Friday, June 13, 2008

Hook of the Hamate Fractures

The first two years of medical school are spent cramming great gobs of information into a brain that has an alarmingly difficult time retaining it.

Much of the information is achingly boring, and sleep-inducing to the extreme. It's not unusual to see a poor medical student head down in a textbook, drool cascading over the page, defeated by sheer dryness of the material.

Photo by umjanedoan
Mnemonics are legion, as they help you retain some of this information less painfully. Many of these mnemonics have sexual overtones, the better to remember them by. One well-known mnemonic describes the carpal bones of the hand:

Some Lovers Try Positions That They Cannot Handle.

This Kama Sutra resonating gem has helped droves of medical student remember:

Scaphoid
Lunate
Triquetral
Pisiform
Trapezium
Trapezoid
Capitate
Hamate

The last bone on this list, the hamate, has a distinctive shape:


On axial MRI scans, the bone is oriented with the hook (blue arrow) facing down:


It should come as no surprise that the name of this bone is derived from the latin word for hook, hamus.

The hamate bone can be fractured one of two locations: the body or the hook.

Hook of the hamate fractures can be painful, and one must look for these carefully on MRI scans of the wrist. Many of these patients present weeks or months after injury, and bone marrow edema may be minimal or absent.

46 year-old female with wrist pain:


(A) Axial T1-weighted image reveals a fracture of the hook of the hamate. Fluid-sensitive images were also performed, but there was no edema associated with this fracture. (B) Comparison image from normal patient depicting normal hook of the hamate.

A common mistake on MRI is to look only at fluid-sensitive images to detect pathologic states. One should examine anatomic images such as T1-weighted, proton-density weighted and intermediate weighted images carefully as well, as some pathologic states are detected best on these images.

This patient had chronic pain related to this fracture. Once it was detected, the hook of the hamate was resected, curing the patient.

One pitfall to avoid is mistaking a bipartite hamate hook (os hamuli proprium) for a hamate fracture:


This accessory ossicle (green arrows) will often be oval or pyramidal in shape, and will typically be embedded in the pisohamate ligament (blue arrow).

Remember- look specifically at the hook of the hamate on axial MRI scans, or you may miss this fracture, particularly if the injury is subacute or chronic in nature.


Vic David MD
Orthoradiology.com

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