Why sitting brings hip pain onStrong evidence
Sitting bends the hip, presses the buttocks and the sitting bones into the seat, and keeps you still, so it shows up several different problems. In young and middle-aged active adults, hip-related pain is mainly femoroacetabular impingement (FAI) syndrome, where the shapes of the ball and socket pinch as the hip bends, hip dysplasia (a shallow socket), and problems with the labrum and the cartilage, an international consensus says. From mid-life, arthritis becomes more common.
On the outside of the hip, the gluteal tendons are made worse by sitting with your legs crossed and staying in one position too long, NHS inform says. Pain at the sitting bone that is worse sitting points to the hamstring tendon, an NHS trust says. Buttock pain made worse by sitting is among the most commonly reported features of piriformis syndrome, though that research is mostly case reports and small series. Tailbone pain is worse while you sit, when you sit down or stand up, and when you bend forward, the NHS says.
Pain travels, too. In 51 people with hip joint pain who had an injection into the joint, the pain was felt in the buttock in 71%, the thigh in 57% and the groin in 55%. And NHS inform says hip problems can come from the back "even though you don't feel pain in your back", often with pins and needles or sharp, hot or burning pain in the leg.
Sources 1, 2, 3, 4, 5, 6, 7, 8, 9
Hip impingement and sittingEmerging evidence
In one US series of 51 people (52 hips) waiting for surgery for hip impingement, with an average age of 35, sitting made the pain worse in 65% of hips, 43% couldn't sit for more than 30 minutes, and changing position often eased the pain in 52%. The pain was mostly in the groin (83%), and it had taken an average of 3.1 years to be diagnosed. These were people whose pain hadn't settled with other treatment, so the figures show what impingement can feel like, not how common it is.
An international agreement says the diagnosis needs three things together: symptoms, signs on examination and imaging. A scan on its own isn't enough.
Sources 2, 10
Arthritis: from 45, and stiff after restStrong evidence
The National Institute for Health and Care Excellence (NICE) diagnoses osteoarthritis without a scan in people aged 45 or over with joint pain on activity and no morning stiffness, or stiffness that lasts no longer than 30 minutes. The NHS describes "increased pain and stiffness when you have not moved your joints for a while", trouble putting on shoes and socks or getting in and out of a car, and pain in the groin or on the outside of the hip.
Sources 11, 12, 13
Does sitting tighten your hip flexors?Emerging evidence
In 98 adults, people who sat for more than 7 hours a day and were inactive had 6.1 degrees less hip extension than active people who sat little. That's one comparison at a single point in time, with no pain measured, so it can't show that sitting causes tight hip flexors, or that tight hip flexors cause pain.
Source 14
When a scan helpsStrong evidence
Not for most hip pain when sitting. NICE says don't routinely use imaging to diagnose osteoarthritis unless the features are unusual. For hip-related pain in younger active adults, the international consensus starts with X-rays of the pelvis and the hip, and keeps more detailed scans, such as magnetic resonance imaging (MRI), for when more detail is needed, for example when planning surgery. It warns that tears and cartilage changes on scans are also found in people without symptoms. Hip impingement is diagnosed from symptoms, examination and imaging together, never from a scan alone.
Sources 11, 1, 10
How it usually goesEmerging evidence
NHS inform says a new hip problem or a flare should begin to settle within 6 weeks, and that outer hip pain "can often take 6 to 12 months of rehabilitation to settle". Hip impingement often goes on for a long time before it's diagnosed; the consensus recommends at least 3 months of exercise first, and in the larger UK trial, people improved with both physiotherapy and surgery. No one can promise a date.
Sources 9, 3, 2, 18, 19, 20