What is actually happening inside the hip joint

The hip is a ball-and-socket joint: the rounded head of the femur (the ball) turns freely inside the cup-shaped acetabulum (the socket). In femoroacetabular impingement — FAI — that clearance is reduced by extra or misshapen bone, and the joint starts to grind rather than glide.

There are two bony culprits, often found together. A cam lesion is a bony prominence at the femoral head-neck junction that makes the ball non-spherical; on hip flexion it jams against the rim of the socket. A pincer lesion is excess bone along the acetabular rim that over-covers the femoral head, trapping and crushing the soft tissue at the socket's edge. Most people with FAI have elements of both — termed mixed type.

The soft tissue at greatest risk is the acetabular labrum, a fibrocartilaginous seal that deepens and stabilises the socket. Each cycle of loading drives the bony prominence into the labrum, fraying and eventually tearing it. Once the labrum is compromised, the underlying articular cartilage begins to wear.

This progression matters beyond pain management. Multiple studies have linked untreated FAI to early-onset hip osteoarthritis, establishing it as a genuine joint-preservation concern rather than an incidental finding. FAI is also among the most common causes of hip pain in active adults under 50 — making it a diagnosis worth identifying early.

Symptoms: what FAI feels like day to day

For most people, FAI makes itself known as a deep ache or sharp catch in the groin — not on the outer hip or buttock, but somewhere inside and forward, often hard to point to precisely. The sensation tends to be intermittent at first and easy to dismiss.

What brings it on is usually predictable: hip flexion under load. Common triggers include sitting for more than thirty or forty minutes (especially in low car seats), squatting, climbing stairs, putting on shoes, or any sport that repeatedly loads the hip — football, cycling, rowing, and gymnastics are among the most frequently reported. Athletes often notice symptoms during or after training rather than at rest, whereas in less active adults the pattern is more positional: sustained sitting provokes the ache, standing or lying down eases it. Restricted internal rotation — the movement that turns the knee inward while the hip is flexed — is a common finding that tends to creep up gradually rather than arriving suddenly.

That said, these symptoms alone do not distinguish FAI from other causes of groin and hip pain. The location and triggers described above overlap with conditions originating elsewhere — referred pain from the lumbar spine can travel convincingly into the groin, and trochanteric bursitis produces lateral hip discomfort that patients sometimes describe as a groin problem. For this reason, an imaging finding of cam or pincer morphology is a contribution to diagnosis, not the diagnosis itself: clinical correlation, examination, and a thorough history are all required before a firm conclusion can be drawn.

How FAI is diagnosed

Pinning down FAI requires more than a scan result — the assessment builds in layers, each one narrowing the picture before the next is added.

History and clinical examination

The starting point is a detailed conversation: where exactly is the pain, what provokes it, what eases it, and how long it has been present. The consultant then examines the hip through a series of movements. The most informative is the FADIR test — the hip is passively moved into flexion, adduction, and internal rotation — a position that recreates the bony contact inside the joint. Reproduction of familiar groin pain during this manoeuvre is a reliable indicator of FAI, though it must be interpreted alongside the history rather than in isolation.

Imaging: what each step adds

Plain X-rays come first. They reveal the overall shape of the femoral head and acetabular rim — an elevated alpha angle suggests a cam lesion; a crossover sign points to pincer over-coverage. X-rays also screen for hip osteoarthritis and other bony pathology that might alter the management plan.

MRI — ideally MR arthrography, where contrast is injected directly into the joint — provides soft-tissue detail that X-rays cannot show: the condition of the labrum, the state of the articular cartilage, and the extent of any chondral wear.

CT is used selectively. Where surgical correction is being planned, a three-dimensional CT reconstruction gives the surgeon a precise map of the deformity that flat imaging cannot fully capture.

Asymptomatic cam morphology is genuinely common in the wider population; the investigations together build a case, they do not independently deliver a verdict.

Conservative management as the first-line approach

Conservative management is the recommended starting point for the large majority of patients with FAI, and giving it a genuine, structured trial matters — both because a meaningful proportion do well without surgery, and because any subsequent surgical decision is better-informed once conservative care has been properly tested.

What physiotherapy involves

Physiotherapy for FAI is condition-specific, not generic. The focus is on strengthening the deep hip rotators and abductors — the muscles that govern how the femoral head sits and moves within the acetabulum — alongside movement re-education to address the compensatory patterns that commonly develop around a painful hip. Bony impingement tends to generate sustained overactivity in surrounding muscles; correcting this neuromuscular component is a core part of the programme, not an optional extra.

Activity modification runs in parallel: temporarily reducing high hip-flexion loading — avoiding deep squatting, prolonged low-seat sitting, or the specific training activities that consistently provoke symptoms — allows inflamed soft tissue to settle while strength and motor control improve.

The role of injection

An image-guided intra-articular injection can be useful when pain is limiting meaningful engagement with physiotherapy. A corticosteroid placed accurately within the joint reduces inflammation to a level where structured exercise becomes practicable. It also carries diagnostic value: a clear symptomatic response confirms the hip joint itself as the primary pain source rather than structures outside it.

What makes a trial adequate

A useful benchmark is at least three months of supervised, progression-tracked physiotherapy — not a brief course of generic exercises or unsupported stretching. Patients who complete a programme of this standard and still carry functionally limiting pain, confirmed at reassessment, are the group for whom arthroscopic correction becomes a realistic consideration rather than a premature one.

When hip arthroscopy becomes the right option

Surgery becomes a realistic option for patients who have completed a structured conservative programme and still carry functionally limiting symptoms. Two conditions must be met before arthroscopy is appropriate: symptoms that have not resolved with adequate conservative care, and a hip joint that is in reasonable structural condition. Hip arthroscopy is a joint-preservation procedure — it corrects the source of mechanical friction rather than replacing the joint — so significant pre-existing hip osteoarthritis shifts the clinical conversation in a different direction.

What the procedure involves

Hip arthroscopy is performed under general anaesthetic, typically as a day case or with a one-night stay. The hip is gently distracted to open the joint space — necessary given the joint's tight anatomy — and two or three small portals admit the arthroscope and working instruments without the need for a large incision.

For a cam lesion, the surgeon performs a femoroplasty: the bony prominence at the femoral head-neck junction is carefully shaved back under direct vision until the femoral head regains a rounder profile, eliminating the point of internal friction. Pincer correction involves trimming the over-prominent acetabular rim to restore normal coverage.

Where the labrum has torn — which is common in FAI — it is reattached to the acetabular rim using suture anchors rather than simply removed. Preserving labral tissue is now the preferred approach, as the labrum contributes to the joint's fluid seal and long-term stability.

In some patients, cartilage damage found alongside the impingement is addressed at the same sitting — techniques such as microfracture may be used — though the extent of any additional work depends on what the surgeon finds intra-operatively.

For appropriately selected patients, published outcomes support arthroscopic correction as an effective means of reducing pain, restoring range of motion, and limiting the longer-term risk of progressive joint damage.

Recovery after hip arthroscopy and long-term outlook

Recovery after hip arthroscopy follows a structured, staged programme — designed to protect what the surgeon has corrected while progressively rebuilding the strength and movement quality needed for full activity.

Protecting the repair

Crutch-assisted weight-bearing for two to four weeks is standard after most FAI procedures. This protects a reattached labrum and any reshaped bone from premature loading during initial healing. Physiotherapy begins promptly — not to load the joint, but to maintain range of motion and limit stiffness while swelling settles.

Building strength and function

As healing allows, the programme shifts to progressive hip strengthening: deep rotators, abductors, and the stabilising muscles surrounding the joint. Movement-quality work continues alongside this, addressing any compensatory patterns that developed before surgery. Progression is guided by the physiotherapist's clinical assessment rather than a fixed weekly schedule.

Return to sport: milestones, not a calendar

Readiness for running, sport, or physically demanding work is determined by functional criteria — demonstrable strength symmetry, consistent pain-free loading through the hip, and movement quality under real conditions — rather than a target week. Published outcomes suggest that most patients return to higher-level activity between three and six months, though the range reflects genuine variation based on the complexity of the procedure and the individual's pre-operative condition.

The longer view

Treating FAI is about more than resolving current symptoms. Correcting the mechanical friction that was repeatedly damaging the labrum and articular cartilage addresses the structural cause. Multiple studies have recognised untreated FAI as a causative factor in the development of hip osteoarthritis; early intervention, in appropriately selected patients, may reduce the risk of progressive joint damage and limit the likelihood of more extensive surgery further down the line. For a hip joint that still has its own cartilage, removing the source of impingement is the most meaningful step toward keeping it that way.

1. [1] Femoroacetabular Impingement. https://en.wikipedia.org/?curid=20754811 https://en.wikipedia.org/?curid=20754811
2. [2] Hip Arthroscopy. https://en.wikipedia.org/?curid=31963181 https://en.wikipedia.org/?curid=31963181