How common it is, and who gets itStrong evidence
Knee pain is common in men, and men consult a GP for it about as often as women do. In 12 English general practices in 2006, the knee was the second commonest joint or muscle problem people consulted for, after the back (324 people per 10,000 a year), and the rates for men and women were almost identical. Boys and men consulted more than girls and women up to the age of 44, and women more from 45. Across 446 UK practices, men consulted GPs 32% less often than women overall, most of all between 16 and 60, but the gap largely disappeared when men and women with comparable illnesses were compared. So the records don't support the idea that men ignore their knees.
It's common from 40: of 4,085 men over 40 registered with 12 practices in the English Midlands, 26.9% had knee pain on most days of the past month, 35.2% of those X-rayed had osteoarthritis on the X-ray, and 3.8% had had a knee replacement.
Injuries lean towards men. At an Edinburgh hospital serving about 535,000 people, 3 in 4 of the knee tendon and ligament injuries were in men, and a meniscus injury was the commonest. In Minnesota, 81.7 men and 55.3 women per 100,000 tore an ACL each year, men most often at 19 to 25. Among athletes, though, women tear it more often: about 1 in 29 female against 1 in 50 male athletes, over follow-ups from a season to 25 years. That more men than women play pivoting and contact sport is the likely reason for the overall gap, but no study we found measured it.
Sources 1, 2, 3, 4, 5, 6
Boys and young men: growth, sport and the hipStrong evidence
In active boys of about 10 to 15, a tender bump just below the kneecap, worse with running, jumping and kneeling, is usually Osgood-Schlatter disease. In Dutch general practice, 4.9 boys and 2.7 girls per 1,000 aged 8 to 18 were diagnosed each year, most often at about 12 in boys. NHS inform says it can last 12 to 24 months, and that sport isn't likely to cause lasting problems.
Rarely, knee or thigh pain with a limp comes from the hip. A slipped growth plate at the top of the thigh bone (slipped upper femoral epiphysis, SUFE) affected 3.34 per 100,000 young people aged 6 to 18 a year in Great Britain, slightly more boys than girls, at a median age of 12.7. NHS inform says it can feel like a pulled muscle in the hip, knee or thigh, isn't normally caused by an injury, and always needs an operation.
In young men who play sport, twisting and landing injuries lead. Football and rugby are strong risk factors for a meniscus tear after a twist, and being male is a risk factor for worn tears later. In English professional rugby, knee injuries cost more days out than injuries anywhere else, ACL and medial collateral ligament (MCL) injuries most of all, mostly in the tackle. Jumper's knee, pain at one point just below the kneecap, affected 10.2% of male against 6.4% of female non-elite athletes in the Netherlands, most of all in volleyball (14.4%).
Kneecap pain, an ache around or behind the kneecap on stairs, in squats and after long sits or drives, is common in young men too: 12% of male entrants to the US Naval Academy had it on arrival (15% of women), though women went on to develop it 2.23 times as often. Those were military cadets, not the general public.
Sources 7, 8, 9, 10, 11, 12, 13, 14, 15
Physical work: bursitis, meniscus tears and arthritisStrong evidence
Repetitive kneeling and squatting, climbing ladders and heavy lifting at work go with knee problems, and the Health and Safety Executive (HSE) names repetitive kneeling as the cause of knee bursitis, the soft swelling on the front of the kneecap also called housemaid's, carpet layer's or beat knee. With elbow bursitis, it affects at least 10 people per 100,000 a year, 80% of them men aged 40 to 60, and about a third of cases are infected. In a US study, carpet layers reported bursitis more often than millwrights and bricklayers (20% against 6%), and how often they used a knee kicker was the only significant predictor.
In 518 people listed for knee surgery and 518 people without, long spells of kneeling or squatting at work went with about twice the odds of knee osteoarthritis (1.9 times), and regularly lifting 25 kg or more with 1.7 times, more with both. Across 80 studies, physically demanding work went with about 1.5 times the odds of desk work, in men (1.61 times, 29 studies) as well as women (1.35 times, 18 studies; the ranges overlap, so it isn't clear that men's risk is higher), and floor layers, bricklayers and carpenters had about 2.5 times. The odds rose by about 26% for every 5,000 hours of kneeling or squatting. Kneeling and squatting at work also go with worn meniscus tears. These are links, not proof of cause.
UK policy recognises the strongest of them. The Industrial Injuries Advisory Council found the risk of knee osteoarthritis "more than doubled" after at least 20 years as a carpet fitter or floor layer, with too little evidence for painters or carpenters. Knee osteoarthritis after 20 years of carpet or floor laying or 10 years in named coal mining jobs (prescribed disease A14), and knee bursitis from pressure at work (A6), are prescribed diseases for Industrial Injuries Disablement Benefit.
Knee pads help within limits, and the evidence is thin. The Health and Safety Executive for Northern Ireland says pads protect on hard floors and help comfort but don't reduce the risks of deep knee bending, and that it isn't known whether they lower the risk of osteoarthritis. Two years after training in new working methods that cut kneeling, 38% of floor layers used them weekly or daily, against 16% of untrained floor layers, and knee complaints were less common in those who had used them for longer.
Sources 16, 17, 18, 19, 20, 21, 22, 11, 23, 24, 25
Mid-life and later: worn tears, gout, torn tendons and arthritisStrong evidence
Worn (degenerative) meniscus tears are common from mid-life and often painless. In 991 adults aged 50 to 90 in a US community study, a tear showed on magnetic resonance imaging (MRI) in 32% of men and 19% of women aged 50 to 59, and in 56% and 51% at 70 to 90, with more tears in men at every age. 61% of the tears were in people with no knee pain, aching or stiffness in the past month, so a tear on a scan isn't always the cause of the pain.
Gout is about four times as common in men: 3.97% of men and 1.05% of women registered with UK general practices had it in 2012, and the gap was widest in the 30s, when men had it about 11 times as often. It causes sudden, severe pain with a hot, red, swollen joint, usually the big toe, but the knee can be affected. A torn quadriceps or patellar tendon is rare, about 0.3 to 0.5 per 100,000 people a year in US emergency departments, and mostly a man's injury: in 726 operated injuries, 91% of quadriceps tendon ruptures (average age 61) and 95.5% of patellar tendon ruptures (average age 39.5) were in men.
Knee osteoarthritis is less common in men than in women: about a third less in a meta-analysis, and women's is more severe, especially from 55. But it's common in men too: 35.2% of UK men over 40 who were X-rayed had it. A past knee injury roughly quadruples the odds (24 studies, 20,997 people). In 1,207 retired professional footballers against 4,085 men from the general population, knee osteoarthritis on X-ray was 2.21 times and knee replacement 3.61 times as common, and the authors call knee injury "the main attributable risk factor". The NHS says osteoarthritis doesn't necessarily get worse over time, and can sometimes improve.
Recreational running isn't linked with more arthritis: across 17 observational studies of 114,829 people, hip or knee osteoarthritis was found in 3.5% of recreational runners, 13.3% of competitive runners and 10.2% of people who didn't run.
Sources 26, 27, 28, 29, 30, 31, 32, 33, 3, 34, 35
Less common causes, and what the warning signs are forStrong evidence
A hot, swollen knee without an injury can be gout, calcium crystal arthritis (pseudogout) or a joint infection, and fluid drawn from the joint is the test that tells them apart. Pseudogout is rare under 60 and affects the knee more than any other joint. A joint infection is rare, about 8 per 100,000 people a year in UK hospital records and 31 per 100,000 over 75, but it's urgent, and the NHS lists people who inject drugs and people with gonorrhoea among those at higher risk. Reactive arthritis starts 1 to 4 weeks after an infection such as food poisoning or a sexually transmitted infection, usually affects the knees and feet, and usually goes within 6 months.
The hip can be felt in the knee. 47% of 60 people waiting for a hip replacement had pain below the knee, but only 2% of 51 people whose hip pain was confirmed with an injection felt it in the knee itself, so studies disagree on how often.
Some causes sit outside the knee. A blood clot in a deep leg vein (deep vein thrombosis) causes throbbing pain and swelling in one calf or thigh; it's more likely over 60, after surgery or a hospital stay, on journeys of more than 4 hours or after an earlier clot, and a clot that reaches the lungs makes breathing suddenly difficult. Numbness around the genitals or bottom, new trouble with your bladder or bowels, problems with erections, or pain, tingling or numbness in both legs can be signs of cauda equina syndrome, a reason to call 999 or go to A&E. Haemophilia, which mainly affects men, can cause bleeding into a joint, and fluoroquinolone antibiotics such as ciprofloxacin can damage tendons within 48 hours of starting them or months later, more often over 60, so the UK medicines regulator now restricts them to when other antibiotics aren't suitable.
Sources 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46
When a scan or test helpsStrong evidence
Most knee pain doesn't need a scan at first. The National Institute for Health and Care Excellence (NICE) diagnoses knee osteoarthritis without imaging from 45, when joint pain comes with activity and any morning stiffness lasts 30 minutes or less, and meniscus tears are common on MRI in knees that don't hurt.
Tests answer specific questions. After an injury, the Ottawa knee rule decides on an X-ray: you're 55 or over, the head of the fibula (the bony bump on the outer side just below the knee) or only the kneecap is tender, you can't bend the knee to 90°, or you can't take 4 steps; it picks up 98.5% to 100% of fractures. A side-on X-ray or an MRI confirms a torn tendon. An MRI is considered for a meniscus tear when symptoms haven't settled after 3 months of non-surgical treatment, or after an acute injury when a repair might be possible. For a hot, swollen knee, fluid drawn from the joint finds an infection or crystals, NICE measures the blood urate level (repeating it at least 2 weeks after a flare if it's low during one), and a suspected infection is usually treated in hospital. A suspected clot means a hospital ultrasound scan within 24 hours, and with bursitis a GP may take fluid with a needle to test for infection and gout.
Sources 47, 26, 48, 49, 50, 36, 39, 43, 51
How it usually goesEmerging evidence
NHS inform says new knee pain or a flare should begin to settle within 6 weeks. A worn meniscus tear improved as much with exercise as with surgery over 2 years. Half of the people offered rehab first for a fresh ACL tear in a Swedish trial had a reconstruction within 5 years, and half didn't; after surgery, sport can take up to a year, the NHS says, and about 1 in 5 people under 25 injure an ACL again.
Jumper's knee can linger: symptoms had lasted 18.9 months on average in non-elite athletes, the fastest return in the largest trial's programme was 4 weeks, and only 43% were back in sport at 24 weeks. Osgood-Schlatter disease can last 12 to 24 months. An untreated gout attack usually lasts 1 to 2 weeks, bursitis should go in a few weeks, reactive arthritis usually goes within 6 months, and osteoarthritis doesn't necessarily get worse. No one can promise a timescale.
Sources 52, 53, 54, 55, 56, 13, 57, 8, 28, 51, 40, 34
