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The Vascular Anatomy of the Capitate: New Discoveries Using Micro-CT Imaging
Assaf Kadar, MD1,2; Mohamed Morsy, MD1; Yoo Joon Sur, MD, PhD1; A.T. Laungani, MD1; Osman Akdag, MD1; Steven L. Moran, MD1
1Mayo Clinic, Rochester, MN; 2Orthopedic Division, Tel Aviv Sourasky Medical Center Orthopaedic Division, Tel Aviv, Israel

Purpose
To study the interosseous 3D micro-vasculature of the capitate bone using a novel high resolution micro-CT (ÁCT) imaging technology, and to examine the blood supply as it relates to the most common fracture types.

Methods
Ten wrists were injected with a lead-based contrast agent. The capitates were harvested and imaged using a ÁCT scanner. The intraosseous vascularity was incorporated into a 3D image. Vascular pattern, as well as vessels' cross sectional area, number and distribution were measured. An average capitate fracture line was calculated using clinical data from 22 patients with capitate fractures. The fracture line was projected on the representative capitate in order to assess its relation with the nutrient vessels entry points.

Results
The capitate is a hyper-vascular carpal bone supplied by dorsal and volar vascular systems which anastomose in 30% of cases. There was no predominance of one vascular system over the other. The majority of vessels enters the capitate at the distal half and supplies the proximal pole in a retrograde fashion. In addition, 70% of the specimens also had at least one vessel entering the proximal pole through the volar capitate ligaments and supplying the proximal pole directly. The average fracture line had an oblique orientation, and 90% of the specimens had a blood vessel enter proximal to that line.

Conclusions
This ÁCT vascular study further verifies that the capitate receives most of its vasculature in a retrograde fashion, but this study also shows that most capitates have vessels supplying the proximal pole directly. These findings might explain why most capitate waist fractures don't progress to proximal pole avascular necrosis.

Figure 1. Three-dimensional rendering of a left capitate specimen showing the microvascular architecture within the bony structure. View of the A, Radial surface; B, Volar surface; C, Ulnar surface and; D, Dorsal surface (red vessels, intraosseous vessels; green vessels, extraosseous vessels entering the bone).

Figure 2. Entry points of nutrient vessels of all capitates projected onto the structure of one right capitate showing the density of nutrient vessels and the relation to the average fracture line. View of the A, Radial surface; B, Volar surface; C, Ulnar surface and; D, Dorsal surface. A predominance of the vessels entering below the fracture is volar (Blue line, average fracture; light blue area, 95% fracture line confidence interval).


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