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Most common knee conditions in the US

Updated: Aug 8

An overview of the most common knee conditions in the US


Physical activity is considered a vital element of health and well-being for individuals of all ages. Physical activity decreases health risks, decreases body mass index, and increases social interaction. Unfortunately, physical activity also carries a risk of injury, which can affect psychological, emotional, physical, social, and economic aspects our lives 1. Some of the major disorders that severely impact physical activity are knee conditions. Our article is concerned about some of the most common knee conditions in the United States including osteoarthritis (OA), rheumatoid arthritis (RA), anterior cruciate ligament (ACL) injury, and traumatic knee injuries. Every disorder will be discussed in detail including its epidemiology, risk factors, management techniques, costs and complications, and why the standard management techniques are not as good as they might seem.

1 | Osteoarthritis (OA)

Osteoarthritis (OA) is a highly prevalent disease affecting more than 240 million persons globally and is the most prominent cause of activity limitation in adults2,3. It is the most common reason people show up in our office and osteoarthritis is the most common type of arthritis3. It can involve almost any joint but typically affects the hands, knees, hips, and feet3. It is accompanied by pathologic changes in cartilage, bone, synovium, ligament, muscle, and periarticular fat, leading to joint dysfunction, pain, stiffness, functional limitation, and loss of valued activities3. Risk factors include age, gender, obesity, genetics, and previous major joint injury. Persons with osteoarthritis usually have more comorbidities and are more sedentary than those without osteoarthritis3.

Approximately 240 million people worldwide suffer from symptomatic, activity-limiting osteoarthritis3. The knee joint is usually one of the most affected joints. Nearly 30% of people over the age of 45 have radiographic evidence of knee osteoarthritis, with half of them experiencing knee symptoms3. Obese people (BMI 30+) and people with prior joint trauma, such as an anterior cruciate ligament rupture or an ankle fracture, have a higher lifetime risk of symptomatic knee osteoarthritis3. Osteoarthritis causes considerable cost and mortality. Forty-three percent of the 54 million US citizens living with arthritis (most of them suffer from OA) experience arthritis-related limitations in daily activities2,3. Women with OA have more severe radiographic findings and symptoms compared to men. The reduced physical activity leads to a 20% higher age-adjusted mortality3.

The main approaches of OA management include prescribed exercises, weight loss if necessary, and education complemented by topical or oral NSAIDs, in those without contraindications2,3. Intraarticular steroid injections provide short-term pain relief and duloxetine has demonstrated efficacy3. Opiates should be avoided. Persons with severe symptoms and complete structural deterioration are candidates for total joint replacement3. Racial and ethnic disparities persist in the utilization and outcomes of joint replacement 3. NSAIDs have important toxicities, including gastrointestinal irritation and ulceration, bleeding, and decreased renal blood flow with azotemia2,3. Patients with conditions in which NSAIDs are contraindicated, or who do not respond, can go for intra-articular corticosteroid injections, which typically alleviate pain for a few weeks3. Some studies reported that corticosteroid injections have no greater effect on pain than placebo after three months, and may be less effective than physical therapy at one year3.

More than 700,000 primary total knee joint replacements are done every year in the US, >90% for osteoarthritis3,4. Ninety-day mortality is <1%, and serious complications at 90 days occur in <5%3–5. About 10% of total knee joint replacements need to be revised over 20 years3,4. Blacks and Hispanics also have a higher risk of adverse outcomes including joint infections following total knee joint replacements3–5. A recent study indicated that outpatient therapist-led rehabilitation did not achieve higher outcomes compared with single physiotherapist review and home exercise-based regimen in patients at risk of poor outcomes after total knee arthroplasty6,7. No clinically relevant differences were observed across primary or secondary outcome measures7.

In 2016, the US spent around 17.8% of its gross domestic product on health care8. While spending in the other countries ranged from 9.6% (Australia) to 12.4% (Switzerland)8. The proportion of the population with health insurance was 90% in the US, lower than the other countries (range, 99%-100%), and the US had the highest proportion of private health insurance (55.3%)8. Wage losses because of osteoarthritis reached $65 billion and direct medical costs exceeded $100 billion3. Patients usually favor elective procedures due to their high expectations of positive outcomes, underestimating the potential harms, and lack of knowledge about alternative treatments9. Educating patients about alternatives and risks can support decision-making by patients and physicians9,10. Well-developed decision aids can delay elective procedures until they are actually required, avoiding unnecessary and more costly revision procedures9,11.

An increasing number of people in the US choose elective joint replacements to maintain active life styles9. Around 505,000 hip replacements and 723,000 knee replacements were done in the United States in 2014 with costs exceeding $20 billion. In a country spending nearly 18% of its gross domestic product on health care with some poor population health outcomes, this is a significant source of potentially controllable spending9. A more recent US study found 34% of 205 knee replacements were considered possibly unnecessary9. Avoiding the potential 34% of possibly inappropriate knee replacements could have saved US payers an estimated $8.3 billion every year9,12. Investigating cost drivers for hip and knee replacements could possibly reduce federal health care spending by millions more9. Medicare paid around $13,000 per hip/knee replacement for 536,000 procedures in the fiscal year 2015, costing an estimated $7 billion. People with knee osteoarthritis spend, on average, around $15,000 dollars (discounted) over their lifetimes on direct medical costs of osteoarthritis. We need new innovative ways to curb structural progression and provide more potent and/or safer pain relief to change the outlook for patients with this painful, costly, disabling condition

2 | Rheumatoid arthritis (RA)

Rheumatoid arthritis (RA) is a chronic autoimmune disease that generally progresses causing functional disability, severe pain, and joint destruction leading to early mortality13. It is estimated that it affects between 0.5 and 1.0 percent of the adult population worldwide13. The prevalence of RA increases with age, and it affects more women than men13. In the past, the size of severe long-term economic consequences of RA was previously underestimated. The majority of patients with rheumatoid arthritis need continuous treatment to hinder or stop progression and to control disease flares13,14. Many also require surgery (often involving total joint replacement) within 10 years of disease onset13,14. In addition to these direct costs, work disability decreases productivity and leads to early retirement, which results in substantial indirect costs13. Currently, the estimated prevalence of RA in Europe and the US is ranges from 0.5 to 1.0%, with an incidence of about 0.03%13. Environmental factors including weather, cigarette smoking, alcohol consumption, stress, and diet may play a role, but it is not clear how much can be attributed to these factors13.

The first four items of the American College of Rheumatology classification criteria indicate disease activity (synovitis and morning stiffness), while the last three items indicate disease severity (erosions, nodules, and rheumatoid factor)13. Patients may take time to fulfil four of the seven items13. Disorders that cause joint pain and loss of mobility are 60–80% more common in women than in men, and this difference is evident across all age groups13. Regarding rheumatoid arthritis, both prevalence and incidence rates are about 2- to 4-fold higher in women, and symptoms appear to be more severe than in men13. The female/male ratio goes down with age13. The causes of the greater prevalence of RA among women are not fully known. Proposed hypotheses include: increased risk of developing RA associated with low testosterone levels, increased prolactin levels during breast-feeding, and women may have more severe symptoms than men13.

Furthermore, the economic costs of rheumatoid arthritis go up with both age and level of disability13,14. The direct costs of RA to patients and their families are those spent on the detection, treatment, and/or prevention of the disease. Expenditures include: physician visits, diagnostic and laboratory tests, medication, ‘iatrogenic costs’ of treating medication-induced adverse effects, hospitalization, surgical procedures, social care, and costs associated with impairment of functional status. Prescription medication and hospitalization costs for joint replacement procedures and management of adverse effects of treatment, notably nonsteroidal anti-inflammatory drug (NSAID)-induced gastrointestinal intolerance, are some of the big contributors to the direct costs of the disease13. In a review of North American studies, the direct costs of RA were found to range from $US2298 (1996 US dollars) per person per year in Canada to $US13 549 per person per year in the US13. Indeed, the direct costs of RA in the US have been estimated to be three or more folds higher than the national average for treating patients who do not have the disease13.

Although only about 10% of the RA population are hospitalized in any given year, hospitalization costs are the largest contributor of direct costs, accounting for at least 50–60% of the total in several studies13. Disease severity is the factor causing hospitalization, with total joint replacement surgery, such as hip or knee replacement, accounting for 50–60% of admissions13,14. Medication costs are usually the second largest contributor to direct costs13; these include expenditure on the medications themselves (mainly DMARDs and NSAIDs)14 and the costs of monitoring their use and managing adverse effects. Indirect costs incurred by patients and their caregivers are those related to reduced productivity, including reduced productivity and absence from work, and losses attributable to the disease, preventing individuals from taking better-paying or full-time jobs13. In studies that analyze the indirect costs of RA, values that range from $US1082 to $US33 000 per patient per year have been reported. At present, the median lifetime incremental costs of RA have been estimated to be between $US61 000–122 000 (1995 US dollars), depending on the patient’s age13.

3 | Anterior cruciate ligament (ACL) injuries

Anterior cruciate ligament (ACL) injuries are the most common ligament injury in the United States15–17. These injuries can be career-ending for athletes and severely disabling for all persons. Over 250,000 anterior cruciate ligament (ACL) injuries occur yearly in the United States15–17, with 125,000–175,000 undergoing ACL reconstruction (ACLR)15. Football players are responsible for the greatest number of ACL injuries (53% of the total) with skiers and gymnasts also at high risk16. The most common causes of an ACL injury may be a noncontact deceleration, jumping, or cutting action, frequently involving changing direction15,16. This frequently involves rotational maneuvers or lateral bending of the knee into a valgus position with the knee extended and the tibia rotated15,16.

Physical examination is usually enough to establish a diagnosis of ACL injury, especially if the examination is done shortly after the injury before swelling, pain, and muscle guarding take place15. The anterior stability of the knee is often evaluated with the Lachman test15. The Lachman test is generally done at a 20-degree to 30-degree angle of knee flexion while stabilizing the distal femur with one hand15. A manual force is then applied to the proximal tibia with the opposite hand, and anterior laxity is assessed in the degree of anterior translation of the tibia relative to the femur. This should be compared with the healthy knee15. The Lachman test has a sensitivity of 85% and a specificity of 94% for ACL injuries15.

Anterior cruciate ligament injuries occur more frequently in women than in men due to a variety of anatomical factors16. The stronger the quadriceps muscles, the bigger and hence stronger the ACL15. Quadriceps muscles, even after adjustments for differences in weight and lean body mass, are larger in male athletes compared with female athletes15. Despite postoperative rehabilitation focuses on quadriceps muscle intentionally, athletes commonly experience quadriceps strength deficits, lower self-reported knee function, and movement asymmetry up to two years after reconstruction15. The importance of quadriceps strength as a dynamic knee stabilizer has been well-recognized, as deficits have been linked to reduced functional outcomes15. Another study comparing operatively and nonoperatively managed patients 2–5 years after ACL injury found no differences in quadriceps strength between the 2 groups concluding reconstructive surgery is not a necessity to restore muscle function15. Regardless of operative or non-operative management, quadriceps strength deficits are very prevalent after ACL injury and can persist for the long term15.

Athletes who undergo reconstruction are not guaranteed to return to their pre-injury sport, and returning to the pre-injury competitive level of sport is unlikely15. In young athletes returning to sport, the risk of a second injury is high, especially in the short term. Secondary injury is more likely in the contralateral limb in females and the ipsilateral limb in males15. The long-term risk of developing osteoarthritis is high regardless of surgical intervention, and it is even higher if a revision procedure is required15. Because of major concomitant medical illnesses such as serious cardiac, renal, or hepatic disease, or because they no longer want to participate in intensive physical activities, some patients with ACL injuries may not be candidates for surgery18,19. Physical therapy with a competent physical therapist or sports trainer aimed at strengthening the muscles around the knee, particularly the quadriceps femoris and hamstring muscles, is pursued by those who choose conservative treatment15,18. The knee, however, remains unstable and prone to additional injury without surgical treatment15,18. Neuromuscular exercises are unlikely to be harmful to patients; however, their impact was small, making them unlikely to result in large improvements in outcomes or help patients return to sports more quickly15,19.

Neuromuscular exercises should not be used in place of strengthening and range-of-motion exercises. Supplemental vitamin C and E do not appear to be beneficial. Although postoperative hyaluronic acid injections may improve some measurable parameters15,18, the cost must be considered. Due to the evident, frequent failure of nonsurgical approaches to manage ACL injuries, surgery remains the gold standard treatment in almost all athletes who want to remain active15,18. Unfortunately, surgery is not universally successful. Some problems that have resulted in failed ACL reconstruction are graft impingement on the intercondylar roof, graft tension, nonanatomic femoral and tibial tunnel placement (not reproducing the histological and biomechanical characteristics of the native ligament), and incomplete replication of an intact ACL15,18. Despite these efforts, 15% to 25% of patients who undergo ACL reconstruction continue to suffer pain and instability in their injured knee15,18.

4 | Knee pain and opioids

Frequent knee pain affects approximately 25% of adults, limits function and mobility, and reduces the quality of life, with osteoarthritis being the most common cause of knee pain in people aged 50 and up20. Patients with knee injuries frequently present to emergency departments, despite knee injuries being treated by a wide range of clinicians (EDs)20. The knee is the most commonly injured joint in adolescent athletes, with an estimated 2.5 million sports-related injuries presenting to emergency departments each year1. The multidirectional forces imposed on the complex knee joint during physical activity explain the various types of severe knee injuries seen in EDs, such as anterior cruciate ligament or posterior cruciate ligament ruptures1. Such injuries frequently necessitate costly surgery as well as extensive rehabilitation1. a financial burden on the healthcare system. A knee injury can end an athlete's competitive career and permanently impair physical activity capabilities in people of all ages, so prevention is critical1. Furthermore, while knee injuries can have a financial impact on the injured person, they also place a burden on the healthcare system1.

The magnitude of the public health and clinical burden posed by knee injuries is clearly evident by the incidence of knee injuries reported in this study (an estimated 6,664,324 knee injuries presenting to U.S1. EDs during a short period), as well as the fact that 1.7% of these knee injuries were so severe to the level the injured person needed hospitalization1. We discovered the most common cause of knee injury, especially among those younger than 25 years, was sports and recreation activities1. Similarly, consistent with previous studies we found the most common diagnoses were strains ⁄ sprains1. The injury rate among the 45 to 64 and 65 years and older age groups rose significantly in the last few years1. Individuals 25 years and older were nearly three times more likely to sustain an injury associated with home structures and home furnishings than those younger than 25, and fractures were more common among seniors than other age groups1. These are important findings given the aging U.S. population, coupled with the relative scarcity of research in the prevention of household-associated knee injuries1.

Drug dependence, as measured by Self-Directed Search (SDS) scores, was found in 40% of patients suffering from chronic noncancer pain21, especially of musculoskeletal origin, such as joint pain21. Aside from the risk of adverse effects such as addiction, there is evidence that even strong opioids are not more effective than acetaminophen or NSAIDs in reducing pain caused by musculoskeletal conditions22. Given the current opioid crisis and the significant and growing population prevalence of OA, appropriately limiting opioid use in OA may have a significant impact on the number of opioids in circulation, resulting in a beneficial public health impact. In addition to improving patients' overall health, addressing patient factors such as depression, smoking, and obesity may be beneficial in reducing opioid use. As evidence mounts that opioid use may have a negative impact on surgical outcomes22, optimized preoperative pain management and presurgical opioid use screening, including potential dependency, may be warranted for patients undergoing OA surgery.


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2. Da Costa BR, Pereira T V., Saadat P, et al. Effectiveness and safety of non-steroidal anti-inflammatory drugs and opioid treatment for knee and hip osteoarthritis: Network meta-analysis. BMJ. 2021;375. doi:10.1136/bmj.n2321

3. Butz AM, Christopher S. von Bartheld JB and SH-H. 乳鼠心肌提取 HHS Public Access. Physiol Behav. 2017;176(12):139-148. doi:10.1001/jama.2020.22171.Diagnosis

4. Health Quality Ontario HQ. Total Knee Replacement: An Evidence-Based Analysis. Vol 5.; 2005.

5. Noble PC, Gordon MJ, Weiss JM, Reddix RN, Conditt MA, Mathis KB. Does total knee replacement restore normal knee function? Clin Orthop Relat Res. 2005;431(431):157-165. doi:10.1097/01.blo.0000150130.03519.fb

6. Zaghlol RS, Khalil SS, Attia AM, Dawa GA. Comparison of two different models of rehabilitation programs following total knee replacement operations. Egypt Rheumatol Rehabil. 2020;47(1):1-9. doi:10.1186/s43166-020-00034-1

7. Hamilton DF, Beard DJ, Barker KL, et al. Targeting rehabilitation to improve outcomes after total knee arthroplasty in patients at risk of poor outcomes: Randomised controlled trial. BMJ. 2020;371:1-8. doi:10.1136/bmj.m3576

8. Papanicolas I, Woskie LR, Jha AK. Health care spending in the United States and other high-income countries. JAMA - J Am Med Assoc. 2018;319(10):1024-1039. doi:10.1001/jama.2018.1150

9. Lam V, Teutsch S, Fielding J. Hip and knee replacements: A neglected potential savings opportunity. JAMA - J Am Med Assoc. 2018;319(10):977-978. doi:10.1001/jama.2018.2310

10. Waimann CA, Fernandez-Mazarambroz RJ, Cantor SB, et al. Cost-effectiveness of total knee replacement: A prospective cohort study. Arthritis Care Res. 2014;66(4):592-599. doi:10.1002/acr.22186

11. Lavernia C, Lee DJ, Hernandez VH. The increasing financial burden of knee revision surgery in the United States. Clin Orthop Relat Res. 2006;446(446):221-226. doi:10.1097/01.blo.0000214424.67453.9a

12. Navathe AS, Troxel AB, Liao JM, et al. Cost of joint replacement using bundled payment models. JAMA Intern Med. 2017;177(2):214-222. doi:10.1001/jamainternmed.2016.8263

13. Kvien TK. Epidemiology and Burden of Illness of Rheumatoid Arthritis. Pharmacoeconomics. 2004;22(1):1-12. doi:10.2165/00019053-200422001-00002

14. Gaffo A, Saag KG, Curtis JR. Treatment of rheumatoid arthritis. Am J Heal Pharm. 2006;63(24):2451-2465. doi:10.2146/ajhp050514

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16. Gans I, Retzky JS, Jones LC, Tanaka MJ. Epidemiology of Recurrent Anterior Cruciate Ligament Injuries in National Collegiate Athletic Association Sports: The Injury Surveillance Program, 2004-2014. Orthop J Sport Med. 2018;6(6):1-7. doi:10.1177/2325967118777823

17. Sanders TL, Maradit Kremers H, Bryan AJ, et al. Incidence of anterior cruciate ligament tears and reconstruction: A 21-year population-based study. Am J Sports Med. 2016;44(6):1502-1507. doi:10.1177/0363546516629944

18. Ap M, Lj D, Hopewell S, et al. Surgical versus conservative interventions for treating anterior cruciate ligament injuries (Review). Published online 2016. doi:10.1002/

19. Dago A. Colaboradores en Pharmaceutical Care. Pharm Care Espana. 2006;8(1):1. doi:10.1016/j.csm.2014.12.008.Controversies

20. Nguyen USDT, Zhang Y, Zhu Y, Niu J, Zhang B, Felson DT. Increasing prevalence of knee pain and symptomatic knee osteoarthritis: Survey and cohort data. Ann Intern Med. 2011;155(11):725-732. doi:10.7326/0003-4819-155-11-201112060-00004

21. Tetsunaga T, Tetsunaga T, Nishida K, et al. Drug dependence in patients with chronic pain. :1-5.

22. Power JD, Perruccio A V., Gandhi R, et al. Factors Associated With Opioid Use in Presurgical Knee, Hip, and Spine Osteoarthritis Patients. Arthritis Care Res. 2019;71(9):1178-1185. doi:10.1002/acr.23831

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