Keywords
hip - impingement - MRI - femoroacetabular - joint
Since the appearance of femoroacetabular impingement (FAI) on the world stage in 2003
following Ganz et al's publication on FAI as a cause for osteoarthritis (OA) of the
hip,[1] the medical and athletic community, and, to a lesser extent, people with hip pain
in the general population, have been taken on a roller-coaster ride: confusing definitions
and promises of pain relief, prevention of the onset of OA, delaying of progression
of OA, overall uncertainty, and mixed results.
How Did We Get Here?
Much of this confusion began with the advent of a surgical technique that allowed
safe dislocation of the hip.[2] Ganz and colleagues meticulously studied hip joint anatomy and, specifically, the
vascular anatomy of the femoral head.[3] After ascertaining that the medial femoral circumflex artery was the main contributor
to femoral head perfusion, and that the ligamentum teres and its associated vestigial
artery had little, if any, role in femoral head perfusion in adults, they developed
a technique for safe surgical dislocation of the femoral head with minimal, if any,
risk of femoral head osteonecrosis. This surgical technical development was a key
factor in the subsequent developments of what we now refer to as femoroacetabular
impingement syndrome (FAI syndrome, or FAIS).
With the ability to dislocate the hip safely, Ganz et al were able to better visualize
the entirety of the femoral head, the femoral head-neck junction, and the acetabular
fossa. This extended visualization allowed them to get a better appreciation of the
three-dimensional morphology of the proximal femur, the acetabulum, and the various
associated lesions. With this improved in vivo visualization, the mechanical concept
of FAI and its association with hip OA was born.[1]
Medicine and Technology
The promises of new technologies (and techniques) seem an appropriate simile for what
we often see in medicine, especially as medicine becomes more and more technological
every year. Consider the remarkable advances in only the last few decades regarding
imaging and surgical tools and techniques. The sheer volume is staggering in general,
and in hip imaging and treatment in particular. Without going into details, in the
United States, hip arthroscopies increased 117% from 2007 to 2014, and extended billing
codes increased 475% in that same period.[4]
In many ways, the technical development of safe surgical dislocation of the hip followed
Roy Amara's law: “We tend to overestimate the effect of a technology in the short
run and underestimate the effect in the long run”(2006).[5]
Amara's Law
The technological development of safe dislocation of the hip not only triggered the
theory of FAI as a cause of OA, it also provided a way to treat what was thought to
be the cause of the symptoms: the so-called bump at the femoral head-neck junction,
what we now refer to as cam morphology. To a lesser degree, at least initially, the
surgical dislocation also allowed surgeons to address the results of the abnormal
contact between the proximal femur and the acetabulum: labral tears and cartilage
lesions.
As per Amara's law, the effect of this technology/technique of safe dislocation of
the hip was initially overestimated. There were promises of prevention of primary OA to the point that some centers were
performing prophylactic osteochondroplasties to correct the cam lesion (morphology)
in asymptomatic patients, believing it would prevent the development of labral lesions,
cartilage lesions, symptoms, and OA. The need for treatment of all hips with a cam
or pincer morphology was, as we now appreciate, overestimated.[6] The ability to decrease pain and prevent OA in all patients may have been overestimated
as well.
On the flip side, the long-term effects of this technology/technique were underestimated.
As open FAI surgery became popular, some pioneers began trying to address the osseous
and soft tissue lesions via arthroscopy. Before then, hip arthroscopy was quite rare,
only performed by a few arthroscopists, and generally at low volumes for very limited
indications. The recognition of FAI as a cause of hip pain lead to an unexpected and,
as per Amara's law, underestimated effect: a rapid and sustained increase in the volume
of hip arthroscopies.[4]
[7] There was an associated improvement in arthroscopic techniques and devices including
specially designed scopes, shavers, and burrs. What was previously a rare procedure
very quickly became a very common procedure that within a short period of time was
being performed by thousands of arthroscopists worldwide ([Fig. 1]). The underestimated long-term effect of Ganz's safe dislocation of the hip was the resulting boom in hip arthroscopies
worldwide and not only for FAI surgery.
Fig. 1 Trends in hip arthroscopy in the United Kingdom (UK), 2002–2013. There was more than
a fivefold increase in the number of hip arthroscopies in 11 years.
This boom in hip surgery, specifically hip arthroscopy, resulted in exponential and
essentially parallel rises in research activity and the number of articles published
regarding hip arthroscopy and hip impingement. The two went hand in hand ([Fig. 2]), with a clear inflection point shortly after 2003 when Ganz's sentinel article
was published.
Fig. 2 Trends in publications for hip arthroscopy and hip impingement, 1980–November 2018.
There was a clear and dramatic increase in the number of publications on hip arthroscopy
(red) and hip impingement (blue) after the publication of the sentinel article by
Ganz et al in 2003 proposing femoroacetabular impingement as a cause of hip osteoarthritis.[8]
The Hype Cycle
In addition to the trends in surgical techniques and associated developments, the
overall concept of FAI including its presentation, diagnosis, and treatment was a
classic example of hype. We often see this type of hype in the world of technology
and medicine. In fact, Gartner refers to the hype cycle as a representation of the
maturation and adoption of technologies and applications ([Fig. 3]) in these steps:[9] (1) technology trigger; (2) peak of inflated expectations; (3) trough of disillusionment;
(4) slope of enlightenment; and (5) plateau of productivity.
Fig. 3 The hype cycle. The phases of the hype cycle as they relate to new technologies (adapted
from reference 9).
Initially, there is a big media blitz about an amazing new discovery (technology trigger).
Headlines and sensationalist stories follow about the promises of the new technology
and how it will change the way we live (peak of inflated expectations). As experience
accumulates, it becomes clear that the new technology, although it may be quite good,
is not as far reaching as initially marketed or anticipated. This leads to a sense
of disappointment and perhaps even deception (trough of disillusionment). However,
as further experience accrues, there is a period during which the true and optimal
use/applications of the new technology become apparent (slope of enlightenment). In
the final phase, the advantages and shortcomings of the new technology are understood
well enough to be able to apply it in a manner that is efficient, productive, and
optimized (plateau of productivity).
Hip Hype
As with the technological hype cycle, FAIS followed, and continues to follow, a similar
cycle ([Fig. 4]).
Fig. 4 The femoroacetabular impingement (FAI) hype cycle. The phases of the hype cycle as
they relate to FAI syndrome. OA, osteoarthritis.
-
Safe surgical dislocation of hip (Innovation trigger): As previously mentioned, the ability to dislocate the hip safely allowed global visualization
of the hip, specifically the variations of femoral head-neck morphology and the location
and types of cartilage and labral damage. This better visualization led to the better
understanding of the three-dimensional interaction between the femur and the acetabulum
and the (re)birth of the concept of FAI. Ganz and colleagues proposed this so-called
new disease as a cause for hip OA and proposed treatments as a way of preventing or
delaying the onset of hip OA.[1] Specifically, they championed the use of osteochondroplasty of the femoral head-neck
junction as a treatment for asphericity of the femoral head and periacetabular osteotomy
as a treatment for acetabular version abnormalities. In essence, this was a “new”
disease with a new treatment.
-
Everyone has FAI and treating it will delay/prevent hip OA (Peak of inflated expectations): The publication and popularization of the concept of FAI and the interest and adaptation
of the surgical techniques proposed by Ganz et al heightened awareness of the concept
of FAI. Also, the potential to prevent or delay hip OA was embraced enthusiastically
worldwide. This resulted in a widespread boom in both the diagnosis and treatment
of FAI. With the description of the magnetic resonance (MR) arthrographic findings
in patients with cam-type FAI,[10] MR arthrography of the hip became the imaging modality of choice in assessing the
extent of intra-articular damage in patients with FAI, in addition to better assessing
the shape of the osseous deformities. Advances in hip arthroscopy also increased access
to surgeons who could treat the anatomical “abnormalities” in and around the hip joint.[11] There was a significant trend toward early surgery for patients with hip pain with
the goal of decreasing pain, improving range of motion, and preventing/delaying OA.
The enthusiasm, particularly in the surgical community, led to certain centers performing
prophylactic surgery on asymptomatic hips that demonstrated the morphological findings
described by the Bern group. The idea was to operate and correct/modify the underlying
osseous anatomy and thus prevent future damage to the cartilage and labrum (unpublished
data). Expectations skyrocketed as did the volume of hip imaging and hip surgeries
for FAI.
-
Does FAI even exist? How should we treat it? (Trough of disillusionment): The heightened awareness of the concept of FAI and the recognition of the osseous
findings on imaging led to the realization that these osseous morphologies were quite
prevalent in the general population. In fact, the more one looked, the more one saw
the bump or the acetabular retroversion on imaging studies done for purposes that
were completely unrelated to hip pain.[12]
[13]
[14]
[15]
[16] If so many people had these osseous morphologies but were asymptomatic, did FAI
even exist?
This could be applied to the ever-common labral tears as well. The prevalence of labral
tears in the asymptomatic population was also found to be quite high.[17] Are labral tears a cause for pain? Is their presence even relevant in the setting
of FAI and hip pain?
In addition, postoperative midterm data began to emerge for both open and arthroscopic
treatments for FAI. Although short-term data had been very encouraging, midterm data
showed significant heterogeneity in outcomes for FAI surgery. Also, there was significant
inconsistency in the manner of reporting outcomes.[18]
[19]
[20] It was thus unclear who truly benefited most from surgery or whether surgery was
the best first-line treatment for FAI.
All of these uncertainties regarding the diagnosis and treatment of FAI led to significant
disillusionment and skepticism in the medical community and, to a lesser degree, the
athletic community.
-
FAI exists but . . . (Slope of enlightenment): The uncertainties and skepticism were recognized, and great efforts were made to
better understand the pathophysiology of FAI. One of the clear shortcomings was the
lack of consensus on the precise definition and terminology that should be used. What
is an abnormal head-neck junction? What thresholds should be used for α angles, lateral
center-edge angles, acetabular version, femoral torsion, and so on? How much is too
much or too little? Are these abnormalities or just morphological variants?
Along those lines, consensus was needed to move forward with more consistent and homogeneous
research. This would help in determining the best means for diagnosing and treating
FAI. The Warwick agreement was an important step in better defining the entity and
proposed calling it femoroacetabular impingement syndrome (FAIS).[21] In addition, definitions were refined including specifying that FAIS is a combination
of symptoms, signs, and imaging findings. All three must be present. Also, regarding
the terminology, it was recognized that cam and pincer so-called deformities were
very common in the asymptomatic population and, for that reason, would best be described
as morphologies as opposed to deformities or abnormalities.
On the diagnostic front, research into best imaging strategies has gained traction.
To date, most imaging research has focused on selecting the best radiographic views
to assess osseous morphologies or assessing whether conventional non-arthrographic
hip MRI can adequately replace the current preferred hip MR arthrography in assessing
the status of the labrum and cartilage.[22]
[23]
[24] Also, recent studies assessed regional variations in hip cartilage properties that
may mimic cartilage damage.[25]
In terms of treatment, there was increasing recognition of the role of nonoperative
management of patients with FAIS. Recently, the results of the first randomized controlled
trial of arthroscopy versus best conservative therapy was published.[26] Other such trials are underway including ones comparing operative with nonoperative
management as well as comparing osteochondroplasty with or without labral repair to
lavage.[27]
[28]
All these active fronts in research are a clear indication of a desire to better understand
FAIS including its pathophysiology, clinical presentation, imaging appearance, and
optimal treatment for different subgroups of patients. These are clear indicators
of the slope of enlightenment.
-
How to address FAI syndrome (Plateau of productivity): This is where we are today, close to the inflection point between the slope of enlightenment
and the plateau of productivity. With a better understanding of the pathology and
the prevalence of imaging findings in the asymptomatic population, a more precise
definition of FAIS (triad of symptoms, signs, and imaging), and the recognition that
not all patients require surgery, the medical community can now make more informed
decisions regarding how to approach patients with FAIS. This should lead to a more
homogeneous and consistent way to manage patients with FAIS. Achieving that level
of homogeneity will be beneficial for the medical community, will allow the scientific
community to perform better mid- and long-term studies regarding the syndrome, and
hopefully lead to better patient care.
In conclusion, hip impingement and FAIS have followed Amara's law with initial overestimation
and subsequent underestimation of the effects of FAI surgery, and they have followed
the roller-coaster pattern of the hype cycle. There was an initial introduction of
a new technique of safely dislocating a hip, a peak of inflated expectation of surgical
treatment of FAIS, followed by a trough of disillusionment after the recognition of
the large prevalence of imaging findings in an asymptomatic population as well as
mixed results and uncertainty. This was followed by the slope of enlightenment as
FAIS was better defined by an international consensus and thus has allowed much progress
on understanding the syndrome and the variety of treatment strategies. Hopefully,
we are near the inflection point where, with this better understanding and more high-quality
research, there will be more precise and effective treatment strategies for patients
with FAIS.
And beware... artificial intelligence (AI) is really starting to take off in clinical
medicine and particularly in radiology. Are we ready for a roller-coaster ride on
the AI hype cycle?
