Isolated Radial Head/Neck Fractures

Introduction

Fractures of the radial head are the most common elbow injuries, accounting for approximately 30% of all elbow fractures in adult patients. The majority of patients are between 20 and 64 years of age with no gender predominance. ^, The mechanism of injury is typically a fall on an outstretched arm with the elbow extended and the forearm pronated.

Radial head fractures occur with associated lesions in one-third of cases with coronoid fractures being the most commonly implicated. These injuries can range from simple nondisplaced fractures to those associated with complex elbow instability. Because the radial head is an important stabilizer of the elbow, displaced fractures, particularly when associated with ligamentous injuries, may lead to elbow dysfunction. Management of these injuries, whether nonoperative or operative, is aimed at maintaining radial head alignment while elbow joint motion is encouraged as rapidly as the stability of the fracture affords.

Anatomy and Biomechanics

The radial head is entirely intra-articular and ensures smooth rotation between the radius and ulna while facilitating elbow flexion and extension. It does this through two articulations at the radiocapitellar (RC) and the proximal radioulnar joints (PRUJs). The radial head has a concave surface that articulates with the convex surface of the capitellum and this provides stability through a concavity/compression mechanism as well as through tensioning of the lateral collateral ligament (LCL) complex. Its elliptical shape produces a cam effect at the PRUJ and the proximal radius of curvature is slightly greater when compared to the capitellum, which limits its constraint. These complexities in the radial head as well as a variable neck-shaft angle can make repair and replacement efforts challenging. ^, This variability mandates that plates are intraoperatively bent to match the uninjured proximal radius.

When surgically approaching the radial head, there exists a safe zone that does not articulate with the PRUJ, which can be easily located between the palpable radial styloid and Lister’s tubercle. These landmarks are then transferred to the proximal radius and represent a safe zone for hardware placement in the nonarticular portion of the radial head. The mean safe zone is an arc of 133 degrees. The posterior interosseous nerve (PIN) winds around the radial neck within the supinator muscle to enter the posterior compartment of the forearm and is located 5–6 cm from the RC joint ( Fig. 44.1 ).

The radial head acts as the main stabilizer of longitudinal forearm stability because it resists proximal axial migration of the radius. On the lateral side of the elbow, the major ligamentous contributors to varus elbow stability are the lateral ulnar collateral ligament (LUCL), the radial collateral ligament (RCL), and the annular ligament. The LUCL courses from the lateral epicondyle to the supinator crest of the ulna and prevents the radial head from subluxating posteriorly, and when injured, plays a crucial role in the development of posterolateral rotatory instability. ^, Therefore when approaching a radial head injury with an intact LUCL, it is imperative to stay above the “equator” of the lateral epicondyle to avoid inadvertently detaching the LUCL ( Fig. 44.1 ). The annular ligament wraps around the radial head and stabilizes the head in the lesser sigmoid notch. Elbow fractures are often associated with injuries to the annular ligament; however, the clinical relevance has not been clarified. The RCL originates from the lateral epicondyle and inserts on the annular ligament.

The radial head acts in concert with the bony and static stabilizers to impart elbow stability. Upon application of a valgus load, the radial head experiences a compressive force making it a secondary contributor to valgus elbow stability. Thus the medial collateral ligament (MCL) and radial head integrity influence each other. This should be acknowledged when dealing with radial head fractures, which are often accompanied by lesions of the collateral ligaments.

The primary biomechanical role of the radial head is to transmit forces across the RC joint and tension the LUCL. At the elbow, approximately 60% of the mechanical load is transmitted through the radial column. ^, This load transmission has been shown to be altered with lengthening and shortening of the radial head as little as 2.5 mm, which affects ulnohumeral kinematics and RC pressures ( Fig. 44.2 ).

Radial head resection shifts 100% of the loading onto the ulnar column, which is discouraged in unreconstructable fractures, particularly in an acute setting. Without the radial head, proximal migration of the radius is likely, which reliably leads to instability, pain, and limited function. A cadaveric study demonstrated increased varus-valgus laxity and altered elbow kinematics after radial head excision and both were corrected after radial head arthroplasty. In the face of biomechanical compromise to the interosseous membrane (IOM), such as in an Essex-Lopresti lesion, disastrous complications may ensue.

Pathoanatomy

Radial head fractures often occur due to a fall onto an outstretched hand where the elbow is extended and the forearm pronated. Because pronation decreases the distance between the radial head and capitellum, substantial force is transmitted in this position. A comminuted radial head or neck fracture is most likely the result of failure in compression due to an axial and valgus load. More substantial radial head fractures are believed to have likely occurred in association with a brief but complete dislocation of the elbow. Concomitant lesions were found in 39% of a study population suggesting that radial head fractures rarely occur in isolation and tend to be a marker of complex elbow trauma. Ligament rupture or avulsion fractures from the coronoid process are, therefore, to be expected. A magnetic resonance imaging (MRI) study of 24 subjects with Mason type II and III fractures demonstrated 54% MCL and 80% LUCL injuries with associated capitellar chondral defects and loose bodies occurring in 30% and 91% of cases, respectively. ⁵ Frequent lateral ligamentous injuries have been noted even in a Mason type I fracture. These studies emphasize the need to appreciate ligamentous and osseous lesions and how it is to be expected that the elbow’s healing response may be a vigorous one that has the potential to lead to stiffness if early motion is not achieved.

Accompanying injuries of the IOM have also been reported with incidence increasing proportionally with the severity of fracture. A complete tear of the IOM was noted in all Mason type III fractures. Even with Mason type I fractures, a partial lesion of the IOM was identified in 9 of 14 individuals. With the increasing severity of the causal injury, the likelihood of wrist or shoulder injuries rises requiring an appropriate emphasis on evaluating these regions as well.

Physical Examination

Elbow swelling, hematoma, and, occasionally, deformity will accompany these proximal radius injuries. Palpation will elicit a point of maximum tenderness, which should correlate with this injury. Palpation along the IOM and distal radioulnar joint stability assessment will identify associated lesions of the forearm and wrist. Active and passive range of motion (ROM) must be documented with attention given to joint crepitus when moving the extremity and, particularly, when rotating the forearm. Varus and valgus stability should be investigated in full extension and 30 degrees of flexion, and, if possible, documented under fluoroscopy.

Classification

The Mason classification system is the most widely used classification system for fractures of the radial head. The classification distinguishes nondisplaced fractures (type I), displaced fractures (type II), and fractures that are displaced with comminution (type III). A fourth type was added by Johnston in 1962, describing a fracture of the radial head accompanied by elbow dislocation ( Fig. 44.3 ). In 1987, a metric definition of displacement (<2 or >2 mm) and an area of involvement of the articular surface (>30%) was included to differentiate between Mason types I and II. The Mason classification, however, has shown low interobserver and intraobserver reliability; hence, it is difficult to derive conclusive treatment algorithms.