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7/27/2019 Fracture of Patella
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FRACTURE OFPATELLA
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Anatomy
The patella is a sesamoid bone in continuity
with thequadriceps tendon and the patellar
ligament (also called the patellar tendon).
There are additional insertions from the vastusmedialis and lateralis into the medial and
lateral edges of the patella.
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The extensor strap is completed by the
medial and lateral extensor retinacula (or
quadriceps expansions), which bypass the
patella and insert into the proximal tibia.
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The mechanical function of the patella is to
hold the entire extensor strapaway from the
centre of rotation of the knee, thereby
lengthening the anterior lever arm andincreasing the efficiency of the quadriceps.
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The key to the management of patellar
fractures is the state of the entire extensor
mechanism. If the extensor retinacula are
intact, active knee extension is still possible,even if the patella itself is fractured.
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Mechanism of injury and
pathological anatomy
Direct injury usually a fall onto the knee or a
blow against the dashboard of a car causes
either an undisplaced crack or else a
comminuted (stellate) fracture without severedamage to the extensor expansions.
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Indirect injury occurs, typically, when
someone
catches the foot against a solid obstacle and,
to avoid falling, contracts the quadricepsmuscle forcefully. This is a transverse fracture
with a gap between the fragments.
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Clinical Features
Following one of the typical injuries, the knee
becomes swollen and painful. There may be
an abrasion or bruising over the front of the
joint. The patella is tender and sometimes agap can be felt.
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Active knee extension should be tested. If the
patient can lift the straight leg, the quadriceps
mechanism is still intact. If this manoeuvre is
too painful, active extension can be tested withthe patient lying on his side. If there is an
effusion, aspiration may reveal the presence of
blood and fat droplets
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X-ray.
The x-ray may show one or more fine fracture
lines without displacement, multiple fracture
lines with irregular displacement or atransverse fracture with a gap between the
fragments (Fig. 30.14). Comparative x-rays of
the opposite knee may help to distinguish
normal from abnormal appearances in
undisplaced fractures
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Patellar fractures are classified as
1. Transverse
2. Longitudinal
3. Polar or comminuted (stellate)
Any of these may be either undisplaced or
displaced. Separation of the fragments is
significant if it is sufficient to create a step onthe articular surface of the patella or, in the
case of a transverse fracture, if the gap is
more than 3 mm wide.
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A fracture with little or no displacement can be
treated conservatively by a posterior slab of plaster
that is removed several times a day for gentle
active exercises.
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With severe comminutions, patellectomy is
arguably the best treatment, although
some surgeons would consider preserving
as many useful fragments as possible
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A fracture line running obliquely across the
superolateral corner of the patella should not
be confused with the smooth, regular line of a
(normal) bipartite patella. Check the oppositeknee; bipartite patella is often bilateral
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Undisplaced or minimally displaced fractures.
If there is a haemarthrosis it should be
aspirated. The extensor mechanism is intact
and treatment is mainly protective. A plastercylinder holding the knee straight should be
worn for 34 weeks, and during this time
quadriceps exercises are to be practised every
day.
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Comminuted (stellate) fracture
The extensor expansions are intact and the
patient may be able to lift the leg However, the
undersurface of the patella is irregular andthere is a serious risk of damage to the
patellofemoral joint. For this reason some
people advocate patellectomy, whatever the
degree of displacement.
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To others it seems reasonable to preserve the
patella if the fragments are not severely
displaced (or to remove only those fragments
that obviously distort the articular surface); ahinged brace is used in extension but
unlocked several times daily for exercises to
mould the fragments into position and to
maintain mobility.
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Fractured patella
transverse Theseparated
fragments (a) are transfixed by K-wires;
(b) malleable wire
is then looped around the protruding ends
of the K-wires and tightened over the front
of the patella
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Displaced transverse fracture
The lateral expansions are torn and the entire
extensor mechanism is disrupted. Operation is
essential.
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Through a longitudinal incision the fracture is
exposed and the patella repaired by the
tension-band principle. The fragments are
reduced and transfixed with two stiff K-wires;flexible wire is then looped tightly around the
protruding K-wires and over the front of the
patella
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The tears in the extensor expansions are then
repaired. A plaster backslab or hinged brace is
worn until active extension of the knee is
regained; either may be removed every day topermit active knee-flexion exercises.
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