Distal radio-ulnar joint Injuries

                     Distal radioulnar joint Injuries

                                         Dr KS Dhillon

Anatomy and biomechanics of the distal radioulnar joint

Bony anatomy

The distal radioulnar joint is found at the distal end of the radius and ulna where the two bones articulate. The convex articular surface of the ulnar head (ulna seat) articulates with the sigmoid notch of the distal radius forming a synovial lined pivot joint. The sigmoid notch has a larger arc of curvature which allows translation of the ulna seat on the distal radius.
The distal radius rotates on the distal ulna and the distal ulna translates on the distal radius. During supination, there is volar translation and proximal migration of the ulna head relative to the distal radius. During pronation, on the other hand, there is dorsal translation and distal migration of the ulnar head.
There is variable articulation between the sigmoid notch and the ulna head during movements where maximum contact is in the neutral position with minimal contact at extremes of rotation. Overall the bony articulation only provides about 20% of the stability at the joint and the rest is provided by the soft tissues.

Soft tissue anatomy

The primary stabilizer (80% of the stability) of the DRUJ is the triangular fibrocartilage complex (TFCC) which consists of :
1.Dorsal and volar radioulnar ligaments
2.Ulnocarpal ligaments; volar ulno-lunate, ulno-triquetral and ulno-capitate ligaments.
3.Triangular fibrocartilage (TFC) disk
4.Meniscal homolog
5.Tendon sheath of the extensor carpi ulnaris

The triangular fibrocartilage (TFC) is a bowtie-shaped disk that separates DRUJ from the carpal joint and lies at the end of the ulna. The central portion is relatively avascular with poor healing power and its peripheral parts which merge with the radioulnar ligament are relatively vascular.
The meniscal homolog lies between the ulnar styloid and triquetrum and it joins with extensor carpi ulnaris tendon sheath and joint capsule to form a ligamentous stabilizer. The meniscal homolog, TFC, extensor carpi ulnaris tendon sheath, and the ulnocarpal ligaments do not significantly contribute to overall DRUJ stability (1).
The main stabilizers of the DRUJ are the volar and dorsal radioulnar ligaments which have both deep and superficial components and these ligaments arise from the medial border of the distal radius. The deep fibres which contribute a major part to the stability of the joint go on to attach to the fovea at the base of the ulnar styloid process. The superficial fibres are inserted into the tip the ulnar styloid (1).
The deep fibres of the radioulnar ligament provide radial stability during supination and pronation. The volar deep fibres prevent volar translation of the radius during pronation and the dorsal deep fibres prevent dorsal translation of the radius during supination. The superficial fibres play an opposing role to the deep fibres where the dorsal superficial fibres provide radial stability during pronation and the volar superficial fibres provide stability during supination (1). More recently, however, it has been suggested that the distal oblique bundle, located distally in the interosseous
membrane also fulfils an important stabilizing role (2).

Distal Radioulnar Joint Subluxation and Dislocation

Distal radioulnar joint subluxation and dislocation may be may be an isolated injury but they are more often associated with distal radius fractures, Galeazzi fractures or Essex-Lopresti injuries. The Essex-Lopresti injury is a proximal radial head or neck fracture which is associated with DRUJ dislocation and a rupture of the interosseous membrane.
Fractures of the distal radius are common and the incidence of DRUJ instability at one year after distal radius fractures ranges from 0 to 35% (3,4,5). Such injuries can be easily missed and awareness of the possibility of the injury would be useful. The dislocations and subluxations are described by the relationship of the ulna to the radius although the radius moves around the distal ulna in forearm pronation and supination. Most often the dislocations are dorsal and they result from axial loading of the extended wrist and pronated forearm. With a dorsal dislocation, the forearm becomes locked in pronation with an inability to supinate. Volar dislocations occur with axial loading in supination and the forearm is locked in supination and there is an inability to pronate (6).

Clinical diagnosis

Although the radius rotates around the ulna at the wrist the disruption of the DRUJ, by convention is described as dislocation of the ulnar head. Following wrist trauma, a disruption of the DRUJ should be suspected when there is tenderness at the DRUJ and there is a limitation of forearm supination and/or pronation. In some cases of isolated dislocation of the ulna head, an empty groove for the ECU (extensor carpi ulnaris) tendon can be palpated with the forearm in full supination. The groove becomes empty when the ECU and the TFCC displaces into the DRUJ (7).
Following acute trauma to the distal radius, DRUJ instability will be difficult to diagnose due to pain, swelling and deformity around the joint. Volar translation of the ulna head seen in chronic DRUJ instability is usually due to radial malunion, rather than to instability of the DRUJ (8).

Instability tests for DRUJ

There are two types of instability of the DRUJ, the static and dynamic instability. Static instability is tested with a static non-rotating radius and dynamic instability is tested while rotating the forearm.
The most commonly used static test is the “piano sign” or the ballottement manoeuvre. It is done with the elbow in 90 degrees of flexion with fingers pointing to the ceiling. Dorsopalmar displacement of the ulnar head in relation to the radius in full supination and pronation is carried out. The test is positive if there is pain or laxity as compared to the uninvolved wrist. It tests the integrity of the volar and dorsal radioulnar ligaments. The diagnostic value of this test, however, remains disputed (9). The sensitivity is this test is about 66% and the specificity is about 68%.
Dynamic instability of the DRUJ can be diagnosed using the clunk test or the extensor carpi ulnaris test.The clunk test is to evaluate the integrity of the interosseous membrane. It is performed by compressing the ulna to the radius during passive pronation and supination and the test is positive if a clunk is palpable. The ECU test is to test the stability provided by the ECU tendon. It is performed by holding the elbow in flexion at 90°, hand in ulnar deviation, and active pronation and supination produce abnormal motion of the ECU tendon. The sensitivity and specificity of these two tests are not known. The press-test is performed by the patient pushing himself up from a seated position with the use of affected wrist and the presences of focal ulnar-sided wrist pain is an indication of a TFCC tear. The clinical value of the press-test remains unclear, since not every TFCC tear is associated with DRUJ instability. Studies also show that the correlation between physical examination and the radiologic outcome is not clear (8).

Radiological evaluation

A posteroanterior (PA) and true lateral view of the wrist is essential for the diagnosis of DRUJ subluxation and dislocation. In patients with a wrist injury, it is usually difficult to obtain true lateral views. Supination and pronation of as little as 10 degrees can alter the alignment on lateral views (10).
The PA view is obtained with the shoulder abducted 90º, elbow flexed 90º, forearm in a neutral position while the lateral view is obtained with the shoulder adducted, elbow flexed 90 degrees and the forearm and hand resting on the ulna side.
In the PA view the extensor carpi ulnaris tendon groove should be profiled at the radial base of the ulnar styloid.On a true lateral image, the pisiform should be located between the volar cortices of the scaphoid and the capitate (scaphopisocapitate (SPC) relationship), the radial styloid should overlap with the proximal pole of the scaphoid and the lunate and the ulna should overlap the radius. On a normal lateral radiograph, the ulna usually projects about 2-mm dorsal to the radius. A distance of 6 mm or more between the distal radius and ulna on a true lateral radiograph would be diagnostic of instability (11).
On the PA view, an increased gap between the distal radius and ulna occurs with dorsal dislocation and with volar dislocation superimposition of the radius and ulna occurs.
A CT scan of the wrist is the modality of choice for evaluating DRUJ stability. Dynamic imaging can be done with the wrist in the neutral position,
full supination, and full pronation. Three methods have been described for evaluating instability namely the Mino method, the congruency method and the epicentre method.
In the Mino method, on a pronated axial CT of the wrist, lines are drawn from the dorsal and volar margins of the distal radius to the ulnar head. Instability is said to be present if more than 25% of the ulna head lies volar or dorsal to these lines (12).
In the congruency, method arcs are drawn across the articular surfaces of the sigmoid notch and the ulna seat, on neutral position axial CT of the wrist and if the distance between these arcs varies at any point along the curve, there is instability (13).
The epicentre method (fig 1) is a bit more complex. In this method, the centre of rotation of the DRUJ is first determined. It lies halfway between the centre of the ulnar styloid and the centre of the ulnar head. A line is drawn from this point perpendicular to a line drawn through the dorsal and volar margins of the sigmoid notch.The ratio of the distance between this perpendicular line and the midpoint of the sigmoid to the length of the sigmoid notch is calculated. Dorsal displacement from the midpoint is recorded as positive and volar translation as negative. The DRUJ is considered normal if the line is in the middle half of the sigmoid notch (14). Sensitivities of these methods range from 55% to 100%, and there are high false-positive rates for the Mino and congruency methods (14). The epicentre method is the most specific because it compensates for the normal translational movement of the DRUJ and is currently the preferred method for detecting subluxation and dislocation (14). The role of MR in evaluating direct signs of DRUJ instability remains unclear (9).

   

Treatment of DRUJ instability

Isolated DRUJ dislocation

Isolated DRUJ dislocations are uncommon and usually occur after a fall on an outstretched hand and sometimes from an impact on the ulnar side of the wrist. The dislocation may be dorsal or volar and simple or complex (15). Close reduction and above elbow cast immobilization will suffice if the reduction is stable. If the reduction is not stable a K-wire fixation of the DRUJ should be carried out along with cast immobilization.
Sometimes close reduction is not possible due to soft tissue interposition in the joint. In such situations, an open reduction, release of interposed soft tissues (usually the ECU tendon) and pinning of the joint is carried out.

DRUJ injuries with associated fractures or fracture dislocations.

DRUJ injuries are usually associated with distal radius fractures. Most of the distal radius fractures (50 to 80%) can be treated conservatively although there is increasing trend toward surgical management of these injuries (16,17).
The Galeazzi fractures and Essex-Lopresti injuries have, however, to be treated surgically by internal fixation of the radius to restore its length and achieve a reduction of the DRUJ dislocation.
The outcome of conservative treatment distal radius fractures is good irrespective of the presence or absence of DRUJ instability at long-term follow-up. Wijffels et al (16) did a retrospective cohort study of patients who had unilateral fractures of the distal radius which were treated conservatively. A physical examination, as well as static and dynamic DRUJ instability testing, was carried out. All patients had CT scans of both wrists. The patients also filled out a questionnaire. Forty-nine patients with distal radius fractures with a mean follow up of 4.2 years (SD 0.5) were assessed. Seventeen patients (35%) tested positive for DRUJ instability. There were no differences in the baseline characteristics between the DRUJ stable and unstable group. Besides wrist flexion, there were no statistically significant differences in outcome between patients with and without DRUJ instability.There was a slight increase of wrist flexion in patients with DRUJ instability. There was no difference in the incidence wrist pain and in the strength in patients with and without instability. The authors did not find arthritic changes in the DRUJ in this study.The authors concluded that the ‘presence of clinical DRUJ instability does not seem to affect functional outcome of conservatively treated distal radius fractures at long-term follow-up’ and that conservative treatment of secondarily diagnosed DRUJ instability after distal radius fractures is justified.
Lindau et al (18) constructed an apparatus to measure the isometric strength forearm in supination and pronation. They selected 20 patients (12 women) with a median age of 40 (20–56) years at the time of fracture of the distal radius from a cohort of 76 patients, who had been followed for 2 years. The clinical evaluation was done at a mean of 5.6 (4.8–6) years after the radius fracture. They found that the stability of the DRUJ had no effect on the strength of forearm rotation. However, there was subjective impairment of hand function in patients with laxity of the DRUJ as judged by a questionnaire.

Chronic DRUJ instability

There is a scarcity of literature on the incidence of symptomatic chronic DRUJ instability. Painless DRUJ instability apparently occurs in about one-third of the patients after a distal radius fracture (4). In such patients, a ‘wait and see’ policy is usually advocated (4). If the DRUJ is congruent, symptomatic DRUJ instability can be treated conservatively with medication and bracing (19).
For operative treatment of chronic DRUJ instability, the first step is to obtain osseous alignment with osteotomy of the bones. The presences of non-union of the ulna does not seem to matter. The second step is a reconstruction of the intrinsic and extrinsic stabilizers of the DRUJ by open or arthroscopic procedures. Non-anatomic stabilization using surrounding tendons such as ECU tendon is usually disappointing (9).
Failure of non-anatomical reconstruction may warrant the use of salvage procedures such as Sauve-Kapandji and the Darrach procedure. The Darrach procedure involves the resection of the distal ulna and the Sauve-Kapandji procedure combines a DRUJ arthrodesis with surgical pseudarthrosis of the distal ulna (20).

References

1. Judy H. Squires, Eric England, Kaushal Mehta and Robert D. Wissman. The Role of Imaging in Diagnosing Diseases of the Distal Radioulnar Joint, Triangular Fibrocartilage Complex, and Distal Ulna. American Journal of Roentgenology. 2014;203: 146-153.
2. Kitamura T, Moritomo H, Arimitsu S, et al. The biomechanical effect of the distal interosseous membrane on distal radioulnar joint stability; a preliminary anatomic study. J Hand Surg am. 2011;36(10):1626-30
3. Lindau T, Adlercreutz C, Aspenberg P. Peripheral tears of the triangular fibrocartilage complex cause distal radioulnar joint instability after distal radial fractures. J Hand Surg [Am] 2000;25(3):464-8.
4. Lindau T, Hagberg L, Adlercreutz C, et al. Distal radioulnar instability is an independent worsening factor in distal radial fractures. Clin Orthop Relat Res. 2000;376:229-35.
5. Krämer S, Meyer H, O’Loughlin P, et al. The incidence of ulnocarpal complaints after distal radial fracture in relation to the fracture of the ulnar styloid. J Hand Surg Eur. 2013;38;710-7.
6. Tsai PC, Paksima N. The distal radioulnar joint. Bull NYU Hosp Jt Dis 2009; 67:90–96.
7. Paley D, McMurry RY, Murray JF. Dorsal dislocation of the ulnar styloid and extensor carpi ulnaris tendon in the distal radioulnar joint: The empty sulcus sign. J Hand Surg Am 1987; 12(6): 1029-32.
8. Kim JP, Park MJ. assessment of distal radioulnar joint instability after distal radius fracture: comparison of computed tomography and clinical examination results. J Hand Surg Am 2008; 33(9): 1486-94.
9. M.M.E. Wijffels, P.R.G. Brink, I.B. Schipper. Clinical and non-clinical aspects of distal radioulnar joint instability. The Open Orthopaedics Journal, 2012, 6, 204-210.
10. Mino DE, Palmer AK, Levinsohn EM. The role of radiography and computerized tomography in the diagnosis of subluxation and dislocation of the distal radioulnar joint. J Hand Surg Am 1983; 8:23–31. 
11. Nakamura R, Horii E, Imaeda T, Tsunoda K, Nakao E. Distal radioulnar joint subluxation and dislocation diagnosed by standard roentgenography. Skeletal Radiol 1995; 24:91–94.
12. Mino DE, Palmer AK, Levinsohn EM. The role of radiography and computerized tomography in the diagnosis of subluxation and dislocation of the distal radioulnar joint. J Hand Surg Am 1983; 8:23–31. 
13. Wechsler RJ, Wehbe MA, Rifkin MD, Edeiken J, Branch HM. Computed tomography diagnosis of distal radioulnar subluxation. Skeletal Radiol 1987; 16:1–5.
14. Chiang CC, Chang MC, Lin CF, Liu Y, Lo WH. Computerized tomography in the diagnosis of subluxation of the distal radioulnar joint. Zhonghua Yi Xue Za Zhi (Taipei) 1998; 61:708–715.
15. Bruckner JD, Alexander AH, Lichtman DM. Acute dislocations of the distal radioulnar joint. Instr Course Lect. 1996;45:27–36.
16. M. M. E. Wijffels · P. Krijnen · I. B. Schipper. Clinical DRUJ instability does not influence the long‑term functional outcome of conservatively treated distal radius fractures. Eur J Trauma Emerg Surg (2017) 43:227–232.
17. Nellans KW, Kowalski E, Chung KC. The epidemiology of distal radius fractures. Hand Clin. 2012;28:113–25.
18. Tommy Lindau, Kerstin Runnquist and Per Aspenberg. Patients with laxity of the distal radioulnar joint after distal radial fractures have impaired function, but no loss of strength. Acta Orthopaedica Scandinavica. 2002; 73:2, 151-156.
19. Millard GM, Budoff JE, Paravic V et al. Functional bracing for distal radioulnar joint instability. J Hand Surg Am 2002; 27(6):972-7.
20. Binu P Thomas and Raveendran Sreekanth. Distal radioulnar joint injuries. Indian J Orthop. 2012 Sep-Oct; 46(5): 493–504.