When you've been told you have femoroacetabular impingement, the theory is that the shapes of your bones is causing you hip pain and range of motion issues.
Doctors often make this claim, although there is a large body of strong evidence that the bone shapes do not have any causal relationship to hip pain or range of motion issues.
Put in simple terms: research shows the bone shapes are NOT the reason hips hurt.
Is there evidence that FAI bone shapes are related to pain?
The list of studies you'll find at the end of this article provides strong evidence that signs of “impingement” in x-rays and MRI is very common in the asymptomatic population. It is therefore highly unlikely that bone shapes alone are responsible for the symptoms of hip pain and movement problems.
Let's take a look at one study that examined over 4000 people: Gosvig, K..K, Jocobsen, S., Sonne-Holme, S., & Gebuhr, P. (2008). The prevalence of cam type deformity of the hip joint: a survey of 4151 subjects of the Copenhagen Osteoarthritis study. Acta Radiol, 49, 436-441.
In this study, they found that cam deformity was common and completely unrelated to the development of hip pain and arthritis. They found cam type bones in approximately 17% of men and 4% of women.
"the distribution of cam deformity was unaltered in subjects with normal joint space width or other features of hip-joint degeneration. we found no significant association with self-reported hip pain…it is a far from uncommon deformity in subjects with no apparent evidence of hip-joint osteoarthritis.”
In plain English, this means that the cam deformity had nothing to do with joint space problems. It had nothing to do with hip pain. And it had nothing to do with arthritis of the hip.
The authors of the study go on...
“We found no significant correlation to hip pain or groin pain, nor did we find any significant relationship between hip dysplasia and cam deformity, or between radiologic evidence of hip-joint OA and cam deformity.”
In plain English, they found that the hip and groin pain aren't even correlated with FAI cam bone shapes!
Normally, you'd want to find correlation AND causation. In this case, they could not even find correlation.
What that means is that the cam-type bone shape seems to be irrelevant in the development of pain and arthritis.
Do FAI bone shapes matter as you get older?
It doesn't even matter if you have FAI bone shapes as you age.
In one study, researchers looked for bone shapes in healthy senior-age athletes (link).
They found that the presence of the cam and pincer bone shapes had no relationship with hip pain or hip function even in this older age group.
....Radiographic findings consistent with FAI in these senior athletes were common and were not associated with the presence of OA (OSTEOARTHRITIS). These data suggest that the need to screen for asymptomatic young athletes for radiographic evidence of FAI and DDH (DYSPLASIA) may not be necessary...
In plain English?
X-rays in these seniors showed FAI bone shapes quite commonly. But those bone shapes had no relationship to hip problems.
So screening younger athletes for FAI bone shapes or dysplasia may not make sense. After all, if the things you're screening for have no relationship to pain, it doesn't make sense to screen for them!
If you know that your test doesn't identify the cause of a problem, then the test doesn't need to be done!
Despite a growing body of evidence that FAI bone shapes are unrelated to pain or movement dysfunction, doctors still commonly assert that FAI bone shapes need to be addressed to improve comfort and function.
The reasons for this are complicated and varied and are beyond the scope of this article. The key takeaway is that it is a good idea to inform yourself and read these studies before committing to any surgical intervention to "correct" bone shapes. The bone shapes, by all accounts, apparently have nothing to do with one's level of pain and discomfort.