Pediatric emergency medicine trisk 0836 0836
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normal if the injury is a nondisplaced Salter–Harris type I fracture. Although not
necessary as part of the ED evaluation, magnetic resonance imaging (MRI) may
be needed when the physis is tender or a large effusion is present.
Acute traumatic avulsion of the tibial tuberosity is caused by acute stress on the
knee’s extensor mechanism. The quadriceps muscle group extends the knee by
way of the patellar ligament. The patellar ligament inserts on the tibial tuberosity
and may avulse it during sudden acceleration (e.g., beginning a jump) or
deceleration (e.g., landing after a jump). The patient will have tenderness and
swelling over the tibial tubercle and be unable to extend the knee fully (or
perform a straight leg raise). A lateral radiograph is diagnostic.
Fractures of the patella are rare in younger children because the patella does
not ossify until 3 to 6 years of age, leaving it with a thick cartilage layer that
protects it from direct trauma. In addition, the soft tissue anchors of the patella are
flexible which diffuses blunt forces. However, a direct impact on the patella into
the distal femur can cause transverse or comminuted fractures. Much more
common in children are avulsion fractures of the patella resulting from forceful
contraction of the quadriceps. With patellar fractures, the patient’s knee will be
swollen, the patella tender, and knee extension painful. A radiograph is usually
diagnostic although care must be taken not to miss small avulsion fragments
including sleeve fractures which are unique to pediatrics (egg-shell–like bony
fragment that dislocates with avulsed soft tissue). Bipartite patellae are a normal
variant and may be confused with an acute fracture.
Osteochondral fractures are fractures of articular cartilage and underlying bone
not associated with ligamentous attachments. These fractures often involve the
femoral condyles or the patella. The injury may follow a direct blow to the knee,
a twisting injury, or patellar dislocation. The patient will have severe pain,
immediate swelling, and will hold the knee partially flexed. Hemarthrosis may be
present. Knee radiographs should include an intercondylar view because the
fracture fragment may be in the intercondylar notch. Osteochondral fractures can
be missed because only the small ossified portion of the osteochondral fragment
is radiopaque. MRI may be necessary for diagnosis.
Analogous to an adolescent who ruptures the anterior cruciate ligament (ACL),
patients 6 to 16 years old may sustain avulsion fractures of the tibial spine at the
point where the ACL inserts. The tibial spine is incompletely ossified and may
avulse before the ligament ruptures. The patient may have a hemarthrosis and will
be unable to bear weight. If the patient tolerates an examination, the Lachman test
(see Fig. 42.3 ) may be positive because the injury is similar mechanically to an
ACL tear. AP, lateral, and intercondylar or tunnel-view radiographs will show the
