Where it hurts is the best clue
The outer thigh has a few common sources of pain, each with a typical pattern. A deep ache from the bony point of the hip down the side of the thigh, worse lying on it, points to the outer hip tendons, which NHS inform says affect the outer side of the hip and thigh. A patch of skin that burns, tingles or feels numb points to a squeezed skin nerve. Pins and needles or a sharp, hot or burning pain can come from the back, even without back pain, NHS inform says. The map above points to a likely cause and its guide; an examination decides.
Sources 1, 2, 3, 4
A burning, numb patch: meralgia parestheticaStrong evidence
Meralgia paresthetica is a squeezed skin nerve, the lateral cutaneous nerve of the thigh, where it leaves the pelvis near the front of the hip. It causes a painful, numb or tingling patch on the outer thigh, often one you can draw round with a finger, and NHS Borders' referral guidance says it causes no other symptoms in the legs, so it never makes the leg weak. In one series of 120 people described in a review, the outer thigh alone was affected in 73% and the front-outer thigh in 26%.
It is often worse with long standing and walking and eased by sitting. Tight clothing, belts, a heavy tool belt, body armour and seat belt injuries are named by the American Academy of Orthopaedic Surgeons (AAOS) and a review, but no study has measured them as causes. The growing womb can press on the nerve in pregnancy, an NHS trust leaflet says, and it can follow some hip operations, when the nerve is stretched.
Sources 3, 5, 4, 6
Who gets meralgiaEmerging evidence
In a US population study, about 32.6 people in 100,000 developed meralgia each year, and 7 times as many of those with diabetes. People with meralgia were twice as likely to be diagnosed with diabetes later, and their average body mass index (BMI) was higher (30.1 against 27.3). In Dutch general practice it was seen in 4.3 in 10,000 people a year, and was linked with carpal tunnel syndrome and with pregnancy, though the pregnancy figure was very imprecise and most cases had no clear cause. NHS Borders' guidance names recent weight gain or pregnancy as the commonest causes. These are links, not proof that one causes the other.
Sources 7, 8, 3
The outer hip tendonsStrong evidence
Greater trochanteric pain syndrome affects the outer side of the hip and thigh, NHS inform says. It's commoner in women and between the ages of 40 and 60, and it hurts lying on that side, crossing the legs, standing on that leg, climbing stairs and getting in or out of a car. The NHS says hip bursitis pain may spread to the upper leg (thigh), and the AAOS that it usually extends to the outside of the thigh.
In 3,026 US adults aged 50 to 79, it was present on one side in 15.0% of women and 6.6% of men, and was linked with knee arthritis and low back pain but not with body weight. It is usually the tendons rather than a bursa: of 877 people scanned for this pain, 49.9% had changes in the gluteal tendons and only 20.2% an inflamed bursa.
Sources 2, 9, 10, 11, 12
IT band syndrome is felt at the kneeEmerging evidence
Iliotibial (IT) band syndrome is the commonest injury on the outside of the knee in runners, affecting an estimated 5% to 14% of them, though studies of its causes conflict. In 15 cadavers there was no bursa under the band, and MRI scans suggested the band squeezes a layer of fat at about 30 degrees of knee bend rather than rubbing over the bone. It is a knee problem, not the usual cause of pain along the thigh.
Sources 13, 14
Your back, the hip joint or a strainEmerging evidence
NHS inform says thigh and hip symptoms can come from the back even without back pain, often as pins and needles or a sharp, hot or burning pain. In 17 people with a trapped third lumbar nerve root (average age 76), 12 had thigh pain and 4 were first treated for hip or knee problems. A study of examination tests for these upper nerve roots found some useful ones, but in small numbers and mostly for the front of the thigh.
It works the other way round too: in one spine clinic, 20.2% of people referred with low back pain had outer hip tendon pain instead. The hip joint itself sent pain to the thigh in 57% of 51 people, and to the buttock in 71%. A sudden pull while kicking or sprinting, or a heavy knock, is usually a thigh muscle strain or a bruised muscle (a dead leg), the AAOS says.
Sources 1, 15, 16, 17, 18, 19, 20
Tests and scansEmerging evidence
Meralgia is recognised from the story and an examination, and NHS Borders' guidance says no further tests are needed. When it's unclear, nerve tests can help, though in the studies a review summarises they picked up only 65% to 81% of cases; a pressure test over the pelvis looked accurate, but in just 20 people.
Outer hip tendon pain is recognised from the history and examination. In 65 people with outer hip pain, pain within 30 seconds of standing on the affected leg made tendon changes on a magnetic resonance imaging (MRI) scan very likely, and no tenderness over the bony point made them unlikely; a review agreed that single-leg standing is one of the most useful tests. But 20 of the 65 had tendon changes on MRI without the matching signs, so a scan alone doesn't make the diagnosis. A scan helps when a tendon tear is suspected, such as a limp that isn't improving, or when another cause is possible; for back and leg pain, the National Institute for Health and Care Excellence (NICE) advises against routine imaging outside specialist care.
Sources 3, 4, 21, 22, 23
How it usually goesEmerging evidence
Meralgia often settles. In the one study that followed it without treatment, 20 of 29 people improved, and when it follows an operation, 99 of 102 recovered completely in the studies a Cochrane review found. NHS Borders' guidance says most people need no treatment, but symptoms can persist.
Outer hip tendon pain is slower. In the LEAP trial, 20 of 68 people left to wait and see reported success at 8 weeks and 31 of 60 at a year; with education and exercise, 51 of 66 and 51 of 65. NHS inform says it can take 6 to 12 months of rehabilitation, with flare-ups along the way, and that most new thigh problems begin to settle within 6 weeks. No one can promise a date.
Sources 24, 3, 25, 2, 1