22 Pain felt at the wrist during pronation and supination movements of the forearm inculpates the distal radioulnar joint. The source can be the joint capsule,1 the ligaments2–4 or the articular disc. When a fracture of the distal part of the radius fails to unite properly, arthrosis at the distal radioulnar joint may follow. Mal-union of the distal part of the ulna does not give rise to persistent problems5 and painless ulnar styloid non-union is a frequent incidental radiographic finding.6 Arthritis may develop without a provable cause such as rheumatoid or traumatic arthritis. Furthermore, the condition will worsen when attempts are made to mobilize the joint. Such a condition responds particularly well to intra-articular triamcinolone.7 Rheumatoid arthritis (RA) involves the wrist in up to 95% of cases. The distal radioulnar joint is affected in 31–75% of these patients and is frequently the first compartment of the wrist involved,8 often bilaterally.9 Triamcinolone suspension injected intra-articularly once or twice a year may keep the joint free from symptoms.10 Long-standing rheumatoid arthritis results in ligamentous laxity. At the distal radioulnar joint this leads to the so-called ‘caput ulnae syndrome’: dorsal subluxation of the distal part of the ulna, supination of the carpus on the forearm, and palmar dislocation of the tendon of the extensor carpi ulnaris.11–14 After a mal-united Colles’ fracture, shortening of the radius may be responsible for an irreversible limitation of supination only, with the end-feel of a bony block.15,16 The movement may be painful in recent cases but should become painless in due course. A dorsal dislocation of the ulna also presents with a block to supination and a visible dorsoulnar prominence. The mechanism for dorsal subluxation and dislocation is extreme pronation and extension, which pull the ulnar head out through the dorsal capsule. Triangular fibrocartilage complex avulsion and attenuation of the palmar radioulnar ligament will allow this dislocation.17 A block to pronation is present in palmar dislocations of the ulna. On inspection–palpation there will be a volar–ulnar prominence and a palpable radial sigmoid notch.18
Disorders of the lower radioulnar joint
Disorders of the inert structures
Capsular pattern
Arthrosis
Monoarticular steroid-sensitive arthritis
Rheumatoid arthritis
Non-capsular pattern
Limited supination
Limited pronation
Disorders of the lower radioulnar joint
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