Understanding partial knee replacements: risks, procedures and outcomes

The knee joint is complex. It is where three bones meet — the bottom of your thigh bone (femur) and the top of your shinbone (tibia) form a hinge, and your kneecap (patella) sits in the front of your knee joint. Any part of your knee joint can deteriorate due to knee osteoarthritis — a condition that causes wear and tear of the joints over time. In the past, your entire knee joint would eventually need to be replaced (total knee replacement), but thanks to advances in surgical techniques, today, often only the affected part of your knee needs to be replaced — this is called a partial knee replacement. 

Is a partial knee replacement suitable for you?

A partial knee replacement offers a faster recovery time, fewer complications and a more natural feeling than a total knee replacement. However, it is only appropriate if just one part of your knee is affected by osteoarthritis. In more severe cases of knee osteoarthritis, where the condition has progressed to other parts of your knee, a total knee replacement is usually needed.

Around 85% of the patients I see with knee osteoarthritis are suitable for a partial knee replacement, with just 15% needing a total knee replacement.

Risk factors for partial knee replacement

Every surgery comes with risks, such as infection, blood clots, blood vessel damage and nerve damage. Additional risks specific to partial knee replacements include a fracture of the bone around your prosthetic implant and dislocation of your knee joint. However, complications are increasingly rare and can be detected and treated early with good follow-up care. These risks are halved in a partial knee replacement when compared to a total knee replacement.

The procedure for partial knee replacement surgery

There are two types of partial knee replacement surgery — traditional and minimally invasive.

Minimally invasive surgery

Minimally invasive partial knee replacement surgery is often a day case, so you can walk, use stairs and usually return home on the same day as your surgery.

The surigcal cut made over your knee is around a third of the size of the cut made with traditional knee replacement surgery. This means there is far less tissue damage compared with the traditional approach, and this allows for a faster recovery, less pain and less weakness in your knee after your surgery.

Patients who have a minimally invasive partial knee replacement are, therefore, able to get moving just a few hours after their surgery, which includes fully bearing weight on their knee, walking and, in most cases, going up and down the stairs.

As around two-thirds of your natural knee is retained, with only the damaged bone resurfaced, your knee will feel less artificial and more natural after surgery, which aids recovery, movement and return to normal activities.

It isn’t just the minimally invasive nature of the surgery that allows for a quicker recovery and less time spent in hospital. The type of anaesthetic used, the type of pain relief provided for you to take home, careful surgical technique and a strict rehabilitation protocol are also essential.

Traditional surgery

Compared with minimally invasive partial knee replacement surgery, traditional partial knee replacement surgery involves making a larger cut over the top of your knee, removing more bone and cutting out ligament tissue to make space for the larger prosthetic implant. This can result in a longer recovery time with a longer stay in hospital.

Recovering from your partial knee replacement

Recovering from a partial knee replacement progresses in stages. When you are ready to get moving, which with minimally invasive surgery will be within a few hours of your surgery, you will bear weight on your joint, walk and try going up and down stairs with the help of a physiotherapist.

After around five days of recovery, during which time you are encouraged to move around the house and walk, you will return to hospital for a follow-up outpatient appointment. Your physiotherapist will now help you perform exercises to first improve your range of motion, then build up strength in the muscles.

As your recovery progresses, you will need continued physiotherapy to help build up the muscles around your knee, especially your quadriceps muscle as this muscle is cut through during knee replacement surgery. As your swelling settles, your range of motion will improve and you will be able to perform more muscle-strengthening exercises.

After around six weeks, most patients are back to full-time work and their usual day-to-day activities. This includes driving if you can comfortably make an emergency stop — however, you should always let your car insurance company know that you have had knee surgery.

It may take several months to a year for the scar tissue to settle fully and your muscles to build maximum strength.

Outcomes from partial knee replacement

More than 90% of partial knee replacements last for over 20 years, which means that they can last just as long, if not longer, than total knee replacements. Consequently, having a partial knee replacement does not mean that you will eventually need a total knee replacement, which is a common misconception.

Situations where you may need further surgery before the expected lifetime of your partial knee replacement elapses includes if another part of your knee or your prosthetic implant wears away. If your implant wears away, surgery to replace it is more straightforward and less complicated than revising a total knee replacement.

However, with modern technology, prosthetic implants do not wear away easily and are aligned in the knee in such a way as to protect other parts of your knee from becoming overloaded and needing other surgery down the line.

Advances in partial knee replacements

Technology and procedures continue to evolve in partial knee replacements, with smaller cuts needed and implants made of more durable materials. This benefits all patients but especially younger patients with active lifestyles, who can get back to activities they enjoy quicker with partial knee replacements that last longer.