Cam Hip: Measurement, Diagnosis, and Management Strategies

How do you measure a cam hip?

Measuring a cam hip primarily involves diagnostic imaging, specifically X-rays, MRI, or CT scans, to quantify the alpha angle, which indicates the extent of the non-spherical femoral head-neck junction characteristic of cam morphology.

Understanding Cam Hip Morphology

A "cam hip," more formally known as cam-type femoroacetabular impingement (FAI), refers to an abnormal bony prominence on the femoral head-neck junction. This non-spherical shape causes abnormal contact between the femur (thigh bone) and the acetabulum (hip socket) during hip movements, particularly flexion and internal rotation. Over time, this repetitive impingement can damage the articular cartilage and the labrum, leading to pain, stiffness, and potentially early-onset osteoarthritis.

Why Measure a Cam Hip?

Measuring a cam hip is crucial for several reasons:

• Diagnosis: It helps confirm the presence and severity of cam morphology as a contributing factor to hip pain and FAI syndrome.
• Treatment Planning: Objective measurements guide decisions regarding conservative management (e.g., activity modification, physical therapy) versus surgical intervention (e.g., arthroscopic osteoplasty).
• Prognosis: The extent of the cam deformity can correlate with the risk of future cartilage damage and the need for more invasive procedures.
• Monitoring: While less common for cam itself, measurements can be part of a broader assessment to monitor hip joint health.

Clinical Assessment: Non-Imaging Methods

Before imaging, a thorough clinical assessment can strongly suggest the presence of a cam hip, though it cannot definitively "measure" the bony deformity.

• Patient History: Look for reports of deep, aching groin pain, especially with prolonged sitting, squatting, or athletic activities involving deep hip flexion and internal rotation. Patients may also describe mechanical symptoms like clicking or locking.
• Physical Examination:
  • Range of Motion (ROM): Often, there is a painful reduction in hip flexion and internal rotation, particularly when combined with adduction.
  • Impingement Tests:
    • FADIR Test (Flexion, Adduction, Internal Rotation): Considered the most sensitive test for FAI. The examiner flexes the patient's hip to 90 degrees, adducts it, and then internally rotates it. A positive test elicits pain in the groin or reproduces the patient's typical symptoms.
    • FABER Test (Flexion, Abduction, External Rotation): While more indicative of sacroiliac or intra-articular pathology, it can sometimes be limited or painful in FAI due to general hip stiffness.
  • Gait Analysis: Subtle compensations to avoid impingement may be observed, though this is less specific.

While these clinical findings are highly suggestive, they are not direct measurements of the bony morphology itself.

Definitive Measurement: Imaging Modalities

The definitive measurement of a cam hip relies on specialized imaging techniques that visualize the bony structure of the femoral head and neck.

• X-ray (Radiographs):

  • Often the first-line imaging. Standard views include an Anteroposterior (AP) pelvis view and a cross-table lateral view of the hip.
  • Specialized Views: A Dunn view (hip flexed to 45 degrees, abducted 20 degrees, neutral rotation) or a modified frog-leg lateral view are often used to better visualize the anterior aspect of the femoral head-neck junction where cam lesions are most common.
  • Measurement: Alpha Angle. This is the primary radiographic measurement for cam impingement.
    • How it's measured: A circle is drawn over the femoral head. A line is drawn from the center of the femoral head along the axis of the femoral neck. A second line is drawn from the center of the femoral head to the point where the femoral head loses its spherical contour (the "cam bump"). The angle between these two lines is the alpha angle.
    • Interpretation: A normal alpha angle is typically less than 50-55 degrees. Values greater than this suggest cam morphology. The specific threshold can vary slightly depending on the radiographic view and literature.

• Magnetic Resonance Imaging (MRI) / MR Arthrography:

  • Provides superior soft tissue detail (labrum, cartilage) and can more accurately assess the extent of damage caused by impingement.
  • MRI can also be used to measure the alpha angle in multiple planes, offering a more comprehensive 3D assessment of the deformity than 2D X-rays.
  • MR Arthrography involves injecting contrast dye into the joint, which further enhances visualization of the labrum and cartilage lesions.

• Computed Tomography (CT) Scan:

  • Offers excellent bone detail and 3D reconstruction of the hip joint.
  • CT scans are particularly useful for precise measurement of the alpha angle in various planes and for surgical planning, as they can provide a detailed map of the bony deformity.
  • The primary drawback is radiation exposure.

Interpreting Measurement Results

A finding of an elevated alpha angle (typically >50-55 degrees, depending on the specific measurement technique and view) on imaging is consistent with cam morphology. However, it's crucial to remember that the presence of a cam deformity on imaging does not automatically equate to symptomatic FAI. Many individuals have cam morphology without experiencing pain or functional limitations. Therefore, imaging findings must always be correlated with the patient's clinical symptoms, physical examination findings, and functional limitations to make a diagnosis of FAI syndrome.

Implications for Fitness and Rehabilitation

For individuals diagnosed with a cam hip, especially if symptomatic:

• Activity Modification: Avoid activities that involve deep hip flexion, internal rotation, and adduction, as these positions can exacerbate impingement. This might include modifying deep squats, certain yoga poses, or specific athletic movements.
• Strengthening and Stability: Focus on strengthening the muscles supporting the hip joint, particularly the gluteal muscles (maximus, medius, minimus), hip external rotators, and core musculature to improve dynamic hip stability and control.
• Mobility: While avoiding impingement positions, maintaining general hip mobility and addressing any associated muscle imbalances is important, often with guidance from a physiotherapist or exercise physiologist.
• Professional Guidance: Working with a healthcare professional experienced in FAI is essential to develop an individualized rehabilitation plan, optimize movement patterns, and determine when surgical consultation may be necessary.

Conclusion

Measuring a cam hip primarily involves objective diagnostic imaging techniques, with the alpha angle being the key quantitative parameter. While clinical assessment can strongly suggest its presence, X-rays, MRI, and CT scans provide the definitive measurements necessary for accurate diagnosis, treatment planning, and understanding the extent of the bony deformity. These measurements, when combined with a thorough clinical evaluation, are critical for managing femoroacetabular impingement and optimizing hip health.