Revision Knee Replacement: When and Why

A knee replacement is designed to last. For the majority of patients it does, for 20 years or more. But no implant is permanent, and some knee replacements fail before their time. When that happens, revision surgery is the answer. This article explains what revision knee replacement involves, why it becomes necessary, and what patients can realistically expect from it.

KEY TAKEAWAYS

Revision knee replacement replaces some or all components of a failed primary knee replacement

The commonest reasons for revision are loosening, infection, stiffness, instability, and wear

Revision surgery is more complex than the original operation and recovery is longer

Outcomes are generally good but less predictable than primary replacement

Early identification of a failing knee replacement leads to better revision outcomes

Not all pain after knee replacement means the implant is failing, assessment before assuming revision is needed

What is revision knee replacement?

Revision knee replacement is the surgical replacement of one or more components of a knee replacement that has failed or is failing. It may involve:

Replacing only the polyethylene (plastic) spacer, leaving the metal components in place, a partial revision, done when the metal components are still well-fixed and positioned correctly
Replacing all components, the femoral, tibial, and patellar components, when the failure is more complete
Adding metal augments or bone grafts to fill areas where bone has been lost around the implant

The operation is categorically more demanding than the primary procedure. Scar tissue from the first surgery must be carefully managed. The original implant must be removed without causing further bone damage. Any bone loss must be addressed before new components are fitted. The surgery takes longer, typically three to four hours, and requires specialised implants designed specifically for revision use.

Why do knee replacements fail?

Aseptic loosening

The most common cause of late failure, typically occurring 10 to 20 years after surgery. The bond between the implant and bone gradually weakens, causing the implant to shift or rock. Patients describe a deep aching pain that worsens with activity and is sometimes accompanied by a sense of instability or a new clicking sensation. X-rays show a radiolucent line, a gap, forming between the implant and bone.

Infection

Infection of a knee replacement (periprosthetic joint infection, or PJI) is rare but serious. It can occur early, within weeks of surgery, or late, often years later when bacteria from another part of the body (a dental infection, a urinary tract infection, a skin wound) seed the implant through the bloodstream.

Late infection is particularly insidious because it can present with gradually worsening pain that mimics loosening. Blood tests and joint aspiration are used to distinguish infection from mechanical failure. The distinction is critical because the treatments are completely different.

Infection typically requires a two-stage revision: the implant is removed, an antibiotic spacer is placed in the knee for six to twelve weeks, and a new implant is inserted once the infection is cleared.

Instability

If the ligaments around the knee were not balanced correctly at the original surgery, the knee may feel unstable, giving way, particularly on uneven ground or when turning. This can also develop late if soft tissue structures stretch over time. Revision to a more constrained implant, one with a built-in mechanism that provides stability the ligaments no longer can, is the surgical solution.

Stiffness

A small number of patients develop significant stiffness after knee replacement. When physiotherapy and manipulation under anaesthesia have not resolved this, surgical release of scar tissue (arthroscopic or open) may be needed. This is technically not always a revision of the implant itself, but it is a return to the operating theatre for a knee replacement that has not functioned as expected.

Wear and fracture

Polyethylene wear becomes visible on imaging and causes symptoms. A periprosthetic fracture, a break in the bone around the implant, usually from a fall, may require revision if the implant is damaged or if the fracture cannot be fixed with the implant in place.

How is a failing knee replacement diagnosed?

Not all pain after knee replacement means the implant is failing. Pain in the first year is common and usually resolves. Persistent or worsening pain after 12 months warrants investigation.

Assessment typically includes:

A detailed history of how and when the pain started, and how it has progressed
Weight-bearing X-rays compared to post-operative baseline films, changes in implant position or bone are visible on careful comparison
Blood tests: ESR and CRP are markers of infection and inflammation
Joint aspiration: fluid drawn from the knee and sent for cell count and culture to look for infection
CT or MRI in selected cases to assess bone and soft tissue

This assessment determines not just whether revision is needed, but what kind of revision, which directly affects surgical planning and outcome.

What does revision surgery involve?

The surgical approach is similar to the original operation but requires additional planning. Specialised instruments are used to remove the existing implant carefully, preserving as much bone as possible. The bone surfaces are prepared for the new implant, with any bone defects filled using metal augments, cones, or bone graft.

The new implant is often more constrained than the original, meaning it provides additional built-in stability that compensates for any ligament deficiency. Components are longer, with stems that extend further into the femur and tibia to achieve stable fixation in bone that may have been compromised.

Recovery from revision surgery

Recovery from revision knee replacement is longer and more variable than from primary replacement. Most patients are in hospital for five to seven days. Physiotherapy begins promptly but progresses more slowly. The bone and soft tissue require more time to heal around a revision implant.

Full functional recovery typically takes six to twelve months. The end result is generally a knee that is significantly better than the failing one, but outcomes are less predictable than primary replacement, and the degree of improvement depends heavily on the reason for revision, the amount of bone lost, and the patient's overall health and compliance with rehabilitation.

Can revision be avoided?

In many cases, yes, with attention to two things:

Protecting the primary implant: Maintaining a healthy weight, avoiding high-impact activities, attending follow-up appointments, and taking antibiotic prophylaxis before dental procedures all reduce the risk of early failure.

Early presentation when something changes: A knee replacement that has been comfortable for years and then becomes painful deserves prompt assessment. Catching loosening or early infection before significant bone loss occurs leads to a simpler revision with a better outcome. Waiting until the knee is severely damaged makes the revision more complex and the outcome less certain.

Questions patients commonly ask

“My knee still hurts two years after replacement. Does it need revision?” Not necessarily. Pain after knee replacement has many causes, including stiffness, soft tissue problems, referred pain from the hip or spine, and low-grade infection. Revision is decided after a proper assessment, not because pain is present.

“How is infection in a knee replacement diagnosed?” Blood inflammatory markers first, then aspiration of fluid from the joint for cell count and culture. Imaging alone cannot rule infection in or out. This matters because an infected implant and a loose implant look similar to the patient but need completely different operations.

“Is recovery from revision surgery longer?” Yes. The operation is bigger, more bone is involved, and rehabilitation takes longer. Most patients get good pain relief and function, but the result is less predictable than a first-time replacement.

“Can a revision be revised again?” It can, and it is done, but each revision is technically harder and the bone stock is more limited. This is why getting the first revision right, in the hands of a surgeon who does them regularly, matters more than most patients realise.

THE BOTTOM LINE

Revision knee replacement is a more demanding operation than the original, but it is a well-established and effective solution for a failing implant. The key is early assessment when something changes. Pain that develops after years of comfort is not something to wait out. The sooner a failing implant is identified and assessed, the better the options and the better the outcome.

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