Distal Radio ulnar joint

Acute dislocations and subluxation of the distal radio-ulnar joint (DRUJ) may be isolated or associated with:

Radial head fracture
Distal radial fracture (Galleazi)
Radius and ulna fracture
Dislocations of the elbow

Consider concept of simple and complex dislocations.

Anatomy

Distal ulna has convex articular surface; this articulates with the concave semicylindrical sigmoid notch of radius.

The important stabilizers of the distal radio-ulnar joint include all of the separate structures composing the triangular fibrocartilage complex. Of great clinical importance is the fact that these structures blend at the fovea, thus creating the potential for instability of the distal radio-ulnar joint when the ulnar styloid process is fractured.

The flat pronator quadratus muscle originates from a long, narrow strip of the volar aspect of the distal part of the ulna and has a broad insertion on the volar aspect of the radius. It acts as a secondary stabilizer of the DRUJ by providing compressive force across the joint during pronation and supination.

Biomechanics

The radius rotates 150° around the fixed ulna . An additional 30° of lateral movement of the radius toward the direction of rotation allows the hand to rotate through a total arc of 180°.

With respect to the fixed ulna, the radius moves dorsally and distally during supination and proximally and volarly during pronation.

The ulna is the stable anatomical point of reference for rotation of the forearm ie. its the radius that dislocates.

Convention dictates however that the direction of dislocation at the distal radio-ulnar joint be described as either ulna dorsal or ulna volar with respect to the distal part of the radius.

Acute Dislocations of the Distal Radio-Ulnar Joint

Isolated Injuries

Uncommon

Mechanism of injury

Ulna dorsal - hyperpronation
Ulnar volar - hypersupination

Essex-Lopresti Injuries (1951)

Comminuted radial head fracture with dislocation of DRUJ.

Longitudinal compression force results in disruption of the DRUJ, interosseous membrane and ends in radial head fracture.

Galeazzi Fracture-Dislocations

Fracture of the shaft of the radius associated with a dislocation of the DRUJ usually ulna dorsal.

MOI - fall on the outstretched hand with the forearm in pronation.

Hyperpronation produces force across the fixed radiocarpal articulation fracturing the radial shaft. The radius shortens, disrupting the TFCC or fracturing the ulnar styloid.

High-energy trauma can produce, in addition, an associated fracture of the ulnar shaft, a segmental fracture of the radius, a dislocation or fracture of the radial head, or a dislocation of the elbow.

Non-operative treatment of Galeazzi injuries in adults leaves persistent symptoms at the DRUJ.

ORIF of the radius leads to less problems at the DRUJ.

Irreducible dislocations of the DRUJ are associated with a displaced fracture of the ulnar styloid and ECU interposition.

Fractures of Both Bones of the Forearm

20% of Galeazzi fractures have fractures of the shafts of both bones of the forearm

Up to 60% of forearm fractures have involvement of the DRUJ.

Fractures of the Distal Part of the Radius

Instability and tenderness of the DRUJ may result from incongruity in the sigmoid notch of the radius, caused by residual displacement of fracture fragments. Late instability of the DRUJ is common and typically occurs as a result of:

Avulsion of fracture fragments at the lateral (radial) insertion of the triangular fibrocartilage complex
Massive tears of the triangular fibrocartilage complex itself
Or avulsion of the ulnar styloid process at the fovea.

Clinical and radiographic assessment of the reduction and stability of the distal radio-ulnar joint at the time of the reduction or fixation of an intra-articular fracture of the distal part of the radius is essential for the effective treatment of these complex injuries.

Diagnosis

Physical Examination

Restricted forearm rotation

Decreased pronation in volar dislocation of the DRUJ
Decreased supination in dorsal dislocation of the DRUJ

Plain Radiographs

Joint above and the joint below.

It is important to obtain a true lateral wrist radiograph.

Align the four ulnar metacarpals
Alternatively with the forearm in neutral rotation, the proximal pole of the scaphoid, the lunate, and the triquetrum should be superimposed, and the radial styloid process centred over them.

A PA wrist in neutral may help

Ulnar volar - radialward displacement of the distal part of the ulna and, possibly, overlap of the distal parts of the radius and ulna.
Ulnar dorsal - distance between the radius and the ulna at the sigmoid notch is generally increased.
An ulnar styloid fracture is an important component of an injury to the DRUJ. Since most of the components of the triangular fibrocartilage complex are attached to the base of the fovea. Detachment of the ulnar styloid process from the shaft may result in destabilization of the DRUJ. If the ulnar styloid process cannot be visualized on the PA radiograph, then the lateral radiograph must be carefully scrutinized for volar or dorsal displacement of the fragment of the ulnar styloid process. Volar or, less commonly, dorsal displacement of the fragment is characteristic of a complex dislocation of the distal radio-ulnar joint and can easily be missed on the initial radiographs (particularly in the presence of severe fractures of the forearm).

Computerized Tomography

Accurate assessment of the stability of the DRUJ is difficult.

CT may be useful when there is persistent pain, loss of range of motion, or deformity of the distal radio-ulnar joint.

If late instability is suspected after the associated fractures have healed, three sets of scans, made with the forearm in pronation, neutral, and supination, are indicated for comparison of the injured and uninjured joints. The scan made with the forearm in pronation is most sensitive for the detection of volar subluxation, while that made with the forearm in neutral is sensitive for the detection of dorsal subluxation and diastasis of the DRUJ. The scan made with the forearm in supination is best for confirmation of the degree of reduction of a subluxation or diastasis. Post operatively a single axial CT scan, through the distal radio-ulnar joint with the forearm in any position of rotation, can aid in the diagnosis of subluxation and dislocation. A line is drawn through the dorsal ulnar and radial borders of the radius and a second line is drawn through the volar ulnar and radial borders of the radius, as described by Mino et al. The adequately reduced ulna must lie between these lines.

Simple Compared with Complex Dislocations

A simple dislocation of the distal radio-ulnar joint can be reduced easily or spontaneously after internal fixation of the associated fracture, or it can be reduced with closed methods if it is an isolated injury.

A complex dislocation is characterized by obvious irreducibility, recurrent subluxations or dislocations, or a mushy sensation caused by soft-tissue interposition when reduction is attempted.

Complex dislocations of the DRUJ are associated with high-energy injuries accompanied by one or two fractures of the forearm. Frequently the ulnar styloid process is also fractured, and usually it is displaced volar to the distal part of the ulna. The extensor carpi ulnaris, because of its firm attachment to the triangular fibrocartilage complex by its fibro-osseous sheath, is usually the structure that prevents spontaneous or easy reduction of the joint in these situations. Typically, after the extensor carpi ulnaris has been detached from the distal part of the ulna together with the triangular fibrocartilage complex and the ulnar styloid process, it slips around either the radial or the ulnar border of the distal part of the ulna to lie volar to it. Consequently, the joint cannot be reduced until the tendon with the attached triangular fibrocartilage complex and styloid fragment has been returned to its anatomical position. To avoid an error in diagnosis in the intraoperative setting, undue force during reduction of the DRUJ must be avoided. When reduction occurs easily, accurate lateral radiographs should be made with the wrist and forearm held in a neutral position without force. Persistent incongruity of the distal radio-ulnar joint in this position suggests the presence of soft tissue interposition.

Soft tissue elements previously reported to cause a block to reduction:

Extensor carpi ulnaris and the ulnar styloid
Extensor digiti minimi
EDC to ring and little fingers

Treatment

Simple Dislocations

Reduce easily

Dorsal dislocations can usually be reduced by supinating the forearm with direct pressure over ulna.

Volar dislocations may be more difficult to reduce because of the deforming force of the pronator quadratus. In this circumstance, the ulna must be mobilized ulnarward and dorsally while the forearm is pronated.

Immobilize 6 weeks, above elbow with forearm in:

Supination for ulna dorsal
Pronation for ulna volar

Late dislocation especially volar after six weeks are difficult to reduce closed. Because of the contracture of the pronator quadratus muscle in volar dislocations. If an open reduction of an irreducible (dorsal or volar) dislocation of the distal radio-ulnar joint is performed, every attempt should be made to repair the triangular fibrocartilage complex or to pin the ulnar styloid process if it is fractured. The distal most fibres of the contracted pronator quadratus often must be released to accomplish an open reduction of a late volar dislocation.

When a simple dislocation accompanies a fracture of the radial head (an Essex-Lopresti injury), every attempt should be made to achieve stable internal fixation of the radial head. If the fracture is severely comminuted and is not repairable, the radial head should be excised and replaced with a prosthesis. Placement of a transfixing 1.6 mm Kirschner wire from the distal part of the ulna to the radius helps to maintain precise reduction of the proximal and distal radio-ulnar joints. After appropriate fixation of all associated fractures, the limb should be immobilized in an above-the-elbow cast for six weeks. The forearm should be in supination for ulna dorsal dislocations and in pronation for ulna volar dislocations.

Simple dislocations of the DRUJ may be stable or unstable.

If the joint is stable and not easily redislocated after the internal fixation of associated fractures, immobilization in an above-the-elbow cast with the forearm in the appropriate position is all that is required. If the joint redislocates easily, a 1.6mm Kirschner wire should be placed from the ulna to the radius, parallel to the radiocarpal joint and just proximal to the distal radio-ulnar joint. Before the joint is transfixed, the forearm should be placed in full supination for ulna dorsal dislocations and in full pronation for ulna volar dislocations. The limb should be immobilized to protect the wire. The Kirschner wire should be removed and range-of-motion exercises started six weeks after fixation.

Complex Dislocations

Complex dislocations of the DRUJ are characterized by:

Obvious irreducibility
Recurrent subluxations or dislocations
A mushy sensation when reduction is attempted.

This mushy sensation/ subtle resistance or springiness is caused by interposition of soft tissue or bone. In this circumstance, forcible reduction of the joint and transfixion with a radio-ulnar pin is contraindicated. Exploration of the joint with use of a dorsal approach is recommended. A longitudinal skin incision should be made just radial to the extensor carpi ulnaris tendon, with care being taken to protect the dorsal sensory branch of the ulna nerve. The extensor digiti minimi should be released from its sheath and retracted radially. At this point, a fracture of the base of the ulnar styloid process can usually be found. This fracture displaces with the attached triangular fibrocartilage complex and its associated structures, the extensor carpi ulnaris tendon and sheath, and the ulnocarpal ligaments. If the ulnar styloid process is fractured, it should be stabilized with a Kirschner wire, a tension band, or intra-osseous wiring. Sometimes, the ulnar styloid process is intact and there is a massive tear of the triangular fibrocartilage complex instead. The torn triangular fibrocartilage complex must then be repaired carefully and reattached to the ulna with use of anchor sutures or pull-out wires.
Even with accurate restoration of osseous and soft-tissue structures, a complex dislocation is still potentially unstable and requires additional fixation of the joint. Pin the distal radio-ulnar joint transversely with a 1.6 mm K wire. The appropriate position of the joint is supination for ulna dorsal dislocations and pronation for ulna volar dislocations.

Postoperatively, the limb should be immobilized in an above elbow cast for six weeks. The K wire removed at six weeks and range-of-motion exercise started. If the radial attachments of the triangular fibrocartilage complex are avulsed along with osseous fragments of the sigmoid notch, accurate reduction and fixation of these fragments is necessary in order to stabilize the DRUJ.

Injuries of the Distal Radio-Ulnar Joint in Children

Most of these injuries should be treated with closed reduction and above elbow cast immobilization.

If the distal radio-ulnar joint is irreducible or the ulnar epiphyseal fracture is completely displaced, the injury is equivalent to a complex dislocation in an adult. In this case closed reduction and percutaneous pinning of the radial fracture and open reduction and pinning of the ulnar epiphyseal fracture is recommended. Postoperatively, the limb should be immobilized in an above elbow cast, with the forearm in supination, for six weeks, at which time the pins can be removed. Immobilization is then continued for another two weeks, after which rehabilitation is begun.

Summary

Dislocations of DRUJ may be simple or complex, stable or unstable. Associated with many fracture patterns.

Treat the associated injury and ensure congruent stable reduction of the DRUJ. Dont forcibly reduce a complex dislocation. If unstable post reduction hold with a transfixing K wire for six weeks.

As a rule of the thumb the position of immobilisation is:

Supination for ulna dorsal
Pronation for ulna volar

JBJS Vol77-A(6) Jun 1995 pp 958-968; Instructional Course Lectures, The American Academy of Orthopaedic Surgeons. Acute Dislocations of the Distal Radio-Ulnar Joint. Bruckner, James D.; Alexander, A. H.; Lichtman, David M.

Mino, D. E.; Palmer, A. K.; and Levinsohn, E. M.: The role of radiography and computerized tomography in the diagnosis of subluxation and dislocation of the distal radioulnar joint. J. Hand Surg., 8: 30, 1983