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.