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Knee · Painful replacement

Does your knee replacement still hurt?

Person seated on a bench, one hand resting on a knee that has been replaced

A knee replacement that still hurts six months after surgery usually has a cause that can be found. The common ones are infection, a loose or worn implant, a knee that is too tight or slightly rotated, a stress reaction in the bone, or pain coming from the hip or back. Dr Yas Edirisinghe, specialist orthopaedic surgeon in Adelaide, works through these in a fixed order. He explains what he finds in plain language.

Ask Dr Yas a questionTake the 2-minute knee check
Person seated on a bench, one hand resting on a knee that has been replaced
More than 200hip and knee replacements a year — a volume the Australian joint registry classes as high1
Around 50revision knee operations a year. The UK guideline sets 15 a year as the level for a specialist revision surgeon; fewer than 1 in 10 surgeons who do revisions reach it2,3
Director of Orthopaedic Surgeon TrainingNorthern Adelaide Local Health Network
Plain-language answersyour scans on the screen, explained so they make sense
In short
  • About 1 in 5 people are not happy with their knee replacement. That is a lot of people, and many of them are simply waiting for it to come good.4,5
  • Most painful knee replacements have a cause you can name. Finding it takes the right tests, in the right order.
  • “Wait and see” is a fair plan for the first six months. After that, it is worth finding out why.
  • Some of the patients Dr Yas sees are sent by their surgeon or GP. Most come on their own, wanting a second set of eyes.

Is it just too early?

Sometimes, yes. A knee replacement is a big operation, and the knee keeps changing for a long time afterwards.

Most of the improvement happens in the first three months. After that the gains are slower, but they are real: on the Forgotten Joint Score — a questionnaire that measures how often you forget you have an artificial knee, where a higher score is better — the average person scores about 59 out of 100 at six months, 72 at one year and 76 at two years.6,7,8

So the knee will keep feeling more natural for a year or two. What it should not do is stay painful. By six months you should be clearly better than you were before surgery, off regular painkillers, and mostly forgetting about the knee.

If you are not, it is worth finding out why. That is the point where Dr Yas likes to take a look.

D3 — Recovery after knee replacement: Forgotten Joint Score rises steeply to three months then flattens; 59 at six months, 72 at one year, 76 at two years FORGOTTEN JOINT SCORE (higher is better) 0100 3 months 6 monthsworth finding out why 59 72 76 6 months1 year2 years Average scores out of 100.
Person walking outdoors a few months after knee replacement surgery

“Six months post-op and still in pain? That isn’t just part of the process.”

What the pain is telling you

What you noticeWhat it often points to
Pain when you first stand up, easing after a few stepsThe implant may be loose in the bone
Pain at night or at rest, a warm or swollen kneePossible infection — even a slow, low-grade one
The knee gives way or feels unsteady on stairsThe knee may be too loose, or slightly rotated
You can’t bend it far, and it feels tight or “full”The knee may be too tight, or scarred
Pain on the outside of the knee when walkingA tight band (the iliotibial band) rubbing on the implant
The same pain you had before surgery, in the same placeThe pain may never have been coming from the knee

Why 1 in 5 knee replacements disappoint

In a study of 1,703 knee replacements, 19% of people were not satisfied a year later. The strongest reason was that the surgery did not meet what they expected — pain relief and function fell short.4 Reviews of the world literature land in the same place: about one person in five.5

When knees are taken out and redone, the reasons are mostly the same few. In one series of 781 revision operations, the implant had come loose in 40%, there was infection in 27%, the knee was unstable in 8%, the bone had fractured around the implant in 5%, and the knee had stiffened with scar in 5%. Infection was the commonest reason in the first two years; loosening the commonest reason later on.9

Balance matters more than most people realise. In one study, surgeons used a tiny sensor inside the knee during surgery to check that the ligaments were evenly loaded. When the knee was balanced, 97% of patients were satisfied a year later; when it was not, 82% were.10

Two honest things about surgeon experience. Surgeons who do a lot of knee replacements have fewer complications and fewer redo operations — the Australian registry’s own high-volume band starts at 100 knee replacements a year.1,11 But experience does not guarantee a happy knee, and nobody’s does. What it buys you is a lower chance of complications, and someone who has seen the unusual problems before.

Dr Yas performs more than 200 hip and knee replacements a year — a volume the Australian joint registry classes as high — and around 50 of those are revision knee operations: knee replacements that have failed or never felt right. In the UK, where revision knee surgery is organised into specialist networks, the national guideline sets 15 revisions a year as the level for a specialist revision surgeon, and fewer than one surgeon in ten who does revisions reaches it.1,2,3

D4 — Why revised knee replacements hurt: loosening 40%, infection 27%, instability 8%, fracture 5%, stiffness 5%, other 15% WHY KNEES ARE REDONE (781 revisions) 781revisions Loose implant 40% Infection 27% Unstable 8% Fracture 5% Stiff, scarred 5% Other 15% Infection is commonest in the first two years; loosening later on.

Dr Yas’s 7-Step Check: how we find the cause

There is a reason the order matters. Some causes hide behind normal tests. Some can be made worse by treating the wrong thing first. So Dr Yas works through the same seven steps, in the same order, for every painful knee replacement — and writes down what each one found.

Dr Yas Edirisinghe reviewing knee scans on screen with a patient
Step 0

Listen, then examine.

Where does it hurt? When did it start — has it hurt since the operation, or is this new? What kind of pain is it: sharp on standing, aching at night, giving way, catching? Your story narrows the list before a single test is ordered. Then a careful examination of the knee, the hip above it and the back behind it.

Step 1 · Infection

Rule out infection.

Every painful joint replacement is treated as possibly infected until proven otherwise. We start with two blood tests, CRP and ESR, which rise when there is inflammation in the body. But a normal result does not clear you. In one study of 215 proven infections, the CRP was normal in more than a third — and almost all of those were slow-growing bugs that barely raise the blood tests at all.12 That is why, if the knee has been painful for months, the next step is to look inside the joint. Fluid drawn off with a needle is a start, but the slow-growing bugs live in the lining of the joint, not the fluid, so often what is needed is a tissue sample — several small pieces of the lining, taken through a keyhole procedure and grown in the lab for two weeks. In one study, fluid alone found 7 in 10 infections; tissue found all of them.13,14,29

Blood test tubes and a request form laid out on a table
Culture plates growing in a microbiology laboratory
Step 2 · Imaging

Is the implant loose or worn?

Plain X-rays are taken standing, with a long view of the whole leg and a view of the kneecap.15 If the story fits loosening — pain on standing up, easing as you walk — the next test is a CT scan or a SPECT-CT scan. A SPECT-CT combines a bone scan, which shows where bone is working hard, with a CT, which shows exactly where. In a study of 214 painful knee replacements it changed the diagnosis or the plan in two out of three patients — often by showing that a knee that looked loose was not, or that one that looked solid was.16,17

CT scanner in a radiology department
Step 3 · Balance

Is the balance right?

A knee replacement is a set of metal and plastic parts held together by your own ligaments. If the parts are a few degrees rotated, or the gap between them is too tight on one side and too loose on the other, the knee can hurt, stiffen or give way even when the X-ray looks perfect. Dr Yas checks this by examination and, when needed, a CT scan that measures the rotation of each part. Redoing a knee to correct rotation gives good results when rotation really is the problem.18,19

Knee being bent and examined for range of movement
Step 4 · Bone

Is it the bone?

The top of the shin bone carries the whole implant. In thinner bone, or when the leg is slightly out of line, the bone under the plate can be overloaded — a stress reaction, and occasionally a small crack. It does not show on X-ray. An MRI or the SPECT-CT from step 2 picks it up.20,21 It is not common, but it is often missed, and the treatment is usually protection and time rather than another operation.

Step 5 · Soft tissue

Is it the soft tissue?

The tissues around the implant can hurt on their own. The most frequent one Dr Yas sees is a tight iliotibial band — the long band of tissue running down the outside of the thigh — rubbing over the edge of the implant. It gives pain on the outside of the knee with walking, is easy to test for, and is simple to treat.22,23 Others include a sore patellar tendon, a small nerve caught in the scar, and scar tissue inside the joint.

Step 6 · Somewhere else

Is it coming from somewhere else?

Pain is made in the brain from signals that travel up the spine. A worn hip or a pinched nerve in the back can be felt in the knee. If the pain you have now is the same pain you had before surgery, in the same place, this step matters most. Dr Yas examines the hip and back at the first visit for exactly this reason.24

D2 — Body map: a pinched nerve in the lower back can be felt in the buttock, groin, thigh and knee Pinched nerve in the lower back Where you feel it: buttock, groin, thigh, knee The spine Pain is made in the brain from signals that travel up the spine.Where you feel it is not always where it comes from.

If the pain is on the side of your hip, read: Is it the hip joint, or the tendons on the side?

Step 7 · Rare

The rare ones.

A small number of people react to the metal in an implant, usually nickel. It is real, it is rare, and it is hard to prove, so it is the last thing to consider, not the first.25,26

The rule at the end of the seven steps: name the cause first.

The UK’s national guideline for problem knee replacements puts it simply — understand the specific problem before deciding anything.15 If the seven steps find nothing, the next step is a second look and a discussion with colleagues, not a guess.

Four causes worth knowing about

Two illustrations of a knee replacement from the front: on the left a balanced knee with the metal resting evenly on the plastic liner; on the right the joint opened on the inner side with a slack, wavy inner ligament, highlighted red

Left: balanced. Right: loose on the inner side — the ligament has too much slack and the joint opens.

Too tight, too loose, or twisted

The parts of a knee replacement have to sit at the right angles and leave the right amount of room for the ligaments. A knee that is too tight feels stiff and “full” and will not bend well. A knee that is too loose feels unsteady, especially on stairs. A part that is rotated a few degrees can cause pain at the front of the knee and a kneecap that tracks badly. These can be measured, and they can be corrected.18,19

Three-dimensional illustration of a knee replacement from the outside: the iliotibial band running over the edge of the metal component, highlighted red where it rubs

The band on the outside

The iliotibial band runs from the hip to just below the outside of the knee. After a replacement it can rub on the edge of the metal, a bit of cement or a bony spur. The pain is on the outside of the knee, worse with walking, and easy to mistake for a problem with the implant itself. In published cases, removing what it was rubbing on cured the pain.22,23 Dr Yas sees this more often than the textbooks suggest, and checks for it in every painful knee.

Outside of the knee, hand pointing to where the iliotibial band crosses the joint
Three-dimensional cut-away of a knee replacement: the metal plate on top of the shin bone with an overloaded zone in the bone beneath one edge

Bone stress under the implant

The shin-bone plate spreads your weight into the bone beneath. If the bone is thin, or the leg is a little out of line, that bone can become overloaded. It aches, it does not show on X-ray, and it often goes unexplained. An MRI or SPECT-CT shows it. Most settle with protection and time; a few need the leg realigned.20,21

Three-dimensional illustration of a knee replacement with the joint lining evenly inflamed all around the implant

Metal allergy

About one person in ten has a skin allergy to nickel. Far fewer react to a knee implant. When it does happen it can cause an unhappy, swollen knee — but the same picture is far more often a low-grade infection, a loose implant or a rotation problem, so those are excluded first. There is no perfect test; the diagnosis is made by ruling everything else out.25,26

What usually helps, once the cause is known

If the cause is…The treatment is usually…
InfectionClearing the infection first — antibiotics with a washout, or replacing the implant in one or two stages
A loose or worn implantRevision surgery — replacing the loose part, or the whole knee, with implants designed for the job
Rotation or instabilityRevision with the rotation corrected and the ligaments rebalanced
A stiff, scarred kneeFreeing the scar — sometimes under anaesthetic, sometimes with surgery
The band on the outsideA small procedure to release the band or remove what it is rubbing on
Bone stressProtection and time; occasionally realigning the leg
Pain from the hip or backTreating the hip or back — the knee is left alone
Nothing foundA second look, a discussion with colleagues, and an honest answer

Some of the patients Dr Yas sees are sent by their surgeon or GP. Most come on their own, wanting a second set of eyes. Either way, the first visit ends with a plan you can read.

Person climbing stairs comfortably after treatment

You don’t need to bring anything

Just come as you are. Dr Yas tracks down what is needed himself — the operation report and the details of the implant from the hospital where the surgery was done, including the public hospitals, and any X-rays and scans you have had. If blood tests or new scans are needed, he arranges them. If you happen to have letters or results, bring them by all means, but nothing is expected of you. A GP referral helps with Medicare but is not required.

Patient arriving at the rooms empty-handed and being welcomed at reception

Common questions

Is six months too early to worry?
No. Six months is the point where the average person is clearly better and mostly forgetting the knee. If you are not, it is the right time to be checked — not because something is definitely wrong, but because if it is, it is easier to fix early.6,7
My X-ray is normal. Doesn’t that mean nothing is wrong?
No. Infection, rotation, a tight knee, bone stress and a rubbing band can all hide behind a normal X-ray. That is why the seven steps exist.
My blood tests are normal. Can it still be infected?
Yes. More than a third of proven infections had a normal CRP in one large study, mostly the slow-growing kind. If the knee has been sore for months, a sample from inside the joint — fluid, and often a small piece of the lining — is the test that matters.12,29
Could it be my back?
It could. A pinched nerve in the back can be felt in the knee, and a worn hip can too. If your pain now is the same as before surgery, this goes to the top of the list.24
Will I need another operation?
Not necessarily. Several of the common causes are treated without one. The first step is a conversation and the right tests — and a clear explanation of what they show.
Will my surgeon mind if I get a second opinion?
Surgeons expect it, and most welcome it. Ideally, everyone ends up on the same page: Dr Yas would like to write to your surgeon, and especially to your GP, with what he finds. But what is said in the consultation is between you and Dr Yas. You decide who is told and what they are told, and he will respect that.
Do I need a GP referral?
A referral helps with Medicare rebates and means your GP stays in the loop, but you can contact the rooms without one.
Questions welcome

Ask Dr Yas about your knee

Dr Yas wants you to ask questions. Send a few details and what has been happening, and the rooms will be in touch within one business day. A GP referral helps but is not required.

  • A proper assessment — your history, an examination and your scans, reviewed with you
  • The seven steps, in order, with the results written down
  • A clear plan — and an honest “we don’t know yet” if that is where the tests land
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References
  1. Vaotuua D, O’Connor P, et al. The effect of surgeon volume on revision for periprosthetic joint infection: an analysis of 602,919 primary total knee arthroplasties (AOANJRR). J Bone Joint Surg Am 2023;105:1663–75.
  2. British Orthopaedic Association / BASK. BOAST: Revision total knee replacement surgical practice guidelines. August 2020.
  3. The effect of minimum volume recommendations on surgeon activity for first revision total knee replacement: an analysis of 2009–2019 UK National Joint Registry data. The Knee 2025.
  4. Bourne RB, Chesworth BM, et al. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res 2010;468:57–63.
  5. Gunaratne R, Pratt DN, et al. Patient dissatisfaction following total knee arthroplasty: a systematic review of the literature. J Arthroplasty 2017;32:3854–60.
  6. Kennedy DM, Stratford PW, et al. Assessing recovery and establishing prognosis following total knee arthroplasty. Phys Ther 2008;88:22–32.
  7. Lenguerrand E, Wylde V, et al. Trajectories of pain and function after primary hip and knee arthroplasty: the ADAPT cohort study. PLoS One 2016;11:e0149306.
  8. Carlson VR, Post ZD, et al. When does the knee feel normal again: a cross-sectional study assessing the Forgotten Joint Score in patients after total knee arthroplasty. J Arthroplasty 2018;33:700–3.
  9. Sharkey PF, Lichstein PM, et al. Why are total knee arthroplasties failing today — has anything changed after 10 years? J Arthroplasty 2014;29:1774–8.
  10. Gustke KA, Golladay GJ, et al. Increased satisfaction after total knee replacement using sensor-guided technology. Bone Joint J 2014;96-B:1333–8.
  11. Wilson S, Marx RG, et al. Meaningful thresholds for the volume–outcome relationship in total knee arthroplasty. J Bone Joint Surg Am 2016;98:1683–90.
  12. Akgün D, Müller M, et al. The serum level of C-reactive protein alone cannot be used for the diagnosis of prosthetic joint infections, especially in those caused by organisms of low virulence. Bone Joint J 2018;100-B:1482–6.
  13. Parvizi J, Tan TL, et al. The 2018 definition of periprosthetic hip and knee infection: an evidence-based and validated criteria. J Arthroplasty 2018;33:1309–14.
  14. Shohat N, Bauer T, et al. Hip and knee section: what is the definition of a periprosthetic joint infection of the knee and the hip? Proceedings of the International Consensus on Orthopedic Infections. J Arthroplasty 2019;34:S325–7.
  15. British Orthopaedic Association / BASK. BOAST: Investigation and management of patients with problematic knee replacements. August 2020.
  16. Murer AM, Hirschmann MT, et al. Bone SPECT/CT has excellent sensitivity and specificity for diagnosis of loosening and patellofemoral problems after total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2020;28:1029–35.
  17. Hirschmann MT, Amsler F, et al. Clinical value of SPECT/CT in the painful total knee arthroplasty: a prospective study in a consecutive series of 100 TKA. Eur J Nucl Med Mol Imaging 2015;42:1869–82.
  18. Lakstein D, Zarrabian M, et al. Revision total knee arthroplasty for component malrotation is highly beneficial: a case control study. J Arthroplasty 2010;25:1047–52.
  19. Pietsch M, Hofmann S. Early revision for isolated internal malrotation of the femoral component in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2012;20:1057–63.
  20. Brumby SA, Carrington R, et al. Tibial plateau stress fracture: a complication of unicompartmental knee arthroplasty using 4 guide pinholes. J Arthroplasty 2003;18:809–12.
  21. Sawant MR, Bendall SP, et al. Nonunion of tibial stress fractures in patients with deformed arthritic knees. J Bone Joint Surg Br 1999;81-B:663–6.
  22. Takagi K, Inui H, et al. Iliotibial band friction syndrome after knee arthroplasty. The Knee 2020;27:263–73.
  23. Hegde G, Subramanian A, et al. Iliotibial band enthesopathy: an unusual cause of lateral knee pain post total knee arthroplasty. J Ultrasound 2022;25:83–7.
  24. Mandalia V, Eyres K, et al. Evaluation of patients with a painful total knee replacement. J Bone Joint Surg Br 2008;90-B:265–71.
  25. Lachiewicz PF, Watters TS, et al. Metal hypersensitivity and total knee arthroplasty. J Am Acad Orthop Surg 2016;24:106–12.
  26. Granchi D, Cenni E, et al. Metal hypersensitivity testing in patients undergoing joint replacement: a systematic review. J Bone Joint Surg Br 2012;94-B:1126–34.
  27. Beswick AD, Wylde V, et al. What proportion of patients report long-term pain after total hip or knee replacement for osteoarthritis? A systematic review of prospective studies in unselected patients. BMJ Open 2012;2:e000435.
  28. Flierl MA, Sobh AH, et al. Evaluation of the painful total knee arthroplasty. J Am Acad Orthop Surg 2019;27:743–51.
  29. Fink B, Makowiak C, et al. The value of synovial biopsy, joint aspiration and C-reactive protein in the diagnosis of late peri-prosthetic infection of total knee replacements. J Bone Joint Surg Br 2008;90-B:874–8.
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