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Cuneiform bones
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The cuneiform (from the Latin for ‘wedge’) bones are a set of three bones in the medial side of the foot that articulate with the navicular proximally and with the proximal surfaces of metatarsal 1-3 distally. A wedge on the plantar surface of the medial cuneiform bone differentiates it from the other two cuneiform bones and is an important factor in the forming the shape of the transverse arch of the foot.
When looking at the proximal surfaces of all three bones we see a concave surface for the navicular to reside in. The navicular possesses three facets for the cuneiform articulation to increase bony conformity. The distal surface creates individual convex surfaces for metatarsals 1-3.
Medial cuneiform
Medial surface
The medial cuneiform is the largest of the three cuneiform bones. As with the other two cuneiforms, there are many rough areas scattered around the articular surfaces for ligament attachment. Its large, square medial surface is easily palpable, rough and is subcutaneous in position. It also acts as a site to receive the tendon of tibialis anterior, an important foot arch muscle, on the distal plantar angle of the medial face.
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Lateral surface
The articulation with the navicular is on the proximal side at the piriform facet which is a concavity that is narrowed dorsally and vertically. As for the lateral surface, the proximal dorsal margin is smooth for articulation with the intermediate cuneiform. The distal lateral surface contains a small facet for a shared articulation with the second metatarsal; the intermediate cuneiform being the other bone which articulates with the second metatarsal. The rest of this surface is rough for the attachment of ligaments and part of the tendon of the peroneus longus.
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Plantar surface
On the plantar surface lies the Lisfranc’s ligament that binds the medial cuneiform to the second metatarsal. At the cornerstone of the mid-foot (the combination of all five tarsometatarsal joints) is the second tarsometatarsal joint to which is attached Lisfranc’s ligament, a pivotal ligament for foot stability.
Anterior surface
The anterior surface, kidney-shaped and much larger than the posterior, articulates with the first metatarsal bone. The posterior surface is triangular, concave, and articulates with the most medial and largest of the three facets on the anterior surface of the navicular.
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Dorsal surface
The dorsal surface is the narrow end of the wedge, and is directed upward and lateralward; it is rough for the attachment of ligaments.
Articulations
The medial cuneiform articulates with four bones:
- the navicular
- second cuneiform
- first metatarsal
- second metatarsal
Intermediate cuneiform
Dorsal surfaces
The intermediate cuneiform bone is the smallest of the three cuneiform bones. It further differs from the medial cuneiform bone by the fact that it has a greater number of smooth surfaces, with the distal, medial, proximal and lateral surfaces all being cartilage covered articular facets. The triangular plantar and dorsal surfaces are rough to allow for the attachment of the interosseous ligaments.
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The interosseous ligament marries the non-articular surfaces to the other cuneiforms. There is an articulation with the navicular proximally and with the base of the second metatarsal and the medial cuneiform distally.
Plantar surface
The plantar surface is narrow and receives the tibialis posterior tendon (second slip), but it shares this accommodation with the other two cuneiforms.
Medial surface
The medial surface is partly articular with the medial cuneiform.
Lateral surface
The lateral surface is similarly articular with the lateral cuneiform. The intermediate and medial cuneiform bones are supplied by the dorsal anterior network and by the deep fibular and medial plantar nerves.
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Articulations
The Intermediate cuneiform articulates with four bones:
- the navicular
- first cuneiform
- third cuneiform
- second metatarsal
Lateral cuneiform
Plantar surface
The lateral cuneiform occupies the center of the front row of the tarsal bones, between the second cuneiform medially, the cuboid laterally, the navicular behind, and the third metatarsal in front.
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The lateral cuneiform is similar to its intermediate cuneiform brother in that it has a rough rectangular wedge. It also receives a slip of the tendon of the tibialis posterior on the plantar surface, which again enables the bone to play an important role in forming the medial foot arch. Various sources suggest that the flexor hallucis brevis tendon inserts into the intermediate cuneiform.
Distal surface
The distal surface has a triangular facet for insertion of the third metatarsal.
Medial surface
Its medial surface contains an indented vertical strip made by the intermediate cuneiform while just distally to this medial surface are two small facets for the lateral side of the second metatarsal base.
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Lateral surface
The lateral surface of the lateral cuneiform contains a triangular or oval insertion point for the cuboid bone. The joint between these bones can become compromised during an inversion trauma of the foot, disrupting the ligaments and producing an everted position on the cuboid or, during progressive laxity of the interosseous ligament, causing a subluxation of the cuboid from the cuboid-lateral cuneiform-navicular joint. The lateral cuneiform is supplied by the dorsal arterial network, and innervated by branches of the deep fibular and lateral plantar nerves.
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Articulations
The lateral cuneiform articulates with six bones:
- the navicular
- second cuneiform
- cuboid
- second metatarsal
- third metatarsal
- fourth metatarsal
Test your knowledge on the bones of the foot with this quiz.
Clinical aspects
Midfoot sprain
Midfoot sprain is an avulsion concerning the ligaments that attach the five metatarsal bones to the four cuneiform bones. Lisfranc’s ligament can avulse, mainly during sporting activities and can lead to a fracture of the medial cuneiform bone to which it attaches. Commonly, a small sprain can result in a full avulsion as the second metatarsal becomes unstable due to the laxity of the LisFranc’s ligament. These fractures are usually due to compression, foot entrapment and falling directly on the toes.
A collapse of the arch can occur if the slight sprain of the ligament is left untreated and constantly played on. Surgery can become necessary, but alternative treatments including manipulation, a cast on the foot to reset the bones and observing non-weight bearing periods may be prescribed.
Stress fractures
Although rare, a stress fracture in a cuneiform bone can be significant. They occur mainly in military personnel and runners, and may be liked to mildly excessive pronation. In the case reviewed by Khan et al (1993), the patient complained of medial foot pain during a run, and a test later revealed that bone sclerosis had occurred in the runner after the stress fracture. Non-weight bearing periods followed by weight bearing rehabilitation lasting from two to four months form the usual basis of the rehabilitation plan.
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