Rupture of the anterior cruciate ligament is rarely seen in children
because the ligament is stronger than the physes during childhood, meaning
that trauma to the knee will more likely result in a physeal
fracture1-3.
DeLee and Curtis, in 1983, reported only three cases of midsubstance rupture
of the anterior cruciate ligament in their study of 388 knee ligament injuries
in children4.
Although some recent studies have demonstrated an increasing prevalence of
midsubstance rupture of the anterior cruciate ligament in children and
adolescents, most of those ruptures occurred during puberty or
adolescence5-7.
Conversely, osteochondral avulsion fractures of the tibial origin of the
anterior cruciate ligament in children are relatively
common8-11.
Injuries that stress the anterior cruciate ligament most often result in an
osteochondral avulsion fracture of the tibial eminence. Although there have
been many studies of osteochondral avulsion fracture of the tibial eminence in
children, only four cases of osteochondral avulsion fracture of the femoral
origin of the anterior cruciate ligament have been
reported12-15.
It is also known that cartilaginous avulsion fractures of the tibial eminence
can occur but are very
rare16,17.
Furthermore, a review of the orthopaedic literature revealed only one report
of an isolated cartilaginous avulsion fracture of the femoral
origin18. That
fracture occurred in a three-year-old boy, but the duration of follow-up was
only ten weeks. Therefore, we are aware of no reports regarding the long-term
effects of cartilaginous avulsion fractures of the femoral origin of the
anterior cruciate ligament. It is known that residual anterior laxity occurs
after an osteochondral fracture of the tibial
eminence19-21.
Growth disturbance is also a concern. Mylle et al. reported on the premature
closure of the anterior half of the proximal physis of the tibia after
transepiphyseal fixation of an osteochondral fracture of the tibial
eminence22.
We report on the case of a three-year-old boy who sustained an avulsion
fracture of the cartilaginous femoral origin of the anterior cruciate ligament
of the left knee. The fracture was treated operatively, and the patient was
followed for thirteen years. The patient and his family were informed that
data concerning the case would be submitted for publication.
Athree-year-old boy fell in September 1989 while riding on a
merry-go-round. The person who had been operating the merry-go-round at the
time of the accident reported that the child's left lower extremity had become
caught between a wooden horse and the flooring, resulting in acute flexion of
the knee combined with internal rotation and anterior displacement of the
tibia relative to the femur. The left knee was immediately painful and rapidly
became tensely swollen, and the boy was unable to bear weight on the limb. The
child was seen later that day by an orthopaedic surgeon, who reported that
routine anteroposterior and lateral radiographs revealed normal findings. That
orthopaedic surgeon did not detail any
Eighteen days later, the boy was seen by one of us (K.K.). Physical
examination revealed a mild effusion, a 30° lack of full extension with
150° of flexion, a positive Lachman test, and a positive anterior drawer
sign. The pivot-shift test was not performed because of pain. Aspiration of
the knee revealed 5 mL of dark blood without fat globules. Repeat
anteroposterior and lateral radiographs of the left knee revealed normal
findings. Lateral radiographs that were made during an anterior drawer test
showed that the anterior displacement of the proximal portion of the tibia was
7.5 mm greater on the left side than on the right
(Figs. 1-A and 1-B). A
tentative diagnosis of midsubstance rupture of the anterior cruciate ligament
was made.
Arthroscopy was performed twenty-three days after the injury. A 10-mm
× 10-mm × 5-mm cartilaginous fragment was found and, after careful
débridement, was determined to be the cartilaginous origin of the
anterior cruciate ligament, which had been avulsed from the lateral femoral
condyle. The posterior cruciate ligament and menisci were intact.
The joint was entered through a medial parapatellar incision, and the
cartilaginous fragment was reattached (Fig.
1-C). Examination of the fracture site revealed only the
cartilaginous surface. Two 1.8-mm drill-holes were made obliquely from the
fracture site, across the epiphysis and the physis, to the lateral aspect of
the distal femoral metaphysis. Because absorbable sutures were not approved
for use in Japan at that time and because metal would show any displacement of
the radiolucent fragment on the radiographs, a 0.5-mm stainless steel wire was
looped around the cartilaginous fragment, passed through the drill-holes, and
tied over a button at the lateral femoral metaphysis
(Figs. 1-D and 1-E). The lower
extremity was then immobilized in an above-the-knee cast, with the knee held
in 30° of flexion, for four weeks. The wire was removed five months after
the operation, at which time there was good tension of the anterior cruciate
ligament on arthroscopy.
Thirteen years later, we requested that the patient be reevaluated because
we had concerns about the long-term effects of this type of injury. Our
patient was then a sixteen-year-old student. He had no pain, instability,
restriction of motion, or limitation of activity, even when playing soccer.
Physical examination revealed no Lachman sign, pivot shift, or rotatory
instability of the left knee. The lower extremities were equal in length, and
there was no varus or valgus deformity of the left knee. Routine
anteroposterior and lateral radiographs revealed normal findings
(Figs. 2-A and 2-B); however,
lateral stress radiographs revealed slight laxity of the anterior cruciate
ligament in comparison with that seen in the contralateral knee. Magnetic
resonance imaging revealed normal findings.
Areview of the literature revealed one case of cartilaginous avulsion
fracture of the femoral origin of the anterior cruciate
ligament18, four
cases of osteochondral avulsion fracture of the femoral
origin12-15,
and two cases of cartilaginous avulsion fracture of the tibial
eminence16,17
(Table I). In the latter two
reports, the cartilaginous fragments had been missed, resulting in an
extension deficit accompanied by growth of the avulsed fragments. If routine
radiographs are interpreted as normal during the first examination of the knee
after an injury, a careful reexamination should be performed, bearing in mind
the possibility of a cartilaginous avulsion fracture or a midsubstance rupture
of the cruciate ligaments. When there is a large effusion of the knee and the
child rejects physical examination because of pain, reexamination should be
performed in approximately one week.
Concern has been raised regarding the potential for physeal injury
resulting from drill-holes crossing the physis during an open reduction of a
cartilaginous avulsion fracture, although small drill-holes that are centrally
placed across the physis probably have minimal effect on
growth23-25.
In one of the previous reports of osteochondral avulsion fracture of the
femoral origin of the anterior cruciate ligament, the child was treated with a
pull-out suture that was placed across the
physis12. The
authors reported no deformity of the distal part of the femur, although the
diameter of the drill-holes was not reported and the patient was considerably
older than our
patient12. Several
authors have reported on open reduction of the avulsed fragments of the tibial
eminence and fixation with a metal pin or wire that was not placed across the
physis in an effort to avoid physeal
injury26-29;
however, Mylle et al. reported that late removal of a transepiphyseal screw
resulted in asymmetrical physeal closure of the anterior aspect of the
proximal tibial epiphysis in an eleven-year-old
girl22. In our
patient, the growth of the distal aspect of the left femur was not affected,
perhaps because of the use of small and centrally placed drill-holes and
comparatively early removal of the wire five months after placement.
In two of the previous reports on osteochondral avulsion fracture of the
femoral origin, mild laxity of the anterior cruciate ligament of the injured
knee was noted at the follow-up
examination12,15.
Follow-up studies of osteochondral avulsion fractures of the tibial eminence
have also shown that intrinsic damage to the anterior cruciate ligament occurs
commonly19-21.
Smith observed anterior cruciate ligament laxity in all fifteen patients who
were studied, even though the fractures healed in anatomical
alignment19. Wiley
and Baxter, in a study of forty-five children with a mean age of eleven years
(range, eight to sixteen years), reported a measurable degree of residual
anterior cruciate ligament laxity (despite the absence of symptoms) as
measured with computed instrument testing in thirty-two patients who had
Type-II or Type-III osteochondral avulsion fractures according to the
classification system described by Meyers and
McKeever20. Fifteen
of the thirty-two patients were managed with closed reduction and seventeen
were managed with open reduction, and both groups showed a mean difference of
3.5 mm in anterior translation between the injured and uninjured knees at the
time of long-term follow-up (three to ten years after the injury). Willis et
al. showed that thirty-seven (74%) of fifty adolescent patients had objective
evidence of anterior cruciate ligament laxity at an average of four years of
follow-up21. Even
when the avulsed fragment is anatomically reduced, intrinsic damage to the
ligament can contribute to a persistent, small, but asymptomatic amount of
laxity on anterior drawer testing. This degree of laxity was noted in our
patient at the time of the thirteen-year follow-up evaluation.
An avulsion fracture of the cartilaginous femoral origin of the anterior
cruciate ligament rarely occurs in childhood but should be suspected in a
young child who has a large effusion of the knee and a mechanism of injury
similar to that of our patient. Although mild residual laxity of the anterior
cruciate ligament may persist, a good result can be anticipated with
appropriate treatment. An associated posterior physeal injury, although not
seen in our patient, may occur with this type of cartilaginous avulsion
fracture. Magnetic resonance imaging can be used to assess and follow this
type of injury.