Hip Impingement (FAI): A Cause of Labral Tears and Early Hip Arthritis

Femoroacetabular impingement — FAI — is one of the most confused diagnoses I encounter in clinic. Patients arrive having been told they have “hip impingement” or “FAI” without a clear picture of what that actually means, how it causes pain, or what to do about it. The clarifying frame is simple: FAI is an anatomic shape mismatch in the hip that loads the joint abnormally during normal motion — and over years, that abnormal loading causes labral tears and accelerates the development of hip arthritis.

What FAI actually is

The hip is a ball-and-socket joint. In a normally shaped hip, the ball (the femoral head) rotates smoothly within the socket (the acetabulum) without bony contact during everyday motion. In FAI, a subtle shape variation causes the bone to pinch the labrum and articular cartilage during certain movements — especially deep flexion, internal rotation, and combinations of the two (think: deep squats, putting on socks, getting out of a low car seat).

Each individual pinching event is small. But repeated over years of normal living, that abnormal contact wears down the labrum and the joint surface in ways that can produce a labral tear, articular cartilage damage, and eventually arthritis.

CAM, Pincer, and Mixed FAI

FAI generally falls into three patterns:

CAM impingement (femur side)

The femoral head-neck junction is more aspherical than normal — slightly bumpier on one side rather than perfectly round. During flexion, that aspherical edge catches against the rim of the socket. CAM-type FAI is more common in men and is associated with sports involving deep hip motion during adolescence (hockey, soccer, basketball, ballet).

Pincer impingement (socket side)

The rim of the socket extends too far over the ball — sometimes because the socket is deeper than normal, sometimes because of a rim overgrowth. The over-coverage pinches the labrum during normal motion. Pincer-type FAI is more common in women and tends to present somewhat later in life.

Mixed FAI

A combination of both CAM and Pincer features. This is the most common pattern in adults presenting with symptoms — and it is also the pattern most likely to accelerate joint damage over time.

How FAI causes hip damage over time

The damage pattern from FAI follows a recognizable progression over years to decades:

1. Labral irritation and tear. The labrum is the first structure pinched by the abnormal contact. Over time it becomes irritated, then frays, and eventually tears. This is why so many FAI patients are first diagnosed with a labral tear — the tear is often the visible result of the underlying impingement.
2. Articular cartilage damage. With continued impingement, the joint cartilage at the site of contact begins to wear or delaminate. This is the start of the arthritis process.
3. Progressive arthritis. Once cartilage is lost, the joint enters the same wear-and-tear process as garden-variety hip osteoarthritis — joint-space narrowing, bone changes, and eventually the symptoms of arthritis.
4. Symptomatic arthritis and replacement consideration. When the arthritis becomes limiting despite nonsurgical care, hip replacement becomes the right conversation.

What FAI feels like

The classic FAI symptom pattern:

Many patients describe the symptoms as “it's been there for years, it comes and goes.” That waxing-waning pattern over time is typical — until either the symptoms become constant, or arthritic changes appear on X-rays.

FAI on the anatomic-cause spectrum

FAI is one of several anatomic conditions that load the hip abnormally and predispose to early arthritis. The closest relative is hip dysplasia — a shallow or under-covered socket, often present from childhood — which causes a different but related pattern of accelerated wear. Many adults have features of both, and the underlying concept is the same: anatomy that loads the hip abnormally over decades.

Understanding FAI, dysplasia, and the related developmental conditions (such as childhood Legg-Calvé-Perthes) as part of one spectrum — rather than completely separate diagnoses — often helps patients make sense of why they are dealing with hip problems in their 30s, 40s, or 50s rather than their 70s.

Where am I on the continuum?

The single most important question once FAI is identified is where you are on the FAI-to-arthritis continuum. That determines everything about treatment. The answer comes from a combination of your symptoms, an exam, and — most importantly — weight-bearing X-rays of the hip.

• Stage 1 — FAI without arthritis. Symptoms but a well-preserved joint on imaging. Preservation surgery (hip arthroscopy, sometimes open surgery) can address the impingement and labral tear, and may help slow progression.
• Stage 2 — FAI with early arthritis. Some cartilage loss or early arthritic changes. Preservation surgery here has less reliable results; nonsurgical management is usually the right starting point.
• Stage 3 — FAI with advanced arthritis. The arthritis is now the dominant problem. Hip replacement becomes the conversation when symptoms become limiting.

Treatment at each stage

Stage 1 — Symptomatic FAI, no arthritis

For younger adults with symptomatic FAI and a healthy joint, hip-preservation surgery is often the right answer — typically hip arthroscopy to repair the labrum and reshape the bone causing the impingement. This is well-studied surgery in well-selected patients, and outcomes are generally good when the hip has not yet developed arthritis.

Stage 2 — FAI with early arthritis

This is the most nuanced group. Preservation surgery in a hip that has already begun to develop arthritis tends to disappoint — the underlying joint surface is the actual driver, and addressing the impingement alone may not change it. The right pathway is usually nonsurgical:

• Activity modification to reduce the impingement-provoking motions
• Physical therapy focused on hip strength and balanced mobility
• Weight management, where it applies
• Ultrasound-guided injections — the hip joint is deep, so accurate placement matters. An ultrasound-guided cortisone injection or PRP injection can provide meaningful relief and also help confirm that the joint itself is the source of pain.

Stage 3 — FAI with advanced arthritis

When the arthritis becomes the dominant problem and is meaningfully affecting your life despite nonsurgical care, hip replacement becomes a reasonable conversation. Modern hip replacement — particularly through the direct anterior approach — is highly durable (more than 90% remain intact at 30 years) and dramatically improves quality of life. For patients who have had previous hip-preservation surgery, the replacement is technically a bit more complex but the outcomes remain excellent.

See the signs you may need a hip replacement for what that conversation usually looks like.

What patients tell me

FAI patients tend to fall into a few familiar archetypes:

The right answer in each case depends on which stage of the continuum you are actually in — not on which label you were given first.

Next step

If you have been told you have hip impingement or FAI, the most useful thing you can do is get an honest assessment of where you are on the continuum. Weight-bearing X-rays, a clinical exam, and an honest conversation about what your hip actually looks like now — not just what the MRI showed years ago — will determine the right next step. For most patients, the answer is nonsurgical care for as long as it works, and then a well-timed hip replacement when it doesn't.