Archive for the ‘wrist and hand’ Category

WRIST – ligaments

Intrinsic Ligaments

= scapholunate ligament
– three portions: volar (trapezoidal), middle (triangular), and dorsal (band — strongest)
– volar and esp dorsal most important for wrist stability
– stretched or torn
– mri 90% accurate:
— discontinuity, absence, irregularity, thinning with hi T2
— increased intercarpal space, sometimes
— elongation (stretching) of undisrupted ligament

- SL abnls may lead to
— rotatory subluxation of scaphoid
— DISI (dorsal intercalated segmental instability) — lunate tilting in dorsal direction ; scaphoid tilting in volar direction
— SLAC wrist (scapholunate advanced collapse)

= lunotriquetral ligament
– smaller than SL ligament, but has similar shape and frequently with hetero lo signal on coronal GRE
– may attach to hyaline articular cartilage or cortical bone
– tears may lead to VISI (volar intercalated segmental instability) — lunate tilting in volar direction.
– strong assoc between triangular fibrocartilage and LT tears

Extrinsic Ligaments

= extrinsic volar ligaments
– radioscaphocapitate – radial styloid -> scaphoid waist -> capitate
– radiolunotriquetral – ulnar side of radial styloid -> lunate -> triquetrium

= extrinsic dorsal ligaments
– radioscaphoid
– radiolunate
– radiotriquetral

Triangular Fibrocartilage Complex

- made up of several soft tissue structures on ulnar side of wrist
— volar and dorsal radioulnar ligaments
— meniscus homologue
— ulnar collateral ligament (UCL)
— sheath of the extensor carpi ulnaris (ECU) tendon

- functions include cushioning forces across the ulnar side of the wrist during axial loading
– stabilizing the ulnar size of the wrist and distal radioulnar joint

= normal triangular fibrocartilage (TFC)
– fibrocartilagenous biconcave disc with asymmetric bow-tie
– positioned in the ulnocarpal space with attachments on the medial side to the ulnar styloid process by two thin bands of TFC tissue, and laterally to the side of the radius
– thickness of TFC inversely proportional to degree of ulnar variance (thinner with + ulnar var ; thicker with – ulnar var)
– should have diffusely low signal (intermediate signal if asymptomatic myxoid degeneration)

= abnormal TFC
– any structure of the TFCC can be abnormal, but the TFC is the main component to show abnls
– TFC evaluated similar to meniscus in knee — high signal extending thru either prox or distal surface of TFC indicates a tear
– tears may be partial or full thickness
– fluid in the radioulnar joint is NORMAL for most individuals

- peripheral 20% of TFC on the ulnar margin is well vascularized and tears may heal with nonoperative therapy
– the remainder of the TFC is essentially avascular, and perforations or tears in the central and radial portions of the TFC usually are debrided
– many people have high signal within the substance of the TFC as well as perforations, but have no sxs; the intrasubstance signal likely 2′ myxoid degeneration
– TFC may be traumatically detached from its ulnar attachment and may even become interposed between the radius and ulna, preventing proper reduction of the DRUJ.
– TFC tears associated with disruption of ECU tendon sheath, tears of lunotriquetral ligament

Radioulnar Ligaments

- volar and dorsal radioulnar ligaments originate on the volar and dorsal cortex of the sigmoid notch of the distal radius
– pass on the volar and dorsal surfaces of the TFC and blend with it
– attach to the ulnar styloid process medially, and to the distal radius laterally
– distinguished from the TFC proper because they have flat superior and inferior margins, rather than being biconcave, and only attach directly to bone, rather than to cartilage on the radius.
– disruption of volar or dorsal RU ligaments associated with instability of the DRUJ (distal radioulnar joint)
– DRUJ instability dx’d when the ulna does not articulate properly with the sigmoid notch of the distal radius, and is displaced in either a dorsal or volar direction from this notch.

Meniscus Homologue
– thickening of the ulnar side of the joint capsule — inconsistently present
– located distal to the prestyloid recess and attaches to the triquetrium
– prestyloid recess is a triangular-shaped space bordered by the meniscus homologue distally, the TFCC atachments to the ulnar styloid process proximally, and the central TFC disc radially.

Extensor Carpi Ulnaris Sheath
– ECU tendon and sheath (component of TFCC) best seen on axial images
– sheath not seen unless fluid is in it
– ECU tendon located in the groove on the dorsum of ulna
– trauma of ECU tendon sheath -> subluxation or dislocation of the ECU tendon at the level of the distal ulna in a MEDIAL direction; associated tenosynovitis is common

Ulnar Collateral Ligament (UCL) of Wrist
– UCL is add’l support structure comprising the TFCC that may be seen on coronal images
– represents a thickening of the wrist joint capsule and provides little mechanical strength
– extends from the ulnar styloid process to the triquetrum
– similar structure exists on the lateral side, the radial collateral ligament, which extends from the radial styloid process to the scaphoid

WRIST – de quervain syndrome

Entrapment / irritation of tendons, first dorsal compartment
– abductor pollicis longus
– extensor pollicis brevis

Associated with
– overuse (manual laborers)
– pregnancy

MRI
– tendons may have normal size and signal, be thickened, or may have intratendinous signal
– abnl signal around tendons is common: lo T1, lo (fibrosis) / hi (tenosynovitis) T2

wrist – carpal tunnel syndrome

MRI features
– swollen median nerve (larger at level of pisiform than at DRUJ)
– flattened (at level of hamate hook), faceted, angled medial nerve
– hi T2
– flexor retinaculum (bowing ratio > 15%

Postop appearance, carpal tunnel release
– flexor retinaculum (absent or incised free ends displaced volarly)
– flexor tendons volarly displaced

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