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Fractures of the Humeral Shaft
Introduction
Fractures of the humeral shaft account for approximately 3% of all fractures and represent an incidence of 19 per 100,000 person-years. The occurrence shows a bimodal age distribution with a peak observed in the third decade, mainly in men as a result of violent high-velocity injuries, and a larger peak in the seventh decade, mainly occurring in women, generally resulting from simple falls and attributed to osteoporotic bone. The primary causes of fracture include traffic accidents, accidental falls, and violent injury. In a consecutive series of 249 fractures, less than 10% were open.
Relevant Anatomy
The humerus shaft is the longest bone of the upper extremity. The proximal cylindrical aspect flattens in the distal direction and is more triangular in shape in the supracondylar area. Proximally at the transition from the humerus head to the shaft lie the lesser and the greater tubercle, where the rotator cuff is attached. The lesser tubercle is continued distally in the crest of the lesser tubercle, and the greater tubercle is continued distally in the crest of the greater tubercle. In between lies the intertubercular groove containing the long biceps tendon. The crest of the greater tubercle divides the anterolateral from the anteromedial surface. The medial and the lateral margins (the proximal continuation of the medial and lateral epicondyle) define the posterior surface. The deltoid tuberosity, a rough area on the anterolateral aspect of the humerus, serves as the attachment of the deltoid muscle and is just proximal and nearly parallel to the groove of the radial nerve. The spiral groove for the radial nerve runs on the dorsal aspect of the humerus and can be found 20 cm proximal to the medial epicondyle and 14 cm proximal to the lateral epicondyle. The three muscles—brachialis, triceps, and brachioradialis—origin from three muscles—pectoralis major, deltoid, and coracobrachialis—insert to the humerus diaphysis. These muscles are innervated by either the musculocutaneous, radial, or axillary nerve. As an exception, the brachialis muscle receives innervation from two nerves, the musculocutaneous (medial part) and radial (lateral part) nerves. Thus splitting the brachialis muscle medially does not jeopardize the innervation. In two-thirds of all humeri, one single nutrient canal lies in a small area on the medial aspect of the distal half of the middle third of the humerus. It can be assumed that the main blood supply will enter this point coming from the brachial artery. In some cases, an accessory nutrient foramen can be found near the groove for the radial nerve on the posterior surface of the humerus. This accessory nutrient foramen receives an accessory humeral nutrient artery that originates from the radial collateral artery.
Mechanism of Injury/Biomechanics
In contrast to the lower extremity, the upper extremity experiences only a few axial loads, and rotational forces dominate. This different load shearing requires adjustment in the osteosynthetic treatment. A plate osteosynthesis will need additional screws on both fracture sides to compensate for these rotational forces.
The degree of displacement is influenced by the height of the fracture level. In fractures above the insertion of the pectoralis muscle, the proximal fragment tends to rotate externally and abduct. The distal fragment dislocates medial and anterior. Fractures above the delta muscle insertion adduct the proximal fragment and proximalize the distal fragment. With the fracture just below the insertion of the delta muscle, the proximal fragment tends to abduct. After all, moderate malalignment (rotation, length, and axis) is well tolerated by the humerus, and a maximum of 15 degrees of malrotation and 20 degrees of anterior angulation, as well as shortening of less than 3 cm, is still acceptable. Varus malalignment is less tolerated and should not be more than 20 degrees. After 45 degrees, the supraspinatus muscle is insufficient.
As a rule of thumb, bending forces will create transverse fractures, and torsion forces will result in a spiral fracture. The combination of both forces will create an oblique fracture with or without a butterfly fragment. Axial compression fractures either the proximal or the distal part of the humerus.
Evaluation
Examination
Neurovascular injuries (mainly lesions to the radial nerve) frequently occur in a humerus shaft fracture, making the preoperative clinical evaluation of utmost importance. Radial nerve impairment is best recognized by examination of the extensor carpi radialis longus function. Inability to oppose the thumb indicates a median nerve lesion, and inability to spread the fingers indicates an ulnar nerve injury. But in all cases, brachial plexus injuries must be ruled out.
An absent radial pulse is the best clinical diagnostic factor for a lesion of the brachial artery, mainly in the proximal and distal thirds where the artery runs in the proximity of the humerus shaft. The degree of ischemia depends on the level of the arterial lesion. Injuries proximal to the profunda brachi artery show a high rate of ischemia and limb loss.
Imaging
Standard radiologic assessment is usually sufficient for the diagnosis of humerus shaft fracture. Analogous to other fractures, computed tomography (CT) scanning and three-dimensional reconstruction can facilitate visualization. If desired, CT angiography or angiography can help to localize vascular impairment.
In pathologic fractures, additional CT scanning, technetium-labeled bone scanning, magnetic resonance imaging (MRI), or angiography might be necessary for preoperative planning and eventual embolization ( Fig. 46.1 ).
Diagnosis and Classification
The classification follows the Müller Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) classification of long bones. The bone number is 1, and the fracture location is 2 (AO 12). Additional numbers and letters address further fracture characteristics. Simple fracture patterns are A type, wedge patterns are B type, and complex patterns are C type ( Fig. 46.2 ). Spiral fractures of the distal one-third of the humerus shaft are called Holstein–Lewis fractures and are commonly associated with neuropraxia of the radial nerve.
Management
Disorder and Injury
Emergent Treatment
Immediate emergent treatment is indicated in concomitant vascular injuries; so, limb amputation rates are low, which is probably related to the rich collateral blood supply.
In open fractures, early soft tissue and bone débridement are essential to decrease the infection rate. The timing is still under debate, and a strict “6-hour rule” has little support in the existing literature.
Indications for Definitive Care
The humerus shaft fracture was historically mainly treated nonoperatively, with good union rates and good shoulder and elbow function. However, in the United States, the utilization of open reduction and internal fixation for humeral shaft fractures has been steadily increasing with time. Surgical interventions seem to be more common with younger patients, female gender, private insurance, and larger hospital size. Perioperative complications of concern included iatrogenic radial nerve damage, nonunion, and infection. Although nonoperative treatment is successful in many fractures, several variables favor operative treatment. In a retrospective study, Denard and colleagues compared 213 patients and showed a higher nonunion rate with conservative therapy. There were no differences in radial nerve palsy, infection rate, range of motion, or time to union. Comparing functional bracing and intramedullary nail fixation found, apart from better free shoulder mobility in the bracing group, no significant differences in shoulder function or fracture alignment. Comparing functional bracing and plate fixation for extraarticular distal-third diaphyseal humeral fractures, operative treatment achieved more predictable alignment and potentially quicker return of function but risked iatrogenic nerve injury, infection, and the need for reoperation. Functional bracing was associated with skin problems and varying degrees of angular deformity, but function and range of motion were similar and usually excellent. Nonoperative management of humeral midshaft fractures can be expected to have similar functional outcomes and patient satisfaction at 1 year, despite an early benefit to operative treatment.
Operative intervention may include compression plate fixation, intramedullary nailing, or external fixation, depending on the properties of the fracture and other associated injuries.
Pathologic Fractures
Pathologic fractures need special consideration concerning the treatment options. These fractures that are due to metastatic tumors are commonly seen in patients with advanced tumor disease. In adults, metastatic disease is the most common malignant neoplasm of bone. Closed reduction and intramedullary fixation and open reduction and internal plate fixation are the most widespread methods for the stabilization of these fractures. Sarahrudi et al. analyzed 56 pathologic humerus shaft fractures mainly related to breast, bronchial, or kidney cancer. Their results show that patients with a metastatic fracture of the humerus survive an average of 2.8 months after pathologic fracture. Conservative therapy resulted in nonunion and inadequate pain relief. For patients in advanced stages of metastatic disease, they recommended closed intramedullary fixation and irradiation due to the faster and less-invasive procedure. Patients with better prognosis and patients with solitary metastasis of the humerus should undergo open reduction curettage of the lesion, cementation, and plate fixation ( Fig. 46.3 ).
Indications for operative treatment are summarized in Box 46.1 .
Box 46.1
Indications for Operative Treatment in Humerus Shaft Fractures
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