Capitate bone

The capitate is the largest carpal bone found within the hand.[2] The capitate is found within the distal row of carpal bones. The capitate lies directly adjacent to the metacarpal of the ring finger on its distal surface, has the hamate on its ulnar surface and trapezoid on its radial surface, and abuts the lunate and scaphoid proximally.[3] ^{: 708–709}

The carpal bones function as a unit to provide a bony superstructure for the hand.[3] ^: 708 They allow movements of the wrist from side to side (medial to lateral) as well as up and down (anterior to posterior). H. A. Harris wrote in the British Medical Journal in 1944 that "the strength of construction of the hand in a man is concentrated in the radius, thumb, and index and middle fingers." Therefore, the capitate is larger to support the strength and stress that the middle finger undergoes.

A capitate fracture accounts for 1.3% of all wrist fractures. Isolated fractures of the capitate comprise only 0.3% and are often non-displaced. This is since the capitate is at the centre of the carpal region and is therefore quite well protected. Capitate fractures occur together with fractures of another carpal bone, the scaphoid.[5]

Various mechanisms for fractures of the capitate have been postulated. Adler et al. described three mechanisms—the first is direct trauma to the dorsal surface of the bone, the second is fall on the palm with the wrist in forced extension and the third is fall on the forcefully flexed hand; the second being the most frequent and the third rarest.[5]

In the case of an acute capitate fracture where there is x-ray evidence of excellent alignment of the fracture fragments, the attending doctor will immobilise the wrist in a plaster or lightweight wrist brace. Once the cast has been removed the patient begins physiotherapy to regain the range of movement of the wrist joint and strength in the muscles involved.

If x-rays show that the capitate fracture fragments are out of alignment, surgery is indicated. A surgeon can use small compression screws or K-wires to unite the two pieces of bone. The headless compression screw has advantage over the K-wire as it provides compression across the fracture site and allows early motion. It may be the case that the ligament between the сapitate and the scaphoid bone is also injured; if so, this would be repaired at the same time.[6]

Because the capitate has a poor blood supply there are sometimes complications with the healing process. This may manifest itself as a diffuse ache in the wrist upon activity, and can persist for many months. This is due to a breakdown of the capitate caused by the lack of blood supply and healing (avascular necrosis). Nonunion has been reported as the most common complication; 19.6% to 56% in isolated capitate fractures. Early diagnosis is key to preventing this.

The name of the bone derives from Latin: capitātus 'having a head', from Latin: capit- 'head'.[7]

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  Position of capitate bone (shown in red). Left hand. Animation.
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  Capitate bone of the left hand. Close up. Animation.
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  Capitate bone of the left hand. Ulnar surface (little-finger-side surface)
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  Capitate bone of the left hand. Radial surface (thumb-side surface)
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  Right hand posterior view (dorsal view). Thumb on bottom.
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  Right hand anterior view (palmar view). Thumb on top.
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  Capitate bone shown in yellow. Left hand. Palmar surface.
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  Capitate bone shown in yellow. Left hand. Dorsal surface.
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  Transverse section across the wrist (palm on top, thumb on left). Capitate bone shown in yellow.
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  Cross section of wrist (thumb on left). Capitate shown in red.

• Carpal bone

This article incorporates text in the public domain from page 226 of the 20th edition of Gray's Anatomy (1918)

Wikimedia Commons has media related to Capitate bone.

• Saladin, Kenneth S. "The Skeletal System." Anatomy and Physiology. 7th ed. New York: McGraw-Hill, 2015. N. pag. Print.
• Harris, H. A. "Fractures Of The Carpal Bones." The British Medical Journal 2.4367 (1944): 381. JSTOR. Web. 28 Nov. 2016.