Cam vs. Pincer Impingement

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. 

Youtube Animation

Overview
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

Pincer-Type FAI
-More common in middle aged women
-Caused by acetabular retroversion, coxa profunda, and other causes

Both cam and pincer lesions clinically present with groin pain during or after flexion type movements. They have increased pain with sitting due to ROM impairments in hip flexion and internal rotation. Upon functional assessment, gait abnormalities may be present as well as deviations with squatting movements. Due to the abnormal shape of the femoral head or acetabulum, labral tears and cartilage breakdown is usually the result of FAI. To diagnose FAI, imaging is required. Clinically, the labral anterior impingement test or labral posterior impingement test can be used to assist the therapist understanding what structure is involved. As with all things physical therapy, we cannot change the anatomy, but knowing an individual has FAI will give us a better understanding of how to treat their movement dysfunction.

-Jim