Hip Dysplasia

What is FAI Femoroacetabular Impingement
(aka Hip Impingement)?

  • Are you suffering from a pain in the groin?  Maybe you’ve been told that you have a ‘groin strain’, but the ache you feel after exercising just isn’t going away?

  • Maybe you’ve been told that you have a ‘groin strain’, but the ache you feel after exercising just isn’t going away?

  • Perhaps you’ve noticed that your hip isn’t moving as well as the other one or that you get a pinching sensation in your groin when you get out of a chair?

Many people with these kinds of symptoms are surprised to learn that typically, it’s actually their hip joint that is causing the pain, because of a condition called FAI – femoroacetabular impingement (aka Hip Impingement).  The pain we feel from the hip joint is in the groin, which is where the ball and socket joint is situated. This can be confusing because in the lay sense, when we say ‘hip’, we tend to mean where you would place your hands on your hips.

What causes Hip Impingement FAI?

It’s a condition caused by a mismatch in bony shapes of the hip. The hip is a ball and socket joint, and the ball (aka femoral head), sits inside the socket (aka acetabulum). Both are covered with hard, shiny, articular cartilage.

Around the entrance to the socket is a soft tissue, gristle ring called the labrum.

In an ideal world, the shape of the ball would perfectly match up with the shape of the socket. Sometimes, however, there can be an error in the shapes, and this may be an error you inherit from your parents.

There are three kinds of impingement:

1. Cam Impingement.

This is the commonest kind of impingement, and there a wider bony area than is desirable, where the neck of the femur meets the femoral head (ball). This ‘Cam’ bump as it’s known, over the years repeatedly rubs against the labrum at the entrance of the hip socket. The labrum frays, and this in turn leads to what’s known as delamination (or ‘lifting off’) of the hard, shiny articular cartilage that lines the socket.

Eventually over many years, the articular cartilage may wear away in some areas, exposing the bone underneath it.  Because the frictional forces increase when the cartilage isn’t functioning properly, this can in turn cause the articular cartilage on the head of the femur to fail.  This bone on bone situation is the beginning of hip osteoarthritis.  Not all causes of FAI go on to become hip arthritis, but many do. Cam impingement tends to occur most frequently in young men, but women can also have cam problems.

2. Pincer Impingement.

In this scenario, it’s the socket that causes the mischief. Excessive bone at the rim of the socket can resulted in the labrum becoming frayed when it makes contact with the neck of the femur during movement of the hip.  It’s a condition that we tend to see in most commonly in middle-aged women. The good news is, the prognosis for a pincer problem is better than for a cam problem, as it’s much less likely you’d go on to develop hip osteoarthritis.

3. Cam and Pincer Impingement.

It’s perfectly possible to have a cam and a pincer! All three types of impingement present in a similar way, and a combined Cam and Pincer Impingement tends be revealed that the time of imaging.

Dr Cath was wonderful. She was kind, thorough, and after an examination and an ultrasound she worked out that I had problem with shoulder tendons and my ‘ACJ’. After an injection and physio exercises, I was back on the court within a month. Fantastic!


What else is involved in Hip Impingement?

Typically, you’ll experience a pain in the groin, but it can extend around the side of the hip (in a ‘C’ shape). You might find that the range of movement in your hip starts to feel limited, and particular positions, e.g. being in a deep squat or pivoting around on you hip, uncomfortable.

Many people report pain swinging their leg in and out of the car, or when getting up quickly from a chair.  You may find that the pain comes and goes with activity. For instance, you might be fine whilst you’re running, but afterwards you get an ache. Many people will also experience a pinching sensation in the groin.

I regularly meet people who believe that they have an ongoing groin strain, or that they have ‘tight hip flexors’ or ‘hip flexor pain’, when in actual fact, they have hip impingement.

How is Hip Impingement diagnosed?

It’s important to say that FAI isn’t diagnosed on an MRI or an X-RAY; in fact, many people will have the appearance of FAI on imaging, but don’t have any symptoms at all.

It starts with taking a proper history, and then examining you. I’ll watch how you move, I’ll examine you, and then I might recommend that we carry out an investigation such as an MRI scan.

X-RAYs aren’t particularly helpful in the diagnostic process, because they are limited to showing us bony shapes.  The gold standard is an MRI scan, but there are MRI scans, and there are MRI scans!

These days, high resolution (3T) MRI scanning, is the best investigation. In the past, lower resolution (e.g. 2T or lower MRI scanning) meant that a radiographic contrast dye (known as an arthrogram) had to be injected into the hip prior to scanning.  I personally avoid using this method if at all possible, because a) it introduces a small risk of possible infection, b) it can over-estimate problems with the labrum, and c) it can be really painful!

As part of the 3T MRI scanning, I like to include what’s called T2 mapping, which gives us further information about the health of the articular cartilage in the joint.

What are we looking for on the MRI scan?

The MRI scan is going to show us the shape of the hips, and whether there are any obvious CAM or Pincer shapes. Sometimes a further test is needed (called Motion Analysis) to determine more information about the shapes and how they fit and move together.

We might also see signs of tearing of the labrum, or small ‘cystic’ areas in the socket cartilage or the neck area of the femur.  If the hip is very irritated or inflamed, we might see an abundance of fluid within the hip joint (known as an effusion).

The MRI scan will give us information about the soft tissues surrounding the hip (e.g. the gluteal tendons and muscles), and we may see other problems which are compounding the situation (e.g. signs of overload of the pubic bones or the symphysis). It will also help us to rule out other conditions which can present in a similar way as FAI (such as Avascular Necrosis).

Many patients I meet, tell me that they have previously been through MRI imaging, and have been told that their scan is normal, and that they don’t have FAI.  But the problem is, the reporting of any scan is a process of giving an opinion, and thus the images are open to interpretation. Sometimes the scans may be reported by a radiologist, who might not specialise in hips.

MRIs can’t definitively tell us if a person’s symptoms are being caused by FAI. Sometimes I may have a very strong conviction that a person’s symptoms are truly coming from within the hip joint, but the imaging is a little, well, ‘meh’. One way to prove or disprove the hip as being the problem, is to carry out a ‘hip block’ injection. This an injection which contains a long-acting local anaesthetic.  If, after the hip has been injected, the symptoms and uncomfortable examination signs temporarily improve, we know that some pain is truly being generated by the hip joint.

What is the treatment for Hip Impingement (FAI)?

There are many myths surrounding what is right or wrong when it comes to the treatment of FAI, and what is right for someone else, may not be right for you.

If you have FAI, I’d always advise that you undergo a course of physiotherapy or osteopathy with a therapist who has a particular interest in hips. It’s also important to get the pain levels down, as pain can inhibit the very muscles we may want to strengthen.

As well as temporarily changing your activity to avoid things that aggravate your symptoms (e.g deep squatting, or kicking in karate), I might recommend that you undergo an injection of the hip joint, (a.k.a. a ‘hip block’ injection).

Good rehab will help identify and rectify biomechanical problems that will be causing poor loading of the hip, and this might include addressing problems outside of the pelvis, such as instability in your ankle, or issues relating to your lumbar spine.

Dr Cath was wonderful. She was kind, thorough, and after an examination and an ultrasound she worked out that I had problem with shoulder tendons and my ‘ACJ’. After an injection and physio exercises, I was back on the court within a month. Fantastic!


Hip arthroscopy surgery

Let’s start by saying that not everybody needs surgery for their FAI problem, but some people do. There have been a couple of key studies worth knowing about.

A study in 2013 looked at how satisfied patients were after their hip arthroscopy surgery (about two thirds were, and a third weren’t).

A further study in 2019 looked at surgery versus physiotherapy and modifying activity levels. The study found that ‘symptomatic FAI patients referred to secondary or tertiary care, achieve superior outcomes with arthroscopic hip surgery than with physiotherapy and activity modification’.

So, what’s my take on this? Start with physio or osteo + pain relief (which may be modifying your activity levels and trying an injection in your hip), and if you’re not making good signs of nice progress after a few weeks, it’s time to maybe consider surgery.

Want to know what you can expect if you undergo hip arthroscopy surgery?  Then read about Hip Arthroscopy Rehab. (Link)

It’s worth saying there is this never any need to rush to make a decision; nothing ‘bad’ will happen, so take your time.

I’m regularly asked to give a second opinion on whether it’s appropriate (or not) to undergo hip arthroscopy surgery, so if you’d like help to make the decision.