The distal radioulnar joint is inherently unstable. Pathologic instability can be acute or chronic; it can be dorsal, palmar, or multidirectional; and it can result primarily from soft-tissue injury or osseous malunion. Recognition of the type and cause of instability is fundamental in order to provide effective treatment. Anatomy of the Distal Radioulnar Joint The distal radioulnar joint is a distal articulation in the biarticulate rotational arrangement of the forearm. This articulation allows only one degree of motion: pronation and supination. The sigmoid notch of the radius is concave and is shallow with a radius of curvature of 15 mm. The ulnar head is semicylindrical and has an articulate convexity of 220° with a radius of curvature of 10 mm1. The ulnar head is surrounded by an ulnar carpal ligament complex. This consists of the ulnolunate and ulnotriquetral ligaments, which originate from the palmar radioulnar ligament near the ulnar styloid process. When seen through an arthroscope, these ligaments appear to be continuous with the triangular fibrocartilage. The triangular fibrocartilage is a fibrocartilaginous disk originating at the junction of the lunate fossa and the sigmoid notch and inserting at the base of the ulnar styloid. Its central portion is cartilaginous, and it is designed for weight-bearing. It is also avascular. The peripheral margins are composed of thick lamellar cartilage designed for tensile loading and are called the dorsal and palmar radioulnar ligaments. The peripheral margins of the triangular fibrocartilage are well vascularized from the palmar and dorsal branches of the anterior interosseous artery and from the ulnar artery. The ulnar styloid is the continuation of the subcutaneous ridge of the ulnar shaft, and it stands as a strut on the end of the ulna to stabilize the ulnar soft tissues of the wrist. The sheath of the extensor carpi ulnaris, the ulnocarpal ligaments, and the triangular fibrocartilage help to maintain the congruency of the distal radioulnar joint with attachments at the base of the ulnar styloid; together, they are known as the triangular fibrocartilage complex2-6. The radius of curvature of the ulna does not equal that of the sigmoid notch. Full congruity of two articulating surfaces is therefore not possible. The shallow sigmoid cavity and the difference between the radii of curvature of the sigmoid notch and the ulnar head cause the ulna to translate volarly in supination and dorsally in pronation. In the extremes of forearm rotation, <10% of the ulnar head may be in contact with the notch1. Translation is normal. In pronation, the ulna translates 2.8 mm dorsally from a neutral position; in supinaton, the ulna translates 5.4 mm volarly from a neutral position7. The stability of the distal radioulnar joint is provided by the joint surface morphology, the joint capsule, the dorsal and palmar radioulnar ligaments, the interosseous membrane, and the musculotendinous units, primarily the extensor carpi ulnaris and the pronator quadratus8,9. The pronator quadratus and the extensor carpi ulnaris are dynamic stabilizers of the distal part of the ulna. The pronator quadratus has a superficial head that is a prime mover in forearm pronation and a deep head that helps to stabilize the distal radioulnar joint10. The pronator quadratus actively stabilizes the joint by coapting the ulnar head in the sigmoid notch, particularly in pronation, and it passively stabilizes the joint by viscoelastic forces in supination11,12. The extensor carpi ulnaris is maintained in its position over the dorsal aspect of the distal part of the ulna by a separate fibro-osseous tunnel deep to and separate from the extensor retinaculum. This separate arrangement allows unrestricted rotation of the radius and ulna. An intact extensor carpi ulnaris and fibro-osseous tunnel partially stabilize the distal radioulnar joint even after the triangular fibrocartilage and other ligaments are sectioned13. The important role of the distal radioulnar joint capsule as a restraint and as a contributor to stability was demonstrated by Ward et al.14, Watanabe et al.15, and Marangoz and Leblebicioglu16. Its complementary role in posttraumatic limitations of forearm rotation was described by Kleinman and Graham17. The triangular fibrocartilage, the ulnar carpal ligaments, the infratendinous extensor retinaculum, the pronator quadratus, and the interosseous membrane provide additional key soft-tissue constraints. The triangular fibro-cartilage attaches to the fovea in the ulna by way of the dorsal and palmar radioulnar ligaments. The fibers that insert into the fovea are separated from those that insert into the styloid by an areolar vascular tissue known as the ligamentum subcruentum18. There is a debate in the literature regarding the radioulnar ligaments. According to Schuind et al., in pronation the dorsal radioulnar ligament tightens as the ulna translates dorsally and in supination the palmar radioulnar ligament tightens as the ulna translates palmarly19 (Table I). In contrast, Ekenstam showed that in pronation the palmar radioulnar ligament becomes taut (although the dorsal capsule tightens) as the ulna translates dorsally, and in supination the dorsal radioulnar ligament tightens (although the palmar capsule becomes tight) as the ulna translates volarly20. Ekenstam believed that stability in pronation depends on the tension in the volar radioulnar ligament and compression between the contact areas of the dorsal aspect of the sigmoid notch and the ulna, whereas stability in supination depends on the tension in the dorsal radioulnar ligament and the triangular fibrocartilage articular disk as well as compression between the contact areas of the volar aspect of the sigmoid notch and the ulna. TABLE I - Effects of Pronation and Supination on the Dorsal and Palmar Radioulnar Ligaments and Joint Capsule Pronation Supination Dorsal radioulnar ligament Tight as ulna displaces dorsally. Dorsal capsule imbrication stabilizes distal radioulnar joint, preventing volar translation of radius Lax Palmar radioulnar ligament Lax Tight as ulna displaces palmarly. Palmar capsule imbrication stabilizes distal radioulnar joint, preventing dorsal translation of radius Adams and Holley measured strain on the surface of the triangular fibrocartilage articular disk and calculated the strain at the dorsal and palmar margins of the disk21. In supination, strain increased dorsally; in pronation, strain increased palmarly. In a biomechanical study of eleven fresh cadavers, Ward et al. measured tension in the dorsal and palmar radioulnar ligaments, joint rotation, and radial translation after sequential excision of the disk, interosseous membrane, joint capsule, and radioulnar ligaments14. This experiment confirmed that the dorsal ligament tightens during pronation while the palmar ligament becomes progressively lax, whereas the converse occurs during supination. The preponderance of biomechanical evidence supports the findings reported by Schuind et al.19, and the inconsistency between their observations and those presented by Ekenstam20 can be resolved because, in pronation, the dorsal radioulnar ligament tightens and tends to displace the ulna dorsally. Left unconstrained, this dynamic tensioning would lead to subluxation and dislocation of the joint. The palmar radioulnar ligament checks that force and keeps the joint reduced. If the interosseous membrane is disrupted and the palmar radioulnar ligament is sectioned, the distal part of the ulna dislocates dorsally in pronation. If the interosseous membrane is disrupted and the dorsal radioulnar ligament is sectioned, the distal part of the ulna dislocates palmarly in supination. Classification Disorders of the distal radioulnar joint can be classified into four categories: (1) impaction, (2) incongruity, (3) inflammation, and (4) instability. All of these disorders can produce pain around the distal radioulnar joint and should be considered when a patient reports symptoms at the distal radioulnar joint. Ulnar impaction is due to a positive ulnar variance that causes the distal part of the ulna to abut against the lunate, often leading to thinning of the triangular fibrocartilage and eventually to a central tear. Some surgeons also refer to this as ulnar abutment syndrome. Incongruity refers to the lack of a smooth interface between the ulnar head and the sigmoid notch. Incongruity can be due to a posttraumatic condition such as a distal radial fracture into the sigmoid notch, or it can be secondary to osteoarthritis or rheumatoid arthritis. Inflammation around the distal radioulnar joint is usually due to extensor carpi ulnaris tendinitis dorsally or flexor carpi ulnaris tendinitis palmarly, and sometimes these disorders can be of a calcific variety. Instability of the distal radioulnar joint may be acute or chronic and may be related to osseous changes after a fracture or to soft-tissue injury. Soft-tissue injury of the triangular fibrocartilage, dorsal radioulnar ligament, palmar radioulnar ligament, interosseous membrane, joint capsule, or any combination of those structures is capable of producing instability of the distal radioulnar joint. Fractures of the distal part of the radius or distal part of the ulna alter the biomechanics of the distal radioulnar joint22. It is important to keep in mind that instability can occur alone or in conjunction with impaction, incongruity, or inflammation. Treatment must be directed at each component of the disease complex. Examination of the Distal Radioulnar Joint To examine the ulnar styloid, one should follow the superficial border of the ulnar shaft distally while the wrist is in radial deviation. The ulnar styloid can be found more volarly than anticipated. This maneuver should be done with the wrist in a pronated position. The distal radioulnar joint is the most complex structure to evaluate. The most common pathological finding is radioulnar incongruity secondary to a malunited distal radial fracture with loss of the pronation-supination arc. With loss of the volar tilt of the radius, the distal part of the ulna appears to be more prominent. With ulnar impaction, ulnar deviation and extension are limited and can be painful. The areas of pronation, supination, and flexion-extension should be determined. To test for instability of the distal radioulnar joint, the examiner should supinate the wrist while supporting the hand, perform a ballottement maneuver of the distal part of the ulna, and compare the affected side with the normal side. During this maneuver, he or she should feel for crepitus and ask the patient if pain occurs. To check for instability of the extensor carpi ulnaris tendon, the patient should be asked to flex the elbow and pronate and supinate the forearm with the hand in slight ulnar deviation while the examiner looks for abnormal motion of the extensor carpi ulnaris tendon. Peripheral tears of the triangular fibrocartilage complex can produce instability of the distal radioulnar joint with the wrist in supination. With the patient's forearm in supination, the examiner should hold the distal part of the ulna between the thumb and index finger and test for dorsal and volar displacement of the distal part of the ulna. The so-called press-test is a simple assessment. The patient is asked to push himself or herself up from a seated position with use of the affected wrist. This test creates an axial ulnar load and has a high sensitivity for detecting a tear of the triangular fibrocartilage complex23. Pain with this maneuver suggests that there is a lesion in the triangular fibrocartilage complex.Fig. 1: Posteroanterior radiograph showing a distal radioulnar joint with chronic palmar instability in a fifteen-year-old girl who had sustained a fracture of the distal part of the radius two years previously. Note the large ulnar styloid nonunion fragment and a fleck fracture representing the site where the triangular fibrocartilage complex avulsed from the fovea.Radiographic Tests Standard radiographs of the distal part of the ulna should be made with comparison views of the unaffected side. The images should include a true lateral radiograph made with the forearm in neutral rotation. Any deviation of >10° from a true lateral view will greatly reduce the accuracy of the examination. Ulnar variance should be measured and compared with that on the contralateral side on radiographs made with the forearm in neutral rotation and the shoulder and elbow in 90° of flexion with the x-ray beam directed from posterior to anterior24. Ulnar variance changes by up to a millimeter as the forearm moves from full supination to full pronation; therefore, this standard position should be used. Ulnar variance is measured by drawing a transverse line at the level of the lunate fossa and a second transverse line at the level of the ulnar head, and determining the distance between the two lines. On the posteroanterior radiograph, one should look for a fleck fracture demonstrating an avulsion of the triangular fibrocartilage complex, an ulnar styloid nonunion, and joint widening between the radius and ulna (Fig. 1). Radiographic signs of injury to the distal radioulnar joint include a fracture at the base of the ulnar styloid, widening of the distal radioulnar joint space seen on the posteroanterior radiograph, >20° of dorsal radial angulation, and >5 mm of proximal displacement of the distal part of the radius. Computed tomography scanning is the technique of choice for evaluating congruity of the distal radioulnar joint, but the same information can be obtained with magnetic resonance imaging (Figs. 2-A and 2-B). There are several methods for evaluating subluxation of the distal radioulnar joint, including the method described by Mino et al.25,26, the congruency method27, the epicenter method27, and the RUR (radioulnar ratio) method28. Magnetic resonance imaging is useful for identifying tears of the triangular fibrocartilage (Fig. 3), but its specificity and sensitivity vary29. It is necessary to use high-resolution magnetic resonance imaging with a dedicated wrist coil to obtain accurate scans30-32. Arthrography is still a valuable examination, and it is even more useful when it is combined with magnetic resonance imaging. Arthroscopy is a sensitive method for evaluating tears of the triangular fibrocartilage complex and is considered the gold standard with which to compare the accuracy of other examinations. Figs. 2-A and 2-B T1-weighted magnetic resonance images of both wrists in pronation made to compare the normal wrist (Fig. 2-A) with the wrist that had a dorsal distal ulnar subluxation (Fig. 2-B). Subluxation and Dislocation By convention, the ulna is considered to dislocate with respect to the radius, but it is the radius that moves and therefore is displaced. With dorsal subluxation, the head of the ulna becomes prominent dorsally, particularly in pronation, and may snap during wrist rotation. This is usually associated with a weak and painful wrist. With complete dislocation, the ulnar head is locked in position, most commonly dorsally but on occasion palmarly. Supination is restricted with either type of dislocation because the radius cannot slip dorsally over the ulnar head. The mechanism of action for a dorsal subluxation or dislocation of the ulna is extreme pronation and extension with the coiled and tightened extensor carpi ulnaris and ulnar carpal ligaments acting as a sling to lift the ulnar head through the dorsal capsule. Weakening of the triangular fibrocartilage complex secondary to its avulsion (or a fracture of the ulnar styloid) and attenuation of the palmar radioulnar ligament will allow the dislocation. Sheer stress during this mechanism may produce associated chondral defects. The clinical appearance of a dorsal dislocation of the ulna is a tender prominent dorsally displaced ulna and a forearm with limited supination or locked in pronation. Direct pressure may reduce the dislocation, but the ulnar head usually springs back into a dorsal position if the forearm remains pronated. There is increased anteroposterior translation of the distal radioulnar joint with passive motion. Routine radiographs may be nondiagnostic. A posteroanterior radiograph can show the ulna overlapping the distal part of the radius. The best study with which to visualize a subluxation or dislocation is a computed tomography examination of both wrists performed in both pronation and supination25,26,33-35.Fig. 3: T2-weighted magnetic resonance image showing a complex peripheral tear (double arrows) and radial tear (single arrow) of the triangular fibrocartilage complex. Figs. 4-A and 4-B Standard posteroanterior (Fig. 4-A) and lateral (Fig. 4-B) radiographs of the wrist, demonstrating palmar dislocation of the ulna. Treatment of Acute Dislocations Dorsal Subluxation and Dislocation An acute dorsal dislocation can be reduced with digital pressure on the distal part of the ulna and forceful supination. The reduction should be maintained for six weeks. Some authors36 have advocated full supination, whereas others37 have recommended the neutral position. Nonoperative methods of treatment should be used only when there is congruity of the distal radioulnar joint in two planes. Open reduction with repair of the triangular fibrocartilage complex should be performed if the joint is locked and cannot be reduced, or if it is incongruous following reduction. Open repair of the triangular fibrocartilage complex is done with a dorsal incision through the fifth compartment with the extensor digiti minimi reflected radially and the extensor carpi ulnaris reflected ulnarly, thereby exposing the triangular fibrocartilage complex and visualizing the dorsal radioulnar ligament. Nonabsorbable sutures should be used to reattach the triangular fibrocartilage complex to the ulnar styloid38. Ulnar styloid fractures have an important effect on the stability of the triangular fibrocartilage complex. These fractures commonly occur together with fractures of the distal part of the radius and can be a sign of instability of the triangular fibrocartilage complex. Symptomatic nonunions of the styloid can occur. Hauck et al. classified these nonunions as type 1 when the distal radioulnar joint is stable and as type 2 when it is unstable2. Type-1 fractures occur through the tip of the styloid, and when they become symptomatic they are often treated successfully with excision. Type-2 fractures occur through the base of the styloid, creating a much larger fragment, and usually open reduction and internal fixation and restoration of the integrity of the triangular fibrocartilage complex is recommended even if there is a nonunion. The distal part of the ulna can dislocate or subluxate palmarly as a result of a fall on a supinated hand or from exertional lifting in supination, with failure of the dorsal radioulnar ligament being the critical event. Clinically, patients present with the forearm held in a supinated position. Pronation is painful and restricted39. The ulnar head is palpable volarly, and ulnar dysesthesias may develop from pressure on the ulnar nerve. Once again, a diagnosis can be made on the basis of good standard radiographs (Figs. 4-A and 4-B) and can be confirmed by comparing computed tomography scans of the affected and normal wrists. A fracture or erosion of the palmar lip of the sigmoid notch may lead to persistent instability. An acute palmar dislocation can be reduced with digital pressure on the distal part of the ulna in a dorsal direction combined with forceful pronation. The treatment for an acute palmar dislocation is closed reduction with immobilization for six weeks in an above-the-elbow cast in a neutral or slightly pronated position. Open treatment is reserved for patients for whom closed reduction has failed. The approach is volar with careful retraction of the volar neurovascular bundle in an ulnar direction. Tears of the Triangular Fibrocartilage Complex Triangular fibrocartilage tears can occur without causing instability of the distal radioulnar joint. The most common tear occurs within the articular disk of the triangular fibrocartilage, near its attachment to the radius, and is not associated with instability of the distal radioulnar joint40-44. The tears themselves, however, can be unstable and symptomatic. Despite the recognition of specific types of triangular fibrocartilage lesions45, the exact mechanisms of injury remain uncertain. Adams et al., using a laboratory model to simulate distraction of the radius and ulna through the distal radioulnar joint, postulated that such a distraction force may result from a violent axial load on the forearm40. This model did not, however, produce the types of tears of the triangular fibrocartilage complex that are seen clinically. Probably, a combination of compression across the wrist trapping the disk in the ulnocarpal joint with distraction or twisting of the distal radioulnar joint then creates enough shear forces to tear the disk. Symptomatic instability and tears of the triangular fibrocartilage complex require surgical treatment. The peripheral rim of the triangular fibrocartilage is well vascularized and has good healing potential. Repair of these lesions with a variety of techniques can lead to healing. Historically, open repair was advocated38, but currently most peripheral tears can be treated arthroscopically. This arthroscopic approach repairs only the superficial fibers of the triangular fibrocartilage complex to the joint capsule and not the deep portion that inserts onto the fovea. There is much less chance that central tears of the triangular fibrocartilage complex will heal because they are in areas of hypovascularity or avascularity. Arthroscopic débridement of these lesions is recommended46. Chronic Distal Radioulnar Joint Instability Dorsal, Palmar, or Bidirectional Instability Chronic distal radioulnar joint instability is a painful and often disabling condition. Functional bracing, which has been tested in a cadaveric model47, can be used for patients who do not wish to have surgery, but most patients prefer surgical treatment. It is necessary to check the osseous anatomy in patients with chronic palmar dislocation. Many patients have had a fracture of the wrist or forearm, sometimes many years before symptoms developed at the distal radioulnar joint. Bilateral radiographs of the entire wrist and forearm, made in the same position, should be compared. Osseous malalignment should be corrected. The status of the triangular fibrocartilage complex is evaluated with either magnetic resonance imaging or arthroscopy. If the triangular fibrocartilage complex is not repairable, a tendon reconstruction is needed and should be tightened in supination48,49. Illustrative Case Report An eighteen-year-old, right-hand-dominant man presented with pain in the left wrist and forearm that had been increasing during the previous two years. He had sustained a fracture of the distal third of the left radius at the age of twelve years and had been treated nonoperatively. One month later, he fell and sustained a refracture of the radius as well as an ulnar styloid fracture. The fracture of the radius was treated with open reduction and internal fixation through a volar approach. It healed without complication, and the patient returned to full participation in volleyball, weight-lifting, soccer, and snowboarding. Figs. 5-A and 5-B Posteroanterior (Fig. 5-A) and lateral (Fig. 5-B) radiographs made three years after plate fixation of a fracture of the distal part of the left radius in a twelve-year-old boy. Note the apex volar angulation of the radius. The normal right side is shown for comparison. Figs. 6-A through 6-D A twenty-eight-year-old man was seen with a Galeazzi-type fracture with an entrapped extensor carpi ulnaris tendon preventing reduction of the ulnar styloid that is attached to the triangular fibrocartilage complex. Note the disrupted distal radioulnar joint in addition to the fractures of the radius and distal part of the ulna. Fig. 6-A Posteroanterior radiograph showing the injury. Fig. 6-B Lateral radiograph showing the injury. Fig. 6-C Posteroanterior radiograph made after initial fixation of the radial and ulnar fractures. Note the widening of the distal radioulnar joint. Fig. 6-D Lateral radiograph made after initial fixation of the radial and ulnar fractures. Note the dorsal displacement of the ulna. This problem occurred because the initial surgeon did not recognize the interposition of the extensor carpi ulnaris tendon, which prevented the reduction of the ulnar styloid/triangular fibrocartilage complex. Reoperation was performed, and anatomical reduction and fixation was possible after the extensor carpi ulnaris tendon was repositioned dorsally. Three years later, he noticed swelling about the wrist and had pain at the distal part of the left ulna in association with many activities. Volar angulation of the radius could be seen on radiographs (Figs. 5-A and 5-B). The triangular fibrocartilage complex appeared normal on the magnetic resonance imaging scan. The symptoms were attributed to malunion of the fracture and angular overgrowth of the radius resulting in palmar subluxation of the distal part of the ulna and instability of the distal radioulnar joint. The hardware was removed, and a dome osteotomy of the left radius with iliac crest bone-grafting was done. A closing-wedge osteotomy of the radius was not performed because of the potential that it could further destabilize the distal radioulnar joint50. Eight months after the surgery, the osteotomy site had healed and the patient had regained the preoperative range of wrist motion. The distal radioulnar joint was stable on examination. He resumed all of his previous activities, including volleyball and weight-lifting, without any symptoms in the left upper extremity, and he was discharged from our clinic. He subsequently joined the Marine Corps and wrote to say that he had remained asymptomatic throughout all physical endeavors involved in his strenuous active training51. Dorsal Subluxation and Dislocations with Fractures Galeazzi Fractures A Galeazzi fracture is a diaphyseal fracture of the radius associated with a dislocation of the radioulnar joint52. A Galeazzi fracture has also been called the “fracture of necessity” because nonoperative treatment so often yields a poor result. The radioulnar joint may be dislocated or subluxated, and it is always affected (Figs. 6-A through 6-D). Detection of the disorder of the distal radioulnar joint in a patient with a radial shaft fracture requires a high level of suspicion. Radiographs of the contralateral side may be helpful. Rettig and Raskin found that twelve of twenty-two fractures of the distal third of the radius (within 7.5 cm of the midarticular surface of the distal part of the radius) were associated with intraoperative instability of the distal radioulnar joint, whereas only one of eighteen fractures in the middle third of the radial shaft (>7.5 cm from the midarticular surface of the distal part of the radius) was associated with intraoperative instability of the distal radioulnar joint53. Open reduction with internal fixation of the radial fracture is the first stage of treatment of a Galeazzi fracture. If the distal radioulnar joint is stable, early motion can be initiated. If it is unstable and reducible, the wrist should be immobilized in slight supination for four to six weeks. If a sizable ulnar styloid fracture is present, fixation may allow early mobilization and should be considered. If the distal radioulnar joint is irreducible, open reduction of the joint is necessary; this usually requires repair of the triangular fibrocartilage or fixation of the ulnar styloid fragment. Six weeks of immobilization in slight supination is recommended if the distal radioulnar joint requires surgical treatment. Rarely, the extensor carpi ulnaris is interposed and prevents reduction; if it is, it needs to be removed from the joint (Figs. 6-C and 6-D)54. Essex-Lopresti Injuries Essex-Lopresti injuries, which are severe and disrupt the entire forearm55, consist of a radial head fracture with proximal migration of the radius. The migration indicates complete disruption of the interosseous ligament and the triangular fibrocartilage complex. These injuries are usually caused by a fall on the outstretched hand with axial loading. The primary stabilizer preventing proximal migration of the radius is the radial head, and the secondary stabilizers are the interosseous ligament and the triangular fibrocartilage. Diagnosing the wrist injury in this complex is important. Treatment consists of open reduction and internal fixation of the radial head if possible, with immobilization of the forearm in supination. Pinning of the distal radioulnar joint is an option, but if the pins break they can be difficult to retrieve. Comminuted radial head fractures often are not repairable and require replacement, usually with a metallic prosthesis. Silicone radial head replacements have not performed well in this situation because they fracture, causing particulate synovitis, when they are placed under load. The operation is best done early as delayed treatment can lead to poorer results. The options for delayed surgery include radial head replacement with a prosthesis or allograft56, or a Sauvé-Kapandji procedure. Multidirectional Instability The axis of forearm motion passes through the fovea of the distal part of the ulna. The deep fibers of the distal radioulnar ligaments, the palmar radioulnar ligament, the triangular fibrocartilage, the ulnolunate ligament, the ulnotriquetral ligament, and the ulnocapitate ligament all insert onto the fovea57. These ligamentous attachments are key to the stability of the distal radioulnar joint. The distal radioulnar joint can be stabilized surgically in one of three ways: (1) a repair of the triangular fibrocartilage complex and the distal radioulnar ligaments, (2) an extrinsic soft-tissue reconstruction either with a direct link (i.e., a radioulnar tether) or an indirect link (i.e., an ulnar carpal sling tenodesis), or (3) a distal radioulnar ligament reconstruction. Procedures for Stabilization of the Distal Radioulnar Joint The first option for stabilizing the distal radioulnar joint is to repair the triangular fibrocartilage complex to the fovea, from which it is usually found to be ruptured. When repair is not possible, reconstruction is indicated. There are several procedures for stabilization of the distal radioulnar joint, as described by Hui and Linscheid58, Tsai and Stilwell59, Breen and Jupiter60, Fulkerson and Watson61, and Ellison, Boyes, and Bunnell1, just to mention a few. The above are all indirect stabilization procedures through an ulnocarpal sling or tenodesis, or a direct radioulnar tether extrinsic to the joint (the technique described by Fulkerson and Watson). Johnson described a dynamic muscle transfer involving use of the pronator quadratus11. Other distal radioulnar stabilization procedures involving reconstruction of the radioulnar ligaments were described by Scheker et al.62, Sanders and Hawkins63, and Bowers64. We are not aware of any long-term follow-up study of an adequate series of patients treated with such procedures. In a biomechanical cadaver model, reconstructions of the radioulnar ligaments were found to be superior to radioulnar tethering procedures although the results of capsular repair alone most closely matched the kinematics of an intact distal radioulnar joint65.Fig. 7: Dorsal and palmar ligament reconstruction, as described by Adams and Divelbiss, for treatment of a chronically unstable distal radioulnar joint. (Reprinted from: Adams BD, Divelbiss BJ. Reconstruction of the posttraumatic unstable distal radioulnar joint. Orthop Clin North Am. 2001;32:353-63; with permission from Elsevier.)Fig. 8: This patient underwent open reduction and internal fixation to treat a fracture of the distal part of the radius, but the dorsal subluxation of the ulna was never corrected. Arthritic changes developed in the distal radioulnar joint, with pain and limitation of pronation-supination. This problem was treated with a Sauvé-Kapandji procedure.I recommend the procedure described by Adams et al. to reconstruct the ligamentous anatomy (Fig. 7)48,49. Their indications and criteria for ligament reconstruction include unidirectional or bidirectional chronic instability of the distal radioulnar joint, absence of substantial arthritis, and a competent sigmoid notch rim with no residual axial instability of the forearm. Any malunion should be mild or corrected concurrently. Adams and Divelbiss cautioned that, if the volar or dorsal lip of the sigmoid notch is incompetent (shallow), ligament reconstruction may not be sufficient and an opening-wedge osteotomy of the distal part of the radius may be required48. The procedure is done with use of a dorsal approach through the fifth extensor compartment, which provides direct access to the distal radioulnar joint. Typical findings are a triangular fibrocartilage complex that is torn from the ulna, a torn extensor carpi ulnaris sheath, concomitant carpal ligament injuries, and perhaps an ulnar styloid fracture. Adams and Berger reported that, of twenty patients (twelve with bidirectional instability and eight with unidirectional instability) followed for a minimum of one year after the procedure, eighteen recovered stability, with an 80% recovery of supination, 84% recovery of pronation, and 88% recovery of grip strength49. Salvage If there is residual instability after a distal ulnar resection, a flexor carpi ulnaris and extensor carpi ulnaris tenodesis, as described by Breen and Jupiter60,66, can be considered. Wolfe et al. reported that the distal part of the ulna will remain stable even after removal of more than a third of it67. This may be true after a tumor resection, but it is not a reliable assumption after traumatic injuries. Wide resections of the distal part of the ulna usually require some additional form of stabilization, and tenodesis of the flexor carpi ulnaris and extensor carpi ulnaris tendons is recommended. Implantation of a metallic prosthesis to replace the distal part of the ulna can also be considered as a salvage procedure for treatment of this difficult problem68. The Sauvé-Kapandji procedure is a useful salvage technique when there is instability of the distal part of the ulna and arthritic changes (Fig. 8). The Sauvé-Kapandji procedure involves fusion of the distal radioulnar joint and creation of a pseudarthrosis of the ulna just proximal to the arthrodesis to allow forearm rotation69. There can be subluxation of the proximal ulnar stump, which can be symptomatic, after a Sauvé-Kapandji procedure, and this can be stabilized with either an extensor carpi ulnaris tenodesis, as described by Minami et al.70, or a flexor carpi ulnaris tenodesis, as described by Lamey and Fernandez71. Overview Acute dislocations of the distal radioulnar joint should be reduced promptly and treated with cast immobilization. If the dislocation is irreducible, open reduction is warranted. The first attempts to treat chronic instability should be directed at repairing the triangular fibrocartilage complex, but only after careful assessment for any osseous malunions along the forearm axis, which must also be corrected. If it is not possible to repair the triangular fibrocartilage complex, the osseous architecture is normal, and no arthritis is present, a ligament reconstruction can be considered, but the competency of the sigmoid notch must be evaluated carefully. If there are arthritic changes at the distal radioulnar joint, a Sauvé-Kapandji procedure should be performed, with stabilization of the proximal stump with a slip of either the flexor carpi ulnaris or the extensor carpi ulnaris.