Plate osteosynthesis of proximal humerus fractures: treatment options and technical advancements| Lo Scalpello - Journal

Abstract

Proximal humerus fractures are the third most common fracture in the elderly, producing an impressive social and economic burden. Their treatment is still controversial in the literature, with unconclusive evidence regarding the best therapeutic choice. Osteosynthesis with locking plates is considered the main surgical treatment, providing good clinical and radiographic outcomes over solid biomechanical bases, even if high complication rates have been reported. The main complications are intra-articular screw penetration, varus collapse, and avascular necrosis of the humeral head. In order to reduce the complication rate, it is necessary to correctly select patients who are suitable for surgical treatment; provide an adequate reduction of the fracture; effectively address medial hinge disruption; avoid complications related low bone quality. Many technical options to achieve better results have been developed, ranging from design modification to allograft augmentation. The aim of this review is to provide up-to-date information to aid the surgeon in choosing the correct treatment for the individual patient.

Introduction

Proximal humerus fractures (PHF) account for 4-5% of all fractures and are the third most common fracture in the elderly after hip and distal radius fractures ^1,2. The mean incidence is 63-105 cases per 100,000 person-years ^2-4, and a 63% increase in incidence has been observed from 1970 to 2002 ⁴. Females are 2.42 times more at risk to undergo a PHF ²; mean age is 68.8 years ⁵ and the incidence increases with age in both sexes ^2,4. The most commonly reported etiology is a fall from standing height ².

PHF produce an impressive social and economic burden, as they cause inability in activities of daily living and, therefore, impose the need for support in previously independent individuals ⁶; hospitalization is often required, with yearly healthcare related costs estimated to reach € 33.6 million ⁷, with mortality during hospitalization reaching 1.1% ⁷ and rising to 7.83% within one year after the injury, which is 5.2 times higher than general population ⁵. Therefore, appropriate treatment of these fractures is of paramount importance to restore shoulder function and independence to treated patients and to avoid complications.

The aim of this review was to report the indications, surgical options, and complications of plating for PHF.

Fracture classification

Various classifications for PHF have been described ^8-10, yet none proved to be definitive. Neer’s four-segment classification is the most commonly used by surgeons in clinical practice, followed by Hertel’s binary description system and AO classification, which give more details on the pattern of PHF but are more complicated to analyze ¹¹. All these classifications are built on a common basis, classifying the fracture by number and characteristics of bone parts generated by the fracture lines; Codman ¹² first described five basic fracture planes that could be reproducibly identified in PHF. Combining these fracture planes, multiple theoretical fracture patterns can be obtained, dividing the proximal humerus in four major segments: the lesser tuberosity, the greater tuberosity, the articular surface, and the humeral shaft. Thus, he created the four-part model that inspired subsequent classifications.

Neer ⁸, following Codman’s observations, defined the four-segment classification system. This classification is based on the presence of displacement of one or more of the four major segments. Displacement of a part is defined as angulation of more than 45° or separation of more than 1 cm. This allows to group together all undisplaced or minimally displaced fractures, regardless of the number and path of fracture lines, and to focus the surgeon’s attention on displaced fractures. Being based on displacement, this classification highlights the effect of muscle attachments on each segment and evaluates the consequences of displacement on vascularity and articular surface. Fractures were classified as: one-part fractures (minimal displacement), two-part articular segment displacement (anatomic neck), two-part shaft displacement (surgical neck), two-part greater tuberosity displacement, two-part lesser tuberosity displacement, three-part displacements, four-part fractures, fracture-dislocations and articular surface defects ¹³. Unfortunately, the classification alone cannot guide treatment, as the patient’s characteristics and available treatment methods must be taken into consideration ¹³.

Hertel et al. ⁹ proposed a classification based on modified Codman’s fracture planes: they believed that the tuberosities should be considered as an intercalated segment between the head and the shaft. For descriptive purposes, the four segments were imagined as four Lego blocks that could be separated from each other. The various combinations of these Lego blocks produced 12 possible fracture patterns. This resulted in 6 fracture patterns dividing the proximal humerus in 2 parts, 5 dividing it in 3 parts, and 1 dividing it in 4 parts. The surgeon must answer 5 yes/no questions and, based on the answer, the fracture will fall into one of the 12 categories. Because of those dichotomous questions, the method was named “binary description system” and the authors claimed that it is easy to teach an apply, providing clear-cut diagnostic subgroups. The main focus of this classification is the assessment of ischemia: 5 fracture types were identified that carried an higher risk of humeral head ischemia; in all, there was displacement of the head segment ⁹.

AO classification ¹⁰, in its latest revision, divides PHF in three types: A. fractures, extraarticular, unifocal, 2-part fracture; B. fractures, extraarticular, bifocal, 3-part fracture; C. fractures, articular or 4-part fracture. Each type comprises further subgroups, and a total of 27 subgroups are described. This classification takes into account fracture patterns, mechanism of dislocation, and risk of head ischemia, but it is complex and rarely of use in clinical practice ¹¹.

Despite the effort to create clear categories and to provide clear information for sorting, all these classifications, when tested, showed unsatisfactory reproducibility. Substantial agreement can be found for Neer’s classification, but with a wide range of results among authors (k 0.33-0.70) ^14-21; fair to moderate agreement could be demonstrated for the AO classification (k 0.31-0.59) ^15,16,19,21, while Hertel’s classification showed moderate to substantial correlation (k 0.39-0.63) ^17,20, with better results when CT assessment was performed, despite not being significantly better than Neer’s classification on direct comparison ²⁰. Neer commented on these results, depicting the difficulties in correctly classifying fractures: exacting radiographic studies, surgeon’s knowledge and experience and, often, intraoperative exploration are needed to correctly classify the fracture and, consequently, plan the correct treatment ¹³. Surprisingly, higher agreement was shown on treatment choice than on fracture classification, despite not exceeding a moderate agreement ^14,18,22. In those cases when agreement was higher, better outcomes were obtained ²². Correlation of one classification with another is controversial: translation cannot be directly done, but single radiographs need to be reassessed ²³.

Treatment

No consensus has been reached on the optimal treatment of PHF. While undisplaced fractures are unanimously treated conservatively with good outcomes ^11,24, the treatment of displaced fractures remains controversial: the lowest agreement is in three- and four-parts fractures ¹¹. According to the analysis of a large population, 49% of PHF are undisplaced and 28% are 2 part fractures. This leaves 23% of fractures in which a high grade of uncertainty exists. The lack of consensus on treatment is confirmed by the variation in surgical procedure rates among different regions ^25,26. Only moderate agreement exists among surgeons regarding treatment choice ^14,18,22, decreasing to fair when evaluators are inexperienced surgeons ²².

Treatment options range from non-operative to plating, pinning, nailing, hemiarthroplasty, and reverse total shoulder arthroplasty ^27-29. In this review, we discuss the various technical options for plate fixation.

In a multicenter study comparing surgical versus conservative treatment for displaced PHF (PROFHER trial), no difference was found between groups in patient-reported outcome measurements ²⁷. Similar results were reported in a 5-year follow-up study ³⁰. Therefore, the authors claimed that surgical treatment of PHF generates high costs without providing health benefits ³¹ and concluded that the increasing trend for surgical treatment was not supported by evidence ²⁷. Similar findings were reported by other authors, who compared the outcomes of conservative and surgical treatment in elderly patients ^28,32. Furthermore, plate osteosynthesis in the elderly tends to have high failure rate, up to 34% ³³, increasing with age and fracture complexity ³³. A recent meta-analysis comparing conservative treatment and plate fixation showed no clinical differences, higher rate of non-unions with conservative treatment, and higher rate of reoperations with surgical treatment ³⁴. The results of the PROFHER trial prompted clinicians to prefer conservative treatment ³⁵, but this choice is debatable. The PROFHER trial excluded patients with a clear indication for surgery, providing useful information for borderline and uncertain cases. Furthermore, information about the surgeons’ experience and operative techniques, stability of fixation, and radiographic outcomes are lacking ^36,37. Thus, careful preoperative planning and surgeon’s evaluation can give good clinical outcomes and minimize the risk of perioperative and postoperative complications, even in elderly patients ^38,39. On the other hand, surgeons need to be aware that surgical treatment after failed conservative treatment and revision surgery provide worse clinical results than primary surgery ^29,40.

Surgical treatment should be recommended in the following conditions: three- or four-part fracture dislocations, head-splitting fractures, pathological fractures, open fractures, severe ipsilateral injuries to the shoulder girdle, and fractures involving the attachments of the rotator cuff tendons and associated neurovascular injuries ^41,42. The choice whether to undergo surgery is often left to surgeon’s experience and beliefs. Several variables can affect the type of surgical treatment ¹³, including age and medical conditions of the patient, involved side, functional requirements of the patient, bone quality, surgeon’s experience, associated neurovascular injuries, and ability of the patient to effectively participate in the rehabilitation protocol ¹¹.

Age is the main factor associated with the risk of failure after plate fixation, and therefore caution is needed when indication for plating is given to individuals aged more than 65 years. Unfortunately, the incidence of PHF increases with age and the majority of patients will be over 65 years ^2,4,5. Patients with higher requirements will benefit more from surgical treatment. Among patients aged 65 or older suffering from a PHF, 38% were, at least in part, dependent and 9% would become so after treatment⁶, hindering participation in the rehabilitation protocol.

Poor bone quality in elderly individuals, increases the risk of impaction, loss of reduction, and failure of the implant, whereas good bone quality facilitates reduction and prevents screw cut-out ^43,44. Evaluation of bone mineral density prior to the operation can, therefore, be of aid in foreseeing complications. It can be reliably measured on preoperative standard X-rays with the deltoid tuberosity index ⁴³. This index is the ratio between the outer cortical diameter and inner endosteal diameter measured on an anteroposterior radiograph directly proximal to the deltoid tuberosity, where the outer cortical borders become parallel. Values lower than 1.4 predict low bone mineral density of the humeral head ⁴³.

Plate fixation

Before introduction of locking plates, internal fixation of PHF is performed with tension band wiring, trans-osseous sutures, blade plates, semi-tubular plates, T-shape, buttress, and cloverleaf plates. The advent of locking plates has shifted the paradigm of internal fixation in PHF (Fig. 1). They are anatomically shaped to accommodate proximal humerus profile and their construct remains in a fixed angle irrespective of screw purchase and bone quality ⁴⁵: it relies on engagement of the screw on the plate, evenly distributing the load throughout the plate. This mechanism is particularly advantageous in osteoporotic bone. The conical pattern of proximal screw distribution supports the articular surface: screws act as pillars for subchondral bone ⁴⁶.

To obtain good results in plating, the first mandatory step is fracture reduction. Anatomically reduced fractures warrant good clinical outcomes ⁴⁷, while a malreduction of greater tuberosity of just 5 mm is associated with a threefold increase in complications, revisions, and risk of unsatisfactory clinical outcomes ⁴⁷. To ease tuberosity reduction, suture augmentation can be used. Sutures are passed through the tendinous insertion and fixed to the plate, relieving muscle stress from the fractured bone. Despite studies failing to demonstrate the biomechanical advantages of this technique ^48,49, it may prove practically useful as a reduction aid. Plate positioning is another important issue. If the plate is placed too proximal, there is a high risk of impingement against the acromion. This can happen because of poor surgical technique, poor fracture reduction, or small proximal humerus size ³⁷. Altogether, plate positioning influences screw positioning and purchase, as locking screws have a fixed trajectory from the plate. Specifically, if the plate are too high, the calcar screw can be mispositioned, reducing construct stability ³⁷.

Significant design differences exists among plates of different manufacturers ⁵⁰, but similar clinical results can be obtained with different designs ^51,52. In a large meta-analysis ⁵³ of patients undergoing internal fixation with locking plate, the average Constant score was 73.6, with better results with two-part fractures and worse results in four-part fractures, DASH score was 26.6, active forward flexion was 98° and average active abduction was 103°. Better results can be obtained in young patients after high energy traumas ⁵⁴, even in head splitting fractures ⁵⁵.

Medial support

Lack of medial support has been shown to cause reduction loss and varus deformity, leading to implant failure and postoperative osteonecrosis ^56,57. Various techniques have been proposed to deal with lack of medial support: use of a calcar screw, use of a strut allograft, cement augmentation, and dual plate fixation.

Calcar screw

The so-called calcar screw is a locking screw inserted through the plate, passing over the inferolateral wall of the great tuberosity, oblique to the medial cortex, directed towards the calcar region, providing additional support to the humeral head ⁵⁸. Ideally, it should be positioned < 12 mm from the apex of the arch of the calcar or within the bottom 25% of the humeral head ⁵⁹, in the inferomedial quadrant of the humeral head ⁶⁰. Calcar screw malpositioning has been reported to occur in 24% of implants ⁶¹. The main predictor of calcar screw malpositioning is the neck-shaft angle ⁶¹. Reducing the head so that the neck-shaft angle fits the 130-150° range significantly reduces the risk of calcar screw malpositioning ⁶¹. The use of a calcar screw provides a six-fold decrease in reoperation due to fixation failure ⁶². In biomechanical testing of absence of medial cortex, it improved axial and shear stiffness ⁵⁸. Furthermore, it provided increased resistance to cyclic loading thanks to a stiffer bone implant structure ⁵⁸. Under the same biomechanical hypothesis, as a substitute of the calcar screw, a blade device has been proposed ⁶³.

Void filling

This is a common finding after PHF reduction in which metaphyseal bone appears void. This can be due to slight malreduction, leaving some gaps, or cortical comminution or, hopefully, to cancellous bone impaction ⁶⁴. A possible solution is filling the defect with calcium phosphate. This decreases postoperative complications and reduces humeral head collapse compared to no augmentation and augmentation with cancellous chips ⁶⁴. Biomechanically, filling the humeral head void with calcium phosphate increases load to failure and stiffness, decreasing interfragmentary motion ^65,66.

Strut graft

The use of a bone strut graft was first introduced by Gardner et al. ⁶⁷ as a means to restore medial support in fractures with comminuted medial column. Fibular allograft has been considered the best choice to obtain medial augmentation: it fills the bone void of the humeral head, having a wide enough diameter to fill the entire proximal metaphysis; provides medial support and stability, preventing varus collapse of the humeral head; provides medial support for the greater tuberosity, allowing an anatomical reduction and restoring the rotator cuff length and function; provides endosteal purchase for locking screws, diminishing the torque placed on screws in case of varus or valgus stress; will not disturb the blood supply to the humeral head, providing altogether stable and osteogenic intramedullary material, fastening fracture healing ^57,68. With the use of a strut graft, biomechanical studies demonstrated an increase in construct stiffness and failure load, reduced fragment motion and change in gap distance ^69-71, ultimately protecting from loss of reduction for varus collapse ⁷². Good results in fractures with medial support loss have been obtained with this technique, with low loss of reduction ^67,68,73,74 and better results compared to non-augmented constructs ^68,74.

Dual plating

In complex PHF with medial cortex disruption, simple locking plates with calcar screw may be unable to grant mechanical stability. Double plating has been proposed as an alternative.

Wanner et al. ⁷⁵ first described the use of an anterior and lateral plate. They reported encouraging clinical and radiographic results, with 12% of reoperations. Good clinical results were afterwards confirmed in a small series ⁷⁶. A biomechanical study did not demonstrate superiority of double plating over locking plate fixation with calcar screw ⁷⁷. Choi and colleagues ⁷⁸ proposed adding a posteriorly placed distal radius locking plate to the standard lateral locking plate. Clinical outcomes of this technique have not yet been published. A finite element analysis ⁷⁹ explored the effect on fracture stability of the addition of a medial plate. This construct demonstrated greater stiffness on axial loads and better restoration of neck-shaft angle compared with standard locking plate, strut graft, and locking plate combined with posterior plate. No clinical data have been provided however.

Bone cement augmentation

Augmentation of screw tips with PMMA increases resistance to failure in varus bending and axial rotation. This effect is markedly exerted on augmented screws purchasing the lowest density bone, and particularly evident in medially unstable fractures ^80,81. From a clinical standpoint, cement augmentation reduced the secondary displacement rate and provided satisfactory fracture healing; a drawback of this technique is in its most common complication: intra-articular cement leakage secondary to screw perforation ⁸².

CF-PEEK Plates

Metal plates are actually the most commonly used kind of implant. Their outcomes have been thoroughly evaluated and long follow-up is available. Recently, the use of carbon fiber-reinforced polyether ether ketone (CF-PEEK) plates has been proposed (Fig. 2).

CF-PEEK is a composite biomaterial composed of carbon fiber sheets embedded in a PEEK matrix. It is chemically inert and insoluble in conventional solvents at room temperature. CF-PEEK plates have many positive characteristics: unique mechanic properties, radiolucency, peculiar plate/screw interaction, and decreased risk of allergic reactions in metal-sensitive patients ⁸³.

Elastic modulus of CF-PEEK is similar to that of cortical bone, conferring both high load-carrying capacity and low rigidity ^84-86. CF-PEEK plates demonstrated similar mechanical properties to that of titanium plates, except for bending strength, inferior by 20% to that of a metal proximal humerus plate, and yet adequate for proximal humerus fixation, with the advantage of decreased debris particles formation ^84,85. Its increased flexibility may exert a positive effect on fracture healing ⁸⁷; its elastic modulus should unload the screw-tip/bone interface and therefore lower the rate of secondary screw perforation and loss of reduction ⁸⁸. The radiolucency grants an easier intraoperative fluoroscopic evaluation of fracture reduction and greater tuberosity position and a clearer post-operative radiographic assessment of reduction loss and fracture healing (Fig. 3). Furthermore, it reduces the “starburst effect” and artifacts on CT and MRI, an advantageous characteristic for post-operative assessment and in the event of future pathologies ^83,89. Due to the difference in material composition, cold welding between plate and screws is avoided, allowing easier and safer hardware removal ⁸³. Locking screws of CF-PEEK plates can cut-through plate material, tapping their thread, or can lock to pre-machined threads in the plate holes ⁸⁷. No changes in biomechanical properties of the plate was detected depending on plate/screw interface ⁸⁶. CFR-PEEK plates show greater load to failure in the interface between distal locking screws and plate, with comparable stiffness with stainless steel plates.

In a multicenter study of 160 cases, at 2-year follow-up, good subjective and objective results were obtained; 5% of screw cut-out was observed, and 1.2% of backing out of screws from the plate. Two cases of non-union were registered and 8.1% of osteonecrosis. No foreign body reaction in tissues surrounding the implant was demonstrated ⁸³. Similar good clinical results were reported in other smaller series ^88,90,91.

A comparison of CF-PEEK and historical cohorts of conventional plates demonstrated better clinical results of CF-PEEK plates over metal plates ⁹⁰, but not confirmed by other authors ⁸⁸. Only one study directly compared the two types of implants: no clinical difference was observed, but greater bone remodelling under the plate was observed in CF-PEEK and higher tuberosity resorption in the metal group ⁹¹.

Complications

A recent meta-analysis reported the complications of PHF treated with a locking plate. The most common complication was intraarticular screw penetration, found in 9.5% of cases, followed by varus collapse in 6.8%, subacromial impingement in 5.0%, avascular necrosis in 4.6%, adhesive capsulitis in 4.0%, non-union in 1.5%, and deep infection in 1.4% ⁹². The cumulative reoperation rate was 13.8% ⁹². Mechanical complications related to failure of the fixation; factors that were proved to be associated with fixation failure and, thus, predisposing to complications, are: low bone mineral density, quality of reduction (reduction of angulation, correction of head-shaft displacement and restoration of medial cortical support), age, screw length in the proximal rows of the plate, number of screws in the inferior part of the humeral head, and distance between screws and the articular surface ^{43,47,59,62,93}.

Intra-articular screw penetration

Intra-articular screw penetration is the most common complication, leading to repeated surgery to remove the screws or even to revise the implant. It can be divided into primary penetration, when intraoperative screw malpositioning occurs, and secondary penetration, when screw penetration occurs after collapse of the humeral head. The majority of screw penetration occurs after avascular necrosis, in displaced articular fractures ⁹⁴. To reduce the incidence of this complication, placing screws at least 2-3 mm from the subchondral bone could be helpful ²⁸.

Varus collapse

Varus collapse is one of the main complications of proximal humerus plating, as it will cause, in turn, screw penetration and subacromial impingement (Fig. 4). Restoration of medial hinge is mandatory to prevent varus collapse: a neck shaft angle reduction typically occurs during the first three months after surgery, with a mean loss of 3.8-4.9° ^95,96, leading, in predisposed cases, to varus collapse. Factors associated with varus collapse are: presence of proximal screw cross-threading, initial calcar disruption, and a lack of reduction of calcar support ⁹⁷.

Subacromial impingement

Subacromial impingement can be caused by positioning the lateral plate too high, malunion of the great tuberosity, or varus collapse of the humeral head. The most common cause is plate malpositioning, thus requiring hardware removal.

Avascular necrosis

Osteonecrosis is a delayed complication, being diagnosed at a mean 11.8 months after surgery ⁹⁸ and, not surprisingly, leading to worse clinical outcomes ⁹⁸. Among predictors of osteonecrosis, varus collapse of the humeral head, disrupted medial calcar, poor reduction, diabetes mellitus, chronic kidney disease, and chronic liver disease were found ^56,99. Development of avascular necrosis depends on a combination of mechanical and biological aspects. Impairment of humeral head vascularization is a common event after a PHF, as vessels are commonly involved. Humeral head ischemia is the first step towards osteonecrosis. Hertel et al. ⁹ evaluated factors associated with humeral head ischemia. These were: short calcar, disrupted medial hinge and anatomic neck fracture ⁹. Posteromedial extension of the humeral head fragment is inversely correlated to humeral head ischemia: the shorter the calcar fragment, the less perfused the head was ⁹. Hertel’s criteria were demonstrated to be predictive of osteonecrosis ⁹⁹. Despite this, even in an ischemic head, revascularization or creepy substitution can happen: only 20% of instrumentally proven ischemic heads suffered, after 2 years, of avascular necrosis ¹⁰⁰.

Conclusions

Locking plate osteosynthesis is widely considered the main option for surgical treatment of PHF. It can provide excellent clinical results, but high complication rates have been reported. Indications for plate fixation are elusive: careful selection of patients based on surgeon’s knowledge and experience is mandatory to avoid unwanted complications. Various augments and plate designs have been proposed, yet none demonstrated clear superiority over the others. Further research, improved techniques, and implant refinements are still needed to clarify the indications and provide uniform results to patients.

Figures and tables

Figure 1.Osteosynthesis with locking plate for proximal humerus fracture.

Figure 2.Osteosynthesis with a CF-PEEK locking plate.

Figure 3.Post-operative imaging after osteosynthesis with a CF-PEEK plate.

Figure 4.Varus collapse of the humeral head and intra-articular screw penetration.

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