Femoro-acetabular Impingement: A Reflection

Volume 01 / Issue 02 / September 2013
boa.ac.uk
Page 67
Peer-Reviewed Articles
© 2013 British Orthopaedic Association
Femoro-acetabular
Impingement:
A Reflection
Richard E Field PhD FRCS FRCS(Orth)
Professor of Orthopaedic Surgery, St George’s University of London Director of Research,
The South West London Elective Orthopaedic Centre Consultant Orthopaedic Surgeon,
Epsom & St Helier NHS Trust
Earlier this year, a
well-known figure
from the popular
music world
cancelled the 21date, US leg, of her
world tour in order to
undergo surgery to
repair a labral tear, of
her right hip joint.
Ten years ago, a labral tear was an
almost unknown diagnosis. It was
certainly not recognised outside
a small clique of orthopaedic
surgeons. Its pathogenesis was
unknown. It was not clear whether
a torn labrum was a clinical
problem. There were no recognised
strategies for treating the condition
and no-one had proven that
surgical intervention would be
advantageous. So how is it that, in
less than ten years, an orthopaedic
curio has developed into a major
show-stopper, a condition that is
familiar to the mainstream press
and one that can be treated with
increasing confidence?
We know that a healthy hip
must satisfy the conflicting
requirements for movement and
stability. The forces and strains
on the hip depend upon the size,
shape and orientation of the
articulating surfaces, the balance
and strength of the surrounding
soft tissue envelope, body
morphology and the activities that
an individual undertakes. The
interplay of these variables makes
every hip a unique structural and
stress environment. The rim of the
acetabular socket, known as the
labrochondral complex, augments
joint stability and helps retain
synovial fluid between the bearing
surfaces2,3,4,5 (Figure 1).
Richard E Field
Figure 1 - The labrochondral complex.
Over a lifetime, the human hip will
be subjected to over 200 million
loading and movement cycles. This
equates to walking more than two
circuits of the earth’s equator. Any
structural incongruity or instability
between the femoral head and
acetabular socket will stress the
labrochondral rim and initiate a
damage cascade that results in
degenerative joint disease.
In July 2005 the British Journal
of Bone and Joint Surgery
published an article, from Ganz’s
team in Berne. The title of the
article was ‘Hip morphology
influences the pattern of damage
to the acetabular cartilage:
Femoroacetabular impingement
as a cause of early osteoarthritis of
the hip6. If I were selecting my ten
‘Desert Island’ papers, it would be
near the top of the list.
Publication of this article was the
tipping point that disseminated
the concept of femoroacetabular
impingement (FAI) from a small
group of hip specialists to the
wider orthopaedic community and
beyond. I first saw the paper a
few months before its publication
and subsequently wrote a ‘further
opinion’ piece for the JBJS’s
online version7. Being anxious
not to make a complete idiot of
myself, I spent a long weekend
reading papers that Ganz’s team
had published in the preceding
few years8,9,10,11.
It was one of those occasions when
you realise that if you’d only been
a bit less lazy and read the papers
being written by the thinkers of the
orthopaedic world you wouldn’t
have missed out on one of the most
important discussions to occur
during your career.
Volume 01 / Issue 02 / September 2013
boa.ac.uk
Page 70
Peer-Reviewed Articles
Journal of Trauma and Orthopaedics: Volume 01, Issue 02, pages 67-72
Title: Femoro-acetabular Impingement: A Reflection
Authors: Richard E Field
Figure 3 - Labral compression and ‘wave sign’ articular cartilage delamination
caused by ‘pincer’ type impingement
Figure 2 - Labral eversion, labrochondral splitting and articular cartilage
damage caused by ‘cam’ type impingement
I realised that Ganz’s group was
creating a vocabulary that would
allow us to visualise and describe
mechanisms by which the hip
can become damaged. Once the
concepts were grasped, it seemed
so obvious and somewhat bizarre
that we hadn’t got it sooner. This
was eight years ago. A mere blink
in orthopaedic history. Yet, in just
a few years, the management of
pre-degenerate hip disease has
been transformed. Surgeons
specialising in joint preserving hip
surgery have developed a range
of new surgical techniques and
people from all walks of life can be
treated successfully, with minimal
soft tissue trauma.
What is a labral tear and
why do they occur?
Most orthopaedic surgeons are
familiar with meniscal and labral
pathology in the knee and shoulder.
In the hip, ‘labral tear’ is a succinct
term that is accepted by patients
and the media. However, it is an
oversimplification that may hamper
our understanding of labral pathology.
The labrochondral complex can be
damaged by compression (being
squashed), tension (being stretched)
torsion (twisting) and shear (sliding)
forces. The combination of stresses
on the labrochondral complex differs
for a degenerate hip, a dysplastic hip,
a cam hip and a pincer hip.
Patients with degenerate hip
disease are referred for orthopaedic
review with a spectrum of osseous
changes; ranging from relatively
mild joint thinning and early
subchondral changes to complete
joint space obliteration, extensive
marginal osteophyte formation,
subchondral sclerosis and
subchondral cyst formation.
While healthcare funders may
deem the degree of radiological
degeneration to be an appropriate
criterion for joint replacement,
orthopaedic surgeons recognise
that any correlation between clinical
symptoms, disability and radiological
changes is far from linear. Indeed,
patients with evidence of advanced
radiological joint degeneration often
report a relatively short duration of
pain. Although this phenomenon
is unexplained, it is interesting to
note that antero-superior labral
swelling and separation is usually
present in such cases. It may be
speculated that entrapment of the
richly innervated12,13, unstable labral
segment is the cause of the patients’
increased symptoms and this would
also explain why some patients
experience such severe symptoms
in the presence of relatively mild
radiological deterioration.
In dysplasia, overload of the
hypertrophied labrochondral
complex provides a readily
understood explanation for labral
separation and the poor clinical
outcome of labral resection or
repair is widely recognised.
Ganz’s team proposed that FAI
could occur by one or more
mechanisms. In cam-type
impingement, the femoral head is
not round. Any segment that sits
proud of the surface of rotation
will bump into the socket rim. As
the prominent segment passes
into the joint, the labrum will be
levered outwards and a grinding
force will be applied on the
adjacent hyaline cartilage. With
time, the labrochondral junction
splits and the adjacent chondral
tissue delaminates or breaks down
(Figure 2). As damage progresses,
subchondral rim cysts develop;
either by repetitive trauma or
pressurised synovial fluid erosion.
In pincer impingement the
femoral neck impacts upon and
compresses the labrum (Figure 3).
This can occur if the acetabular
socket is deep (coxa profunda), if
the front of the acetabular socket is
prominent (acetabular retroversion),
if the femoral neck is retroverted,
if the individual has sufficient
ligamentous flexibility that they
are able to move their joint to an
osseous limited endpoint or if the
joint is forced into such position.
Volume 01 / Issue 02 / September 2013
boa.ac.uk
Page 71
© 2013 British Orthopaedic Association
Journal of Trauma and Orthopaedics: Volume 01, Issue 02, pages 67-72
Title: Femoro-acetabular Impingement: A Reflection
Authors: Richard E Field
What can we do
about FAI?
As Personal Trainers,
Physiotherapists, General
Practitioners and Orthopaedic
Surgeons become more attuned to
the symptoms and physical signs
of FAI lesions; our first priority is to
identify whether patients symptoms
will settle with modification of
activities, physiotherapy or steroid
injections. Professor Damian Griffin
is currently coordinating the ‘UK
FASHION’ study to determine a
whether patients deemed suitable
for surgical treatment can be treated
by non-surgical means. If this
proves to be the case, a burgeoning
branch of Orthopaedic practice
will be arrested. Alternatively, if
the ‘UK FASHION’ study does
lend support to the premise
that surgical intervention can be
advantageous, our task is to ensure
that the appropriate intervention is
undertaken in each case.
Plain radiographs usually signpost
the type of impingement that a
patient may be experiencing. The
AP standing view provides an
abundance of useful information
including: joint space narrowing,
saucil angle, centre-edge angle,
subchondral sclerosis, marginal
and saucil subchondral cyst
formation, cross-over sign, ischial
spine sign and labral calcification
or ossification. Augmented by
turned lateral and cross-table
true lateral views it is usually
possible predict the findings of
further imaging studies such as
MR, MR arthrograms and CT
reconstructions. Plain radiographs
also enable a surgeon to provide
patients with rapid feedback on
the structure and condition of their
hips with appropriate guidance
for further investigations and
treatment. The value of these
simple radiographic views cannot
be over emphasised.
Over the last few years, a number
of research groups have developed
motion analysis software using CT
data to analyse the geometry of
a patient’s hip and compare the
potential ranges of joint movement
against known population
norms14,15,16 (Table 1).
Such software also enables
surgeons to understand the
location and quantity of bone
that would need to be removed
to provide impingement free
movement during activities of daily
life (Figures 4 and 5)17.
Future refinements of these tools
should incorporate the additional
complexity of ambulation as well
as the orientation and movement
of adjacent and more distant joints.
Surgical treatment of FAI is
increasing. When surgery works
well, the patients are able to return
to competitive sport, at the highest
level18,19,20. Joint replacement
cannot achieve this goal. However,
we do not yet know whether such
individuals are being provided with
a license to further damage their
natural joints or the prospect of
prolonged healthy joint function.
TABLE 1
Motion Test
Target
This Hip
120o 50o 60o 60o 40o 30o 50o 40o 30o 15o 106o
67o
101o
87o
36o
20o
78o
33o
12o
16o
Maximum flexion Maximum abduction Max internal rotation Max internal rotation at 30o flexion Max internal rotation at 60o flexion Max internal rotation at 90o flexion Max internal rotation at 30o flexion + 20o adduction Max internal rotation at 60o flexion + 20o adduction Max internal rotation at 90o flexion + 20o adduction Maximum extension at 15o external Figure 4 Acetabular resection option to restore a normal ROM
Table 1: The figures in the
left column show normal
ranges of hip movement.
The figures in the right
column are those of a
patient with cam type FAI.
Figure 5 Femoral resection option to restore a normal ROM
Volume 01 / Issue 02 / September 2013
boa.ac.uk
Page 72
Peer-Reviewed Articles
Journal of Trauma and Orthopaedics: Volume 01, Issue 02, pages 67-72
Title: Femoro-acetabular Impingement: A Reflection
Authors: Richard E Field
There is growing evidence that
open FAI surgery causes more
iatrogenic morbidity than miniopen and arthroscopic procedures.
However, arthroscopic FAI
hip surgery is not easy. To be
undertaken successfully, special
equipment and new surgical
skills are essential. Great strides
have been made to develop
a community of UK surgeons
with the expertise to undertake
and develop FAI surgery and
these individuals deserve our
encouragement and support to
ensure that they provide safe and
effective interventions.
Most importantly, FAI affects the
lives of young people whose ability
to work, pay tax and play
an active role in our community
may be compromised by the
sequelae of FAI. In the case of the
popular music star, cancellation of
her US tour dates meant that the
concert promoters were obliged to
refund some $25M to disappointed
ticket holders.
References
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Correspondence:
Richard E Field
The South West London Elective
Orthopaedic Centre
Dorking Road
Epsom
Surrey KT18 7EG
Email: [email protected]