Three ways to cross your legs, and what each does to the kneeEmerging evidence
Knee over knee on a chair keeps the top knee bent for as long as you sit, and the back of it rests on the bottom knee, pressing on the outer calf just below the top knee, where a nerve runs. An ankle on the other knee (the figure 4) lets the top knee bow outwards, which stretches the ligament on the outer side. Sitting cross-legged on the floor bends the knee furthest: about 130 to 135 degrees, with the shin turned in on the thigh, in two lab studies of young, healthy adults, and the lotus position goes further still.
That is our reading of the angle studies and the anatomy; no study has tested pain in each position. The NHS says a meniscus tear can come from a minor twist and makes the knee hard to bend, and a deep bend with a turned shin is the kind of load that can bother a worn or torn meniscus (our reading).
Sources 1, 2, 3, 4
The nerve below the outer knee: the best-known linkStrong evidence
The NHS lists "crossing your legs, kneeling or squatting for long periods of time" among the causes of injury to the nerve that lifts the foot. The common peroneal (fibular) nerve winds round the bony bump just below the outer knee, with little padding over it, and it is the commonest trapped nerve in the leg. It usually shows as numbness or a weak, dropping foot rather than knee pain: pain was uncommon (16.5%) in a series of 116 cases.
In 69 people with this nerve problem across 11 Italian centres, prolonged postures were the cause in 23.1%, surgery in 20.3% and weight loss in 14.5%. Rapid weight loss makes the nerve easier to squeeze: in 380 published cases after weight loss, leg crossing or similar postures were recorded in about 9%, and two men losing weight quickly on a weight-loss medicine developed foot drop within days of habitual leg crossing. These are case series, not population counts, so how often crossing causes it isn't known.
Sources 5, 6, 3, 7, 8, 9, 10
Kneecap pain and long bendsStrong evidence
Kneecap (patellofemoral) pain is defined by pain around or behind the kneecap with weight-bearing on a bent knee, such as squatting and stairs; pain on sitting, or on straightening the knee after sitting, is a supporting sign rather than an essential one. Of 458 people with kneecap pain, 54% reported problems with long sits, and NHS inform lists "pain after maintaining a sitting position for a period of time, such as driving or at the cinema". So a knee-over-knee cross or a floor sit can bring it on, and the pain often comes as you straighten up afterwards.
Sources 11, 12, 13
Floor sitting, the lotus position and the meniscusMixed evidence
Does sitting on the floor wear knees out? The studies disagree. Floor sitting wasn't linked with knee arthritis in Tehran or Jakarta, and lotus sitting wasn't in 261 Thai monks, but lotus and squatting went with painful arthritis in a sample of 576 Thai villagers; long daily squatting has the more consistent (still weak) link. The meniscus root tear often blamed on floor sitting was linked with being a woman, heavier and bow-legged in 476 Korean knee operations, not with lotus or squatting. All of these studies asked people to recall a lifetime of habits, so none can show cause and effect.
For the lotus position, the evidence is thin: lotus and half lotus were linked with 5.3% of named injuries in an Australian yoga survey, people who do yoga had more meniscus injuries in observational studies (mostly one study of scan findings in Chinese women), and the US National Center for Complementary and Integrative Health advises beginners to avoid the lotus position. A review still says "There is no need to discourage yoga practice for healthy people".
Sources 14, 15, 16, 17, 18, 19, 20, 21, 22, 23
Other causes: the outer ligament, a Baker's cyst, arthritis and the hipEmerging evidence
IT band syndrome is described in runners (5% to 14% of them), and no source links it to crossing your legs. A Baker's cyst, a fluid-filled lump behind the knee, is commoner from 35 to 70, usually comes from arthritis or an injury, and can make the knee tight and hard to bend. Arthritis is diagnosed from 45 by its pattern: pain with activity and morning stiffness of 30 minutes or less.
The hip can show up as knee pain. Crossing bends and turns the hip, and in 60 people waiting for a hip replacement, 47% had pain below the knee; Arthritis UK says knee pain can be the only sign of a hip problem. In a child or teenager, knee or thigh pain with a limp needs a same-day check.
Sources 24, 25, 26, 27, 28, 29, 30
What tests show, and what they don'tStrong evidence
The National Institute for Health and Care Excellence (NICE) says don't routinely use imaging to diagnose osteoarthritis. Meniscus tears are common in knees that don't hurt: in 991 people aged 50 to 90, 61% of those with a tear on MRI (magnetic resonance imaging) had no knee pain in the past month. An MRI matters when surgery is being considered.
An ultrasound scan can confirm a Baker's cyst, though cysts are common chance findings (9.1% of leg vein scans), and a scan of the leg veins rules a clot in or out. For the nerve, nerve conduction tests, not a scan, find where it's squeezed and help predict recovery.
Sources 27, 31, 25, 32, 33, 7, 34, 35
How it usually goesEmerging evidence
A leg that goes to sleep and clears when you uncross is pressure that recovers. Even true compression palsies mostly recover: about 90% regained good strength by a mean of about 9 months in one series, and 29 of 30 after weight loss within 3 weeks to 3 months. In 40 young women with kneecap pain, 85% were back in sport without pain a year after a 12-week programme, though in a smaller group followed for 5 to 8 years, more than half still had symptoms. Worn meniscus tears did as well with exercise as with surgery at 2 years, and a Baker's cyst "can take a few months to a few years to get better", the NHS says. NHS inform expects new knee pain to begin to settle within 6 weeks. No one can promise a date.
Sources 9, 35, 10, 36, 37, 38, 25, 39
