What is the carpal boss?

The is a moderately common condition of a small area of wear and tear arthritis (osteoarthritis – OA) at the back of the CMC (basal) joints of the index or middle fingers.

The typical symptoms are of a hard swelling on the back of the hand which is often mistaken for a ganglion (see information sheet) which may be painful but usually is not. It usually presents in young adult (20s and 30s).

Large carpal boss top view

Why does it occur?

The pathology i.e. the abnormality is of a limited area of arthritis at the back 1/3 of the joint. In essence the articular cartilage lining at the back of the joint thins and spurs of new bone are formed as a natural response by the joint. This causes the bulk of the prominence although sometimes there will be local soft tissue thickening also causing some swelling. Normally the index and middle finger CMC joints have limited movement unlike the more mobile ring and little finger CMC joints. The index and middle finger CMC joints have quite a keyed in close fit. This may be why this occurs. Why it does not occur in most people and generally is not painful is unclear.

What happens if nothing is done?

(This is referred to as the natural history i.e. what happens if Nature runs its own course.) Most people are only troubled enough if they have pain. Usually this settles with time or simple treatments (see below). Only occasionally is this a significant problem.

Making the diagnosis

The Hand specialist who sees the patient will ask questions about their symptoms, when they started, how they progressed, what treatment (if any) they have had and other questions relevant to the problems. They will then examine the patient looking at their wrists and hands. It is usually necessary to demonstrate some tenderness to confirm the site of the symptoms by pressing around the area but this should not be too painful.

What test(s) might be performed?

Tests (also known medically as Investigations) include X-rays, scans, blood tests and particularly in the hand electrical tests (known as EMGs or Neurophysiology). These may be used to help make or confirm a diagnosis after a patient has described their symptoms and been examined.

With a carpal boss the diagnosis is usually obvious after listening to and examining a patient. Typically an X-ray is performed the same day to show the area of osteoarthritis and bony prominence.

The other possible causes of the symptoms are a ganglion but this probably comes from an arthritic CMC joint.


What are the non-operative treatments?

Treatment should start with non-operative options. The first step is activity modification which usually helps as the pain often only occurs with a few activities. Pain killers (analgesics) particularly anti-inflammatory analgesics, such as Ibuprofen (Nurofen) and Diclofenac (Voltarol) can be very helpful for the pain. These can be applied as a gel, massaging the area, or taken orally, assuming there is no history of indigestion. A wrist splint for certain activities can also be of value. If this is insufficient then a steroid injection would usually be recommended. An injection is given of a long-acting steroid, such as Depomedrone or Triamcinolone, with some local anaesthetic into the joint at the bottom of the thumb.  The body naturally produces steroids to help dampen down inflammation. This appears to be one of the actions at this site.  Success cannot be guaranteed but in 70-80% of patients there is some significant benefit.  How long this lasts is unpredictable.  Some people only have a few weeks or months of benefit.  Others may have years or even life-long benefit such that they do not require further treatment, although may still have some mild on-going symptoms.  If one injection provides only short term benefit then it may well be repeated.  Patients often ask how many injections can be given.  There is no set rule about this. Typically, however, a second injection will work a little less well than the first (although this is not inevitable).  By the time three injections have been given, if this is over a shortish period, i.e. less than 1 year, then it is unlikely the third injection will be successful and most surgeons would recommend an alternative approach.  There are risks from steroid injections but generally they are small. The biggest risk is of failure. There are risks of some pain for a few days, although that is usually minimised by taking pain-killers, starting while the area is still numb from the local anaesthetic.  In theory there is a risk of infection, but this seems very rare and has not occurred in our Practice in over 10 years.  The main other risk is some thinning of the skin. This can present with some pallor and a little less bulk at the site and occasionally an increased tendency to bleeding if the area is knocked.  This is not common with this injection but is common with some other injections.  If it does occur then that is a relative contra-indication to further injections, i.e. the patient’s surgeon would probably decide not to go ahead with further injections because of the risks of further local damage.

What does the operation involve?

The operation is called excision of carpal boss. It is only required infrequently. The operation is almost always performed under local anaesthetic. A band, like a blood pressure cuff, is placed around the top of the arm. It is inflated (tightened) during the operation to reduce bleeding, which makes the operation easier and safer.  It can be a little uncomfortable, but is almost always well tolerated for the 15-20 mins or so that it is inflated (this happens just before the surgeons starts the operation). Before that the arm is painted with an antiseptic with a pink dye in it. This is used to help minimise the risk of infection.

The surgeon makes a 2-3 cm cut across the back of the hand over the swelling. The abnormality is found and the arthritic part of the joint and any soft tissue swelling cut out (excised).  The skin is then stitched up usually with absorbable stitches. A supportive dressing is applied and the patient’s arm(s) elevated.

The total time in hospital is usually 2-3 hours.

What happens in the next few weeks?

The care of the hand in the post-operative period is very important in helping to ensure a good result. Initially the aims are comfort and elevation. These are met by keeping the hand up (elevated) especially in the first few days and by use of a long acting local anaesthetic (Bupivicaine). The local anaesthetic lasts at least 12 hours and sometimes 48 hours. Patients should start taking painkillers before the pain starts i.e. on return home and for at least 24 hours from there. This way most of our patients report little or any pain.

The bandage can be removed after 2-7 days, leaving a sticky dressing beneath. The patient or GP practice nurse can do this. If well healed at that stage then the wound can be left open (exposed). If in doubt it can be covered with a light dressing for a few more days.  The patient is reviewed in clinic between 2-4 weeks following the operation.  Typically dissolvable stitches are used so they should not require to be removed.

The hand can be used for normal activity after the first few days.  Most patients can drive after a 5-7 days.  Most patients return to work in 1-2 weeks, but this varies with occupation; heavy manual work usually takes about 4-6 weeks. The wound should be massaged by the patient 3 times a day with a bland soft cream for 3 months once the wound is well healed (typically after 2 weeks). This reduces the scar sensitivity which can be a nuisance. If this is marked a Physio may be organised to help reduce the scar tenderness but this is rarely required. Patients should avoid heavy gripping until the hand is comfortable.

What are the results of the operation?

At least 85% of patients in studies say they have a good or excellent result following this operation, with relief of the pain and swelling. It may however take several months to achieve a good result.

Are there any risks?

All interventions in medicine have risks. In general the larger the operation the greater the risks. For carpal boss the risks are small but include:

  • The scar may be tender, in about 20% of patients. This usually improves with scar massage, over 3 months.
  • Aching,at the site may last for several months
  • Grip strength can also take some months to return to normal.
  • Stiffness may occur in particular in the fingers. This is usually short-term and only infrequently requires physiotherapy. But it is very important that it is resolved quickly to avoid permanent stiffness. This occurs rarely but can do associated with CRPS (see below)
  • Numbness can occur around the scar but this rarely causes any functional problems.
  • Wound infections occur in about 1% of cases. These usually quickly resolve with antibiotics.
  • Recurrent swelling and pain is reported but has never occurred in our practice.
  • Chronic Regional Pain Syndrome “CRPS”. This is a rare but serious complication, with no known cause or proven treatment.  The nerves in the hand “over-react”, causing swelling, pain, discolouration and stiffness, which improve very slowly.
  • Any operation can have unforeseen consequences and leave a patient worse than before surgery.

Large carpal boss excised – wound closed at the end of the operation