Cam deformity means asphericity of the femoral head, It is very common in active people and most do not develop any problems from it. Cam impingement occurs when cam deformity causes hip pain and cam pattern of acetabular damage seen during surgery. It is commonly treated with shaving of the head neck junction to improve the sphericity (cam osteoplasty) with open or arthroscopic techniques. Cam deformity extending too medial for resection is treated with head reduction techniques.
Cam deformity is best seen on 3D CT reconstructed images and the resection can be planned with computer simulation. With experience plain radiographs give a good idea of the deformity and it can see well during surgery. Reddish band at the site of impingement on the femoral head and impingement cysts show the site of impingement. Though the resection also can be visualized during surgery, fluoroscopy decreases the chances of under and over resection.
Technique – I start at 45 -50 degrees of flexion of the hip and 20 degrees lateral rotation of the C arm. That should show 3-4 o clock position of the head neck junction. Mark the alpha point where the asphericity starts with flouroscopic guidance and start shaving from there towards 6 o clock using the medial synovial fold as the land mark. Shave laterally towards the anterior neck cortex. I move superiority by extending the hip and verifying the medial and lateral extents of the osteoplasty. I even hyper extend the hip to get beyond 12 o’clock position. Internal and external rotation allow reaching more medial and lateral aspects and give different perspectives of the contouring. Finally, watch the head neck junction against the Labrum dynamically while going from full extension to maximum flexion. The scope has to be held pushed in because high flexion pushes it out. The leg can be removed from the table to get more flexion in adduction and check internal rotation.
Ashish Bedii et al described 6 views to check for adequacy of the osteoplasty. The most common errors I make are not going medial enough and going deeper than required medially giving a shark bite appearance. Flouroscopy helps in decreasing these errors.
Anterior cam deformity of the left hip seen after surgical dislocation
Cam osteoplasty of the left hip with surgical dislocation