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Kneecap resurfacing has been argued about in operating rooms for forty years. In June 2026, that argument got its best answer yet. Teams at the University of Oxford and the University of Aberdeen published 20 year results from the Knee Arthroplasty Trial.
It is the longest randomized study ever run in knee replacement surgery. I have followed it since the early reports. The final numbers are worth a careful read.
This article is about the evidence. If you want the step by step of how the choice gets made for your knee, that lives in my patellar resurfacing decision guide.
What Kneecap Resurfacing Actually Changes Inside the Knee
Your kneecap rides in a groove at the end of your thigh bone. The back of it is coated in cartilage. Arthritis wears that coating down the same way it wears down the rest of the joint.
In a total knee replacement, the ends of the thigh bone and shin bone are always capped with metal and plastic. The kneecap is the one surface a surgeon can choose to leave alone.
Kneecap resurfacing means shaving a thin layer off the back of the kneecap. A small plastic button is then cemented in its place. That button glides against the metal, so raw bone never rubs on it.
The front of the kneecap and the tendons that lift your leg stay untouched. The short video below shows what happens to the kneecap during surgery.
The 20 Year Trial Behind the New Evidence
About one in five people who have a knee replacement still report pain or limited function. Much of that traces back to the front of the knee. That is the territory the kneecap controls, which is why this question has stayed alive so long.
How the Knee Arthroplasty Trial Was Built
The Knee Arthroplasty Trial, known as KAT, opened in 1999. It ran across 34 UK centers with 116 surgeons taking part.
Patients were assigned at random to have the kneecap resurfaced or left alone. In all, 1,715 people entered that comparison.
Random assignment matters here. It strips out the surgeon habits and patient picking that cloud most other studies on this topic. Enrollment ran from April 1999 through January 2003, and follow up reached the 20 year mark.
What the 20 Year Results Showed
The main measure was the Oxford Knee Score, which runs from 0 to 48. Resurfaced knees scored 0.76 points higher. The margin of error crossed zero, so that counts as no real difference.
The money side told another story. Resurfaced patients gained 0.380 more quality adjusted life years over 20 years. That gap was large enough to be real.
Total health care cost per patient came out nearly the same: about $10,825 for resurfaced knees against $10,889 for the rest. The cost of the extra implant was offset by fewer trips back to the hospital.
The authors put the odds of resurfacing being good value at 99 percent. Their stated conclusion: the evidence now leans toward resurfacing as the first choice.
Why a Result That Missed the Mark Still Points One Way
Here is the part I find most useful as a surgeon. Knee scores, general health scores, quality of life, readmissions, kneecap operations, major operations, and complication rates all pointed the same way.
Not one of them favored leaving the kneecap alone.
A single weak result means little. Ten separate measures that all tilt the same direction mean something. That pattern is what tipped the authors toward resurfacing, and it matches what joint registries have shown for years.
What Joint Registries Add to the Picture
Trials give you clean comparisons on modest numbers. National registries give you huge numbers with messier comparisons. When both point the same way, the signal is worth trusting.
Kneecap Resurfacing and the Reoperation Question
The Australian registry reviewed 570,735 knee replacements done between 1999 and 2017. Knees left unresurfaced carried a 31 percent higher rate of revision surgery.
A review pooling randomized trials found front knee pain in 24.1 percent of unresurfaced patients. Among resurfaced patients, the figure was 12.9 percent. Front knee pain is the top reason a patient comes back unhappy.
Inside KAT itself, some unresurfaced patients came back later to have the button added. Those late operations helped less than resurfacing done the first time.
Imaging adds one more clue. An MRI study scanned patients every year after surgery. In knees left alone, the remaining kneecap cartilage thinned to less than half its starting thickness within five years.
Where the Evidence Is Still Open
I would be doing you a disservice if I called this settled. Real gaps remain.
Resurfacing carries its own small risks. Those include kneecap fracture, a loose button, and tracking trouble. They are rare with careful technique, and they were already counted in the trial results above.
KAT also cannot tell us whether selective resurfacing beats routine resurfacing. Judging each kneecap during surgery was never tested as its own group.
The Cost Numbers Do Not Transfer to the United States
KAT ran inside the UK National Health Service. The pricing and the value thresholds are British.
The clinical findings travel fine across borders. The pound figures do not. Any US surgeon quoting them as local cost data is stretching the study past what it says.
Habits differ by country too. Surgeons in the United States and Australia resurface in roughly nine of ten cases. In Norway and Sweden, that figure sits near 2 to 3 percent. Much of that gap is tradition, not data.
How I Apply Kneecap Resurfacing Evidence in My Practice
I perform more than 700 hip and knee replacements a year at the Bone and Joint Institute of Tennessee in Franklin. I resurface the kneecap in most knee replacements. The KAT results reinforced that habit rather than changed it.
My reasoning is simple. When long term data tilts one way on every measure, and cost is a wash, the burden of proof sits with leaving the surface alone.
Alignment matters as much as the button itself. A kneecap tracks well when the thigh and shin components sit where they belong. That is one reason I use CT based planning with the Mako® system for many cases, which you can read about on my robotic joint replacement page. I am a paid consultant to Stryker for that platform, and I say so to any patient who asks.
Technique still decides the result. Leave enough bone behind. Keep the cut even. Set the button slightly toward the inner edge. Those three details prevent most of the problems people worry about.
I pair kneecap resurfacing with the subvastus approach, which spares the quadriceps muscle. Quad strength drives how the kneecap tracks in the first months, and it shapes how kneeling feels after knee replacement.
What to Ask at Your Consultation
Bring these questions to whichever surgeon you see. They are the ones I would want answered if I were the patient.
- How much arthritis shows on the back of my kneecap on imaging?
- What is your usual approach to the kneecap, and why?
- How thick is my kneecap, and does that change the plan?
- If we leave it alone and my front knee pain lasts, what happens then?
A surgeon who resurfaces every kneecap and one who selects carefully can both give you a fine knee. What you want is a clear reason behind the choice, not a reflex. You can read the full 20 year trial in The Lancet.
If knee arthritis is limiting what you can do, Dr. Calendine sees patients from Franklin, Brentwood, Nashville, and across Middle Tennessee at the Bone and Joint Institute of Tennessee, 3000 Edward Curd Lane, Franklin, TN 37067. No referral is required. Schedule a consultation or call (615) 791-2630.
This article is for education only. It does not replace personal medical advice. Every knee is different, so talk with a qualified orthopedic surgeon about your own condition and options.
References
- Murray DW, Hudson J, Dakin H, et al. Patellar resurfacing in total knee replacement: 20-year clinical and economic results of a large multicentre, randomised controlled trial in the UK. The Lancet. 2026. View study
- Coory JA, Tan KG, Whitehouse SL, Hatton A, Graves SE, Crawford RW. The outcome of total knee arthroplasty with and without patellar resurfacing up to 17 years: a report from the Australian Orthopaedic Association National Joint Replacement Registry. J Arthroplasty. 2020;35(1):132-138. View study
- Li S, Chen Y, Su W, Zhao J, He S, Luo X. Systematic review of patellar resurfacing in total knee arthroplasty. Int Orthop. 2011;35(3):305-316. View study
- Sato D, Inoue M, Sasaki T, et al. No patella resurfacing total knee arthroplasty leads to reduction in the thickness of patellar cartilage to less than half within 5 years: a quantitative longitudinal evaluation using MRI. J Exp Orthop. 2021;8(1):107. View study
- Adam R, Moldovan C, Tudorache S, et al. Patellar resurfacing in total knee arthroplasty, a never-ending controversy: case report and literature review. Diagnostics. 2023;13(3):383. View study
- Murray DW, MacLennan GS, Breeman S, et al. A randomised controlled trial of the clinical effectiveness and cost-effectiveness of different knee prostheses: the Knee Arthroplasty Trial (KAT). Health Technol Assess. 2014;18(19). View study
