractures, and C for complex fractures. Subtype A fractures are further divided into spiral, oblique, and transverse patterns. Subtype B fractures are further divided into spiral wedge, bending wedge, and fragmented wedge patterns. Subtype C fractures are further divided into spiral, segmental, and irregular patterns.

Treatment Options

Treatment options for humeral shaft fractures vary broadly; choice in the management of select humeral shaft fractures must be carefully guided by patient factors, associated injuries, fracture characteristics, and patient preferences. Indications for nonoperative versus operative management of select humeral shaft fractures are discussed in detail in the following section. Techniques for surgical management include open reduction and internal fixation, MIPO, and intramedullary nailing.

Nonoperative Treatment With Fracture Brace

Nonoperative treatment is appropriate for many patients presenting with isolated spiral or oblique humeral shaft fracture. Patients are initially placed in a coaptation splint or hanging arm cast for 1 to 2 weeks after injury. A custom fracture brace is fabricated using two plastic sleeves encircled with two adjustable Velcro straps ( Fig. 31.5 ). For fractures of the proximal diaphysis, an over-the-shoulder addition is applied to the brace. Patients are instructed to maintain the brace at all times except for bathing and must tighten the straps several times daily to allow for swelling subsidence and muscle atrophy. Gravity-assisted pendulum exercises and elbow range of motion are encouraged. Radiographs are obtained at the time of brace application, at 6 weeks post injury, and every 6 weeks thereafter to assess for union. Patients are examined clinically at 6 weeks; gross fracture site mobility at 6 weeks is an independent predictor of nonunion formation and should be discussed with the patient as a possible indication for transition to surgical care.

Open Reduction and Plate Osteosynthesis

Open reduction and plate osteosynthesis is considered to be the most practical means of surgical treatment for most humeral shaft fractures. Because of the high rotational forces through the humerus and propensity for nonunion, strict adherence to sound orthopedic principles is especially important in the management of humeral shaft fractures. In particular, careful soft tissue handling and avoidance of periosteal stripping are critical to successful outcome. The ultimate goal is to obtain an anatomic reduction with absolute stability for most simple fracture patterns. Oblique and spiral fractures are ideally managed with single or multiple lag screw fixation and neutralization plating. Transverse fractures are optimally suited for compression plating with a carefully under-contoured plate ( Fig. 31.6 ). Comminuted fractures not amenable to anatomic reduction are best treated with relative stability via bridging plate constructs with long working lengths or intramedullary nailing ( Fig. 31.7 ). Large fragment 4.5-mm broad plates are often preferred due to their biomechanical superiority over 4.5-mm narrow plates and small fragment 3.5-mm plates and are optimal for supporting early weight-bearing or crutch use. Broad plates of 4.5 mm also typically have staggered holes which may decrease the risk of a linear stress riser. In certain cases, the narrow 4.5-mm plate may be optimal to allow for plate contouring in more complex anatomical areas such as the distal aspect of the humerus. Eight cortices of screw purchase are desired on either side of the fracture whenever possible. Locking screw fixation has not been shown to be biomechanically superior to nonlocking screw fixation for diaphyseal humerus fractures, although it is recommended to use locking screws in the setting of pathologic fracture, osteoporotic bone, or humerus nonunion. When desired, dual plating has been advocated by some authors to increase construct stiffness, and orthogonal plating has been shown to be superior to side-by-side plating ( Fig. 31.8 ). For fractures of the proximal humeral diaphysis, 3.5-mm anatomic proximal humerus plates are ideally suited to obtaining purchase in the humeral head but may require elevation of a portion of the anterior deltoid insertion. For fractures of the distal humeral diaphysis, a stout 3.5-mm posterolateral extra-articular distal humerus plate is commonly used but is frequently prominent on the posterior aspect of the lateral column of the elbow resulting in symptomatic hardware. If the patient desires a late hardware removal, the radial nerve must be elevated to remove the plate safely which can result in a radial nerve palsy. For this reason, our preferred technique for most supracondylar distal humerus fractures that have at least 3 to 4 cm of bone proximal to the olecranon fossa is to use a long proximal humerus flipped upside down along the anterior humerus ( Fig. 31.9 ).