DISTAL RADIOULNAR JOINT INSTABILITY

Abstract

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 of the Ulnar variance should be measured and with that on the side on radiographs made with the forearm in neutral rotation and the and elbow in of with the directed from to Ulnar variance changes by up to a as the forearm from supination to this position should be Ulnar variance is measured by a at the of the lunate fossa and a at the of the ulnar and the between the two the one should for a fleck fracture an of the triangular fibrocartilage an ulnar styloid and joint between the radius and ulna of injury to the distal radioulnar joint include a fracture at the base of the ulnar styloid, of the distal radioulnar joint seen on the of dorsal radial and mm of displacement of the distal part of the is the of for congruity of the distal radioulnar joint, the can be with and There are for subluxation of the distal radioulnar joint, the described by et the congruency the and the is for tears of the triangular fibrocartilage its and sensitivity It is to use with a wrist to is a and it is even more when it is with is a for tears of the triangular fibrocartilage complex and is considered the with which to compare the of other and images of in pronation made to compare the normal wrist with the wrist that had a dorsal distal ulnar subluxation and the ulna is considered to with to the radius, it is the radius that and therefore is With dorsal the head of the ulna becomes dorsally, particularly in pronation, and may during wrist rotation. This is usually with a and wrist. With the ulnar head is in most dorsally on palmarly. Supination is with type of dislocation the radius dorsally over the ulnar The of for a dorsal subluxation or dislocation of the ulna is pronation and extension with the and extensor carpi ulnaris and ulnar carpal ligaments as a to the ulnar head through the dorsal of the triangular fibrocartilage complex secondary to its a fracture of the ulnar and of the palmar radioulnar ligament will the during this may produce The of a dorsal dislocation of the ulna is a dorsally ulna and a forearm with limited supination or in pronation. may reduce the the ulnar head usually into a dorsal position if the forearm There is increased translation of the distal radioulnar joint with radiographs may be radiograph can the ulna the distal part of the The study with which to a subluxation or dislocation is a of in pronation and showing a complex peripheral tear and radial tear of the triangular fibrocartilage complex. and Standard and lateral radiographs of the palmar dislocation of the ulna. Treatment of Dorsal and An acute dorsal dislocation can be with on the distal part of the ulna and supination. The should be maintained for Some supination, whereas the neutral position. of should be only when there is congruity of the distal radioulnar joint in two with of the triangular fibrocartilage complex should be if the joint is and be or if it is of the triangular fibrocartilage complex is done with a dorsal through the with the extensor and the extensor carpi ulnaris the triangular fibrocartilage complex and the dorsal radioulnar should be to the triangular fibrocartilage complex to the ulnar Ulnar styloid an important on the stability of the triangular fibrocartilage complex. occur with of the distal part of the radius and can be a of instability of the triangular fibrocartilage complex. of the styloid can et al. classified these as type when the distal radioulnar joint is and as type when it is occur through the of the styloid, and when they they are often with occur through the base of the styloid, a and usually and and of the of the triangular fibrocartilage complex is even if there is a The distal part of the ulna can or palmarly as a result of a on a hand or from in supination, with of the dorsal radioulnar ligament the with the forearm in a position. Pronation is and The ulnar head is and ulnar may from on the ulnar a can be made on the of radiographs and and can be confirmed by of the affected and normal fracture or of the palmar of the sigmoid notch may lead to instability. An acute palmar dislocation can be with on the distal part of the ulna in a dorsal with pronation. The for an acute palmar dislocation is with for in an in a neutral or pronated position. is for for has The is volar with of the volar in an ulnar of the fibrocartilage tears can occur instability of the distal radioulnar joint. The most common tear occurs the articular disk of the triangular fibrocartilage, near its to the radius, and is not with instability of the distal radioulnar The tears can be and the of of triangular fibrocartilage the of injury Adams et al., a to of the radius and ulna through the distal radioulnar joint, that such a force may result from a axial load on the This produce the of tears of the triangular fibrocartilage complex that are seen a combination of compression the wrist the disk in the ulnocarpal joint with or of the distal radioulnar joint creates forces to tear the instability and tears of the triangular fibrocartilage complex treatment. The peripheral of the triangular fibrocartilage is well vascularized and has of these with a of can lead to was most peripheral tears can be This only the superficial fibers of the triangular fibrocartilage complex to the joint capsule and not the deep portion that the There is that central tears of the triangular fibrocartilage complex will they are in areas of or of these is Distal Radioulnar Joint Instability or Instability distal radioulnar joint instability is a and often which has in a can be for who not to most treatment. It is to check the osseous in with chronic palmar had a fracture of the wrist or sometimes years symptoms at the distal radioulnar joint. radiographs of the wrist and made in the should be should be The of the triangular fibrocartilage complex is with or If the triangular fibrocartilage complex is not a is and should be in An presented with pain in the wrist and forearm that had during the two had sustained a fracture of the distal of the radius at the of years and had he and sustained a of the radius as well as an ulnar styloid The fracture of the radius was with and through a volar It and the patient to in and and Posteroanterior and lateral radiographs made years after of a fracture of the distal part of the radius in a Note the volar of the The normal side is for through was seen with a fracture with an extensor carpi ulnaris preventing of the ulnar styloid that is to the triangular fibrocartilage complex. Note the disrupted distal radioulnar joint in to the of the radius and distal part of the ulna. Posteroanterior radiograph showing the injury. radiograph showing the injury. Posteroanterior radiograph made after of the radial and ulnar Note the of the distal radioulnar joint. radiograph made after of the radial and ulnar Note the dorsal displacement of the ulna. This the not the of the extensor carpi ulnaris tendon, which the of the ulnar fibrocartilage complex. was and and was after the extensor carpi ulnaris was dorsally. years he the wrist and had pain at the distal part of the ulna in with of the radius be seen on radiographs and The triangular fibrocartilage complex normal on the The symptoms to of the fracture and of the radius in palmar subluxation of the distal part of the ulna and instability of the distal radioulnar joint. The was and a of the radius with was of the radius was not of the that it the distal radioulnar after the the site had and the patient had the of wrist The distal radioulnar joint was on of and any symptoms in the and he was from the and to that he had in Dorsal and with Fractures Fractures fracture is a fracture of the radius with a dislocation of the radioulnar fracture has also called the of often a The radioulnar joint may be or and it is affected through of the of the distal radioulnar joint in a patient with a radial shaft fracture a high of of the side may be and found that of of the distal of the radius of the surface of the distal part of the with instability of the distal radioulnar joint, whereas only one of in the of the radial shaft from the surface of the distal part of the was with instability of the distal radioulnar with of the radial fracture is the of of a If the distal radioulnar joint is motion can be If it is and the wrist should be in slight supination for four to If a ulnar styloid fracture is may and should be If the distal radioulnar joint is of the joint is this usually of the triangular fibrocartilage or of the ulnar styloid of in slight supination is if the distal radioulnar joint treatment. the extensor carpi ulnaris is and if it it to be from the joint and which are and the of a radial head fracture with of the The of the interosseous ligament and the triangular fibrocartilage complex. are usually by a on the hand with axial The preventing of the radius is the radial and the secondary stabilizers are the interosseous ligament and the triangular fibrocartilage. the wrist injury in this complex is Treatment consists of and of the radial head if with of the forearm in supination. of the distal radioulnar joint is an if the they can be to radial head often are not and usually with a radial head not well in this they when they are The is done as can lead to The for include radial head with a or or a Instability The of forearm motion 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 ligament insert the attachments are key to the stability of the distal radioulnar joint. The distal radioulnar joint can be in one of (1) a of the triangular fibrocartilage complex and the distal radioulnar ligaments, (2) an soft-tissue with a a radioulnar or an an ulnar carpal or (3) a distal radioulnar ligament for of the Distal Radioulnar Joint The for the distal radioulnar joint is to the triangular fibrocartilage complex to the from which it is usually found to be When is not is There are for of the distal radioulnar joint, as described by and and and and and and to a The are through an ulnocarpal or or a radioulnar to the joint described by and described a dynamic use of the pronator distal radioulnar of the radioulnar ligaments described by et and and are not of any study of an of with such In a biomechanical of the radioulnar ligaments found to be to radioulnar the of alone most the of an intact distal radioulnar Dorsal and palmar ligament as described by Adams and for of a distal radioulnar joint. Adams of the posttraumatic distal radioulnar joint. with from This patient and to a fracture of the distal part of the radius, the dorsal subluxation of the ulna was changes in the distal radioulnar joint, with pain and of This was with a the described by Adams et al. to the and for ligament include or chronic instability of the distal radioulnar joint, of and a sigmoid notch with axial instability of the forearm. Any should be or Adams and if the volar or dorsal of the sigmoid notch is ligament may not be and an of the distal part of the radius may be The is done with use of a dorsal through the extensor which to the distal radioulnar joint. findings are a triangular fibrocartilage complex that is from the ulna, a extensor carpi ulnaris carpal ligament and an ulnar styloid Adams and reported of with instability and with for a of one after the with an of supination, of pronation, and of If there is instability after a distal ulnar a flexor carpi ulnaris and extensor carpi ulnaris as described by and can be et al. reported that the distal part of the ulna will even after of more than a of This may be true after a it is not a after of the distal part of the ulna usually additional of and of the flexor carpi ulnaris and extensor carpi ulnaris is of a to the distal part of the ulna can also be considered as a for of this The is a when there is instability of the distal part of the ulna and changes The of the distal radioulnar joint and of a of the ulna to the to forearm There can be subluxation of the ulnar which can be after a and this can be with an extensor carpi ulnaris as described by et or a flexor carpi ulnaris as described by and of the distal radioulnar joint should be and with If the dislocation is is The to chronic instability should be directed at the triangular fibrocartilage only after for any osseous the forearm which must also be If it is not to the triangular fibrocartilage the osseous is and is a ligament can be the of the sigmoid notch must be If there are changes at the distal radioulnar joint, a should be with of the with a of the flexor carpi ulnaris or the extensor carpi