In part one of this series on FAI, we looked at the cause of FAI. Time today to look at if FAI causes premature wear of the hip.
With the extra bone that is present in FAI, movements involving hip flexion (bending knee towards chest) or hip rotation (particularly internal rotation), can cause the two bony surfaces to impinge on one another which can cause premature bony damage, or damage to the lining of the socket (called the labrum)
This Youtube video shows the mechanics of how hip impingement causes damage to the hip.
As we mentioned in part one of this blog, FAI didn’t exist as a published and understood condition until 2003 – and it’s now through that about 28% of people have some form of FAI. Another medical condition with similar circumstances I am not aware of!
Naturally, with the new barrage of information on FAI, a lot of research has looked at whether this condition causes premature osteoarthritis of the hip. Osteoarthritis (OA) of the hip is a big issue, particularly for the athlete – it causes marked activity limitation and eventually leads to the necessity of hip joint replacement.
Reinhold Ganz, the Swiss surgeon who first used the term ‘FAI’, was one of the first to propose that FAI caused OA. From his 2003 paper:
And again in 2008 he provided some diagrammatic explanation of the mechanism of FAI causing OA:
However neither of these two articles gave any hard data on whether FAI really does cause OA. Determining this does present some research difficulties – what you need to do is find a group of youngish people with FAI and then follow them through for perhaps 20-60 years and see how quickly they wear their hips out!
Given that a) no one really knew a lot about FAI until ~11 years ago and b) some of the people with FAI would likely want a surgery if they think it will help; it presents more than a few issues!
Let's have a look at some of the research investigating the relationship between hip OA and FAI.
Firstly, Doherty’s group in 2008 (from the UK), did find there was an association between CAM lesions and hip OA, but found merely that the two coexisted. This means they didn’t find that CAM lesions caused OA, but that people with OA hips had CAM lesions.
Secondly, the fantastically named Professor Hartofilakidis from Greece looked at 96 painfree hips who had X-Rays showing FAI. The X-Rays were taken as part of a procedure for looking at the opposite hip, which is the reason the patients has been in the medical surgery in the first place. Anyway, the 96 hips were followed up, on average, about 18 years later. The majority of these hips - 82% - remained free of osteoarthritis at this time. Of the 17% that did develop osteoarthritis, their first symptoms were reported at an average age of 63 years - not that unusual.
So a very useful study showing that purely having FAI DOESN'T cause early hip OA. We need to bear in mind that the participants in this study had injuries (and surgery!) on their opposite hip - which would mean they were dramatically less likely to participate in sports or occupations involving flexion and rotation, the movements that cause impingement in FAI.
Tanzer et al., in 2004, had an interesting paper where they described 200 hips that were to undergo hip replacement. Once 75 were excluded with other causes (avascular necrosis, rheumatoid arthritis etc), the remaining 125 hips ALL had a pistol grip deformity (another term for Ganz or CAM lesion). This is a bit of a strange one! They are basically saying that all the hips that come in with ostoarthritis have FAI. They did have some interesting methods of diagnosing FAI on XRay, and their data isn't presented in full, so I'm not going to take too many message out of this paper.
Finally, Gosvig and colleagues in 2010 present an article which is the cream of the crop, and answer some of the questions we have posed earlier in the blog post.
The Scandinavians (the article is Danish) have a wonderful public health funding and it pays dividends here. As part of a big public health study, they had collected hip XRays from 3620 individuals between 1991 and 1994. Later when FAI was recognised, they looked at the scans and divided them into groups:
- CAM lesion (20% males, 5% females)
- Pincer lesion (15% males, 19% females)
- Both Pincer and CAM lesion (3% males, 1% females)
So these numbers are somewhere near the 28% of people having FAI that Ganz mentioned all those years ago.
They followed these hips up in around 2009, when the participants had an average age of about 60.
So here is the big data
- if you had a CAM lesion, you were 2.2 times more likely to develop hip OA
- if you had a pincer lesion, you were 2.4 times more likely to develop hip OA
(no data was available on those people with combined pincer and CAM lesions)
So, what can we take from a review of the literature?
The best study is the Gosvig paper, it shows that FAI does increase the risk of OA. The increase is significant but not outstanding. I think this paper would confirm what Ganz has thought of back in 2003 when he first proposed the mechanisms for FAI causing OA.
Up next is Part 3 - when we will look at what sports and activities increase the risk of OA and propose about whether it is a specific combination of hip shape and sport/occupation that causes early hip OA.
Part 4 will look at the evidence for surgery in slowing or stopping the progression of OA in those with FAI.