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Posted by firstname.lastname@example.org, 8/15/03 at 2:51:48 PM.
The wrist, with its enormous range of motion, is one of the most complex and frequently used joints within the human body. However,
because of the prominent role it plays in normal daily activities, the
wrist can oftentimes wind up being a source of significant disability
The proximal bones of the wrist (scaphoid, lunate, and triquetram) have no muscular attachment. As
a result, their main purpose is to stabilize the wrist joint and
provide a focal plane to help transmit the force generated by the
flexors and extensors of the arm.
help them in this task, numerous strong ligaments bind the proximal
bones together, allowing them to function more cohesively. Damage
to any of these ligaments results in either acute symptoms or a less
noticeable but possibly more dangerous malalignment of the carpal bones
that, if left uncorrected, will accumulate abnormal wear and tear --
eventually leading to severe and debilitating osteoarthritis.
Ligamentous injuries and subsequent carpal instability tend to occur in young and middle aged patients. This
is because as people age, their bones become more fragile and thus
trauma in the elderly tends to cause outright bone fractures instead of
soft tissue damage. The most frequently encountered ligamentous
injury of the wrist is scapholunate instability.
Three main ligaments bind the Lunate and Scaphoid bones together:
· Volar radioscapholunate ligament
· Scapholunate interosseous ligament
· Dorsal scapholunate ligament
Scapholunate instability is defined as significant injury to two or more of these ligaments.
instability is usually caused by stress placed on a hyperextended
wrist, especially in ulnar deviation (such as frequently happens when
patients fall on an outstretched hand). When
this occurs, the ligaments binding the scaphoid and lunate bones begin
to tear, starting with the scapholunate interosseous ligament.
When a ligamentous wrist injury occurs, patients will generally describe one or more of the following symptoms:
- "Giving way"
- A "clunk, snap, or click" during use
One of the easiest ways to evaluate these patients is with a simple physical exam maneuver known as the Watson test.
Watson HK, Ashmead D4, Makhlouf MV: Examination of the scaphoid. J Hand Surg Am. 1988; 13: 657-660.]
painful snap is obtained when pressing hard on the scaphoid tubercle
volarly and moving the wrist from ulnar to radial deviation, the wrist
being maintained in axial compression. If clinical suspicion is high, further evaluation with imaging studies can be done.
the ligaments binding the scaphoid and lunate bones are damaged, the
scaphoid begins to move out of its normal position and rotationally
sublux. This leads to several noticeable findings on radiographic examination.
On AP plain films of the wrist, an abnormally large gap between the scaphoid and lunate bones can oftentimes be seen. This is known as the Terry Thomas sign,
in reference to the British comedian with a sizeable gap between his
two front teeth (or David Letterman or any other person with a gap in
their teeth, sign).
a scapholunate interval of > 2mm is suspicious and > 4 mm is
virtually diagnostic for scapholunate dislocation or instability.
X-rays of scapholunate instability may also demonstrate an increased
capitolunate angle > 15 degrees as well as increased scapholunate
angle > 60 degrees.
sensitive, plain films will sometimes fail to see the early signs of
scapholunate instability when the ligaments are torn but the scaphoid
has yet to sublux. In these situations when
suspicion is high, or when plain films have already detected the
dislocation and further evaluation is needed to plan treatment,
arthography is the next logical step in radiologic evaluation.
wrist can be divided into three discrete compartments with ligamentous
borders that prohibit the movement of fluid from one compartment to the
next. The scapholunate ligaments comprise
part of this border and any tear can be diagnosed on arthrography when
contrast injected into one compartment can be seen abnormally flowing
into a neighboring compartment.
while often diagnostic, contrast leakage does not always signal a
significant tear within the ligaments but instead may only represent a
ligamentous perforation without significant consequences. If
this is suspected to be the case, contrast injection can be coupled
with CT scan or MRI of the joint to directly assess the health of the
carpal ligaments. Furthermore, CT scan or
MRI can directly determine the site and length of ligament tears and is
a critical tool when planning any surgical repair.
scapholunate injuries can sometimes present without symptoms yet if
left untreated can eventually result in further carpal derangement and
debilitating osteoarthritis, prompt diagnosis and repair is extremely
the injury is thought to be minimal, conservative treatment with
splinting and NSAIDS can be used to provide symptomatic relief. However, any significant degree of injury necessitates surgical correction.
overall aim of surgery is to restore a normal orientation of the
scaphoid with the proximal pole appropriately articulating with the
radius and to correct any other abnormalities that have occurred if the
original injury was undiagnosed and uncorrected.
surgical techniques have been described, but generally revolve around
soft tissue repair, where the carpal ligaments are modified or
restored, or limited carpal arthrodesis, where the wrist bones are
either orthopedically fixed or fused.
scapholunate insufficiency is left untreated long enough, further
shifts of the carpal bones can occur, eventually leading to a syndrome
known as scapholunate advanced collapse, or SLAC:
As the scaphoid moves further from the lunate, the normal load-bearing ability of the capitolunate joint disappears. Among
other things, this results in the migration of the capitate bone
proximally, driving a further wedge between the scaphoid and lunate.
Check out the following scapholunate instability case in John Hunter's file.
Another example of scapholunate ligament tear seen on arthrography can be seen in this case.