Traumatic Elbow Ligamentous Injury

Introduction

The elbow is the second most commonly dislocated joint in the human body after the shoulder joint. This is likely to be due to the relatively small surface area of the joint, the short working length of stabilizing structures, and the large moment arms on either side of the articulation that magnify the forces applied to the limb. Stability of the elbow comes from the interplay between static stabilizers (the bones and ligaments) and dynamic neuromuscular stabilizers. While dislocation may be the result of violent trauma, there is a spectrum of injury that may occur to the elbow depending on the energy applied, the direction of forces, and possibly individual factors such as collagen properties, bone density, and reaction times. Isolated ligament injuries can be difficult to diagnose without a high index of suspicion, and if missed may result in chronic instability issues, elbow stiffness, or rapid chondral damage and arthritis. This chapter will review the anatomy, useful imaging, diagnosis, and management of traumatic ligament injuries around the elbow.

Anatomy

The elbow is a complex asymmetrical articulation between the humerus, ulna, and radius. The radius and ulna are related throughout their length within the forearm joint and neither the elbow nor the forearm can be considered in isolation. Neuromuscular structures crossing the joint act to pull the forearm onto the end of the humerus and to generate angular displacement (joint movement). This action brings the coronoid process of the ulna and radial head into apposition with the trochlea and capitellum, anteriorly when the elbow is flexed and distally when the elbow is extended. The coronoid process is fundamental to stability of the ulnohumeral joint and consists of the anteromedial facet, the anterolateral facet, and a medial projection, the sublime tubercle, into which the anterior band of the medial collateral inserts ( Fig. 39.1 ). The fulcrum for varus and valgus moments across the elbow lies between the two facets. The surface area of the anteromedial facet is much greater than that of the anterolateral facet and is almost equal to that of the radial head. When the forearm goes into valgus, a greater load is shared by the anterolateral facet and the radial head. Conversely, a varus load is transmitted to the anteromedial coronoid facet. The olecranon process, which meets the coronoid process at the bare area of the articulation to form the greater sigmoid notch, contributes to elbow stability in extension when it will engage with the olecranon fossa of the humerus and resist varus and valgus moment. On the medial side of the elbow, the greater sigmoid notch covers the medial trochlea through an arc of 170 degrees, whereas the radial head only covers a 90-degree arc of the capitellum so the relative contribution of the osseous elements is unbalanced. On the lateral side of the elbow, the ligaments and neuromuscular elements must compensate to provide adequate stability.

The lateral ligament complex is a broad interwoven thickening of the lateral capsule that is considered as four separate elements. The annular ligament (AL) arises from the anterior lip of the lesser sigmoid notch, wraps around the radial head, and inserts into the supinator crest. The radial collateral ligament (RCL) arises from the anterior part of a small elevation on the lateral condyle, the lateral epicondyle, and passes distally to blend with the AL. The lateral ulna collateral ligament (LUCL) arises from the anteroinferior portion of the lateral epicondyle to pass dorsally and distally to the supinator crest and blends with the AL, and the accessory LUCL made up of superficial fibers passing from the LUCL to the AL and supinator crest distally. The relative importance of each of these elements is debated in the literature, but in truth they are all interdependent, with disruption of one element affecting the function of another. Recent studies have indicated an additional posterolateral ligament (Osborn-Cotterill ligament) arising from the inferior part of the lateral epicondyle that passes dorsally to attach to the rim of the greater sigmoid notch and produces a sling dorsal to the radial head. This ligament appears to provide stability to the radial head in posterior drawer, performed by applying a posterior force to the radial head that is gripped between the examiner’s finger and thumb with the elbow relaxed in a posture between 30 and 90 degrees of elbow flexion ( Fig. 39.2 ). In a positive test, the radial head can be felt to subluxate dorsally. Comparison can be made to the uninjured elbow.

On the medial side, the medial ligament has three elements. The anterior bundle of the medial collateral ligament (aMCL) arises from the anteroinferior part of the medial epicondyle (ME), a much larger osseous protuberance that arises from the medial condyle. The origin of the ligament is roughly midway between the base on the trochlea and the tip of the ME. The aMCL passes distally to insert into the sublime tubercle of the coronoid process of the ulna. The posterior band of the medial collateral ligament (pMCL) arises from the inferior border of the ME and fans out to insert into the rim of the greater sigmoid notch of the ulna. The transverse or oblique medial ligament passes from the medial side of the olecranon to the ulna just dorsal to the sublime tubercle and does not appear to contribute to elbow stability. The anterior band of the ligament is tighter in extension and the posterior band in flexion.

The origin of both medial and lateral ligament complexes is often thought to lie in the center of the distal humeral spool. Anatomical footprint studies appear to indicate that on both the medial and the lateral sides of the humerus the center of the ligament footprint on the humerus lies 2 mm posterior to the center of the spool. The reason for this is not clear. It may be to give a cam effect such that the ligaments tighten in flexion increasing stability when carrying objects in this position, but it is important when considering repair or reconstruction of the medial ligaments ( Fig. 39.3 ). Although the ligaments act as static restraints, they also contain the important sensory organs for proprioception of the elbow. The anterior and posterior capsules are relatively deficient in these receptors, which means injury to the ligaments can have a detrimental effect on joint movement.

The third layer of stability comes from the neuromuscular elements around the elbow. Anteriorly and posteriorly there are three principle flexors and extensor elements. Anteriorly, the brachialis is muscular almost to its insertion and has a short moment arm lying close to the joint line, and the short and long head of biceps have a long tendinous insertion to the bicipital tuberosity on the radius with a longer moment arm for elbow flexion forces. Posteriorly, the triceps has three heads, the medial head lies close to the joint line, has a short moment arm, and is muscular almost to its insertion. Additionally, the long and lateral heads have a lengthy tendon and insert further from the joint line to the olecranon process. It is the tendinous insertions that are most prone to rupture. Medially, the pronator teres, flexor carpi radialis, flexor digitorum superficialis, palmaris longus, and flexor carpi ulnaris contribute to valgus stability, particularly in the absence of a functional MCL. Laterally, the brachioradialis, extensor carpi radialis longus and brevis, extensor digitorum communis, and extensor carpi ulnaris all contribute to varus stability, particularly in the absence of a functional lateral ligament complex. Anconeus is thought to be a dynamic stabilizer on the lateral side of the joint although the contribution is debated. ^, The resultant moment from all these elements acts to pull the forearm bones proximally and dorsally onto the end of the humerus. Loss of the medial or lateral secondary stabilizers in the presence of ligament injuries can result in significant instability of the elbow.

Diagnosis and Imaging

The diagnosis of acute ligament injury requires an index of suspicion based on the history of the injury and reported symptoms. In complete elbow dislocation, the diagnosis is rarely challenging with obvious deformity following a fall or high-energy injury. Usually the skin is intact but evidence of an open injury typically necessitates urgent surgical management. It is important to examine for neurological and vascular compromise and document the presence of any deficit. Prompt reduction is essential to relieve pain, limit the extent of cartilage compromise, and reduce the risk of neurovascular or cutaneous damage. Ideally, at the time of elbow reduction an assessment would be made of elbow stability looking at joint gapping with a fluoroscope on varus and valgus stress of the joint and assessing congruency of the elbow in full extension. Widening of the usually parallel joint line of >10 degrees has been associated with a five-fold increase in the risk of recurrent instability. The standard teaching of stability at 30 or 60 degrees of flexion determining the need for surgical intervention carries no scientific basis or obvious logic. The elbow should be stable through a full arc to confidently allow active mobilization.

In most cases, the patient will have had the elbow reduced in the emergency department and present to the specialist with a congruent elbow. The extent of the soft tissue injury is difficult to determine on clinical grounds. A history of a high-energy injury, extensive soft tissue injury, neurological compromise, or significant displacement on plain radiographs may all suggest more significant injury but do not precisely identify which of the stabilizers are damaged. The elbow will be swollen and painful and assessment of stability is unlikely to yield additional useful information. The clinician can, therefore, take a view that the overall likelihood of recurrent instability is low and treat accordingly or may choose to try to stratify the injury using radiographic imaging. ^,

Plain X-rays will confirm that the elbow remains satisfactorily reduced and that there is no bony injury. Flakes of bone from the lateral or ME may indicate a ligamentous avulsion. A “drop sign,” with gapping between the ulna and the distal humerus, may be visible in the early stages after injury but does not in itself mandate surgical intervention. Possible causes for this appearance include hemarthrosis, temporary muscle inhibition, or ligament injury. An isolated coronoid fracture, with radial head intact, indicates a posteromedial rotatory instability (PMRI) fracture-dislocation and needs further investigation. This is not a minor avulsion injury but suggests an impaction or punch injury of the trochlea through the coronoid process.

Computed tomography (CT) is not usually indicated in simple dislocation as by definition the skeleton should be intact. It can be helpful, however, if there is any doubt about the diagnosis and is often used in cases of PMRI to assess the amount of bone lost from the coronoid and the presence of ulnohumeral joint subluxation.

Magnetic resonance imaging (MRI) is a useful investigation in the dislocated elbow as it can be used to identify torn structures and stratify the injury. Simple elbow dislocation is graded from 1 to 4 based on the presence of avulsion of the medial ligament, lateral ligament, common flexor origin, and common extensor origin according to the scheme in Table 39.1 . Those patients with grade 4 injuries where all the soft tissues have been avulsed from the epicondyles are thought to be at greatest risk of recurrent instability. MRI can also be used to identify the presence of ligament injury with a PMRI with particular attention paid to the lateral ligament complex, common extensor origin, and pMCL.

Isolated ligament avulsion injuries can be diagnosed using MRI where there is an index of suspicion. Hyperextension injuries of the elbow can result in a spectrum of injury similar to a simple dislocation and at the lower end of the scale isolated injuries to the anterior band of the MCL are seen. Bruising over the ME, with tenderness over the anterior band and pain from the medial ligament on valgus stress testing or modified milking maneuver will indicate a need for further investigation. The moving valgus stress test is usually reserved for chronic injuries.

Isolated lateral ligament injuries or injuries to the posterolateral ligament are more challenging to diagnose and many go unnoticed leading to chronic posterolateral rotatory instability (PLRI). Lateral ligament injury should be considered in any patient presenting with lateral elbow pain and a history of trauma. Some patients will report a clunk or click on the lateral side of the joint on mobilization and very occasionally the patient will be aware of frank instability of the radial head on the capitellum. Persistent stiffness after elbow trauma, particularly segmental radial head fractures with no or minimal displacement that fail to recover normal function in the usual time period, should raise a suspicion of ligamentous injury, as elbow instability is one of the hidden causes of posttraumatic stiffness. The presence of bruising over the lateral side of the elbow may indicate a high-grade injury, as it suggests that the tough lateral fascia has been torn, allowing hematoma to escape to the subdermal layers. The pivot shift test is difficult to perform in the acutely injured elbow but as the swelling settles a posterior drawer test may indicate posterolateral instability. ^,

Particular attention should be paid to the patient falling backwards on to the hand, sometimes ending up with their arm stuck underneath them, who reports that they can straighten their elbow but cannot flex beyond 90 degrees. This is highly suggestive of a PMRI fracture-dislocation pattern. They may have a visible cubitus varus on elbow extension.

MRI is a useful tool to investigate a suspected ligament injury. Arthrography is not usually required in the acute setting because of hemarthrosis but injectable contrast or saline injection can be used to enhance the imaging if necessary. On the medial side the anterior band is most easily visualized on coronal T1 and T2 slices passing from the ME to the sublime tubercle. Fluid between the ligament and tubercle, the “T” sign, is suggestive of a medial ligament injury but can be a normal appearance in some. As a result, clinical correlation and the presence of edema are required to confirm diagnosis. The ligament may tear from the tubercle, the humerus, or there may be a “Z”-shaped tear starting anteriorly from the sublime tubercle, passing up the ligament and then posteriorly off the humerus ( Table 39.2 ). This may give the impression of a midsubstance tear. Posterior ligament injuries can be visualized on the axial slices and will normally be avulsed from the humerus. MRI will identify fracture or contusion to the coronoid process and radial head. The sagittal images should be inspected for joint subluxation with incongruence of the trochlea in the greater sigmoid notch. On the lateral side, the ligament is usually avulsed from the humeral origin. The tear may extend into the common extensor origin which makes persistent instability more likely. This is best seen on coronal slices. Avulsion of the posterolateral ligament, with or without a bony ossicle, from the posterior capitellum can be identified on sagittal slices and can occur as an isolated injury or as part of a lateral ligamentous complex tear.

Ultrasound can be used to perform a dynamic assessment of acute ligament injury. It is, however, limited by the comfort of the patient and the availability of skilled practitioners in the acute setting. Joint gapping medially on valgus stress may indicate a torn MCL. Assessment of lateral instability is more challenging because of the variability of the position of the radial head on the capitellum in the normal population. Soft tissue avulsion injury can be demonstrated in skilled hands.

Pathlogy