Background
Due to current demographic changes, the number of proximal humeral fractures will continue rising dramatically, especially in female individuals [
1]. Non-operative treatment with short-term immobilization is a well-approved treatment option and has shown good clinical results in stable and minimally displaced fractures as well as in certain displaced fractures. However, conservative therapy regimes are not reserved to simple fractures alone, as the functional outcome primarily depends on age and less on deformity [
2,
3]. It is to be expected, though, that particularly complex proximal humeral fractures with severe displacement will occur more often in the aging society with longer life expectancy and notable comorbidities [
4]. Despite latest developments of fixation techniques and implants, the surgical treatment of these—mainly osteoporotic—fractures remains challenging. Primary arthroplasty has to be considered in fractures where sufficient reduction and stable fixation cannot be achieved and the vascularity of the head fragment is impaired or at risk. In most remaining cases, especially when displacement of the tuberosities is present, locking plate fixation has proved to be the gold standard. Anterograde intramedullary nailing is often not an option for complex fractures and has the considerable disadvantage of affecting the rotator cuff. Intramedullary locking nails are best applicable in displaced two-part fractures or three- and four-part fractures with meta- or diaphyseal involvement and no significant displacement of the tuberosities [
5]. This article aims to summarize available classification systems, indications for operative treatment, important pathoanatomic principles, and latest surgical strategies in locking plate fixation. The importance of correct reduction of the medial cortices, the use of calcar screws, augmentation with bone cement, double-plate fixation, and auxiliary intramedullary bone graft stabilization are discussed in detail.
Methods
For the arrangement of this narrative non-systematic review, an exploratory search in the MEDLINE database using the keywords “proximal humeral fracture,” “locking plate,” “classification,” and “treatment” was conducted. Clinical and experimental studies were included in a detailed review. In addition, references of reviewed articles were searched for relevant studies not yielded by the initial search.
Fracture classification
The classification of proximal humerus fractures has always suffered from poor intra- and interobserver reliability [
6,
7], especially in plain radiographs. Thus, many classification models have been proposed over the decades. Codman’s illustrative classification system proposed in 1934 is the most influential concept and serves as basis for many classification models in clinical practice. Based on the configuration of the four main segments—namely the humeral head, the shaft, the greater tuberosity, and the lesser tuberosity—12 fracture patterns can be distinguished. Neer’s analysis of 300 displaced proximal humeral fractures in 1970 led to a modification with additional subgroups and focus on the pathoanatomy regarding presence or absence of displacement of the four bony segments rather than fracture lines [
8]. The definition of displacement was “arbitrarily set” and requires at least 1 cm of separation and 45° of angulation between fragments [
9]. As displacement is a continuum, he further clarified that these limits were not intended to dictate treatment but simply to define the minimal displacement category (1-part) and to support standardization in future outcome studies [
9]. Neer was not surprised about the poor reproducibility of his classification system in radiologic studies as a pathoanatomic classification may even require intraoperative assessment. Although the accuracy in its application often has been questioned [
6,
10‐
12], Neer’s classification still enjoys broad acceptance and common use.
Hertel et al. introduced a further development of Codman’s concept taking the fracture planes but not the number of fragments into account [
13]. Combining the five basic fracture planes (between greater tuberosity and head, greater tuberosity and shaft, lesser tuberosity and head, lesser tuberosity and shaft, and between lesser and greater tuberosity) yields 12 basic fracture patterns. More precisely, there are six possible fractures dividing the humerus into two fragments, five possible fractures dividing the humerus into three fragments, and a single fracture dividing the humerus into four fragments [
7,
13]. When the dichotomizing questionnaire for determining the fracture morphology could not be certainly answered on plain radiographs, additional imaging studies (computed and/or magnetic resonance tomography) should be demanded. The evaluation of seven accessory questions provides important information for further treatment planning, especially on the probability of humeral head ischemia (Table
1). Compared to the other available classification systems, the
κ coefficient for interobserver reliability ranked highest in the Codman-Hertel classification [
7].
Table 1
Predictors of humeral head ischemia after intracapsular fracture of the proximal humerus [
13]
• Metaphyseal extension < 8 mm • Disrupted medial hinge • Basic fracture morphology • Head-split component (> 20% head involvement) • Angular head displacement > 45° • Tuberosity displacement > 10 mm • Glenohumeral dislocation | |
Despite recent modifications, the AO classification system for proximal humerus fractures plays a rather scientific role and—in contrast to other fracture sites—has not found its way into clinical use due to its complexity with a total of 27 subtypes [
14,
15].
As a supplement to the Codman-Hertel classification system, Resch proposed a classification addressing fracture angulation and pathomechanics [
16]. It further evaluates the head-to-shaft relationship and, thus, is supposed to facilitate reduction and fixation during surgery.
Indications for operative treatment
The heterogeneity of proximal humerus fractures not only complicates the search for a reproducible classification system but also—as a consequence of poor comparability—delays the definition of coherent treatment protocols. Despite the frequency of proximal humerus fractures, until now, there is no solid evidence on treatment indications [
17,
18].
Absolute indications for an operative treatment of proximal humerus fractures are rare. These comprise three- or four-part fracture dislocations, head-splitting fractures, pathological fractures, open fractures, severe ipsilateral injuries to the shoulder girdle, and accompanying neurovascular injuries [
17,
18]. However, with a displacement greater than 5 mm, reduction and internal fixation is recommended as secondary salvage surgery after failed non-operative treatment with a corrective osteotomy or secondary arthroplasty is more difficult and less promising [
19].
Along with the fracture pattern, patient age, and overall state, comorbidities and associated medication, handedness, and expected demands on the injured extremity have to be taken into account. If the bone quality is unknown, the deltoid tuberosity index is a simple tool to estimate the bone quality in an anterior-posterior radiograph [
20]. Especially in geriatric patients, close cooperation with a geriatric physician is advisable to facilitate early active rehabilitation after operative treatment [
21].
In unreconstructable humeral head fractures, head-split fractures or fracture dislocations, and patients older than 70 years with high risk of osteonecrosis or previously impaired shoulder, function primary (reverse or anatomic) arthroplasty may be the best therapeutic option. This also includes patients with delayed presentation and glenoid damage or wear [
18,
22].
Non-operative treatment
Despite the risk of nonunion, symptomatic malunion or osteonecrosis, non-operative therapy even of complex proximal humerus fractures may be adequate in the very elderly or cognitive impaired population and in patients with a nonfunctional limb, well advanced drug or alcohol abuse or severe medical comorbidities [
17]. These settings often require close cooperation with a geriatric physician in order to prevent secondary conditions and further falls. Non-operative treatment usually comprises a short interval of sling immobilization (i.e., 3 weeks) and subsequent early pendulum exercises, followed by active rehabilitation to restore shoulder function and achieve independency [
23,
24].
Non-displaced one- and two-part fractures typically are treated conservatively and thereupon yield excellent radiographic union rates and good functional range of motion [
25,
26]. However, age has been found to be a predictor of impaired outcome in this patient group [
27].
Serial radiographs are necessary to monitor the course of treatment. In order to obtain comparable radiographs, it is important to appreciate a proper arm positioning. Sling immobilization puts the arm in internal rotation, which misleadingly increases the head-shaft angle and simulates a valgus malalignment [
28]. Thus, neutral arm with the palm of hand on the lateral thigh is crucial for initial and follow-up examinations. The angulation on Y view best correlates with the functional outcome and best predicts the angulation at union [
29,
30].
Discussion
The locking plate osteosynthesis of displaced proximal humerus fractures remains a challenge for the upper extremity surgeon. Despite development of new implants and awareness of new biomechanical fracture characteristics, the complication rate stagnates on a high level.
Especially varus impaction with penetration of proximal screws is a frequent complication [
32,
42,
82,
83]. Even in cases of anatomic reduction and the use of calcar screws, in 6 to 8% of the patients a screw cutout is seen [
39,
53]. In general, complications occur within the first 3 weeks after surgery, when patients start physical therapy [
84]. However, for monitoring the vitality of the humeral head, a follow-up over 2 years seems appropriate.
In view of these severe complications, most proximal humerus fractures can be treated non-operatively. However, in selected patients with fractures with relevant intraarticular damage or displacement and after failed non-operative treatment, operative treatment is the preferred strategy to improve the patient’s functional outcome. In these patients, locking plate fixation provides an established mode of fixation.
To reduce peak stresses at the bone-implant interface that lead to screw cutout and early loosening, the ideal implant needs to provide elastic characteristics [
38]. However, the initial stiffness of locking plates is needed for stability especially in osteoporotic bone—the higher the stability, the faster the bone healing [
85]. In our group’s biomechanical in vitro study, the combination of locking plate osteosynthesis and intramedullary cortical bone graft seems to have met these opposing demands [
63].
Neviaser et al. delivered the clinical evidence of this method in a case series of 34 patients with intramedullary fibula grafts [
61]. In this series, only one patient presented secondary displacement but did not need revision surgery. The appearance of only one patient with partial humeral head necrosis defuses the fear of humeral head necrosis caused by compromised intramedullary blood supply. To avoid ischemic humeral head necrosis, precise anatomic knowledge of the posteromedial periosteal blood support and a careful surgical dissection is an essential demand.
The posterior circumflex humeral artery covers two third of the proximal humeral blood supply [
44]. In proximal humerus fractures, this artery remains the last supplying vessel. Uncontrolled shear forces between the humeral diaphysis and the humeral head need to be avoided. The disruption of the posteromedial periosteum appears with a head displacement of about 3 mm. The complete disruption is seen with an average displacement of 30 mm.
In summary, the intramedullary bone grafting should be reserved for osteoporotic proximal humerus fractures with a significant displacement of the humeral head and medial comminution. The economic costs of allogenic bone grafts or the comorbidities of the autologous bone grafting technique, respectively, should be regarded critically.
Augmented osteosynthesis with bone cement should also be mentioned as a treatment option, although removal of the incorporated cement represents considerable disadvantages in case of secondary prosthetic joint replacement.
Retrograde intramedullary nailing is a new stabilization approach. Dietz et al. compared retrograde nailing versus locking plate systems as treatment option for two-part proximal humeral fractures. They could not find any differences in stability for axial and torsional loading [
86].
Especially in elderly patients with humeral head fractures with high risk of osteonecrosis or previously impaired shoulder function, primary shoulder arthroplasty may be the best therapeutic option. Reverse total shoulder arthroplasty shows reliably good results with relatively low complication rates compared to osteosynthesis in the same patient population [
69]. Hemiarthroplasty fails if concomitant irreparable rotator cuff damages or non-malunion of the tuberosities are present.