Image Quiz

Injury to the Dorsum of the Foot (continued)

Answer: Isolated plantar dislocation of the intermediate cuneiform bone.


Fig. 1		 Fig. 1 Anteroposterior (left) and lateral (right) plain radiographs of the left foot, showing an isolated plantar dislocation of the intermediate cuneiform bone (asterisk) with slight displacement of the first metatarsal.

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Fig. 2		 Fig. 2 Computed tomographic scan of the left foot, showing a complete plantar dislocation of the intermediate cuneiform (arrowhead). The single asterisk indicates the medial cuneiform, and the double asterisk indicates the lateral cuneiform.

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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 points. Radiographs showed no recurrence of dislocation (Fig. 4), and magnetic resonance imaging showed no signs of osteonecrosis of the intermediate cuneiform (Fig. 5).


Fig. 3		 Fig. 3 Postoperative anteroposterior (left) and lateral (right) plain radiographs of the left foot, showing that the intermediate cuneiform bone (asterisk) has been reduced and fixed with two crossed Kirschner wires.

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Fig. 4		 Fig. 4 Plain anteroposterior (left) and lateral (right) radiographs of the left foot, made two years after surgery, showing no recurrence of the dislocation of the intermediate cuneiform bone (asterisk).

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Fig. 5		 Fig. 5 T1-weighted (left) and T2-weighted (right) magnetic resonance images of the left foot, acquired two years after surgery, showing no signs of osteonecrosis of the intermediate cuneiform (single asterisk). The double asterisk indicates the medial cuneiform, and the triple asterisk indicates the lateral cuneiform.

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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.


Fig. 6-A		 Figs. 6-A, 6-B, and 6-C Descriptive illustrations of the anatomy as related to the mechanism of injury. The single asterisks indicate the navicular, and the double asterisks indicate the second metatarsal.
Fig. 6-A When a plantar flexion force was applied to the midfoot, the intermediate cuneiform (arrowhead) displaced dorsally.

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Fig. 6-B		 Fig. 6-B When a similar plantar flexion force was applied to the midfoot while manual pressure was applied dorsally to the intermediate cuneiform (arrowhead), the intermediate cuneiform did not dislocate dorsally.

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Fig. 6-C		 Fig. 6-C When a flat piece of steel was used to apply force to the dorsal aspect of the midfoot in order to depress the transverse and longitudinal arches of the foot (left), the intermediate cuneiform (arrowhead) displaced plantarly.

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Discussion

Since Clark and Quint first reported an isolated dislocation of the intermediate cuneiform bone in 1933, there have been eight reported cases, including seven cases of dorsal dislocation and one case of plantar dislocation. 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 dislocation.

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 bone. 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 follow-up 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.

Reference

1. Nishi H, Takao M, Uchio Y, Yamagami N. Isolated plantar dislocation of the intermediate cuneiform bone. A case report. J Bone Joint Surg Am. 2004;86:1772-7.