Why the back and the hip are easily confusedEmerging evidence
The lower back can send pain to the buttock, the outside of the hip and down the leg. Arthritis UK says back problems can be felt only in the buttocks, down the back of the legs, over the outside of the hip and occasionally the front, and NHS inform says a problem felt in the hip can occasionally come from the back 'even though you don't feel pain in your back'. An NHS physiotherapy leaflet says low back pain affects 80% of adults at some point, can spread into the hips, buttocks or a leg, and is rarely serious.
The hip joint is felt mainly in the buttock, thigh and groin: when 51 people's hip joint pain was confirmed with an injection, 71% felt it in the buttock, 57% in the thigh, 55% in the groin and 22% below the knee. The SI joint is felt in the buttock too: 94% of 50 people whose SI joint pain was confirmed with an injection felt it there, and 72% low in the back. And in 60 people with hip arthritis, 47% had pain below the knee, which most trainee surgeons in the study didn't expect.
Sources 1, 2, 3, 4, 5, 6
Other causes to know
The tendons on the outside of the hip (greater trochanteric pain syndrome, often called hip bursitis) cause pain over the bony point on the outside of the hip, worse lying on that side, crossing the legs or on stairs. It is commonest in women aged 40 to 60, affected 15.0% of women and 6.6% of men aged 50 to 79 on one side in a US study, and is often mistaken for back pain: 20.2% of 252 people referred to spine surgeons with back pain had it. Deep buttock pain can come from the piriformis area (deep gluteal syndrome) or from the hamstring tendon at the sitting bone, a US family doctors' review says.
Two patterns need a GP. Heavy, aching or tingling buttocks and legs on standing and walking that ease when you sit or bend forward point to spinal stenosis, mostly in older adults: having no pain when sitting was one of the strongest clues. Back and buttock pain that started before 45, wakes you in the second half of the night and eases with exercise points to inflammatory back pain (axial spondyloarthritis), which the National Institute for Health and Care Excellence (NICE) asks GPs to refer to a rheumatologist, and which takes 6.7 years on average to be diagnosed.
Some causes aren't in the back or hip at all: the kidneys (pain in the side or back under the ribs with a high temperature and pain when peeing, or a kidney stone's severe pain that can spread to the groin); an abdominal aortic aneurysm (sudden, severe tummy or back pain, most common in men aged 65 or over and in people who smoke, and NICE adds high blood pressure and age over 60); endometriosis (pain in the lower tummy and back); and, in pregnancy, pelvic girdle pain, which affects up to 1 in 5 pregnant women.
Sources 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
How to tell the back from the hipEmerging evidence
In 97 people with leg pain, a limp, groin pain or a hip that wouldn't turn inwards made a hip problem (alone or with a spine problem) 7, 7 and 14 times more likely than a spine problem alone, and groin pain was much commoner with hip arthritis than with spinal stenosis. Pain in the low back above the buttock, a history of back trouble, tenderness over the lower spine and tingling or pain below the knee point to the back, a US family doctors' review says, and in people about to have a hip replaced, pain below the knee went most closely with spine problems.
Buttock pain on its own doesn't decide it, because the buttock is the commonest place for both hip joint pain and SI joint pain. No single test confirms SI joint pain: three or more positive pain tests out of six picked up 94% of people whose SI joint pain was confirmed with an injection. When it remains unclear, a hip X-ray and, in specialist care, an anaesthetic injection into the hip joint help separate the two.
Sources 20, 6, 10, 21, 4, 5, 22
When a scan helpsStrong evidence
Routine imaging isn't recommended for low back pain, and NICE diagnoses osteoarthritis without imaging in people aged 45 or over with joint pain on activity and no morning stiffness, or stiffness lasting no more than 30 minutes. When the hip is imaged, a standing X-ray of the pelvis comes first. After a fall, a magnetic resonance imaging (MRI) scan is offered if a broken hip is suspected despite normal X-rays. Scan findings are common without pain: disc bulges in 30% of pain-free 20-year-olds and 84% of 80-year-olds.
Sources 23, 24, 10, 25, 26
How it usually goesEmerging evidence
New low back pain mostly improves within 6 to 8 weeks, an NHS physiotherapy leaflet says, and the NHS says sciatica usually gets better in a few weeks to a few months. Outer hip pain is slower: with education and exercise, 51 of 66 people reported success at 8 weeks in a trial, and an NHS trust leaflet expects improvement over 8 to 12 weeks, sometimes up to a year. In spinal stenosis, physiotherapy gave similar function to surgery at 2 years in people who were candidates for an operation, though 57% of the physiotherapy group went on to have surgery. No one can promise a timescale.
Sources 3, 27, 28, 7, 29