Scaphoid fracture

The scaphoid, a small bone on the thumb side of the wrist causes more hassle to patients and surgeons than all the other wrist bones put together. It is an important bone in the wrist, in that it bridges two rows of wrist bones (the carpus) and takes about 60% of the total load. That means that when you put full weight through your hand, such as arising from the bath, the amount of force going through the wrist is equivalent to your full body weight and compared to all the other bones in wrist the scaphoid takes 60% of that weight, hence its importance. It is notorious because fractures of it do not always immediately come to light.

scaphoid-vasc001

It is a common scenario that someone falls onto their wrist, goes to casualty and has a x-ray which is reported as normal and the injury is classified as a sprain and yet later on it is revealed that the scaphoid was actually fractured. When the bone does not heal it is called a non-union. Sometimes the time frame to diagnosis is short but sometimes it may not be made until many years later when arthritis has developed. The reason for this is entirely due to the blood supply of the scaphoid.

If you look at the bone as if you were looking at the back of your hand/wrist, then virtually half of the scaphoid nearest the forearm bone (the radius) is inside the joint (it is called the proximal pole). This means that it is covered by articular cartilage and does not have any soft tissue attachments.In general the blood supply to a bone comes from its soft tissue attachments so the only way the proximal pole can receive any blood supply and nutrients is through the rest of the bone. The articular cartilage can obtain some nutrients from the joint fluid but not much will pass into the bone itself.

Scaphoid-fracture-blood001

Thus if there is a fracture of the scaphoid in the proximal pole or waist where there is little or no soft tisssue attachment, then the blood supply will be damaged reducing the chances of primary healing and increasing the risk of a non-union.

Scaphoid-fracture-blood003

There is now good evidence that smoking delays the healing and there is a much higher risk of non-union in smokers (see general complications section) and the following link.