Femoroacetabular impingement
Femoroacetabular impingement (FAI) is a
condition in which the head of the femur
(also known as the femoral head or
thighbone) rubs abnormally against the rim
of the hip socket (acetabulum) or does not
have full range of motion in the socket,
creating too much friction and damage to
the hip joint. The femur is the long bone of
the leg that runs from the hip to the knee.
In a healthy hip, the head of the femur
should fit perfectly in the hip socket.
The two types of FAI: Pincer and Cam
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Damage (e.g., tissue breakdown) from FAI can occur to the articular cartilage. Articular
cartilage is the soft slippery tissue on the smooth white surface of the ball (head of the
femur) or socket that creates a smooth, low friction surface which allows the bones to
glide easily across each other. Damage (e.g., tearing) can also occur to the labral
cartilage, which is the soft but strong ring of tissue around the socket that creates a tight
seal and helps provide stability to the joint.


Yes. There are three types of FAI. The first type is known as Cam impingement, with
Cam being the Dutch word for "cog." In this type, the relationship between the femoral
head and femoral neck (the part below the femoral head) is not perfectly round due to an
excessive growth of bone along the upper surface of the head of the femur.

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This loss of roundness contributes to abnormal contact between the
femoral head and the rim of the hip socket. Thus, the femoral head is
unable to rotate smoothly within the hip socket. The result is that the
bump on the edge of the head of the femur grinds against the
cartilage within the hip socket, causing damage to it.

The Cam form of impingement often occurs in patients with
deformities of the hip and/or femur area after trauma, avascular
necrosis (dead bone caused by lack of blood flow), SCFE (slipped
capital femoral epiphysis), and coxa vara. SCFE refers to fracture of
a growth plate that results in slippage of the overlying epiphysis
(rounded end of a long bone).
Growth plates are areas of developing cartilage in children near the ends of long bones. Coxa vara is a
hip deformity in which the angle between the head and shaft of the femur is less than 120 degrees.

The second type of FAI is known as the Pincer form, with pincer coming from the French word "pincier"
meaning "to pinch." In this form, the hip socket overhangs and covers too much of the femoral head,
usually over the front rim of the socket. This blocks normal movement of the femur and results in the
cartilage being pinched between the rim of the socket and the front connection between the femoral head
and femoral neck.

The Pincer form is due to either the hip socket being too deep (known as profunda), the hip socket turning
back (known as retroversion), or the femoral head extending into the pelvis (known as protrusio). The
Pincer form causes degeneration, bone formation, and tearing and/or crushing of the anterior (front)
superior labrum. By labrum, this refers to the acetabular labrum which is a ring of cartilage that surrounds
the hip joint. In the Pincer form of FAI, the labrum often ossifies (turns into bony tissue), which deepens
the hip joint and decreases range of motion. The Pincer form of FAI is often seen in patients with
acetabular retroversion, which is when the alignment of the front wall of the hip socket lies more to the
posterior and the side than it should be.

The third type of FAI, which happens the most often (about 80% of cases), is known as mixed
impingement and is a combination of the Cam and Pincer forms. The Pincer and Cam forms of FAI are
shown in the pictures above.


The signs and symptoms of FAI often include degeneration of the hip, reduced hip
movement/function/flexibility and pain from the front, side, or back of the hip and loss of hip motion (e.g.,
high flexing, crossing the legs, extreme internal hip rotation). Hip pain from FAI is usually towards the front
than the side. Hip pain is usually provoked by high flexing, crossing the legs, exercise, and sports.

There can be give way buckling of the hip. For unclear reasons, low back pain is often reported by
patients who have FAI. However, pain is sometimes localized to the buttocks, side of the thigh/hip, or the
back of the pelvis. The area in the back of the pelvis specifically affected is the sacroiliac joint, which is
the joint in the pelvis between the ilium and the sacrum. The ilium is the uppermost and largest bone in the
pelvis. The sacrum is a large triangle shaped bone in the lower part of the spine which forms a wedge
between the two hip bones. Pain from FAI usually does not go below the knee.

Groin and hip pain are usually intermittent in FAI. The groin pain usually follows prolonged sitting or
walking. Athletes with groin pain usually experience this after deep flexion or rotation of the hip when
active. The pain usually develops gradually although it can occur suddenly if it follows an injury. The pain
tends to worsen with specific movements and can be sharp, catching, or locking. Locking of the hip is
consistent with disease of the labrum. Sharp stabbing pain may occur with turning, twisting, and squatting,
but it is sometimes just a dull ache. There may be a popping or clicking sound in the front of the hip. Pain
should not happen at rest. The onset of symptoms may be sudden, follow an injury, or occur slowly and
gradually after prolonged exertion.

The trochanteric C sign can occur in FAI. This is when the person is asked to show the location of the
hip pain and places the fingers in front of the hip and the thumb on the side of the hip or cups the
trochanter with the index finger and thumb. The trochanter is any of two bony protruberances by which
muscles are attached to the upper part of the femur. When removing the hand from the hip with the
fingers still in the position of the areas just touched, the fingers form a shape that looks like the letter "C".


FAI is associated with low back pain, excessive hip joint movement, cartilage tears and labrum tears. By
labrum, this refers to the acetabular labrum which is a ring of cartilage that surrounds the hip joint. FAI is
also associated with hernias caused by sports. Hernia is when a part of a structure sticks out through the
tissues that normally contain it. Some experts believe FAI to be a major cause of early hip arthritis
(known as hip osteoarthritis), you can still have FAI without arthritis. If treatment is not implemented to
preserve the hip, there is a high likelihood of developing osteoarthritis and needing a hip replacement. |

Although pain is common in FAI, it does not always occur. FAI can be associated with stiffness and
progressive loss of hip range motion instead. Stiffness is more likely to occur with the pincer form of FAI.
Some people with the condition may limp. There are some people who may live long and active lives with
FAI and never have problems. For this reason, it is unknown how many people have FAI. However, when
symptoms develop, it usually means that there is damage to the cartilage or labrum and the condition is
likely to worsen.


FAI commonly occurs in high level athletes but also occurs in other active people. Young adults are more
likely to develop the condition but middle aged adults are known to develop it as well. Men (especially
young men) who are physically active or heavy laborers are more likely to develop the Cam impingement
form of FAI than women, likely because this form is associated with significant contact sports. Women
(especially middle-aged women) engaging in activities requiring extreme hip motions (e.g., ballet, yoga)
may be more likely to develop the Pincer form of FAI. One of the most famous sports athletes, baseball
player Alex Rodriguez, developed FAI in 2009 (reportedly due to a misshapen femoral head) and
underwent surgery to correct the condition.


FAI is associated with sports activities such as ice hockey, field hockey, football, soccer, baseball,
tennis, lacrosse, rugby, tennis, golf, horseback riding, ballet, acrobatics, dance, gymnastics, ice-skating,
bike riding, cycling, martial arts, mixed martial arts, surfing, rowing sports (e.g., kayaking), and deep
squatting activities (e.g., power lifting). Significant athletic activity prior to the maturity of the skeletal
system may increase the risk of FAI, according to some experts. However, FAI-related pain may also
occur after normal range of motion activities such as sitting down and standing up. It is also associated
with yoga, car riding, and flying in an airplane due to deep seated or bucket seated positions.


It is unknown if FAI is inherited or is acquired over time due to excessive physical activity that stresses
the joints. While it is possible that either may occur, most cases are probably a combination of both. For
example, someone may be born with a slight hip abnormality (e.g., deep socket) or femur abnormality
(e.g., bump on the femoral head) causing the bones not to form normally during the childhood years and
then engage in excessive repetitive leg and hip activities which puts too much pressure on the hip joint.
Repetitive movements of the hip joint and extreme range hip motions increase the frequency of abnormal
contact in between the femur and hip socket. Thus, active athletes may experience pain earlier than
those who are less active. Exercise does not cause FAI, however. When someone is born with
abnormally shaped hip bones, there is little that can be done to prevent FAI as even normal range hip
movements will cause abnormal contact between the femur and hip joint.


First, it is important to note that a correct diagnosis can take years because many physicians have not
heard of FAI and there are numerous other conditions that cause similar symptoms (see below). The
diagnosis of FAI is usually based on the doctor obtaining a good medical history, performing a physical
examination, and obtaining the results of x-rays or other diagnostic tests. The history will elicit information
on the context of the symptoms, length of symptoms, severity of symptoms, location of the pain, and what
makes the symptoms feel better or worse. The history should also discuss prior athletic history, prior
trauma to the hip, prior hip surgery, and a history of prior hip conditions, particularly degenerative hip

The physical examination assesses the range of motion in the leg in relation to the hip, should confirm the
patient's symptoms, and exclude other causes of hip pain (e.g., spinal conditions, other neurological
causes). Others aspects of the physical examination include closely evaluating the patient's walking,
posture, and stance. Abnormal signs of walking include the trunk of the body moving towards the weak
side (known as abductor lurch), shortened stance phase (not standing as much on the extremity that is
painful), circumduction gait (walking with a stiff leg with each step rotated away from the body and then
towards it like a semicircle), and steppage gait (walking such that the toes actually clear the ground in the
affected leg). The doctor may feel around the joints to see if this elicits pain.

One physical examination technique is called an anterior impingement test. This test involves the doctor
bringing the knee up to the chest (flexing 90 degrees) and rotating it inwards towards the shoulder. If this
test recreates the pain normally experienced, impingement (abnormal contact between the femur and
front rim of the hip socket) is considered to be present. When this test is positive, FAI is a very likely
explanation. In the posterior impingement test, pain may also be recreated by rotating the hip outwards
and flexing outwards (e.g., sitting cross-legged). When this happens the pain can be due to abnormal
contact between the femur and back rim of the hip socket but it can also be related to many factors
besides FAI. Sometimes the patient may dangle their legs off the examination table and the doctor
rotates one outwards to perform the posterior impingement test. During the test, the opposite leg is held
and flexed by the patient.

Patients with hip damage may also develop shortening of the muscle (contracture) when the hip is flexed.
This can be assessed with the Thomas test. In this test, the patient lies on his/her back, brings one knee
to the chest, while the other remains extended. If the patient cannot keep the leg extended during the
test, the task is considered to reflect the presence of a muscle contracture.

An x-ray is typically ordered if there is limited flexibility on the physical examination. FAI is easily detected
through x-rays, which provides good images of bone and a two dimensional view of the hip joint. X-rays
of the pelvis and top of the femur will determine the size and shape of the femoral head and hip socket as
well as the amount of joint space in the hip. It will be able to tell if the bones are abnormally shaped and
can help look for bumps on the femur. Less joint space on the x-ray is usually associated with more
arthritis. The head of the femur may show a characteristic pistol grip deformity in which the head/neck
junction is flattened, not as spherical as it should be, and has herniation pits. Herniation pits are round to
oval abnormal areas on the neck of the femur surrounded by a thin layer of sclerosis (thickening) of bone.
If the fovea capitis is high, this can also indicate that the femoral head is not spherical (which it should
be), although this may not be seen on the anterior-posterior X-ray view. The fovea capitis is an oval-
shaped depression located a little below and behind the center of the femoral head.

For the x-ray, the two positions that are sufficient in most cases are the supine AP (anterior posterior)
pelvis view and the hip cross lateral table view. The supine AP pelvis view involves lying on the back with
the face upwards and helps view the pelvis. This must be a well centered view to show a clear outline of
the hip socket. The hip cross lateral table view involves lifting one leg up while an x-ray is taken of the
opposite femoral head and femoral neck connection. This view involves internally rotating the lower left
leg 15 degrees. Another view sometimes obtained is the frog leg lateral position, which is also known as
a lateral or side view. There is another technique known as false profile radiography (FPR) that depicts
damage on the front side of the wall of the hip socket and head of the femur. The FPR view is an oblique
(diagonal) view. Measurements of angles between different parts of the hip can be taken from this view to
assess for abnormal bone development. Another view is known as the Dunnview, in which the hip is
flexed 90 degrees and moved away from the center of the body outwards by 20 degrees. The Dunn view
is the most sensitive one for detecting a non-spherical formation of the head/neck of the femur. The x-
rays obviously need to be of good quality to aide in the diagnosis and should be no older than six months.

X-rays may show layers of new bone added to the rim of the hip socket. This is known as os acetabuli
and can be an indicator of pathology. Another finding can be the crossover sign in which the front wall of
the hip socket "crosses over" and projects lateral to the back wall of the hip socket.

A computerized axial tomography (CT) scan of the pelvis may also be ordered to look for abnormalities.
CT scanning is a more advanced imaging technique that uses x-rays and computer technology to
produces more clear and detailed pictures of bones and abnormal bone development than a traditional x-
ray. CT scans often show the structure of the hip joint bones and can detect abnormalities of these
structures but the test is not needed to diagnose FAI. The concern about CT scans is that it uses
radiation (especially 3D CT scans), so this is where MRI (magnetic resonance imaging) comes in. CT
and MRI scans can produce three dimensional views of the hip sockets and can be helpful in examining
the condition of the hip cartilage and exploring for the presence of osteoarthritis. Osteoarthritis is a
disease of the joints that is made worse by stress.

Magnetic resonance imaging (MRI) of the hip will often confirm damage to the joint surface or the
presence of a labral tear. MRI scans produce extremely detailed pictures of the inside of the body by
using very powerful magnets and computer technology. MRI is better than x-rays and CT scans at
visualizing soft tissue. The MRI is most helpful in eliminating other causes of hip pain such as avascular
necrosis, which is dead bone caused by lack of blood flow. It can also rule out the presence of dead
tissue. If the MRI is normal, FAI can still be present, as can a labral tear or cartilage injury. The MRI is
sometimes performed after contrast material known as gadolinium is directly injected into the joint as it
helps visualize the joint structures better and show areas of damage more clearly. This is known as
magnetic resonance arthrography and is sometimes referred to as "delayed gadolinium-enhanced MRI of
cartilage (dGEMRIC)." This is an experimental type of study and is not needed to diagnose FAI.

The MRI may also done with a pain test, in which a local pain killing medication (anesthetic) is injected
into the hip joint with the contrast dye. This helps to determine if the pain is coming from inside the hip
joint if the pain goes away after the injection.

X-rays, CT scans, and MRIs show the alpha angle, which is a measurement taken of the junction
between the head and neck of the femur. It quantifies the degree of femoral head/neck deformity and is
most accurately measured on MRI. This angle is not needed to diagnose FAI but it helps determine how
much Cam impingement exists. The larger the alpha angle, the larger the Cam impingement. The general
rule is that if the alpha angle is larger than 50 to 55 degrees, this is consistent with the presence of Cam
impingement. The alpha angle is most accurate when obtained from a special MRI scan that controls for
hip rotation. If the junction between the femur and hip socket is poorly positioned, this is an indicator of
FAI. Imaging studies also tell if the head of the femur or hip socket are deformed.

If an X-ray and MRI are negative, this eliminates many other diagnoses from being the cause of the
problem such as cancer, bone death of the femoral head due to poor blood supply to the area,
degradation of the joint (osteoarthritis), and transient (short-lived) osteoporosis of the hip. Osteoporosis
is an abnormal loss of bone thickness and a wearing away of bone tissue. There are times when an MRI
may appear normal, but there may be subtle findings upon re-examining the films indication impingement
or damage to the labrum. In the case of normal appearing X-rays and MRIs, the patient's history, x-ray
results, and physical exam findings indicate FAI. When this occurs, the doctor may want to explore the
area further through arthroscopic surgery. Arthroscopic surgery is described in the section on treatment


FAI is treated by orthopedists and orthopedic surgeons specializing in hip pathology. The surgeom should
have experience with either arthroscopic hip surgery or open hip surgery with surgical dislocation (see

The longer that painful symptoms of FAI go untreated, the more hip damage FAI can cause. FAI may be
able to be managed without surgery, which is generally recommended as the first option for most
patients. This involves being less active (e.g., resting, modifying activities, avoiding activities that cause
symptoms) and taking steps to increase hip strength. Rest can allow tears of the labrum to heal with time.
While lifestyle changes can resolve symptoms in most people, it will restrict attempts to return to sports.

Some people try to treat FAI with physical therapy, over-the-counter anti-inflammatory and/or pain
medications (e.g., ibuprofen, naproxen; sometimes in prescription strength form), and medication
injections in the hip joint. These injections include anesthetics (pain killers) and medication that reduce
inflammation such as steroids. Pain medications and anti-inflammatory medications help temporarily
relieve the pain.

A good physical therapy program focused on core strengthening and stabilization of muscles that support
the hip joint, optimizing hip alignment, improving soft tissue flexibility, and optimizing hip joint mobility can
be helpful because this decreases excessive force on weakened or irritated/injured tissue (e.g, cartilage,
labrum) in the hip joint. A good physical therapist can identify specific movement patterns that may cause
injury to the hip and help correct for this, decreasing pain and swelling in the joint.
While these non-surgical approaches can provide some relief, FAI does not typically respond to non-
surgical treatment over the long-term. In fact, in some cases, physical therapy can actually cause
worsening of the condition. Hip stretching (e.g., yoga exercises) can also worsen FAI symptoms. It is
also worth keeping in mind that non-surgical approaches will not change the underlying mechanical
problems that contribute to FAI and may lead to further degeneration of the hip and weaken the hip
cartilage. This is why some people who chose the non-surgical route initially may eventually need a hip
replacement later in life.

Some believe that FAI that causes symptoms should be evaluated for surgery because it is the best way
to treat painful FAI (although there is a small chance that it may not work). A surgical treatment option is
particularly important for people with a worse form of the condition. For example, an elderly person with
FAI and advanced osteoarthritis may be better off with a hip replacement. The main goals of surgery are
to change the shape of the bones that cause impingement, which improves hip rotation and improves

There are two main types of surgery for FAI that can be used to prevent the need for a total hip
replacement. This is especially important for younger people diagnosed with FAI. The first surgical
technique is arthroscopic surgery. Arthroscopic surgery is surgery that involves using a flexible viewing
tube (known as an arthroscope) to view a joint, such as the hip joint. The endoscope is inserted through
tiny incisions (2 to 4 cm for FAI surgery; about the size of a button hole) in the skin after a light pain-
numbing medication is used. Other instruments may be inserted through small incisions to treat the
problem. This helps prevent the large scars that occur from a regular surgery after long incisions are
needed to slice the skin open.

Arthroscopes can repair labral tears, cartilage damage, or friction between the femur and hip joint. New
cartilage growth can be stimulated through the procedure. One technique that is used when there is an
exposed area of bone underneath the cartilage is the microfracture technique. This involves creating tiny
fractures in the bone to stimulate the development of new cartilage. An arthroscopic procedure can help
treat loose fragments of cartilage or bone, flaps of cartilage only attached on one side, and damage to
the ligament of the head of the femur. A ligament is a tough band of tissue that attaches to joint bones.

During arthroscopic treatment, the surgeon should be able to see two parts of the hip joint. The first part
is the central component, which is made of the labrum, the surfaces of the femoral head, the hip socket,
and the soft tissues. Arthroscopic procedures performed in this area include treatment or the soft
tissues/cartilage. The second part is the peripheral component, which refers to the rest of the hip joint
and the area along the connection of the head and neck of the femur. The areas in the peripheral
component are inside the joint capsule. A joint capsule is an envelope of tissue surrounding the joint.
Arthroscopic procedures performed in the peripheral area include treatment of bone spurs and the joint
capsule. In all forms of FAI, bone spurs can develop around the femoral head and/or along the hip socket,
causing joint damage and pain. Removal of bone spurs can restore the concave shape of the femoral

Unlike the central and peripheral areas, the lateral compartment (also known as the peritrochanteric
component) is outside the hip joint. The surgeon can enter the lateral component and evaluate and treat
hip muscle and tendon tears, snapping hips, piriformi syndrome (see above), and hip inflammation (also
knows as trochanteric bursitis).

If all that is done in the arthroscopic procedure is labral debridement (cutting away loose or frayed parts
of the labrum) without any repair or removal of bone (known as decompression), the procedure usually
takes less than an hour. If the procedure involves repair of the labrum or cartilage and there is removal of
bone (e.g., shaving down the femoral head or the bony rim of the hip socket), this can take between two
to four hours. Recovery after arthroscopic surgeries is about 3 to 4 months for the person to return to full
unrestricted activity. About 80% of patients undergoing this surgery are cured after 3 to 4 months and up
to 95% have improved symptoms by a year. Most professional athletes undergoing arthroscopic
treatment are able to return to play at a professional level. About 5% of patients have complications
related to this form of surgery.

The second main type of hip surgery is open hip surgery with surgical dislocation (see above) which may
be performed if the hip joint has an abnormal angle. People with more severe cases tend to undergo the
open surgeries. During the procedure, the vulnerable hip blood supply must be protected. The procedures
change the angle of the hip socket in a way that reduces contact between the femoral head and hip
socket. This allows for increased range of movement.

Before the hip is partly or completely dislocated, an evaluation of the hip's range of movement is
performed because it helps decide how to treat the condition. After the hip is dislocated, the labrum of the
hip socket and the articular cartilage next to it are evaluated and abnormalities are tested for partial and
complete tears/separation from the rim of the hip socket. Articular cartilage is the smooth, white tissue
that that covers the ends of bones where they come together to form joints. The extent, severity, and
location of the lesions are identified and their identification with FAI is confirmed by moving (flexing and
internally rotating) the femur with the femoral head relocated. Depending on how much the rim of the hip
socket is covering the head of the femur and how damaged the labrum and articular cartilage of the hip
socket is, this will determine the type of treatment of the rim of the hip socket. When the rim of the hip
socket over-covers the head of the femur (which frequently happens when the hip socket is turned
around), a resection osteoplasty is performed of the front upper hip socket in which prominent parts of
bone in the head and rim of the hip socket are removed.

In a further open procedure known as a periacetabular osteotomy, a series of angular cuts are made on
the pelvis, separating the hip socket from the pelvis, which allows the socket to rotate freely in three
dimensions. The femur can be sculpted in these surgeries, which allows for a better overall fit in the hip
joint. These procedures usually takes a few hours, involve larger incisions than arthroscopic surgeries (6
to 10 inches), are usually used in older patients, patients with significant athletic or activity demands,
and/or those who have significant hip degeneration. Recovery from open surgery usually takes 12
months, with the periacetabular osteotomy version usually taking 18 months. Revision surgery, which is a
repeat surgery, may involve a much longer recovery than the original surgery.

One type of open surgery is referred to as a rotational osteotomy. The procedure involves cutting the
upper thigh bone, dislocating the femoral head from the hip socket, and repositioning the ball of the femur
in the hip socket. This exposes all parts of the joint, allowing treatment of labral tears and abnormal
contact between the femoral head and hip socket. The procedure allows for a broader and less
transmission of pressure on the joint. This can decrease pain and protect the articular damage from
further degeneration. The procedure can also cause a more functional arc of motion.

For patients presenting with FAI in the presence of acetabular retroversion (when the hip socket is turned
back), a deficiency in the back (posterior) wall of the hip socket, or at least lack of posterior
overcoverage, some recommend treatment with a reverse periacetabular osteotomy. This is a type of
periacetabular osteotomy in which the hip socket is moved to cover less of the head of the femur.

Another type of osteotomy is a Bernese (also known as the Ganz) periacetabular osteotomy. This is for
patients with symptoms of hip instability, impingement, or damage/failure of the joint due to excess stress
caused by the hip socket's coverage of the head of the femur being too shallow. The procedure involves
reorienting the joint surface of the hip socket by allowing for large corrections of abnormal bone sections
in all directions, including anterior (front), lateral (side), and medial (middle) rotation of the hip joint. It
involves a series of straight, relatively reproducible cuts outside the joint. The back column of the pelvis
remains intact. As a result, not much internal fixation is needed, which is when implants (e.g., screws,
pins, rods, pins, wires, nails) are needed to repair bone. The surgery also allows the person to begin
walking early after it is performed, even without a brace or external immobilization. External immobilization
is when a body structure is prevented from moving by an external structure keeping it in place.

Osteotomies are offered to young patients who are symptomatic due to abnormal formation of the hip
socket without excessive migration of the center of rotation, who have no more than mild degenerative
changes of the joint surface. The major advantage of an osteotomy (cutting bone to change its alignment)
on the hip socket part of the joint is that it corrects that major structural abnormality that is present there.
An osteotomy on this side of the joint is more advantageous than an osteotomy on the femoral side of the
joint because it does not create a second deformity of the femur. However, in cases where there are
significant structural abnormalities of the femur, both types of osteotomies may be performed.

In general, recovery from surgery depends on the surgeon's recommendation, the type of surgery, and
condition of the hip joint at the time of surgery. The surgeries described above can decrease pain,
improve performance, prevent future hip arthritis, and prevent the need for a hip replacement.

Some people chose to wait and have a total hip replacement because the rehabilitation involved for this
type of surgery is much less than for an FAI surgery. However, the new hip does not last as long in
younger patients and there may be a need for further hip replacements regardless of age. In addition, one
cannot accomplish as much with an artificial hip compared to a real hip.

Hip resurfacing is another surgical option, in which a metal cap is placed over the head of a femur while a
matching metal cup is placed in the socket. This procedure replaces the joint surface and removes very
little bone compared to a total hip replacement. However, both techniques involve removing the diseased
joint surfaces and replacing it with man-made material (i.e., metal, ceramic, plastic). The man-made
materials are subject to wear, which can result in debris in the joint that may shorten the life of the
replacement. Thus, there may be a need for additional surgeries in the future.

Using metal-on-metal hip bearings is controversial in patients with metal sensitivities and women of child
bearing age. This is because the metal on metal contact can release metal substances that can cross the
placenta. The placenta is an organ in the uterus (a hollow organ in which a baby develops) that links the
blood supply of the mother to the developing baby and by which the baby can release wastes. It is
suggested that women avoid getting pregnant for a year after this type of surgery because this is the
greatest period of time that metal substances are released.


Complications following surgery for FAI are uncommon but include infection, which is the main risk factors
of all surgeries. More specific to FAI surgery, the bones of the femoral head and hip socket may not fuse
together properly in the open form of surgery. The hip may be unstable or dislocated after surgery. The
neck of the femur may develop a fracture. Another risk is a blood clot (also known as a deep vein
thrombosis or DVT). Avascular necrosis is another risk factor, which is dead bone caused by lack of
blood flow. Another problem can be heterotopic ossification, which is an abnormal formation of bone in
soft tissue. Scarring and adhesions can be another problem.

There is risk that the surgeon damages the blood supply to the head of the femur (through the retinacular
vessels) when repairing or altering the bone through an arthroscopic procedure. These blood vessels are
generally more protected if the surgeon does an open surgical procedure, although that procedure is a
more drastic one as described above.

Pain can be referred to the hip from problems in the lumbar (lower) spine. Nerves can also be damaged
such as the sciatic nerve, peroneal nerve, pudendal nerve, lateral femoral cutaneous nerve (LFCN),
ilioinguinal nerve and the obdurator nerve. The sciatic nerve was described earlier. The peroneal nerve is
a branch of the sciatic nerve, which supplies movement and sensation to the lower leg, foot, and toes.
The pudendal nerve is a nerve in the pelvis that provides signals to the genitals and the bladder and
rectum sphincters. A sphincter is a muscle that forms a circle around a tube, natural opening, or duct in
the body. The LFCN nerve is a nerve of the thigh that sends signals to the skin on the side part of the
thigh. The ilioinguinal nerve is the first branch of the lumbar nerve. The obdurator nerve is responsible for
allowing sensory information to reach the middle of the thigh.


A course of rehabilitation must take place after surgery for FAI. This takes the form of physical therapy
exercises under the care of a physical therapist on an outpatient basis but exercises will also be
prescribed for home. Recovery after hip arthroscopy usually takes about three to four months. Recovery
after open hip surgery is usually a year, although the periacetabular osteotomy has about an 18 month
recovery time frame.


There are many conditions that can have symptoms similar to FAI, which need to be ruled out before FAI
is diagnosed. In general, any chronic pain syndrome can masquerade as FAI. A specific example of a
condition that can seem like FAI is hip dysplasia, which is when the hip joint is misaligned or deformed. In
hip dysplasia, the hip socket coverage of the femoral head is not sufficient (too shallow). This condition
causes concentrated force within the hip joint compared to other conditions in which the hip socket
sufficiently covers the femoral head. Hip dysplasia is associated with tears of labral and articular
cartilage. Labral cartilage is the soft tissue bumper of the socket. Articular cartilage is the smooth tissue
that covers the ends of bones where they come together to form joints. Hip dysplasia and FAI can
sometimes co-occur. If a labral tear was treated and pain still exists, the person may have unrecognized
FAI causing additional hip cartilage degeneration or tearing.

Another condition that can mimic FAI is sacroiliitis, which is inflammation of the sacroiliac joints that
connect the lower spine and pelvis. This condition causes pain in the back of the pelvis. Another
condition that can mimic FAI is trochanteric bursitis, which is painful inflammation of the bursa (fluid-filled
sac or sac-like cavity) located just superficial to the greater trochanter of the femur. The trochanter is any
of two bony protruberances by which muscles are attached to the upper part of the femur. Trochanteric
bursitis causes pain in the lateral/outer part if the hip.

Another condition that can mimic FAI is piriformis syndrome (also known as deep gluteal syndrome)
because it causes pain in the back of the hip. Piriformis syndrome is when the piriformis muscle
compresses the sciatic nerve, causing pain (e.g., in the back of the hip) and numbness and tingling in the
buttocks, lower thigh, and leg. The piriformis muscle is one of the small muscles deep in the buttocks that
rotates the leg outwards. The sciatic nerve is a long nerve that extends through the muscle of the thigh,
leg, and foot.

Since low back pain occurs in FAI, low back for other reasons (e.g., slipped disk, pinched nerve, facet
disease) can seem like low back pain from FAI. Facet disease is when the facet joints degenerate. Facet
joints connect to veretebrae and allow them to move. Vertebrae are bones that form an opening in which
the spinal cord passes.

Apophysitis of the hip can mimic FAI. This condition is irritation and inflammation of the apophysis, which
is a growth plate in the hip that provide a point for muscles to attach to. There are several such growth
plates in the hip and pelvis. This condition causes pain in the front of the pelvis. Growth plate injuries can
mimic FAI. Growth plates are areas of developing cartilage tissue in children near the ends of long bones.

A groin strain can mimic the groin pain that can occur in FAI. Technically, a groin strain is a tear or
rupture to any one of the adductor muscles (also known as groin muscles). Cysts of the ovary can also
mimic groin pain from FAI because ovarian cyst pain often feels like it is coming from the join.

Another condition that can mimic FAI is snapping hip syndrome (also known as coxa saltans, iliopsoas
tendinitis, or dancer's hip), in which a snapping sensation occurs when the hip is flexed or extended. It
may be accompanied by hip pain. Inflammation of the hip flexor muscle can occur.

An abdominal muscle strain such as through a hernia caused by sports can mimic FAI. Hernia is when a
part of a structure sticks out through the tissues that normally contain it. A strain of the quadriceps (front
thigh muscles) can also mimic FAI. Hamstring tendonitis can mimic FAI because it causes pain felt on and
just below the boney part of the buttocks. It is caused by inflammation, irritation, and swelling of the
hamstring tendon. The hamstring muscle runs down the back of the upper thigh and is connected to the
knee by a large tendon (groups of fibers that attach muscle to bone).

Essentially, any bruise, strain, or sprain around the hip can mimic FAI as can inflammation of muscles,
tendons, ligaments, or bursa near the hip. A ligament is a tough band of tissue that attaches to joint
bones. Injuries to the bone, such as fractures can mimic FAI. Joint dislocations and stress injuries to hip
areas can mimic FAI. If there are any loose bodies in the hip joint, this can mimic FAI.

Endometriosis can cause pain that can mimic FAI. Endometriosis is a condition in which the tissue that
normally lines the inside of the uterus is found outside the uterus. Infections and inflammatory conditions
can mimic FAI. Even pain from psychological stress (known as a psychosomatic pain disorder) can
present similarly to FAI.


FAI is usually not disabling, unless the afflicted person is a professional athlete.


FAI is also known as hip impingement.


Femoroacetabular impingement comes from the Latin word "femur" meaning "thigh," the Latin word
"acetabulum" meaning "a shallow vinegar cup" and the Latin word "impingere" meaning "strike against. "
Put the words together and you get "strike against (the) femur (and) a shallow vinegar cup. "