Knee Replacement Surgery


Arthritis is pain from a joint. It can be caused by a number of things, but most commonly it simply develops over time as a result of normal wear and tear.

Arthritis can broadly be divided into Osteoarthritis which is mechanical wear and tear, and Rheumatoid Arthritis, which is caused by the body’s own immune system attacking a joint.

While arthritis technically just means “joint pain” it is commonly used to describe the condition where a joint becomes painful, stiff and deformed as the normal joint cartilage wears away. In bad arthritis a patient can even begin to wear away the bone itself. 

Sometime knee osteoarthritis can develop as a result of a joint fracture or injury in the past, or as a consequence of a joint infection. For some people it runs in their family, and we are still discovering the genetic factors that can contribute to arthritis.

Knee arthritis can involve the joint spaces between the thigh bone and the shin bone, or between the shin bone and the knee cap. Commonly there is a component of both of these wear patterns.

Most people who develop knee arthritis will start to become “bow legged” as they wear out the cartilage on the inner half of the knee joint – a condition we call “Varus” alignment. A smaller proportion of patients will predominantly wear out on the outer half of the knee joint, and will become “knock knee”, or valgus. While each of these do have associated soft tissue deformities, the surgical treatment and outcomes are essentially the same.

Treatment Options

Rheumatoid arthritis is often diagnosed before there is significant and irreversible damage to a joint. It is generally managed with medicines by a GP and a Rheumatologist, and the newer generations of diagnostic blood tests and medicines for treating rheumatoid disease are extremely effective at preventing progression of joint damage. Patients may still progress over time to needing surgery, but this may be from simple wear and tear rather than the immune destruction of joints that we saw in the past.

Osteoarthritis is initially managed with non-surgical treatments. This commonly includes simple pain killers like paracetamol and anti-inflammatories. Physiotherapy can help, by keeping joints mobile and maximising the strength and coordination of the muscles that move and stabilise the painful joint. Some patients with knee arthritis are suitable for specialty knee braces to correct the alignment of a knee with early to moderate degeneration, to reduce pain and slow progression of the wear. Moderate, low impact exercise is important for cartilage health, as well as general mind and body fitness, and should be continued as much as possible. Maintaining a healthy diet and weight will mean the joint has less to carry around, and weight loss can often extend the lifespan of a joint with early arthritis by many years.

Finally, when the non-surgical treatments aren’t working, surgical treatments can be can be considered.

Knee Arthritis Surgery Options

Some patients who are typically younger (in their 40’s or 50’s) and who are still in physically demanding jobs may be suitable for an operation called an osteotomy. This involves making a cut on the shin bone or thigh bone near the knee joint, and then using a plate a screws to move that cut so that the overall mechanical axis of the leg is altered. This will cause the knee to put more force through the healthy side of the knee and offload the arthritic side. This typically delays the need for a knee replacement for 8-10 years in most studies.

Other patients who have only one section of the knee worn may be suitable for a partial, or “unicompartmental” knee replacement. Most studies suggest something like 1 in 8 arthritis patients have knees suitable for this type of surgery. Partial knee replacements are faster to recover from, and once healed are typically reported to function more like an original knee. Unfortunately however they are also much more likely to need further surgery than a total knee replacement, and the main reason for this is simply that one of the other sections of the knee will wear out and become painful enough to need treating.

Finally, a total knee replacement is a generally very effective and commonly long lasting options to treat painful arthritis.

When to have a knee replacement

A knee replacement is a routine and successful operation, but it is still major surgery with rare but serious potential complications, and should not be done until the expected benefits outweigh the risks. 

Patients will reach the stage where their knee will prevent them walking any significant distances, will wake them at night, cause them pain most days, and simple pain killers like paracetamol and anti-inflammatories will no longer be enough to control the pain symptoms. It becomes hard to sit in a chair or a car for long periods, patients have troubles going up or down stairs, kneeling or squatting, and they limp heavily when they first stand up to start walking. 

Recreational activities, tasks around home and work, and dressing and washing become challenging. 

When the knee is beginning to make life a misery, that is when knee replacement should be considered. 

What is a knee replacement

A knee replacement operation involves removing the worn out sections of the knee joint and replacing them with artificial parts.

Roughly 1cm of bone and cartilage is removed from the shin (tibia), thigh (femur) and the underside of the knee cap (patella). Metal implants are attached to the femur and tibia, and high density polyethylene plastic sections sit in the space between those metal parts, and are attached to the patella. These can then move smoothly over each other like the original knee cartilage would have.

The metal and plastic parts come in a variety of sizes, and are matched individually to each patient during the surgery. This allows adjustments to be made to maximise movement and stability for each patient’s anatomy. The amount of bone that is cut off is also customised for each patient using computer navigation or robotic assistance systems to gauge the amount of knee bend, and the stability side-to-side and front-to-back.

Broadly there are two ways that the implants can be held in place. An acrylic cement can be used to create a strong connection between the bone and the replacement parts – this is called a cemented knee replacement. It is still the most common way to hold the implants in place. In particular, it provides excellent longevity of the implants in those who are older and with softer bone. The alternatively is called an Uncemented or Porous knee replacement, where the implants have a rough under surface that allows the bone to grow onto and permanently attach to the implants, creating a biological attachment.

The knee replacement experience

Knee replacement begins with a consultation with me at the clinic. I ask you about your knee and your health, examine your knee, and look at the xrays and scans your GP has done. I discuss what stage your arthritis is at, and what non-surgical or surgical treatment is best for you. 

Some patients have early stage arthritis and either do not need a surgery yet, or just need a less major arthroscopic keyhole procedure.

If a knee replacement is the best option I explain the process, the risks and the usual benefits of knee replacement surgery. We complete the booking and consent process and I give you forms to get blood test and additional xrays done, if they are necessary for surgical preparation.

On the day of the surgery you come to the hospital to be admitted. The anaesthetist will talk to you and discuss what anaesthetic is safest and best for you personally. Common options include a spinal anaesthetic combined with sedation, or a general anaesthetic. The anaesthetists are the trained and experienced experts at this and will guide you to the safest option, taking your experiences and preferences into account.

The operation usually takes roughly an hour and a half, and afterwards you are in the recovery area for another 30-60 minutes before going up to the ward. Most patients spend 2-5 days in hospital after the surgery before going home. You can go home when your pain is controlled with tablet painkillers, and the physiotherapists think you are walking safely and can get yourself out of bed, into the shower, and on and off the toilet safely. This is most commonly on the third day after the operation. 

On the first day after the operation we get blood test and an xray done to double check the position of the replacement parts. The physiotherapists assess you and take you for a supervised walk. The nurses will help you shower if you want. 

What are the outcomes?

Knee replacement surgery is generally very successful surgery at treating pain. It doesn’t alway completely remove all pain – occasional aches, like a normal knee, can continue to occur from time to time. This is normal, but the constant intrusive pain from the arthritis is usually removed.  

A knee replacement is not really designed to be run on regularly for exercise, but pretty much any other moderate physical and social activity is fine. Walking, swimming, cycling, hiking, bowls, golf, tennis, all are fine if you want to return to them.

Patients who had pain or difficulty kneeling before having a knee replacement may not necessarily find that they return to being able to kneel afterwards, but there is no mechanical reason you should be unable to kneel or squat with a knee replacement if you want to.

Depending on the age you are when you have a knee replacement the risk of wearing the knee out varies, but even in very young active patients we can generalise that 9 out of 10 knee replacements will still be functioning well 10 years after the surgery. 

What are the risks?

As with any surgery, knee replacement has risks which we cannot always prevent or avoid. 

Serious complications are rare, but include events like heart attacks or strokes during the surgery, infections in the replacement pieces, or even death during or after the operation. 

More minor complications are more common, but also temporary or fixable, and include things like:

  • The operated knee being stiff enough that additional procedures are required in order to get an acceptable range of bend.
  • A fracture during the operation that requires fixing
  • Injuries to ligaments or tendons that require repair. 
  • Injuries that cause nerves to stop working normally, temporarily or permanently
  • Shallow infection at the surgical scar. 
  • A scar that is over-sensitive, or which is raised or discoloured after healing.
  • Altered skin sensation near the scar that can be temporary or permanent
  • Clots in the veins of the legs, or clots that form on the lungs. 
  • Pneumonia, stomach ulcer, or temporary bowel obstruction in response to the surgery.

In the long term the replacement pieces can wear down or work themselves loose, requiring further surgery. A major injury like a fall or a car crash can fracture around the replacement and require further surgery. Any infection that gets into the blood stream in the future can settle around the replacement pieces, and this can require further surgery. Sometimes some of the tendons around the knee will get inflamed in response to the replacement pieces and require treatment, which sometime is surgical. 

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