The terrible triad of the elbow is a difficult injury with historically poor outcomes. Improved experience, techniques, and implants have advanced to the point where restoration of elbow stability can be expected. Careful attention to each destabilizing element of the injury pattern is essential and places high demands on the surgeon’s mastery of the anatomic complexity of the elbow. Technically, the surgeon must bring every skill to bear, as soft tissue techniques, fracture repair, and joint arthroplasty are routinely required to adequately treat these complex constellations of injury.
Key Points
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The elbow is a 3-dimensionally complex joint where stiffness is poorly tolerated and instability is devastating.
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Although multiple periarticular fracture patterns and soft tissue injuries of the elbow have been described, the combination of coronoid process fracture, radial head fracture, and elbow dislocation has earned the moniker “terrible triad” by virtue of its challenging treatment and historically poor outcomes.
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This injury represents a failure of each bony and ligamentous stabilizer of the elbow; therefore, treatment must restore sufficient stability to permit early motion, thereby avoiding disabling stiffness.
Introduction
The elbow is a 3-dimensionally complex joint where stiffness is poorly tolerated and instability is devastating. Although multiple periarticular fracture patterns and soft tissue injuries of the elbow have been described, the combination of coronoid process fracture, radial head fracture, and elbow dislocation has earned the moniker “terrible triad” by virtue of its challenging treatment and historically poor outcomes. This injury represents a failure of each bony and ligamentous stabilizer of the elbow; therefore, treatment must restore sufficient stability to permit early motion, thereby avoiding disabling stiffness.
Introduction
The elbow is a 3-dimensionally complex joint where stiffness is poorly tolerated and instability is devastating. Although multiple periarticular fracture patterns and soft tissue injuries of the elbow have been described, the combination of coronoid process fracture, radial head fracture, and elbow dislocation has earned the moniker “terrible triad” by virtue of its challenging treatment and historically poor outcomes. This injury represents a failure of each bony and ligamentous stabilizer of the elbow; therefore, treatment must restore sufficient stability to permit early motion, thereby avoiding disabling stiffness.
Relevant anatomy
The elbow supports the intersection of 3 bones, between which are 3 articulations: ulnohumeral, radiocapitellar, and proximal radioulnar ( Fig. 1 ). The first two of these articulations are ginglymus (hinge) joints, whereas the last is a trochoid (pivot) joint. The terrible triad injury destabilizes the relationship between the humerus and the forearm bones, whereas the relationship between the ulna and radius (including the interosseous membrane) is rarely disrupted in this injury pattern.
While the elbow shares the humerus in common with the shoulder joint, its personality could not possibly be more different. Unlike the relatively straightforward spheroidal glenohumeral joint with its complex circumferential soft tissue stabilizers, the elbow has a complex three-dimensional bony anatomy but relatively simple soft tissue structure consisting of medial and lateral collateral ligaments as well as anterior and posterior capsular elements.
The trochlea of the distal humerus is located centrally, in line with the shaft of the humerus, and articulates with the greater sigmoid notch of the proximal ulna. The apex of the trochlea articulates with the sagittal ridge of the greater sigmoid notch, making the ulnohumeral joint a highly congruent and inherently stable articulation.
The radiocapitellar joint is also a hinge but has much less intrinsic stability. Nevertheless, it functions as an important stabilizer of the elbow against valgus stress. The radial head is elliptical, so as to allow the bicipital tuberosity to not impinge on the ulna when the forearm is in full pronation, but this elliptical shape is not consistent between individuals. The anterior and posterior capsules are relatively uniform, without discrete thickenings. Laterally and medially, however, distinct thickenings form the collateral ligament complexes, each of which is composed of multiple components.
The medial collateral ligament (MCL) complex is composed of 3 bands: anterior, posterior, and transverse ( Fig. 2 A). The first two originate from the inferior aspect of the medial epicondyle, whereas the last one does not cross the elbow joint itself. The anterior band is the most distinct and significant of these bundles and inserts on the sublime tubercle of the coronoid. Inserting more posteriorly, on the olecranon, is the posterior band, whereas the transverse band is attached at both ends to the ulna, spanning the distance from the tip of the olecranon to the coronoid process.
Laterally, the collateral ligament complex is similarly made of up of 3 components: the lateral ulnar collateral ligament (LUCL), the radial collateral ligament, and the annular ligament (see Fig. 2 B). Similar to the MCL complex, the first two components attach proximally on the epicondyle, whereas the annular ligament is a proximal radioulnar joint stabilizer that both originates and inserts on the ulna. The LUCL, which inserts on the crista supinatoris of the posterior proximal ulna, is a major stabilizer against varus stress and also supports the radial head like a sling, preventing posterolateral rotatory subluxation. The radial collateral ligament does not attach to the radius or ulna directly, but rather to the annular ligament.
Biomechanics
Load bearing across the elbow is predominantly at the radiocapitellar joint (60%), rather than at the ulnohumeral joint (40%). The latter, with its highly congruent configuration, is structured primarily for stability rather than for load bearing and contributes as much as 50% of the overall stability of the elbow. The stability conferred by these bony structures is what allows most simple elbow dislocations to remain stable after reduction. As displacing forces most commonly act on the elbow in a posteriorly directed manner, the coronoid is particularly vital. Large coronoid fragments destabilize the elbow considerably and even very small fractures may portend a great deal of instability by virtue of their unique anatomic shape and attachment to the anterior capsule. The latter are more common with terrible triad patterns. Fractures of the anteromedial coronoid are associated with a different mechanism of injury and are uncommon in terrible triad injuries.
As mentioned above, the ulnohumeral and radiocapitellar articulations are hinge joints, but their axis of flexion/extension varies with position, by approximately 3° to 6° in orientation and 1.4 to 2.0 mm in translation. On average, however, this axis runs from the anteroinferior aspect of the medial epicondyle (just anterior to the origin of the anterior band of the MCL) to the center of the trochlea and the center of the capitellum on lateral radiography. The location of this axis has important implications for the placement of hinged external fixators in particular. Normal range of motion in this plane is 0° to 140° of flexion, although most activities of daily living may be performed with a limited range of 30° to 130°.
Forearm rotation normally encompasses an arc of 180°, divided equally between pronation and supination, although a loss of 30° at either end is usually well tolerated and permits typical activities of daily living. Abduction at the shoulder does compensate for limited pronation, but no similar compensatory movement can substitute for supination. Forearm rotation also affects elbow stability. For example, supination of the elbow increases the joint reactive force at the ulnohumeral joint and increases stability against elbow dislocation. However, in the LUCL-deficient elbow, supination is also implicated in posterolateral rotatory instability, whereby the radial head subluxates posterolaterally, whereas the ulna tilts apex lateral. A position of pronation protects against this posterolateral rotatory instability.
In response to valgus stress, the radial head abuts the capitellum and provides approximately 30% of total elbow stability in this scenario, more so when the MCL is incompetent. Restoration of the radial head restores valgus stability to nearly that of the intact elbow. The MCL, with its anterior band taut in extension and its posterior band taut in flexion, also resists valgus stress throughout the range of elbow motion.
The lateral collateral ligament (LCL) complex is hypothesized to be the first structure to fail in dislocation of the elbow. The LUCL, as described above, is necessary to prevent posterolateral rotatory instability, and it is the major soft tissue stabilizer of the elbow, against varus stress. Although there is some controversy as to the exact contribution of each element of the LCL complex, it has been demonstrated that reconstruction of the LUCL alone reliably restores posterolateral stability, suggesting that LUCL is the primary critical stabilizer against this particular instability pattern.
The terrible triad injury pattern most commonly results from the axial loading of a relatively extended elbow with the forearm in supination ( Fig. 3 ). This position encourages posterolateral escape of the radial head after failure of the LUCL, whereas the axial loading causes shearing of the radial head and coronoid process. In fact, the terrible triad can be conceptualized quite accurately as the ultimate posterolateral rotatory instability.
Presentation
The terrible triad is an injury of the adult elbow. The mechanism may be either high or low energy. In Ring’s series of 22 patients, 12 occurred as a result of a fall from standing, with the remaining 10 caused by a fall from a greater height. In Mckee’s series of 40 patients, 14 were attributed to falls from standing, 11 to higher energy falls, 5 to bicycle accidents, 4 to sports injuries, and 1 each to motorcycle accident and crush injury.
Typically, the most obvious component of the injury is dislocation of the elbow. However, spontaneous reduction may prevent radiographic documentation of frank instability. A thorough history can reveal such an episode, or alternatively, dislocation can be inferred in the presence of hallmark fractures of the radial head and coronoid. Nerve involvement, particularly of the ulnar nerve, must be rigorously elicited and documented, after a closed reduction if need be. The presence of ulnar nerve symptoms may dictate whether or not a medial surgical approach is anticipated, as will be discussed later.
Imaging
Standard anteroposterior (AP) and lateral radiography should be performed as part of the initial evaluation. Oblique radiographs may better characterize a radial head or coronoid fracture pattern. The AP image should also be carefully scrutinized for a fleck of bone off of the lateral epicondyle, representing a bony avulsion of the LUCL. In exceptional circumstances, when the dislocated status of the joint is identifiable on physical examination and a qualified provider is immediately available, closed reduction of the elbow may be performed before standard imaging studies are performed; otherwise, both injury and postreduction images should be evaluated for bony fragments, which can frequently be subtle findings.
Although careful examination of plain radiographs is invaluable, the overlap of the proximal ulna and proximal radius on lateral radiography, as well as the overlap of the coronoid process on the trochlea on AP radiographs, means that conventional radiographs may obscure significant bony injuries. Computed tomography (CT) has been used extensively and effectively as an adjunct imaging modality. However, as with fractures of the distal humerus and proximal ulna, universally accepted indications for CT imaging of terrible triad injuries have not been produced. The authors see CT to be most helpful in identifying occult fractures of the coronoid and/or radial head when such injuries are suspected but not visualized on plain radiographs. In such circumstances, CT findings can change the management profoundly, from closed treatment to open surgery. CT scan has also been identified as a critical imaging modality to assess and characterize the size and morphology of coronoid fractures and radial head articular fragmentation. Both the size of the coronoid fracture and the degree of articular fragmentation of the radial head alter operative fixation techniques and should be well understood preoperatively.
Acute management
After a thorough history taking and physical examination, closed reduction of the elbow should be performed. An immediate postreduction examination defining the stable range of motion is helpful when fractures of the radial head and coronoid have not been identified on injury radiographs. When the terrible triad injury pattern has already been diagnosed based on initial radiographs, this postreduction assessment may cause additional harm to the already damaged articular surfaces.
A posterior splint is applied with the forearm in neutral position and the elbow reduced in a position of approximately 90° of flexion. While the instability conferred by the terrible triad injury pattern is such that reduction rarely requires extreme effort, soft tissue interposition can occasionally be a block to reduction and fracture fragments may become incarcerated, leading to an incongruous reduction ( Fig. 4 ). A failed reduction demands consideration for either a repeat attempt using (1) closed means and a general anesthetic if the initial attempt was under conscious sedation or (2) an open reduction to clear interposed soft tissues or incarcerated fracture fragments.
After achieving reduction, most terrible triad injuries can be adequately held reduced in a splint, with definitive management scheduled on an elective basis. However, if the reduction is unstable, and the surgeon or circumstances (staff, equipment, etc.) are not optimal for acute definitive management, the elbow may be temporarily stabilized, with a static external fixator or transarticular fixation.
Definitive management
Stabilization of the terrible triad using internal means should, as with any complex periarticular fracture, be carefully planned and performed under optimal conditions. A rested and familiar staff is beneficial. Despite appropriate planning, many decisions affecting implant choice are made intraoperatively. The necessary equipment for stabilization of a terrible triad elbow is listed in Box 1 .
Hand table
Large fluoroscope
Sterile tourniquet
Surgical headlight
Hand set
2.4- and 2.7-mm screws
Mini fragment plates
Radial head arthroplasty
Hinged elbow external fixator
No. 2 braided nonabsorbable suture
Hewson suture passer
Suture anchors
Semitendinosus allograft
The goal of surgical treatment is to restore stability to the ulnohumeral and radiocapitellar joints, allowing early flexion/extension and pronosupination and avoiding crippling stiffness. In the most successful case series in the literature, coronoid and radial head fractures as well as the soft tissue stabilizers of the elbow were addressed. Therefore, we recommend addressing all 3 elements of the terrible triad injury in all cases rather than addressing just 1 or 2 and hinging decisions for further stabilizing measures on intraoperative assessment of stability with dynamic fluoroscopy.
Exposure, then, must be extensive enough to allow access to the coronoid, radial head, and collateral ligaments. The radial head and LUCL are both lateral structures that are, naturally, best accessed laterally. The MCL is a medial structure that can only be exposed medially. It is the coronoid that represents a quandary; being more midline than medial in the coronal plane, its key feature is how anterior it is located. Therefore, it may be approached either medially or even laterally. Regardless, the challenge in its exposure comes from the overlying brachialis and flexor–pronator mass, as well as the close proximity of the median nerve and bifurcating brachial artery. Last, it is worth mentioning an injured ulnar nerve, which for reasons other than stability may need exposure and release, both of which are possible only with a medial approach.
The possibility of needing simultaneous access to the medial as well as the lateral elbow has led some surgeons to recommend a midline posterior skin incision, the so-called global approach to the elbow. Skin flaps are then raised medially and laterally until the appropriate deep dissection can be performed on both sides. This utilitarian approach permits full exposure of the elbow and provides a window for revision surgery, such as a capsular release.
The authors use a single lateral skin incision, accompanied by a separate medial incision if required for coronoid exposure, MCL repair, or ulnar nerve transposition. This approach has been popularized by King. The lateral approach is ideal for supine positioning with a fluoroscopically compatible hand table extension. The incision is typically centered over the lateral epicondyle. Distally, the incision is carried out in line with the radius. Once the fascia overlying the extensors is exposed, multiple options exist for deep dissection, including intervals between the extensor carpi radialis longus (ECRL)/extensor carpi radialis brevis (ECRB) and extensor digitorum communis (EDC) (Kaplan) or the extensor carpi ulnaris (ECU) and anconeus (Kocher). The former is marked by a fat stripe visible through the extensor fascia ( Fig. 5 ). It has 3 distinct advantages over the ECU–anconeus approach. First, it allows the surgeon to stay anterior to the main substance of the LUCL, without violating it. In this approach, the annular ligament must be divided, but this is a proximal radioulnar joint stabilizer and not a radiocapitellar stabilizer. Second, the more anterior approach allows better access to the anterolateral radial head, which is key in the prevention of posterior dislocation. Last, because of the quite anterior location of the coronoid, highlighted previously, the more anterior approach to the radial head also makes for an easier coronoid exposure from the lateral side. Despite these advantages, the principle of working through traumatic intervals should remain a guide; frequently, the injury itself will present the surgeon with a workable plane that requires minimal further insult to the soft tissues.
