Cam Deformity: Causes, Risk Factors, and Its Impact on Hip Health

What causes cam deformity?

Cam deformity is primarily a developmental abnormality characterized by an abnormal bone growth on the femoral head-neck junction, leading to a non-spherical femoral head. While often idiopathic (of unknown cause), it is strongly associated with genetic predisposition and repetitive, high-impact athletic activity during adolescence.

Understanding Cam Deformity

Cam deformity refers to an abnormal shape of the femoral head (the ball of the hip joint) and its junction with the femoral neck. Instead of a perfectly spherical head that smoothly rotates within the acetabulum (the hip socket), a cam deformity presents with an aspherical, "pistol grip" shaped bulge on the anterior-superior aspect of the femoral head-neck junction. This bony prominence effectively increases the radius of the femoral head in certain areas, leading to abnormal contact with the acetabulum.

The Biomechanics of Cam Deformity

The hip joint is a ball-and-socket joint designed for a wide range of motion. In a healthy hip, the spherical femoral head rotates freely within the acetabulum. With a cam deformity, the bony bulge on the femoral head-neck junction impinges against the rim of the acetabulum, particularly during movements involving hip flexion, adduction, and internal rotation (e.g., squatting, sitting deeply, cutting movements in sports).

This repeated abnormal contact, known as femoroacetabular impingement (FAI), can lead to:

• Damage to the articular cartilage: The smooth, protective cartilage lining the femoral head and acetabulum can be worn down or detached.
• Labral tears: The labrum, a ring of cartilage that deepens the hip socket and provides stability, can be pinched and torn.
• Subchondral bone changes: Stress on the bone beneath the cartilage.
• Eventually, osteoarthritis: The chronic wear and tear can accelerate the degenerative process of the hip joint.

Primary Causes and Risk Factors

The exact etiology of cam deformity is multifactorial and not fully understood, but current evidence points to a combination of genetic and mechanical factors:

• Developmental Anomaly:

  • It is largely considered a developmental condition that occurs during the period of rapid skeletal growth in adolescence, typically between the ages of 10 and 16.
  • The growth plate (physis) at the top of the femur is particularly susceptible to abnormal bone modeling during this period. Instead of the normal process where bone is reabsorbed and remodeled to maintain a spherical shape, the cam deformity results from a failure of this remodeling process, leading to excess bone deposition.

• Genetic Predisposition:

  • There is a recognized familial component, suggesting that genetic factors play a significant role in determining an individual's hip morphology and susceptibility to developing a cam deformity.
  • Individuals with a family history of FAI or hip osteoarthritis may have a higher likelihood of developing a cam deformity.

• High-Impact Sports and Activity Levels During Adolescence:

  • This is a highly significant contributing factor. Repetitive, high-stress movements and extreme ranges of motion during crucial periods of skeletal maturation are strongly associated with the development of cam deformities.
  • Sports that involve deep hip flexion, internal rotation, and axial loading, such as ice hockey, soccer, basketball, football, martial arts, and ballet, are commonly implicated.
  • The theory is that the repetitive compressive and shear forces across the open growth plate stimulate abnormal bone growth at the femoral head-neck junction, leading to the cam morphology. The physis, or growth plate, responds to these mechanical stresses by laying down more bone than is necessary for a spherical shape.

• Slipped Capital Femoral Epiphysis (SCFE):

  • While not a direct cause of cam deformity in the same developmental sense, a history of SCFE (where the growth plate slips) can lead to an altered femoral head shape that mimics or contributes to a cam-type morphology. The resulting deformity after SCFE can lead to similar impingement issues.

• Other Contributing Factors:

  • Gender: Cam deformities are more prevalent and often more pronounced in males, which aligns with the higher participation rates in high-impact sports among adolescent males.
  • Hip Morphology Variations: Subtle differences in hip anatomy can predispose individuals to developing cam morphology or experiencing symptoms from it.

Understanding Femoroacetabular Impingement (FAI)

Cam deformity is one of the three primary types of Femoroacetabular Impingement (FAI), a condition where the bones of the hip joint abnormally come into contact. The other types are:

• Pincer deformity: Characterized by excessive bone growth on the acetabulum (hip socket rim).
• Mixed impingement: A combination of both cam and pincer deformities, which is the most common presentation.

In cam FAI, the aspherical femoral head repeatedly jams into the acetabular rim, particularly the anterior-superior aspect, causing damage to the labrum and articular cartilage. This mechanical impingement is the direct consequence of the cam deformity and is what leads to symptoms such as groin pain, stiffness, and reduced range of motion.

Diagnosis and Management

Diagnosis of cam deformity and FAI typically involves a physical examination and imaging studies such as X-rays (especially specific views like Dunn or cross-table lateral), MRI (Magnetic Resonance Imaging) to assess soft tissue damage (labrum, cartilage), and sometimes CT scans for detailed bone morphology.

Management strategies range from conservative approaches (rest, activity modification, physical therapy to improve hip mechanics and strength) to surgical intervention (arthroscopic hip surgery to reshape the femoral head and address labral tears), depending on the severity of symptoms, extent of damage, and patient's activity level.

Conclusion

Cam deformity is a complex morphological alteration of the hip joint that is primarily developmental, influenced by genetic predisposition, and significantly exacerbated by high-impact athletic activity during the vulnerable adolescent growth period. Understanding its causes is crucial for early identification, appropriate management, and potentially guiding activity modification in at-risk youth to mitigate the long-term risk of hip pain and premature osteoarthritis.