A fifty-six-year-old man who worked as a crane operator was injured when
the 300 kg of iron material that he was attempting to lift with a crane fell
from a height of 2 m onto the dorsum of his left foot. He was immediately
brought to our hospital with severe foot pain. Physical examination showed
severe swelling of the left foot, without an open wound, and demonstrated
tenderness of the plantar and dorsal surfaces of the midfoot. The patient had
no sensory or motor disturbances. Plain radiographs showed an isolated plantar
dislocation of the intermediate cuneiform bone, with slight displacement of
the first metatarsal (Fig. 1).
A computed tomographic scan (Fig.
2) with three-dimensional reconstruction showed a complete
dislocation of the intermediate cuneiform bone in the plantar direction. An
attempt at a closed manipulative reduction was unsuccessful; therefore, an
open reduction through a combined dorsal and plantar approach was performed.
We initially tried to reduce the intermediate cuneiform through the plantar
incision, but this proved to be impossible as its wide dorsal aspect blocked
reduction. We therefore removed the intermediate cuneiform bone and placed it
back into the foot through a separate, second dorsal incision. After the
intermediate cuneiform was reduced, it was secured in place with two crossed
Kirschner wires (Fig. 3).
Postoperatively, the foot was immobilized in a short-leg cast for four weeks,
after which the cast and the Kirschner wires were removed. The patient was
allowed to begin partial weight-bearing three weeks after surgery. At three
months after surgery, he was able to walk without discomfort. At six months
after surgery, he had no pain when running and was able to participate fully
in athletic activities. At two years after surgery, the midfoot had a full
range of motion and the American Orthopaedic Foot and Ankle Society score was
100 points9.
Radiographs showed no recurrence of dislocation
(Fig. 4), and magnetic
resonance imaging showed no signs of osteonecrosis of the intermediate
cuneiform (Fig. 5).
Descriptive Anatomic Dissection
To clarify the mechanism of isolated plantar dislocation of the
intermediate cuneiform bone, we performed an anatomic dissection of four fresh
cadaveric feet from two men who had been forty-six and seventy-one years of
age at the time of death and who had had no foot abnormalities. We exposed the
tarsal bones and cut the dorsal and plantar ligaments, which connect the
intermediate cuneiform to the medial and lateral cuneiforms, the first and
second metatarsals, and the navicular.
When a plantar flexion force was applied to the midfoot, the intermediate
cuneiform displaced dorsally (Fig.
6-A). When a similar plantar flexion force was applied to the
midfoot but pressure was simultaneously applied dorsally to the intermediate
cuneiform, the intermediate cuneiform was prevented from dislocating in a
dorsal direction (Fig. 6-B).
When a flat piece of steel was used to apply force to the dorsal aspect of the
midfoot to compress and decrease the transverse and longitudinal arches of the
foot, a plantar dislocation of the intermediate cuneiform was produced
(Fig. 6-C). Subsequently, the
dislocation could not be reduced through a plantar approach.
Since Clark and Quint first reported an isolated dislocation of the
intermediate cuneiform bone in
19335, there have
been eight reported cases, including seven cases of dorsal
dislocation1-6,8
and one case of plantar
dislocation7.
Because the intermediate cuneiform is wedge-shaped and its base is positioned
dorsally, it has a tendency to dislocate dorsally. Dorsal dislocation of the
intermediate cuneiform usually results from direct injury but occasionally
results from indirect injury as a variant of the Lisfranc
dislocation10.
To our knowledge, the mechanism of plantar dislocation of the intermediate
cuneiform bone has not been reported in the literature. Our anatomical study
showed that plantar dislocation of this bone did not occur when a plantar
flexion force was applied to the midfoot while dorsal pressure was applied to
the intermediate cuneiform to obstruct dorsal dislocation. This mechanism was
previously reported to cause isolated dorsal dislocation of the intermediate
cuneiform bone8.
Rather, we found that the intermediate cuneiform was displaced plantarly when
force was applied to the dorsal aspect of the midfoot to depress the
transverse and longitudinal arches of the foot. With regard to the mechanism
of injury in our patient, we speculate that when the iron material fell on the
dorsum of the foot, the transverse and longitudinal arches were depressed,
thereby widening the plantar window around the intermediate cuneiform
sufficiently to allow extrusion of that bone plantarly. Unfortunately, we
could not clarify why only the ligaments around the intermediate cuneiform
were ruptured without disruption of the other structures. The intermediate
cuneiform forms the keystone of the tarsometatarsal joint. It is possible that
when force is applied to the dorsal aspect of the midfoot, the resultant
forces may concentrate at the intermediate cuneiform. When this occurs,
ligament injury may be limited to the ligaments about the intermediate
cuneiform bone.
In the case of our patient, the intermediate cuneiform bone was completely
devoid of a blood supply, yet the followup magnetic resonance imaging scans
showed no evidence of osteonecrosis. This finding may be attributable in part
to the fact that the anatomical reduction of the intermediate cuneiform was
performed immediately after the injury.