The “Fight Bite” Injury

What is a “Fight Bite?”
This is an injury to the metacarpal-phalangeal joint or to the proximal inter-phalangeal joint as a result of direct puncture of the joint by a tooth. This injury occurs when you punch someone in the mouth, and the knuckle hits the tooth. The injury is potentially serious because of the infection which can set into the joint following penetration by a tooth.

Who gets this injury?
Very few people who present with this injury are keen to report how it happened, so on paper, hardly anyone! In practice, however, this is a common injury and has major consequences for hand function if it is missed or not reported.

What are the symptoms?
Other than the pain from a cut to the hand, there are often no symptoms from this injury for a few days. When early infection sets in, there is usually increased pain, swelling, loss of movement and sometimes pus coming from the wound. As infection proceeds then it can produce a swinging temperature characterised by attacks of shivering.

How is the injury diagnosed?
With a clenched fist, the extensor tendons sit tight over the joints of the hand, and when the fist hits the edge of a tooth, the tooth cuts through the tendon and penetrates the underlying joint. When the fist is then released, the tendons shift in their position such that the skin laceration and tendon laceration no longer match up – this makes the injury one that is often missed by an examiner because the tendon immediately underneath the skin laceration looks normal.

If the hand is then clenched into a fist, the tendon laceration lines up with the skin cut again, and the examiner can then usually see right down to the joint surface.
The injury is usually diagnosed, therefore, by the presence of a laceration of around the width of a tooth over the joint;

A fight bite laceration with early infection

How is a fight bite treated?
The fight bite injury is treated as very high priority – saliva from the tooth that enters the joint is loaded with bacteria which, in this setting, often causes a really nasty infection in the underlying joint. Left untreated, many of these injuries will result in complete destruction of the joint, and sometimes amputation of the finger!
The mainstay of treatment, therefore, is to surgically open up the joint and wash out the bacteria. The surgery is fairly simple, but hugely effective in preventing serious infection. Intravenous antibiotics are also given to kill the types of bacteria often seen in saliva.

Once the joint has been washed out and antibiotics given, the wounds are left open rather than sutured. In some cases, there is complete division of the extensor tendon which pulls the first knuckle joint straight. In most cases, however, there is only partial division of the tendon, and the surgeon will often split the tendon to allow access to the joint. A split tendon will usually work reasonably well following the surgery, so the lack of formal tendon repair does not usually give rise to any major problems. Even when the tendon is completely divided, the resulting loss of ability to pull the finger straight can be surprisingly unimpressive.

What happens after surgery?
– Antibiotics: Intravenous antibiotics are given for 2-5 days after this injury, directly into a vein. Antibiotic tablets are then started and these usually continue for around 2 weeks.
– Mobilisation: Immediate movement of the hand is necessary following this injury. This pumps any collection fluid from the joint out into the dressings, and helps the body clear the infection. In addition, because stiffness of the hand is so common after joint surgery, it is really important to start moving the affected joint in order to preserve movement.
– Wound Management: Because the wound is left open, the wound is inspected every few days, cleaned and re-dressed. Any residual infection will drain into the dressings, and if the wound is failing to progress with healing, a second look operation will be recommended in order to wash out any residual infection. The open wounds usually heal over in 2-4 weeks, leaving a prominent scar, which then fades over the course of several months.

What are the complications of this injury?
Fight bite injuries often present late because they do not initially look very serious. When picked up early, the results of treatment are generally good. Where infection has set into the joint, the results are less predictable, and complications relatively common:
– Stiffness: This is always a risk of a fight bite injury. Where the underlying joint is not damaged, the prognosis is good. Physiotherapy will help with the mobility of the joint, and if stiffness is persistent, then late surgery may be recommended to release the joint. This surgery is usually undertaken at around 6 months after the initial infection.
– Loss of extensor tendon function: Where the tendon has been completely divided, the affected finger usually appears to droop when the hand is out straight. This can be addressed at around 6 months after the initial injury with surgery to reconstruct the tendon. Although many patients initially feel that this will be necessary, by the time the 6 months is up, few patients still want something done about it. Scar tissue forming around the joint tends to contract with time and the dropped finger often finds its own way back into line with the other fingers.
– Joint destruction or arthritis: Where infection has been present in the joint, the cartilage may be irreversibly damaged, and sometimes this damage extends to the underlying bone. This usually results in loss of the knuckle, with degree of pain and stiffness in the affected joint. It can be surprisingly well tolerated at the metacarpo-phalangeal joint, but is usually a disaster at the proximal inter-phalangeal joint. There is no good treatment for this and usually the recommendation is that the loss of function should be accepted rather than any attempt made to intervene. If pain is a real issue, then the surgeon may recommend taking out the joint and using the tissues from around the joint to buffer the bones and allow a degree of movement.
– Persisting severe infection: In around 2% of these injuries, infection spreads into the finger and destroys the bones and tendons. This situation is irreversible, and the surgeon will usually strongly recommend amputation of the affected finger in order to gain control of the infection and stop it spreading up the arm.

© Fife Hand Service 2020

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