Diagnostic injections and femoroacetabular impingement

If you suspect you have hip pain from femoroacetabular impingement, you may be considering a hip injection. 

I've been doing a lot of research on FAI. In a recent YouTube comment, an orthopedic physician angrily pointed out that hip joint injections supposedly identify whether hip pain is caused by problems IN the hip joint, like FAI. 

I found his comment interesting, so I did more research on hip injections for FAI. I am going to share some of the results of this research here.

Hip injections for FAI - is the pain caused by what's in the joint?

I started going through the available medical literature on femoroacetabular impingement and I came across this study published in 2008: The Diagnostic Accuracy of a Clinical Examination in Determining Intra-articular Hip Pain for Potential Hip Arthroscopy Candidates. 

You can read the abstract at the link provided. If you have access through a library, I'd suggest looking at the full text as well. Because most of you won't have access, I'm going to share a few highlights here. 

This study looks at diagnostic injections for the hip. It tests the idea that hip injections are helpful in determining the true causes of hip pain. 

The normal argument is as follows: if the hip injection relieves pain, then you have a problem IN the joint (intraarticular cause). Examples would be labral tears, arthritis, or FAI.

If the hip injection does not relieve pain, then the pain is from outside the joint (extraarticular). An example would be some sort of muscle tension issue. 

This study found that in 43% of individuals, extraarticular structures may be a major source of pain even though a labral tear is suggested on MRI arthrogram...The findings of this study provide objective evidence that even if a labral tear is present on MRI arthrogram, it may not be responsible for a majority of the patient’s pain complaints.

Let's unpack this a little bit. They are saying that MRI arthrograms can show you labral tears, and that this still doesn't show you the cause of pain. Put another way: even if you have a labral tear, it might not have anything to do with your hip pain. This was true in almost half the cases in this study. 

It's important to remember also that labral tears are common in asymptomatic people.  This study further supports the idea that labral tears should not automatically be blamed as the cause of one's hip pain. It's a convincing story, but it's not sound. 

This study further examined signs and symptoms correlated with relief of hip pain from a hip injection. One of the common stories in the orthopedic world is that more than 50% relief from a hip injection means you have a problem that needs surgery. Supposedly the relief indicates intraarticular problems. And these intraarticular problems should have predictable symptoms.

So if you have intraarticular problems, do you have a predictable array of symptoms?

...symptoms of groin pain, clicking, pinching pain with sitting, and lateral thigh pain, as well as results of the FABER test, flexion–internal rotation–adduction impingement test, and palpation for greater trochanteric tenderness, could not identify those who would report greater than 50% relief of pain with intra-articular injection.

Unpacking this: the types of pain, the friction, the different range of motion tests, and the places where you feel pain are NOT AT ALL connected to whether the injection is helpful. 

The hip injection may help. It may not. But the hip injection result doesn't tell you anything about the nature or cause of your hip pain. 

Put another way, if labral tears cause specific types of pain (e.g. clicking and pinching, reduced range of motion), then the hip injections should help reduce the symptoms. But the injections do not have any reliable effect for any of those issues. 

Surprising? Given the faith surgeons place in hip injections, it should be.

What about hip injections as they relate specifically to FAI?

There's even more to the story on hip injections for FAI.

Many people are told that if a hip injection relieves their hip pain, they have problems in their hip joint (intraarticular problems). The solution is arthroscopic surgery to repair the FAI and/or labral tears. 

But is this true? Does hip pain research prove that relief from a hip injection means surgery will work? 

I found this 2014 study: Pre-operative intra-articular hip injection as a predictor of short-term outcome following arthroscopic management of femoroacetabular impingement

The paper points is clear on hip joint injections for those with FAI: 

...the data suggests that a positive response from an intra-articular hip injection is not a strong predictor of short-term functional outcomes following arthroscopic management of FAI. However, a negative response from an intra-articular hip injection may predict a higher likelihood of having a negative result from surgery.

This study shows that diagnostic hip joint injections are NOT reliable indicators of success from surgery. If you do have improvement from hip joint injection, it's not predictive of success. Read that again. 

A successful hip injection does not mean FAI surgery will work. At all. 

What does this all mean for hip injections for FAI?

All this means hip injections for FAI are oversold. Surgeons claim they're useful based on no solid evidence.

Femoroacetabular impingement as a diagnosis is very new. If you dig into the research on its creation and treatment, you will find a lot of evidence that the entire diagnosis is a fiction. It's a convincing-sounding story (your bones cause you pain, so we can just shave down bones), but it's not supported by any solid science (read more here). 

If you're struggling to make sense of femoroacetabular impingement and are considering a hip injection for FAI, take the time to do your homework. Ask your doctors for studies to support what they claim. And remember to double check what you're being told.

Medical science changes fast, and it can take years before new knowledge filters into medical practice.