Cam Deformity

A cam deformity is an aspherical prominence at the femoral head-neck junction. During hip flexion and rotation, the prominence can contact the acetabular rim and produce shear at the anterosuperior chondrolabral junction. Arthroscopic femoroplasty removes the abnormal prominence and restores a smooth transition from the femoral head to the neck. This section will discuss the basic principles of femoroplasty to correct cam deformities.

General steps:

1. Define the location and size of the deformity before surgery

AP pelvis imaging is combined with a lateral projection such as a Dunn, cross-table lateral, or frog-leg lateral view. Different projections show different parts of the femoral head-neck junction. A normal AP image does not exclude an anterolateral cam lesion. A CT scan can be considered if the lesion is atypical or poorly visualized on X-rays.

2. Access and exposure

Cam resection is performed in the peripheral compartment after traction is released. The hip is commonly flexed approximately 30-45 degrees to relax the anterior capsule and increase working space. The anterolateral portal is commonly used for viewing, with the mid-anterior and/or distal anterolateral portal used for instrumentation.

An interportal capsulotomy may provide enough exposure for a small lesion. A larger lesion may require a T-capsulotomy. Capsular traction sutures can be useful to further retract the capsule and visualize the lesion.

Extra caution should be taken when working around the posterosuperior aspect of the femoral neck to prevent disruption to the retinacular blood supply to the head of the femur,

3. Defining the cam deformity intraoperatively

The deformity should be defined with direct visualization, fluoroscopy, and a dynamic examination before substantial bone is removed.

The femoral head should be fully seated in the acetabulum while the resection boundaries are being judged. If the head remains partially distracted or subluxated, the apparent head-neck junction can be misleading.

One fluoroscopic method for visualizing the deformity is to examine the cam circumferentially in six positions. These views are repeated during and after the femoroplasty. These positions are hip extension with neutral rotation, ~30 degrees internal rotation, or ~30 degrees external rotation and hip flexion in neutral rotation, ~ 30 degrees external rotation, and ~ 60 degrees external rotation.

4. Resect the deformity

There is no single accepted sequence for cam resection. Two commonly described approaches are summarized below. Both depend on repeated fluoroscopic and dynamic checks rather than on a fixed amount of bone removal.

Technique	Basic concept
Distal-to-proximal	Begin on normal distal femoral neck and work toward the head-neck junction reshaping the native contour.
Trough technique	Create a trough at the planned deepest portion of the correction, then blend the resection proximally toward the head and distally into the neck.

Common technical problems

1. Under-resection

Residual cam deformity is a common reason for revision hip arthroscopy. The lesion is hardest to visualize at its superolateral and most posterior extent.

2. Over-resection near the articular margin

Removing too much bone proximally can create a mismatch between the femoral head and labrum and compromise the suction seal.

3. Femoral neck notching

A focal notch creates a stress riser and excessive resection can weaken the femoral neck.

4. Injury to retinacular vessels

Avoid unnecessary posterolateral dissection and maintain orientation to the synovial folds and posterosuperior neck to preserve blood supply.

References