The proximal humerus has three ossification centers: humeral head, greater tuberosity, and lesser tuberosity (Fig. 4.4). The ossification center for the humeral head appears between 4 and 6 months of age; the greater tuberosity, at 3 years; and the lesser tuberosity, at 4–5 years. The tuberosity ossification centers fuse together at 5 years of age [16], and this combined ossification center fuses with the humeral head ossification center between ages 7 and 13 years [17]. The combined humeral epiphysis fuses with the shaft by age 19 years [17]. This period of growth and maturation when the three centers combine to form a common humeral epiphysis may reflect a relative time of weakness in the apophysis of the lesser tuberosity, which may account for the higher incidence of isolated avulsion lesser tuberosity fractures in the adolescent population. In fact, Codman [18] and Neer [19] observed that fractures of the humeral head tend to occur along physeal scar lines, which ultimately form the basis for tuberosity fracture propagation. Researchers have hypothesized that a lesser tuberosity fracture propagates through a thin connection between the lesser tuberosity apophysis and the rest of the proximal humerus apophyseal segment, resulting in a “transitional” fracture in adolescents similar to those seen in tibial tubercle and juvenile Tillaux fractures [8, 20].

The humeral head develops in a retroverted position relative to the long axis of the humerus, which results in medial displacement of the intertubercular groove (Fig. 4.5). Consequently, the lesser tuberosity displaces medially and is smaller than the greater tuberosity. The tendon of the long head of the biceps runs through the intertubercular groove, with the greater and lesser tuberosities forming its medial and lateral walls, respectively [16]. The subscapularis muscle inserts on the lesser tuberosity, with the most superior portion resembling a distinct tendinous structure [16]. Muscular deforming forces from the subscapularis result in medial and inferior displacement of the lesser tuberosity fracture fragment. The biceps tendon within the groove is stabilized by the transverse humeral ligament and by fibers from the most superior portion of the subscapularis tendon (Fig. 4.6). In a clinical anatomic study, Arai et al. [21] demonstrated that the most superior insertion of the subscapularis tendon and the superior part of lesser tuberosity are important stabilizers, preventing medial dislocation of the biceps tendon.

A thorough understanding of the vascular supply of the humeral head is essential for treating proximal humerus fractures, allowing the surgeon to avoid damaging vital structures either by direct means or indirectly through aberrant retractor placement and inadvertent disregard for the soft tissue envelope (Fig. 4.7).

The blood supply to the humeral head consists of an extensive anastomic arterial network arising from branches of the subclavian and axillary arteries. The primary blood supply to the rotator cuff is derived from the ascending branch of the anterior humeral circumflex artery, the acromial branch of the thoracoacromial artery, the posterior humeral circumflex artery, and the suprascapular artery [22]. The main supply to the humeral head is divided between the anterolateral branch of the anterior humeral circumflex artery and the posterior humeral circumflex artery. In their qualitative anatomic study, Gerber et al. [23] concluded that the primary blood supply to nearly the entire humeral epiphysis derived from the anterolateral branch of the anterior humeral circumflex artery, whereas the posterior humeral circumflex artery vascularized the posterior aspect of the greater tuberosity along with a small posteroinferior aspect of the humeral head. Hettrich et al. [24] contradicted this finding in a more recent quantitative study, elegantly showing that the posterior humeral circumflex artery supplies 64 % of the blood supply to the overall humeral head and the anterior humeral circumflex artery is responsible for 36 % of the vascular load. When open approaches to the shoulder are performed, protection of the posterior soft tissue envelope and careful manipulation of fracture fragments are critical to avoiding further vascular insult to the humeral head.

Through small tributary branches, the anterior humeral circumflex artery supplies the lesser tuberosity and the subscapularis tendon as it inserts on the tuberosity before it divides into the terminal arcuate artery [16] (Fig. 4.7). The arcuate artery enters the intertubercular groove to provide the major intraosseous supply to the humeral head [25]. The tuberosities also receive vascularity from multiple extraosseous anastomoses between circumflex arteries and surrounding thoracoacromial, suprascapular, and subscapular arteries, which explains the low incidence of humeral head osteonecrosis with isolated tuberosity fractures [3].

The greater and lesser tuberosities serve as attachment points for the rotator cuff muscular network. Familiarity with the insertion pattern is critical to understanding tuberosity fractures, as displacement can occur along the lines of pull for these muscles. The subscapularis insertion onto the lesser tuberosity measures approximately 6.0 cm and consists of two anatomically distinct regions: an upper 60 % tendinous portion designed for strength and a lower 40 % muscular insertion allowing for further excursion [26]. The greater tuberosity, which can be divided into the superior, middle, and inferior facets, serves as the insertion for the supraspinatus, infraspinatus, and teres minor (Fig. 4.8). The supraspinatus attaches to the superior facet and the superior half of the middle facet, whereas the infraspinatus attaches to the entire length of the middle facet, overlapping the supraspinatus on the bursal side at the superior half of the middle facet (Fig. 4.9). The teres minor inserts onto the inferior facet of the greater tuberosity [27]. Fractures of the lesser tuberosity, therefore, tend to displace medially along the pull of the subscapularis, whereas fractures of the greater tuberosity tend to displace proximally and posteriorly along the pull of the external rotators. Inferior displacement of the greater tuberosity fragment also has been described and is most likely the result of the mechanism of injury rather than the pull of the rotator cuff muscles [28].

The lesser tuberosity is protected from direct injury by its small size and its location on the medial side of the humeral head. Authors of larger case series reporting on isolated lesser tuberosity fractures in adults have demonstrated that these fractures typically occur in young to middle-aged men and often result from high-energy events, such as falls from a height, motorcycle accidents, or high-contact sports [5, 6, 29]. Most patients cannot describe the exact details of injury because of the rapid sequence of energy transfer during the injury. However, the injury can be hypothesized to occur from a fall on an outstretched upper extremity with avulsion of the lesser tuberosity due to eccentric contraction of the subscapularis tendon when the extremity is forced into abduction or external rotation [3, 5]. A second mechanism of injury resulting in isolated lesser tuberosity fractures is described in the adult population with two-part posterior fracture-dislocations. These patients have injuries from seizures or electroconvulsive therapy for psychiatric disorders that result in posterior shoulder dislocations. As the shoulder dislocates posteriorly, sudden involuntary contraction of the subscapularis combined with a shear force on the lesser tuberosity against the anterior glenoid rim results in a tuberosity fracture [30]. In patients with locked posterior fracture-dislocations, the lesser tuberosity fracture propagates from the acute osteochondral fracture on the anterior humeral head (reverse Hill-Sachs defect) as it engages on the posterior glenoid rim [30–32].

In adolescents, isolated lesser tuberosity fractures result from high-energy falls during sports [6, 33, 34]. More specifically, contact sports, such as martial arts or wrestling [6], and overhead sports [35–37] have been identified. Three different mechanisms have been described to account for these injuries. Similar to adults, the first and most common mechanism is an avulsion through the lesser tuberosity apophysis with the shoulder in a forced sudden abduction and external rotation movement and the subscapularis muscle eccentrically contracting to resist this force [6, 33]. The second mechanism is an axial load along the long axis of the humerus applied to the extended and externally rotated shoulder. For example, when an athlete falls down backward with the upper extremity extended, the contact of the hand against the ground results in an axial load, causing anterosuperior migration of the humeral head and increasing tension on the subscapularis and superior glenohumeral ligament. This sudden increase in tension results in a fracture from traction on the lesser tuberosity through eccentric contraction of the subscapularis [35]. The third mechanism of injury occurs in adolescent overhead throwing athletes and results from microtrauma or repetitive injury leading to an incomplete traction injury of the lesser tuberosity. In these patients, repetitive contraction of the subscapularis results in a fatigue failure of the lesser tuberosity, and occasionally slow displacement of all or a portion of the tuberosity occurs over time [36, 37].

Various mechanisms of injury for tuberosity fractures have been proposed in the literature; however, the exact pathomechanics remain controversial [3, 38]. Some researchers have proposed an avulsion-type mechanism where the rotator cuff musculature pulls against a dislocating shoulder, resulting in an avulsion of the greater or lesser tuberosities [39–41]. This type of mechanism seems likely in a pediatric patient in whom unfused ossification centers are relatively weak compared with the strong tendon attachment, subsequently resulting in a Salter-Harris type of avulsion fracture.

Bahrs et al. [28] concluded that a specific mechanism of injury must exist either directly, such as a direct blow to the shoulder or a fall onto the shoulder, or indirectly, such as through a fall on the outstretched upper extremity, flexed elbow, or extreme abduction and external rotation. We submit an elaboration to the theory of an avulsion mechanism, contending that all fractures of the tuberosities are direct creations of a “subcortical weak link.” This weak link is created through a direct impact-type mechanism and the forceful eccentric load of the rotator cuff. This direct impact could be with the acromion, coracoid, or glenoid rim and may occur in the setting of humeral head malposition, dislocation, or subluxation during an injury.

Both adolescents and adults with lesser tuberosity fractures present with similar symptoms. They are often unaware of the details regarding the mechanism of injury. Most patients present with the injured extremity held close to the axial skeleton in an antalgic position and report nonspecific tenderness over the anterior aspect of the shoulder. In the acute setting, patients have symptoms similar to those with a rotator cuff tear, including nighttime pain and activity-related pain exacerbated by placing the shoulder in an externally rotated position [3].

Physical examination should include a thorough evaluation with inspection, palpation, range-of-motion testing, strength testing, neurovascular examination, and provocative testing of the shoulder for early diagnosis and treatment. Inspection of the shoulder may reveal swelling and ecchymosis extending into the axilla and distally into the arm. Tenderness over the anterior aspect of the shoulder, the lesser tuberosity, and even coracoid may or may not be present depending on the chronicity of the injury. Range-of-motion testing reveals pain with passive external rotation in the acute setting; however, patients often present with hyperexternal rotation and decreased internal rotation of the involved extremity compared with the contralateral side in the chronic setting [6]. Patients may not be able to tolerate manual muscle testing with resistance to internal rotation due to pain. Examination findings of weakness with internal rotation on manual muscle testing and weak lift-off and positive belly-press signs should increase the examiner’s suspicion for a lesser tuberosity injury and heighten the process to confirm or refute this suspicion [2, 7]. With acutely or chronically displaced lesser tuberosity fragments, patients often have impingement with the coracoid or conjoined tendon [42, 43]. In the chronic setting, patients often present with significant anterior apprehension with the upper extremity in 90° of abduction and external rotation. It is unclear if this apprehension occurs due to a loss of the anterior stabilizing effect of the subscapularis or due to associated capsuloligamentous injuries [33, 44]. Patients with associated dislocation of the long head of the biceps tendon often present with pain in the bicipital groove, weakness on strength testing, and a provocative Speed’s or O’Brien’s test [34, 45].

In a recent case series involving adolescent overhead athletes who had delayed presentations with displaced lesser tuberosity avulsion fractures, Neogi et al. [35] presented a diagnostic treatment algorithm for early detection of these injuries via physical examination and appropriate imaging to avoid long-term sequelae of missed injuries in patients who have confounding initial presentations (Fig. 4.10).

The presence or history of previous anterior dislocation should alert the examiner to the possibility of a greater tuberosity injury. The presence or history of a posterior dislocation instead should alert the examiner to the possibility of a lesser tuberosity fracture. Documentation of a detailed neurovascular examination is imperative to ruling out a concomitant arterial or nerve injury that can be associated with these fractures.

In non-displaced or minimally displaced fractures of the tuberosities, physical examination findings frequently are similar to those seen in acute rotator cuff pathologic lesions. In both scenarios, pain is present on palpation of the tuberosity and also is elicited during resisted muscular testing of the rotator cuff [46]. The examiner must possess a high index of suspicion because isolated fractures of the greater tuberosity can be overlooked or misdiagnosed as rotator sprains or rotator cuff tears. Ogawa et al. [46] determined that the rate of missed diagnosis was 64 % in one-part isolated greater tuberosity fractures and 27 % in two-part fractures. Most missed fractures occurred at the supraspinatus fossa of the greater tuberosity, with smaller fragments possessing a significantly higher rate of missed diagnosis [46].