About Patello-femoral Joint Replacements

The metal groove of a patello-femoral joint replacement, made by ZimmerBiomet

A patello-femoral joint replacement (PFJR) is a metal groove that covers the end of the femur, with a plastic button on the underside of the patella (knee cap). These implants are suitable for patients with isolated patello-femoral arthritis, where there is no arthritis between the femur and the tibia. This is not common and these implants are used less often than other types of knee implant. At the time of surgery I will inspect the rest of the knee joint and it may rarely be necessary to convert to a total knee replacement.

The worn joint surfaces are shaped to accept the new prosthesis. These come in a variety of sizes to ensure an accurate fit. The prosthesis is inserted using acrylic bone cement to lock the prosthesis to the bone, and the cartilage on the underside of your kneecap will be removed and replaced with a polyethylene button.

The aim of a patella-femoral joint replacement is to relieve your pain, while maintaining or improving your movement. You can expect gradual improvement up to 18 months following knee replacement, although the most rapid improvement is between 6 weeks and 6 months.

An X-ray demonstrating a patello-femoral joint replacement.

Prior to surgery, you will have a pre-operative assessment to ensure that you are fit to undergo the operation. You will also see a physiotherapist, who will show you exercises and teach you to use crutches. On the day of the operation, you will be seen by me and by the anaesthetist before surgery. Your leg will be marked and the consent form signed. The operation itself will usually take around 1 hour. The majority of these operations are carried out under a spinal anaesthetic, where the legs are numb, but sedation can also be given to ensure that you are sleepy.

Following surgery, you will be transferred back to the ward. Pain control is prescribed to allow you to undertake your exercises; please alert the nursing staff if more pain relief is required. You will be seen by the physiotherapists to encourage you to move the knee and start mobilising.

Most patients are able to return home within 3 days, once safely mobilising with crutches and able to climb stairs. You will be able to put your full weight through the operated knee. The knee will be somewhat stiff and sore for the first few weeks following surgery and regular pain relief may be required. It is important to maintain your exercises in these first weeks to ensure a good range of movement of your knee, as well as to decrease the risk of a blood clot. The incision is usually closed with a dissolvable stitch and skin glue, so there are usually no staples or sutures to remove. I encourage patients to keep the waterproof dressing in place for 2 weeks, although showering with the dressing on is permitted.

You will be seen by me or my team at the six week mark to ensure that all is progressing well. An X-ray is not usually required at this visit. If all is well, your next appointment will be at the 6 month mark, with an X-ray at that visit.


Outcomes of Patello-femoral Joint Replacement

All of my joint replacement patients are invited to participate in the National Joint Registry which monitors outcomes of hip and knee replacement. Using this national data, we can predict that approximately 85% of PFJRs are still functioning well after 10 years. Should you develop arthritis in the remaining parts of the knee, or develop wear or loosening of the PJFR, it is usually possible to exchange the PFJR for a standard total knee replacement prosthesis.


Complications of Patello-femoral Joint Replacement

All operations come with attached risks. These can include:


Bleeding – a blood transfusion may be required but this is rare.

Infection – This is a potentially devastating complication and all efforts are taken to prevent this. These include the use of antiseptic skin preparations during surgery, ultra-clean air laminar flow operating theatres with every care taken to maintain sterility during surgery, and the use of antibiotics during and after surgery. Despite this infections can still occur. These may be superficial wound infections which can be successfully treated with antibiotics, but a severe deep infection is likely to need further surgery to wash out the knee, or even to remove and replace the components. The risk of a deep infection is less than 0.5%.

Blood clots – a blood clot in the leg (a deep vein thrombosis; DVT) or in the lung (a pulmonary embolus; PE) is a potentially serious complication. The risk is decreased by giving you blood thinning medication for 14 days following surgery. The most important factor to reduce this risk is getting you mobile as quickly as possible. The risk of a DVT that causes symptoms is approximately 2%; the risk of a PE is 0.5%. If you are unfortunate enough to develop either of these, then blood thinning medication such as warfarin is usually required for 3-6 months.

Knee stiffness – Although relatively uncommon following PFJR, the knee may become stiff following surgery. Manipulation of the joint under general anaesthetic to bend the knee and break down scar tissue within the joint may be required.

Numbness – it is common to have some numbness over the outside of the knee. This is because the small skin nerves running across the knee are cut at the time of surgery. This numbness does not usually cause problems.

Wear – Modern knee prostheses mean that your joint replacement should last many years. If the remaining joint surfaces become worn and painful, then the knee may need to be revised to a total knee replacement.

Revision – Although generally PFJRs have a higher rate of revision compared to unicompartmental or total knee replacements, the majority of patients with them do well. Should your knee ever need to be revised, it is likely that a standard total knee replacement prosthesis can be used.