Carpal Bone Injuries
- Author: Bryan C Hoynak, MD, FACEP, FAAEM; Chief Editor: Sherwin SW Ho, MD more...
Background
The carpus, or wrist, is a complex joint that provides abduction and adduction in the frontal plane of the upper extremity, extension and flexion for hand movements, and supination and pronation in the coronal plane.
In the early 1800s, Colles was the first to differentiate between wrist fractures and wrist dislocations.
Epidemiology
Frequency
United States
The frequency of carpal bone injuries cannot be specifically determined because they encompass a range and variety of injuries near and around the wrist joint. Additionally, retrospective analysis by diagnosis category grossly underestimates the number of incidents.
The author's perspective is from a personal observation made one weekend day during a 12-hour shift several years ago in Wildomar, California. Seven fractures or fracture-dislocations of the wrist presented to the emergency department; all were related to roller blades, and all involved children aged 5-16 years.
The rate of chronic overuse injuries and other sports-specific injuries approaches 35-50% of all carpal injuries in the sports world. Fractures of the distal radius account for one sixth of all fractures seen and treated in the emergency department. These injuries are most common in patients aged 6-10 years and those aged 60-69 years.
International
International rates approximate the US rate.
Functional Anatomy
The wrist joint, or carpus, is a complex arrangement between the forearm and the carpal bones, stabilized by strong, ligamentous attachments.[1, 2] The average wrist movement is 80º in flexion, 70º in extension, 30º in ulnar deviation, and 20º in radial deviation. Pronation and supination occur at the radioulnar articulation in the forearm, not at the wrist. The majority of injuries to the wrist occur with the wrist in the flexed position.
The muscles of the hand originate primarily in the forearm and pass over the wrist; the flexor carpi ulnaris inserts into the pisiform bone and is the only muscle that inserts into the wrist. The second and third metacarpals are fixed at the base and are immobile.
Carpal bones
The 8 carpal bones are arranged in 2 rows and are cuboid, with 6 surfaces. Of these 6 carpal surfaces, 4 are covered with cartilage to articulate with the adjacent bones, and 2 are roughened for ligament attachments. The proximal row, which contains the scaphoid, lunate, triquetrum, and pisiform, articulates with the radius and triangular cartilage to form the carpus. The distal row contains the trapezium, trapezoid, capitate, and hamate.
The ulnar nerve runs deep to the flexor carpus ulnaris tendon through the canal of Guyon. The median nerve lies between the flexor carpus radialis and the palmaris longus tendon in the carpal tunnel. Blood is supplied via the radial and ulnar arteries, which form the dorsal palmar arch. The scaphoid bone receives its blood supply from the distal part of this arch, which is prone to injury.
Anatomic considerations
The carpus is composed of the interval between the distal end of the radius and ulna and the proximal end of the metacarpal bones. A complex system of articulations works in unison to provide a global range of motion for the wrist joint. As noted above (see Functional Anatomy, Carpal bones), 8 carpi are arranged in 2 rows to form a compact, powerful unit. The distal row articulates with the proximal surface of the metacarpal bones. The proximal row articulates with the distal end of the radius and the fibrocartilaginous end of the ulna. The ulna does not articulate with the carpus.
The wrist has 5 large joint cavities in addition to the intercarpal joint spaces: (1) radiocarpal joint, (2) distal radioulnar joint, (3) midcarpal joint, (4) large carpometacarpal joint (between the carpus and the second, third, fourth, and fifth metacarpals), and (5) small carpometacarpal joint (between the first metacarpal and trapezium).
Motion at the wrist joint occurs between the radius and carpal bones. The size, position, and relation to the radius and surrounding carpal bones render the wrist joint vulnerable to injury. With dorsiflexion and radial deviation of the wrist, the joint is impinged by the radius; because of its narrow mid portion, the wrist joint is predisposed to injury. Healing depends on blood supply to the area; at this joint, blood enters the bone along the dorsal surface near its mid portion. Thus, the scaphoid is prone to avascular necrosis.
Sport-Specific Biomechanics
Sport-specific biomechanics focus on the unique characteristics that place the carpal bones at risk for injury during a sporting activity. This can be as obvious as a fall onto an outstretched hand during a roller sport to the hand plant that is involved in a gymnastics move.
Chronic use and movements in racquet sports, golf, and baseball require the carpus to resist torque stress. Depending on the strength of the weakest link, acute or chronic injury can ensue, which can be especially true in the hyperpronation-supination activity that is involved in the modern golf swing. The key to wrist injury prevention is to improve strength and flexibility in all planes of motion.
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