Bulletin of the NYU Hospital for Joint Diseases 2010;68(2):70-570
Kaplan KM, Shah MR, Youm T. Femoroacetabular impingement: diagnosis and treatment. Bull NYU Hosp Jt Dis. 2010;68(2):70-5.
Abstract
Femoroacetabular impingement results from an abnormal
contact between the femur and the pelvis. This abnormal
contact leads to developmental changes in the femoral
neck, labrum, and acetabulum. Secondary to the altered hip
joint mechanics, chondral damage occurs and initiates the
degenerative process, eventually leading to osteoarthritis.
Numerous etiologies have been implicated in femoroac-
etabular impingement, and a variety of treatment algorithms
have been established, with no definitive gold standard.
However, the treatment of this disorder with joint preserving
techniques offers a viable option between the extremes of
nonoperative treatment and total joint arthroplasty.
In 1974, Stulberg1 noted the association between subtle anatomic abnormalities of the hip and the development of osteoarthritis (OA). This report was one of the earliest
descriptions of what is now referred to as femoroacetabular
impingement (FAI). Stulberg described decreased head-neck
offset and found that the subset of patients with this find-
ing developed early OA. Harris2 reviewed 75 patients with
idiopathic OA in 1986 and showed that 80% had a subtle
femoral or acetabular abnormality. It was not until more
recently, after 2000, that the majority of literature regard-
ing FAI was published. Although the association between
anatomic abnormalities and OA is not a novel concept,
previous studies did not attempt to delineate the mechanism
and implications of the morphologies.
Ganz and colleagues3 summarized the mechanism of FAI,
in which morphologic abnormalities of the acetabulum and
proximal femur lead to anterosuperior soft tissue damage and
continued bony contact. At terminal ranges of hip motion,
abnormal contact can occur between the femoral neck and
acetabular rim, creating developmental lesions in the labrum
and adjacent acetabular cartilage. With continued loading,
these lesions will progress and lead to the development of
a degenerative joint.
Etiology
FAI is considered an abnormal contact between the femur
and acetabulum, with numerous potential etiologies that
include but are not limited to prior femoral neck fracture,
prior periacetabular or femoral osteotomy, acetabular ret-
roversion, and slipped capital femoral epiphysis. However,
many patients do not have a clear history predisposing them
to the development of FAI.
Classification
The most common classification system is based on a re-
view of 600 surgical dislocations performed by Ganz and
coworkers.4 They classified FAI as either cam or pincer type
(Fig. 1). Cam impingement is typical in young, active male
patients (Fig. 1B). Radiographically, these patients will have
a prominence on the femoral neck, which, when forced into
the acetabulum, will result in a tearing or avulsion of the
labrum; the damage then progresses with continued load-
ing of the joint, notably in the anterosuperior cartilage, as
previously stated.
Femoroacetabular Impingement
Diagnosis and Treatment
Kevin M. Kaplan, M.D., Mehul R. Shah, M.D., and Thomas Youm, M.D.
Kevin M. Kaplan, M.D., was an Administrative Chief Resident, De-
partment of Orthopaedic Surgery, NYU Hospital for Joint Diseases
and currently is Orthopaedic Surgeon, Jacksonville Orthopaedic
Institute, Jacksonville, Florida. Mehul Shah, M.D., is Assistant
Professor, NYU School of Medicine, Hospital for Joint Diseases
and within the Division of Sports Medicine, Department of Ortho-
paedic Surgery, NYU Hospital for Joint Diseases. Thomas Youm,
M.D., is Clinical Assistant Professor of Orthopaedic Surgery, New
York University School of Medicine, and within the Division of
Adult Reconstructive Surgery, Department of Orthopaedic Surgery,
NYU Hospital for Joint Diseases, NYU Langone Medical Center,
New York, New York.
Correspondence: Thomas Youm, M.D., 1056 5th Avenue, New
York, New York 10028; thomas.youm@med.nyu.edu.

71Bulletin of the NYU Hospital for Joint Diseases 2010;68(2):70-5
Pincer impingement presents more commonly in middle-
aged athletic females (Fig. 1C). The femoral head may be
normal; however, acetabular over-coverage is the mechanism
responsible for the abnormal contact. This over-coverage
may be a result of conditions such as coxa profunda or
abnormal acetabular version.
With pincer impingement, failure occurs first in a limited
area of the labrum that appears benign. With continued
abutment of the femoral neck against the rim, patients will
exhibit degenerative changes in the labrum. As a result,
the acetabulum may deepen, causing worsening of the
over-coverage. Thus, chondral injury will ensue, leading to
acetabular degeneration.
The common final pathway for both types of impinge-
ment involves a morphologic abnormality that leads to
abnormal contact. As a result of abnormal contact, the
labrum and cartilage become damaged. McCarthy and
associates5 reviewed 463 hip arthroscopies in patients
with reproducible mechanical symptoms and no evidence
of OA on radiographs. The prevalence of labral tears was
55%. Additionally, 94% of the patients had chondral
damage in continuity with the labral pathology. They
concluded that in young, healthy patients strenuous ac-
tivity may lead to recurrent microtrauma and eventual
attrition of the labrum, with associated chondral injury.
This, in turn, leads to abnormal contact and deterioration,
which predisposes these patients to end stage OA.
History
FAI typically presents in active young or middle-aged
patients.6 These patients typically begin to have symptoms
insidiously or after minor trauma. Pain is localized to the
groin and is often unilateral. They may complain of inter-
mittent pain that worsens with activity or prolonged sitting
and, occasionally, the symptoms are bilateral. Patients may
describe mechanical symptoms, such as locking, catching,
and giving way. These findings are pathognomonic for labral
pathology. Burnett and colleagues7 reviewed 66 patients
with pain from FAI; 91% of their cohort had activity-related
pain, and 47% had night pain. Jager and coworkers8 reported
a mean delay of greater than 5 years between the onset of
symptoms and a definitive diagnosis of labral tears, while
Burnett and associates7 reported a mean delay of 21 months,
with an average of greater than three doctor visits prior to
diagnosis.
Radiographs in young to middle-aged patients with hip
pain are consistently nondiagnostic. These patients may
be subject to unnecessary general surgery procedures, as
well as an extensive orthopaedic work-up, in an attempt to
determine the location of the pathology.
Physical Examination
Examination of patients with FAI will demonstrate a nor-
mal neurovascular examination, with no deficit in motor
strength.9 Range of motion will be limited in internal rota-
tion and adduction, which is unlike the globally restricted
motion found in advanced cases of OA.
Several tests can be performed to identify FAI in patients
with hip pain. The anterior impingement test (Fig. 2) is
performed with the patient in the supine position. The hip
is internally rotated as it is passively flexed to 90°. Flexion
and adduction results in contact between the femoral neck
and labrum, which leads to the aforementioned degenerative
cycle of chondral damage.
Figure 1 Anterior femoroacetabular
impingement. A, Normal hip. B, Cam
impingement. C, Pincer impingement.
D, Mixed. (Reproduced from: Lavigne
M, Parvizi J, Beck M, et al. Anterior
femoroacetabular impingement: part I.
Techniques of joint preserving surgery.
Clin Orthop Relat Res. 2004;418:61-6.
Copyright © 2004 The Association of
Bone and Joint Surgeons. With permis-
sion.)
D
C
B
A