➢ Injuries along the length of the forearm, including distal radial fractures with or without ulnar styloid fractures, disruption of the radioulnar ligaments, triangular fibrocartilage complex tears, midshaft radial fractures, and injuries to the interosseous membrane, may lead to acute distal radioulnar joint instability.
➢ Acute distal radioulnar joint instability is primarily a clinical diagnosis, and physical examination remains a mainstay of diagnosis.
➢ Anatomic reduction and stabilization of fractures frequently leads to stabilization of the distal radioulnar joint.
➢ Ligamentous injuries and injuries to the triangular fibrocartilage complex may be treated acutely with immobilization alone, without the need for repair.
➢ The distal radioulnar joint should be immobilized in a position of stability. Transosseous Kirschner wires may be used for unstable joints.
Acute instability of the distal radioulnar joint most commonly results from traumatic injury to the distal part of the radius or the ulnar styloid, although injury to any portion of the radius or ulna may cause distal radioulnar joint instability. Instability between the radius and the ulna at the wrist may limit forearm rotation and may prevent stable transmission of load across the radiocarpal and ulnocarpal joints. Instability is diagnosed primarily on the basis of physical examination. Imaging studies and wrist arthroscopy may be used to distinguish deficient structures and to assist with surgical planning. The treatment of acute distal radioulnar joint instability should address the structures that are injured and should take into account the anatomic variability and the presence of arthritis or other conditions affecting the distal radioulnar joint. Prompt recognition of these injuries and treatment of deficient structures may limit morbidity associated with instability of the distal radioulnar joint.
The distal radioulnar joint is an incongruent, diarthroidal joint between the sigmoid notch of the distal part of the radius and the seat of the ulna. Rotation of the radius about the stable ulna allows for forearm pronation and supination. The longitudinal axis of rotation is along a line that passes through the center of the radial head proximally and extends through the foveal sulcus of the ulna distally. A normal arc of motion is between 150° and 180° at the distal radioulnar joint. Stability is maintained through static osseous and ligamentous restraints as well as dynamic muscular restraints.
Osseous contact accounts for only about 20% of stability1. The radius of curvature of the sigmoid notch is 15 to 19 mm, nearly twice that of the ulnar head, which measures 8 to 10 mm2,3. This joint incongruity leads to both rotational and translational motion as the radius moves about the ulna. In pronation the ulna translates as much as 2.8 mm dorsally to sit against the dorsal lip of the sigmoid notch, whereas in supination the ulna translates as much as 5.4 mm volarly to rest at the volar lip of the sigmoid notch2,4. Approximately 80% of wrists have been found to have an additional palmar osteocartilaginous lip, which forms a stable, extra-articular buttress against palmar dislocation of the ulna2. Anatomic reduction may play an important role in reestablishing stability of the distal radioulnar joint after a distal radial fracture.
The distal part of the ulna has two articular surfaces: the seat, which articulates with the sigmoid notch, and the pole or dome, which forms the gliding surface of the triangular fibrocartilage complex. The ulnar styloid is an osseous prominence that serves as the origin of the ulnar collateral ligament, the ulnocarpal ligaments, and the superficial fibers of the radioulnar ligaments. At the base of the ulnar styloid is a shallow depression called the fovea, which is devoid of cartilage but is well vascularized. The fovea is the primary attachment of the deep fibers of the radioulnar ligaments and the ulnocarpal ligaments.
Intrinsic Ligamentous Stabilizers
The triangular fibrocartilage complex extends radially from its ulnar attachments to the dorsal and palmar aspects of the sigmoid notch in the shape of a fan. The most dorsal and palmar bundles are the two primary stabilizers of the distal radioulnar joint, the dorsal and palmar radioulnar ligaments. Other components of the triangular fibrocartilage complex include the articular disc, the extensor carpi ulnaris tendon subsheath, and the meniscus homolog (Fig. 1). The triangular fibrocartilage complex serves both to stabilize the distal radioulnar joint and to transmit load from the carpus.
Both the dorsal radioulnar ligament and the palmar radioulnar ligament form two distinct limbs at their ulnar attachments: the deep limbs, which attach at the fovea, and the superficial limbs, which attach at the base of the ulnar styloid. A highly vascular connective tissue between the insertions of the deep fibers of the dorsal and palmar radioulnar ligaments forms a complex called the ligamentum subcruentum. Although the deep fibers of the radioulnar ligaments are thought to contribute more substantially to distal radioulnar joint stability, they work in concert with the superficial fibers to restrain the ulna within the sigmoid notch5. With forearm pronation, the superficial dorsal radioulnar ligament tightens, displacing the ulna dorsally6. The deep fibers of the palmar radioulnar ligament are also tensioned, pulling the ulna radially into the dorsal lip of the sigmoid notch and preventing further dorsal translation of the ulna3-5. With supination, the superficial palmar radioulnar ligament fibers pull the ulna palmarly, whereas the deep fibers of the dorsal radioulnar ligament pull the ulna radially into the volar buttress of the sigmoid notch, preventing further palmar translation of the ulna3,5-7.
The articular disc of the triangular fibrocartilage complex extends from the distal rim of the sigmoid notch and blends with the dorsal radioulnar ligament and palmar radioulnar ligament. The disc may be partially excised with no impact on distal radioulnar joint stability as long as at least two-thirds of the total disc remains and the outer 2 mm remains undisturbed8. The joint capsule also contributes to distal radioulnar joint stability5.
Extrinsic Ligamentous Stabilizers
Extrinsic stabilizers of the distal radioulnar joint include the interosseous membrane, the extensor carpi ulnaris tendon and sheath, and the pronator quadratus muscle. The interosseous membrane, particularly the central band, helps to prevent proximal migration of the radius, providing 71% of the soft-tissue contribution to the longitudinal stability between the bones9. The interosseous membrane also resists distraction of the radius and ulna when compressive forces are applied to the hand10. The distal portion of the interosseous membrane adds to volar and dorsal stability of the distal radioulnar joint6 and may resist dorsal and palmar instability when the radioulnar ligaments are sectioned11. A distal oblique bundle of the interosseous membrane has also been described in approximately 40% of examined specimens and may add substantially to distal radioulnar joint stability when the forearm is neutrally positioned12.
The extensor carpi ulnaris glides through a fibro-osseous tunnel measuring approximately 2 mm in length, which is continuous with the triangular fibrocartilage complex. The extensor carpi ulnaris compartment contributes to distal radioulnar joint stability and can prevent complete instability even when all other ligaments of the triangular fibrocartilage complex are sectioned13. The pronator quadratus is another active stabilizer of the distal radioulnar joint, pulling the ulna into the sigmoid notch during active pronation and passive supination14,15.
Injuries Associated with Distal Radioulnar Joint Instability
Instability of the distal radioulnar joint can present following injuries along the entire course of the forearm. Acute instability of the distal radioulnar joint may occur after isolated injury to the triangular fibrocartilage complex, but is more commonly associated with other injuries. Distal radial fractures, with or without fracture of the ulnar styloid, and radial shaft fractures may result in instability after disruption of the distal radioulnar ligaments or a tear of the peripheral triangular fibrocartilage complex. Injuries to the more proximal aspects of the forearm, such as radial head and neck fractures, also may result in distal radioulnar joint instability, although this instability generally manifests as longitudinal instability of the forearm, which is beyond the scope of this article.
Triangular Fibrocartilage Complex Tears
Isolated tears of the triangular fibrocartilage complex may result in instability of the distal radioulnar joint. Avulsion of the triangular fibrocartilage complex at its insertion on the distal part of the ulna, a Palmer class-1B injury, can occur either from the base of the ulnar styloid or the ulnar fovea16. Other classes of traumatic injury to the triangular fibrocartilage complex also may be associated with distal radioulnar joint instability, including distal avulsions of the ulnolunate and ulnotriquetral ligaments (Palmer class-1C injuries) and avulsions of the radial insertions of the triangular fibrocartilage complex (Palmer class-1D injuries)16,17.
Distal radioulnar joint instability after a triangular fibrocartilage complex tear is frequently associated with other injuries. Mikic reported on a series of 130 patients who had distal radioulnar joint instability with associated injuries to the triangular fibrocartilage complex18. In that group, only twenty patients (15%) experienced instability of the distal radioulnar joint after isolated triangular fibrocartilage complex disruption. The remaining patients had additional concomitant injuries to the forearm.
Distal Radial Fractures
Distal radioulnar joint instability is commonly present in association with distal radial fractures, usually those associated with complete tears of the distal radioulnar ligaments19,20. Lindau et al. arthroscopically evaluated the triangular fibrocartilage complex in fifty-three patients with distal radial fractures21. At the time of the one-year follow-up, residual instability of the distal radioulnar joint was noted in ten of eleven patients with a complete peripheral tear of the triangular fibrocartilage complex, compared with seven of thirty-two patients with a partial tear or no tear of the triangular fibrocartilage complex. Given the high association of distal radioulnar joint instability with complete peripheral triangular fibrocartilage complex tears, that study highlights the importance of the peripheral triangular fibrocartilage complex as stabilizer of the distal radioulnar joint after distal radial fractures.
Large, displaced ulnar styloid fractures associated with distal radial fractures may result in distal radioulnar joint instability. May et al. evaluated 130 distal radial fractures for both distal radioulnar joint instability and associated ulnar styloid fractures22. The authors noted that all fourteen patients with distal radioulnar joint instability (11%) had sustained an ulnar styloid fracture and that ulnar styloid fractures that were associated with distal radioulnar joint instability more commonly involved greater portions of the ulnar styloid and were displaced by >2 mm. In the absence of distal radioulnar joint instability after operative fixation of a distal radial fracture, an ulnar styloid fracture does not require operative stabilization. However, larger, displaced fractures of the base of the ulnar styloid more likely involve a greater portion of the insertion of the ligamentum subcruentum and may result in persistent distal radioulnar joint instability following stabilization of the distal part of the radius.
Galeazzi fractures are fractures of the radial shaft near the junction between the middle and distal thirds with associated distal radioulnar joint instability. In one series, concomitant distal radioulnar joint instability was present in nine (25%) of thirty-six patients with a radial shaft fracture15. Distal radioulnar joint instability also may be associated with combined fractures of the radial and ulnar shafts, with concomitant injury to the triangular fibrocartilage complex and dislocation of the ulnar head23.
Acute instability of the distal radioulnar joint can occur in association with multiple forearm and wrist fractures. Instability of the distal radioulnar joint may lead to impaired forearm rotation, altered load transmission across the wrist, and loss of function. Various studies have demonstrated the importance of recognizing distal radioulnar joint instability when treating associated injuries as prompt recognition and treatment may improve function. It is therefore important to evaluate the distal radioulnar joint when examining patients with injuries along the length of the forearm.
The evaluation of distal radioulnar joint instability can be difficult, and no standard method exists for establishing this diagnosis. Specific examination maneuvers may lead to a diagnosis of instability after clinical suspicion is raised on the basis of adequate imaging studies.
When used alone to diagnose distal radioulnar joint instability, physical examination is moderately sensitive but quite specific. Lindau et al. demonstrated that physical examination had a sensitivity of 59% and a specificity of 96% for the diagnosis of distal radioulnar joint instability21. Findings on physical examination that suggest distal radioulnar joint instability include >1 cm of dorsal-to-palmar translation of the distal part of the ulna, decreased range of motion in pronation or supination, or a “clunk” at the wrist with forearm rotation24. The examination begins with an evaluation of the upper extremity for traumatic injury, which should include forearm range of motion and a neurovascular examination. Stability of the ulna should be tested in neutral, pronation, and supination, and the affected extremity should be compared with the contralateral extremity to account for each patient’s anatomic idiosyncrasies.
After a general examination has been completed, more specific maneuvers may be used to establish the diagnosis of distal radioulnar joint instability. Ballottement of the distal radioulnar joint is the most commonly described test and may demonstrate the so-called piano key sign. The test is positive when the distal part of the ulna is prominent dorsally and reduces with volarly directed pressure, similar to pressing a piano key25,26. There also may be a palpable clunk with reduction of the joint. For the compression test, the examiner compresses the radius and ulna across the distal radioulnar joint during pronation and supination of the forearm. The compression test is positive if compression accentuates pain or results in a clunk as the ulnar head dislocates and reduces within the sigmoid notch of the radius during rotation of the forearm27. The bilateral test was described by Hahn et al. and involves the use of the contralateral extremity as a basis for comparison28. The distal radioulnar joint is assessed for provoked subluxation of the ulna or a difference in movement of the radius against the ulna.
Distal radioulnar joint instability generally is determined with use of the tests described above. After the presence of distal radioulnar joint instability has been established, additional examination maneuvers may be used to determine which structures have been disrupted to permit this instability.
The “ulnar fovea sign” as described by Tay et al. is used to diagnose foveal disruption and was shown to have a sensitivity of 95.2% and a specificity of 86.5%29. The test is positive when compression within the sulcus bounded by the flexor carpi ulnaris and ulnar styloid in the volar-dorsal direction and by the distal part of the ulna and pisiform bone in the proximal-distal direction elicits pain. The so-called press test as described by Lester et al. is used to diagnose tears of the triangular fibrocartilage complex, which may be associated with distal radioulnar joint instability30. This test recreates an axial load in ulnar deviation at the wrist as the seated patient lifts the body off of the chair with use of the hands. Lester et al. determined that, when used to diagnose triangular fibrocartilage complex tears, the press test had a sensitivity and specificity of 100% and 79%, respectively, when compared with the findings of arthroscopic examination.
Routine radiographs should be evaluated for evidence of distal radioulnar joint instability. More advanced imaging studies or procedures may be conducted in order to help to confirm the diagnosis of instability at the distal radioulnar joint and to determine which structures are deficient.
Initial imaging consists of orthogonal radiographs of the forearm, wrist, and elbow31. Volar or dorsal prominence of the ulnar head may be present in association with subluxation or dislocation of the distal radioulnar joint, although no minimum amount of prominence has been described as being diagnostic of instability.
It is important to make true lateral radiographs of the wrist with the forearm in neutral rotation as slight rotation of the forearm may affect the ability to evaluate for distal radioulnar joint subluxation32. In the study by Mino et al., lateral radiographs demonstrating complete overlap of the proximal aspects of the scaphoid, lunate, and triquetrum with the radial styloid midway between the volar and dorsal aspects of the wrist could be used to determine subluxation of the distal radioulnar joint32. Other authors have described an adequate lateral radiograph of the wrist as one that places the anterior border of the pisiform halfway between the volar borders of the scaphoid and capitate.
The posteroanterior radiograph of the wrist should be scrutinized for changes in ulnar variance and either widening or overlap of the radius and ulna at the distal radioulnar joint (Fig. 2). Proximal displacement of the radius of >5 mm is indicative of distal radioulnar joint instability. Small avulsion fractures off of the sigmoid notch of the distal part of the radius and ulnar styloid fractures that are displaced by >2 mm also may be indicative of injury associated with distal radioulnar joint instability22. The posteroanterior radiograph should demonstrate an extensor carpi ulnaris groove that is located radial to a straight line passing tangential to the radial edge of the ulnar styloid at the fovea33. Widening of the distal radioulnar joint may be demonstrated on static or dynamic posteroanterior radiographs of the wrist34. Iida et al. added the distances between the volar and dorsal corners of the distal part of the radius and the ulnar head34. Clenched-fist radiographs of unstable distal radioulnar joints demonstrated separation of approximately 3.6 mm between the distal part of the radius and the ulna, compared with 3.0 mm in stable joints (p < 0.05)34.
Computed tomography (CT) scans of the distal radioulnar joint may assist in the diagnosis of distal radioulnar joint instability and are indicated when there is continued suspicion of instability despite negative findings on radiographs. Bilateral CT scans of the wrist with the forearm in pronation and supination should be made for comparison of the involved and contralateral sides and to evaluate for sigmoid notch morphology (Fig. 3). Multiple methods have been described for evaluating distal radioulnar subluxation with use of CT scans, including the modified radioulnar line method, the epicenter method, and the radioulnar ratio method. Described initially by Mino et al. and modified by Nakamura et al., the radioulnar line method involves comparing the amount of ulnar head lying outside of lines drawn across the dorsal and volar borders of the radius to the cross section of the sigmoid notch32,35. Abnormal subluxation is present when the ratio of ulnar head outside of the sigmoid notch as compared with inside the notch is >25%35.
The epicenter method of determining distal radioulnar subluxation involves the use of a line that is drawn from the volar and dorsal margins of the sigmoid notch and the establishment of two lines perpendicular to this line. One of these lines passes through the middle of the sigmoid notch, and another passes through the center of the ulnar head. The distance between these two lines should be ≤25% of the total length of the sigmoid notch. Values of >25% denote subluxation of the distal radioulnar joint36.
The radioulnar ratio method was more recently described by Lo et al.37. This method involves the use of a line between the volar and dorsal corners of the sigmoid notch and establishment of the center of the ulnar head. The ratio of sigmoid notch volar and dorsal to the line from the center of the ulnar head is calculated, and normal values (along with standard deviations) have been described. Subluxation is diagnosed if the ratio is more than two standard deviations from the mean value37.
In two separate studies, Lo et al. and Kim and Park evaluated the accuracy of CT for the diagnosis of distal radioulnar joint instability with use of these three methods37,38. The two studies demonstrated conflicting results but were primarily limited by low numbers of patients. Physical examination was the gold standard that was used to establish the diagnosis of distal radioulnar joint instability in each study, limiting the reliability and reproducibility of the results.
CT scanning also may help to delineate osseous injuries involving the distal radioulnar joint that should be addressed in the course of operative fixation. Unstable volar or dorsal ulnar corner fragments associated with fractures of the distal part of the radius may be difficult to assess on radiographs but may be more easily appreciated on CT scans. Distal radioulnar joint stability is often restored with appropriate reduction of these fragments.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is useful for evaluating soft-tissue structures about the wrist that may need to be addressed during the treatment of distal radioulnar joint instability (Fig. 4). Acutely, MRI is indicated for the evaluation of triangular fibrocartilage complex tears. Multiple studies have demonstrated the high sensitivity and specificity of MRI when used to diagnose injuries involving the triangular fibrocartilage complex. In those studies, sensitivity has approached 100%, with a specificity of >90%39-41. MRI also may demonstrate tears of the extensor carpi ulnaris sheath, a secondary stabilizer of the distal radioulnar joint, that may require repair in the course of treating distal radioulnar joint instability.
The treatment of distal radioulnar joint instability is based on whether a stable reduction of the distal radioulnar joint can be obtained and what associated injuries are present (Table I). If present, injuries to the osseous structures of the wrist and forearm should be anatomically reduced and stabilized first, followed by repeat assessment of the distal radioulnar joint. In the absence of other osseous injuries, the distal radioulnar joint should be reduced, and, if the joint is stable after reduction, splinting of the wrist and forearm in a stable position often leads to satisfactory results. Distal radioulnar joints that remain unstable after reduction may require the placement of pins transfixing the radius and ulna or may require surgery to address associated injuries. Irreducible dislocations of the distal radioulnar joint require exploration of the joint for interposed structures.
Instability of the Distal Radioulnar Joint with Associated Triangular Fibrocartilage Complex Tear
In the absence of other osseous injuries, instability of the distal radioulnar joint generally results from a tear of the triangular fibrocartilage complex. Instability may manifest as volar or dorsal displacement of the ulna, although dorsal displacement is far more common. If treated acutely, these injuries may be successfully treated with immobilization alone, without the need for repair of the triangular fibrocartilage complex. Mulford et al. described a case of locked volar dislocation of the distal radioulnar joint and performed a review of the literature42. The authors found twenty-two cases of isolated volar dislocation of the distal radioulnar joint that had been described since 1960. Nine of eleven cases were successfully treated with closed reduction. Most chronic cases required a salvage procedure.
After reduction of a distal radioulnar joint dislocation, successful outcomes have been described in association with immobilization with use of a long arm splint and/or Kirschner wires. The forearm should be immobilized in supination when the distal radioulnar joint is dislocated dorsally and in pronation when the distal radioulnar joint is dislocated volarly. In the series described by Mikic, all twenty patients with distal radioulnar joint instability and isolated triangular fibrocartilage complex tears were managed with stabilization with use of Kirschner wires and splinting in a neutral position18. Mikic explained his rationale for immobilizing the distal radioulnar joint in a neutral position by noting that full pronation or supination of the forearm translates the ulna out of the sigmoid notch and places at least one of the bundles of distal radioulnar ligaments on stretch. Mikic noted that “the best articular contact and stability are found in mid-forearm rotation.”18 If a stable position is not found, the joint may require exploration for interposed structures followed by splinting or pinning of the distal radioulnar joint.
Instability of the Distal Radioulnar Joint with Associated Fracture of the Radius
In patients with Galeazzi fractures, the distal radioulnar joint should be tested for instability after fixation of the distal part of the radius or radial shaft. The primary focus should be on achieving stable, anatomic restoration of the radius because doing so may address instability at the distal radioulnar joint. If the distal radioulnar joint remains unstable, attention is then turned to the ulnar styloid. Small ulnar styloid fractures rarely contribute to distal radioulnar joint instability. If a large associated ulnar styloid fracture is noted, fixation of this fracture may restore the insertion of the triangular fibrocartilage complex with the volar and dorsal radioulnar ligaments at its base. However, Kim et al. demonstrated that distal radioulnar joint stability often can be restored with splinting alone43. The size and amount of displacement of an ulnar styloid fracture was not related to distal radioulnar joint instability or functional outcome following volar plate fixation of a distal radial fracture. At this time, the literature does not clearly support operative fixation or splinting for the treatment of large ulnar styloid fractures, other than in the setting of distal radioulnar joint instability.
Irreducible Dislocations of the Distal Radioulnar Joint
Interposition of the triangular fibrocartilage complex, extensor tendons (most commonly the extensor digiti minimi), and extensor retinaculum and blocking of the pronator quadratus have been described. A dorsal approach to the distal radioulnar joint through an incision over the fifth extensor compartment allows access to the distal radioulnar joint. After removal of the interposed structures, the distal radioulnar joint is reduced and stabilized as noted above. In a case report, Mulford et al. described an irreducible volar dislocation of the distal radioulnar joint due to impaction of the ulnar head on the sigmoid notch42.
The distal radioulnar joint is an essential joint within the forearm as it permits stable load transmission through the wrist while allowing pronation and supination of the forearm. Distal radioulnar joint instability is primarily diagnosed on the basis of clinical findings at the time of a thorough physical examination. Imaging studies can assist in the diagnosis of distal radioulnar joint instability as well as in the determination of which structures may need to be addressed to stabilize the joint. With early recognition and treatment of distal radioulnar joint injuries, good outcomes can be expected.
Source of Funding: No funds were received in support of this work.
Investigation performed at the Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
- Copyright © 2014 by The Journal of Bone and Joint Surgery, Incorporated