Proximal Humerus Fracture: Reverse Arthroplasty

Matthew L. Ramsey

DEFINITION

Proximal humerus fractures are defined as fractures that occur above the surgical neck of the humerus involving the humeral head, greater tuberosity, lesser tuberosity, and shaft in isolation or in combination.
Codman described these injuries typically occurring along the physeal lines of the humerus. Neer further characterized these fractures in a four-part classification system and defined displaced fractures as those where the fracture fragments are displaced greater than 1 cm and/or angulated greater than 45°.¹
Proximal humerus fractures are the second most common fracture of the upper extremity and represent 5% to 8% of all fractures.
There is a bimodal distribution of these fractures with younger patients typically sustaining higher injury trauma and older patients sustaining these fractures with lower-energy mechanisms of injury. In this older cohort of patients, females sustain these injuries two to three times more often than men and are often associated with osteoporosis.

ANATOMY

The proximal humerus is composed of four parts: the humeral head (articular surface), the greater tuberosity, the lesser tuberosity, and the humeral shaft. The humeral head articulates with the glenoid and is covered with articular cartilage.
The top of the humeral head is on average 8 to 10 mm above the top of the greater tuberosity.
The posterosuperior rotator cuff (supraspinatus, infraspinatus, and teres minor) attaches to the greater tuberosity. The anterior rotator cuff (subscapularis) attaches to the lesser tuberosity. The long head of the biceps lies within the bicipital groove that separates the greater and lesser tuberosity.
The humeral head is normally retroverted between 25° and 35°, although individuals may vary outside of this typical range.
Consideration of reverse shoulder arthroplasty (RSA) for four-part proximal humerus fractures is based on concerns for disruption of the blood supply to the humeral head, which increases the risk of avascular necrosis.
The main blood supply to the humeral head is the arcuate artery, which is a terminal branch of anterior humeral circumflex artery. The posterior portions of the humeral head and greater tuberosity receive their blood supply from branches of the posterior humeral circumflex artery.
The axillary nerve arises from the posterior cord of the brachial plexus and courses laterally and posteriorly below the shoulder joint. It enters the quadrilateral space and curves around the humerus deep to the deltoid innervating the muscle from posterior to anterior.

PATHOGENESIS

There is a bimodal distribution of these fractures, but the majority of these fractures that require RSA occur in elderly patients older than 65 years.
The vast majority of proximal humerus fractures are nondisplaced or minimally displaced and can be treated nonsurgically. However, in older patients with poor bone quality, displacement can occur where surgical intervention is the preferred method of treatment.
Proximal humerus fracture classification was described by Neer to include displacement and/or angulation of the fracture fragments. While the reproducibility of this classification system has been questioned,² being able to classify these injuries guides decision making based on prognosis.
Valgus-impacted fractures have an intact medial periosteum that may preserve some of the blood supply to the humeral head and may be amenable to treatment other than RSA (Figure 32-1).
When the humeral head is separated from the shaft, particularly in elderly patients, the risk of a poor result is heightened and RSA is an appropriate treatment consideration.

FIGURE 32-1 AP radiograph of a valgus impacted 4-part proximal humerus fracture.

NATURAL HISTORY

The vast majority of these fractures are minimally or nondisplaced. Only about 15% of proximal humerus fractures are displaced.¹
Displaced fractures treated nonoperatively can lead to limited function and pain.
The risk of avascular necrosis is notably higher in four-part fractures with loss of the medial periosteal hinge.

PATIENT HISTORY AND PHYSICAL EXAMINATION

A detailed history is elicited from the patient including their age, hand dominance, mechanism of injury, occupational and recreational demands on the extremity, medications that might impede healing, and active smoking status.
An assessment of their psychosocial risk factors is critical in order to define the site of service and any postoperative needs. A routine part of any preoperative evaluation should be a risk assessment that can be a critical factor in successful treatment.
A thorough physical examination needs to be performed in order to identify any associated injuries, the neurovascular status of the extremity, and the functional status of the extremity.
Assessment of the active use of the arm is typically limited by pain and of limited value.
A careful examination of the neurovascular status of the extremity is critical. Assessment of axillary nerve motor function can be difficult because of pain, but axillary nerve sensory function is easier to assess. The vascular status of the extremity is carefully assessed. Peripheral pulses are
examined and compared with the opposite unaffected extremity. Any concern for a vascular injury should be assessed before surgery.
The skin should be inspected for any abrasions or open wounds that might influence timing of treatment. Assessment of the soft tissues of the shoulder for the degree of swelling and ecchymosis is performed.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Standard shoulder images including an anteroposterior in the scapular plane, scapular Y, and axillary view are ideal. However, positioning for an axillary view can be difficult because of pain. In this case a Velpeau view can be helpful.
Vascular injuries are rare but are associated with dislocation of the humeral head and displacement of the humeral shaft medial to the coracoid into the axilla.³
If vascular injury is suspected, a vascular ultrasound scan or an angiogram is required in order to appropriately plan for surgery (Figure 32-2).
Advanced imaging is occasionally required. Magnetic resonance imaging is rarely indicated, but computed tomography² scans can be very helpful in assessing the fracture pattern and quality of the tuberosity fragments. Reformatted 3-dimensional images can provide improved understanding of the fracture pattern (Figure 32-3).

FIGURE 32-2 Angiogram demonstrating injury to the axillary artery.

Note the preserved collateral flow about the shoulder.

FIGURE 32-3 3D reconstructed CT scan demonstrating a 4-part proximal humerus fracture.

NONOPERATIVE MANAGEMENT

The majority of proximal humerus fractures are nondisplaced and can be treated nonoperatively.
Displaced fractures of the proximal humerus do poorly with nonoperative management.
Nonoperative treatment of displaced fractures of the proximal humerus is reserved for patients whose medical and psychosocial comorbidities make them too high risk for surgical intervention.
If nonoperative treatment is elected, the patient is placed in a sling for comfort for the first few weeks. They are encouraged to perform active motion of the elbow, wrist, and hand. When comfort allows, pendulum exercises are initiated.
Once fracture healing is noted radiographically, passive, active-assisted, and finally active range-of-motion exercises are begun.
Realistic expectations for shoulder function must be reenforced as these patients will often have functional limitations.

SURGICAL MANAGEMENT

Shoulder arthroplasty is considered for displaced 3- and 4-part proximal humerus fractures when anatomic reduction cannot be reliably achieved with nonreplacement options.
Hemiarthroplasty has historically been the preferred treatment of unreconstructable proximal humerus fractures. Reproducible results with hemiarthroplasty have been elusive and rely on appropriate implant positioning and tuberosity healing.⁴^, ⁵ ^and ⁶
RSA has become the preferred method for managing these injuries. The intrinsic stability of the implant and the ability of this implant to function reasonably well without tuberosity healing makes this an attractive option in elderly patients with osteoporotic bone.

Patient Positioning

The patient is placed in the beach chair position with the back of the table elevated approximately 30° and a bump under the knees.
A shoulder-specific operating room table with a breakaway back allows free mobility of the operative extremity.
The surgical extremity is prepped and draped to facilitate free mobility of the extremity. The arm can be positioned using a sterilely draped padded Mayo stand or a sterile arm holder (Figure 32-4).
The patients receive a long-acting Exparel (Pacira Biosciences, Parsippany, NJ) interscalene nerve block and a general endotracheal anesthesia.
C-arm fluoroscopy can be used intraoperatively to assess stem placement and adequacy of tuberosity reconstruction. The C-arm should be positioned on the contralateral side of the patient. The ability to obtain adequate imaging should be ascertained prior to prepping and draping the patient. The position of the C-arm where adequate images are obtained is marked to facilitate efficient intraoperative imaging (Figure 32-5).

FIGURE 32-4 Patient positioning for surgery.

The patient is positioned on a shoulder operating room table with the arm draped to allow free movement of the arm during surgery. The arm holder assists with positioning the extremity.