Femoroacetabular impingement (FAI): symptoms, diagnosis and treatment

The Royal National Orthopaedic Hospital (RNOH) lists the common symptoms of FAI syndrome. MyHealth Devon, an NHS site, adds that the most common movement to bring on pain is hip flexion (knee towards the chest), and that pain is usually in the groin but sometimes further down the front of the thigh, or at the side or back of the hip.

• Deep pain in the front of the hip or groin, sometimes spreading to the outer hip, back of the hip and thigh.

• Stiffness of the hip.

• Hip pain at the end of a movement.

• Pain on squatting, sitting and lunging.

• Night pain, if the hip is irritable.

• Clicking, catching, locking and giving way of the hip in some people.

• MyHealth Devon notes that sitting for a long time, for example on a long car journey, often brings on groin pain, and that activities involving hip flexion such as football, cycling, dancing and aerobics make pain worse.

The hip is a ball-and-socket joint. The ball (femoral head) is the top of the thigh bone and the socket (acetabulum) is in the pelvis. Versus Arthritis says FAI is a condition where the ball and socket do not move freely through their normal range of movement, either because the top of the ball is not completely round or because the socket is too deep, and notes that it is not fully understood why this happens.

The RNOH explains the shapes. Cam morphology is a bump of varying size at the junction of the femoral head and neck, which affects the round shape of the ball. Pincer morphology is a deeper socket, extra bone on the socket rim, or a change in the socket's orientation. A combination is called mixed morphology. Changes in shape can increase load through the hip cartilage and labrum (the rim of cartilage around the socket) and sometimes cause tears of the labrum.

The RNOH says primary cam morphology develops in young, active people, including athletes, and is more common in males. It likely develops during childhood and adolescence while the skeleton is maturing, and is described as a normal response to physical load, not linked to previous injury or disease. Conditions such as Legg-Calve-Perthes disease and slipped capital femoral epiphysis can increase the likelihood of changes in hip shape, which it calls secondary cam morphology.

MyHealth Devon says research from Oxford has shown a strong genetic predisposition to the condition. Versus Arthritis says it is not fully understood why FAI happens and that in most circumstances no specific treatment is needed.

The RNOH says a doctor or physiotherapist will usually suspect FAI syndrome from your symptoms and a number of physical examination tests. To confirm FAI syndrome, three elements are needed: clinical symptoms, clinical signs, and variations to the shape of the hip bones on imaging. It stresses that changes to hip shape without symptoms are common, so a person without symptoms does not have FAI syndrome even if imaging shows typical findings.

MyHealth Devon says X-rays and scans may be needed if symptoms remain severe despite conservative management. X-rays look for arthritis, other causes of hip pain and the subtle bony changes of FAI; an MRI scan can show whether the labrum is torn or the cartilage damaged; and a CT scan may show the bony anatomy in more detail. Sometimes a local anaesthetic is injected into the hip to see if the pain comes from within the joint.

Versus Arthritis adds that if X-rays and scans of the hip are normal, symptoms may be caused by referred pain from the lower back, felt in the buttocks, down the back of the legs, over the outer hip, and occasionally in the front of the hip.

The RNOH says recent evidence suggests both physiotherapy and surgery can be helpful in symptomatic FAI syndrome, and that exercise-based physiotherapy should be the first-line treatment for at least 3 months. Treatment consists of activity modifications to manage load on the hip and reduce irritability, an exercise programme to improve control and strength of the muscles around the trunk, hips and pelvis, exercises for function and balance, hip joint movement optimisation, a graded return to sport and function, and cardiovascular fitness. If you are not improving, you are reviewed by the surgical team to discuss risks and benefits for your situation.

Other options include a corticosteroid injection, which the RNOH says has evidence of a short-term effect on symptoms. MyHealth Devon describes lifestyle and activity modification, physiotherapy to reduce pain and stiffness and optimise strength and motion, injections, and surgery. The NHS hip pain page lists physiotherapy, occupational therapy, steroid injections and referral to a specialist, and says some people with a damaged hip joint may eventually need a hip replacement.

The FAIT trial, a randomised trial across seven NHS England sites, compared arthroscopic (keyhole) hip surgery with physiotherapy and activity modification in 222 people aged 18 to 60 with symptomatic FAI. At eight months the hip outcome score was on average 10 points higher in the surgery group, and no serious adverse events were reported in either group. The physiotherapy programme was a maximum of eight sessions over five months. The authors concluded that people with symptomatic FAI referred to hospital achieve better outcomes with arthroscopic surgery than with physiotherapy and activity modification.

The trial authors note that the number of hip arthroscopy procedures in England increased by 727% between 2002 and 2013, with substantial regional variation. Versus Arthritis says it is not clear whether surgery helps prevent arthritis developing in the long term. The RNOH says that to maximise recovery, surgery should be done together with a physiotherapy-led exercise programme, and that in some cases physiotherapy and surgery do not achieve full, pain-free hip movement.

The RNOH suggests understanding which positions aggravate your hip, and gives some examples.

• Sitting: reduce time on low chairs, sit with hips higher than knees (a wedge cushion may help), and consider a sit-stand desk to change position regularly.

• Sleeping: a pillow between the knees can support a sore hip, or sleep semi-prone, halfway between lying on your tummy and your side, with pillows supporting the top leg.

• Activity: your therapist may discuss changes to work and leisure activities, weight management, stopping smoking and diet.

• The NHS suggests for hip pain generally: keep moving but do not overdo it, use paracetamol or ibuprofen gel, wear comfortable shock-absorbing shoes, lose weight if overweight, and avoid sitting in low chairs.

MyHealth Devon says FAI may increase the risk of developing arthritis later in life, although not everyone with impingement will develop it, and that most experts agree there is a close association between hip impingement and hip osteoarthritis, though it is not well understood why some people develop it and others do not. The FAIT trial authors report that FAI shape is seen in about one fifth of the general population, fewer than 25% of whom develop pain or osteoarthritis. Versus Arthritis says surgery may improve movement, but it is not clear if it prevents arthritis in the long term.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you have severe hip pain that started suddenly without a fall or injury, your hip is swollen and feels hot, the skin has changed colour, or you have hip pain with feeling generally unwell and a high temperature. Call 999 or go to A&E if you have severe hip pain after a fall or injury, cannot walk or put weight on your leg, or have tingling or loss of feeling in your hip or leg after an injury. See a GP if hip pain stops you doing normal activities or affects sleep, keeps getting worse or coming back, or has not improved after 2 weeks of home treatment.

Versus Arthritis and the NHS describe several conditions that can cause hip pain. The table shows how FAI differs.

On the NHS, many areas allow self-referral to a community musculoskeletal (MSK) service for physiotherapy without a GP referral. Hospital orthopaedic teams assess people whose symptoms do not respond to physiotherapy, arrange scans, and discuss surgery.

Private hip clinics and physiotherapists also see people with FAI. Whichever you choose, ask what first-line rehabilitation is offered before surgery, how long it will last, and what the evidence suggests for people like you. The RNOH advises that surgery works best with physiotherapy-led rehabilitation.