Fractures of the coronoid process: state of the art

Abstract

Coronoid fractures are rarely isolated and are much more frequently associated with other osseous or ligamentous structures injuries. On the basis of the coronoid fracture patterns, described by the O’Driscoll classification, it is possible to recognize three main patterns of injury that differ on traumatic mechanism and on associated lesions: posterolateral rotatory instability, posteromedial rotatory instability, and axial load injuries. The management of coronoid fractures is challenging and varies according to characteristics of the fracture, associated lesions, and amount of elbow instability. In general, operative treatment is indicated in every case the fracture is at least 50% of the whole coronoid, whether the sublime tubercle is involved, and whether the ulno-humeral joint is not perfectly reduced. In conclusion, the correct management of the coronoid, especially in the setting of complex elbow instability, represents a predictive factor for patient outcomes and functional results. The stability of the elbow, rather than the size of the coronoid fragment, is the main parameter for surgical indication, aimed to fix the coronoid and/or repair the associated lesions.

Introduction

The coronoid process plays a key role in elbow stability. It is the unique primary bony elbow stabilizer, and acting as an anterior buttress, it provides stability against posterior and varus dislocation of the joint. The coronoid process provides the insertion for important soft tissue stabilizers of the elbow (anterior capsule, medial collateral ligament (MCL), brachialis muscle). Its fracture can undermine the global stability of the elbow joint and correct treatment is the key to prevent dislocation, pain, stiffness, and early arthritis. The incidence of coronoid fractures is reported between 7.5 and 14 per 100,000 persons per year [1], and they represent approximately 10–15% of all elbow fractures [2].

Only rarely are coronoid fractures isolated. More commonly [3] they are associated with osseous and ligamentous injuries of the elbow. For this reason, in most cases, coronoid fracture is highly suggestive of elbow instability and identifies a complex elbow instability pattern. In case of an elbow fracture–dislocation, the coronoid fracture can be considered the “black box” useful to decoding the dynamic of trauma: based on its size, location, morphology, it is possible to trace the traumatic mechanism and to define the injury pattern and the associated soft tissue lesions [4]. Moreover, in case of complex elbow dislocations in which the dorsal cortex of the ulna is fractured, it is possible to distinguish three main patterns according to what the coronoid remains attached to: (a) trans-olecranon fracture–dislocations, (b) Monteggia variant fracture–dislocations, and (c) transulnar basal coronoid fracture–dislocations. They present different prognosis and require different treatment strategy [5].

The management of coronoid fractures is a topic of interest in the literature, and still remains a challenge for expert elbow surgeons as well. The coronoid can be involved in multiple patterns of injuries, and its management, especially in the setting of complex elbow instability, represents a predictive factor for patient outcomes and functional results. The aim of the present study is to offer an overview on coronoid fractures and their appropriate management, from diagnosis to surgical approaches and fixation techniques.

Anatomy

The coronoid process is a primary stabilizer of the elbow.

It provides stability to the elbow for three main reasons: it has a bony buttress effect preventing posterior dislocation of the ulna, it resists varus stress forces, and it provides a bony insertion site to important capsular, ligamentous, and muscular structures [6]. The coronoid has a pyramidal shape, and it can be divided into three main portions: body, base, and tip, with an articular surface and a cortical one. The base of the coronoid is continuous with the ulnar metaphysis. The tip, curved upward, is received in flexion into the coronoid fossa of the distal humerus. The articular surface of the coronoid constitutes the anterior portion of the greater sigmoid notch, and it is formed by an anterolateral and an anteromedial facet (AMF). The anterior capsule inserts 2–6 mm from the coronoid tip. More distally, the brachialis muscle has a broad insertion on the base of the coronoid, while the oblique cord inserts onto its antero-inferior portion. Medially, the anterior bundle of the MCL inserts onto a prominent surface, the sublime tubercle. The lateral aspect of the coronoid process presents an articular depression, the lesser sigmoid notch, which articulates with the radial head (Fig. 1).

Fig. 1.

Anatomy of the coronoid with its soft tissue insertions. a/p MCL anterior and posterior bundle on medial collateral ligament, AL annular ligament, BM brachialis muscle, ST sublime tubercle, AC anterior capsule

Classification

The classifications of the coronoid fractures evolved over time (Table 1): initially, in 1989, Regan and Morrey [7] proposed the first classification of coronoid fractures into three types on the basis of the amount of the process that is involved evaluated on lateral view X-rays: type 1 fractures are smaller then 25%; type 2 fractures involve 25–50% of the coronoid height; and type 3 fractures involve large fragments more than 50% of the coronoid height (Fig. 2). In type 2 fractures a line drawn from the apex of the olecranon through the base of the fractured coronoid is roughly parallel to the ulnar longitudinal axis (Fig. 3) [6].

Table 1.

Classifications of coronoid fractures

Classification of coronoid fractures		Evaluated features	Imaging
Regan–Morrey	Type 1: < 25% Type 2: 25–50% Type 3: > 50%	Percentage of the fractured fragment in respect to total coronoid height	Lateral X-rays
O’Driscoll	Tip (PLRI) -Subtype 1: (< 2 mm) -Subtype 2: (> 2 mm) AMF (PMRI) -Subtype 1: (AMF) -Subtype 2: (AMF + tip) -Subtype 3: (AMF + sublime tubercle ± tip) Basal (Axial load) -Subtype 1: isolated basal -Subtype 2: Transulnar basal fracture-dislocations	Size, location/morphology, traumatic mechanism, treatment algorithm	2D and 3D CT scan
Wrightington	A: anteromedial coronoid fracture associated with LCL ± pMCL lesion B: bifacet/basal B+: bifacet/basal + radial head fracture C: combined/comminuted (anterolateral facet + radial head fracture)	Location, associated lesions, treatment algorithm	2D and 3D CT scan

AMF anteromedial facet, PLRI posterolateral rotatory instability, PMRI posteromedial rotatory instability

Fig. 2.

Regan Morrey classification of isolated coronoid fractures based on lateral radiographic view

Fig. 3.

A In a normal elbow the longitudinal ulnar axis and the line connecting the apex of the olecranon and coronoid process form a 30° angle. B When the fracture involves 50% of the coronoid, the lines become parallel

Over the last three decades, with the widespread use of computed tomography (CT) technology, a greater understanding of coronoid fracture patterns has become possible. In 2003, O’Driscoll [4] introduced a new classification, still commonly used, based on CT evaluation of the size, location, and traumatic mechanism of the coronoid fractures: tip fractures, further divided into subtype 1 (< 2 mm) and subtype 2 (> 2 mm); AMF fractures, divided into subtype 1 (anteromedial rim), subtype 2 (anteromedial rim and tip) and subtype 3 (anteromedial rim involving the sublime tubercle with or without the involvement of the tip); and basal coronoid fractures, divided into subtype 1, isolated basal; and subtype 2, transulnar basal fracture–dislocations (Fig. 4). Recently, Watts and colleagues [8] introduced the Wrightington classification of the elbow fracture–dislocations, which, focusing on the coronoid involvement of its anteromedial and/or anterolateral facet and if it is accompanied with a radial head fracture, identifies six different patterns, each requiring specific treatment strategies.

Fig. 4.

O’Driscoll classification of coronoid fractures based on CT

Imaging

Standard anteroposterior and lateral elbow X-rays are usually the first exam for the assessment of coronoid fractures. Lateral X-rays are generally the most significant: in case of tip fractures the coronoid fragment is dislocated superiorly due to the traction forces of the anterior capsule and the brachialis muscle. Instead, in case of anteromedial facet fractures, it is possible to detect the double contour sign. On radiographs it is also possible to assess joint congruity and associated lesions such as proximal radial and/or proximal ulnar fractures. The use of CT with two-dimensional (2D) and 3D reconstruction is recommended in almost all coronoid fracture cases to assess joint congruency, to better evaluate the morphology of the fracture and its possible comminution, to identify the injury pattern, and to plan surgery if needed.

Patterns of injury

Coronoid fractures are rarely isolated and are much more frequently part of complex elbow instability injuries. On the basis of the morphology of the coronoid fracture, described by the O’Driscoll classification, it is possible to recognize three main patterns of injury that differ on traumatic mechanism and on associated lesions: posterolateral rotatory instability (PLRI) associated to coronoid tip fractures, posteromedial rotatory instability (PMRI) associated with AMF fractures, and axial load injuries associated with basal coronoid fractures [9–11].

The tip fractures subtype 1 are a small flake of the tip (< 2 mm) and are associated with simple elbow dislocations. Further, tip fractures subtype 2, which involve a larger part of the tip (> 2 mm), are rarely more than one-third of the height of the coronoid and are typically present in the terrible triad injuries, caused by PLRI that results from axial loading with valgus stress and supination of the forearm [12]. Associated lesions are radial head fractures and lateral collateral ligament (LCL) complex tears. The MCL is frequently, but not always, injured.

Anteromedial facet fractures are typically associated with varus posteromedial rotatory instability (PMRI) [5], which consists of a subluxation of the elbow causing the impaction of the medial trochlea onto the anteromedial coronoid. PMRI results from axial loading, varus stress, and pronation of the forearm. Associated lesions involve tear of the posterior bundle of the MCL and of the lateral collateral ligament complex. The radial head occasionally can be involved, however, the anterior bundle of the MCL is not injured.

Basal coronoid fractures are caused by an axial load on the elbow in which the distal humerus is driven across the greater sigmoid notch causing the fracture of the coronoid process and possibly the fracture of the proximal ulna, creating a transulnar basal coronoid fracture–dislocation. The radial head is often fractured, and the ligamentous injuries can result in avulsion fractures of the crista supinatoris or of the medial region of the ulnar metaphysis [13].

Surgical approaches to the coronoid

The decision on which surgical approach to use for coronoid fractures depends mainly on fracture type and dimensions, the presence of associated lesions, and the planned fixation method.

• Medial approaches (Fig. 5)

Fig. 5.

Six medial approaches to the coronoid. A Hotchkiss (over the top) approach. B Smith approach. C Extended anteromedial approach (EMEA). D FCU-split approach. E Taylor Scham approach. F Orbay approach. UN ulnar nerve, PT pronator teres, FCR flexor carpi radialis, PL palmaris longus, FDS flexor digitorum superficialis, FCU flexor carpi ulnaris

There are six possible approaches into the flexor-pronator muscles to expose the coronoid.

1. The Hotchkiss (over the top) is the most anterior one. This approach was initially described for elbow stiffness release, but it is also useful for treating fractures of the anteromedial coronoid facet [14]. The medial intermuscular septum is identified proximally and excised from from the supracoldylar ridge. The internervous plane passes between the flexor-pronator mass (median nerve) and the flexor carpi ulnaris (FCU) (ulnar nerve). The pronator teres, the flexor carpi radialis, and the palmaris longus are excised with the anteromedial capsule from the medial supracondylar ridge and medial epicondyle, leaving the humeral head of the flexor carpi ulnaris (FCU) attached to the medial epicondyle to protect the MCL insertion and the ulnar nerve. Reflecting anterolaterally the flexor-pronator mass together with the adjacent brachialis, the median nerve and brachial artery are protected.

This approach allows for good exposure of the tip of the coronoid, but little or no exposure of the sublime tubercle. The over the top is indicated to treat tip fractures and anteromedial coronoid fractures not involving the sublime tubercle, especially the inveterate ones, because its wide anterior exposure allows for an extensive capsular release.

• (2)Jost et al. [15] described the extended medial elbow approach (EMEA), which is a combination of the over the top approach and the Smith approach and requires the detachment of the FDS, FCU, and the ulnar head of the PT to expose the whole medial bony surface of the proximal ulna [16].
• (3)The Smith approach [17] (Figs. 6, 7) was developed to repair the anterior band of the UCL and allows for visualization of the sublime tubercle and the coronoid area anterior to it. The approach is centered over the sublime tubercle and consists in a muscle splitting approach through the posterior one-third of the flexor tendon mass. The internervous plane between the FCU and Palmaris Longus (PL) superficially and the FCU and flexor digitorum superficialis (FDS) deeper is developed. To repair or reconstruct the MCL the split extends from the medial epicondyle to a point 1 cm distal to the MCL insertion on the sublime tubercle, but for plating the coronoid the approach can be extended distally. This is our suggested approach to fix anteromedial coronoid fracture subtype 2, and some selected subtype 3, where a screw or plate fixation is expected.
• (4)The FCU-split approach develops the interval between the humeral and ulnar head of the muscle, where the ulnar nerve runs. Proximally the flexor pronator mass is released off the medial epicondyle for about 1 cm, leaving a portion of soft tissue attached for later repair. The UCL is isolated from the muscular layers and the flexor-pronator mass is retracted anteriorly.

Fig. 6.

Smith approach. Superficially the internervous plane between the FCU and PL is developed. UN ulnar nerve, PT pronator teres, PL palmaris longus, FCU flexor carpi ulnaris

Fig. 7.

Smith approach. The internervous plane between the FCU and FDS is developed deeper. UN ulnar nerve, PL palmaris longus, FDS flexor digitorum superficialis, FCU flexor carpi ulnaris, T trochlea, C tip coronoid tip

This approach allows for better visualization of the structures that are posterior to the anterior band of the UCL, including the sublime tubercle [16]. This approach is indicated for anteromedial fractures, especially those involving the sublime tubercle where a screw or plate fixation is expected.

• (5)The Taylor–Scham approach is used to reduce and fix large fragments that extend to the base of the coronoid process. This approach consists in elevating up the flexor-pronator mass from the dorsal ulna. This approach is usually required in case of transulnar basal fracture–dislocation.
• (6)The Orbay approach [18] is a medial approach to the coronoid where the fexor-pronator mass is released from its humeral origin by creating a proximally based tendinous flap. This approach is especially indicated for anteromedial subtype 3 involving the sublime tubercle, the anteromedial facet, and the coronoid tip.

In summary, Hotchkiss and Smith approaches allow for direct visualization of the anterior bundle of the UCL, its insertion, and the regions anterior to it, without allowing exposure of the regions posterior to the sublime tubercle. EMEA and FCU-split approaches offer a direct view of the sublime tubercle and of the regions both anterior and posterior to it. Taylor–Scham approach shows primarily the areas posterior to the anterior bundle of the UCL, without allowing exposure of the anterior part of the coronoid. The FCU-split and the Taylor–Scham allowed for visualization of the posterior bundle of the UCL. All the approaches develop an internervous plane, except the FCU approach. The Orbay medial approach allows for wide exposure of the whole coronoid and can be especially indicated for plating type 3 anteromedial coronoid fractures.

All those medial approaches require protection of the ulnar nerve during the reduction maneuvers and fixation phases of the surgery. Its exposure is mandatory using the FCU-split approach; using the other three approaches is indicated in every case that the fracture pattern or the local situation require direct visualization of the ulnar nerve to safely protect it. At the end of the procedure the tendon insertions detached to the medial column are repaired by sutures through bone tunnels or directly repaired if a tenotomy was used.

• Lateral approach

Tip fractures of the coronoid, in the presence of a terrible triad, can be managed with a lateral approach used to address the radial head fracture and the LCL tear as well. Usually the coronoid tip is exposed through the window created by the radial head fracture or osteotomy performed in preparation of the prosthesis. In case of partial radial head fracture without indication for replacement, the lateral approach to the tip of the coronoid is more difficult and requires the dissection to be extended more proximally, detaching part of the brachioradialis from the lateral supracondylar ridge.

• Posterior approach

The posterior approach to fix the coronoid is used in case of transulnar fracture–dislocations. In those cases the coronoid can be usually addressed through the window created by the olecranon fracture from a posterior approach to the elbow. The fracture is then fixed either with screws through the posterior plate or with free screws.

• Anterior approach

The direct anterior approach for anterior buttressing of large coronoid fragments has been proposed as another option to treat anteromedial coronoid fractures (type 2 a,b).

Through a transverse split of the bicipital aponeurosis, the vascular–nervous structures (brachial artery, vein, and median nerve) are exposed. Just more distally, the interval between brachioradialis and pronator teres muscle is developed and the brachial artery, biceps tendon, and brachioradialis are retracted laterally, whereas the median nerve and pronator teres are retracted medially, providing exposure of the brachial muscle that can be longitudinally split and retracted to visualize the coronoid fracture fragment and base of the coronoid process. This approach is rarely used due to the risk of damage to the neurovascular structures [19, 20] and the limited possibility to manage any associated lesions.

• Arthroscopic approach

Coronoid fractures are one of the main indications for elbow arthroscopy in the trauma setting. The arthroscopic approach to the coronoid is particularly indicated in case of AMF subtype 2 (without the involvement of the sublime tubercle), which are associated with PMRI.

Compared with the open technique, the arthroscopic approach has the evident advantage of preventing a double skin incision that is usually required in these fracture patterns. Moreover, elbow arthroscopy can also play a role in selected terrible triad cases, with tip fractures of the coronoid and minimally displaced, fixable, radial head fractures [21]. In those cases, arthroscopic technique allows for removal of crushed osteochondral fragments and fixation of small radial head and coronoid fracture [22]. On the basis of the size and comminution of the coronoid fracture, it can be arthroscopically fixed by cannulated screws, Kirschner wires (K-wires), or osteosutures; combinations among the different fixation techniques are also possible.

At the end of fixation of the bony stabilizers, PLRI can be evaluated using specific arthroscopic rotatory instability tests [23]. With the scope in the posterolateral compartment through the posterolateral portal, the radiocapitellar joint can be visualized. In case of PLRI, with the elbow flexed at 30° and applying a supination of the forearm, widening of the radiocapitellar joint can be seen. If an axial traction is applied, the pathological gap becomes even more evident. If the test is positive, the LCL may be reinforced with an arthroscopic imbrication [24].

However, elbow arthroscopy for fixing complex fracture patterns is a highly demanding surgical procedure and is not exempt from complications [25].

Nonoperative treatment

The concept of conservative treatment for selected cases has increasingly gained interest over the last 10 years since the publication of relevant papers on the topic [26–30]. Nonoperative treatment can be considered if the fracture is small (< 50%), without involvement of the sublime tubercle and if the joint is perfectly reduced and stable until the last 30–40° of extension. Detailed indications for nonoperative treatment are further described below.

• Elbow dislocation with coronoid flake

More than 90% of simple elbow instability cases can be treated conservatively and the presence of a coronoid flake does not change the treatment algorithm. If the elbow after the reduction is concentrically reduced, a conservative treatment is usually indicated.

• Terrible triads

Essential criteria for the nonoperative treatment of terrible triads include a concentric joint reduction, through a stable range of motion up to a minimum of 30° extension, a minimally displaced radial head fracture less than 30% of the articular surface, with absence of mechanical block to forearm rotation, and a smaller coronoid tip fracture (Regan–Morrey type 1–2) [28, 29]. Terrible triads treated nonoperatively need to be assessed clinically and radiographically with a strict follow-up every 7–10 days for the first month. There are clinical and radiographic red flags that can help to identify highly unstable cases at acute evaluation: the presence of (1) a massive ulno-humeral dislocation, (2) gross clinical instability with difficulty in maintaining joint reduction even in a cast or brace, (3) signs of radiographic elbow subluxation after reduction, and (4) displaced coronoid or radial head fragments. After a few days, other detectable red flags are the presence of extensive lateral and medial hematomas and persistent drop sign at the lateral X-rays. CT scan signs suggestive for instability are not concentric ulno-humeral or radio-humeral reduction on the sagittal plane and a severe Osborne–Cotterill lesion (Table 1).

• Anteromedial facet fractures

There is agreement in the literature regarding the indication for conservative treatment of AMF fractures when all the following criteria are respected: concentric joint reduction, coronoid fragment smaller than 50% of the coronoid height (Morrey type 1–2), intact sublime tubercle, and stable range of motion up to 30° of extension [31, 32]. According to most studies, the cutoff for conservative treatment of coronoid fractures based on the dimension of the fragment is between 5 and 6 mm. As for the terrible triads, concentric joint reduction needs to be assessed clinically and radiographically, not only at the first evaluation but also at a strict follow-up at 7–10 days after the trauma. Elbow stability through range of motion (ROM) can be assessed clinically, with the support of specific tests such as the varus posteromedial rotatory instability grind test. It consists of active flexion–extensions with the shoulder abducted and is considered positive if crepitus and varus laxity are detected, as they are indicative for AMF fracture of the coronoid and attenuation/tear of the LCL complex. However, in clinical practice, the evaluation of patients with acute fractures is often limited by the presence of pain and swelling of the elbow. In all unclear cases the fluoroscopy evaluation performed under narcosis can be a useful tool to detect signs of instability and guide to the most appropriate treatment. In case of AMF fractures, where the elbow is typically subluxed rather than fully dislocated, a varus stress test under fluoroscopy can confirm the presence of a consistent instability and the necessity to repair the LCL and to fix the coronoid fracture.

• Nonoperative treatment of coronoid with operative treatment of associated injuries

In some cases of complex elbow instability, coronoid fractures do not need to be fixed, because the joint stability can be achieved by repairing the other stabilizers. For example, in terrible triads, if the elbow is stable after having repaired (or replaced) the radial head and the collateral ligaments, small tip fractures can be left untreated without causing instability [30, 32, 33]. In the same way, in some selected cases of AMF fractures with sublime tubercle intact, it is possible to reach elbow stability only repairing the LCL complex and leaving the small coronoid fragments untreated.

Nonoperative treatment: rehab protocol

The rehabilitation protocol for patients treated nonoperatively usually involves an initial immobilization with a splint at 90° of flexion and neutral forearm rotation for 1–3 weeks depending on type of fracture and soft tissue involvement. An early referral to physical therapy is usually advised, starting with active and active-assisted elbow flexion/extension with neutral forearm rotation and forearm rotation exercises with the elbow flexed at 90° for progressive recovery of ROM. All patients treated nonoperatively need to be reassessed weekly for both clinical and radiographic evaluation to rule out complications such as early elbow subluxation/dislocation. The use of the splint is fully discontinued at 4 weeks, after the X-rays show correct joint reduction, but patients and therapists should be advised to avoid shoulder abduction for at least 6 weeks to protect the coronoid and the LCL from varus stresses. Strengthening exercises are usually started at 6–8 weeks when patients have reached a range of motion of at least 100 degrees in flexion–extension.

Operative treatment

Tip fractures

Tip fractures of the coronoid process are typically caused by a PLRI traumatic mechanism in the setting of the so-called terrible triads of the elbow. Small fractures of the tip of the coronoid can represent capsular avulsion and can imply an extensive soft-tissue injury associated with severe elbow instability. As stated above, tip fractures can be addressed from the same lateral approach used to treat the radial head fracture and the LCL tear. Small tip coronoid fractures, as well as comminuted ones, can be fixed with the Lasso-Loop technique: two high-strength sutures are passed through the medial and lateral portion of the coronoid still attached to the anterior capsule and then tied on the posterior aspect of the ulna through drill holes (Fig. 8). If the fragment is big enough, 1–2 retrograde cannulated screws or 2–3 K-wires can be used [34, 35].

Fig. 8.

Intraoperative image and schematic drawing of a coronoid tip fracture fixed with a Lasso-Loop technique using two high-strength sutures passed through the medial and lateral portion of the coronoid still attached to the anterior capsule and then tied on the posterior aspect of the ulna through drill holes

Anteromedial facet fractures (subtype 1 and 2)

The most frequent subtype of AMF fracture is O’Driscoll subtype 2, involving both the anteromedial facet and the tip of the coronoid. Anteromedial facet fractures, with or without the involvement of coronoid tip, are typically caused by a PMRI traumatic mechanism and are associated with LCL and posterior bundle of the MCL tears. If not properly treated, PMRI instability determines recurrent subluxation of the elbow, where impaction of the medial trochlea on the fractured coronoid occurs. This condition can rapidly cause the onset of elbow arthritis due to the continuous subluxation of the elbow [36].

Treatment options for anteromedial facet fractures include fixation with transosseous sutures, K-wires, screws, or plates depending on dimension and comminution of the fragment. As previously described, transosseous sutures, K-wires, or screws fixation can be performed with an open or arthroscopic approach (Fig. 9) [37]. The LCL repair is also often required to ensure elbow stability.

Fig. 9.

Anteromedial coronoid facet fracture. A, B 3D CT scan and lateral X-ray of a fracture of the anteromedial facet (subtype 2). C, D 1-year postoperative X-rays: fixation with cannulated screw and K-wires performed with arthroscopic technique

Anteromedial facet fractures (subtype 3)

The involvement of the sublime tubercle, which is the insertion site of the anterior bundle of the MCL, is a clear indication for operative treatment. Treatment requires an open medial approach and fixation using an anteromedial buttress plate (Figs. 10, 11) [38]. In case of severe comminution, additional transosseous sutures can enhance stability of the fragments. The LCL is usually torn and often requires repair using transosseous sutures or suture anchors.

Fig. 10.

Anteromedial coronoid facet fracture (subtype 3). A, B X-rays and 3D CT scan of anteromedial coronoid facet fracture with involvement of sublime tubercle. C, D 1 year postoperative X-rays: fracture fixation with a dedicated anteromedial buttress plate and screws

Fig. 11.

Anteromedial buttress plate fixation. FCU flexor carpi ulnaris, PL palmaris longus, T trochlea, ST sublime tubercle, C tip coronoid tip, B Brachialis muscle

Transulnar basal coronoid fractures

The importance of the coronoid process in the evaluation of complex elbow fractures dislocations has been clearly highlighted in the 2023 Mayo Classification [39]. In the three groups described by Barlow and colleagues [5] the transulnar basal coronoid is used to describe fracture dislocations of the elbow in which the coronoid process results to be neither attached to the ulnar metaphysis nor to the olecranon process. This group has been previously included as basal coronoid, subtype 2 [3] in the O’Driscoll coronoid classification. These fractures are commonly caused by an axial load associated with a rotational component that might lead to ligamentous injuries. The X-ray study must be completed by a CT scan for correct understanding of the fracture pattern. These fractures all require proper surgical treatment and the most important prognostic factors are the coronoid status, ability to treat the coronoid fracture, and the associated ligamentous injuries.

The key goals of the surgical treatment of transulnar basal coronoid fractures are:

1. The correct restoration of the proximal ulna dorsal angle (PUDA).

2. The correct restoration of the proximal radioulnar joint (PRUJ).

3. The correct reduction and fixation of the coronoid fracture.

Many authors have previously described the possible negative effects of an insufficient primary surgical treatment that can lead to poor clinical outcomes, nonunion, and development of early osteoarthritis [40].

Moreover, the treatment of sequelae of these fracture–dislocations is very complex.

A posterior approach is usually indicated for the treatment of these fractures. If the coronoid fragment is of sufficient dimensions, the first choice of fixation has to be through a posterior screw either coming from the ulnar plate or not [40]. This technique allows for a strong fixation of the fragment to be obtained without the need to add any other fixation device. If the comminution of the coronoid process does not allow for the possibility of the previously described fixation method, the suture Lasso-Loop technique should be considered: this technique allows for stable reduction of the coronoid fragments through a suture of the anterior capsule that is then fixed to the posterior aspect of the ulna. In case of extreme comminution of the coronoid process, an autograft or allograft reconstruction can be also considered: many techniques have been described, but our suggestion is to use the autologous radial head if a concomitant not-fixable radial head fracture is present, or homologous radial head or proximal ulna, according to hospital’s availability [41–43] (Fig. 12). If comminution of the coronoid metaphysis is present, reduction and fixation through a dedicated anteromedial coronoid plate, to be associated to the posterior plate, should be taken into consideration (Fig. 13). The coronoid plate provides a buttress effect that allows support to the small bone fragments allowing good support for healing [44].

Fig. 12.

A, B, C intraoperative images of coronoid reconstruction with homologous radial head. D, E Lateral X-rays and sagittal CT scan at 6 months showing the reconstructed coronoid with graft healing

Fig. 13.

ATransulnar coronoid fracture-dislocation (basal subtype 2). B Fixation of the basal coronoid fracture with screws through the posterior plate and K-wires

The Mayo clinic group also recently published their personal case history with a final cohort of 28 transulnar basal coronoid fractures treated between 2002 and 2019 [39]. All the elbows were treated through a posterior skin incision, with 11 requiring an additional deep surgical approach (7 lateral and 4 medial) and 5 elbows requiring an additional skin incision. The coronoid was treated with screw fixation 21 times (17 with separate lag screws and 4 with screws coming from the posterior plate), coronoid plating 4 times, and suture fixation 2 times. One coronoid was not treated and the patient developed early arthritis. The lateral ulnar collateral ligament was repaired 13 times (46%); 36% of these elbows developed complications, with 4 deep infections, 2 ulnar neuropathies, 2 elbow contractures, and 2 nonunion, with an overall requirement of 11 reoperations.

Complications

Complications as a result of a coronoid fracture and its associated lesions are relatively common.

Elbow stiffness, due to capsular contracture and/or to heterotopic ossification (HO) formation, is the most common complication. In these cases, if the elbow is stable and the joint has healed in a concentric reduction, a capsular release and HO removal can improve the final range of motion. Even if there are no evidence-based protocols, NSAID therapy is usually suggested to prevent HO formation, both in conservative or postoperative treatment.

Early fixation failure, joint instability, post-traumatic arthritis (Fig. 14), and ulnar nerve symptoms are also common complications of coronoid fractures and their treatment.

Fig. 14.

Fixation with double plate in a transulnar fracture–dislocation followed up at 5 years after surgery. Common complications of these fracture–dislocations are heterotopic ossifications and joint arthritis

Conclusions

The coronoid process plays a key role in elbow stability. The management of coronoid fractures is still a topic of interest in the literature, as the coronoid can be involved in multiple patterns of injuries and its management, especially in the setting of complex elbow instability, represents a predictive factor for patient outcomes and functional results. The use of CT scan is recommended in almost all coronoid fracture cases to assess joint congruency and to better evaluate the location, size, and comminution of the fracture. Stability of the elbow, rather than the size of the coronoid fragment, is the main consideration for surgical indication, aimed to fix the coronoid and/or repair the associated lesions.

In general, operative treatment is indicated in every case in which the fracture is at least 50% of the whole coronoid, if the sublime tubercle is involved, and if the ulno-humeral joint is not perfectly reduced.

Nonoperative treatment can be considered if the fracture is small (< 50%), without the involvement of the sublime tubercle, and if the joint is perfectly reduced and stable until the last 30–40° of extension. It is important to underline that even small coronoid tip fractures can be associated with severe instability and can require additional treatment of the associated lesions.

Take-home messages:

1. Coronoid process is a primary stabilizer of the elbow joint. It acts as a bony anterior buttress and provides insertion to soft tissues stabilizers: anterior band of the MCL, anterior capsule, brachialis muscles, and annular ligament.

2. In most cases a CT scan is necessary to assess the coronoid fracture pattern.

3. The treatment and the prognosis of the coronoid fracture is based on the pattern of fracture and its associated lesions.

4. Nonoperative treatment can be considered if the fracture is small (< 50%), without the involvement of the sublime tubercle, and if the joint is perfectly reduced and stable until the last 30–40° of extension.

5. Operative treatment is indicated in every case in which the fracture is at least 50% of the whole coronoid, if the sublime tubercle is involved, and if the ulno-humeral joint is not perfectly reduced.

Abbreviations

AMF

Anteromedial facet

PLRI

Posterolateral rotatory instability

PMRI

Posteromedial rotatory instability

LCL

Lateral collateral ligament

MCL

Medial collateral ligament

ROM

Range of motion

FCU

Flexor carpi ulnaris

FCR

Flexor carpi radialis

FDS

Flexor digitorum superficialis

PT

Pronator teres

PL

Palmaris longus

PUDA

Proximal ulnar dorsal angle

H.O.

Heterotopic ossifications

PRUJ

Proximal radioulnar joint

Author contributions

A.M, M.R., F.C, M.M., and G.C. conceived and wrote the article and E.G. supervised the work. All authors discussed the results reviewed and edited the manuscript and approved the final version of the manuscript.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Data availability

Not applicable.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Written informed consent was obtained from the patients for their anonymized images, to be published in the present review.

Competing interests

The authors declare that they have no competing interests in this section. The authors, their immediate families, and any research foundation with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.