When arthritis wears away the knee cartilage and the pain becomes unbearable, it could be time to consider joint replacement. In practice, that often means TKA (total knee arthroplasty) – an operation that swaps out the whole of the damaged joint for a new, artificial implant.
But a patellofemoral knee replacement? That’s a slightly different operation. As the name suggests, this type of replacement surgery focuses on a very specific part of the knee – the patella, or kneecap.
So how does the procedure work – and who would it be appropriate for?
How does patellofemoral arthritis affect the knee?
As you probably know, osteoarthritis is what happens when the smooth cartilage on our joints breaks up or wears away, either through injury or long-term wear-and-tear. Quite often, the damage is spread across the knee. But sometimes – in about 10% of cases or fewer – it’s concentrated in the front ‘compartment’ of the knee: the patellofemoral joint. This is where you lose cartilage on the underside of your kneecap and along the trochlea, a groove in the thighbone that allows your knee to flex and extend smoothly.
What does patellofemoral arthritis feel like?
Patellofemoral osteoarthritis tends to cause isolated pain at the front of the knee, especially when crouching, walking up or down stairs and slopes, or after sitting or lying down for an extended period of time, or getting up from a low chair. It can also cause swelling, stiffness and instability, where the knee gives out during activity. Patellofemoral arthritis often has its origins in a previous injury (such as in a high-impact car crash), a naturally unstable kneecap, or because of malalignment in your leg.
How does patellofemoral knee replacement work?
A patellofemoral prosthesis is much smaller than a TKA implant. It comes in two parts: a shiny metal component that sits against the thighbone (femur) and a polyethylene (high-density plastic) button that covers the rear surface of the kneecap. To place the implant, the surgeon removes small sections of cartilage damage from both bones before fixing it in place with cement. The operation happens under a general anaesthetic and usually takes about 40-60 minutes.
What are the advantages of a patellofemoral knee replacement?
A patellofemoral implant is a type of partial (or unicompartmental) knee replacement. Partial knee replacements have a number of benefits. Firstly, they’re less invasive, because we’re removing less material from the knee and resurfacing a smaller section of the joint. That generally means less time in hospital, a shorter recovery time and, potentially, the ability to return to a wider range of activities when everything has healed. This is one reason why patellofemoral replacements are popular among younger, very active patients. (You can find out more about partial versus total surgery in this article: Partial or total knee replacement? Understanding the differences.)
Is a patellofemoral replacement right for me?
The time to seriously consider knee joint replacement, whether partial or total, is only when alternative treatments – such as painkillers, anti-inflammatory injections, cartilage repair, and activity modification – have been exhausted. If we suspect you have significant osteoarthritis damage in your kneecap, we can confirm it using X-ray or MRI scans. This will also tell us if the rest of your knee is well preserved – ie, there’s little or no cartilage damage in the inner and outer compartments of your joint. If you’re otherwise fit, healthy and active – and want to remain as active as possible in the years to come – you could be a good candidate for the implant. Patellofemoral knee replacement may be a relatively uncommon procedure but, in the right circumstances, it can be a very effective solution to painful knee arthritis.
Further reading on knee replacement surgery
Looking into the options and alternatives? You may find these articles helpful
What causes a painful kneecap?
Case study: Ed’s partial knee replacement with robotic surgery
Knee resurfacing or partial replacement – what’s the difference?
The extraordinary Lindsey Vonn: Pro skiing… after a knee replacement
Why robotic surgery can be a good option for partial knee replacements
