What femoroacetabular impingement actually does to your hip

Picture a ball rolling smoothly inside a cup — that is how a healthy hip joint works, with the rounded femoral head gliding freely within the acetabulum during every step, squat, or turn. In femoroacetabular impingement (FAI), the ball or the rim of the cup — or both — has grown with a subtle irregularity in its shape. That small bony mismatch means that instead of smooth movement, the joint creates friction: soft tissue at the hip's rim gets pinched or abraded during hip flexion and internal rotation, the positions your hip reaches when you sit deeply, squat, lunge, or swing your leg inward.

FAI is not the same as hip arthritis. It is a structural precursor — a mechanical problem that, if left unaddressed, can tear the labrum (the cartilage seal around the socket rim) and, over time, accelerate cartilage wear, increasing the risk of early-onset hip osteoarthritis. The condition most commonly affects younger and middle-aged adults, particularly those with physically active lifestyles, which is precisely why early recognition matters.

Cam, pincer and mixed: the three structural types

Three distinct bone-shape problems can cause this friction, and specialists classify them by where the irregularity sits.

Cam impingement arises when a bony bump forms at the junction where the femoral head meets the neck of the femur, making the ball slightly non-spherical. As the hip bends or rotates inward, that bump catches against the socket rim and shears the soft tissue just inside it. This pattern is more commonly seen in young, athletic men — particularly those who played high-flexion sports during adolescence — though it is by no means exclusive to that group.

Pincer impingement occurs when the acetabular rim extends too far over the femoral head (think of a lid that overhangs its jar), so the labrum gets compressed between the rim and the femur rather than being able to absorb movement freely. This type tends to be more common in active middle-aged women, again as a tendency rather than a firm rule.

Mixed (combined) impingement — where both a cam bump and excess rim coverage are present — is the most common finding in clinical practice. When both features coexist, cam morphology usually predominates in terms of the mechanical damage it drives.

There is considerable symptom overlap between all three types, so the subtype a patient has cannot be determined from a scan report alone. A specialist will draw on the full clinical picture — symptom pattern, physical examination findings, and imaging together — before characterising which structural problem is clinically relevant.

What FAI feels like day to day

For most people, FAI does not arrive as a sudden dramatic injury. The more typical experience is a dull, deep ache in the front of the hip or groin that builds gradually — often first noticed during or after activities that load the hip in flexion.

Getting in and out of a car is one of the most commonly reported triggers: the sharp hip bend needed to swing into a low seat can produce a catching pain deep in the groin that eases once you are walking again. Prolonged sitting — at a desk, in a car, or on a low sofa — often causes a similar, nagging discomfort that prompts patients to shift their weight constantly or stand to relieve it. Squatting, lunging, climbing stairs, and walking uphill tend to reproduce the same sensation. Pain may also radiate to the outer hip, thigh, or buttock, though these are secondary to the anterior hip and groin ache that remains the hallmark.

Stiffness after a period of rest — getting up from a chair or out of bed — and a reduced ability to rotate the hip inward (making it difficult to cross legs or put on shoes) are common early signs. Some patients also notice a clicking, catching, or locking sensation deep inside the joint; this may suggest that the labrum has become involved, though a clinical assessment is needed to clarify this.

Symptoms often stay mild and intermittent for months before becoming more persistent — many people first realise something is wrong when a familiar activity starts to feel reliably uncomfortable rather than occasionally so.

How FAI is diagnosed

Confirming FAI begins in the consulting room, not the scanner. A specialist will take a detailed history — asking about the pattern, location, and triggers of the pain — before moving to physical examination. The key clinical test is FADIR: the examiner places the hip into Flexion, ADduction, and Internal Rotation simultaneously; reproducing the patient's familiar groin or anterior hip pain is a positive finding that points strongly towards impingement.

If examination supports the diagnosis, the first imaging step is a plain X-ray: an AP view of the pelvis alongside a lateral view of the femoral neck. Together these reveal the bony architecture — a cam bump, acetabular over-coverage, or both — and give the surgeon an initial sense of how significant the structural problem is.

Where soft-tissue involvement is suspected, an MRI arthrogram is the preferred next investigation. This differs from a standard MRI: contrast dye injected into the joint distends the capsule and makes labral tears and cartilage damage far more visible. A standard MRI alone may miss subtle labral pathology, so the arthrogram is the definitive tool when surgical planning is being considered.

One important principle carries through the whole process: a scan showing cam morphology or rim prominence in someone with no meaningful symptoms and no clinical signs does not, on its own, indicate that treatment is needed. Imaging is one piece of information a consultant weighs alongside the history and examination findings — it is not a standalone verdict.

When to move beyond your GP

Knowing when to push beyond a GP consultation is perhaps the most practically useful question this article can answer. A reasonable first step is rest, simple analgesia, and avoiding the activities that consistently trigger pain — but if symptoms have not improved after six to eight weeks, a specialist opinion is warranted.

Several situations justify moving sooner. If pain is reliably limiting daily tasks — sitting at work, getting in and out of a car, playing sport, or managing a physically demanding job — there is little to be gained by waiting out further weeks. The same applies if a catching, locking, or giving-way sensation has developed, as this may suggest labral involvement that benefits from earlier evaluation.

The underlying reason to act is not simply pain relief: untreated FAI can contribute to labral damage and, over time, to early-onset hip osteoarthritis. Several studies have identified FAI as a potential causative factor in hip OA development. Early specialist assessment does not mean surgery is imminent — it means understanding what is happening structurally before changes become harder to address.

In the UK, the standard pathway is a GP referral to a consultant orthopaedic surgeon specialising in hip preservation or young adult hip surgery. Patients who prefer not to wait for a GP referral can self-refer directly to specialist hip services — an option that removes delay when symptoms are escalating. For those in Lincolnshire and the surrounding region, Lincolnshire Hip is part of the MSK Doctors group and accepts patients without a GP referral, with hip assessment clinics in Sleaford and Grantham.

The treatment pathway: conservative care to hip arthroscopy

For most patients with FAI, the first months of management involve conservative measures rather than surgery. A structured physiotherapy programme targeting hip stability, movement quality, and muscle control around the joint forms the foundation — the aim is to reduce the mechanical load that provokes impingement and to improve function enough that daily activities become manageable. Activity modification sits alongside this: practical adjustments such as avoiding low chairs, reducing prolonged sitting, and temporarily scaling back high-flexion sport can meaningfully lower symptom burden.

Where pain is difficult to settle with physiotherapy alone, an image-guided intra-articular injection — typically corticosteroid — may be used as an adjunct to support rehabilitation rather than as a standalone treatment.

When conservative care has not resolved symptoms after a sustained period, or when imaging confirms significant labral damage, hip arthroscopy is the established surgical option. This keyhole procedure allows the surgeon to reshape the femoral head-neck junction (femoroplasty) or trim the acetabular rim (acetabuloplasty), removing the bony conflict that drives impingement. Where a labral tear co-exists with the structural problem — which is common — the labrum is repaired at the same procedure. Addressing the bone abnormality and the labral damage together is important: repairing the labrum without correcting the underlying impingement risks early re-tearing.

Outcomes from arthroscopy are generally better when cartilage wear is still limited, which is why early specialist assessment matters — it keeps joint-preserving options viable.

1. [1] Femoroacetabular impingement – Wikipedia. https://en.wikipedia.org/?curid=20754811 https://en.wikipedia.org/?curid=20754811