Anatomy and Classification of Proximal Humerus Fractures

Fig. 1.1

The average humeral neck angle is 130°. The superior aspect of the articular surface is 8 mm above the greater tuberosity. Average retroversion values are 18–33°

The proximal humeral articular surface is a segment of a sphere that measures from 37 to 57 mm in diameter [5]. The average neck angle is 130°. The humeral head average offset from the shaft is 3 mm posterior and 7 mm medial. The most superior portion of the humeral head is typically 8 mm above the height of the greater tuberosity [2]. Humeral retroversion has been found to vary widely with reported average values ranging from 18° to 33° [5–9]. Retroversion has been found to average 4° more in the dominant shoulder [7]. Wide ranges in retroversion values have led to the use of bony landmarks, such as the bicipital groove, in proximal humerus reconstruction. Strong bone can be found in the subchondral area of the head; however, the cancellous bone of the proximal humerus does lose density with aging [10–12].

Musculature

The pectoralis major has a broad insertion along the lateral lip of the bicipital groove. It acts as a major deforming force in proximal humerus fractures as it causes the humeral shaft to be displaced anteriorly and medially. The supraspinatus, infraspinatus, and teres minor attach to their respective facets on the greater tuberosity. The supraspinatus can cause superior displacement while the infraspinatus can cause posterior displacement of greater tuberosity fragment. The tuberosity can be a single fragment or multiple with the cuff tendons attached to independent fragments. The lesser tuberosity is the site of attachment of the subscapularis; lesser tuberosity fragments can be displaced medially by the pull of the subscapularis tendon (Fig. 1.2).

Fig. 1.2

Displacement of fracture fragments is determined by the pull of the attached muscles

In three-part proximal humerus fractures with either a greater or lesser tuberosity fracture the displacement of the head fragment will be dictated by the rotator cuff insertion to the intact tuberosity. If the greater tuberosity is fractured but the lesser tuberosity is intact, then the head fragment will rotate internally from the attachment of the subscapularis. In three-part lesser tuberosity fractures the humeral head segment rotates externally from the pull of the infraspinatus on the intact greater tuberosity.

Vascular

Outcomes after proximal humerus fractures are affected by the fracture pattern and its relationship to the vascular anatomy. Understanding the local vascular anatomy is important to understanding this relationship. The perfusion of the proximal humerus is derived from terminal branches of the axillary artery, the anterior and posterior humeral circumflex arteries. Due to the location of these vessels in close proximity to the fracture, they can be injured in significantly displaced fractures and fracture-dislocations.

The anterior humeral circumflex artery arises from the axillary artery and courses along the inferior border of the subscapularis. The artery gives off an anterolateral ascending branch that courses along the lateral aspect of the bicipital groove before entering the humeral head and becoming the arcuate artery. The main portion of the anterior humeral circumflex vessel continues posterolaterally to anastamose with the posterior humeral circumflex vessel. There are numerous extraosseous anastomoses with the anterolateral branch and ligation of the anterior humeral circumflex proximal to these can be compensated by this collateral circulation. The posterior humeral circumflex artery arises from the axillary artery and travels with the axillary nerve through the quadrilateral space before it goes on to its anastomosis with the anterior humeral circumflex artery. Posteromedially it gives off branches that enter the humeral head (Fig. 1.3).

Fig. 1.3

Vascular supply of the proximal humerus

Based on the work of Laing and Gerber et al. [13, 14] it has been believed that the anterolateral branch of the anterior humeral circumflex artery is the main source of perfusion of the humeral head with the posterior vessels only perfusing a small portion of the head. Later work by Brooks et al. [15] agreed that the head was predominantly perfused by the anterolateral branch. However, they found that even after ligation of this vessel as it enters the head, the head could be well perfused by intra-osseous anastomoses with the posteromedial vessels, metaphyseal vessels, and branches from the greater and lesser tuberosities. In a study [16] performed on patients with proximal humerus fractures the anterior humeral circumflex vessel was found to be disrupted in 80 % of cases. The posterior vessel was found to be normal in 85 % of cases. While rates of avascular necrosis after three-part and four-part fractures have been reported in the literature to range from 0 to 34 % [17–28], these findings would suggest a much higher rate of avascular necrosis should be seen if the anterolateral branch is the main source of perfusion for the head. A recent study [29] used MRI imaging to do a quantitative analysis of the perfusion of the humeral head. Their work identified that 64 % of the humeral head blood supply was derived from the posterior humeral circumflex artery and the anterior vessel only accounted for 36 % of the perfusion. The authors questioned the methodology of the earlier literature and felt their improved methods allowed them to better assess the perfusion of the humeral head.

Nerves

The shoulder is innervated by the brachial plexus (C5-T1 nerve roots) with small contributions from the C3 and C4 nerve roots. The nerve roots give rise to the upper (C5–6), middle (C7), and lower (C7-T1) trunks. The trunks are the source for the lateral, posterior, and medial cords of the plexus which are named according to their relationship to the axillary artery. The axillary nerve and subscapular nerves arise from the posterior cord; they innervate the deltoid and teres minor as well as the subscapularis, respectively. The suprascapular nerve arises from the upper trunk and innervates both the supraspinatus and the infraspinatus. Articular innervation is primarily from branches of the axillary, suprascapular, and lateral anterior thoracic nerves [30].

In a study of 143 consecutive patients with low energy proximal humerus fractures nerve injuries were documented by EMG in 67 % of patients [31]. The axillary nerve was the most commonly injured nerve. After arising from the posterior cord it passes through the quadrilateral space, wraps around the humerus, and then runs on the deep surface of the deltoid. It gives off three motor branches that innervate the teres minor and the deltoid. The lateral brachial cutaneous nerve arises from the axillary and penetrates through the deltoid to innervate the overlying skin. Anatomic studies have shown the nerve to pass an average of 1.7 cm from the surgical neck of the proximal humerus [32].

The suprascapular nerve is the second most commonly injured nerve in proximal humerus injuries. The nerve arises from the upper trunk and then passes through the scapular notch before innervating the supraspinatus. It then passes around the base of the scapular spine and through the spinoglenoid notch to innervate the infraspinatus. It is susceptible to traction injury at its origin from the upper trunk and as it passes through the scapular notch [31, 33].

The musculocutaneous nerve originates from the lateral cord with input from the C5–C7 nerve roots. It passes through the conjoined tendon at an average distance of 5.6 cm from the coracoid process, but can be found as close as 3.1 cm [34]. After innervating the flexor compartment of the arm it terminates in the lateral antebrachial cutaneous nerve. Injury to this nerve is uncommon but can occur with blunt trauma, traction injuries, or iatrogenic injuries during surgery.

Pathomechanics of Proximal Humerus Fracture

The most common mechanism of injury for a proximal humerus fracture is a fall on an outstretched arm in an elderly patient with osteoporotic bone [1]. The fracture can be caused by a direct blow to the upper arm or occur when the humeral head strikes the glenoid or the acromion [35]. Less frequently, fractures are seen in younger patients after high-energy injuries such as motor vehicle accidents or falls from a height. A rare potential mechanism is violent muscle contraction caused by electric shock or seizure [36].

Isolated greater tuberosity fractures are a common injury making up approximately 20 % of proximal humerus fractures and 5 % of fractures treated with surgery [37]. Tuberosity fractures can be due to multiple mechanisms [38]. These include a direct blow in a fall onto the shoulder or a shearing mechanism as the tuberosity strikes the glenoid rim or acromion. The fracture can also be caused by avulsion from the pull of the rotator cuff tendons. Greater tuberosity fractures are commonly seen in anterior dislocations as the tuberosity is fractured as it contacts the glenoid rim. Isolated lesser tuberosity fractures are much less common accounting for approximately 2 % of proximal humerus fractures [37].

Diagnosis

History and Exam

The most common patient with a proximal humerus fracture is an elderly patient who has sustained a ground level fall. Younger patients sustain this fracture after higher energy injuries. Regardless of mechanism the entire extremity should be assessed for any evidence of other injury. In patients with higher energy injuries care should be taken to observe for evidence of rib fractures, scapula fractures, head or spine injuries, and intra-abdominal or intra-thoracic injuries.

The history should include the age and hand dominance of the patient. The mechanism and velocity of injury should be recorded. Occupation and the patient’s premorbid level of function should be noted. The patient should be assessed for the ability to participate in a structured rehabilitation program. A thorough medical history should be obtained including the presence of any significant comorbid conditions and any history of malignancy. Any previous shoulder surgeries to the affected shoulder should be noted. The review of systems should include loss of consciousness, any paresthesias, and any elbow, wrist, or hand pain of the affected extremity.

Ecchymosis and swelling of the shoulder are common physical exam findings. These will appear in the first 24–48 h after injury and can be present for many days. Ecchymosis and swelling can extend to affect the entire extremity down to the level of the hand, as well as affect the chest wall and the breast. The condition of the skin should be examined. Crepitus can sometimes be felt as the shoulder is palpated and range of motion is attempted. The examiner can attempt to assess fracture stability by palpating the humeral head while gently rotating the humeral shaft. In stable fractures the head and shaft will move as a single unit. Patients will often have significant pain and hold the arm in an internally rotated position. The patient will guard against significant active or passive range of motion. A complete neurovascular evaluation including an evaluation of the axillary nerve, brachial plexus, and vascular status should be performed. The surgeon should be concerned for a possible axillary artery injury in a four-part fracture dislocation with axillary dislocation of the humeral head. A palpable radial pulse does not completely rule out the possibility of vascular injury and an angiogram should be obtained.

Imaging

X-Rays

Radiographic evaluation is typically sufficient for assessment and classification of a proximal humerus fracture. Carefully positioned radiographs can give detailed information about fracture pattern and displacement. The surgeon should be prepared to position the patient if necessary to obtain the needed views. Radiographic evaluation will usually include an AP scapular view (true AP), axillary lateral view, and a scapular Y view.

The AP scapular view or true AP view requires understanding of shoulder anatomy to properly obtain the film. The scapula is not positioned in the coronal plane on the chest wall; it sits approximately 30°–40° angled anterior from the coronal plane. To obtain the AP view the unaffected shoulder is angled approximately 40° toward the beam to allow the affected side to lie flat against the X-ray plate (Fig. 1.4). AP views taken with the arm in external rotation (greater tuberosity) and internal rotation (lesser tuberosity) can be useful in evaluation of tuberosity fractures.

Fig. 1.4

Scapular AP radiograph technique

The scapular Y view can be obtained with the arm maintained in a sling. The patient is positioned with the anterior aspect of the shoulder against the X-ray plate. The unaffected shoulder is rotated towards the beam approximately 40° (Fig. 1.5).

Fig. 1.5

Scapular Y radiograph technique

The axillary lateral view is vital for assessing the position of the greater tuberosity, the glenoid articular surface, and the relationship of the humeral head to the glenoid. The X-ray is obtained by placing the cassette on the superior aspect of the shoulder. The arm is held in a position abducted away from the body. The X-ray beam is then directed cephalad from a position inferior to the shoulder with the beam aimed at the axilla of the patient (Fig. 1.6). The Velpeau axillary lateral is an alternative for the patient that cannot tolerate abducting the arm for the axillary lateral. This view is taken with the arm in a sling. The cassette is placed on a flat surface. The patient then leans back over the cassette as the X-ray beam is aimed from superior to inferior at the cassette (Fig. 1.7).

Fig. 1.6

Axillary lateral radiograph technique

Fig. 1.7

Velpeau lateral radiograph technique

CT

Computed tomography (CT) images can be a useful tool in evaluation and classification of proximal humerus fractures. The detailed bony detail of images can be used to evaluate tuberosity displacement, humeral head splitting and impaction components, degree of comminution, and any involvement of the glenoid articular surface (Fig. 1.8). The advent of three dimensional reconstruction views has been a useful advance to allow the surgeon to further assess fractures (Fig. 1.9). While traditional two-dimensional CT has not been shown to improve the reliability of classification, the use of three-dimensional imaging has been shown to improve both intra- and inter-observer reliability of both the AO/ASIF and the Neer classification system [39].

Fig. 1.8

This axial CT image demonstrates a head-split component as well as comminution of the tuberosity fragments

Fig. 1.9

Three dimensional CT imaging can further enhance the surgeon’s ability to characterize fractures. The comminuted tuberosity fragments with extension into the articular surface are visualized in this CT image

MRI

Magnetic resonance imaging (MRI) plays a limited role in the assessment of acute proximal humerus fractures. While playing a limited role in assessment of acute fractures MRI can be useful in diagnosing non-displaced greater tuberosity fractures (Fig. 1.10).

Fig. 1.10

MRI images clearly show this minimally displaced greater tuberosity fracture

Classification

History

As early as the late nineteenth century efforts were made to classify proximal humerus fractures. Kocher described proximal humerus fractures based on location of the fracture [35, 40]. Fractures were divided into supratubercular, pertubercular, infratubercular, and subtubercular. In 1934 Codman described proximal humerus fractures as occurring along the lines of the epiphyseal scars. He noted four possible fracture fragments: the articular surface, the humeral shaft, the greater tuberosity, and the lesser tuberosity (Fig. 1.11). Codman stressed the importance of vascular considerations to fractures of the articular segment of the proximal humerus [1, 35, 41].

Fig. 1.11

Codman’s fragments: articular surface, greater tuberosity, lesser tuberosity, and humeral shaft

Later classification systems attempted to classify fractures based on mechanism of injury [42, 43]. The Watson-Jones classification system was published in 1940 and described fractures that occurred by impacted abduction, impacted adduction, and minimally displaced “contusion-crack” fractures. Dehne’s classification system, published in 1945, also classified fractures based on the mechanism of injury. He felt that forced abduction created a “three-fragment” fracture with head, greater tuberosity, and shaft fragments. Forced extension created a “two-fragment” fracture with the humeral head separated from the shaft at the surgical neck. Impaction of the head into the glenoid created “head-splitting” fractures. Dehne did not include lesser tuberosity fractures in his classification but did recognize the presence of more complex fractures and fracture-dislocations. The utility of classification of these injuries by mechanism is limited. As recognized by Neer [44] abduction and adduction injuries could be mistaken for each other due to differing rotation of the arm during radiography (Fig. 1.12). These systems do not assess the details of fracture anatomy and management is not dictated by these systems due to fact that there is no correlation between mechanism and outcomes [45].

Fig. 1.12

Classification by mechanism can be a source of confusion. The left radiograph shows a valgus positioned adduction fracture. The right film shows a varus positioned abduction fracture. The films are actually internal and external views, respectively, of the same malunited fracture

In 1950 De Anquin and De Anquin proposed a classification that divided the proximal humerus into three fracture zones and fragments. In their work they noted a difference between impacted and non-impacted four-part fractures [35, 46]. Like Codman, they stressed the importance of vascular considerations on fractures that involved the articular segment [1, 46]. Depalma recognized the roll that displacement had on vascular status when he differentiated between fracture dislocations when there was a complete loss of contact between the humeral head and the glenoid surface and those with a rotational deformity but the head remained within the capsule [47].

Neer utilized Codman’s idea of four possible fracture fragments when he developed his classification system [44]. Published in 1970, his system was based on an observation study of 300 displaced proximal humerus fractures (Fig. 1.13). He focused on the patterns of displacement rather than the location of fracture lines. His retrospective study attempted to correlate the classification with outcomes. He attempted to identify which fracture types were best treated with open reduction and to identify which fracture types had a high risk of avascular necrosis and were best treated with prosthesis [28].

Fig. 1.13

Neer classification scheme as originally depicted in 1970 (Reprinted with permission from ref. [44])

Developed in the 1980s the AO/ASIF classification system was an attempt to make a classification system that was inclusive of all fracture types [17, 48]. The system includes 27 subgroups distinguished by articular surface involvement, location, and degree of comminution and dislocation (Fig. 1.14). There is an emphasis placed on the integrity of the vascular supply to the humeral head. There is a distinction made between valgus-impacted four-part fractures and the classic four-part fracture described by Neer [17]. The valgus-impacted fracture has an intact medial soft tissue hinge and a much lower observed rate of avascular necrosis. The cumbersome nature of this system has led to minimal utilization of it on a regular basis. However, when compared to the Neer classification system, it has shown similar inter- and intraobserver reliability [49]. There are no long-term studies evaluating treatment based on the AO classification system.