Femoroacetabular impingement

Editor-In-Chief: Prab R Tumpati, MD
Obesity, Sleep & Internal medicine
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Femoroacetabular impingement
Synonyms	FAI
Pronounce	N/A
Specialty	Orthopedic surgery
Symptoms	Hip pain, stiffness, limitation of movement
Complications	Osteoarthritis
Onset	Typically young adults
Duration	Chronic
Types	N/A
Causes	Abnormal contact between the femur and acetabulum
Risks	Athletic activities, genetic predisposition
Diagnosis	Physical examination, X-ray, MRI
Differential diagnosis	Hip dysplasia, labral tear, osteoarthritis
Prevention	Avoidance of activities that exacerbate symptoms
Treatment	Physical therapy, arthroscopic surgery
Medication	NSAIDs
Prognosis	Variable, depending on severity and treatment
Frequency	Common in athletes
Deaths	N/A

Femoroacetabular impingement (FAI) is a condition involving abnormal contact between the femur and the acetabulum of the hip joint, which can lead to joint damage and pain. This condition is often seen in young and active individuals and can be a precursor to osteoarthritis of the hip.

Types of Impingement

FAI is generally classified into three types:

Cam Impingement

X-ray showing cam impingement

Cam impingement occurs when the femoral head is not perfectly round and cannot rotate smoothly inside the acetabulum. This results in abnormal contact and damage to the cartilage and labrum.

Pincer Impingement

X-ray showing pincer impingement

Pincer impingement is characterized by excessive coverage of the femoral head by the acetabulum. This can lead to the labrum being pinched between the acetabulum and the femoral head.

Combined Impingement

In many cases, individuals may have a combination of both cam and pincer impingement, leading to a more complex clinical presentation.

Diagnosis

Diagnosis of FAI typically involves a combination of clinical examination and imaging studies.

Clinical Examination

Patients often present with hip or groin pain, especially during activities that involve hip flexion. A thorough physical examination can reveal limited range of motion and pain during specific movements.

Imaging Studies

X-rays

X-rays are commonly used to assess the bony structures of the hip and identify signs of FAI.

Center-Edge Angle

Diagram showing the center-edge angle of Wiberg

The center-edge angle of Wiberg is used to assess the coverage of the femoral head by the acetabulum.

Crossing Sign

Diagram showing the crossing sign of the hip

The crossing sign is an indicator of acetabular retroversion, which can be associated with pincer impingement.

Alpha Angle

Diagram showing the alpha angle in a 45-degree Dunn view

The alpha angle is used to quantify the asphericity of the femoral head-neck junction, which is indicative of cam impingement.

Hip Offset Percentage

Diagram showing hip offset percentage

The hip offset percentage is a measure used to evaluate the lateralization of the femoral head.

Tönnis Angle

Diagram showing the Tönnis angle of the hip

The Tönnis angle is used to assess the inclination of the acetabulum.

Treatment

Treatment for FAI can be conservative or surgical, depending on the severity of the condition and the patient's symptoms.

Conservative Management

Conservative treatment includes activity modification, physical therapy, and non-steroidal anti-inflammatory drugs (NSAIDs) to manage pain and improve hip function.

Surgical Intervention

Surgical options, such as hip arthroscopy, aim to correct the bony abnormalities and repair any damage to the labrum or cartilage.

See also

• Hip joint
• Osteoarthritis
• Hip arthroscopy