Knee
> Kneecap Dislocation
What is the Patella?
The kneecap (patella)
is a small, triangular bone in the front of your knee
that moves and glides up and down along a track (trochlea)
at the end of the thighbone (femur). The kneecap gives
the front thigh muscles (quadriceps) extra leverage
for straightening the leg, and protects the other bones
in the knee against collisions and falls. There are
several tendons and ligaments, including those attached
to the upper leg and lower leg, connected to the kneecap.
The kneecap (patella) is a small, triangular bone in
the front of your knee that moves and glides up and
down along a track (trochlea) at the end of the thighbone
(femur). The kneecap gives the front thigh muscles (quadriceps)
extra leverage for straightening the leg, and protects
the other bones in the knee against collisions and falls.
There are several tendons and ligaments, including those
attached to the upper leg and lower leg, connected to
the kneecap. A dislocation is when your kneecap is completely
off its normal track, and is visibly sitting off to
one side. When your kneecap is partially off its normal
track, it is called a subluxation.
Kneecap (patellar) dislocations are
usually the result of a dramatic event in which sudden
contraction of the front thigh muscles (quadriceps)
with a partially- flexed and twisted knee causes the
kneecap to displace out of its normal track and dislocate
to one side. These twisting motions and quick directional
changes while running at high speeds often occur in
soccer, gymnastics, and basketball. Your kneecap can
also be pulled out of its track if your overall knee
alignment is off-balance. Physicians call this a biomechanical
problem. If your lower extremity biomechanics are abnormal,
your knee joint may be malaligned, the muscles attached
to your kneecap may pull unevenly on your kneecap and
predispose it to subluxating or dislocating to the side.
In general, women are at greater risk for dislocating
their kneecaps as their kneecaps tend to sit off more
to the side than their male counterparts.
Orthopedic Evaluation |
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There usually are three parts to an
orthopedic evaluation: medical history, a physical examination,
and tests that your doctor may order.
Your doctor
will ask you how and when you injured your knee, how
it has been feeling since the injury, and if your knee
has been previously injured. Physicians also typically
ask if you have any other conditions, have had prior
surgery, are taking any medications, or have any allergies
to medications. The doctor may also ask about your physical
and athletic goals - information that will help him
decide what treatment might be best for you in achieving
those goals.
A physician can often diagnose a dislocated
kneecap by asking you about the details of your accident
and examining you. Your physician will examine your
knee and focus on the area of tenderness, swelling,
and deformity. Since the kneecap is easily palpable
and readily visualized, it can quickly be examined.
If your kneecap is dislocated, it will displace to the
side. Your physician will also ask you to raise your
leg and/or extend your knee, possibly after giving you
a local anesthetic to eliminate pain, to help determine
whether there may be additional injuries in and around
your knee. After your kneecap has been moved back to
its correct location, your physician may flex and extend
you knee.
TESTS
Your physician will obtain X-rays of your knee and may
obtain CT or MRI
(magnetic resonance imaging) scans if other injuries
are suspected.
X-rays,
taken from different angles, are the best way to determine
if a kneecap is dislocated and successfully moved back
into place (reduced). X-rays are also the best test
to screen for additional injuries, including associated
fractures.
MRI
may be obtained to see if the kneecap dislocation has
caused any damage to soft tissue (i.e. muscle, ligament,
tendon, and meniscus) structures. MRI results are usually
available in one to two days after the study is performed.
RELATED TOPICS
Imaging
techniques
Kneecap dislocations can damage the
joint cartilage under your kneecap, which can eventually
cause pain from chondromalacia and arthritis. Recurrent
dislocations cause progressive damage to the joint cartilage
with increased associated pain and greater instability,
which make repeated dislocations more likely. It is
important to seek treatment from an orthopedist soon
after your first kneecap dislocation. Most people respond
well to non-operative treatments and are able to return
to their previous activities after a kneecap dislocation.
In rare cases, surgery is performed soon after the injury
to repair the medical retinaculum, which is torn when
the kneecap displaces laterally, or if a fracture or
loose body occurs with the dislocation. Surgery is reserved
for those cases with recurrent dislocations or severe
pain due to chondromalacia or arthritis that have failed
non-operative treatment, such as temporary immobilization
followed by physical therapy and, if necessary, bracing
or taping.
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