Femoroacetabular Impingement (FAI): Types, Causes, Symptoms, Diagnosis, and Treatment

What is FAI medical?

Femoroacetabular Impingement (FAI) is a medical condition characterized by abnormal contact and friction between the femoral head/neck and the acetabular rim of the hip joint, leading to pain, restricted movement, and potential damage to the articular cartilage and labrum.

Understanding Femoroacetabular Impingement (FAI)

Femoroacetabular Impingement (FAI) is a structural abnormality of the hip joint where the bones of the hip are shaped in a way that causes them to rub or "impinge" on each other during movement. This abnormal contact can lead to progressive damage to the soft tissues within the hip joint, including the labrum (a ring of cartilage that deepens the hip socket) and the articular cartilage (the smooth surface covering the ends of the bones). Over time, this chronic friction can result in pain, stiffness, and potentially contribute to the early onset of osteoarthritis in the hip.

Anatomy of the Hip Joint

To understand FAI, it's essential to recall the basic anatomy of the hip. The hip is a ball-and-socket joint, designed for a wide range of motion and stability.

• Femoral Head: The "ball" at the top of the thigh bone (femur).
• Acetabulum: The "socket" in the pelvis that cradles the femoral head.
• Articular Cartilage: A smooth, slippery tissue covering the surfaces of the femoral head and acetabulum, allowing for frictionless movement.
• Labrum: A ring of fibrocartilage that surrounds the rim of the acetabulum, deepening the socket and providing stability and shock absorption.

In FAI, the abnormal bone shapes lead to an incongruent fit between the ball and socket, causing impingement during certain hip movements, particularly flexion and internal rotation.

Types of FAI

FAI is typically classified into three main types based on the location of the abnormal bone growth:

• Cam Impingement: This type involves an abnormal shape of the femoral head and/or neck. Instead of being perfectly spherical, the femoral head might have an extra bony bump or "pistol grip" deformity. This non-spherical shape causes the femoral head to grind against the acetabular rim, particularly when the hip is flexed and internally rotated. This can shear the articular cartilage away from the bone.
• Pincer Impingement: This type is characterized by excessive bone growth on the rim of the acetabulum, making the socket too deep or covering too much of the femoral head. This overgrowth leads to the labrum being pinched between the femoral head and the prominent acetabular rim, often resulting in labral tears. Pincer impingement is more common in women.
• Mixed Impingement: The most common form of FAI, mixed impingement involves a combination of both cam and pincer deformities. This means there are bony abnormalities on both the femoral head/neck and the acetabular rim, leading to combined mechanisms of impingement.

Causes and Risk Factors

The exact cause of FAI is not always clear, but it's believed to be multifactorial:

• Developmental Factors: Many cases of FAI are thought to arise during skeletal development in childhood or adolescence, particularly during periods of rapid growth. The abnormal bone shapes may develop as a response to repetitive microtrauma or genetic predispositions.
• Genetics: There may be a genetic component, as FAI can sometimes run in families.
• Activity Level: While FAI is a structural issue, high-impact activities and sports involving repetitive hip flexion, internal rotation, and pivoting (e.g., hockey, soccer, martial arts, dance) can exacerbate symptoms and potentially contribute to the development of the bony deformities over time due to adaptive bone growth.
• Trauma: Less commonly, a traumatic injury to the hip could contribute to the development of FAI, though this is not the primary cause for most individuals.

Signs and Symptoms

The symptoms of FAI typically develop gradually and worsen with activity. Common signs and symptoms include:

• Groin Pain: This is the most common symptom, often described as a deep, aching pain in the front of the hip or groin area. Pain can also radiate to the side of the hip, buttock, or even down the thigh.
• "C" Sign: Patients often describe their pain by cupping their hand around the side of their hip in a "C" shape.
• Pain with Specific Movements: Symptoms are frequently aggravated by activities that involve deep hip flexion, such as sitting for long periods, getting in and out of a car, squatting, lunging, or performing certain athletic maneuvers.
• Stiffness: A feeling of stiffness or limited range of motion in the hip joint.
• Clicking, Catching, or Locking: Mechanical symptoms within the hip joint, indicative of labral tears or cartilage damage.
• Reduced Range of Motion: Especially noticeable in hip flexion and internal rotation.

Diagnosis of FAI

Diagnosing FAI involves a comprehensive approach, combining a detailed medical history, physical examination, and imaging studies.

• Medical History: The physician will inquire about the nature, location, and aggravating factors of the hip pain, as well as the patient's activity level and past medical history.
• Physical Examination: This involves assessing the hip's range of motion, strength, and performing specific provocative tests. The FADIR (Flexion, Adduction, Internal Rotation) test is a common maneuver that often reproduces the patient's pain, indicating impingement.
• Imaging Studies:
  • X-rays: Initial imaging to identify the characteristic bony deformities (cam or pincer lesions) and assess the overall joint space. Specific views are often required.
  • Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues, allowing for assessment of the labrum, articular cartilage, and any bone marrow edema or cysts. An MR arthrogram (MRI with contrast injected into the joint) can further enhance the visualization of labral tears and cartilage damage.
  • Computed Tomography (CT) Scan: May be used to provide a more precise 3D assessment of the bony morphology and quantify the extent of the deformities, especially for surgical planning.

Treatment and Management

Treatment for FAI aims to alleviate pain, improve hip function, and prevent further joint damage. The approach depends on the severity of symptoms, the extent of joint damage, and the patient's activity level.

• Conservative Management:

  • Activity Modification: Avoiding positions and activities that provoke pain (e.g., deep squats, prolonged sitting).
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): To reduce pain and inflammation.
  • Physical Therapy: A cornerstone of conservative management. A skilled physical therapist will focus on:
    • Hip and Core Strengthening: Strengthening the muscles around the hip and core to improve stability and control.
    • Movement Pattern Retraining: Educating the patient on proper body mechanics and movement strategies to avoid impingement positions.
    • Flexibility and Mobility: Addressing any muscle imbalances, but carefully avoiding aggressive stretching into impingement.
  • Injections: Corticosteroid injections into the hip joint can provide temporary pain relief and help confirm the hip as the source of pain.

• Surgical Intervention (Hip Arthroscopy):

  • If conservative measures fail to provide adequate relief, or if there is significant structural damage, surgical correction via hip arthroscopy may be recommended. This minimally invasive procedure involves:
    • Femoral Osteoplasty: Reshaping the femoral head and neck to remove the cam deformity.
    • Acetabular Rim Trimming: Removing the excess bone from the acetabular rim to correct the pincer deformity.
    • Labral Repair or Debridement: Repairing or removing damaged portions of the labrum.
    • Chondroplasty: Addressing any damaged articular cartilage.
  • The goal of surgery is to restore normal hip mechanics, eliminate impingement, and preserve the joint.

The Role of Rehabilitation and Exercise

Whether managed conservatively or surgically, rehabilitation and targeted exercise are critical components of FAI recovery and long-term joint health.

• Pre-Operative (if applicable): Strengthening and improving hip mobility can help optimize outcomes if surgery is pursued.
• Post-Operative: A structured rehabilitation program is essential after surgery. This typically progresses through phases:
  • Early Phase: Protecting the repaired tissues, managing pain and swelling, and gentle range of motion exercises.
  • Intermediate Phase: Gradual increase in strength, balance, and neuromuscular control exercises.
  • Advanced Phase: Sport-specific drills, agility training, and return to activity.
• Conservative Management: Physical therapy focuses on improving hip stability, strengthening the gluteal muscles and core, and educating patients on avoiding pain-provoking movements. The emphasis is on optimizing biomechanics to reduce stress on the hip joint.

Prognosis and Long-Term Outlook

The prognosis for individuals with FAI is generally good, especially with timely and appropriate management. If left untreated, the chronic impingement can lead to progressive degeneration of the articular cartilage and labrum, potentially accelerating the development of hip osteoarthritis. Early diagnosis and intervention, whether conservative or surgical, are key to preserving hip function and improving long-term outcomes. Many individuals, particularly athletes, are able to return to their previous activity levels after successful treatment and rehabilitation.

Conclusion

Femoroacetabular Impingement (FAI) is a complex hip condition resulting from abnormal bone shapes that cause friction within the joint. Understanding its types, causes, symptoms, and the various treatment options is crucial for effective management. By addressing the underlying mechanical issues through activity modification, physical therapy, or surgical intervention, individuals with FAI can often achieve significant pain relief, improved hip function, and a better quality of life, minimizing the risk of future joint degeneration.