THUMB MP JOINT
What is the thumb MP joint and what problems occur?
The MP joints are the first obvious joint of the thumb where it joins the hand. They are shaped as a dome on the hand side and a shallow curve on the finger side. This allows mobility in sideways and twisting movement as well as bending and straightening. It also means that the joint is generally forgiving of injury except when instability occurs (this is aside from fractures that are described in the fracture section).
The common problems are related to wear and tear arthritis(osteoarthritis) and instability. (Problems in rheumatoid arthritis are described in the section on inflammatory arthropathy/rheumatoid arthritis).
Arthritis(osteoarthritis): Arthritis is either primary i.e. occurring for no obvious reason or secondary i.e. occurring due to an underlying cause. The most common cause of secondary arthritis is previous injury particularly a fracture (break) into the joint (intra-articular).
Patients typically present in later middle age (50+) with gradually increasing stiffness/pain. They main run together or one or other may predominate. Sometime the symptoms will come on quite quickly following a sudden injury which may be quite mild but then tips the elbow over from being potentially symptomatic to being symptomatic. The symptoms may increase giving marked disability due to restricted movement and pain both at night and in the day.
Instability: The shape of the joint (described above does not resist side to side movement. This is important as the thumb needs to resist the pinch forces of the fingers or it will collapse and there will be no useful pinch. The main important ligaments around the thumb are the ligaments at the side, the radial (outer) and ulnar (inner i.e. hand side) collateral ligaments and to a lesser extent the palmar (volar) and dorsal (over the back) ligaments. They are typically damaged following a fall although can gradually wear out due to overuse (the classical gamekeepers thumb where the instability was though to be due to breaking birds necks repeatedly. This is now rare. If treated promptly and accurately there should be few problems (see information sheets on trauma) but if the treatment fails or is never undertaken the instability may occur. The patient typically complains of weakness and discomfort in the thumb. In time (years to decades) this may progress to MP joint arthritis.
Thumb MP joint arthritis
Why does it occur?
Arthritis: Normal joints are lined with articular cartilage and lubricated with a little bit of fluid that is continually renewed. Either due to general wear and tear, an inherited tendency or a structural abnormality in a joint such as a previous fracture (break) or operation the lining of the joint thins and may wear away leading to bone rubbing on bone. This is not necessarily painful but may be. The joint tries to protect itself by forming a little more new bone at the edges and producing more joint fluid. These lead to stiffness and deformity. Sometimes the spurs of bone at the sides of joint trap the ligaments and the finger catches when it bends.
Instability: When the ligament restraints are weakened or fail the thumb can often maintain some useful grip or pinch through the strength of the other soft tissues. Gradually they weaken and the thumb becomes more unstable with increasingly abnormal wear of the joint cartilage.
What happens if nothing is done?
(This is referred to as the natural history i.e. what happens if Nature runs its own course.)
Arthritis: Some people's symptoms resolve, even though the arthritis persists, especially if the activities that cause pain are avoided. Most people develop more stiffness with time but if there is not much pain they are generally not too troubled. A small percentage of patients develop marked pain and increasing disability in their hand affecting both dexterity and grip strength.
Arthritis: Some people's symptoms resolve improve with activity modification but almost inevitably the symptoms will recur and increase without treatment.
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 the wrists and hands. Stressing i.e. pushing on the affected joint is usually uncomfortable. It is necessary to demonstrate some tenderness to confirm the site of the symptoms 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.
The diagnosis is usually obvious after listening to and examining a patient. Typically an X-ray is requested on the same day to delineate the extent of joint damage, although the X-ray findings do not correlate well with the symptoms with some patients having few X-ray changes but marked symptoms and vice versa.
Thumb MP joint arthritis
What are the non-operative treatments?
Treatment should start with non-operative options. The first step is activity modification which the patient may well already have tried. 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 splint for certain activities can also be of value particularly for instability. If these measures are insufficient then a steroid injection would usually be recommended particularly for arthritis but also for instability where pain rather than weakness is the main symptom. 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 of benefit although may still have some mild on-going symptoms. If one injection provides only short term benefit then it may well be repeated for arthritis but probably not for instability. 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 any further injections will be successful and most surgeons would recommend an alternative approach. If, however, injections are only required infrequently, perhaps once every 2-3 years, then having a fourth or fifth injection would, in themselves, be a lot safer than having an operation, and if they give benefit this is reasonable. There are risks. 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?
For arthritis the 2 main operations are either to clean out the joint called: MP joint debridement or with more severe disease: MP joint fusion (arthrodesis) (joint replacement is not typically undertaken for this joint as patients typically tolerate a stiff thumb MP joint very well):
MP joint debridement is the first step in a joint replacement so the second is simply an extension of the first. The operations are performed local anaesthetic.
The surgeon makes a cut over the back of the joint. The joint is opened up and cleaned out. If the joint cartilage is suficiently worn the surgeon may fuse the joint. At the end of the operation the deep tissues are closed and the skin is then stitched up usually with absorbable stitches. A supportive dressing is applied and the patient's arm elevated.
The total time in hospital is usually 2-4 hours.
MP joint fusion obliterates the joint creating a solid bony link between the bones. This is stable, usually painless and very functional. The operation is performed under local anaesthetic. The surgeon makes a cut over the back of the joint. The joint is opened up and cleaned out. The thickened bone ends are trimmed to bone tissue with better healing tendencies. The bones are fixed together with a screw or wire construct. At the end of the operation the deep tissues are closed and the skin is then stitched up usually with absorbable stitches. A supportive dressing/plaster of Paris is applied and the patient's arm elevated.
The total time in hospital is usually 2-4 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 patient is reviewed in clinic in the first 2 weeks following the operation. Typically dissolvable stitches are used so they should not require to be removed. A splint may be provided by the physiotherapists particularly following joint replacement. Careful follow up is required to ensure a successful result with good relief of pain and a good range of movement.
The hand can be used for gentle activity after the next few days. Most of the movement gained following surgery occurs in the first 6 weeks and this time must be used productively to ensure a good result. The key is regular long gentle stretches both into straightening and into bending. Ideally these should be performed for 5 mins in each direction (feeling the stretch but without pain) once an hour. In practical terms most people mange 5-6 times a day. Elevation and icing the elbow also help reduce swelling and thus pain and improve movement.
Most patients can drive after a 2-3 weeks (slightly longer after fusion). Most patients return to work in 5-6 weeks, but this varies with occupation; heavy manual work usually takes about 3 months if ever. 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 pressing heavy use of the hand for a good 3 months from surgery.
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 a reasonable range of movement. Some patients develop recurrent symptoms following debridement and require reoperation.
Are there any risks?
All interventions in medicine have risks. In general the larger the operation the greater the risks. For thumb MP joint debridement and fusion the risks 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. For joint fusion there is a risk of failure to achieve bone to bone union of to gain union with some malalignment. Either may (but not of necessity) require reoperation.
- 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.