Cam Injury: Understanding Femoroacetabular Impingement, Symptoms, and Treatment

What is a cam injury?

A cam injury refers to a specific type of structural abnormality in the hip joint, characterized by an excess bone growth on the femoral head and neck, leading to impingement and potential damage to the articular cartilage and labrum.

Understanding Femoroacetabular Impingement (FAI)

A "cam injury" is not a standalone injury in the traditional sense, but rather a morphological variation of the hip joint that predisposes individuals to femoroacetabular impingement (FAI). FAI is a condition where the bones of the hip joint abnormally contact each other during movement, leading to pain and progressive damage. The hip is a ball-and-socket joint, with the femoral head (the "ball") fitting into the acetabulum (the "socket") of the pelvis. In FAI, either the ball, the socket, or both, are shaped abnormally, causing them to "impinge" or bump into each other.

There are three primary types of FAI:

• Cam Impingement: Occurs when there is an extra bone growth or an abnormally shaped femoral head and neck junction, making the femoral head less spherical.
• Pincer Impingement: Occurs when the acetabulum (socket) has too much coverage of the femoral head, often due to extra bone growth on the rim of the socket.
• Mixed Impingement: A combination of both cam and pincer types, which is the most common presentation.

The Mechanism of Cam Impingement

In a healthy hip joint, the femoral head glides smoothly within the acetabulum through its full range of motion. With a cam deformity, the non-spherical shape of the femoral head and neck junction causes it to abnormally butt against the rim of the acetabulum, particularly during hip flexion, adduction, and internal rotation.

Imagine a perfectly round ball rotating smoothly within a cup. Now, imagine a slightly egg-shaped or "bumpy" ball. As this misshapen ball rotates, the bump will inevitably collide with the rim of the cup. This repeated collision, or "impingement," causes:

• Compression of the articular cartilage: The smooth, protective cartilage lining the femoral head and acetabulum can be crushed and worn away.
• Labral tears: The labrum, a ring of cartilage that deepens the acetabulum and helps stabilize the joint, can be pinched and torn.
• Subchondral bone edema: Swelling within the bone directly beneath the cartilage due to repetitive stress.
• Cyst formation: Small fluid-filled sacs can develop in the bone.

Over time, this chronic impingement and subsequent damage can lead to premature osteoarthritis of the hip joint.

Signs and Symptoms

The symptoms of cam impingement typically develop gradually and can be exacerbated by physical activity. Common signs include:

• Groin pain: This is the most prevalent symptom, often described as a deep ache.
• Pain in the outer hip or buttock: Less common but can occur.
• Pain aggravated by specific movements: Activities involving deep hip flexion, such as squatting, sitting for long periods, driving, or getting in and out of a car. Pivoting or cutting motions in sports can also trigger pain.
• Stiffness or limited range of motion: Particularly noticeable in hip flexion and internal rotation.
• Clicking, locking, or catching sensation: May indicate a labral tear or loose bodies within the joint.
• Difficulty with activities of daily living: Such as tying shoes or putting on socks.

Causes and Risk Factors

The exact cause of cam deformity is not fully understood, but it is believed to be a developmental anomaly that occurs during childhood or adolescence, particularly during periods of rapid bone growth.

Key risk factors and contributing factors include:

• Genetic predisposition: There may be a genetic component influencing hip morphology.
• High-impact sports during adolescence: Repetitive stress on the developing hip joint, especially in sports requiring deep hip flexion and rotation (e.g., hockey, soccer, basketball, martial arts, dance), is thought to influence the development of the cam deformity. It's important to note that the deformity itself is not an injury from trauma, but rather an adaptation or growth anomaly that can be exacerbated by certain activities.
• Gender: Cam deformities are more commonly diagnosed in young athletic males.

Diagnosis

Diagnosing cam impingement involves a thorough clinical evaluation and imaging studies.

• Medical History and Physical Examination: The physician will inquire about symptoms, activity levels, and perform specific physical tests. The FADIR (Flexion, Adduction, Internal Rotation) test is a common diagnostic maneuver where the hip is flexed, adducted, and internally rotated, which typically reproduces the impingement pain.
• X-rays: Standard hip X-rays are crucial for identifying the bony morphology of the femoral head and acetabulum, including the presence of a cam deformity (often seen as a "pistol grip" deformity or reduced head-neck offset).
• Magnetic Resonance Imaging (MRI): An MRI provides detailed images of soft tissues, allowing for assessment of the articular cartilage, labrum (especially with an MR arthrogram, where dye is injected into the joint), and presence of bone marrow edema.
• Computed Tomography (CT) Scan: A CT scan offers excellent bony detail and can be used for more precise 3D mapping of the deformity, which is particularly useful for surgical planning.

Treatment Options

Treatment for cam impingement aims to reduce pain, improve function, and prevent further joint damage. Options range from conservative management to surgical intervention.

Conservative Management

Initial treatment is typically non-surgical, focusing on symptom management and activity modification.

• Activity Modification: Avoiding movements and activities that provoke pain (e.g., deep squats, prolonged sitting, certain sports).
• Physical Therapy: A structured rehabilitation program can help. This includes:
  • Strengthening exercises for core, hip abductors, and rotators to improve hip stability.
  • Stretching and mobility work to improve range of motion, but avoiding impingement positions.
  • Neuromuscular re-education to optimize movement patterns.
• Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): To reduce pain and inflammation.
• Corticosteroid Injections: Injections into the hip joint can provide temporary pain relief, often used diagnostically to confirm the hip as the source of pain.

Surgical Intervention

If conservative measures fail to provide sufficient relief, or if there is significant structural damage (e.g., large labral tear, extensive cartilage damage), hip arthroscopy is often recommended.

• Arthroscopy: A minimally invasive surgical procedure where small incisions are made, and a camera and instruments are inserted into the joint.
  • Cam Osteoplasty (Femoral Osteochondroplasty): The excess bone on the femoral head and neck is carefully reshaped and removed to restore a more spherical contour and create proper clearance, preventing impingement.
  • Labral Repair or Debridement: If the labrum is torn, it can often be repaired (sutured back to the bone) or, less commonly, debrided (trimmed) if extensively damaged.
  • Chondroplasty: Addressing damaged articular cartilage.

Post-Surgical Rehabilitation

Following surgery, a comprehensive rehabilitation program is essential for restoring strength, range of motion, and function. This typically involves:

• Initial protected weight-bearing: Using crutches for a few weeks.
• Gradual increase in range of motion and strengthening exercises.
• Return to activity/sport-specific training.

Prevention and Management for Athletes

While the cam deformity itself develops during growth, managing its impact on athletes involves:

• Proper Movement Mechanics: Emphasizing correct form in strength training (e.g., squatting, lunging) to avoid excessive hip impingement.
• Hip Mobility and Stability: Incorporating exercises that promote a healthy balance of hip mobility and dynamic stability.
• Progressive Loading: Gradually increasing training intensity and volume to allow the hip joint to adapt.
• Early Recognition: Athletes experiencing persistent groin or hip pain should seek early medical evaluation to identify and manage FAI before extensive damage occurs.
• Cross-Training: Varying activities to reduce repetitive stress on the hip joint.

Long-Term Outlook

The long-term prognosis for individuals with cam impingement varies. If left untreated, the repetitive impingement can lead to progressive cartilage damage, labral tears, and ultimately, early-onset hip osteoarthritis. Surgical correction of the deformity, especially when performed before significant cartilage damage occurs, can often alleviate pain, improve function, and potentially slow the progression of degenerative changes. Adherence to post-operative rehabilitation and activity modification is crucial for achieving the best possible long-term outcomes.