Assistant
Definition
By Gregory R. Waryasz, MD
The lunate of the musculoskeletal system is characterized by being the “carpal keystone”.
It is part of the upper limb. The lunate articulates with the radius proximally and the capitate and hamate distally, the scaphoid and the triquetrum. It consists of bone and cartilage tissue once mature.
Its unique structural features include its being moon-shaped. It is wider anteriorly than posteriorly. The lunate rests in the lunate fossa of the distal radius and is anchored to the scaphoid and triquetrum by interosseous ligaments.
The superior surface is convex and smooth.
The inferior surface is deeply concave.
The scaphoid surface is flat and narrow.
The triquetral surface is smooth with a quadrilateral facet.
The lunate receives its blood supply from the proximal carpal arcade.
The lunate ossifies at age 4 to 5. The lunate as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in embryo.
The function of the lunate is to stabilize the wrist and allow for wrist movement. During wrist dorsiflexion, the lunate is displaced volarly.
Common diseases of the lunate include arthritis, fracture, Kienbock’s disease, and dislocation.
Arthritis can occur at any of the articulations. Common arthritis types that can occur at these locations include osteoarthritis and rheumatoid arthritis.
Fracture of the lunate can occur with trauma.
Dislocation of the lunate can occur with trauma. It is the most common carpal bone to dislocate.
Kienbock’s disease is a condition of avascular necrosis of the lunate. There is collapse of the lunate bone and in later stages fracture. It can become very painful and limit wrist range of motion.
Commonly used diagnostic procedures include clinical history, physical exam, x-ray, MRI, bone scan, and CT scan.
It is usually treated with internal or external surgical fixation or non-operative approaches for fractures. Dislocations are usually treated operatively. Arthritis is treated initially with physical therapy, NSAIDs, and steroid injections. Kienbock’s disease can be treated non-operatively or operatively depending upon the stage.
References
Elstrom J, Virkus W, Pankovich (eds), Handbook of Fractures (3rd edition), McGraw Hill, New York, NY, 2006.
Koval K, Zuckerman J (eds), Handbook of Fractures (3rd edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.
Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Wheeless’ Textbook of Orthopaedics: Lunate (http://www.wheelessonline.com/ortho/lunate)