Hip Impingement (FAI): What Is It and Why Does Your Hip Catch?
Hip impingement is also called femoroacetabular impingement (FAI). It happens when extra bone on the hip joint causes the ball and socket to rub together abnormally. This pinches the tissue around the joint when you move. It leads to groin or hip pain, stiffness and a catching feeling. It is one of the most common causes of hip pain in active adults.
Key points
- FAI is caused by an irregular shape of the ball, the socket, or both.
- There are two main types: cam (ball side) and pincer (socket side). Many people have a mix of both.
- Pain usually appears in the groin or the front of the hip, especially during deep bending, sitting or twisting.
- Standard scans done lying down may not show how the joint behaves under your full body weight.
- A standing, whole-body EOS scan can show how the shape of your hip affects your alignment from feet to spine.
What is the difference between cam and pincer impingement?
Cam impingement is a bump of extra bone on the ball (femoral head). Pincer impingement is extra bone on the rim of the socket (acetabulum). Cam lesions are more common in younger men and athletes. Pincer lesions are seen more often in women. Many people have a combination of both. This is sometimes called mixed-type FAI.
The type matters because it affects where the joint catches and which movements bring on pain. A cam bump tends to jam during deep flexion (bending the hip). A pincer overhang tends to pinch during rotation. Knowing the type helps your clinician plan the right approach.
What does hip impingement feel like?
Hip impingement usually causes a deep ache or a sharp pinch in the groin or the front of the hip. You might feel it most when bending, sitting for a long time, getting in and out of a car, or playing sport. Some people also feel stiffness first thing in the morning. Others notice a clicking or locking feeling in the joint.
Important: If you notice sudden weakness in your leg, numbness spreading below your hip, or any loss of bladder or bowel control, please get urgent medical help. Contact your doctor straight away or go to your nearest emergency department. These symptoms need immediate assessment, not a routine scan.
What causes hip impingement?
The bone shape that leads to FAI usually develops in childhood and the teenage years, as the hip joint grows. Most people never know they have it until symptoms begin. Symptoms are often triggered by a change in activity level, repeated sport, or simple wear over time.
The body works as a connected chain from feet to head. So the position of your pelvis, spine and knees all affect how your hip joint sits under load. A problem somewhere else, such as a small leg length difference, can change how the ball meets the socket. This can push an otherwise mild impingement into painful territory.
How is hip impingement assessed when you are standing up?
Most hip scans are done while you lie flat on a table. This relaxes your muscles and takes the load off the joint. It also lets the pelvis settle into a position it would never take when you are actually on your feet. A standing, weight-bearing EOS scan captures the hip in real-life conditions.
An EOS scan images your whole body from head to feet while you stand naturally. It shows your true pelvic tilt, your leg length, and how the hip socket faces under load. This gives your clinician a complete picture of the forces acting on the joint. EOS uses about 90% less radiation than a standard X-ray, around ten times less.
A conventional X-ray, CT or MRI taken lying down takes gravity and muscle tension out of the picture. The pelvis may look level when it is not. The socket angle can look normal even though it pinches when you stand. Lying-down imaging still has an important role, but it cannot show how the joint takes load in real life.
This matters because hip impingement is not just about bone shape. It is about what that shape does under load. Two people with the same bone bumps can have very different symptoms if their pelvic tilt or spinal posture is different. A whole-body standing image captures these links in a single scan.
When MRI is the better choice: EOS is excellent at showing bones, joints and alignment. If your clinician suspects a labral tear, cartilage damage or another soft-tissue injury inside the hip, MRI is usually the better tool. In many cases, both types of imaging work together to build the full picture.
Not sure which type of imaging you need? A short, free video consultation can help you decide before you plan a trip to London.
Book a free video consultationHow is hip impingement usually managed?
Treatment for FAI depends on how severe it is and the type of impingement. ScanAlign is a diagnostic imaging clinic and does not provide treatment. But knowing the common ways it is managed can help you have a better informed talk with your orthopaedic specialist or physiotherapist.
- Changing activities. Avoiding positions that bring on the pinch, such as deep squats or sitting for a long time with crossed legs, can reduce day-to-day pain.
- Physiotherapy. Strengthening the muscles around the hip (especially the gluteal muscles) and improving movement control can ease pressure on the joint.
- Injections. A guided injection into the hip joint can help confirm the diagnosis and give short-term pain relief.
- Arthroscopic surgery. If conservative measures are not enough, keyhole surgery can reshape the bone and repair damaged tissue. The approach depends on whether the impingement is cam, pincer or mixed.
Accurate imaging before any procedure is important. Understanding the bone shape, the position of the pelvis and the alignment of the whole leg helps your treating clinician choose the right plan. You can read more about hip alignment and EOS imaging at ScanAlign.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
Frequently asked questions about hip impingement
Hip impingement is about an abnormal bone shape that makes the joint pinch during movement. Arthritis is wear of the cartilage lining the joint. However, untreated impingement can speed up cartilage wear and lead to arthritis over time. That is one reason early assessment matters.
The bone shape itself does not change without surgery. Symptoms can improve with physiotherapy and changes in activity, but the bump or overhang underneath remains. Getting an accurate diagnosis helps you decide whether conservative management is enough.
Low-impact activities such as swimming, cycling with a raised seat, and targeted gluteal strengthening are often well tolerated. Avoid deep squats, lunges, and anything that forces the hip into extreme flexion or rotation until a physiotherapist has assessed you.
Your clinician will usually start with a physical examination, including the FADIR test (flexion, adduction, internal rotation). Imaging then confirms the bone shape. A standing EOS scan can add alignment information that conventional X-rays taken lying down may miss.
When you lie down, your pelvis tilts differently and the angle of the hip socket changes. A standing scan shows how the joint actually takes load under gravity. This can reveal impingement that looks mild, or even absent, on a lying-down image.
Yes. The EOS system uses about 90% less radiation than a standard X-ray, around ten times less. You can find more details on the FAQs and safety page.
No. ScanAlign accepts self-referrals. You can book a free video consultation to discuss your symptoms and decide whether an EOS scan is right for you.
The price for patients travelling from abroad is confirmed during the free video consultation. You can find more information on the ScanAlign FAQs page.
Yes. A stiff or painful hip can change the way you walk and stand. Over time, your lower back, knee, or even your other hip may start to compensate. That is why a whole-body scan can show more than imaging one joint on its own.
You stand naturally inside the EOS scanner at 19 Harley Street, London. The scan takes about 20 seconds. There is no enclosed tunnel and no need to change into a hospital gown. A specialist radiographer reviews the images and prepares a detailed report. Learn more about what ScanAlign offers.
Wondering if your hip pain is caused by impingement?
A free video consultation with a specialist radiographer can help you understand whether a standing alignment scan in London is the right next step for you.
Book a free video consultationSources
- Griffin DR, Dickenson EJ, et al. "The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome)." British Journal of Sports Medicine, 2016;50:1169-1176.
- Ganz R, Parvizi J, et al. "Femoroacetabular impingement: a cause for osteoarthritis of the hip." Clinical Orthopaedics and Related Research, 2003;(417):112-120.
- NHS. "Hip pain in adults." nhs.uk. Available at: https://www.nhs.uk/conditions/hip-pain/
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.