Cuneiform Bones

What are the Wedge-shaped Bones

Wedge-shaped bones are a set of three bones found in the midfoot.  The term ‘wedge‘ in Latin denotes a wedge, while the word ‘shaped’ indicates the form. Therefore, these tarsal bones are called so due to their wedge-shaped structure.

From inner to outer, these bones are known as:

1. Inner Wedge-shaped Bone
2. Intermediate Wedge-shaped Bone
3. Outer Wedge-shaped Bone

Where is the Position of the Three Wedge-shaped Bones in the Foot

The wedge-shaped bones are positioned towards the inner side of the midfoot. They are situated on the inner side of the cuboid and between the navicular and the first three metatarsal bones.

Facts about Wedge-shaped Bones

Functions

The wedge-shaped bones assist in forming the transverse arch of the foot, which helps in maintaining body balance while standing or walking.

Structure and Anatomy of the Wedge-shaped Bones

1. Inner Wedge-shaped Bone

Also referred to as the first wedge-shaped bone, it is the largest among the three wedge-shaped bones. It is positioned on the inner side of the foot, ahead of the navicular bone, behind the first metatarsal, and on the outer side of the intermediate wedge-shaped bone. It displays numerous facets separated by bony ridges, articulating with the adjacent bones.

Bony Landmarks

The inner surface is rough, substantial, square, and subcutaneous, making it easily palpable.

The lower surface features a large kidney-shaped facet for the attachment of the first metatarsal bone.

The upper surface bears a pear-shaped facet for the navicular.

The outer surface is marked by an inverted L-shaped facet along the rear and upper edges for the intermediate wedge-shaped bone. A vertical ridge separates the front upper part of the facet. The second metatarsal bone is attached here.

Articulations

The inner wedge-shaped bone articulates with four bones:

1. Navicular
2. Intermediate wedge-shaped bone
3. First metatarsal
4. Second metatarsal

Muscle Attachments

Two muscles, tibialis anterior and peroneus longus get inserted at the inner wedge-shaped bone.

2. Intermediate Wedge-shaped Bone

It is also known as the second wedge-shaped bone or middle wedge-shaped bone, as it is situated between the other two. This is the smallest among the three.

Bony Landmarks

The upper and lower surfaces bear triangular articular facets for the second metatarsal bone and navicular, respectively.

Its inner surface partly articulates with the inner wedge-shaped bone.

The outer surface bears a vertical facet along its rear margin that articulates with the outer wedge-shaped bone. 

Articulations

It articulates with four bones:

1. Navicular
2. Inner wedge-shaped bone
3. Outer wedge-shaped bone
4. Second metatarsal

Muscle Attachments

Its plantar surface receives the tibialis posterior tendon.

3. Outer Wedge-shaped Bone

The outer wedge-shaped bone, also known as the third or external wedge-shaped bone, is of medium size compared to the other two.

Bony Landmarks

The lower surface is rough in its lower one-third and has a triangular facet in its upper two-thirds for the navicular bone.

A triangular or oval facet marks the outer surface for the cuboid. It also features an articular surface on the inner side for the attachment of intermediate wedge-shaped bone.

Articulations

The outer wedge-shaped bone articulates with four bones:

1. Intermediate wedge-shaped bone
2. Cuboid
3. Navicular
4. Third metatarsal

Muscle Attachments

Two muscles get attached to the outer wedge-shaped bone. The tibialis posterior inserts into the bone, while the flexor hallucis brevis originates from it.

References

1. Wedge-shaped bones – Kenhub.com
2. Wedge-shaped bones – Radiopaedia.org
3. Wedge-shaped bones – Anatomy.net
4. Wedge-shaped bones – Earthslab.com