carpal bones get no respect

Monday, September 9, 2013

When it comes to anatomy, the carpal bones are the Rodney Dangerfield of the skeleton. The two rows of bones that connect the wrist to the hand increase the ability of the wrist to move and rotate but are so forgotten that most doctors can’t remember their names or identify the individual bones on x-ray.  So it comes as no surprise that the injury sustained by New England Patriot running back Shane Vereen was described only as a broken small bone in his wrist, even though the unnamed culprit required surgery.

 

carpal

 

Fractures of the carpal bones are relatively frequent, but since the scaphoid bone (sometimes called the navicluar) accounts for 70% of fractures and the triquetrum another 14%, the other bones get forgotten. However, damage to the lunate and hamate can have significant complications and the diagnosis is often missed immediately after injury. However, the diagnosis can be hinted at based upon the mechanism of injury and even if x-rays are negative, a high index of suspicion for fracture is often maintained by the doctor.

The mechanism of injury for a scaphoid fracture is a fall on an outstretched hand. The scaphoid is located at the base of the thumb. Extend the thumb like an aggressive hitch hiker and two tendons frame the snuffbox, a sunken area so named because English gentlemen would use it to hold the snuff they sniffed. If broken, the area swells and is painful to palpate or feel. X-rays may miss a fracture of this bone (remember that fracture, break and crack all mean the same thing) and if clinically indicated, the doctor may place the wrist in a splint and re x-ray it in a week to look for changes associated with a healing fracture. Sometimes a CT scan needs to be done to find the fracture. Scaphoid fractures tend not to heal well, a design flaw provides the bone poor blood supply and surgery is sometimes required.

The reverse mechanism, falling on a curled up wrist will cause the triquetrum to break. This causes swelling on the back of the hand and x-rays usually show a small fleck of bone in the swollen area. These chip fractures heal well with a little rest. If the body of the triquetrum is damaged, surgery may be required to pin the bone and stabilize it.

The hamate gets no love. It is located between the little finger of the hand and the ulna of the forearm. Fractures occur because of a fall or direct blow or crush injury, causing immediate pain but occasionally patients ignore the initial injury and present late because of decreased grip strength. The initial complication is ulnar nerve damage because of its close location to the hamate. The nerve can stop working, causing the ring and little fingers to become numb, because bone fragments touch it or because swelling associated with the broken bone causes irritation. The later complication is non-union, the same as with scaphoid fractures, meaning that the bone fragments fail to heal….poor design, poor blood flow to the bone. Historically, a hamate fracture was treated by casting and time, but more than half would fail to heal. Now, surgery is often a first consideration.

The lunate is the bone that butts up against the radius and is an integral part of the wrist joint. It can be broken by one direct blow or by repetitive small blows that cause microfractures and eventually, collapse of the bone. This can lead to significant arthritis and may need surgery to repair, replace or fuse the joint. A tear of the ligament that holds together the scaphoid and the lunate in their relationship to the wrist can be torn with a direct blow and can be suspected by subtle changes in an x-ray only if the doctor has that index of suspicion. CT and MRI can help sort out the anatomy and injury.

If this were a game of Clue, we could take an educated guess about Mr. Verren’s wrist injury: a small bone, some nerve involvement, return to play in many weeks. The answer: The hook of the hamate fracture with ulnar nerve impingement, surgery to remove the fragment of broken bone, and 6-8 weeks of physical therapy and rehab to regain range of motion, power and endurance in the hand. Unfortunately, for Mr. Vereen, the game is real and his commitment to rehabilitation is real, even if the bone he broke gets no respect.

 

 

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