Dislocation of the patella generally results from a traumatic
event. It is most commonly due to a direct blow to the flexed knee.
Many patients may not notice the dislocation as it may spontaneously
reduce immediately after the injury. There are numerous theories
as to the predisposition, if any, to a patellar dislocation.1,2 This
condition is most common in adolescents and females.
The knee consists of the patellofemoral and the tibiofemoral
joints. The patellofemoral joint is a gliding joint. The patella
is an oval-shaped sesamoid bone that develops in the tendon of the
quadriceps muscle. It is attached to the quadriceps superiorly and
the tibial tuberosity inferiorly. The patella articulates between
the femoral condyles. It is held in place by the vastus medialis
muscle, the medial retinaculum, the medial and lateral patellofemoral
ligaments, and the patellotibial ligament.
The patella may dislocate in numerous directions (Figure 72-1).
Lateral dislocations are the most common type (Figure 72-2). The
patella usually dislocates laterally due to its asymmetrical shape and
the normal upward and lateral pull of the quadriceps muscle. The
patella may also dislocate superiorly, medially, and intraarticularly
in rare instances.3,4
Types of patellar dislocations.
Anatomy of a lateral patellar dislocation. A. Anteroposterior view. B. Lateral view.
The clinical determination of a lateral patellar dislocation
is usually simple and quite obvious (Figure 72-3). The knee is held
in partial flexion. The patella can be seen and palpated on the
lateral surface of the knee. This may be accompanied by edema and/or
ecchymoses over the anterolateral knee.
The lateral patellar dislocation. The presentation is
often clinically dramatic. (Photograph courtesy of Dr. Robert R.
Pain over the parapatellar ligaments may be the only clinical
sign in patients whose patellar dislocation has spontaneously reduced.
The physical examination usually reveals mild edema in the parapatellar
recesses. There is often laxity in the tendons and ligaments surrounding
the patella. A patellar apprehension test is generally positive.
The knee joint is usually stable.
The pathophysiology of this dislocation may include abnormalities
secondary to malalignment, laxity, and hyper-elasticity of the joint.
Osteochondral fractures are common but seen only on arthroscopy.1,2,5 Magnetic
resonance imaging, bone scans, and arthroscopy are considerations
for further evaluation and diagnosis of the patellofemoral joint
by the Orthopedic Surgeon.
Pre-reduction radiographs should be obtained to document patellar
fractures or other bony abnormalities prior to the reduction. Radiographs
may also be used to identify a foreign body if abrasions or lacerations
are present over the knee. The patella often reduces spontaneously
in the radiology suite as the leg is extended to obtain the radiographs.
Any medial or lateral patellar dislocation that does not reduce
spontaneously should be reduced manually.
As with any traumatic injury, the evaluation and management of
the patient’s airway, breathing, circulation, and other
significant injuries takes priority over the reduction of a patellar
dislocation. There are a few relative contraindications to the reduction
of a patellar dislocation. An Orthopedic Surgeon should be consulted
for the evaluation and reduction if the dislocation is superior,
horizontal, intercondylar, or associated with fractures of the distal
femur or proximal tibia. The only exception
to this is if there is neurologic and/or vascular compromise
of the distal extremity. This
requires immediate reduction by the Emergency Physician if, after
phone consultation, the Orthopedic Surgeon is not immediately available
to perform the reduction.
No special equipment is required for the reduction of the dislocation.
A knee immobilizer or splinting material (plaster, fiberglass, prepackaged
splints) should be available to temporarily splint the patella after
Patient preparation is minimal in the case of a lateral or medial
patellar dislocation. Explain the risks, benefits, complications,
and aftercare to the patient and/or their representative.
Obtain an informed consent prior to performing the procedure. Verbal
consent is usually sufficient, since the reduction of a patellar
dislocation is relatively simple, with infrequent complications.
Place the patient supine on a gurney. No premedication or sedation
is required for this procedure.
The technique for the reduction of a lateral patellar dislocation
is rather simple (Figure 72-4). Flex the patient's hip to release
the tension on the quadriceps muscles. Slowly and gently extend
the knee (Figure 72-4A). The patella
may relocate spontaneously by simply extending the knee. If it is
still dislocated, apply gentle and medially directed pressure to
the lateral surface of the patella (Figure 72-4B).
This will allow the patella to move into its normal anatomic position
in the intercondylar fossa of the femur. The technique to reduce
a medially dislocated patella is similar with the exception of the
application of a laterally directed force on the patella.
Reduction of a lateral patellar dislocation. A. Manipulation of the knee begins
with gradual extension. B. Medially
directed pressure applied to the patella reduces the dislocation.
Intraarticular and horizontal patellar dislocations are sometimes
reduced by closed manipulation, although most require open reduction.
Superior patellar dislocations require operative reduction. These
dislocations should not be reduced in the Emergency Department.
Patients with these types of patellar dislocations require urgent
consultation with an Orthopedic Surgeon and hospital admission for
Obtain a post-reduction radiograph to rule out any osteochondral
fractures that were not diagnosed initially and to ensure proper
positioning of the patella. Maintain the ...
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