Introduction
Humeral shaft fractures are defined as fractures in which the major fracture line occurs distal to the insertion of the pectoralis major and proximal to the supracondylar ridge. It is estimated that these fractures comprise 3-5% of all fractures in adults. Epidemiologic studies have clearly demonstrated the incidence had a bimodal distribution with a small peak in the third decade for men and much larger peak in the seventh decade for women. There appears to be a clear association between fractures of the humeral shaft and osteoporosis with an increasing incidence from the fifth decade onward. In the young adult, these fractures usually occur due to direct high energy trauma or penetrating trauma, while in the elderly, the most common mechanism is a fall from a standing. Humeral shaft fractures in the elderly should be considered to have occurred through pathologic osteoporotic bone and thus, osteoporosis evaluation and treatment and fall prevention are indicated.
Anatomy
The humeral shaft comprises the portion of the humerus between the region just distal to the surgical neck to the area immediately proximal to the supracondylar ridge. The proximal portion of the diaphysis is cylindrical and tapers to a triangular shape distally. The medullary canal also diminishes in diameter and ends just superior to the olecranon fossa. This abrupt tapering of the humeral canal differs from the canal of the femur and tibia in which the metaphysis widens. Unfamiliarity with this anatomy may lead to distraction of humeral shaft fractures during antegrade humeral nailing.
The humerus has an abundant vascular supply and is enveloped in soft tissue which aides in healing. The medial and lateral muscular septa divide the arm into anterior and posterior compartments. The median nerve, musculocutaneous nerve and brachial artery traverse the anterior compartment. The ulnar nerve begins proximally in the anterior compartment and passes through the medial intermuscular septum to enter the posterior compartment near the distal third of the humerus. The radial nerve begins in the posterior compartment and crosses the posterior aspect of the humerus 20 cm proximal to the medial epicondyle and 15 cm proximal to the lateral epicondyle in a region known as the spiral groove. The radial nerve then passes through the lateral intermuscular septum to enter the anterior compartment.
Classification
Classification of these fractures has historically been descriptive. The fracture is often described as open or closed, by the location within the humeral shaft (proximal, middle or distal third) and overall character of the fracture pattern (transverse, oblique, spiral, comminuted). The Orthopaedic Trauma Association Classification may be used for more formal classification of the fracture types.
Presentation
Humeral shaft fractures in younger patients tend to occur through direct impact to the humerus while in the elderly these fractures are often isolated injuries suffered after a fall from standing. The patient will typically present with arm pain, swelling and often visible deformity.
In the elderly patient, the cause of the fall will need to be investigated as it may have occurred secondary medical comorbidities.
Diagnosis
Radiographic evaluation should include AP and lateral view of the entire humerus, including the humeral head and elbow on a single radiograph (Fig. 11). In order to obtain the orthogonal views, the cassette or patient should be moved, as moving the arm will cause rotation of the distal fragment through the fracture site. Appropriate well-padded splinting or immobilization should be applied for immediate comfort until definitive treatment is rendered.
The patient should be fully assessed for associated injury and the skin over the humerus inspected for open fracture. A detailed nerurovascular exam should be performed and documented as injury to the radial nerve has been reported to occur in up to 18% of these fractures. Vascular injury is rare, but constitutes an emergency when present.
Treatment
Most humeral shaft fractures are successfully managed non-operatively. The tremendous range of motion of the glenohumeral joint allows for functional compensation of moderate malunion and shortening. It is generally accepted that up to 3cm of shortening and 20-30 degrees of varus, anterior or rotational deformity will result in an acceptable upper extremity function.
The current standard of care for non-operative treatment is the application of a functional brace with or without closed reduction once initial swelling has subsided. Functional bracing consists of a circumferential off-the-shelf orthosis secured with Velcro straps and a cuff and collar to support the forearm. A sling should be avoided as it may contribute to varus angulation. The brace should extend as far proximally into the axilla as the patient's skin and neurovascular structures can tolerate. This is especially important for fractures of the proximal third of the shaft.
The functional brace works through three basic principles. The first is the hydraulic effect, in which circumferential compression helps to achieve reduction, restore humeral length and confer stability. The second is that active muscle contraction within the brace will aid reduction. Lastly, the effect of gravity will counteract shortening and aid fracture reduction.
While the majority of humeral shaft fractures are appropriately treated non-operatively, there are humeral shaft fractures which are best treated operatively to ensure optimal function. The indications for operative intervention for humeral shaft fractures include: segmental fractures; floating elbow injuries; transverse diaphyseal fractures; open fractures; nonunions; and polytraumatic injuries in which partial upper extremity weight bearing would facilitate recovery of other injuries and allow early patient mobilization. The effects of associated trauma should also be considered when treating a humeral shaft fracture. Associated injuries, especially lower extremity fractures, may necessitate upper extremity weight bearing to avoid the detrimental effects of inactivity, deconditioning and bedrest, thus making operative intervention an option. Humeral plating has been shown to allow for upper extremity weight bearing and crutch or walker assisted ambulation 278-280.
For nonunions, plate stabilization with bone grafting often leads to union and is the treatment of choice. Less common indications for operative treatment include nerve deficit after reduction, segmental fractures and open fractures. Additionally, obesity, large breasts and frail skin may make functional bracing technically impossible and would also be indications for surgery.
Humerus can be approached via anterolateral approach for proximal third fractures or the posterior approach for middle and distal third fractures. Radiographs of the opposite humerus may be helpful in preoperative planning of comminuted fractures. Plate should purchase 8 cortices.
External fixation may be used for severe open fractures.
Complications
Radial nerve palsy has been reported to occur in up to 18% of these fractures. More common in middle and distal third fractures.
Beware of soft tissue pressure in the axilla when applying a coaptation splint.
Nonunion is rare but more common with transverse fractures and segmental and open fractures.
Malunion may not affect function.
Vascular injury is extremely rare but constitutes an emergency.
Red Flags and controversies
The timing of the application of the functional brace is somewhat controversial. Some prefer the initial application of a coaptation splint for more immediate immobilization until soft tissue swelling has subsided. Conversion to a functional brace then occurs 1-2 weeks after injury. Others prefer immediate application of a functional brace. Regardless of timing, early shoulder, elbow, wrist and hand therapy should be instituted.
Humeral Plating vs. Intramedullary nailing: Humeral plating is generally the treatment of choice when operative intervention is indicated. Nonunion rates have been higher for intrmedullary nailing for nearly all series reported
Locked plates vs. traditional plating
Outcomes
It is generally accepted that up to 3cm of shortening and 20-30 degrees of varus, anterior or rotational deformity will result in an acceptable upper extremity function.
A large series of patients treated with functional bracing found a 2% non-union rate in closed fractures and a 6% non-union rate in open fractures. This study also found that over 80% of patients healed with <16 degrees of angulation and 98% of patients had minimal loss of shoulder motion. 478-486.
For nonunions, plate stabilization with bone grafting often leads to union and is the treatment of choice.
