Cam Bump in the Hip: Understanding Causes, Symptoms, Diagnosis, and Treatment

What is a cam bump in the hip?

A cam bump is an abnormal bony prominence that forms on the femoral head-neck junction of the thigh bone (femur), leading to an irregular, non-spherical shape. This anatomical variation can cause the femur to abnormally contact the rim of the hip socket (acetabulum), often resulting in a condition known as femoroacetabular impingement (FAI).

Understanding Hip Anatomy: The Ball-and-Socket Joint

The hip is a crucial ball-and-socket joint, designed for a wide range of motion and weight-bearing. It consists of two main components:

• Femoral Head: The "ball" at the top of the thigh bone (femur), which is normally spherical.
• Acetabulum: The "socket" in the pelvis, which cups the femoral head.

Both surfaces are covered with smooth articular cartilage, allowing for frictionless movement, and the acetabulum is further deepened by a ring of fibrocartilage called the labrum, which enhances stability and provides a suction seal.

What Exactly is a Cam Bump?

A cam bump, or cam deformity, refers to an area of excess bone that develops on the anterior-superior (front-top) aspect of the femoral head, specifically at the junction where the femoral head transitions into the femoral neck. Instead of a perfectly smooth, spherical contour, the femoral head becomes more "pistol-grip" shaped, with a flattened or convex prominence.

This bony overgrowth disrupts the normal spherical shape of the femoral head, making it less congruent with the acetabular socket. It's often subtle but can have significant biomechanical consequences.

How a Cam Bump Leads to Femoroacetabular Impingement (FAI)

The primary clinical significance of a cam bump is its role in cam-type femoroacetabular impingement (FAI). FAI is a condition where extra bone grows along one or both of the bones that form the hip joint – the femoral head (ball) or the acetabulum (socket) – causing them to abnormally rub against each other during hip movement.

In cam-type FAI, the cam bump on the femoral head-neck junction collides with the rim of the acetabulum, particularly during movements that involve hip flexion, internal rotation, and adduction (e.g., squatting, sitting deeply, pivoting). This repeated impingement can lead to:

• Cartilage Damage: The abnormal contact can shear and delaminate the articular cartilage lining the acetabulum, especially at the anterosuperior aspect.
• Labral Tears: The labrum, caught between the cam bump and the acetabular rim, can be pinched, frayed, or torn.
• Cyst Formation: Bone cysts can develop at the site of impact.

Over time, this chronic wear and tear can progress to early-onset hip osteoarthritis.

Common Causes and Risk Factors

The exact cause of cam bump formation is not fully understood, but several factors are believed to contribute:

• Developmental Factors: Many cam deformities are thought to develop during adolescence, particularly during periods of rapid skeletal growth. The bone may remodel in response to mechanical stresses.
• Sports Participation: High-impact and repetitive hip flexion activities, common in sports like hockey, soccer, basketball, football, and martial arts, are strongly associated with the development of cam deformities. The theory is that repetitive loading during growth can stimulate bone growth at the femoral head-neck junction.
• Genetics: There may be a genetic predisposition in some individuals.
• Sex: Cam deformities are more common in males.

Signs, Symptoms, and Diagnosis

Individuals with a cam bump, especially when it leads to FAI, typically experience:

• Groin Pain: This is the most common symptom, often described as a deep, aching pain in the front of the hip or groin. It can sometimes radiate to the side of the hip or the buttock.
• "C-Sign": Patients often describe their pain by cupping their hand around the greater trochanter (bony prominence on the side of the hip) and pointing to the groin, forming a "C" shape.
• Stiffness: A feeling of stiffness or limited range of motion in the hip.
• Clicking, Catching, or Locking: Sensations within the hip joint, particularly with certain movements.
• Pain with Specific Activities: Worsened by prolonged sitting, squatting, climbing stairs, or sports activities involving deep hip flexion and rotation.

Diagnosis involves a multi-faceted approach:

• Clinical Examination: A physical therapist or physician will assess hip range of motion, muscle strength, and perform specific impingement tests (e.g., FADIR test – Flexion, Adduction, Internal Rotation) that reproduce the patient's pain.
• Imaging:
  • X-rays: Used to evaluate the bone structure, identify the cam bump (loss of sphericity of the femoral head), and assess for signs of osteoarthritis. Specific measurements like the alpha angle help quantify the deformity.
  • MRI (Magnetic Resonance Imaging): Provides detailed images of soft tissues, including the labrum and articular cartilage, to assess for tears or damage.
  • CT Scan (Computed Tomography): Offers a 3D view of the bone structure, which can be particularly useful for surgical planning.

Conservative Management and Treatment Options

Initial treatment for symptomatic cam bumps and FAI often focuses on conservative management:

• Activity Modification: Avoiding positions and activities that provoke pain (e.g., deep squats, prolonged sitting, specific sports movements).
• Anti-inflammatory Medications: Non-steroidal anti-inflammatory drugs (NSAIDs) can help manage pain and inflammation.
• Physical Therapy: A structured program focusing on:
  • Hip Strengthening: Targeting core and gluteal muscles to improve hip stability.
  • Mobility Training: Restoring pain-free range of motion without impinging.
  • Movement Pattern Retraining: Modifying biomechanics during activities to reduce impingement.
  • Patient Education: Understanding the condition and self-management strategies.

If conservative measures fail to provide adequate relief and symptoms significantly impact quality of life, surgical intervention may be considered.

• Hip Arthroscopy: This minimally invasive procedure is the gold standard. A surgeon uses small incisions and a camera to visualize the hip joint. The cam bump is then carefully reshaped (a procedure called femoral osteochondroplasty or femoral head-neck osteoplasty) to restore a more normal, spherical contour to the femoral head-neck junction, removing the source of impingement. Any associated labral tears or cartilage damage can also be addressed during the same surgery.

Long-Term Implications and Prognosis

Untreated symptomatic cam bumps leading to FAI can significantly increase the risk of developing early-onset hip osteoarthritis due to chronic cartilage and labral damage. Early diagnosis and appropriate management, whether conservative or surgical, are crucial for preserving hip joint health and function.

Following surgery, a comprehensive rehabilitation program is essential to restore strength, mobility, and return to desired activity levels. The prognosis after successful surgery and rehabilitation is generally good, with many individuals experiencing significant pain relief and improved function.

Prevention Strategies

While it's challenging to prevent the developmental formation of a cam bump, especially if there's a genetic component, some strategies may help:

• Proper Movement Mechanics: For athletes, ensuring correct technique in sports that involve repetitive hip flexion and rotation may theoretically reduce excessive stress on the developing femoral head.
• Early Recognition: For young athletes experiencing hip or groin pain, early evaluation can help identify cam deformities and FAI, allowing for timely intervention and activity modification before significant damage occurs.