The real history of femoroacetabular impingement

Maybe you've been told you have femoroacetabular impingement. Maybe you suspect it's what's causing your hip pain. Let's take a look an honest look at the theory behind femoroacetabular impingement and the science behind it. You'll soon discover that femoroacetabular impingement (FAI) isn't all that it's cracked up to be.

An overview of femoroacetabular impingement

  • why people develop labral tears
  • why people develop osteoarthritis of the hip
  • why people have hip pain and range of motion issues

Surgeons did case studies on patients. After performing surgery to shave down the "deformed" bones and repair labral tears, the surgeons reported good outcomes for their patients. They pointed to their successes as evidence that the theory was true and the treatment ready for mass market.

There's just one problem.

The science has not proven the femoroacetabular impingement theory. In fact, if you look at the research, the entire theory of FAI seems to fall flat on its face. 

This page will take you through the history of FAI and show you where the evidence just doesn't hold up.

We will go over logical fallacies in the femoroacetabular impingement theory. We'll look at the growing body of medical research that undermines basic tenets of the theory. We'll examine how the femoroacetabular impingement diagnostic process is full of holes. And we'll look at what research says about success rates for femoroacetabular impingement surgery. 



A small group of surgeons perfected a new surgical technique. They found a way to dislocate the hip joint so that they could examine the insides of the joint. This was something nobody had safely done before. It was called open dislocation. 

Looking at the inside of the joint, the surgeons found small "abnormalities" that they believed could explain arthritis and hip pain.

This small group continued to publish papers on their new technique and proposed that they had solved an age-old question: what causes hip arthritis?

Of the top 8 studies cited in the research and discussion of femoroacetabular impingement there are several surgeons who were involved multiple times. In the top 8 studies, Reinhold Ganz, MD; Michael Leunig, MD; Javad Parvizi, MD; Martin Beck, MD; and Klaus Siebenrock, MD appear several times each.

Top authors in femoroactebular impingement

To be clear, it is not a problem that a small group spends a lot of time researching one topic.

But it is a problem that these articles cite their own research papers as evidence to support their own assertions. This creates the illusion of good research.

Imagine if I told you that I believed I had a new way of understanding and curing cancer. Cancer is the result of overgrown finger nails. Cutting down finger nails improves my patients' lives 87% of the time! I publish an article stating these ideas and findings.

A colleague and I publish another article that has the following passage: "Fingernail length has been recognized as a cause of cancer..." We cite my paper as evidence.

Two other colleagues and I publish a third article. "Fingernail length has been shown to be a cause of cancer..." it says.

We cite the previous two papers.

A group of all of us then publish another article. "Because recent advances in cancer treatment with fingernail therapy have been effective..." and we cite the first three papers.

If you don't look at our citation list, you don't even notice what we've done. But our paper looks like it is more believable because we have citation numbers!

This would not be considered sound science. And my  theory would not be convincing once you realized what was happening. 

I would be creating an echo chamber of my own opinion. 

That's exactly what happened with early femoroacetabular impingement research papers.


Here's the history in simplified form. Patients had hip pain. Doctors weren't sure what was causing the hip pain. 

Surgeons looked for something they could say causes hip problems. They were looking for something they could fix. 

Surgeons started to label certain phenomena as "pathologies" (i.e. bad things). They found labral tears, joint space narrowing, bone and cartilage damage. 

They believed that there was something causing these pathologies.

With a new surgical procedure, they were able to see into the hip joint. They saw small "abnormalities." They proposed that these bone shapes were the cause of all the other pathologies. You know these bone shapes as cam and pincer impingement. 

They performed more surgeries based on this theory. They published papers claiming excellent results. 

But nobody examined whether the small abnormalities had any relationship to pain.

In order to examine the relationship between femoroacetabular impingement bone shapes and pain, the surgeons would have to look at larger groups of people. They would have to look at people WITHOUT pain (asymptomatic) as well as WITH pain (symptomatic).

But they did not do those studies until much later.

Many studies on asymptomatic populations have been completed since the inception of the femoroacetabular impingement theory. The results have been consistently one-sided.

The final result of the large population-based studies is that the abnormalities have no correlation with symptoms. Femoroacetabular impingement bone shapes DON'T seem to cause hip pain.


This does not mean anyone deliberately skewed femoroacetabular impingement research to be deceitful. It means that surgeons chose metrics that weren't chosen well. This is a form of inadvertent bias.

Let's look at an example. In some studies, surgeons claim success without any clear patient feedback. It's as if removing a piece of bone or removing a labrum is the only measure of success. If the surgeon says it worked - it worked.

In other studies, surgeons used disability scores to measure success. If patients' scores increased after surgery, the surgery was considered a success. But in all instances, the scores were nearly guaranteed to increase. The improvements necessary to increase the score are minimal, so patients score better but don't necessarily feel better.

To the patient, a reduction in pain and disability is the key measure of success. Return to sports and other activities without pain and without limitation are the goal.

In recent studies where patients rate their own satisfaction, surgery for femoroacetabular impingement does not produce good results.


Uncovering the bias in studies on femoroacetabular impingement.

This section examines several key studies that illustrate problems in the early research. Much of the early research has a huge surgical bias from a small group of the same surgeons.

Such an interest is not an indication of intentional corruption of data or deliberate deception.

Quite to the contrary, some of the early papers do mention that more critical studies should be performed to prove the femoroacetabular impingement theory.

But the studies to truly examine the link between bone shapes and symptoms would not get published until well after the early stage of femoroacetabular impingement research.


Ganz, R., Gill, T. J., Gautier, E., Ganz, K., Krügel, N., & Berlemann, U. (2001). Surgical dislocation of the adult hip. Bone & Joint Journal83(8), 1119-1124.


“We describe a technique for operative dislocation of the hip, based on detailed anatomical studies of the blood supply…

We report our experience using this approach in 213 hips over a period of seven years and include 19 patients who underwent simultaneous intertrochanteric osteotomy…

….Surgical dislocation gives new insight into the pathogenesis of some hip disorders and the possibility of preserving the hip with techniques such as transplantation of cartilage.

Summary and analysis

This paper and the technique presented appear to be the beginning of the growth of the idea of femoroacetabular impingement. 

This article describes how surgeons can dislocate the hip joint (open surgical dislocation)  to perform more detailed examinations that were previously impossible. By doing these dislocations, surgeons can spot small bone abnormalities.

Reinhold Ganz, MD is one of the senior authors of many of the following articles on femoroacetabular impingement.

Ganz, R., Parvizi, J., Beck, M., Leunig, M., Nötzli, H., & Siebenrock, K. A. (2003). Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clinical orthopaedics and related research417, 112-120. (full text available at research gate)


  • Based on clinical experience, with more than 600 surgical dislocations of the hip, allowing in situ inspection of the damage pattern and the dynamic proof of its origin, we propose femoroacetabular impingement as a mechanism for the development of early osteoarthritis for most nondysplastic hips. The concept focuses more on motion than on axial loading of the hip. Distinct clinical, radiographic, and intraoperative parameters can be used to confirm the diagnosis of this entity with timely delivery of treatment. Surgical treatment of femoroacetabular impingement focuses on improving the clearance for hip motion and alleviation of femoral abutment against the acetabular rim. It is proposed that early surgical intervention for treatment of femoroacetabular impingement, besides providing relief of symptoms, may decelerate the progression of the degenerative process for this group of young patients.
  • Although detailed analysis of the outcome of surgical intervention still is ongoing, the preliminary results indicate that surgical dislocation of the hip and improvement of the head and neck offset was successful in addressing these patients’ symptoms arising from the underlying impingement.

Summary and analysis

This is the first real proposal of FAI as a cause of arthritis.

In this paper, several surgeons lay out their belief that the small bony abnormalities cause arthritis. They refer to cam and pincer impingement are the primary causes of the development of arthritis. 

It's important to note that the entire theory rests only on the observations and reports of these surgeons. There is no objective evidence about the actual results of the surgeries. 

There is no information about how successful the preliminary results were - no patient satisfaction surveys, no actual data on whether the surgeries did anything to relieve the symptoms patients had.

In addition, there is no evidence that the abnormalities being targeted are actually causing any symptoms. This is an assertion the surgeons are making without adequate evidence. And they have already performed their procedure hundreds of times. 

Siebenrock, K. A., Schoeniger, R., & Ganz, R. (2003). Anterior femoro-acetabular impingement due to acetabular retroversion. J Bone Joint Surg Am85(2), 278-286. 


This study was performed to evaluate whether symptomatic anterior femoro-acetabular impingement due to acetabular retroversion can be treated effectively with a periacetabular osteotomy.

The average Merle d’Aubigné score increased from 14.0 points (range, 12 to 16 points) preoperatively to 16.9 points (range, 15 to 18 points) postoperatively (p < 0.001), and the result was good or excellent for twenty-six hips.

Summary and analysis

This is the 6th most cited article related to FAI. 

In this study, they performed surgeries and measured outcomes at an average 30 months.  

The surgeons claim that the high percentage of improvement is evidence that the treatment is fairly reliable and useful. The increase in the patient's Merle d’Aubigné score is the key indicator of success.

In brief, the Merle d’Aubigné score is focused mostly on limited goals.  Walking normally and being able to get around "with tolerable amounts of pain". These are not ambitious. This score is a clear case of "success" being measured in a way that does not line up with a real person wants.

More details on this particular score will be found in a later section as we examine the alleged success rates of hip surgeries.

Murphy, S., Tannast, M., Kim, Y. J., Buly, R., & Millis, M. B. (2004). Debridement of the adult hip for femoroacetabular impingement: indications and preliminary clinical results. Clinical orthopaedics and related research429, 178-181.


“Untreated femoro-acetabular impingement is a common cause of osteoarthrosis of the hip. Surgical debridement of the adult hip with femoro-acetabular impingement recently has been advocated with the aim of relieving symptoms and slowing or halting progression of the arthrosis…

…The current study assesses a group of 23 hips in 23 patients treated by surgical debridement for impingement. Twenty-two patients were treated by full surgical dislocation and one patient was treated by relief of impingement without dislocation. Followup ranged from a minimum of 2 years to 12 years. At most recent evaluation, seven patients had been converted to total hip arthroplasty, one had arthroscopic debridement of a recurrent labral tear, and 15 patients have had no further surgery.”

Summary and analysis

This article is number 14 in the top most cited articles about femoroacetabular impingement.

Many studies cite this paper as evidence that hip bone abnormalities cause hip pain.

This paper does not provide any such evidence.

This paper claims that FAI is a common cause of osteoarthritis. However, this paper does not provide any evidence of that. No large scale population studies had been done to examine the relationship between bone abnormalities and symptoms. 

The surgeons used the open surgical dislocation to attempt to fix hip problems. However, 7 out of 23 of the patients ended up needing more surgery following their intervention.

Notice that is a 30% failure rate. 

Beck, M., Kalhor, M., Leunig, M., & Ganz, R. (2005). Hip morphology influences the pattern of damage to the acetabular cartilage. Bone & Joint Journal87(7), 1012-1018.


“In cam impingement the damage to the acetabular joint is located anterosuperiorly. This accords with arthroscopic studies which showed that most of the lesions were found in this area. In flexion this extension squeezes into the anterosuperior acetabulum; it is made worse by internal rotation…”

“In coxa profunda, the prototype for pincer impingement, the deep socket limits movement in all directions and leads to a more circumferential pattern of damage. These labral lesions explain the different findings at arthroscopy with more posterior lesions.”

Summary and analysis

The authors describe the classic characteristics of cam and pincer deformities. The authors propose cam and pincer deformities are linked to different kinds of degeneration of the hip.

At the beginning of the article, the authors cite the 2003 Ganz article as evidence that these bone deformities are recognized as a cause of arthritis. Here, it’s important to note two things.

  1. The 2003 Ganz article was authored by several of the same authors of this study.
  2. The 2003 article does not prove that bone shape is a cause of hip pain. It is merely proposing a theory. The proposal of a theory is not evidence that a theory is true. 

This is a clear example of the echo chamber effect.

The authors cite their own papers to add credibility to their theory. Their theory still lacks key pieces of evidence.

The authors do note that there have still been no population-based studies done to prove the link between bone shapes and hip symptoms.

Ganz, R., Leunig, M., Leunig-Ganz, K., & Harris, W. H. (2008). The etiology of osteoarthritis of the hip. Clinical orthopaedics and related research,466(2), 264-272.


  • Two recent developments strengthen the hypothesis and play a predictive role in confirming the hypothesis. The two key developments are (1) the recognition of the mechanism for the development of the hip OA caused by mild deformities and (2) the possibility that correction of that mechanism could retard the development of the OA.”
  • Since 2005, a prospective population-­based study has been underway (NFP53 405340­104778). Based on a cohort of more than 1100 young men, this study was initiated to address the prevalence of FAI in this population and to determine whether these morphologic alterations are associated with an increased rate of early OA (natural course study).

Summary and analysis

In this paper, the authors discuss the history of the idea of cam and pincer impingement. Note, again, that there are some familiar names authoring this article.

The authors trace a long path of development of the idea from a 40 year old hypothesis. In the quote above, the authors note that the identification of potential bone abnormalities (cam and pincer morphologies) via open surgical dislocation lend some evidence to the idea that bone shapes are the primary cause of osteoarthritis.

They also focus on surgical intervention. They claim it has the potential to solve the proposed bone problem. They claim that if the hip surgery improves hip pain, then this is proof that the theory is correct.

This sounds seductively sensible, but it's not true. This has been the same justification for knee meniscus surgeries, spinal fusions, and shoulder impingement surgery. All these procedures eventually turned out to be expensive and invasive placebos. Surgeons were over-reporting positive results in early research. 

The authors do make one crucial point: they need to do large scale population studies to verify the effect of the bone “deformities.”

In fact, some of the authors of this paper were part of a large scale population study to determine the correlation between the abnormalities and pain and arthritis.

In 2010, they published the findings of that study. The results were a surprise to them. What they found completely undermined the femoroacetabular impingement theory.


The results of studies on hip abnormalities undermine the bone theory of FAI and arthritis.

Cam and pincer bone shapes aren't related to

Before we go further, we need to differentiate between FAI bone shapes (morphology) and FAI as a “disease.”

The term FAI is used interchangeably to refer to the fact that you may have the bone shapes and/or that you have the symptoms of a disease. This usage creates confusion when we discuss the truth about FAI, so we should clarify this.

FAI bone morphology exists. This is what you have heard referred to as cam, pincer, and mixed impingement. These are terms that describe the shape of your hip bones. Bones come in different shapes. Some have cam, pincer, or mixed impingement shapes. It is important to realize that the criteria for determining these shapes were set out by surgeons who were convinced that certain amounts of size difference were significant. In other words, the criteria are artificially created and are quite open to bias.

This section presents the studies done on the relationship between bone shapes, arthritis, and hip pain / range of motion loss. 

As mentioned earlier, the only way to determine whether cam and pincer bone shapes and other abnormalities are related to actual hip symptoms is to do a careful study of large groups of people. You want to see whether the bone shapes do, in fact, relate to the hip symptoms. Looking at patients who have hip pain only does not give you good evidence. 

If, for example,  you find that everyone in your office with hip pain has black hair, you might incorrectly assume that black hair is a cause of hip pain. But if you expand your view to the larger world, you find that black hair is actually a normal variation not at all related to hip pain. 

And that is essentially what the studies on hip morphology have found. 

The cam and pincer bone shapes are just normal anatomic variations that are not related to hip pain. Labral tears and other pathologies have not been shown to be related to pain either.

In 2010, the paper with the results of that large scale population study was published. Both Ganz and Leunig were co-authors of the paper. 

Reichenbach, S., Jüni, P., Werlen, S., Nüesch, E., Pfirrmann, C. W., Trelle, S., ... & Leunig, M. (2010). Prevalence of cam‐type deformity on hip magnetic resonance imaging in young males: A cross‐sectional study. Arthritis care & research62(9), 1319-1327.

  • Cam-type deformities can be found on MRI in every fourth young asymptomatic male individual and in every second male with decreased internal rotation. The majority of deformities are located in an anterosuperior position.
  • In our population-based sample of 244 asymptomatic young Swiss males, the overall prevalence of a definite cam-type deformity of 24% was surprisingly high.

This study showed a surprising lack of correlation between bone shapes, range of motion, and pain. 25% of of the asymptomatic men they examined actually had the FAI bone shapes. This should have led to some very hard questions. The hardest question: "does the bone theory hold up if so many asymptomatic individuals can have the deformities without symptoms?" 

For whatever reason, that question did not get asked strongly enough. 

But many more studies have been done to examine the relationship between bone shapes, hip range of motion, and arthritis. 

To really find out if FAI bone shapes cause pain, you need to look at the whole population. You want to see if you can have FAI bone shapes and no pain.

Imagine this scenario. I am a physician, and I tell you: “I have many patients with headaches. 60% of them have black hair. I think black hair is correlated with headaches.” I shave the heads of everyone in my headache group with black hair and remove their hair follicles. I find that there is some improvement in 83% of their headaches. Have I proved that black hair caused the headaches? No.

We would need to look to see how many people in the general population have black hair and no headaches. This will show how strong the correlation is between black hair and headaches. Also, we need to look at the possibility that something about the intervention may be affecting factors not accounted for in my original black hair theory of headaches.

This is what needed to happen with FAI and hip pain. 

The studies below all examine the link between FAI bone morphology and hip pain. What researchers have found is that FAI bone morphology is quite prevalent in the asymptomatic general population.

What's that mean? Well, if a large proportion of people with black hair don’t have headaches, it’s probably not the black hair. If a large proportion of people with FAI bone morphology don’t have symptoms, it’s probably not the FAI bone shapes causing the problems.

Population studies are finding that the FAI bone morphology just doesn’t cause symptoms.


Gosvig, K. K., Jacobsen, S., Sonne-Holm, 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 Radiologica49(4), 436-441.


“The overall prevalence of cam deformity was approximately 17% in men and 4% in 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.”“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.”

Weir, A., de Vos, R. J., Moen, M., Hölmich, P., & Tol, J. L. (2011). Prevalence of radiological signs of femoroacetabular impingement in patients presenting with long-standing adductor-related groin pain. British journal of sports medicine45(1), 6-9.


There was no correlation between hip ROM and the number of radiological signs.

“Radiological findings of hip impingement are often present without the anterior hip impingement test being painful. The anterior hip impingement test may not be specific for femoroacetabular impingement.”

Chakraverty, J. K., Sullivan, C., Gan, C., Narayanaswamy, S., & Kamath, S. (2013). Cam and pincer femoroacetabular impingement: CT findings of features resembling femoroacetabular impingement in a young population without symptoms. American Journal of Roentgenology,200(2), 389-395.


“At least one abnormal parameter was present in 66% of joints, and two or more abnormal parameters were present in 29% of joints. In seven patients the findings were bilateral. Parameters of mixed morphologic characteristics (cam and pincer) were found in 22% of joints. In side-by-side comparison, high alpha angles were seen in 36 joints measured in the radial plane compared with only three joints measured in the axial oblique plane…The CT finding of FAI-like features was made with high frequency in a young symptom-free population.”

Jung, K., Restrepo, C., Hellman, M., AbdelSalam, H., Morrison, W., & Parvizi, J. (2011). The prevalence of cam-type femoroacetabular deformity in asymptomatic adults. J Bone Joint Surg Br93(10), 1303-1307.


In a sample of 215 asymptomatic men, 13.95% were classified as “pathological.”Of 540 women, 5.56% were pathological.

“It appears that the cam-type femoroacetabular deformity is not rare among the asymptomatic population. These anatomical abnormalities… appear to be twice as frequent in men as in women. Although an association between osteoarthritis and femoroacetabular impingement is believed to exist, a long-term epidemiological study is needed to determine the natural history of these anatomical abnormalities.”

Nardo, L., Parimi, N., Liu, F., Lee, S., Jungmann, P. M., Nevitt, M. C., ... & Osteoporotic Fractures in Men (MrOS) Research Group. (2015). Femoroacetabular impingement: prevalent and often asymptomatic in older men: the Osteoporotic Fractures in men study. Clinical Orthopaedics and Related Research®473(8), 2578-2586.


“Pincer, cam, or mixed types of radiographic FAI had a prevalence of 57% (1748 of 3053), 29% (886 of 3053), and 14% (419 of 3053), respectively, in this group of older men. Both pincer and mixed types of FAI were associated with arthrosis but not with hip pain.

"FAI is common in older men and represents more of an anatomic variant rather than a symptomatic disease."


It should be clear at this point: the FAI bone shapes are common. They are not at all rare. And they do not correlate at all with symptoms of disease at any age. 

FAI bone shapes don't lead to arthritis

If FAI bone morphology does indeed lead to severe, debilitating arthritic hip joints, it certainly makes sense to prevent that outcome with surgery.

Remember, at the beginning of the FAI theory, FAI bone morphology presented a promising explanation for degeneration of hip joints. But the belief that FAI bone shapes lead to arthritis was an untested hypothesis. It was supported by case studies finding only weak statistical correlation when investigating populations of people with hip pain.

Long term studies to investigate the link between FAI and arthritis have come out and show important results.

FAI bone shapes do not have any connection to the development of arthritis.



Bardakos, N. V., & Villar, R. N. (2009). Predictors of progression of osteoarthritis in femoroacetabular impingement. Bone & Joint Journal91(2), 162-169.


In this study, they followed 43 patients with cam impingement for 10 years to see if arthritis developed or worsened.

“The results of this study suggest that mild to moderate osteoarthritis in hips with a pistol-grip deformity will not progress rapidly in all patients, with one-third of them taking at least ten years to manifest, although we have no evidence that it will ever do so…A hip with cam impingement is not always destined for end-stage arthritic degeneration.”

Agricola, R., Heijboer, M. P., Roze, R. H., Reijman, M., Bierma-Zeinstra, S. M. A., Verhaar, J. A. N., ... & Waarsing, J. H. (2013). Pincer deformity does not lead to osteoarthritis of the hip whereas acetabular dysplasia does: acetabular coverage and development of osteoarthritis in a nationwide prospective cohort study (CHECK). Osteoarthritis and Cartilage21(10), 1514-1521.


This study took 720 people with pincer impingement or acetabularundercoverage (dysplasia) and followed them for five years to determine the risk of developing osteoarthritis.

“A pincer deformity was not associated with OA, and might even have a protective effect on its development, which questions the supposed detrimental effect of pincer impingement.”

Hartofilakidis, G., Bardakos, N. V., Babis, G. C., & Georgiades, G. (2011). An examination of the association between different morphotypes of femoroacetabular impingement in asymptomatic subjects and the development of osteoarthritis of the hip. J Bone Joint Surg Br93(5), 580-586..


This study followed 96 patients with cam, pincer, and mixed impingement from ages 16 to 65. They concluded that surgery to prevent arthritis is “not warranted.”

82.3% of the hips remained arthritis free for an average of 18.5 years. Only 17.7% developed arthritis at an average of 12 years.

“We conclude that a substantial proportion of hips with femoroacetabular impingement may not develop osteoarthritis in the long-term. Accordingly, in the absence of symptoms, prophylactic surgical treatment is not warranted.”


The results of these studies are as clear as can be. There is no clear relationship between FAI bone shapes and arthritis.

Arthritis and hip pain

The studies above are all important because they demonstrate a total lack of correlation between FAI bone morphology and arthritis. The assumption, of course, is that arthritis as we understand it is a fully developed and well-understood disease process. Joint space narrowing, damage to cartilage and bone, and the destruction of soft tissue structures in the joint all lead to pain and dysfunction in the classic understanding of arthritis. Take an X-ray and you'll be able to see evidence of the arthritis, and you'll know that someone is in pain. 

It's a very clear, cut-and-dried theory that seems to make sense.

As a result of that theory, medical advice to those with arthritis has long been to rest. Don't use the joint. Just rest. 

But that advice has changed in recent years because people have started to notice that exercise actually seems to help people with joint pain. Proper exercise can actually make things much better. This sounds like it shouldn't be the case.

Recent evidence, however, shows that our classic understanding of osteoarthritis in the hips and knees may not be anywhere near accurate. 

Take, for instance, the following two studies:

Hannan, M. T., Felson, D. T., & Pincus, T. H. E. O. D. O. R. E. (2000). Analysis of the discordance between radiographic changes and knee pain in osteoarthritis of the knee. The Journal of rheumatology27(6), 1513-1517.

Radiographic stage 2-4 knee OA was found in 319 subjects (3.7%); only 47% of these individuals reported knee pain, and only 61% reported that a physician had told them that they had arthritis. Knee pain was reported by 1004 subjects (14.6%), only 15% of whom had radiographic stage 2-4 changes of OA, and 59% of whom reported having a diagnosis of arthritis by a physician. A report of arthritis diagnosed by a physician was given by 1762 subjects (25.6%), of whom only 11% had stage 2-4 radiographic knee OA and 34% reported knee pain.

Substantial discordance exists in this population based study between radiographic OA of the knee versus knee pain, versus a diagnosis of arthritis by a physician.

In this study, researchers looked at the relationship between signs of moderate to severe arthritis of the knee, actual knee pain, and a diagnosis from a doctor. What they found was that even if you had "severe" arthritis in your knee on an X-ray, it had no bearing on whether or not you had any symptoms of knee pain. This should plant some doubt into your mind about what it even means to find signs of arthritis in an X-ray. 

If the signs of arthritis don't mean you'll have symptoms and you can still have the symptoms without signs of arthritis, do those alleged signs of arthritis have anything to do with your symptoms? Probably not. 


Kim, C., Nevitt, M. C., Niu, J., Clancy, M. M., Lane, N. E., Link, T. M., ... & Guermazi, A. (2015). Association of hip pain with radiographic evidence of hip osteoarthritis: diagnostic test study. Bmj,351, h5983.

Hip pain was not present in many hips with radiographic osteoarthritis, and many hips with pain did not show radiographic hip osteoarthritis. Most older participants with a high suspicion for clinical hip osteoarthritis (groin or anterior pain and/or painful internal rotation) did not have radiographic hip osteoarthritis, suggesting that in many cases, hip osteoarthritis might be missed if diagnosticians relied solely on hip radiographs.

In this study, they examined the relationship between arthritis in an X-ray of the hips and actual hip pain. What they found was that there was absolutely no correlation between X-ray evidence of arthritis and hip pain.

You could have osteoarthritis in the X-ray and no hip pain. You could also have hip pain and no osteoarthritis. The surprising and somewhat comical conclusion offered is that doctors should be ready to diagnose arthritis based on hip pain alone, since X-rays will "miss" arthritis. This is an example of researchers' bias based on what is believed to be undeniably already true (i.e. Hip osteoarthritis is when you have hip pain. Hip pain is caused by joint damage. If you have hip pain but you can't see the joint damage, you still have hip osteoarthritis). Despite being illogical, this is the conclusion that makes sense if you assume that the classic arthritis theory is unassailable. 

The more reasonable conclusion is one that undermines the classic theory of arthritis altogether. The joint space narrowing, cartilage damage, etc. that we thought was causing the pain is not, in fact, related to the pain at all. 

So, even if FAI bone shapes were in some way related to the development of arthritis (which they are not, as we've seen), it still wouldn't matter!

Labral tears are not related to pain

Many times people who have been told they have FAI have been told that their labrums are “shredded up” or “badly damaged” or something similarly scary sounding.

When you read articles on the internet, it seems like labral tears have been definitively shown to cause you pain and that nothing but surgery could possibly help you.

The perspective that is often missing is that labral tears have not been shown to definitively lead to pain. In fact, it is not a secret that there is little to no correlation between a labral tear and pain. This is the same situation we have for FAI bone morphology and pain. The belief is there, but the evidence is not. On top of this uncertainty, it’s not yet even clear that a labral tear has a destabilizing effect on the hip joint or that predictable pain patterns are even part of labral tears as you’ll see in this list of studies.

The main point is this: there is no demonstrable relationship between labral tears and actual hip symptoms. 


Lee, A. J. J., Armour, P., Thind, D., Coates, M. H., & Kang, A. C. L. (2015). The prevalence of acetabular labral tears and associated pathology in a young asymptomatic population. Bone Joint J,97(5), 623-627.


“Labral tears were found in 27 volunteers (38.6%); these were an isolated finding in 16 (22.9%) and were associated with other intra-articular pathology in the remaining 11 (15.7%) volunteers. Furthermore, five (7.1%) had intra-articular pathology without an associated labral tear.

Given the high prevalence of labral pathology in the asymptomatic population, it is important to confirm that a patient’s symptoms are due to the demonstrated abnormalities when considering surgery.”

“Acetabularparalabral cysts were identified in 11 of 42 (26.2%) and 9 of 42 (21.4%) hips…in addition, acetabularlabral tears were identified in 36 of 42 (85.7%) and 34 of 42 (80.9%) hips…

…we report the previously undescribed prevalence of acetabularlabral pathological abnormalities and paralabral cysts in a young, asymptomatic population. This emphasizes the importance of correlating patient symptoms with history and physical examination when evaluating patients with hip pain and radiographic abnormalities as defined by MRI criteria. These data demonstrate that labral tears can occur without symptoms.”

“The MR appearance of the hip labrum is varied in asymptomatic volunteers. Intralabral increased signal intensity and absent anterosuperior labra are especially frequent and may represent asymptomatic lesions or normal variations.”

There was no significant difference in stability ratio after circumferential tears 3 cm or less in size compared with the intact labral state. Strain in the anterior and anterior-superior labrum was either unchanged or increased after circumferential labral tear.
There was no significant difference in stability ratio after a radial tear or a 1-cm partial labrectomy compared with the intact labral state. A 2-cm partial labrectomy significantly decreased the stability ratio. Anterior and anterior-superior labral strain significantly decreased after a radial tear.
The findings suggest that the acetabular labrum continues to function to resist femoral head translation despite chondral-labral separation and that labral preservation, particularly with larger tears, may be important for maintaining hip stability.

Injections don't tell you what's causing your pain

The studies above demonstrate that labral tears are not definitive causes of pain and instability and should not be treated as such without further investigation. They do not prove that labral tears cannot cause pain. Doctors currently rely on further diagnostic techniques to attempt to determine if problems in the joint are actually causing you pain.

The chief technique to do this is with hip injections. It’s believed that anesthetic hip injections can definitively tell you whether arthroscopic surgery to repair your labrum and repair the FAI bone shapes is a good idea. Many people email me telling me that they are considering an injection to really find out what's causing their hip problems.

The belief is this: if the problem is the labrum, cysts, bone damage, and/or the bone shapes, the injection will relieve your pain. Therefore surgery will address the problem.

If the problem is from something outside the joint, like iliopsoastendinopathy or bursitis, the injection won’t be as big a help.

Unfortunately, the belief is not backed up by solid evidence. In fact, the basic belief that injections can reliably separate out intraarticular pain from extraarticular pain does not seem to be true as you’ll see from the studies below.

This means it's actually unnecessary to do the injections at all (which is the conclusion of one of the studies). 


Byrd, J. T., & Jones, K. S. (2004). Diagnostic accuracy of clinical assessment, magnetic resonance imaging, magnetic resonance arthrography, and intra-articular injection in hip arthroscopy patients. The American journal of sports medicine32(7), 1668-1674.


“In this series, clinical assessment accurately determined the existence of intra-articular abnormality but was poor at defining its nature…Response to an intra-articular injection of anesthetic was a 90% reliable indicator of intra-articular abnormality.”

This study is listed here not because it demonstrates the inaccuracy of hip injections. It is here because it is very often cited as proof that hip injections are reliable at finding intraarticular causes of hip pain. In fact, this study only shows that hip injections often provide relief for people with hip pain and is not rigorous enough to provide the proof that it is believed to provide.

This study looked at a group of individuals who all had hip pain and were suspected of having intraarticular pathologies. Nearly all the people got relief from the hip injections, and nearly all were discovered during surgery to have had intraarticular hip pathologies. Remember though, that hip pathologies are extremely common, even in asymptomatic people. To really test the accuracy, hip injections would need to be given to people with hip pain and no sign of intraarticular pathology to see how they react.

Let’s go look at a similar scenario. I believe black hair causes headaches. I suspect that the darkness of black makes a difference.

I have devised a test to measure the importance of black hair to headaches. I take 50 headache suffers with black hair and inject anesthetic into their scalps to block the effect of the black hairs. If it reduces their headaches, I conclude they have sufficiently black hair to cause headaches.

Does this experiment provide enough evidence for that conclusion? No. The relationship between the black hair and headaches is simply assumed and never proven, and the effect of the anesthetic could clearly have effects on pain in ways that I may not anticipate.

It’s the same setup. Because the conclusion flatly states that the injections are 90% accurate, many surgeons and researchers claim that injections are very accurate. Often, they have not read the paper in detail to see just how wildly inaccurate the injections actually are. You can read more about the inaccuracies in this study here


Martin, R. L., Irrgang, J. J., & Sekiya, J. K. (2008). The diagnostic accuracy of a clinical examination in determining intra-articular hip pain for potential hip arthroscopy candidates. Arthroscopy: the journal of arthroscopic & related surgery24(9), 1013-1018.


In those with definite tears or possible tears, 39% (n = 7) and 45% (n = 13), respectively, did not achieve a greater than 50% reduction of pain. Groin pain, clicking, pinching pain with sitting, lateral thigh pain, flexion abduction external rotation test, flexion-internal rotation-adduction test, and trochanteric tenderness were not useful in identifying those with greater than 50% pain relief from those with 50% relief or less.”

The symptoms and signs investigated in this study did not accurately or consistently identify subjects with primary intra-articular pain sources. Furthermore, candidates for hip arthroscopy with a labral tear identified on MRI arthrogram had varied responses to anesthetic intra-articular injection. Therefore all labral tears identified on MRI arthrogram may not be a major contributor to patients’ pain complaints, and medical personnel should look for other causes of pain.

This study demonstrates a lack of correlation between symptoms and types of intraarticular pathology. It also demonstrates that anesthetic hip injections do not, in fact, help identify the cause of pain and do not in any reliable way relieve pain from intraarticular pathologies. More troubling, the positive or negative responses of patients to surgery were not predicted by anesthetic injections. 



Ayeni, O. R., Farrokhyar, F., Crouch, S., Chan, K., Sprague, S., & Bhandari, M. (2014). Pre-operative intra-articular hip injection as a predictor of short-term outcome following arthroscopic management of femoroacetabular impingement. Knee Surgery, Sports Traumatology, Arthroscopy22(4), 801-805.


“In this study, 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.”

The importance of this for most people considering surgery is that if an injection works, it doesn't mean surgery will work. If it doesn't relieve pain, it still doesn't mean surgery will work and in fact might be loosely related to a surgery NOT working. It is essentially useless as a diagnostic tool.


Kivlan, B. R., Martin, R. L., & Sekiya, J. K. (2011). Response to diagnostic injection in patients with femoroacetabular impingement, labral tears, chondral lesions, and extra-articular pathology.Arthroscopy: The Journal of Arthroscopic & Related Surgery27(5), 619-627.


The presence and severity of FAI and labral pathology did not influence the percent relief from injection. Concurrent extra-articular pathology did not alter the interpretation of the percent relief from injection. Therefore the interpretation and diagnostic value of an anesthetic injection in those with primary intra-articular pathology does not need to be altered by the presence of coexisting extra-articular hip pathology.

This paper drives home the point one more time. Whether or not you have FAI bone morphology or problems with your labrum, the injection makes no difference.

The last excerpted sentence, however, is interesting to look at. What they discovered was that intraarticular abnormalities were not related to how much relief and injection gave you. They also found that if you had extraarticular abnormalities, it did not affect the amount of relief you got.

What you might logically conclude from both those facts is that the intraarticular and extraarticular pathologies apparently aren't the things that they should be looking at as pain generators. Instead, the last sentence proposes that instead of looking at something different, we should all keep looking at the intraarticular abnormalities and just ignore the extraarticular abnormalities. The importance of the intraarticular abnormalities is taken for granted as an unassailable fact, despite the evidence to the contrary. This is yet another example of bias strongly influencing the interpretation of data based on prior beliefs (that is itself based on shaky prior research). 


A brief overview of the entire faulty diagnostic process

This video walks you through the FAI diagnostic process, step-by-step, so you can see how conventiona

medical assumptions lead so many people to a recommendation for surgery.


Success rates aren't as good as once believed.


Early research into surgery for FAI showed promising results. Early papers suggested that surgery was extremely effective in treating the cause of hip pain. By necessity, the followups were often very short term. This is problematic as many other surgeries that have seemed useful in the short term have turned out to be no better than placebo in the long term (example: knee meniscus surgery).

Sometimes, there were no specific measurements to measure success in an objective way beyond the opinion of the surgeon. Sometimes, a score based on a questionnaire was used. In these cases, the score needed to be scrutinized to see how the outcomes related to actual success from a patient's perspective.

When more thorough studies have been done to closely examine patients' ideas of success, the results have not been anywhere near as good as the other measures of success.

Byrd, J. T., & Jones, K. S. (2009). Arthroscopic femoroplasty in the management of cam-type femoroacetabular impingement. Clinical orthopaedics and related research467(3), 739-746.

In this study on 200 patients an extremely encouraging 83% were reported to have had improvement from arthroscopic surgery (instead of open dislocation) for cam and mixed (cam and pincer) impingement.  There are no details on how much improvement each of these 83% had, but the study notes that the average improvement for those who got improvement was 20 points on the Harris Hip Score. The range of scores went from -17 (meaning someone got much worse) to +60 (meaning someone felt much better). 

To determine success, the study used the Harris Hip Score to judge improvement following surgery. In general, to be considered a successful hip surgery, the patient must score at least 20 points higher post-op than they did pre-op. In this study, any improvement in the Harris Hip Score was considered improvement. 

In a paper like this, we need to look closely at how the Harris Hip Score is calculated.


Siebenrock, K. A., Schoeniger, R., & Ganz, R. (2003). Anterior femoro-acetabular impingement due to acetabular retroversion. J Bone Joint Surg Am85(2), 278-286. 

This study was performed to evaluate whether symptomatic anterior femoro-acetabular impingement due to acetabular retroversion can be treated effectively with a periacetabular osteotomy.
The average Merle d’Aubigné score increased from 14.0 points (range, 12 to 16 points) preoperatively to 16.9 points (range, 15 to 18 points) postoperatively (p < 0.001), and the result was good or excellent for twenty-six hips.

We looked at this study in earlier sections and talked about the scoring system they used: the Merle d’Aubigné score. While thinking about the improvement in score, we again have to look at how the score is calculated. 

Learn about the scoring systems

The Harris Hip Score

The Merle d'Aubigne score

As you can see, the scores are arbitrary and based on extremely limited goals for the patients. At a bare minimum, walking without any pain should be a reasonable expectation, but these scoring systems do not use that as a minimum satisfaction threshold. Scores like these only cloak the results of surgeries in numbers that appear to denote success. 

But these are not the only ways in which surgical success can be measured. If you want to find out how patients fare after surgery, you can simply ask them.


Finally, a study done in 2012 called Fulfilment of patient-rated expectations predicts the outcome of surgery for femoroacetabular impingement looked at 86 patients’ experience with surgery to fix their FAI. They studied the patient motivations and expectations for surgery to see how motivations and expectations affected the patients’ outcomes.

In this study, the patients had very normal motivations for surgery. The top most important reason to get surgery was to alleviate pain, followed by preventing worsening of the situation, and then followed by improvement in physical capabilities. 57% of the patients expected their hip pain would get “much better” and that a further 40% expected it to be “better” post-surgery. 46% expected their ability to do sport to be “much better,” and 37% expected it to be “better.” These are normal expectations by most people’s standards.

At 12 months, the results were not good.

Those are sobering numbers for anyone who thinks that they are going to have a huge improvement in their quality of life from undergoing surgery. 

50% of patients did not have their expectations met for hip pain, sport, and general physical capacity. 34-46% were disappointed in terms of independence, mental well-being, and walking capacity. 

The results of a study like this demonstrates that success is far from guaranteed and that expectations of drastic improvement are not likely to be met with surgery. Not only is surgery for FAI not particularly effective, but it is likely being oversold as a cure that ends up disappointing a significant number of patients. The hit-or-miss results of the surgery is only clear when you examine the reports from the patients themselves instead of relying on the objective scores like the Harris Hip Score or the Merle d’Aubigné score.

Where should we put our attention for hip pain?

While it’s conceivable that the many small abnormalities may have some effect on hip function, they appear to be of extremely limited value when identifying the cause of hip pain and immobility. Study after study demonstrates that these anatomical variations have little discernible effect on the actual movement available in a hip joint. 

What does affect movement at a joint? Muscles.

Muscles move bones. They are responsible for very large movements and very small movements. You want to bend your elbow? Muscles. You want to lift your leg? Muscles! The way muscles pull on bones observably and undeniably affects the way bones are positioned. That is what they are made to do, and that is what they do on a regular basis.

I believe that restoring proper muscle function needs to be the number one priority whenever persistent nagging pain appears in the hip (or anywhere else in the body for that matter). The mistake that has been made is to assume that all hip pain is caused by these small "pathologies," and that addressing those pathologies can fix everything. The reality is that people's hips can feel bad for a variety of reasons.

Muscles may be very tense. Muscles can be very weak. The relative strength and activation levels between muscles around the hip can be grossly out of balance. All these issues can and will cause movement problems at the hip joint. 

Are there studies to prove the idea that muscles are more important?

At the time of this post, not that I'm aware of. Because hip pain and discomfort have all been lumped under the FAI diagnostic umbrella, almost all studies on hip pain and FAI have focused on surgical interventions. In the medical community, there is little serious attention paid to the function of muscles and the retraining of muscles. The physical therapy community unfortunately is often subordinated to the diagnostic ideas of surgeons and other physicians, so little research has been done on addressing the problem in a way that I believe makes good sense. 

Anecdotally, I've personally helped many people overcome hip limitations that have fallen under the umbrella of FAI. Oftentimes, lifestyle changes have to be made to encourage appropriate muscle development. Some examples of changes: More exercise needs to be done. Better exercises need to be used. More stretches need to be used on a regular basis. Less sitting needs to happen. Also anecdotally, there have been many people all around the world who have used the FAI Fix program to gradually retrain their hips to full function. 

While these anecdotes are currently only anecdotes, they are extremely important to notice. They show that it is possible for people with an FAI diagnosis to actually improve their hip function without any invasive treatment for their hips. 


The bone theory of FAI has almost no evidence beyond a large number of heavily biased early papers written by surgeons. The bone theory also provides no explanation for why so many surgeries turn out disappointing and how it is possible that so many people with the FAI bone morphology and labral tears are able function perfectly well.

The muscular theory has explanatory power greater than the bone theory of FAI. It explains why people's hip pain can vary so widely from individual to individual and why current medical investigative techniques seem so prone to error (current diagnostics are barking up the wrong tree). It also explains why surgery may actually have some effect (since the act of surgery itself and the rest period thereafter also affects the muscles). 

When dealing with hip pain, we should take a moment to step back, look at the anatomy, and realize that there are twenty muscles around each hip joint that directly affect the way the joints articulate. Short, half-hearted stretches, generalized massage, and admonitions to "get stronger" are not enough to retrain proper hip function. It does take time. It does take effort. And it takes a lot of attention. For the longevity of any person's hips, it makes far more sense to leave the joint intact for as along as possible and to learn how to train the muscles for optimal function. 

While as a society are in the early stages of combatting hip dysfunction and pain, my own years of experience retraining my hips and helping others retrain their hips out of pain have made it clear that it is possible to do. It's helpful to have someone troubleshoot and guide you along the way. These days, there are very few people on the planet who know how to do that, and finding them is difficult.

If you cannot find someone who is able to help you make progress, we have made a do it yourself program called the FAI Fix that takes in all the information we've gathered over the years and gives you a principle based system to help yourself. The process is more difficult on your own, but this is the best solution we could offer to help the millions of people suffering with hip pain right away. It is constantly under review and being updated as our understanding and experience with more and more complex hip pain cases grows. 

Learn more about our DIY program to help you train out of hip pain.


About the Author

Matt Hsu is a trainer and orthopedic massage therapist. He fought a long battle with chronic pain all over his body and won. He blends the principles he learned in his journey, empirical observations with clients, and relevant research to help others get their lives back.

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