Fractures of the proximal part of the humerus represent 4% to 5% of all fractures1,2. Older individuals are more likely to sustain these injuries: 71% of proximal humeral fractures occur in patients over the age of sixty years3,4. As the population ages, such data suggest a potential increase in the total number of proximal humeral fractures. Some authors have estimated a threefold increase in the upcoming thirty years5. Neer asserted that most proximal humeral fractures are minimally displaced or nondisplaced, allowing nonoperative treatment to yield high rates of union and functional restoration6; however, a recent multicenter study noted that 64% were displaced7. Management strategies for displaced fractures have evolved recently because of advances in technology and improved understanding of pathophysiology. Unless contraindications exist, the recommended general strategy for the management of displaced proximal humeral fractures is operative, with use of various forms of internal fixation. These include pins, screws, tension-band wires, plate and screw constructs, heavy sutures, and intramedullary devices. Arthroplasty, which has also undergone dramatic advances in recent years, is an additional option. Each technique has particular indications, and each is subject to its own set of potential complications. Therefore, familiarity with all of these techniques is essential for the practitioner caring for fractures of the proximal part of the humerus.
To understand the pathophysiology of fractures of the proximal part of the humerus, knowledge of the osseous, muscular, and vascular anatomy is imperative. The commonly used classification schemes rely on this anatomy as do the deforming forces that must be overcome by reduction maneuvers and fixation. Furthermore, prognostic information is a direct correlate of the specific sites of anatomic disruption. The proximal part of the humerus initially had a primary ossification center and two secondary ossification centers (greater and lesser tuberosities) that fuse, but as Codman first recognized, fractures tend to occur along these physeal lines, even with skeletal maturity6.
The supraspinatus, infraspinatus, and teres minor muscles attach to the greater tuberosity and exert abduction and external rotation forces. The subscapularis tendon attaches to the lesser tuberosity and exerts a medial and internal rotation vector. The deltoid, pectoralis major, and latissimus dorsi muscles all insert distal to the tuberosities. The pectoralis major muscle is a strong deforming force, and it is important to recognize this during reduction maneuvers and when fracture fixation is selected and placed8.
The vascular anatomy of the proximal part of the humerus is complex, and has implications for the risk of the development of osteonecrosis of the humeral head after a fracture. The principal vascular supply to the humeral head is via the anterolateral branch of the anterior humeral circumflex artery, which arises from the axillary artery9,10. The anterior circumflex system courses at the inferior border of the subscapularis tendon near its insertion to the lesser tuberosity, and then underneath the biceps tendon to penetrate bone at the superomedial border of the greater tuberosity9,11,12. A relatively minor segment of the posteromedial aspect of the humeral head is directly supplied by the posterior circumflex artery9. There is a rich network of other arteries, including the profunda brachii, thoracoacromial, subscapular, and suprascapular arteries10, that can sustain the humeral head even in the event of injury to both circumflex systems or axillary artery disruption13,14. An injury in which both tuberosities are fractured with a concomitant metaphyseal fracture places the patient at high risk for osteonecrosis of the humeral head15. The operating surgeon must be aware of this risk to make educated decisions about fixation or arthroplasty, the importance of anatomic reductions, as well as to appropriately counsel the patient.
The most widely used classification scheme for proximal humeral fractures is the Neer classification system6,16,17. In this system, the humeral articular surface, greater tuberosity, lesser tuberosity, and humeral shaft are considered the parts of the proximal aspect of the humerus. A part is considered to be displaced if it is angulated ≥45° or displaced ≥1 cm. Recently, a valgus-impacted subset of four-part fractures was added18. This is an important addition because valgus-impacted fractures retain an intact medial calcar hinge, which makes them biomechanically relatively stable and likely to have a preserved blood supply to the humeral head. Therefore, percutaneous fixation is a viable option and the prognosis is good8. Head-splitting fractures and large (>40%) humeral impression fractures compose a separate category, for which arthroplasty is considered.
The AO classification system is based on the vascular supply to the humeral head19. It consists of three main types: extra-articular unifocal, extra-articular bifocal, and intra-articular. Each type contains three subtypes based on the severity of the injury as indicated by displacement, comminution, or glenohumeral joint dislocation. This scheme is more complex than the Neer classification system, yet there is no evidence that it is more reliable17,20.
Evaluation of the patient with a fracture of the proximal part of the humerus begins with a history and physical examination. Relevant medical comorbidities must be identified. A social history should be obtained to assess the patient's level of activity and demand on the shoulder, as well as his or her expectations after intervention. Physical examination should begin with assessment of the skin condition and the neurovascular status. Motor function of the deltoid muscle should include voluntary isometric contraction of all three heads. Palpation of the distal pulses and careful inspection for signs of arterial injury should be performed acutely. Any question about vascular compromise should prompt Doppler examination and, if necessary, angiography.
Imaging assessment begins with a standard series of radiographs, including anteroposterior, true anteroposterior, axillary lateral, and scapular-Y radiographs of the proximal humeral fracture. Anteroposterior radiographs with the arm in internal and external rotation may better characterize tuberosity fractures or occult fractures of the surgical neck. Computed tomography (CT) can provide additional information for both classification and preoperative planning21, particularly with a fracture of the lesser tuberosity22. CT is also helpful in fractures with articular surface involvement and for enumeration of fracture fragments (Figs. 1-A, 1-B, and 1-C). The number of fragments in the setting of severe comminution is underestimated by standard radiography in >60% of cases23.
Magnetic resonance imaging (MRI) is not part of the routine evaluation of proximal humeral fractures. While traumatic rotator cuff tearing at the time of a proximal humeral fracture is rare, some authors have recommended consideration of the use of MRI24. Rutten et al. recently described an ultrasonographic sign that reliably detected occult proximal humeral fractures25. The so-called double-line sign was present in 93% of patients with occult fractures.
Many proximal humeral fractures with minimal displacement are amenable to nonoperative treatment. Displaced two, three, and four-part fractures are indications for surgical management to optimize anatomic healing and improve functional outcome. Displacement of the tuberosities above the humeral head, as in three or four-part fractures or in varus two-part fractures, often yields a poor functional outcome, even if healing occurs nonoperatively. Surgery is aimed at restoring the proximal humeral anatomy, including the neck-shaft angle, version, and tuberosity-to-head and tuberosity-to-tuberosity relationships, and bone-preserving options include percutaneous techniques, intramedullary nailing, and locked plating.
Indications
Percutaneous fixation with pins is a minimally invasive strategy with a theoretically lower rate of osteonecrosis than that with open fixation. However, it offers less stability than other forms of fixation, and is technically demanding. It is advocated for unstable two-part surgical neck fractures, but also has a role in more complex three-part and valgus-impacted four-part fractures8 (Fig. 2). This form of fixation is generally reserved for patients with good bone quality; minimal comminution, particularly involving the tuberosity; and an intact medial calcar. It is also essential that patients are compliant with postoperative follow-up and immobilization8.
Technique
A detailed description of the percutaneous pinning technique has been previously published26. Pearls of management are discussed below. Percutaneous techniques should be performed within five to seven days of injury to avoid difficulties associated with early callous and scarring.
Proper setup and timing of surgery is critical to outcome. The patient is placed in a supine or modified beach-chair position on a radiolucent table with the shoulder and arm off the edge of the bed. It must be ensured that a good anteroposterior and axillary radiograph can be made prior to skin preparation. Once the c-arm fluoroscopic image intensifier is properly positioned, sterile preparation and draping of the shoulder is performed.
Careful pin placement is essential to avoid neurovascular injury. Lateral pins should be distal to the anterior branch of the axillary nerve27 but proximal to the deltoid insertion to avoid the radial nerve. The musculocutaneous nerve, cephalic vein, and biceps tendon are at risk from placement of the anterior pins.
Reduction of the humeral shaft under the humeral head is done by applying longitudinal traction with a posterolateral force to the arm. If this does not reduce the fracture, a 2.5-mm terminally threaded pin inserted through the greater tuberosity into the humeral head can be used as a so-called joystick. Another reduction technique is to use a small so-called reduction portal to manipulate the fragments with instruments such as elevators, tamps, or hooks28 (Figs. 3-A and 3-B).
Once adequate reduction is achieved, a 2.5-mm terminally threaded pin is driven from the lateral metaphysis into the humeral head. As the pin nears the articular surface of the humeral head, driving it in by hand with use of a T-handled chuck rather than a power driver provides better tactile feedback and minimizes the risk of penetrating the articular cartilage. Insertion should also be done under image guidance to further minimize the risk of pin penetration. If penetration occurs, the pin must be removed and a completely new track created—if the pin is simply withdrawn, it may migrate and penetrate over time. When inserting the pin, the surgeon must recognize that the humeral head is retroverted 20° to 40°. Two or three antegrade pins in a parallel configuration are usually adequate for fixation of the humeral head to the shaft29, although a retrograde pin from the greater tuberosity to the humeral shaft is sometimes used to augment stability30. Fixation of the tuberosities in displaced three and four-part fractures is achieved with 3.5 or 4.0-mm cannulated screws placed antegrade from the tuberosity either bicortically into the calcar (for the greater tuberosity) or unicortically into the head (for the lesser tuberosity). Pins and screws are buried underneath the skin (Fig. 3-C). The arm is immobilized for three to four weeks, and the pins are removed after four to six weeks.
Prognosis and Outcomes
Functional outcome is correlated with the adequacy of reduction and the residual deformity. Union rates are high, and good results should be expected with two-part and three-part fractures28,31,32. If acceptable alignment cannot be obtained at the time of surgery, open reduction is recommended.
Complications
Malunion
Malunion rates have been reported to be as high as 28%31. Patients with osteoporotic bone and those who have fracture comminution have the highest risk. Varus angulation of the humeral head with posterosuperior displacement of the greater tuberosity is the most common deformity8.
Pin Migration and/or Loosening
Despite the use of terminally threaded pins, the migration of pins occurs in up to a third of patients28,31. Migration into the chest and other vital structures has been described8. Weekly evaluation and radiographs are performed to monitor fracture reduction and pin alignment. Pins that become loose or migrate should be removed prior to four weeks.
Pin-Track Infection
Superficial infections are treated with local wound care, antibiotics, and pin removal. Ensuring that the pins remain below the skin lessens the chance of infection. One must beware of a deeper infection including osteomyelitis.
Osteonecrosis
Osteonecrosis of the humeral head is most likely related to the magnitude of the injury, with four-part fractures associated with a prevalence of osteonecrosis of up to 28%28,31,33. Kralinger et al. found a significantly lower rate of osteonecrosis after percutaneous pinning compared with open reduction and internal fixation34.
We followed a series of twenty-seven patients treated with percutaneous pin fixation for a minimum of three years after surgery. Osteonecrosis was noted in 26% at an average fifty months (range, eleven to 101 months), including half of the four-part fractures, two of the twelve three-part fractures, and none of the two-part fractures. The mean American Shoulder and Elbow Surgeons (ASES) score was 65 for patients with osteonecrosis and 84 for patients without osteonecrosis26.
Neurovascular Injury
Despite cadaveric studies demonstrating potential neurovascular injury with percutaneous fixation, clinical rates are low27,35,36. A good knowledge of anatomy and normal variants is essential to prevent complications.
Indications
Intramedullary nails are accepted as an effective method to treat two-part surgical neck fractures, although their use in more complex proximal humeral fractures has varied37-39. Small incisions, closed reduction, and excellent nail-bone purchase in osteoporotic bone are advantages.
Gradl et al. treated displaced proximal humeral fractures with an antegrade nail (Targon PH; Aesculap, Tuttlingen, Germany) and had better functional results in patients with two-part and three-part fractures than in those with four-part fractures40. The published results have varied41-45. The intramedullary nail may be rigid and locked or flexible and unlocked. Locked intramedullary nails are axially and rotationally stable, whereas flexible intramedullary nails are not. Shoulder impairment and iatrogenic fractures are risks with locked intramedullary nails46-48. Advantages of the flexible intramedullary nails are relatively little blood loss, no soft-tissue stripping at the fracture site, minimal muscular trauma, and low risk of radial nerve injury. A disadvantage of flexible intramedullary nails, particularly among patients with osteoporotic bone, is restricted early motion and delayed physiotherapy due to relatively low construct stability49.
Technique
Rigid Intramedullary Nail
The patient is placed supine in the beach-chair position, and the image intensifier device is positioned to ensure that anteroposterior and axillary radiographs of the affected shoulder can be obtained intraoperatively.
A 4-cm longitudinal incision is made anterolateral to the acromion. The deltoid is split from the anterolateral corner of the acromion distally for 4 cm. The humeral head fragment is exposed, and the head fragment is reduced, with use of a 2.5-mm Kirschner wire or Steinmann pin, under fluoroscopic guidance. For displaced four-part fractures, 1.25-mm Kirschner wires can be used for temporary fragment reduction. A 1-cm incision is made in the supraspinatus tendon in line with its fibers. An awl or a guide pin is used to enter the medullary canal. For the straight 150-mm Targon PH nail (Aesculap), the recommended entry point is about 8 mm medial to the cartilage-bone transitional zone at the sulcus between the humeral head and the greater tuberosity50. For the 6° angled Stryker T2 Proximal Humerus nail (Stryker, Kiel, Germany), the recommended entry point is 10 mm posterior to the anterior edge of the supraspinatus and at the junction of the greater tuberosity and the articular cartilage50. The entry point for the proximal humeral nail (Synthes, West Chester, Pennsylvania) is just lateral to the articular margin in the sulcus between the greater tuberosity and the articular margin38. The entry point of the intramedullary nail is important; however, cortical apposition may be lost following the insertion of the nail as a result of the specific humeral pathology and anatomic characteristics50. The medullary canal is reamed. The nail is inserted manually with its targeting device. The depth of nail insertion may vary according to manufacturer and design. Precise orientation of the targeting device is necessary to avoid injury to the long head of the biceps and neurovascular structures51. Fixation screws are inserted. We recommend placement of all of the proximal screws, particularly if the tuberosities are fractured. The rotator cuff tendon and deltoid are repaired, and active-assisted to active shoulder motion is begun on the third postoperative day.
Flexible Intramedullary Nails
Retrograde flexible intramedullary nailing utilizes more than one 2-mm-diameter, curved, flexible nail to achieve multiple-point intramedullary fixation. The fracture pattern and the diameter of the medullary canal dictate the number of nails that are inserted. Usually, three, four, or five nails are necessary to obtain sufficient stability. Once closed reduction has been achieved, the nails are advanced from distal to proximal from an entry point 3 cm proximal to the olecranon tip under fluoroscopic guidance to the medial half of the humeral head, diverging in the subchondral region37.
Pendulum movements of the shoulder are started on the first postoperative day, with mobilization of the elbow joint. Passive movement exercises may be initiated on the third week, and active exercises may be started on the fourth week onward.
Prognosis and Outcomes
When appropriate patients are chosen, careful placement of the nail entry point and effective postoperative rehabilitation lead to a successful result38,40,50.
Rigid Intramedullary Nail
Several recent cohort studies have demonstrated 100% union rates, low complication rates, and favorable subjective outcomes with rigid intramedullary nailing38,52,53. Three recent comparisons of rigid intramedullary nailing and locked plate fixation did not reveal a significant difference in objective or subjective outcomes54-56. One study did show a trend of more complications and lower relative Constant scores with nail fixation, but this did not reach significance55. Another showed a higher rate of complications but better outcome scores with locked plate fixation at one year; however, no difference was detected between the locked plate group and the nail fixation group at three years56.
Matziolis et al. found no significant difference in absolute Constant scores between Zifko nailing and fixed-angle plating for two-part fractures. The score for the subitem “activity of daily life” was significantly higher in the plate group than in the Zifko group37.
Complications
Nonunion
In a systematic review by Lanting et al. (sixty-six articles with results on 2653 fractures), nonunion was as high as 4% in two and three-part fractures39.
Nail Migration
Verbruggen and Stapert stated that rates of flexible nail migration as high as 29% and rates of fracture distraction of up to 41% have been reported48.
Malunion
Malunion is one of the commonly reported complications, and the rate of postoperative varus deformity of the humeral neck has been reported to be as high as 7.7% to 37%39,54,57.
Nerve Injury
The locking screws that are used with the nails may pose a danger to the axillary nerve51. Closed reduction and implant insertion place the radial nerve at risk. Blunt dissection and use of protection sleeves during drilling and screw insertion can prevent this injury.
Rotator Cuff Injury
Insertion of the nail through the rotator cuff tendon causes different degrees of injury to the supraspinatus tendon that can lead to shoulder pain38,46,52. Care should be taken in the dissection of the supraspinatus tendon and in its meticulous repair.
Background
Prior to the advent of locked plating, hemiarthroplasty had been advocated for most three and four-part fractures. Anatomic proximal humeral locking plates represent an advance in construct stability58,59 and have a lower rate of implant failure compared with unlocked plating. However, the complication rate remains substantial. Continued innovation in technology (i.e., polyaxial systems and suture eyelets) and technique (i.e., structural allograft and rotator cuff sutures) are aimed at improving current outcomes.
The importance of medial cortical support has been demonstrated with the locking construct, as the screw buttressing the inferomedial portion of the proximal segment aids in medial column support60. Restoration of medial calcar and medial support plays an important role in maintaining reduction61. This screw functions as a so-called kickstand and is beneficial in maintaining the stability and ultimate reduction of the construct. Additionally, anatomic or slightly impacted reductions aid in construct stability61.
Other constructs have attempted to utilize pegs as alternatives to screws to prevent articular perforation. Schumer et al. found no significant difference in joint perforation between the two constructs62. Newer locking constructs offer polyaxial locking mechanisms. In a comparison of monoaxial and polyaxial constructs, the polyaxial system had equal biomechanical performance with the advantage of more head fixation63.
In a comparison of a locked plate and locked nail, plates were found to be stronger in torsion, equivalent in axial stiffness64, and superior in varus bending65. In comparison with proximal humeral blade plates, locking plates provided better torsional fatigue resistance and stiffness66.
Proximal humeral fracture fixation fails because of bending and rotational moments60-67. Because locking plates are biomechanically more stable than the tested constructs under these circumstances, the added stability may reduce the fracture failure rate.
Indications
Most displaced two, three, or four-part fractures of the proximal part of the humerus can be treated with locked plates. Fracture dislocations and head-splitting fractures in patients older than forty years are relative contraindications to plate fixation. Both are higher-energy injuries associated with risk of osteonecrosis of the humeral head; however, in younger patients in whom joint-preserving strategies are most appropriate, head-splitting and high-energy fractures may be fixed with a locked plate (Figs. 4-A, 4-B, and 4-C). Few other contraindications exist, except prohibitive medical comorbidities, pediatric fractures, or patterns of injury amenable to less invasive techniques68,69.
Proximal Humeral Exposures70
Multiple exposures for the proximal part of the humerus, including the classic deltopectoral, anterolateral deltoid-splitting approach, and two-incision techniques9,71-73, have been described. There are advantages and disadvantages of each. The anterolateral and two-incision approaches were developed with the primary purposes of improving visualization, minimizing soft-tissue dissection, and allowing more direct plate application, which may permit improved preservation of the blood supply. However, these approaches may place the axillary nerve at risk72-77. Conversely, the classic deltopectoral approach is the only truly internervous approach and is the most widely utilized exposure. Controversy exists as to what approach to use for locking plate fixation9,71-74. We use the deltopectoral approach because of its extensile nature and long track record of safety.
Deltopectoral Approach
The deltopectoral approach utilizes the internervous plane between the deltoid (axillary nerve) and the pectoralis major (medial and lateral pectoral nerves)70. The patient can be positioned in the beach-chair position or supine, depending on the available equipment and the surgeon preference. The skin incision is approximately 10 to 15 cm long, beginning at the coracoid and angled distally to the deltoid tuberosity.
The cephalic vein is identified in the deltopectoral interval and is usually mobilized laterally to protect the many deltoid branches78; however, it may be taken medially as well. The clavipectoral fascia is opened, and the conjoint tendon is retracted medially. Deltoid or pectoralis major detachment is not needed, and no more than one-fifth of each should be released79.
Continuity of the axillary nerve can be tested with the so-called tug test80 at the inferior border of the subscapularis and beneath the deltoid. The distance from the coracoid to the point of entrance of the main musculocutaneous nerve trunk into the coracobrachialis averages 5.6 cm (range, 3 to 8 cm)81.
The rotator cuff interval may be incised at the level of penetration of the biceps tendon to mobilize the tuberosities and to allow visualization and palpation of the articular surfaces. The long head of the biceps tendon is uncovered in its groove and is followed proximally to its insertion on the superior aspect of the glenoid. The tendon may be tenotomized and tenodesed to the pectoralis major, removing a source of postoperative pain82. It is important to avoid excessive dissection and cauterization in the bicipital groove to preserve the ascending branch of the anterior humeral circumflex artery.
Reduction
Control of the rotator cuff is the most important step to reduce and control the multiple fracture fragments. Nonabsorbable sutures are placed in the subscapularis to control the lesser tuberosity, and in the supraspinatus and infraspinatus to control the greater tuberosity and humeral head. Elevators, if necessary, are placed in the fracture planes to disimpact the fragments and to correct varus or valgus positioning of the head. The tuberosities are reduced to their anatomic position with respect to the head and the metaphysis and shaft. Tuberosity reduction is a key predictor of functional outcome83,84. If there is insufficient metaphyseal bone, the surgeon may place a fibular strut allograft within the intramedullary canal and impact the head onto it to provide control and structural support85.
Fixation
Locking plates have a low profile, a hole for a kickstand screw to buttress the medial calcar, divergent proximal locking screws, and eyelets to allow passage of rotator cuff sutures through the plate68. The plate should be placed lateral to the bicipital groove, 1.5 to 2 cm distal to the greater tuberosity (2 to 3 cm from the superior aspect of the head). If the plate is placed too high, there is a risk of impingement. If it is placed too low, head fixation can be compromised. Proximal screws should remain short of the subchondral bone to reduce the risk of perforation with humeral head collapse. Rotator cuff sutures are then tied to the plate to neutralize the displacing force of the cuff muscles and offload the proximal screws. Screw penetration into the joint is a risk, and rotator cuff sutures add additional stability and are believed to stabilize the fracture enough to allow early motion and decrease fixation failure86-88. After completion of fixation, fluoroscopy should be utilized and the humeral articular surface should be palpated to ensure that no screws violate the joint.
Rehabilitation
Postoperative rehabilitation is a balance between early motion and not disrupting the fixation89. Initially, the arm is placed in a sling. Active range of motion of elbow, wrist, and hand, as well as pendulum exercises may begin on the first postoperative day. Gentle passive range of motion of the shoulder is started as soon as the patient is comfortable. Active shoulder motion should begin at four to six weeks, and strengthening exercises should not be started until twelve weeks.
Results and Complications
The results of locked plate fixation are evolving, but the overall complication rate remains high86,90-94. The most common complications are screw joint perforation (13.7% to 23%) and osteonecrosis (3.1% to 16.4%). The rate of revision surgery has been reported to range from 13% to 26.7%. However, in a study comparing the functional outcomes of patients with three and four-part proximal humeral fractures treated with locked plating or with a hemiarthroplasty, the University of California at Los Angeles shoulder score, the Constant score, patient satisfaction, and motion were superior in the locked-plate group95.
Strategies to augment locked plate fixation and minimize complications are being developed. Improved results and decreased complications were detailed in a series by Ricchetti et al., in which the authors supplemented plate-and-screw fixation with suturing of the rotator cuff tendons to the plate69. Hettrich et al. used endosteal fibular strut allografts or medial semitubular plates and noted only one substantial loss of reduction and no implant failures or screw cutout96. Egol et al. used calcium phosphate cement to prevent settling and screw cutout, and less humeral settling was seen97.
In conclusion, locked plating has been a major advance in the treatment of displaced proximal humeral fractures, and has allowed many more fractures to be successfully treated with a joint-preserving method instead of arthroplasty. Complications remain substantial, but the techniques and technology of proximal humeral locked plating are areas of active research.
Percutaneous, intramedullary, and locked-plate fixation can be reliable fixation strategies for proximal humeral fractures with the correct indications and careful patient selection, which are based on an understanding of the anatomy and biomechanics of the injury. Each method has advantages and disadvantages that the surgeon must consider and individualize for a particular patient. Regardless of the technique selected, meticulous surgical technique and anatomic reduction are essential. Careful postoperative rehabilitation is essential. Each method also has specific complications, which may be mitigated as techniques and technology continue to evolve.
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Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.