6.4 The distal radioulnar joint

DRUJ Stabilizers:

Investigations:

TFCC Pathology:

DRUJ OA:

Derangements of the distal radioulnar joint (DRUJ) are common causes of acute and chronic ulnar wrist pain and dysfunction. This chapter will focus on triangular fibrocartilage complex (TFCC) disorders, ulnar impaction, instability, and degenerative arthroses. Fractures and dislocations, congenital and developmental disorders, and rheumatic diseases affecting the DRUJ are covered in other chapters.

The anatomy and biomechanics of the DRUJ are complex and interplay with the proximal radioulnar joint, interosseous membrane, and the ulnar carpus during forearm and wrist motion. Pathology at any one of these may affect their composite function.

The DRUJ is a trochoid articulation between the sigmoid notch of the radius and the ulnar head. The sigmoid notch has a 47–80-degree arc of curvature and a radius of approximately 15mm. The ulnar head is semicylindrical in cross-section. It has articular cartilage covering 90–135 degrees of its circumference and a radius of curvature of 10mm (Box 6.4.1 and Figure 6.4.1). Although 60–80 degrees of the ulnar articular surface engages the sigmoid notch in neutral rotation, the contact is less than 10 degrees at the extremes of rotation. Minimal bony constraint allows a wide arc of motion but at the expense of intrinsic instability that is limited primarily by soft-tissue restraints.

The primary soft tissue stabilizer of the DRUJ is the TFCC (Figure 6.4.2). It separates the DRUJ and the radiocarpal joint, and comprises the triangular fibrocartilage (TFC), the dorsal and palmar radioulnar ligaments, the ulnocarpal meniscus homologue, and the sheath of the tendon of the extensor carpi ulnaris (ECU). The palmar ulnocarpal ligaments are intimately related to the TFCC and contribute to ulnar wrist stability.

The TFC is triangular in shape and biconcave on its distal surface. It arises from the distal margin of the sigmoid notch and courses medially where its apex inserts into the fovea at the base of the ulnar styloid. It is thickest (approximately 5mm) at its ulnar insertion, and thinnest centrally at its origin from the radius (approximately 2mm). The central portion, or articular disc, is avascular chondroid fibrocartilage with interwoven collagen fibres arising from the hyaline cartilage of the lunate fossa, and is adapted to compressive loading. The origin is reinforced by thick collagen bundles projecting 1–2mm from the radius creating a juncture that is a common site of TFC tears. In contrast, the TFC thickens dorsally and volarly to become the dorsal and volar radioulnar ligaments, comprising well-vascularized connective tissue with longitudinally oriented collagen fibres that arise from and insert into bone and are best suited to resisting tensile loads.

Perforations of the TFC are found with increasing prevalence with age over 30 years Excessive length of the ulna with respect to the radius (positive ulnar variance) is directly proportional to the age-related incidence of TFCC perforation, and inversely proportional to TFCC thickness.

Of the TFCC components, the palmar and dorsal radioulnar ligaments are the primary stabilizers of the DRUJ, and the joint is most stable when these are in tension at the extremes of rotation. The sheath of the ECU, the floor of which has been called the ulnar collateral ligament, extends from the ECU groove on the dorsal ulna to insert on the dorsal base of the fifth metacarpal. Its role in stabilizing the distal ulna is augmented by the dynamic effects of the ECU tendon.

The volar ulnolunate and ulnotriquetral ligaments arise at the base of the ulnar styloid, where the apex of the TFCs attaches. They course along its volar margin to diverge and insert independently into the lunate and triquetrum and into the lunotriquetral interosseous ligament. They act primarily in stabilizing the ulna and palmar carpus and resist dorsal displacement of the distal ulna.

The secondary stabilizers of the DRUJ include the bony conformation of the sigmoid notch, the interosseous membrane, the extensor retinaculum, the dorsal carpal ligament complex, and the forearm muscles that cross the pronation/supination axis, especially the pronator quadratus (Box 6.4.2). Watanabe and colleagues found that sectioning the joint capsule affected DRUJ stability in pronation and supination. They also demonstrated that dorsal capsular imbrication contributed to stability in pronation and volar capsular imbrication contributed to stability in supination. This effect was seen in positions of rotation greater than 60 degrees and was most evident in full pronation and supination.

The central 80–85% of the TFC is avascular and has no potential for healing. The peripheral 15–20% of the articular disc and the dorsal and palmar ligaments are well vascularized and are capable of healing (Figure 6.4.3).

The radiocarpal joint carries about 80% of the compressive load across the wrist; 20% is transmitted via the TFC and ulna in wrists with neutral ulnar variance. The load distribution between radius and ulna shows only a weak positive relationship to ulnar variance, probably because negative ulnar variants have thicker TFCs. However, surgical changes in ulnar variance alter force transmission dramatically: a 2.5-mm increase raises the ulnocarpal load to 42%; and a 2.5-mm decrease or excision of the disc lowers it to 4.3%. Up to two-thirds of the articular disc can be excised before changes in axial load transmission occur.

The clinical assessment of patients with ulnar wrist pain includes the history of injury or onset of symptoms, the nature of the symptoms, and a provocative examination directed at localizing the pathological anatomy.

Provocative manoeuvres such as the ‘ballottement’, ‘shuck’, and ‘shear’ tests attempt to distinguish lunotriquetral abnormalities from the TFCC disorders. A positive ‘ulnar fovea sign’ identifies foveal disruption of the distal radioulnar ligaments and ulnotriquetral ligament injuries. The DRUJ is assessed by palpation, the ‘grind test’, attempting to elicit the ‘piano key’ sign and comparison with the opposite side, bearing in mind that signs may be dependent on the rotational position of the forearm (Table 6.4.1).

Since the relative length of radius and ulna varies with rotation of the forearm, standardized positioning with the forearm in neutral rotation is critical for meaningful study and comparative measurements of the DRUJ (Figure 6.4.4).

Stress or provocative views causing subluxation or ulnar impaction, such as full pronation while making a tight fist, may be useful in demonstrating instability patterns or impingement.

Arthrography can demonstrate the integrity of the soft tissue structures around the DRUJ (Figure 6.4.5).

While intercompartmental dye tracking may suggest an anatomical abnormality, the relation to symptoms is far from clear. Attritional abnormalities increase with age such that up to 50% of asymptomatic wrists will demonstrate ‘lesions’ by age 50. In a study of post-traumatic wrist pain, 74% of patients had ‘abnormal’ communications in the asymptomatic opposite wrist.

Computed tomography (CT) is useful in diagnosing DRUJ subluxation and dislocation, as well for assessing the congruity of the articular surfaces in fractures and arthritic conditions of the sigmoid notch and ulnar head (Figure 6.4.6). To assess subluxation, CT scans of both wrists in neutral and both full supination and pronation are recommended and stress CT scans may be helpful.

While CT scanning best defines bony anatomy, magnetic resonance imaging (MRI) is the preferred method for non-invasive evaluation of the soft tissues, in particular the TFCC and associated ligaments. Using a wrist coil, T₂-weighted images best demonstrate traumatic tears, as synovial fluid has a high-intensity signal that provides contrast to fill defects (Figure 6.4.7). With T₁-weighted images, degenerative and traumatic tears are seen but difficult to distinguish. Radiocarpal joint injection of gadopentetate dimeglumine augments diagnostic accuracy for TFCC tears and has taken over from standard arthrography.

Arthroscopy is the ‘gold standard’ assessment of the wrist and TFCC but the DRUJ is difficult to visualize and so arthroscopy of the DRUJ is performed infrequently.

DRUJ disorders can be classified as acute, i.e. fractures and dislocations (see Chapter 12.9) or chronic. Chronic DRUJ disorders include TFCC tears, instability, arthritis, extensor carpi radialis subluxation, and contracture.

Palmer classified TFCC lesions as traumatic (type I) and degenerative (type II) (Table 6.4.2). Class II lesions are generally associated with ulnocarpal impaction syndrome. Traumatic and degenerative lesions may lead to DRUJ instability, which may be static or, more commonly, dynamic.

Type I injuries may result from various combinations of distal–proximal compression, shear, torsion, and radioulnar tension. Acute lesions are most frequently secondary to a fall on an outstretched hand in a patient who has ulnar neutral or positive variance.

Patients often present weeks or months after injury. Treatment is directed at relieving pain and restoring stability, with the specific approach being determined primarily by the vascularity of the injured TFCC component and its potential for healing. If positive ulnar variance or significant cartilage damage exists, consideration should be given to ulnar recession to avoid persistent ulnar impaction postoperatively.

Type I injuries are further subclassified.

Type IA lesions occur in the central articular disc and are not associated with DRUJ instability. As this avascular area has no ability to heal, arthroscopic debridement is the treatment of choice. Up to two-thirds of the central TFC can be excised without altering force transmission or DRUJ stability providing the peripheral 2mm of the disc, and the dorsal and volar radioulnar ligaments, are preserved.

Type IB lesions occur in the well-vascularized periphery of the TFC, at the base of the ulnar styloid. They may be associated with an ulnar styloid fracture and/or mild instability of the DRUJ. Significant displacement of the ulnar styloid fragment in unstable injuries requires reduction by closed means or by internal fixation. Type IB injuries may also be associated with acute ECU subluxation that will require reduction and possibly stabilization. Because these tears are located in the well-vascularized periphery of the TFC, they have potential to heal, therefore surgery is not required if the DRUJ is stable. If the DRUJ is unstable, the TFC should be repaired using either an open or arthroscopic technique. Each technique has its proponents.

Type IC injuries are least common and involve disruption of the ulnocarpal ligaments. Although readily diagnosed arthroscopically they may be repaired by open or arthroscopic methods.

Type ID lesions occur when the TFC detaches radially, from the sigmoid notch of the distal radius. Like IC tears, these injuries are also uncommon. They are frequently painful and destabilizing but are difficult to treat because of the avascularity of the radial margin of the articular disc. Management is controversial, but successful reattachment of the disc margin to the radius has been described both open and closed.

These disorders comprise a spectrum of clinical and pathological sequelae resulting from recurrent compressive loading through the ulnar carpus, TFCC, and ulna, and have been variably referred to as ulnocarpal ‘loading’, ‘abutment’, ‘impaction’, or ‘impingement’ syndrome.

There are five stages, beginning with TFCC wear and progressing through perforation, lunate and/or ulnar chondromalacia, lunotriquetral ligament disruption, and finally ulnocarpal arthritis.

Clinical features may include: ulnar wrist pain accentuated by rotation (especially pronation), ulnar deviation, and clenched fist loading; tenderness and/or crepitation in the region of the TFCC; and a tendency to ulnar neutral or positive variance. Sclerosis and/or cystic changes in the ulnar head and/or lunate may be seen with plain radiography, joint narrowing, and/or chondromalacia on tomography, and TFC perforations and/or lunotriquetral tears on MRI/arthrography (Figure 6.4.8).

The onset of symptoms may vary from insidious to abrupt depending on any predisposing condition or injury, the pattern and repetitive use of hand, wrist, and forearm, and the loading applied. Positive ulnar variance may be a congenital variant of normal or may be acquired, e.g. post-traumatic radial shortening, premature physeal closure including Madelung deformity, and, most commonly, age-related relative radial shortening due to thinning of the radial head articular cartilage.

Non-operative treatment includes activity modification, anti-inflammatory medications, splints, and steroid injections.

A positive ulna variance can be corrected by shortening the ulna (Figure 6.4.9) (which is simpler) or lengthening the radius which is typically performed when there are other concomitant abnormalities such as dorsal tilt of the radius following fracture malunion.

If length discrepancy osteotomies will leave the DRUJ incongruous or if degenerative changes are already present then new or persistent symptoms are likely postoperatively and additional procedures as for DRUJ arthritis need to be considered (see later).

Alternatively, the ‘wafer’ procedure may be performed with minimal effect on radioulnar relations at the DRUJ. It involves resection of 2–3mm of the distal ulnar pole, leaving the styloid intact (Figure 6.4.10), via an open approach or arthroscopically through the perforated TFC.

The need to treat accompanying TFCC lesions is controversial. Some authors recommend arthroscopic or open debridement of central perforations and repair of any destabilizing peripheral lesions of the TFCC. Others believe that decompression of the ulnocarpal space by ulnar recession will suffice in most cases.

By convention, instabilities, subluxations, and dislocations of the DRUJ have been described in terms of the direction of the ulnar head displacement relative to the radiocarpal unit. Strictly speaking though, it is the radiocarpal structures that move about the stationary ulna.

Although sometimes occurring in isolation, acute DRUJ instability or dislocation is seen in up to 60% of forearm fractures. It is especially common in complex distal radius fractures, where the TFCC and/or the sigmoid notch may be disrupted. Failure to recognize and manage these injuries adequately can result in chronic DRUJ dysfunction and instability.

Chronic DRUJ instability may result from disruption of any of the three major determinants of stability: the ulnar head/sigmoid notch articular congruence and alignment; the relative length, rotational, and angular relationship of the radius and ulna; and the integrity of the primary soft tissue stabilizers of the DRUJ (i.e. the TFCC). The adequacy of each must be ensured to restore stable DRUJ function. The presence and degree of instability and malunion is best evaluated clinically, and confirmed and quantified with plain radiography and a CT scan of both the involved and contralateral forearms and wrists.

Instability that results from malunion of forearm fractures may be improved by corrective osteotomy. Reattachment of the TFCC to the fovea has been described for minor degrees of instability, and if associated with an ulnar styloid fracture the bone fragment may be reduced and internally fixed if large or excised if small (Figure 6.4.11).

In the absence of a radial or ulnar malunion, soft tissue reconstruction alone can be undertaken. Many techniques for reconstruction of the distal radioulnar ligaments have been described. Each uses a tendon graft, which is weaved through drill holes in the distal radius and ulna and tied onto itself. The most anatomic, and the one most commonly used, is the technique described by Adams and Berger (Figure 6.4.12). It has been reported to restore clinical stability in 12 of 14 patients, and recovery of strength and range of motion averaged 85% of the unaffected wrist.

Chronic DRUJ instability may also be treated with hemiresection interposition arthroplasty. In a series of 23 patients, 17 had good to excellent results, and 21 had increased range of motion. Radioulnar fusion (a one-bone forearm) should be considered in patients doing heavy labour or who have failed soft tissue reconstructions (Figure 6.4.13).

DRUJ arthritis may be primary or secondary to fracture malunion. The commonest cause is inflammatory arthropathy, e.g. rheumatoid arthritis (RA).

Non-operative management includes activity modification, anti-inflammatories, splinting, and steroid injections. Four types of DRUJ ‘arthroplasty’, with multiple variations, are in common use: excision of the distal end of the ulna (Darrach procedure); hemiresection interposition arthroplasty; DRUJ arthrodesis with creation of a proximal ulnar pseudarthrosis (Sauvé–Kapandji procedure); and ulna hemiarthroplasty.

The Darrach procedure is a subperiosteal excision of the ulnar head with or without the ulnar styloid. It may be considered in any condition that interferes with DRUJ function, causing painful or limited motion as a result of articular surface destruction (Figure 6.4.14). Because the ‘DRUJ’ is rendered unstable it is best performed with a minimal resection in low demand patients, typically patients with inflammatory arthropathy or elderly patients following a Colles’ fracture.

Several variants of this procedure have been described. They attempt to minimize instability of the distal ulna by maintaining bony contact between the ulnar shaft and the TFCC attachments. In the hemiresection interposition arthroplasty of Bowers, only the articular portion of the ulnar head is removed, retaining the shaft/styloid relationship and interposing tendon, muscle, or joint capsule between the distal ulna and radius to limit contact. This procedure requires an intact or reconstructable TFCC to confer any advantage over a Darrach procedure.

Stylocarpal impingement may occur as the ulna migrates toward the radius. Concomitant ulnar shortening osteotomy should be performed in ulnar positive wrists, or if impingement can be anticipated preoperatively.

In the ‘matched’ distal ulna resection, the ulnar head is partially resected in an oblique fashion parallel to the inclination of the sigmoid notch. The ulnar styloid is removed and ulnar shortening distally is possible. Most are pain free and the remainder are significantly improved (Figure 6.4.15).

The arthritic DRUJ is fused and a mobile pseudarthrosis is created by excision of segment of distal ulnar shaft (Fig 6.4.16). While effective in relieving pain at the DRUJ, adequate bone must be resected at the proposed pseudarthrosis to allow full forearm rotation but prevent ossification between the segments of ulna.

The indications for this procedure remain unclear. Excellent results for relief of pain, range of motion, and patient satisfaction have been reported. Instability of the proximal ulna segment and radioulnar convergence are the commonest problems. Although infrequently symptomatic, when they are they can be difficult to treat although ulna hemiarthroplasty articulating with the underside of the fused ulna head is a recent salvage option.

Replacement arthroplasty of the ulnar head is an emerging technology with promising early results. The primary indication for ulnar head arthroplasty is pain and stiffness secondary to rheumatoid, degenerative, or post-traumatic arthritis; failed excisional arthroplasty (Darrach or hemiresection interposition arthroplasty); bone tumour (Figure 6.4.17); and less commonly, an unreconstructable fracture of the ulnar head or neck due to comminution or poor bone stock. Ulnar stump instability or radioulnar impingement syndrome after excisional arthroplasty can also be successfully managed with this technique. There are various metal or pyrocarbon options. Silastic replacements have been abandoned because of implant failure. While the solid prostheses have shown favourable early results, long-term outcomes have not yet been reported.

The course and action of the ECU tendon change with forearm rotation. In full pronation the ECU is linear and acts as an ulnar deviator while in supination it is an extensor of the wrist. In full supination, especially with ulnar deviation, the course of the ECU tendon is angular with the tunnel at its apex. Forcible contraction of the ECU in this position creates a strong ulnar translocating force that may disrupt the ECU sheath. This position and mechanism are often recalled by patients, in conjunction with a ‘snapping’ or ‘popping’ sensation. Examination in the acute setting will reveal local features of inflammation and painful ulnar subluxation of the ECU provoked by supination and ulnar deviation. Treatment acutely is with 6 weeks of forearm immobilization in pronation with the wrist slightly extended and radially deviated to reduce the tendon. Surgical repair may also be used acutely and is appropriate for chronic painful ECU snapping that has been untreated or failed non-operative immobilization. Operative treatment may consist of repair of the sheath lesion, reefing of local tissues, reconstruction of the tunnel using retinacular flaps or other tissues, and/or deepening of the ulnar groove.

Restriction of forearm motion may result from a multitude of pathological processes occurring in isolation or combination at the wrist, elbow, or forearm. Among these are bony abnormalities (congenital or acquired shaft or articular incongruence of the radius and ulna, synostoses), neuromuscular disorders (paralytic, spastic, or post-traumatic contractures), interosseous membrane insufficiency (instability, contracture), and proximal or distal radioulnar joint restrictions (articular deficiency, mechanical interference, soft tissue instability, or capsular contracture).

DRUJ capsular contracture is uncommon and generally post-traumatic. It may be associated with bony abnormalities. It may also result from prolonged forearm immobilization. Pathologically, the normally lax joint capsule becomes shortened and thickened with fibrosis, especially on the palmar side. Contracture of the palmar capsule restricts supination; contracture of the dorsal capsule limits pronation. Pronation contractures with restricted supination are most common. However, global limitation due to involvement of both the dorsal and volar capsule may occur.

Non-operative treatment with physiotherapy, dynamic splinting, and serial casting is often effective; if it fails, surgical release may be useful provided that there is no suggestion of joint incongruency. A volar capsulectomy is performed, proceeding dorsally as needed to restore motion. Care must be taken to preserve the radioulnar ligaments, TFCC, and articular surfaces. Intra-articular adhesions are lysed and the forearm is gently manipulated in rotation and translation under anaesthetic.

Derangements of the DRUJ are a significant cause of ulnar wrist pain that have traditionally been poorly understood. Our improved understanding of the normal anatomy and biomechanics of this region has lead to a more successful approach to the diagnosis and treatment of DRUJ disorders.