What Is TKR Surgery? Procedure, Risks, and Recovery

Total knee replacement, often abbreviated TKR or referred to by surgeons as total knee arthroplasty (TKA), is a surgical procedure in which damaged bone and cartilage in the knee joint are removed and replaced with artificial surfaces made of metal alloys and medical-grade plastic. It is one of the most common and successful elective surgeries performed worldwide, primarily for people whose knee arthritis has stopped responding to other treatments. About four out of five replacement knees are still functioning well at the 25-year mark, but the path from operating table to that long-term payoff involves real decisions about surgical approach, pain management, rehabilitation, and risk tolerance.

Who Needs a Total Knee Replacement

The typical candidate is someone with advanced osteoarthritis whose daily life has become limited by knee pain, stiffness, or loss of function. Surgeons weigh several factors before recommending the procedure: the severity of pain, how well you can walk and manage stairs, what your X-rays or other imaging show, and whether you have already tried and failed conservative treatments like physical therapy, anti-inflammatory medications, injections, or bracing. A review of published indication criteria found that pain, functional limitation, radiographic changes, and failed conservative therapy were the domains that appeared most consistently across clinical guideline sets, though specific thresholds for “bad enough to operate” were rarely defined and the overall level of evidence supporting any one cutoff was low.¹ In practice, the decision is a conversation between you and your surgeon rather than a checklist with a hard pass/fail line.

Partial Replacement as an Alternative

If only one compartment of the knee is damaged, you may be offered a partial (unicompartmental) knee replacement instead, which resurfaces only the worn section and leaves the healthy bone and ligaments intact. The TOPKAT trial, the largest randomized comparison of the two procedures, found no significant difference in knee scores between partial and total replacement at five years. Patients who received a total replacement did have a higher complication rate, with roughly 27% experiencing at least one complication compared to about 20% in the partial replacement group.² A separate meta-analysis found that partial replacement patients had shorter hospital stays, better functional scores in observational studies, and lower rates of serious complications like blood clots and cardiac events. The tradeoff is that partial replacements carry a higher five-year revision rate across all study types.³ So partial replacement tends to feel better sooner and carries fewer perioperative risks, but the implant is more likely to need additional surgery down the line.

What Happens During the Procedure

The surgery itself typically takes between one and two hours. The surgeon makes an incision over the front of the knee, moves the kneecap aside, and removes the damaged cartilage and a thin layer of bone from the ends of the thighbone (femur) and shinbone (tibia). Metal components are then fitted to these reshaped surfaces: a curved piece on the femur, a flat tray on the tibia, and often a dome-shaped button on the underside of the kneecap. A medical-grade polyethylene spacer sits between the metal surfaces to allow smooth gliding.

One of the surgical decisions your team will make is whether to use bone cement to hold the implant in place or to use a cementless design that relies on bone growing into a textured surface over time. Cemented fixation has been the standard for decades, and most surgeons still prefer it. Interest in cementless implants has grown, however, as designs have improved. A randomized trial comparing cemented and cementless versions of the same implant found no difference in clinical outcomes at two years, no loosening in either group, and about 10 minutes of shorter operating time in the cementless group.⁴ A longer follow-up study of 200 knees at a minimum of 11 years found survival rates of about 90% for cemented and 95% for cementless implants, with no statistically significant difference between them.⁵ For most patients the choice between the two will not meaningfully affect how the knee performs.

Robotic-Assisted Surgery

A growing number of hospitals now offer robotic-assisted TKR, in which the surgeon uses a robotic arm or guidance system to improve the precision of bone cuts and implant positioning. The technology does deliver on accuracy: one study found that robotic-assisted knees deviated significantly less from the surgical plan on every measured angle compared with manual technique.⁶ A systematic review reported that the rate of alignment outliers dropped dramatically in robotic groups. In one included study, 0% of robotic knees fell outside the target mechanical axis versus 24% of conventional knees; in another, the overall outlier rate was 19% with robotic assistance versus 91% without it.⁷

Whether this precision translates into knees that last longer or feel better is less clear. Reviews describe improved short-term clinical outcomes, but long-term data comparing robotic and conventional TKR survival are still sparse.⁸ The technology adds cost and operating time. If your surgeon offers it, the most honest summary is that it makes the technical execution more consistent, but the jury is out on whether patients notice a meaningful difference years later.

Pain Control After Surgery

Knee replacement is known for being one of the more painful common orthopedic procedures in the first few days. Modern pain management usually involves a combination of approaches rather than relying on opioids alone. One widely used technique is the adductor canal block, a nerve block that numbs part of the inner thigh to reduce knee pain while preserving most of your quadriceps strength. A scoping review found the block to be safe and effective, particularly when combined with a local anesthetic injection around the joint itself.⁹ In a randomized trial testing the block as rescue analgesia for patients in severe post-TKR pain, pain scores during active knee bending dropped by an average of 32 points on a 100-point scale, and the proportion of patients with more than mild resting pain fell from 57% to 8%.¹⁰

Compared with the older femoral nerve block, which numbs the entire front of the thigh, the adductor canal block provides similar pain relief but better preserves quadriceps strength, which matters because you need that muscle to stand and walk safely. A meta-analysis confirmed better quadriceps strength and faster mobilization with the adductor canal approach, with no meaningful difference in pain scores or opioid use between the two blocks.¹¹

The First Days and Early Rehab

You will be encouraged to start moving the knee very quickly. In many centers, a physical therapist will have you sitting up within a couple of days and walking with a walker or crutches shortly after. One study recorded average times of about 2.3 days to sit, 2.6 days to stand, and 2.9 days to walk, with a mean hospital stay of roughly 4.6 days.¹² Those numbers are falling as enhanced-recovery protocols become more widespread; some programs now aim for same-day or next-day discharge.

Starting rehabilitation within 24 hours of surgery appears to help. A randomized trial comparing early rehab (within 24 hours) to a later start found that the early group had a hospital stay roughly two days shorter, about 16 degrees more knee flexion at discharge, better muscle strength, and lower pain scores.¹³ Physical activity parameters improve steeply in the first four days and continue to climb over the following weeks, though they typically have not returned to preoperative levels by five weeks.¹⁴

Does Prehabilitation Help

Prehabilitation, or exercise therapy before surgery, is frequently recommended. It does seem to make the early recovery smoother. A systematic review with meta-analysis found that prehab improved knee function before surgery and for up to three months afterward. By six to twelve months, however, the advantage had disappeared, with no significant difference between patients who did prehab and those who did not.¹⁵ A similar pattern emerged in a smaller trial, which showed better knee scores in the prehab group up to six months but no difference at one year.¹⁶ If you are deconditioned or anxious about surgery, prehab is worth doing for the short-term boost and the confidence it brings. But do not postpone surgery indefinitely waiting for the “perfect” preparation; the long-term outcome seems to end up in the same place.

Supervised Therapy vs. Home Exercise After Discharge

Once you leave the hospital, you will face a choice between formal outpatient physical therapy and a self-directed home exercise program. The research on this is perhaps surprisingly equivocal. A systematic review and meta-analysis concluded that supervised therapy did not provide clinically significant benefits over unsupervised home exercise programs following primary TKR, and that routine referral to supervised therapy after discharge may not be necessary for everyone.¹⁷ A separate meta-analysis reached the same conclusion, noting that short-term improvements in function and range of motion did not clearly differ between the two settings, although the evidence was highly varied across studies.¹⁸ This does not mean therapy is useless. It means that a motivated patient who faithfully follows a home program can do well. If you have limited mobility, balance problems, or trouble staying consistent on your own, supervised therapy is the safer bet.

Risks and Complications

Like any major surgery, TKR carries risks. The ones that get the most attention are blood clots, infection, and stiffness.

Blood clots in the leg veins (deep vein thrombosis) or lungs (pulmonary embolism) are a known hazard after lower-limb surgery. Prevention typically involves blood-thinning medication, compression stockings, and early mobilization. For many patients, plain aspirin may be enough. A meta-analysis of randomized trials comparing aspirin to oral anticoagulants for clot prevention after knee replacement found no significant difference in the rate of blood clots, deep vein thrombosis, pulmonary embolism, bleeding, wound complications, or death.¹⁹ An earlier systematic review reached a similar conclusion when comparing aspirin to rivaroxaban.²⁰ This shift toward aspirin matters because it is cheaper, more accessible, and carries a lower bleeding risk than stronger anticoagulants.

Infection around the implant occurs in roughly 1 to 3% of cases. The most common culprits are staphylococcal bacteria. When infection occurs early, a debridement procedure that cleans the joint and swaps the plastic spacer while leaving the metal implant in place is sometimes sufficient. A chronic infection, by contrast, typically requires a two-stage revision in which the implant is removed entirely, the infection is treated, and a new implant is placed weeks or months later.²¹

Stiffness, or arthrofibrosis, is another potential issue. If the knee fails to regain adequate range of motion despite physical therapy, your surgeon may recommend manipulation under anesthesia, in which the knee is bent forcefully while you are asleep to break up scar tissue. For more severe cases, arthroscopic lysis of adhesions, a procedure where scar bands are cut through small incisions with a camera, can be added. A matched cohort study found that combining arthroscopic lysis with manipulation produced significantly greater improvements in range of motion compared to manipulation alone, particularly in patients whose knee could not bend past 60 degrees beforehand.²² Revision surgery for stiffness is a last resort and generally has poorer outcomes than these less invasive options.²³

How Long a Replacement Knee Lasts

A large systematic review and meta-analysis pooling data from national joint registries across 14 countries estimated that about 82% of total knee replacements survive 25 years.²⁴ That is a reassuring number, but averages mask individual variation. Age and sex influence durability: younger patients and men face higher revision rates. Among women under 55, about 21% needed a revision within 10 years, compared to roughly 8% of women aged 75 to 79.²⁵ This is part of why surgeons sometimes counsel younger patients to delay the procedure if they can.

When implants do fail, infection is the leading cause, accounting for about 30% of failures, followed by loosening at about 20% and instability at about 18%. Wear of the polyethylene liner, driven by factors like activity level and implant design, also plays a role over decades.²⁶ If a first revision is needed, the replacement implant has a shorter expected life span. Registry data show that about 20% of first-revision knees required a second revision within 13 years, and each successive revision fails faster.²⁵

Getting Back to Sports and Daily Activities

Most people return to low-impact physical activities within three to four months. A systematic review found that 36 to 89% of total knee replacement patients returned to some form of sport, with mean time to return of about 13 weeks, overwhelmingly in low-impact activities.²⁷ Cycling and swimming tend to hold up best: a survey of nearly 800 recreational athletes found that participation rates for cycling and swimming were nearly the same before and after surgery. Running and skiing were a different story, with running participation dropping from 84% preoperatively to under 49% at follow-up, and skiing from about 73% to 46%. Dissatisfaction was highest among runners.²⁸ If you are an avid runner hoping to continue after TKR, the honest answer is that fewer than half manage to get back to it, and those who do usually reduce their intensity.

Persistent Pain After Replacement

One of the least-discussed realities of TKR is that up to about 20% of patients report ongoing pain in the replaced knee.²⁹ In most cases the cause is not a failed implant. The pain may be related to nerve irritation, soft-tissue sensitivity, patellar tracking issues, or central pain sensitization, a condition in which the nervous system amplifies pain signals even after the original structural problem has been fixed. This is an active area of research and a frustrating one, because the X-rays can look perfect while the patient is still hurting. If you are considering TKR, it is worth having realistic expectations: the vast majority of patients get dramatic relief, but a meaningful minority find the knee never feels entirely right.

Researchers have been working on better tools to measure this. The Forgotten Joint Score asks patients how often they are aware of their artificial joint during daily activities. It captures something that older scoring systems miss: the difference between a knee that functions adequately and one the patient genuinely stops thinking about.³⁰ The score has been validated with good reliability and a lower ceiling effect than the Oxford Knee Score, meaning it can distinguish between knees that are merely good and those that feel truly natural.³¹

Metal Allergies and Implant Materials

Standard TKR implants contain cobalt-chromium and nickel alloys. If you have a known metal allergy, particularly to nickel, it is worth raising this before surgery. Hypoallergenic alternatives exist, including implants coated with titanium nitride, oxidized zirconium components, and ceramic options. A scoping review found that hypoallergenic implants are a viable alternative when metal hypersensitivity is identified before surgery, with ceramic implants outperforming titanium-nitride-coated ones in longer-term data.³² That said, the clinical significance of metal sensitivity in knee replacements remains debated. Skin-patch testing is positive in a large percentage of the general population, and a positive test does not necessarily predict implant problems. Unless you have a clear history of reactions to metal jewelry or prior implants, routine allergy screening before TKR is not standard practice.

Cost-Effectiveness

TKR is expensive upfront, but it is generally regarded as good value in health-economic terms because it produces large, durable gains in quality of life. A U.S. analysis estimated incremental cost-effectiveness ranging from about $9,700 per quality-adjusted life year for low-risk patients to about $28,100 for high-risk patients, both well below the threshold at which health economists typically consider an intervention worthwhile.³³ A prospective cohort study calculated a total incremental cost per replacement of roughly $20,000, with cost-effectiveness ratios varying depending on how much improvement you define as clinically meaningful.³⁴ An Indian economic evaluation came to the same conclusion from a very different healthcare system, finding TKR cost-effective compared to nonsurgical management regardless of age or disease severity.³⁵ Patient time lost from work and daily activities was the single most influential variable in one sensitivity analysis, a reminder that the real cost of severe knee arthritis is not just what you pay for the surgery but what you lose by not having it.