Entiende, evalua y trata de una manera diferente las patologias de cadera. El impingemet (FAI) es una entidad muy estudiada medicamente y muy poco desarrollada y entendida en kinesiologia. Aprende nuevas formas de trabajar la cadera www.kinedecadera.com, cursos de manejo de la cadera en www.cursosdekine.com

1. 1
©2010 British Editorial Society of Bone and Joint Surgery
Focus On
Femoroacetabular
impingement
Introduction
Tears of the acetabular labrum are a recognised cause of hip
pain.1-4
Possible causes of labral tears include trauma, hypolaxity
of the anterior capsule, dysplasia, bony impingement and reduced
biomechanical properties in the area most susceptible to tears.5,6
Impingement of the proximal femur against or within the
acetabular rim is a common underlying cause of a labral tear in
the non-dysplastic hip.7,8
Leunig et al9
defined morphological abnormalities in the
shape and orientation of the femur and acetabulum that charac-
terised femoroacetabular impingement (FAI) and proposed a
causative link between FAI and the development of osteoarthri-
tis.9-12
Wagner et al13
showed that the cartilage from the non-
spherical portion of the femoral head in FAI showed histological
changes similar to those of an arthritic hip, and different to a
spherical head control group.
Chondral damage is associated with FAI in a predictable man-
ner,14,15
and damage to the acetabular rim has been postulated
as part of a sequence of events causing hip osteoarthritis.16
The key morphological characteristics of FAI relate to abnor-
malities in the shape and orientation of the femoral head and
neck (cam impingement) or to abnormalities in the shape and
orientation of the acetabulum (pincer impingement). While gross
examples of cam impingement (pistol-grip deformity, post
Slipped Upper Femoral Epiphysis) and pincer impingement
(severe acetabular retroversion) have been recognised for many
years, the recognition of more subtle variants of these condi-
tions and their links to the early development of arthritis has
allowed greater understanding of early adult arthritis and facili-
tates the development of new treatment options.
Cam Impingement
The basic hypothesis is that cam impingement arises when the
radius of curvature of the femoral head or neck profile exceeds
the radius of curvature of the acetabulum, and can arise from a
number of basic abnormalities. A key element of cam impinge-
ment is a reduced or absent offset between the femoral head
and neck (Fig. 1). The degree of cam deformity has been defined
Offset ratio = x/y
y x
Alpha angle
Alpha angle
Ideal hip Retroverted Beta angle
Beta angle
Alpha angle
Beta angle
Alpha angle
Beta angle
Aspherical hip
Broad hip
Fig. 1
Varieties of cam femoroacetabular impingement

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THE JOURNAL OF BONE AND JOINT SURGERY
by measurements of offset-ratio, alpha and beta angles on
radiographs17,18
or MRI.19
As the aspherical, expanded portion of the femoral head-neck
complex encroaches on the acetabular rim, the labrum displaces
outwards resulting in increased tensile stress at the labrochon-
dral junction resulting in labral type-1 tear separation from the
adjacent articular cartilage at the watershed.20
As the aspherical
portion rotates further within the acetabular rim, compressive
forces and shear stress at the osteochondral junction increase,
resulting in delamination of the chondral surface from the under-
lying bone and producing the so called 'wave sign' visible at
arthroscopy. Fissure fractures created by traction forces at the
labrochondral junction expose the edge of the chondral surface
to the advancing 'front' of the femoral cam lesion, and result in
the creation of chondral flap tears or 'carpet lesions' (Fig. 2). This
hypothesis is supported by McCarthy et al,21
who confirmed that
73% of hips with labral tears had adjacent acetabular chondral
damage. Johnston et al15
confirmed that cam impingers with high
alpha angles were associated with labral injury, chondral damage
and decreased range of movement.
Pincer Impingement
The femoral neck of a hip with adequate head-neck offset can
impinge on the rim of the acetabulum at the extremes of its
range of movement. However, if the shape or orientation of the
acetabular rim results in impingement before the hip has
achieved its required functional range of movement, impact
damage to the labrum will occur.
Radiographic features suggesting a susceptibility to pincer
impingement include a deep socket (coxa profunda or protrusio),
high centre-edge angle, low sourcil angle and signs of global or seg-
mental retroversion or anteversion of the acetabular rim (Fig. 3).
Dynamic pincer impingement can occur in 'normal' hips if the
required range of movement is large (e.g. dancers and gym-
nasts) or translated (e.g. hockey players22
).
Labral impact damage frequently manifests signs of a thick-
ened, patulous labrum with 'blunting' of the labral edge and
cystic change. Alternatively, the labrum may be almost non-exist-
ent as a result of intra-substance calcification,14
which com-
pounds the problem of a reduced range of movement. Pincer
impingement is associated with a lower incidence of anterior
acetabular chondral damage than cam impingement, although it
still occurs as a 'contrecoup' degeneration on the posterior
aspect of the femoral head and acetabulum (Fig. 4).23
While isolated cam and pincer impingement can occur, the
majority of hips present with a mixed pattern.
Presenting Symptoms
FAI commonly presents in younger adults as a deep intermittent
groin discomfort during or after activity.24
Fig. 2
Chondral flap tear or 'carpet lesion'
Fig. 3
Abnormalities of acetabular version

3. 3
The cam variety of impingement presents with intermittent
discomfort in the groin during or after repetitive or persistent hip
flexion. Sprinting or kicking sports, ascending hills or stairs, pro-
longed sitting in low chairs, driving or getting in and out of low
vehicles are common exacerbating activities. Pain may be
referred to the anterior thigh, to the region of the symphysis
pubis and to the ipsilateral testicle in men.
Anterior pincer impingement presents with similar symptoms as
cam impingement. However, symptoms of posterior impingement
may be experienced in the buttock or sacro-iliac region. These
symptoms are more common in women, occur when the hip is
repeatedly hyperextended as in fast walking or walking downhill
and are often difficult to differentiate from pain referred from the
low back and sacro-iliac joint. Women with posterior impingement
frequently complain of posterior hip pain during intercourse.
Mechanical symptoms of catching, clicking and a feeling of
giving way are commonly associated with labral tears secondary
to hip impingement.
Examination
The hip is examined in a methodical manner, which should
include an assessment of rotational abnormalities in the
femur. Hip flexion, adduction and internal rotation most com-
monly replicate the pain experienced during anterior hip
impingement.25,26
In flexion, the hip is progressively rotated from external to
internal rotation while moving from abduction to adduction.
Using this technique, it is possible to identify the most likely posi-
tion of impingement and the most likely area of acetabular rim
injury. A similar examination of the hip in hyperextension may
help with the diagnosis of posterior impingement.
Investigations
Radiology. A systematic approach to the plain radiographic evalu-
ation of these patients is essential. An anteroposterior (AP) pelvis
film should be supported by a cross-table lateral or Dunn view.18
Key acetabular features on the AP film include the presence of
a deep or shallow socket (dysplasia, coxa profunda, protrusio) and
an assessment of acetabular version (anteverted, retroverted,
focal or global). Pattern recognition of subtle abnormalities takes
a long time to develop and is fallible; modern Picture Archiving and
Communications System (PACS) facilities allow accurate meas-
urement of centre-edge and sourcil angles as a minimum. Key
femoral measurements include head sphericity, neck-shaft angle,
alpha angle and offset ratio. The Academic Network for Hip Out-
comes Research (ANCHOR) study group27
has published an excel-
lent systematic guide to evaluating plain images.
MRI. To identify the most subtle cam imperfections in proximal
femoral anatomy, an MRI arthrogram with intra-articular contrast is
required. This investigation should include radial sequence scans
(Fig. 5) to allow a tangential view perpendicular to the acetabular
rim and a detailed analysis of the proximal femoral morph-
ology.28,29
Rakhra et al30
showed that the maximum alpha angles
obtained on radial scanning were abnormal in 54% of patients with
apparently normal alpha angles on conventional oblique axial
scanning. We also recommend acquiring cuts through the distal
femur to assess abnormalities of femoral torsion.
Fig. 4
Contrecoup posterior acetabular damage secondary to anterior pincer impingement
Fig. 5
A radial MRI scan
Fig. 6
Three-dimensional (3D) CT reconstruction showing a small cam lesion at the femo-
ral anterior head-neck junction

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THE JOURNAL OF BONE AND JOINT SURGERY
CT. The use of 3D reconstruction of CT scans has proved useful in
the recognition of subtle femoral deformities (Fig. 6) and in pre-
operative planning during the management of complex deformi-
ties.17
It is particularly helpful in achieving appropriate orienta-
tion of the hip during arthroscopic femoral osteochondroplasty.
Management of FAI
Femoroacetabular impingement is a mechanical problem that
requires a mechanical solution. A common presenting feature is
failure to respond to analgesia and physiotherapy; stretching
exercises and yoga may aggravate the condition. Reduction in
the symptoms associated with pincer impingement might be
amenable to sports therapy that focuses on modifying the
dynamic hip flexion element of pincer impingement by maintain-
ing core stability and a more upright stance during activity (e.g.
skiing moguls or deep powder).
Surgical correction of the deformity remains the mainstay of
management, and has been shown to be effective in the short
term. Beaulé, Le Duff and Zaragoza31
showed that quality of life
scores such as the Short Form (SF)-12 score or Western Ontario
McMasters Universities (WOMAC) index increase after FAI surgery.
FAI comprises a broad spectrum of disorders that require a wide
range of surgical options. With increased understanding of the con-
dition, and cross-fertilisation of surgical principles, it is clear that
both hip arthroscopy and open surgery have a valuable role to play.
Surgical dislocation of the hip using the Ganz trochanteric flip
approach is based on a thorough understanding of the vascular
anatomy of the femoral head32-34
and allows unparalleled access
to the femoral head and acetabulum. A full description of the
technique has been summarised by Norton, Fern and Williams.35
The technique facilitates the key elements of basic FAI surgery,
namely femoral osteochondroplasty, labral repair or resection or
replacement, reshaping of the acetabular rim and acetabular
chondral debridement. With adequate experience, the versatility
of the technique allows extremely complex hip reconstruction
(Fig. 7) to be performed safely and predictably.36,37
Clohisy and McClure38
reported good to excellent results in
24/25 patients at 1.5 years after an anterior exposure of the hip
through a limited Smith-Petersen approach (Fig. 8) combined
with hip arthroscopy, despite the restricted exposure compared
with formal hip dislocation.
Although favourable long-term results can be achieved with
simple arthroscopic labral resection,39 the early acceptance of
the principles of FAI has resulted in considerable advances in
both the techniques and equipment associated with arthro-
scopic hip surgery.
Fig. 7
The Ganz approach (top left) facilitates safe access to the hip and allows correction of the severe deformity which may be seen in slipped upper femoral epiphysis (top
row) and Perthes' disease (bottom row)

5. 5
Labral refixation provides better results than simple excision,40
and correction of the underlying structural deformity produces a
better result than dealing with the labrum in isolation.41,42
These
results mirror those achieved by open surgery.33
Philippon et al24
reviewed the arthroscopic treatment of FAI and concluded that
ther technique had particular relevance to high-demand patients,
particularly athletes seeking a return to high-level sport.
It is apparent that the key elements of surgery for FAI which
have been developed through open surgery are achievable by
skilled hip arthroscopists. Avoiding the need for trochanteric
osteotomies and prolonged periods of limited post-operative
weight-bearing has obvious advantages.
Zebala, Schoenecker and Clohisy43
summarised that FAI was
a diverse disease with evolving treatment options; the under-
standing of the genetic elements of FAI44
might allow selective
screening and earlier diagnosis of the condition. Long-term out-
come studies showing a beneficial effect of peri-acetabular oste-
otomy after 20 years support the use of biological solutions.45
Although FAI surgery is effective in the short term, evidence is
still required that early intervention prevents or delays the devel-
opment of arthritis in the long term.
Surgically induced acetabular dysplasia as a result of inappropri-
ate acetabular rim trimming has been linked with a poor outcome
after FAI surgery,46
and has prompted a change in management,
emphasising femoral correction and minimal removal of the
acetabular rim and/or labral calcification in our centre.
Publication of definitive reference ranges for femoral cam
lesions43
and acetabular rim morphology in the near future
should allow surgeons to become more accurate with patient
selection in the future.
In return for professional services, 2 authors (MN and EDF) obtained or will obtain outside
funding from a commercial group (Corin Group PLC). This is not directly related to the
preparation of material for this article. In addition, Corin Group PLC support a research
fund directed by the same 2 authors.
ED Fern MR Norton
Cornwall Hip Foundation
Truro, Cornwall
Correspondence to:
Darren Fern
Point Quay House, Point, Devoran, Truro, Cornwall, TR3 6NL
e-mail: edfern@btinternet.com
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Limited access via a limited Smith-Petersen approach

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