Forceful loading of the forearm and elbow during a fall on an outstretched hand can lead to fracture of the radial head with concomitant injury to stabilizing ligamentous structures. Proximal translation of the radius occurs when a radial head fracture happens in association with disruption of the longitudinal stabilizers of the forearm. The clinical presentation ranges from acute disruption of the distal radioulnar joint to insidious ulnocarpal impingement with worsening pain and loss of motion.
Curr and Coe1 first reported a fracture-dislocation of the radial head with dorsal dislocation of the distal ulna. Essex-Lopresti2 later described two cases of acute radial head fractures with disruption of the distal radioulnar joint, and his name has been given to these uncommon injuries. Subsequent knowledge of the biomechanics of radioulnar dissociation has led to the development of a schema for diagnosis and treatment.
Pathoanatomy and Biomechanics
Load is transmitted from the wrist to the humerus during grip and lifting activities. Studies of load sharing in the forearm show that the radius bears most (about 80%)3 of the load at the wrist but that the load-sharing ratio equalizes toward the elbow. Halls and Travill4 reported that the radiocapitellar joint bears 57% of the load in the proximal forearm and the ulnohumeral articulation bears 43%. Subsequently, Morrey et al5 studied changes in force transmission with variations in forearm rotation and found that the most force was transmitted from the wrist to the radial head with the elbow in extension and the forearm in pronation.
The primary restraint to proximal migration of the radius is the intact radial head abutting the capitellum.6-8 Soft-tissue structures that provide additional forearm longitudinal stability include the interosseous membrane of the forearm, the triangular fibrocartilage, and the ligaments of the distal radioulnar joint (volar and dorsal radioulnar ligaments). With injury or excision of the radial head, normal load sharing at the radiocapitellar joint no longer can occur and all compressive load is transferred from the distal radius to the ulna through the interosseous membrane and distal radioulnar joint.9 The surrounding soft tissues thus act as secondary restraints to proximal radial migration. Longitudinal radioulnar dissociation can ensue if a radial head fracture occurs in association with damage to any of these stabilizing soft-tissue structures (Fig. 1).
The interosseous membrane of the forearm, which consists of fibrous tissue running obliquely from the radius to the ulna, transfers load from the radius to the ulna. The interosseous membrane plays an important role in load sharing; sectioning of the interosseous membrane prevents force transmission from the distal radius to the ulnohumeral articulation.10 The existence of a central band of collagenous tissue approximately twice the thickness of the remaining membrane is a constant finding in cadaveric studies.7 This central band, also called the interosseous ligament of the forearm, is consistently located at a distance from the radial styloid of about 62% of the length of the radial shaft.11 The central band functions as an extra-articular ligament and accounts for 71% of interosseous membrane stiffness. It is also the principal longitudinal stabilizer of the radius after radial head fracture or resection.7,12
The triangular fibrocartilage complex stabilizes the radius and ulna at the distal radioulnar joint, thus preventing longitudinal displacement.3 The complex has several individual components, of which the volar and dorsal radioulnar ligaments are the most important for maintaining longitudinal stability. The dorsal radioulnar ligament provides stability to the distal radioulnar joint in pronation, while the volar radioulnar ligament does so in supination.13 Hotchkiss et al7 demonstrated that the triangular fibrocartilage complex provides 8% of the forearm's mechanical stiffness. Subsequent studies confirmed that the triangular fibrocartilage complex resists proximal radial migration and participates in load transfer.12 Moreover, Rabinowitz et al14 suggested that clinical migration of the radius >7 mm under axial load implies disruption of both the triangular fibrocartilage complex and the interosseous ligament.
Subtle proximal migration of the radius usually occurs after fracture or excision of the radial head, but it is rarely symptomatic.5,8,9 However, patients with greater proximal translation may present with loss of wrist extension and forearm rotation. Positive ulnar variance from proximal radial translation of 2 mm increases the load maintained by the ulna at the wrist from 20% to 40%, potentially leading to ulnocarpal impaction symptoms and wrist pain.15 Patients with proximal radial translation >1 cm usually experience pain and loss of motion, whereas patients with translation <1 cm report pain but retain motion.16 With proximal translation of the radius, the distal ulna loses its position in the sigmoid notch of the radius. The dorsal position of the distal ulna limits supination as the carpus abuts the ulnar head. Loss of wrist extension occurs when the ulnar head comes into contact with the dorsal carpus. In addition, proximal migration of the radius may cause radiocapitellar abutment, leading to elbow pain and limitation of elbow motion.
Longitudinal instability of the forearm often is missed during assessment at the time of injury. Although a fracture of the radial head usually is apparent, involvement of the interosseous ligament and distal radioulnar joint is not always appreciated. A high index of suspicion during clinical evaluation of the wrist is essential to recognize the injury. During the physical examination, particular attention should be paid to whether there is tenderness or dorsal prominence of the ulna at the distal radioulnar joint and any wrist pain when gentle rotation is applied to the forearm. Tenderness along the forearm also should be assessed because it may indicate injury to the interosseous membrane. The presence or absence of symptoms at the forearm and wrist should be documented clearly in the patient's chart.
Anteroposterior and lateral radiographs of the elbow as well as posteroanterior and lateral radiographs of the wrist should be obtained when patients present with wrist pain or loss of motion. The optimal view of the distal radioulnar joint is obtained using a posteroanterior radiograph with the shoulder at 90° of abduction, the elbow flexed at 90°, and the forearm in neutral rotation.17 However, Yeh et al18 have shown that ulnar variance can be assessed adequately with a routine posteroanterior radiograph of the wrist. Comparison radiographs of the contralateral wrist may be useful in select cases, and true lateral radiographs may help detect dorsal subluxation of the distal ulna.
In using magnetic resonance imaging to diagnose injury to the interosseous ligament, Starch and Dabezies19 found that the ligament is best visualized on axial T2-weighted images. The addition of fat-suppression techniques allowed better evaluation of the extent of edema in the soft tissues. Although the authors concluded that magnetic resonance imaging is useful for evaluating the interosseous ligament, clinical correlations in the setting of an acute disruption have yet to be established.
The goals of treatment of acute injuries are restoration of load sharing and prevention of proximal migration of the radius.
Radial Head Fractures
Radial head fractures usually are described with the Mason classification scheme. Type I fractures are minimally displaced and do not require surgical treatment, type II fractures are displaced sufficiently to require internal fixation, and type III fractures require excision because of excessive comminution.20
Because of its essential role in maintaining forearm stability, the radial head should be preserved to prevent proximal radial migration, especially when the secondary restraints to forearm stability, such as the interosseous ligament and distal radioulnar joint, have been disrupted. Internal fixation of type II fractures can be done with screw fixation alone or with screws and plates when the fracture extends to the radial neck. Impingement at the proximal radioulnar joint may be avoided by placing hardware in the nonarticulating safe zone of the radius. Bone graft may be required after extensive bone loss.20
In type III fractures, the radial head cannot be repaired with internal fixation, so excision is necessary. In patients with isolated fractures of the radial head, excision of the fractured head is a reliable form of treatment, and excellent results are achieved. Morrey et al9 reported an average proximal radial migration of 1.9 mm in 13 patients and excellent outcome in those who had radial head excision for isolated injuries.
In patients with injury to the interosseous ligament and distal radioulnar joint, however, excision of the radial head will lead to forearm instability and potentially disastrous consequences. Prosthetic replacement has been advocated to minimize the likelihood of radial migration in such cases (Fig. 2). Since prosthetic replacement with ferrule caps was first described in 1941,21 a variety of materials has been used. Flexible Silastic radial head prostheses implanted in the 1970s initially produced good clinical results.22,23 Subsequent biomechanical studies, however, showed no improvement in longitudinal forearm stability compared with radial head excision.7,24 In addition, implant fracture, capitellar wear, silicone synovitis, and continued radial proximal translation were found in long-term follow-up series.22,25-27
Metallic prostheses have become the preferred implants. In a cadaveric study, Sellman et al24 noted an increase of 145% of normal in forearm stiffness after titanium radial head replacement. Knight et al28 reported good clinical success with Vitallium prostheses. Although adequate elbow stability and forearm rigidity were documented, followup was short (mean, 4.5 years), and most patients had isolated radial head fractures without associated ligamentous damage. A morphometric study of metallic radial head prostheses found that inadequate sizing often leads to difficulty in fitting the components,29 but recently introduced modular implants may eradicate this problem.
No long-term studies exist documenting implant wear behavior or clinical outcome. Additionally, there are no published reports describing the treatment of acute Essex-Lopresti injuries with prosthetic radial heads. Nonetheless, titanium and titanium alloy implants currently are the mainstay of treatment in prosthetic replacement of the radial head in cases of comminuted fractures with associated ligamentous disruption.
Although the anatomy and functional mechanics of the interosseous ligament have been investigated extensively, its healing potential has not been studied. Flexor carpi radialis tendon grafts have been used to reconstruct the central band in cadavers.30 On biomechanical testing, the repair was successful in preventing complete migration of the radius to the capitellum but not in restoring full longitudinal stability of the forearm. Few reports of central band repair in a clinical setting have been published. Bone-tendon-bone graft has been suggested, but no followup data are available. Hotchkiss31 attempted one case with a palmaris longus tendon weave, but the patient manifested continued proximal migration and required a salvage procedure. Interosseous ligament repair is not an accepted treatment option for the management of acute longitudinal radioulnar dissociation.
Pinning of the radius and ulna at the distal radioulnar joint is the recommended treatment for acute radioulnar dissociation. Patients then are immobilized in anticipation of healing of the interosseous ligament and the ligaments of the distal radioulnar joint. The optimal immobilization position for dorsal ulnar subluxation or dislocation is in supination, maintaining the reduced distal radioulnar joint.32 Direct repair of the triangular fibrocartilage and/or dorsal and volar radioulnar ligaments has not been advocated because reduction of the distal radioulnar joint is enough to stabilize the distal forearm.16
Management is complex in chronic cases in which longitudinal radioulnar dissociation is diagnosed after radial migration has occurred. Edwards and Jupiter33 reported on seven adults with radioulnar dislocation, three of whom achieved excellent functional results when radial length was immediately restored. Suboptimal results were evident in the four patients whose diagnosis and treatment were delayed 4 to 10 weeks. Similarly, Trousdale et al34 reviewed 20 patients with radioulnar dissociation and found poor clinical results in 15 patients whose injuries were diagnosed after a mean delay of 7 years 11 months (range, 1 month to 26 years). Treatment goals in those cases included normalization of the radioulnar relationship at the distal radioulnar joint and prevention of further migration of the radius.
Restoration of the Radial Head
Szabo et al35 treated five patients with disabling proximal migration of the radius after radial head excision with implantation of a frozen-allograft radial head. At a mean followup of 3 years (range, 1 year to 7 years), forearm rotation and wrist motion improved and patients were satisfied with the outcome. Although these results were encouraging, the number of patients and length of follow-up were limited, and indications for allograft radial head replacement remain uncertain. No published studies explore the use of a metallic radial head prosthesis to treat chronic radioulnar dissociation.
Length-equalizing procedures have been attempted in patients with significant proximal translation. Although procedures such as distal ulnar resection, the SauvéKapandji procedure, and segmental shortening of the ulna reestablish normal ulnar variance in the early postoperative setting, they do not restore the soft-tissue stabilizers of the forearm, and patients experience continued proximal radial migration.10,34,36 Ulnar shortening leads to readjustment of the radius with continued proximal translation, producing radiocapitellar abutment, persistent elbow pain, and loss of forearm rotation.
There are no reliable reconstructive surgical techniques to restore forearm stability in patients with chronic radioulnar dissociation. The creation of a one-bone forearm, or radioulnar synostosis, has been advocated as the salvage procedure that is the most reliable solution to this problem. A review of one-bone forearm reconstructions done for radioulnar instability secondary to trauma, tumor resection, and congenital deformities showed good union rates and reasonable functional results in patients who underwent the procedure after radial head excision.37 The optimal rotational position of forearm synostosis is in neutral or slight pronation,38,39 but preoperative trial bracing may be useful in optimizing individual forearm position.
Proximal translation of the radius is an uncommon complication after fractures of the radial head. When recognized early, treatment involves prevention of radial migration with preservation of the radial head, reduction of the distal radioulnar joint, and, when appropriate, softtissue reconstruction. When fracture comminution makes primary bony repair impossible, prosthetic replacement of the radial head is necessary to prevent proximal radial migration. Although there are several reconstructive options for treating chronic radioulnar dissociation, such as allograft radial head replacement, length equalizing, and salvage procedures, no clear treatment solutions exist. Early recognition of longitudinal forearm instability is critically important in the treatment of longitudinal radioulnar dissociation.
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