5.3 Chronic instability of the elbow

Elbow instability is relatively uncommon in the general population. However, in the past few years it has received a lot of attention as the mechanism of elbow dislocation and types of elbow constraint have become much better understood.

Elbow dislocations or subluxations typically occur as a result of a fall onto the outstretched hand. The elbow experiences an axial compressive force as the hand hits the ground and the elbow starts to flex. The body then rotates internally on the elbow (forearm rotates externally on the humerus) resulting in a supination moment at the elbow. A valgus moment also occurs as the mechanical axis passes through the lateral side of the elbow. This combination of valgus, supination, and axial compression during flexion is the mechanism responsible for subluxation or dislocation of the elbow (Box 5.3.1). It can be divided into three stages. In stage 1 the ulnar part of the lateral collateral ligament is disrupted. This results in posterolateral rotatory subluxation of the elbow, which reduces spontaneously. With additional disruption, the capsule tears anteriorly and posteriorly. The elbow in stage 2 instability is capable of an incomplete posterolateral dislocation in which the medial edge of the ulna rests on the trochlea such that a lateral radiograph gives the impression of the coronoid being perched under the trochlea (Figure 5.3.1A). This can be reduced readily with minimal force or by the patient self-manipulating the elbow. In stage 3, the coronoid and radial head are fully posterior to the trochlea and capitellum, respectively. Depending on the severity of tissue disruption in stage 3 (A, B, or C) the elbow will be stable in valgus (stage 3A), unstable in valgus (stage 3B), or grossly unstable except when flexed greater than 90 degrees after reduction (stage 3C). In stage 3C, the entire distal aspect of the humerus is stripped of soft tissues, rendering the elbow extremely unstable even in a cast (Table 5.3.1). The pathoanatomy of these stages of elbow dislocation represent a circle of progressive soft tissue disruption from the lateral to the medial aspect of the elbow (Figure 5.3.1B).

The elbow has both static and dynamic constraints (Figure 5.3.2). The three primary static constraints are the ulnohumeral articulation, the medial collateral ligament, and the lateral collateral ligament, especially the ulnar part (the lateral ulnar collateral ligament). The secondary constraints include the radial head, the common flexor and extensor origins, and the capsule. The dynamic stabilizers include the muscles that cross the elbow joint and produce compressive forces across the joint. The anconeus, triceps, and brachialis are the most important muscles in this regard. If the coronoid process is fractured, the radial head becomes a critical stabilizer and must not be excised if the coronoid and the ligaments cannot be securely repaired.

Five criteria should be considered when evaluating elbow instability in order to help plan appropriate treatment:

Two categories of elbow instability exist according to the articulation(s) involved: the hinge joint (the radius and ulna as a unit articulating with the humerus) and the proximal radioulnar joint leading to subluxation or dislocation of the radial head from the ulna. Dislocation of the radial head from the ulna is usually traumatic and often part of a Monteggia fracture-dislocation. Instability can also involve both joints in a combined fashion.

In posterolateral rotatory instability (PLRI) the radius and ulna rotate externally in relation to the distal humerus, leading to posterior displacement of the radial head relative to the capitellum. Here, the proximal radioulnar joint is intact and both forearm bones rotate as a single unit. This differentiates PLRI from isolated dislocation of the radial head, where the proximal radioulnar joint is disrupted and the ulnohumeral articulation is intact. It is usually posterolateral rather than direct posterior so that the coronoid can pass inferior to the trochlea. The main static constraints to posterolateral laxity are the lateral ligament complex, the radial head, and the coronoid process, with a smaller contribution from the common extensor origin.

Traumatic: as the lateral ligament is the first to be disrupted, PLRI is the most common instability seen following elbow dislocation. It represents a spectrum of instability (see Figure 5.3.1). The Horri circle (stage I to III) represents the soft-tissue disruption that occurs in a circular fashion from lateral to medial when the elbow dislocates. The lateral ligament is usually avulsed from its humeral origin. Radial head and capiteller fractures can contribute to loss of height on the lateral side of the elbow, loss of congruity, and slackening of the lateral ligament complex. Therefore every attempt should be made to preserve the radial head and capitellum in good alignment following fractures, and when excision is necessary, arthroplasty should be considered.

Damage to the lateral ligament complex may also be due to chronic attenuation or iatrogenic injury.

Iatrogenic: PLRI can occur following a lateral epicondylitis release, or may result from surgical approaches to the lateral side of the elbow joint and radial head.

Chronic attenuation of the lateral ligament complex may occur in long-standing cubitus varus and secondary to overuse, such as in patients with poliomyelitis who use crutches to walk. In these chronic conditions the ligament stretches, losing its normal tension. In addition, the direction of pull of triceps is altered and exerts an external rotatory moment on the ulna which is an important component of PLRI. The lateral ligament complex may be inherently lax in conditions of generalized ligamentous hyperlaxity, for example, Ehlers–Danlos syndrome.

Valgus instability is seen in one of two varieties: post-traumatic or chronic overload. Post-traumatic valgus instability implies rupture of the media1 collateral ligament. It may be associated with disruption of the common flexor and pronator origin. Valgus instability is usually found in patients with radial head fractures that are associated with tears of the medial collateral ligament, or in patients with stage III elbow dislocations. The medial collateral ligament usually heals after elbow dislocation, perhaps because of the vascularity of the surrounding muscles.

In the throwing athlete, valgus instability can occur from repetitive microtrauma or overload that leads to attenuation or rupture of the anterior band of the medial collateral ligament.

Varus instability is attributable to disruption of the lateral collateral ligament complex and can be shown acutely in patients with elbow dislocations and in many patients with recurrent or chronic instability when this ligament fails to heal. As the forces across the elbow are principally valgus because of the anatomic alignment, it is not often subjected to varus stress and this pattern of instability may not be obvious.

Anterior instability of the elbow is rare and typically is seen in association with fractures of the olecranon.

Varus posteromedial rotatory instability occurs when a varus and internal rotation moment is applied to the elbow during axial loading of the elbow in flexion. It is usually associated with an anteromedial facet fracture of the coronoid process. Due to the varus force the radial head remains intact and there is usually an avulsion of the lateral collateral ligament. This instability pattern is clinically noticed with the shoulder in 90 degrees of abduction and the elbow in 90 degrees of flexion. This is a significant injury as it results in ulnohumeral joint incongruity and medial loading of the elbow, which can lead to premature arthritis. It is therefore recommended to internally fix the anteromedial coronoid fact even when the fracture fragment is small. This injury can be subtle and can pass unrecognized in the acute phase and a high index of suspicion is needed particularly when there is an isolated fracture of the coronoid without a fracture of the radial head. The implications of not recognizing this varus posteromedial rotatory instability are potentially devastating, as subsequent reconstructive options are difficult.

PLRI can be considered a spectrum consisting of three stages according to the degree of soft tissue disruption (see Figure 5.3.1). Each stage has specific clinical, radiographic, and pathological features that are predictable and have implications for treatment.

Elbow instability can be acute, chronic, or recurrent. Acute instability occurs with acute elbow dislocations or fracture-dislocations. All patterns of instability can occur acutely with PLRI being the most common. Traumatic valgus instability implies rupture of the medial collateral ligament and, usually, a fracture of the radial head. It is a distinct problem, separate from dislocation. Recurrent instability occurs when soft tissue healing after elbow dislocation is incomplete and is almost always PLRI. Chronic elbow instabilities present to the clinician as either chronic unreduced dislocations or fracture dislocations. Chronic dislocations, whilst infrequently seen in the developed world, are unfortunately still common in some developing countries and their management is challenging.

When an elbow dislocation is associated with an elbow fracture(s) it is referred to as a complex dislocation. Fracture-dislocations most commonly involve the coronoid and radial head and are referred to as a terrible triad. This name has been coined since it often results in persistent instability, non-union, malunion, and proximal radioulnar synostosis. Other fractures include avulsion fractures of the lateral collateral ligament, impression fractures of the radial head or the posterior part of the capitellum, and olecranon fractures. The goal of management of fracture-dislocations of the elbow is to restore the osseous-articular restraints and convert the injury to a simple dislocation. This has been demonstrated to have a generally favourable long-term prognosis. The recognition of an anteromedial facet fracture of the coronoid as a distinct and important type of coronoid fracture makes an important addition to the Regan and Morrey classification, which is based on fragment size alone.

PLRI is the commonest pattern encountered in clinical practice. In this type of instability patients may present with a spectrum ranging from vague symptoms in the elbow to frank recurrent posterolateral dislocation. Symptoms include: lateral elbow pain, recurrent clicking, popping, snapping, or locking of the elbow. The elbow position most typically associated with symptoms is approximately 40 degrees of flexion with the forearm in supination. The subluxation reduces on pronation. Symptoms are often brought on by activities such as pushing up with the arms when rising from an armchair or doing press-ups. These activities place the elbow in an unstable position of external rotation of the forearm with valgus and axial loading of the elbow. This in the presence of a previous history of dislocation or even an injury without dislocation suggests PLRI. A history of surgery on the lateral side of the elbow and a family history of ligamentous laxity should be sought. A thorough examination to identify signs of previous trauma or surgery, cubitus varus deformity, and range of movement is essential. Several clinical tests for PLRI have been described (see Table 5.3.1 and Figures 5.3.3–5.3.7) All these place the elbow in a position of maximal instability, with a combination of external rotation of the forearm, valgus, and axial loading, which try to reproduce either the symptoms or displacement of the radial head. It is important to look for coexistent valgus or varus instability as well as generalized ligamentous hyperlaxity.

Valgus stress testing is performed with the forearm fully pronated so that PLRI is not mistaken for valgus instability. Forced pronation prevents PLRI because the intact medial soft tissues are used as a hinge or fulcrum. Clinical examination may elicit point tenderness distal to the medial epicondyle along the ulnar collateral ligament. The location of tenderness is important to differentiate ulnar collateral ligament injury from medial epicondylitis and flexor–pronator mass strains. Flexing the wrist and pronating the forearm to decrease traction on the flexor–pronator mass can assist in differentiating these entities although they may coexist. Palpating with the elbow in 50–70 degrees of flexion moves the flexor mass anterior to the ulnar collateral ligament, allowing direct palpation of the ligament. The milking manoeuvre (Figure 5.3.8) is performed by abducting the shoulder and flexing the elbow to 90 degrees and the thumb is pulled posteriorly to create a valgus stress on the elbow. Comparison is then made with the opposite elbow. Medial opening and pain signify a positive test.

Varus stress testing is easiest to perform with the shoulder fully internally rotated. Both valgus and varus stress testing are performed with the elbow in full extension and in 30 degrees of flexion which unlocks the olecranon from the olecranon fossa.

Plain radiographs of the elbow are often normal but occasionally demonstrate an avulsion fracture of the origin or insertion of the lateral ligament complex. The presence of fractures of the radial head, coronoid process, and capitellum can be demonstrated as well as the presence of degenerative changes. Impression fractures of the radial head or the posterior part of the capitellum may also be seen. The drop sign—an ulnohumeral distance greater than 4mm on the plain lateral film of the unstressed elbow—may be present on immediate post-reduction lateral radiographs but usually disappears after muscle loading with mobilization. Concern is warranted only when the sign is still present on follow-up radiographs as it can be indicative of residual instability following elbow dislocation. It has been shown that properly performed magnetic resonance imaging (MRI) is sensitive and specific in demonstrating lateral collateral ligament pathology. However, PLRI is a clinical diagnosis, and the MRI should not be relied upon to make the diagnosis. Arthroscopic examination of the elbow may show posterior displacement of the radial head, an elongated lateral ligament complex, or widening of the lateral joint space. The diagnosis of PLRI remains a clinical entity with a combination of the history, active and passive apprehension tests, and examination of the elbow under anaesthesia. Apprehension is usually all that can be elicited when the patient is awake and general anaesthesia is needed to demonstrate displacement of the radial head and/or dimpling of the soft tissue.

With the patient under general anaesthesia, examination should be performed for valgus and varus instability as previously described. Testing for valgus instability with the forearm in supination may give a false positive result in the presence of PLRI, and so this should be performed with the forearm in pronation. Inability to demonstrate varus instability does not imply that the lateral ligaments are intact, as the ulnohumeral articulation is the main constraint to varus. PLRI is tested using the pivot shift and posterolateral drawer tests. If these fail to demonstrate instability the elbow should be screened using the image intensifier and the test repeated to detect dislocation or subluxation of the radial head (Figure 5.3.9).

Treatment depends on the severity of the patient’s symptoms. The ligament does not become stable over time, except possibly when a patient is seen in the very early stages. Conservative treatment by avoiding provocative activities and bracing to limit supination and valgus loading may be offered to some patients if surgery is declined. Surgical management is the standard and aims at reattaching, retensioning, or reconstructing the lateral ligament complex together with treating any bone deficiency of the radiocapitellar and ulnohumeral articulation by replacement of the radial head or coronoid reconstruction, and correcting any varus deformity of the humerus by osteotomy prior to ligament reconstruction. One or a combination of these may be necessary, depending on individual assessment and the underlying pathology.

Reattachment and retensioning of the lateral ligament complex with imbrication and advancement have been used, but reconstruction with a graft usually provides a more reliable construct. A tendon graft is used, with fixation achieved by bone tunnels, anchor sutures, or interference screws. The docking technique provides a stable construct and allows tensioning of the graft. Although an autograft of palmaris longus is commonly employed, the use of a strip of triceps tendon, semitendinosus, gracilis, plantaris, and synthetic ligaments have also been used. The latter is worth considering in cases of generalized ligament hyperlaxity. If both medial and lateral ligaments need to be reconstructed, a circumferential graft can be used and attached to both sides of the ulna. Arthroscopically-assisted repair of the avulsed lateral ligament complex has been described. Arthroscopic electrothermal shrinkage of the lateral ligament complex as the sole treatment for posterolateral elbow instability has also been used.

Valgus instability is usually treated in a similar fashion to ligament reconstruction procedures on the medial side of the elbow.

Generally if there is no degenerative arthritis and if the radial head is intact, approximately 90% of patients have a satisfactory outcome with no subsequent recurrent subluxation. If the radial head is excised or if there is degenerative arthritis of the ulnohumeral joint, the outcome is less satisfactory at between 67–75%. The results are not good in patients with generalized ligamentous laxity.

O’Driscoll described an algorithm that helps in decision-making once the elbow is reduced (Figure 5.3.10).

Subluxation or dislocation must be detected by careful examination throughout the comfortable range of motion and by radiographic examination, with anteroposterior and lateral radiographs made initially after the reduction and every 5–7 days for the first 3 weeks.

When the elbow is stable to valgus stress only with the forearm in pronation (that is, a stage-3A dislocation), the injury is treated immediately in a cast-brace that allows unlimited flexion and extension and holds the forearm in full pronation.

The presence of fractures usually changes the management, and almost always these fractures should be treated surgically. In general, the approach to the unstable elbow is to fix the bones internally and then repair the ligaments (particularly on the lateral side) so that early motion can be commenced.

Coronoid process fractures that are type I and type II (those involving 50% of the height of the coronoid process or less) should be fixed if the joint is subluxated or dislocated. Type III fractures (those involving more than 50% of the coronoid process) cause instability and must always be fixed.

Fractures of the radial head are best managed by internal fixation when technically possible. When the radial head is comminuted and has to be excised, prosthetic replacement is indicated if the elbow is unstable and cannot be rendered stable by ligament reconstruction alone.

Repair of an acute ligament injury is indicated in all fracture-dislocations requiring internal fixation of the radial head or the coronoid process, or both, and following reduction of a dislocation if gross instability does not allow early protected motion in a cast-brace without subluxation.