- Osteoarthritis is common in those with past knee injury/menisectomy.
- Arthroscopic debridement and washout may delay the need for surgery.
- Partial and full knee replacements are constantly evolving.
- The main benefit of total knee replacement is the abolition of pain.
- Research is aimed at replacing osteoarthritic articular cartilage.
1. KNEE DEGENERATION
This week, we are concentrating on the problems encountered as the knee ages. As people grow older, knee degeneration becomes more common.
Osteoarthritis (OA) of the knees is particularly common in patients who have had previous injuries, especially if they had a menisectomy in the past. However, there is evidence that previous sport and exercise do not result in a predisposition to OA, although some activities may cause injuries that in themselves may cause long-term problems.
Taking no exercise at all does not protect people from OA, as evidenced by couch potatoes to whom the merest exertion is an anathema. Such individuals often become obese and suffer from arthritis in their weight-bearing joints as a consequence.
Joint degeneration may present with gradual pain, swelling, a decrease in range of movement and crepitus. In severe cases, a fixed flexion deformity may develop.
With the addition of a worsening varus or valgus deformity, the severity and duration of pain is increased, often waking a patient from sleep.
Unfortunately, hyaline articular cartilage in adults is one of those specialised tissues in the body that cannot repair itself following injury.
Hip pain has a habit of radiating to the knee, and any patient presenting with knee pain deserves an examination of both the hip and knee. Hip movements may not be painful, but they will be reduced in hip pathology.
If arthritis of the hip is suspected, then an X-ray of the pelvis should be taken. This may reveal ipsilateral OA of the hip which should be managed accordingly.
If both the hip and the knee are affected, classical teaching is that the hip should be replaced first.
As with most joint degeneration, conservative measures can be initiated before surgical intervention. Simple analgesia, walking aids and activity modification are all eminently sensible. Physiotherapy may be of benefit, and in certain circumstances joint aspiration and injections including steroids can be useful adjuncts to therapy and can give temporary relief.
- Joint degeneration presents with pain, swelling and reduced range of movement.
- Knee pain is often referred from the hip.
- Hips must be examined and, if necessary, X-rayed.
- Conservative measures can be useful before surgical intervention is considered.
- Joint aspiration and steroid injection can give temporary relief.
2. THE ROLE OF ARTHROSCOPY
There is still considerable debate regarding the value of arthroscopic washout and debridement procedures, especially in the elderly. Many surgeons use them as holding procedures in the belief that they can delay the need for a total knee arthroplasty.
Debridement covers procedures such as drilling of bone, shaving loose flaps of cartilage and chondral abrasion.
Temporary pain relief
In the 1940s, orthopaedic surgeons realised that if a knee was opened and thoroughly washed out, many patients would experience a temporary relief of their symptoms. Unfortunately, recovery was slow due to wound healing after the open procedure.
However, since the advent of keyhole surgical techniques, the procedure has become more popular. By injecting fluid through small portals, an arthroscopic washout procedure can be performed as a day case. The only absolute contraindication is local infection.
Many patients with degenerate knees describe relief of pain lasting from a few weeks to many months. The injection of corticosteroid may have a similar effect, and is often used. When patients have bone-on-bone articulation with full-thickness cartilage loss, the procedures have a poorer outcome in terms of pain relief. Unfortunately, some patients may gain no relief, and occasionally their symptoms are worse.
In 2002, some US surgeons used a control group of patients who were anaesthetised and given a sham operation. Sham patients were found to have similar relief of their symptoms to those who had the real operation. This reminds us that the partial relief of chronic mild to moderate pain is difficult to judge, and there is a powerful placebo dimension.
Arthroscopy certainly provides the surgeon with a remarkable view of the knee joint that is better than from open surgery. There is often a poor correlation between the damage seen on arthroscopy and the patient's symptoms.
The knee can also be examined under anaesthesia. Rough areas of articular cartilage can be shaved, larger loose bodies can be removed, and a symptomatic degenerate meniscus may be shaved back to a clean edge.
Although articular cartilage cannot repair itself, small defects in the articular surface may be filled by fibrocartilage that is attempting to function as scar tissue.
There is some evidence that abrasion to the surrounding articular cartilage during arthroscopy encourages the growth of fibrocartilage. If the subchondral bone is breached to form a microfracture, this allows mesenchymal stem cells, marrow and other factors to form a clot while maintaining bone plate integrity. The clot may then lead to cartilage regeneration.
- The value of arthroscopic debridement and washout is still debated.
- A series of washouts may delay the need for total knee replacement for several years.
- The only absolute contraindication is local sepsis.
- Relief may last for several months, but there is a placebo component.
- Symptoms and arthroscopic appearances do not always correlate well.
3. SUB-TOTAL ARTHROPLASTY
Studies have shown that patients presenting for knee arthroplasty weigh more than those needing total hip arthroplasty. The main problem is that obese younger patients will outlive their prostheses, although the elderly are less likely to outlive theirs.
Advantages The main advantage of a sub-total arthroplasty for younger patients is that if they fail, they can be converted to a conventional total knee replacement. Indications for surgery include symptoms not controlled by conservative measures, worsening deformity and loss of independence. Usually the results are excellent and active movement restored. Infection is the main complication.
There are many designs of partial knee replacement on the market and there is constant evolution of prostheses and associated equipment. Degenerate knees are more heterogeneous in their anatomy than degenerate hips, and the variety of types of prosthesis reflects this.
Uni-compartment replacements There are three compartments in the knee - the medial, lateral and the patellofemoral - and if only one compartment is affected, it is possible to replace just that one. The medial compartment is the most commonly affected part.
Arthroscopy will confirm that the other compartments are relatively well preserved and that the anterior and posterior cruciate ligaments are intact, and any deformity is correctable.
Uni-compartmental replacement is technically more difficult than an ordinary total knee replacement, but the inpatient stay is often much shorter. It may even be done as a day case.
Another approach for younger patients with an isolated area of arthritis is to perform a high tibial osteotomy. The aim of this procedure is to realign a varus deformity in the knee and so spread the loads in the joint.
This may delay a knee replacement by many years. However, very few tibial osteotomies are done and younger surgeons are losing familiarity with the procedure.
Both knee and hip arthrodesis (fusion) used to be common, but hip fusion is now obsolete. When all else fails, knee fusion in 15 degrees of flexion is still occasionally performed. Afterwards there will be no joint movement at all, and this can make life difficult, especially sitting in confined spaces, but many patients are grateful for the relief of pain.
This rather drastic measure may be done where there is uncontrolled septic arthritis, complete joint destruction, neuropathic joints, or failed total knee replacements.
- Obese younger patients may outlive their prosthesis, making sub-total arthroplasty a better choice.
- Results are excellent if infection is avoided.
- Partial replacements can avoid the need for total knee replacement.
- Fusion of the knee can give pain relief to those unsuitable for total knee replacement.
4. TOTAL KNEE REPLACEMENT
Total knee replacements have not been around as long as total hip replacements, but confidence is growing, and the NHS now performs more total replacements of knees than it does of hips.
The great triumph of a successful total knee replacement is that it abolishes pain, but the range of movement is usually not increased beyond the preoperative level. This means a patient with a stiff knee with limited movement but little pain is not a good candidate.
Early prostheses used a metal hinge, such as the Stanmore joint, but did not reflect the complex biomechanics of the real joint, which is not a rigid hinge but has rotational and other components. Most modern knee prostheses essentially involve resurfacing and attempt to replicate the shape and biomechanics of the joint.
How long will it last?
High-demand users will get fewer years out of their knee, and while revisions are possible, the risks increase with each one because good bone is lost each time. The 10-year results of two prostheses, the Kinemax and Insall-Burstein knees, show low revision rates. Overall mortality is comparable to total hip replacement at about one in 400, rising to one in 1,000 in young patients.
About 1 in 1,000 patients are thought to have a fatal pulmonary embolism, therefore prophylaxis with anticoagulants, aspirin and TED stockings is essential.
Early deep infection is about 1 per cent higher in revision surgery and in the immunocompromised. There are also risks of general or regional anaesthesia and damage to neurovascular structures. A patch of numbness below the patella is not uncommon.
Micro-organisms can live on cement, metal and plastic, and it is almost impossible to eradicate infection on a prosthesis using antibiotics alone.
Usually the prosthetic material is removed and an antibiotic-impregnated cement spacer inserted instead. After some weeks, reinsertion of a total knee prosthesis can be considered.
Revision surgery Most knee revisions follow aseptic loosening and component failure, with the patellar component the most likely to fail. Revision is more difficult than primary surgery and involves bone loss.
Patients must have functional extensor muscles, demonstrated by the ability to do a straight leg raise.
Severe neuromuscular dysfunction mitigates against success, and acute sepsis precludes operation. Previous surgical fusion almost always rules out a total knee replacement, and a neuropathic joint is not suitable for replacement.
- Successful total knee replacements abolish pain but do not usually increase range of movement.
- Patients with a stiff knee with limited movement but little pain will gain little benefit from the procedure.
- Overall mortality is comparable to that of total hip replacement.
- Prophylaxis against embolism with anticoagulants, aspirin and TED stockings is essential.
5. ARTICULAR CARTILAGE REPAIR
The holy grail of orthopaedic research is to be able to replace damaged articular cartilage in osteoarthritis, and a number of techniques are starting to provide encouraging results. The simplest approach is to fill a defect using fibrocartilage, and this can be encouraged using the previously described microfracture technique.
Chondrocyte transplantation However, the definitive method is chondrocyte transplantation. This procedure involves harvesting a patient's cartilage cells arthroscopically and sending them to a laboratory to be cultured. Once sufficient cells have been produced they are implanted in a gel, and introduced into the defect under a periostial seal. They then implant and produce fibrocartilage which, it is claimed, changes over the course of the next three years into a more hyaline-like configuration.
These procedures are subject to NICE guidelines that were published in May 2005 and are not available on the NHS, but a small number of centres are testing them.
Mosaicoplasty is another way to try to deal with chondral defects, and involves harvesting cylindrical osteochondral plugs from a non-weight-bearing area in the knee and implanting them into areas within the defect.
The intervening small, bare areas fill with fibrocartilage.
Some good results have been obtained, especially with isolated chondral defects of appropriate size and position in the knee.
Hyaluronic acid Patients may ask about hyaluronic acid injections for arthritic joints.
Patients receiving weekly injections anecdotally report marked improvement.
However, some trials have produced results that are less than flattering, and there is some debate about whether they are really effective. One point that carries weight is that although they cost about £100 each, they are cheaper than an arthroscopic washout.
- Various methods of replacing articular cartilage are on trial.
- Chondrocyte transplantation has received the most attention.
- Mosaicoplasty transfers plugs of cartilage from non-weight-bearing areas in the knee to a defect.
- These procedures are not available on the NHS.
Cutts S, Edwards A and Price R. Primary Care Orthopaedics. RCGP (2004)
See Medicine on the Web, page 32.
Previously in Clinical Review
You can print an A4 copy of any Clinical Review published in the past year by logging on to GPonline.com. Recent issues have covered:
Knee problems, part one (16 June)
- Gastro-oesophageal reflux disease (9 June)
- Dealing with long-term illness (26 May)
- Ovarian cancer (19 May)
NEXT WEEK: Headache - part one, by Dr Andy Dowson.