The final days before the OCS examination are upon me. As I answer different practice exam questions, I often come across answers not fully explained in my readings. In these instances I search the internet for reputable sources to gather further information on the question or diagnosis. Recently there was a question on femoral-acetabular impingement (FAI) and cartilage breakdown. To answer the question, a thorough understanding of cam vs. pincer lesions, hip mechanics, aggravating factors, and how the abnormal stresses cause breakdown of the cartilage were all necessary. In this post, I am going to discuss the two types of FAI. I recommend checking out the link as well because it shows MRI and x-ray imaging of the hip with great explanations of what pathology you are viewing.
FAI is a common pathoanatomic problem due to abnormal contact between the femoral head and acetabular rim. In a normal hip, the femur translates in the acetabulum without interruption. Stresses are dissipated throughout the labrum, minimizing the risk of breakdown. In FAI, abnormal stresses are placed between the femoral head/neck and the acetabular rim. These abnormal stresses are the sensation of 'impingement' the patient reports when you bring them into hip flexion or IR. The source of pain can either be due to abnormal shape of the femoral head-neck junction (Cam-type) or more prominent acetabular rim (Pincer-type).
Cam- Type FAI
-Generally occurs in young athletic males
-Commonly caused by femoral retroversion
-More common in middle aged women
-Caused by acetabular retroversion, coxa profunda, and other causes