carpal instability Flashcards
carpal anatomy
biomechanics
sagittal plane 10°, ulnar inclination of 24°
lunate type I - only joint to the capitate
lunate type II - small articulation to the hamate
ligamenteous anatomy:
extrinsic ligaments:
radiopalmar:
radio-scaphoid, radioscaphoid-capitate (space of Poirier between them), long radiolunate and short radiolunate (very strong - keeps intact with perilunate fracture-dislocation
ulnopalmar:
ulnocapitate, ulno-triquetral, ulno-lunate
radio-dorsal:
from the dorsal radius to the triquetrum (prevent ulnar shifting)
there are not ulno-dorsal ligaments!!!!
scapholunate interosseous ligament
three distinct structures - strongest is the dorsal part (260 N) - holds scaphoid and lunate together - palmarly (118 N) more for rotation and oblique fibres
ulnotriqutral interosseus ligament
stongest palmarly (301 N) - with weaker part dorsally (121 N)
distal row - not so much movement - strong ligementous structures - movement is in block not intercarpal
Biomechanics:
proximal row - no attachements of tendons or other structures - with different portions of possible rotations
scaphoid: 90%, lunate 50%, triquetrum 65% - lunate can go to flexion in 76° and about 35° in extension
proximal row in flexion with radial deviation and extension in ulnar deviation - most indiviuums have this type of movement the so called column writs (other few individuals have a medial-lateral movement - the so called row wrist)
with wrist flexion the proximal row goes ulnarly - with extension the proximal row goes radially
carpal kinetics
force is increased over the whole carpus - in maximum about 10 times of the applied forces at the finger tips - maximum strength men 52kg and women 31kg - so there is potential strength of 520kg and 310kg in the carpal kinetics
axial load is divided through the forearm
60% of axial load goes through the scapholunate-capitate joint in the midcarpal level
radiocarpal:
50-56% radioscaphoid joint
29-35% radiolunate joint
10-21% ulnar lunate joint
lunate fossa gets increased load in ulnar deviation - scaphoid fossa gets more load in radial deviation
stabilizing the carpus
the carpal movement is organized in an equilibrium of forces in which the carpus returns - every injury or damage or changing in bone geometry, articular inclination, ligament integrity or muscle dyfunction with a little amount of change in the carpal motion in returning to this equilibrium lead to a carpal instability with pathologic changings
stabilizing radial and ulnar - over the flexor tendons of the small finger to the hamate hook and the FPL at the ridge of the trapezium
secondary midcarpal stabilizer:
radial are the STT joints with the ligament
ulnar the triquetrum-hamate-capitate ligament
carpal condyle (scaphoid, lunate, triquetrum) - does not articulate with a flat surface - therefore there is ulnar inclination with a tendency to shift ulnarly and palmarly - this tendency is hold by the palmar and dorsal radiocarpal ligaments which is perfectly adjusted against the subluxation forces
pathomechanism of carpal ligament injuries
2 mechanism:
direct trauma which leads to a damage or ligamenteous injury
indirect over forces going through the ligaments with secondary damage
direct mechanism - crushing by a wringer-type machine or explosion
indirect mechanism mostly occur through a hyperextension falling to the outstreched hand with variable angle of ulnar deviation and midcarpal supination
progression of ligamenteous damage is explained by the work of Mayfield and collegeous with cadaver studies
similar pathomechanism - co called “progressive perilunate instability”
the have decribed 4 stages:
stage I: scapholunate dissoziation or scaphoid fracture
STT and scaphoid capitate become extremly taut - lunate fixed and taut by the radiolunate ligaments - in this torsion the SL ligament ruptures from palmar to dorsal
when the same process occur with radial deviation the scaphoid will fracture
very rare dissociation between the scaphoid and the trapezium
stage II: lunocapitate dislocation
force go on - distal row translate dorsally and maybe the capitate fractures - radioscaphoid-capitate ligaments tear off - great ruptur in the space of Poirier
stage III: lunate triqetrum disruption of triquetrum fracture
capitate goes dorsally the triquetrum-hamate-capitate ligamentous complex becomes extremely tensed - dorsal translation moment for the triquetrum with fracture or rupture of the luno-triquetrum ligament
stage IV: lunate dislocation
if the capitate comes back (only the dorsal capsule and the radiolunate ligaments hold the lunate in place) the lunate is dislocate volarly with maybe a rotation of about
type I: minor rotation <90°
type II: rotation >90° with a undisrupted capsule (short radiolunate ligament)
type III: complete enucleation of the lunate through the disrupted capsule
there are no ulnar perilunate patterns of instability are seen -
cave:
hyperpronation of the wrist extended and the carpus goes more in radial deviation (backward fall of the outstretched hand to the hypothenar) - triquetrum maybe forced by the pisiforme to displace dorsally - reversed destabilization pattern
stage I: lunate triquetrum dissociation
stage II: lunocapitate dislocation
stage III: scapholunate dissoziation
radiographs
after good examination
ap (Gilula arcs), lateral, oblique scaphoid, Stecher view
additional: clenched fist to higher the axial load - ap
posterior anterior view with 10° tube angulation from the ulna to the radius
mostly additional views are not necessary - if there is the suspicion of a carpal instability CT and MRI should be done
measurement in radiographics:
capitolunate angle - ratio should be 0,74 plusminus 0,07
scapholunate angle - 30 - 60° (average 47°) (smaller than 30° are not unusual with patients in STT joint arthritis)
radiolunate angle - best for VISI and DISI - between +15° and -15°
ulnar variance
carpal height ratio: carpal height / length of the 3. MC - 0,54 plusminus 0,03
capitato-radius index
ulnar translocation ratio: distance between the capitate head and the radial aspect of the radius lenghtened distally diveded through the length of the 3. MC
normally: 0,28 plusminus 0,03
maybe CT and MRI
distraction views with unsymmetric Gilula arcs
stress views in flexion, extension, ulnar- and radial deviation
cineradiography
arthrography
MRI best with MRI arthrography more sensitive
best is the arthroscopy to view all ligaments and surfaces of the radiocarpal and midcarpal joint - get a good routine in diagnostic not to overseen ligament injuries
