What is happening inside the hip joint with FAI

During normal hip movement, the rounded femoral head glides smoothly within the cup-shaped acetabulum. In femoroacetabular impingement (FAI), that smooth glide is interrupted — a bony irregularity causes the femoral head or its neck to catch against the acetabular rim, creating repeated mechanical friction with every hip flex or rotation.

There are three structural patterns. In cam FAI, a bony prominence forms at the femoral head–neck junction, giving the ball an asymmetric, non-spherical shape that jams into the socket at the end of movement — much like a cam catching on a rotating surface. In pincer FAI, the acetabular rim over-covers the femoral head, so the socket itself clips the femoral neck during flexion. A mixed type, where both abnormalities are present, is also common.

Cam morphology is the most frequently seen type and is considerably more common in males. Evidence suggests it develops gradually during adolescence, when the hip's growth plates are subjected to repeated physical loading — a physiological response to sport and activity rather than any single injury. FAI is therefore a structural mismatch, not the result of a specific trauma.

The long-term consequence matters. Each episode of abnormal contact places stress on the acetabular labrum — the fibrocartilaginous ring that deepens the socket and stabilises the joint — and on the articular cartilage beneath it. Over time, this cumulative damage may lead to labral tears and cartilage wear. Based on experience with more than 600 surgical hip dislocations, FAI has been identified as an important mechanism for early osteoarthritis in otherwise healthy, non-dysplastic hips.

What FAI feels like day to day

For most people with FAI, the first clue is a nagging ache deep in the groin or at the front of the hip — not sharp to begin with, but reliably triggered by particular movements. Sitting in a low car seat for more than twenty minutes, squatting to lift something from the floor, pedalling a bicycle, or lunging during exercise are among the most commonly reported triggers. The discomfort often builds rather than strikes immediately, so patients may initially put it down to a muscle problem or a pulled groin.

That pattern of groin pain is worth noting, because deep hip-joint pain and a groin muscle strain can feel remarkably similar from the inside. Pain referred from the lower back can also settle around the hip and groin, which is one reason a clinical assessment rather than self-diagnosis is the appropriate next step when the pattern described here sounds familiar.

Beyond the activity-related ache, a few other features frequently appear:

• Morning stiffness or stiffness after sitting — the hip feels locked or heavy for the first few minutes of movement, then loosens slightly.
• Clicking, catching, or a locking sensation inside the joint — these mechanical feelings commonly reflect involvement of the acetabular labrum, which can become frayed or torn as impingement progresses.
• Night discomfort — a proportion of patients report an aching or difficulty finding a comfortable position when lying on the affected side.

None of these features on their own confirm FAI, and some people with confirmed FAI experience only one or two of them. Their value is pattern recognition: if several apply, the hip joint warrants proper evaluation.

Getting an accurate diagnosis

The diagnostic process is stepwise: clinical examination comes first, and any imaging that follows is interpreted in light of it — not the other way around.

During a consultation, two standardised physical tests are used to reproduce the patient's symptoms. The FADIR test (flexion, adduction, and internal rotation of the hip) is the most commonly used provocative manoeuvre; if it reliably recreates the familiar groin or anterior hip pain, it points strongly towards impingement. The FABER test (flexion, abduction, and external rotation) provides complementary information and helps distinguish hip-joint pain from referred symptoms originating elsewhere.

When clinical findings support the possibility of FAI, plain X-rays of the hip and pelvis are the first imaging step. These identify the characteristic bony changes — the elevated alpha angle seen in cam morphology, and the cross-over sign associated with pincer over-coverage. MRI or MR arthrogram follows when the clinician needs to assess the condition of the acetabular labrum and articular cartilage in detail. CT scanning is reserved for cases where complex three-dimensional bony anatomy needs to be mapped before any intervention.

One principle governs interpretation throughout: an incidental cam-shaped femoral head on a scan is not the same as symptomatic FAI. Cam morphology is common in active adults, many of whom have no pain whatsoever. A valid diagnosis of FAI requires the imaging finding, the clinical examination, and the patient's reported symptoms to tell a consistent story. When they do, that combined picture gives a clinician the information needed to build a genuinely individualised management plan.

Non-surgical management: the first step for most patients

For the majority of patients, conservative care is the appropriate and recommended starting point — and for a meaningful proportion, it is sufficient to bring symptoms under control without surgery.

Activity modification comes first. This means identifying and temporarily reducing the specific movements that provoke pain — deep hip flexion, high-impact loading such as running or jumping, and sustained postures like prolonged sitting in low seats or squatting. This is not permanent restriction; it is a short-term strategy to settle inflammation and allow rehabilitation to begin.

Supervised physiotherapy is the evidence-based foundation of non-surgical management, but the word 'physio' deserves unpacking. For FAI, the most effective programmes are active and specific: they target gluteal strengthening, hip abductor activation, and core stability rather than generic stretching or passive treatments such as ultrasound or massage. Published evidence is clear that supervised programmes focused on active and core strengthening produce significantly better outcomes than unsupervised or predominantly passive approaches. In practice, this means working with a physiotherapist who understands hip-joint mechanics and can progress load in a structured way over a course of weeks.

NSAIDs (such as ibuprofen or naproxen) can manage pain during flare-ups, supporting the patient's ability to engage with rehabilitation rather than serving as a standalone treatment.

Intra-articular injections — most commonly corticosteroid — can settle an irritable hip when pain is limiting progress with physiotherapy. Hyaluronic acid and platelet-rich plasma (PRP) are emerging as adjuncts with promising early evidence, though the evidence base for both continues to develop. Injection options and their respective evidence are a substantive topic in their own right and are beyond the scope of this article.

Conservative care does not guarantee resolution of symptoms, and it will not correct the underlying bony morphology. The realistic aim is meaningful pain reduction and functional improvement sufficient to return to the activities that matter to the patient. Where that goal is not achieved after a supervised programme, surgical assessment becomes the logical next step.

Hip arthroscopy: when surgery becomes the right option

Surgery becomes a realistic conversation when a structured, supervised conservative programme has not delivered sufficient symptom relief — not before. The step from physiotherapy to the operating theatre is a clinical decision shaped by the patient's age, activity goals, the degree of cartilage and labral damage seen on MRI, and how much the symptoms are limiting daily life.

Hip arthroscopy — keyhole surgery performed through small portal incisions — is the established surgical standard for FAI. Using a camera and slender instruments, the surgeon performs an osteoplasty to trim or reshape the cam prominence, the pincer over-coverage, or both, eliminating the source of mechanical friction. Where the labrum has been torn or detached, it is repaired or, where necessary, reconstructed during the same procedure. Because only small incisions are required, recovery is considerably faster than with open hip surgery, and patients are typically mobilising the same day.

Published outcomes support the procedure's effectiveness. A systematic review of 43 studies covering more than 4,100 patients found that approximately 80% returned to sport at the same or higher level after hip arthroscopy for FAI, with a mean time away from sport of around eight months and full return at a mean of 14 months. Critically, that return is criteria-based — guided by functional testing, symmetry, and graded load progression — rather than a fixed date on a calendar.

Longer-term data are similarly encouraging. A 10-year follow-up study in athletes reported a survivorship of 85.7% — meaning that proportion avoided conversion to total hip replacement — alongside sustained improvement across all patient-reported outcome measures. These figures reflect outcomes in appropriately selected patients and should be understood as population-level evidence, not individual guarantees; suitability for surgery depends on a thorough consultant assessment.

For younger, active patients in particular, arthroscopy carries a hip-preservation rationale: by correcting the structural abnormality, it may slow the cartilage deterioration that otherwise risks early osteoarthritis. Patient selection remains the key variable, and the decision is always individualised.

When to get a specialist opinion on your hip

Several signals suggest the time is right to seek a hip specialist's opinion rather than continuing to manage symptoms alone.

Pain that persists beyond six to eight weeks of activity modification and rest — particularly if it is consistently limiting daily tasks such as getting in and out of a car, sitting at work, or returning to exercise — is a practical threshold worth acting on.

Mechanical symptoms — a catching, locking, or giving-way sensation deep in the hip — deserve earlier attention even when the overall pain level feels tolerable. These may indicate labral damage, and a clinical examination combined with targeted imaging is needed to assess it properly.

A specialist assessment is also appropriate when a GP or physiotherapist has already raised the possibility of FAI but conservative management has not produced sufficient improvement. A first consultation typically involves a structured clinical history, a hands-on physical examination, and a review of any existing scans; further MRI or MR arthrogram may be arranged to assess labral and cartilage status in detail before any decisions are made.

Lincolnshire Hip is part of the MSK Doctors group and accepts patients without a GP referral for hip assessment, with clinics in Sleaford and Grantham.

FAI does not inevitably progress to osteoarthritis, but the window for hip preservation — addressing the structural problem before cartilage deterioration accumulates — narrows over time. Earlier specialist input keeps more options open.

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