MSK: Trauma and Overuse, Hand and Wrist Flashcards
What is the most common carpal bone fracture?
Scaphoid
Perilunate dislocations have a 60% association with _____
Scaphoid fractures
Which portion of the scaphoid is the most susceptible to avascular necrosis and non-union?
The proximal pole
Note: Arterial supply to the scaphoid is retrograde (distal to proximal) because approximately 80% of the scaphoid is covered in cartilage.
Avascular necrosis of the proximal scaphoid
Note: Sclerosis is the first sign of avascular necrosis.
What is the most common site of a scaphoid fracture?
Waist (70%)
Concern for scaphoid fracture but radiographs are negative…
Recommend repeat in 7-10 days
Note: 5-20% of scaphoid fractures have negative initial radiographs.
A scaphoid fracture with displacement of more than ____ will likely need surgery (fixation screw)
> 1 mm displacement
What are the components to the scapholunate ligament?
- Dorsal (most important for carpal stability)
- Volar
- Middle
Imaging finding of scapholunate ligament disruption on wrist radiographs
Separation of the scaphoid and lunate by > 3 mm
Scapholunate ligament disruption
Note: If scaphoid and lunate are separated by > 3 mm.
Scapholunate ligament disruption
Note: If scaphoid and lunate are separated by > 3 mm.
Disruption of the scapholunate ligament predisposes to…
DISI (Dorsal Intercalated Segmental Instability)
AND
SLAC (Scaphoid-Lunate Advanced Collapse)
Distal radius and/or carpal fractures are associated with _____ in 10-30% of cases
Scapholunate ligament disruption
Humpback deformity of the scaphoid (due to angulation of the proximal and distal fragments of a scaphoid waist fracture)
Note: This can lead to progressive collapse and non-union and is associated with DISI.
Prieser disease
Atraumatic avascular necrosis of the scaphoid
Avascular necrosis of the scaphoid
Note: The scaphoid is T1 dark.
SLAC wrist
Scaphoid-Lunate Advanced Collapse: When the capitate drops between the scaphoid and lunate due to disruption of the scapholunate ligament (either due to injury or CPPD degeneration)
SLAC (Scaphoid-Lunate Advanced Collapse)
Note: The capitate is dropping between the scaphoid and lunate.
SNAC wrist
Scaphoid Non-union Advanced Collapse: Early radial styloid osteoarthritis due to increased mobility of the distal scaphoid fragment in fracture nonunion (the proximal fragment usually remains attached to the scapholunate ligament, keeping its motion limited)
SNAC (Scaphoid Non-union Advanced Collapse)
Note: Focal osteoarthritis at the raadial styloid due to scaphoid fracture non-union (the distal scaphoid fragment is rubbing against the radial styloid).
Treatment for SLAC/SNAC wrists
- Wrist fusion (better strength, worse flexibility)
- Proximal row carpectomy (better flexibility, worse strength)
The scaphoid and lunate want to rotate away from each other, but are kept in place by the scapholunate ligament. Which ways do the scaphoid and lunate want to rotate (and would if the ligament was disrupted)?
The scaphoid wants to flex (rock to the volar side)
The lunate wants to extend (rock to the dorsal side)
DISI
Dorsal Intercalated Segmental Instability (AKA dorsiflexion instability): When a radial-sided injury disrupts the scapholunate ligament, allowing the lunate to rock dorsally, resulting in dorsiflexion instability and widening of the scapholunate angle
What is the normal scapholunate angle?
30-60 degrees (between the long axis of the scaphoid and the midaxis of the lunate on a lateral/sagittal image)
Note: > 60 indicates DISI and < 30 indicates VISI.
VISI
Volar Intercalated Segmental Instability (AKA volar/palmarflexion instability): When an ulnar-sided injury disrupts the lunotriquetral ligament and the “loose” lunate rocks volar because its being pulled by the scaphoid
Note: This is very rare because lunotriquetral ligament injuries are not common (if you think you see this, its probably actually just a normal variant from wrist laxity).
A scapholunate angle of ______ indicates DISI
> 60 degrees (widening of the scapholunate angle)
Note: Disruption of the scapholunate ligament causes them to angle farther apart.
A scapholunate angle of ______ indicated VISI
< 30 degrees (narrowing of the scapholunate angle)
Note: Disruption of the lunotriquetral ligament causes the lunate to be pulled closer to the scaphoid.
What view can you do to see if there is a scapholunate ligament dissociation?
Clenched fist view (if scaphoid-lunate interval is > 3 mm there is dissociation)
Right scapholunate ligament dissociation
Note: Asymmetric widening of the scapholunate interval on clenched fist view.
Perilunate dislocation
Note: Lunate is still on the radius, but the other carpal bones have dislocated.
Perilunate dislocation
Note: Lunate is still on the radius, but the other carpal bones have dislocated.
Rank the carpal dislocations from least severe to most severe
- Peri-lunate dislocation (least severe)
- Mid-carpal dislocation
- Lunate dislocation (most severe)
Mid-carpal dislocation
Note: Both the lunate and capitate have lost their radial alignment.
Lunate dislocation
Note: Only the lunate has lost its radial alignment.
Perilunate dislocation
Note: The lunate has maintained its radial alignment.
Mid-carpal dislocations are associated with…
Lunotriquetral interosseous ligament disruption
And/or
Triquetral fracture
Lunate dislocations are associated with…
Dorsal radiolunate ligament injury
Lunate dislocation
Note: Disruption of the carpal arcs I and II and the lunate is shaped like a piece of pie.
Trans-scaphoid perilunate dislocation
This indicates that there is a scaphoid fracture and perilunate dislocation
Note: Carpal dislocations can only happen if there is ligamentous injury or carpal bone fractures.
Vulnerable zones theory of carpal dislocation
States that injuries occur through the lesser arc (ligamentous injuries only) or greater arc (associated with carpal bone fractures)
Space of Poirier
A ligament free area in the capitolunate space that is an area of weakness
The synovial space of the radiocarpal joint communicated with the…
Pisiform recess
Note: Excess fluid in the pisiform recess is normal in the setting of a radiocarpal joint effusion.
Are the pisiform recess and radiocarpal joint communicating synovial spaces?
Yes
Are the glenohumeral joint and subacromial bursa communicating synovial spaces?
No, these should not communicate
Note: Communication between these spaces implies a full thickness rotator cuff tear.
Are the ankle joint and common/lateral peroneal tendon sheath communicating synovial spaces?
No, these should not communicate
Note: Communication between these spaces implies a tear of the calcaneofibular ligament.
Are the Achilles tendon sheath and posterior subtalar joint communicating synovial spaces?
No, the Achilles tendon does not have a true synovial tendon sheath
What is the function of the TFCC (triangular fibrocartilage complex)?
It functions as the primary stabilizer and shock absorber of the distal radioulnar joint
What are the 5 components of the TFCC (triangular fibrocartilage complex)?
- Articular disc (triangular fibrocartilage)
- Radioulnar ligaments (volar and dorsal)
- Meniscus homologue
- Ulnar collateral ligament
- Tendon sheath of the extensor carpi ulnaris
What are the most important components of the TFCC (triangular fibrocartilage complex) when planning for surgery?
- Articular disc
- Radioulnar ligaments (volar and dorsal)
How should the TFCC articular disc appear on MRI?
Dark on all sequences
Note: The ulnar and radial attachments often looks intermediate in signal.
What are the two major categories of TFCC injury?
- Acute injuries (usually due to a fall on an extended wrist)
- Chronic degeneration (more common and associated with positive ulnar variance)
TFCC tear
Note: This is the thicker portion representing a radioulnar ligament tear.
Small central tear of the TFCC articular disc (arrow) and a partial thickness undersurface tear (arrowhead)
Arrow
Normal intermediate signal intensity at the ulnar attachment of the TFCC articular disc
Central tear of the TFCC articular disc (typical of a degenerative tear)
Arrow
Avulsion of the ulnar styloid attachment of the TFCC articular disc
Note: The foveal attachment is still intact (arrowhead).