Hip and knee replacement rates are climbing because several forces are converging at once: populations are aging, obesity rates are rising, surgical techniques have become safer and faster, and both patients and doctors have grown more willing to pursue the procedure at younger ages. Across nearly every country tracked by the OECD, the number of replacements per 100,000 people increased over the past decade. The trend shows no sign of slowing, and projections for the coming decades suggest the current volume is modest compared to what lies ahead.
More People Living Longer With Worn-Out Joints
Osteoarthritis is the primary reason people end up needing a new hip or knee. The cartilage that cushions the joint gradually breaks down over decades, and age is the single strongest predictor. As life expectancy rises and the proportion of older adults in the population grows, the raw number of people living with advanced joint disease increases in lockstep. An analysis of aging-population effects on hospital services concluded that the growing elderly population will drive up demand for hip replacements and place additional strain on hospital capacity.1PubMed. Effects of an aging population on hospital costs related to elective hip replacements
The OECD’s most recent health indicators report confirmed this pattern globally: the number of hip and knee replacements per 100,000 people rose in virtually all member countries over the past decade, driven by the rising incidence and prevalence of osteoarthritis tied to aging populations and growing obesity rates.2OECD Publishing. Health at a Glance 2025: OECD Indicators Only New Zealand and Mexico bucked the trend. This is not a story unique to the United States or any single healthcare system; it is a demographic wave playing out across wealthy nations.
Sex-based differences in cartilage also matter here. Women carry a greater risk of developing osteoarthritis than men, partly because of smaller cartilage volume relative to bone size, but also because of qualitative changes in cartilage composition and faster degeneration rates after menopause.3PubMed Central. Are there gender-specific differences in hip and knee cartilage composition and degeneration? A systematic literature review That biological vulnerability helps explain why women account for a disproportionate share of joint replacement procedures in most registries around the world.
The Obesity Factor
Carrying extra weight accelerates joint wear. Every additional pound of body weight adds roughly four pounds of force across the knee during walking, so even moderate weight gain compounds cartilage damage over time. Higher body mass index is a well-known risk factor for developing hip and knee osteoarthritis and predicts the need for a total hip or knee replacement at an earlier age.4The Journal of Arthroplasty. Effects of the Obesity Epidemic on Total Hip and Knee Arthroplasty Demographics Because obesity rates have climbed steadily across OECD countries for decades, there is now a much larger pool of people whose joints are failing prematurely.
This creates a compounding effect when layered on top of population aging. A seventy-year-old who has also been carrying significant extra weight since middle age arrives at surgery with more advanced disease than a seventy-year-old of healthy weight would. And a fifty-year-old with severe obesity may already have the joint deterioration typically seen a decade or two later. Both ends of the age spectrum are being pushed toward surgery by a single risk factor that is growing more common.
Replacements Are Happening at Younger Ages
One of the most striking shifts in joint replacement over the past two decades is how much younger the typical patient has become. National data show a substantial rise in the prevalence of total hip and knee replacements over time, accompanied by a shift to younger ages.5PubMed Central. Prevalence of Total Hip and Knee Replacement in the United States Where joint replacement was once seen as a last resort for people in their seventies and eighties, it is now routine for people in their fifties and sixties, and not unusual for those even younger.
Several things drive that change. Younger people are heavier, on average, than previous generations were at the same age. Sports injuries in youth can set the stage for early osteoarthritis; one study found that young athletes who suffered a knee joint injury were nearly four times as likely to be overweight or obese years later and had measurably worse knee function compared to uninjured peers.6PubMed Central. Outcomes associated with early post-traumatic osteoarthritis and other negative health consequences 3-10 years following knee joint injury in youth sport Those early injuries accelerate cartilage loss, and by middle age the damage can be severe enough to warrant replacement.
Expectations have also changed. A fifty-five-year-old today is less willing to accept chronic pain and limited mobility for decades than prior generations might have been. The cultural framing of joint replacement has shifted from a major, risky operation to a well-understood procedure with high satisfaction rates, and that reframing encourages people to pursue surgery sooner.
Surgeries Have Gotten Safer and Faster
Improvements in surgical technique, anesthesia, and post-operative care have dramatically lowered the barriers to joint replacement. One large cohort study of over 1,600 joint arthroplasty patients found that the in-hospital mortality rate was extremely low, and that the vast majority of serious complications occurred within the first four days after surgery.7JBJS / Ovid. Total Joint Arthroplasty: When Do Fatal or Near-Fatal Complications Occur? That kind of safety profile, combined with decades of accumulated data on outcomes, gives both surgeons and patients confidence to proceed with the operation.
Perhaps the most visible change is the rise of same-day surgery. Traditionally, a hip or knee replacement meant several nights in the hospital. That changed sharply when Medicare removed total knee replacement from its Inpatient Only list and the COVID-19 pandemic pushed hospitals to minimize overnight stays. By December 2020, same-day total knee and total hip replacement accounted for more than half of all cases performed in the United States.8PubMed. Same-Day Total Joint Arthroplasty in the United States From 2016 to 2020 When you can go home the same day you get a new knee, the perceived burden of the operation drops significantly, and people who might have delayed surgery feel more comfortable moving forward.
Robotic-Assisted Surgery and Its Growing Footprint
Robotic technology has steadily worked its way into the operating room. The proportion of hospitals and surgeons using robotic assistance increased from roughly 16% of hospitals and 6% of surgeons in 2008 to about 29% of hospitals and 17% of surgeons by 2015.9PubMed. Technology-Assisted Hip and Knee Arthroplasties: An Analysis of Utilization Trends Growth continued from there. A nationwide assessment found that robotic total knee arthroplasty grew from about 0.35% of all knee replacements in 2010 to 3.45% in 2022, while robotic hip arthroplasty went from 0.26% to 2.36% over the same period.10PubMed. Trends of robotic total joint arthroplasty utilization in the United States from 2010 to 2022
Surgeon adoption has accelerated, too. In 2018, about 10% of joint replacement surgeons had adopted robotic technology. By 2023, that number had jumped to 35%. Surgeons earlier in their careers showed the greatest interest, and the main reasons cited for adopting robotics were surgical efficiency and ease of use.11PubMed. The Perception and Adoption of Robotic Total Joint Arthroplasty: An Analysis of the United States Whether robotic assistance produces meaningfully better long-term outcomes for patients is still being studied, but the technology clearly makes the procedure more standardized and appeals to hospitals as a marketing differentiator. That visibility feeds public awareness and can encourage patients to seek out joint replacement.
Loosening Thresholds and Direct-to-Consumer Advertising
There is no universal consensus on exactly when someone “qualifies” for a hip or knee replacement. A systematic review of indication criteria found that specific cut-off values or ranges were often not stated, and the overall level of evidence supporting existing criteria was low.12PubMed Central. Indication criteria for total hip or knee arthroplasty in osteoarthritis: a state-of-the-science overview In practice, the decision is a negotiation between surgeon judgment, imaging findings, and a patient’s reported pain and functional limitations. That gray area means thresholds can shift with cultural norms and financial incentives without any formal guideline change.
One English study modeled what would happen if evidence-based referral thresholds were applied uniformly. The result: thousands of additional referrals per year, with estimates suggesting roughly 13,000 extra knee replacements and 4,500 extra hip replacements annually across England.13BMJ Open. Who gets referred for knee or hip replacement? In other words, even under standardized criteria, there would likely be more surgeries than are currently performed, because many eligible patients are not being referred. The current rise in volume reflects both a genuine increase in disease burden and a gradual broadening of who is considered a candidate.
Advertising plays a role here, too. A study of direct-to-consumer advertising in orthopaedics found that more than half of patient respondents recalled seeing or hearing ads related to hip or knee replacement. Those patients were more likely to request a specific type of surgery or brand of implant and to consult more than one surgeon before deciding on the operation.14Clinical Orthopaedics and Related Research. The Impact of Direct-to-Consumer Advertising in Orthopaedics Advertising does not create a diseased joint, but it accelerates the path from symptom awareness to surgical consultation.
What Patients Expect From Their New Joints
Patient expectations have evolved beyond basic pain relief. In a qualitative study exploring recovery expectations after total knee replacement, participants expressed strong hopes for improved mobility and re-engagement in meaningful activities. Many anticipated returning to hobbies, social roles, and work, and frequently described regaining independence and emotional well-being as goals.15PubMed. A Qualitative Study to Explore Patient Expectations of Recovery After Total Knee Replacement Surgery The modern patient does not just want to walk without pain; they want to hike, garden, travel, and play with grandchildren.
Those rising expectations create a feedback loop. When a neighbor or coworker has a successful replacement and returns to an active life, that visible outcome encourages others dealing with similar symptoms to pursue surgery rather than manage conservatively. The cultural narrative around joint replacement has moved from “last resort for the elderly” to “a way to reclaim your life,” and that narrative shift is itself a driver of volume.
Stark Geographic and Racial Disparities
The upward trend in joint replacement is not distributed evenly. Among Medicare beneficiaries in 2017, total hip replacement rates varied more than threefold across U.S. hospital referral regions, from about 2 per 1,000 beneficiaries in one Louisiana region to roughly 7.5 per 1,000 in a Michigan region. Total knee replacement rates showed similar variation, ranging from about 5 to 16 per 1,000.16PubMed Central. Geographic Variation and Disparities in Total Joint Replacement Use for Medicare Beneficiaries: 2009 to 2017
Racial disparities are equally pronounced. In the same dataset, the mean rates for White beneficiaries were roughly 4.8 hip and 9.9 knee replacements per 1,000, compared to about 2.8 hip and 6.1 knee replacements per 1,000 for Black beneficiaries. In fewer than 8% of hospital referral regions did the rate for Black beneficiaries even reach the national average for White beneficiaries.16PubMed Central. Geographic Variation and Disparities in Total Joint Replacement Use for Medicare Beneficiaries: 2009 to 2017 These gaps reflect differences in access, referral patterns, trust in the healthcare system, and insurance coverage rather than differences in disease prevalence. As access expands to underserved populations, total volumes will likely rise further, because many people who need the surgery currently are not getting it.
Where Non-Surgical Treatments Fit In
Joint replacement does not happen in a vacuum; it sits at the end of a treatment ladder that includes physical therapy, injections, weight loss, and bracing. Non-surgical treatment before a knee replacement can delay surgery substantially. One review found that supervised physical therapy delayed the need for total knee replacement in 95% of patients at one year, and that weight reduction improved pain and function enough to reduce the urgency for surgery.17PubMed Central. Surgical Versus Non-Surgical Treatments for the Knee: Which Is More Effective?
A randomized trial comparing physical therapy to glucocorticoid injections for knee osteoarthritis found that patients in the physical therapy group had less pain and better function at one year than those who received the injection.18PubMed. Physical Therapy versus Glucocorticoid Injection for Osteoarthritis of the Knee That result underscores the value of non-surgical management, but it also reveals a limitation: these approaches delay surgery rather than eliminate the need for it. For many patients, the underlying cartilage loss continues, and replacement eventually becomes the only option that provides lasting relief. The availability of effective conservative care may slow the rate of increase somewhat, but it cannot reverse the demographic and lifestyle forces pushing volume upward.
The Projections Are Staggering
Several modeling studies have attempted to forecast where replacement volumes are headed, and the numbers are striking. One analysis using National Inpatient Sample data projected that by 2040, annual primary hip replacements in the United States could reach roughly 1.4 million and primary knee replacements could reach about 3.4 million, representing increases of about 284% and 401%, respectively, compared to 2014 volumes.19The Journal of Rheumatology. Rates of Total Joint Replacement in the United States: Future Projections to 2020–2040 Using the National Inpatient Sample
Looking further out, a study focused on Medicare patients projected that primary total joint arthroplasty could grow to nearly 4.9 million procedures annually by 2060, a roughly 559% increase from 2019 counts.20PubMed Central. Projections and Epidemiology of Primary Hip and Knee Arthroplasty in Medicare Patients to 2040-2060 These are projections, not certainties, and they assume current trends in aging, obesity, and surgical uptake continue. But even if the actual numbers land well below these forecasts, the direction is clear: the healthcare system needs to prepare for dramatically more joint replacements.
A Growing Wave of Revision Surgeries
There is a less-discussed consequence of operating on younger, more active patients: implants do not last forever. A replaced hip or knee eventually wears out, loosens, or develops complications that require a revision procedure. When the typical patient was seventy-five, many did not live long enough to need a second surgery. When the typical patient is fifty-five, the odds of outliving the implant go up substantially.
Projections for revision total joint arthroplasty in the Medicare population suggest that revision knee replacements will double by 2040 and revision hip replacements will double by 2060, compared to 2020 rates. The core issue is that younger patients subject their implants to higher activity levels, which can cause earlier failure and lead to an increased risk of needing a revision.21Arthroplasty Today. Medicare Projections for Revision Total Joint Arthroplasty From 2040 to 2060 Revision surgery is more complex, more expensive, and typically has less favorable outcomes than the original procedure. The shift toward younger patients is front-loading relief but back-loading a significant wave of revision demand that the surgical workforce and hospital infrastructure will need to absorb.
How Hospital Economics Shifted
Joint replacement did not always make financial sense for hospitals. One teaching hospital documented that primary total knee replacement went from generating a loss of over $2,000 per case in 1991 to producing a profit of nearly $3,000 per case by 2008, driven largely by shorter hospital stays and reduced implant costs.22PubMed Central. Hospital economics of primary total knee arthroplasty at a teaching hospital That turnaround made joint replacement one of the more reliably profitable elective procedures for hospitals, and financial incentives naturally encourage capacity expansion. When a hospital builds a new joint replacement center or adds an additional surgical robot, it is investing in a procedure that generates revenue reliably, and that investment creates capacity that then gets filled.
The economic picture reinforces every other driver. Aging creates demand. Obesity accelerates it. Younger patients expand the eligible population. Surgical advances reduce risk and length of stay. Patient expectations rise. Hospitals find it profitable. Advertising raises awareness. Each of these forces would increase volume on its own; together, they create a trend that has reshaped orthopedic surgery over the past two decades and will continue reshaping it for decades to come.