Wrist

Wrist • Long bones have two growth plate epiphyseal plates • Short bones (metacarpals proximal growth plate) • Phalanges (distal growth plate) – Thumb (proximal growth plate)

Common Conditions • Scapholunate Ligament • Lunotriquetral Lig • Triangular Fibrocartilage Tear • Intra articular Radius Fx • Scaphoid Fx • AVN Scaphoid • Kienbock’s Dz • Carpal Tunnel Syndrome

• The distal base of the ulna should line up with the distal base of the radius • Too short (N): ulna short • Too long (P): ulna long

Wrist joints • • • • • •

Triangular fibrocartilage joint Radio ulnar joint Midcarpal joint Common carpometacarpal jt First carpometacarpal joint Intermetacarpal joint

Scapholunate Ligament Tear • • • • • • • • •

Dissociation between scaphoid and lunate Scaphoid becomes flexed relative to lunate Scapholunate (SL) angle increases to more than 70 degrees SL ligament made up of dorsal, membranous and volar fibers Discrete linear signal n partial or complete tear Complete ligamentous disruption Synovial fluid communication between radiocarpal and midcarpal compartment MR arthrography may assist in identifying flap tears, perforations and the integrity of the dorsal compartment Clinical Issues – Excessive loading to dorsal capsule with trauma – Associated with a scaphoid fracture – Seen in DISI (dorsal intercalated segment instability) Widened scapholunate space (SLAC: scapholunate articular collapse): David Letterman or Terry Thomas = gap between teeth

0 - 30 •

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When scapho – lunate is ruptured, more than 4 mm, the lunate will rock back and the scaphoid will go  Inc angle Lunate – Capitate: 0 – 30 Lunate – Scaphoid: 30 - 60

Dorsal

Capitate Lunate

Volar 30 - 60

Instability Patterns • • • • • •

2 degrees to ligament disruption @ lunate attachments DISI (refer to direction of lunate rock): Dorsal intercalated (lunate) segment instability VISI (refer to direction of lunate rock): Volar intercalated (lunate) segment instability Lunate is intercalated: a part b/t other parts that moves passively VISI: tearing of lunate & triquetrum DISI: tearing of lunate & scaphoid

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SLAC wrist: scapho – lunate advanced collapse Scaphoid usually looks like a kidney bean Signant ring side: “stone” look on the scaphoid  is abnormally aligned due to volar flexion; distal pole superimposes over the proximal pole Pie wedge of lunate is abnormal

Lunotriquetral Ligament Tear • • • • • • • • • • • • • • • • • •

Dissociation between triquetrum and lunate Volar flexion of lunate Lunotriquetral (LT) ligament made up of dorsal, membranous and volar fibers Associated VISI pattern Ulnar shortening if no VISI but positive ulnar variance present Normal LT ligament does not extend into LT joint Delta shaped or linear ligament is Traumatic injuries (Class I) Degenerative injuries (Class II) Centrum of TFC is thin and is most common site of tear Tearing of dorsal or volar margins of the TFC plus centrum (disc) leads to DRUJ instability TFC tear = a cause of ulnar sided wrist pain*********** Normal TFC is biconcave disk of hypointense signal Primary sign of TFC tear is the presence of fluid extension across articular disc or discontinuity Partial tears frequently seen with contour irregularities Positive ulnar variance Higher incidence of ulnar sided tears in younger patients Asymptomatic tears increase after age 35

Intra Articular Radius Fractures

Scaphoid Fracture • • • • • •

Most common fracture of the carpus Assoc dorsiflexion loading and radial deviation mechanism 70% involved in the middle 1/3 of scaphoid Waist fractures are at risk for delayed union and AVN Pain over anatomical snuffbox Stick hand into snuffbox and tell them to ulnar deviate, a bump (scaphoid) hits your hand. A lot of pressure shouldn’t hurt but if they do it is a fracture • Fracture line hypointense on T1 weighted images / acute fracture is hyperintense on T2 weighted images • Sagittal images show scaphoid flexion (humpback deformity) • Fracture extension to ulnar or radial cortex differentiates acute from chronic fractures

AVN Scaphoid • Secondary to proximal pole waist fractures • Proximal pole sclerosis assoc with osteopenia and edema • Necrotic bone hypointense on T1 and hyperintense on FST2 FSE or STR • As sensitive or more as bone scans • Hypointense signal in the proximal pole on T1 and T2 weighted images • Reactive marrow edema

Kienbock’s Dz • AVN lunate • Peak age 20 to 40 with 2:1 male:female • Hx of trauma and ulnar negative variance (short ulna)