Distal Radioulnar Joint: Anatomy, Instability, and MRI
A practical radiology review of Distal Radioulnar Joint: Anatomy, Instability, and MRI, focused on imaging findings, differential diagnosis, reporting points, and high-yield...
A practical radiology review of Distal Radioulnar Joint: Anatomy, Instability, and MRI, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.
Anatomy & Biomechanics
- Pivot joint → pronation/supination
- Intrinsically unstable → relies on soft tissues
Articular surfaces
- Radial sigmoid notch
- Ulnar head (hub + seat)
- Fovea = key stabilizer attachment site
- Sigmoid notch larger → allows translation → instability
Stabilizers
- Intrinsic (primary)
- TFCC (main stabilizer)
- Central disk (shock absorber, avascular)
- DRULs (true stabilizers )
- Ulnocarpal ligaments
- ECU subsheath
- Ulnomeniscal homologue
- DRUL biomechanics
- 4 components → dorsal/volar + superficial/deep
- Tighten depending on pronation/supination
- Deep (foveal) fibers = most critical
- Extrinsic (secondary)
- Pronator quadratus → dynamic stabilizer
- Interosseous membrane
- Distal oblique bundle (secondary DRUJ stabilizer)
Imaging Approach
X-ray
- Alignment, ulnar variance, instability clues
- 6 mm radioulnar distance → instability
CT
- Best for bone + DRUJ instability (dynamic CT)
- Compare both wrists
US
- ECU pathology, synovitis
- Dynamic but limited TFCC evaluation
MRI
- Best for soft tissue (TFCC)
- 3T preferred
- MR/CT Arthrography
- Near 100% accuracy for TFCC tears
- Gold standard imaging (after arthroscopy)
- TFCC Tears
Palmer Classification
- Type 1 (Traumatic)
- 1A Central perforation (non-repairable)
- 1B Ulnar avulsion → instability
- 1C Ulnocarpal ligament avulsion
- 1D Radial avulsion
- Type 2 (Degenerative)
- 2A Thinning
2B–E Progressive
- Chondrosis → perforation → LT tear → arthritis
- “Iceberg Concept”
- Arthroscopy sees only distal TFCC
- Proximal (foveal) fibers = real stabilizers
DRUJ Instability
- Defined by ulnar head position
- ⬆ Dorsal > volar instability (more common)
- Subtle → positioning critical in imaging
- CT (dynamic) = gold standard
Fracture Associations
- Distal radius fractures → TFCC injury (>75%)
- Ulnar styloid base fracture → instability
- Galeazzi fracture = distal radius + DRUJ injury
- Essex-Lopresti = radial head + IOM + DRUJ
ECU Pathology
- Tenosynovitis (overuse / RA)
- Tendinosis → degeneration
- Partial tears → split appearance
- Subsheath injury → tendon subluxation/dislocation
- Pseudolesion = normal intratendinous signal
Degenerative Conditions
- Ulnar variance
- Positive → impaction
- Negative → impingement
- Ulnar impaction syndrome
- TFCC + lunate/triquetrum overload
- DRUJ arthritis
- Usually post-traumatic
- Late: JSN, osteophytes
- Early: cartilage + synovitis
Inflammatory
- Rheumatoid arthritis
- DRUJ = earliest involvement
- ECU tenosynovitis = early marker
- Erosions (sigmoid notch “scallop sign”)
- Crystal disease (CPPD, gout)
- Chondrocalcinosis (TFCC)
Developmental
- Madelung deformity
- Distal radius growth arrest
- Vickers ligament (key feature)
- Carpal triangulation + dorsal ulna
- Key Takeaways
- DRUJ = soft tissue–dependent stability joint
- DRUL (foveal fibers) > central disk for stability
- MRI/arthrography → TFCC
- CT → instability
- Always assess: TFCC, Ulnar variance, ECU tendon, Associated fractures
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