Hello, my name is Sanjeev Bhatia from Northwestern Medicine, and I'm excited to tell you more about FAI Hip Imaging 101, which is a very useful thing to know as you're evaluating patients in the office. I have no disclosures relevant to this talk. We all know that FAI has been something that's really exploded in recent years, and there's been a plethora of research. One of the best papers on FAI syndrome is the Warwick Agreement, which is an international consensus statement on standards as well as current concepts in managing this. FAI syndrome is a motion-related clinical disorder of the hip with a triad of symptoms, clinical signs, and imaging findings, and represents a symptomatic premature contact between the proximal femur as well as the acetabulum. Visually, what this looks like on the femoral side is you can get a convexity at the femoral neck called a cam lesion, which then can result in impingement as the patient flexes and internally rotates the hip. Namely, this convexity can pinch against the anterior superior aspect of the acetabulum, pushing the labrum, and also causing disruption to the underlying anterior superior acetabular cartilage, one of the chief causes with which people develop early arthritis. It's cousin is the pincer lesion, which is when you have an over coverage of the socket rim. This also causes a pinching between the acetabulum as well as the femoral neck, and sometimes this also causes a levering effect on the posterior aspect of the femoral head, resulting in a contracoup chondrolesion. Labral tears are very common with FAI syndrome and are resultant of the premature contact that these two bones often will cause. This is what labral tears look like arthroscopically. Most frequently, labral tears are in the anterior superior quadrant and rarely do they ever occur without some type of bony abnormality, specifically of the cam pincer or dysplasia. 90% of patients with labral tears have at least one bony abnormality. The Warwick Agreement has a very good summary of diagnostic imaging criteria that can be used to help diagnose patients with FAI properly. Specifically, this involves radiographs, namely the AP pelvis as well as a lateral femoral neck view. You wanna assess for joint space and then also utilize advanced imaging to your benefit to assess the cartilage, labral tears, as well as bony pathology, oftentimes for preoperative planning purposes. At a 50,000 foot overview, this is a rough overview of the different types of morphologies that can happen of the acetabulum. You can have overcoverage and you can have dysplasia, which is when there's a shallow hip socket. Both of these are negative predictors for outcomes and often lead to persistent pain and other disabilities. Normal hip has adequate coverage. From an acetabular standpoint regarding the pincer, you can have local pincer lesions, which often are resulted from retroversion of the acetabulum, or you can have a global pincer condition resulting from coxa profunda or protrusio acetabuli. We'll talk more about that in just one second. From a local standpoint, signs of acetabular retroversion occur when the anterior aspect of the, when the acetabulum is tilted posteriorly or retroverted, allowing the anterior aspect of the femoral neck to often pinch. And signs of this on x-ray involve the crossover sign, where you see the anterior rim of the acetabulum cross with the posterior rim. From a global standpoint, one thing to know is that in a normal hip, the femoral head and the floor of the acetabular fossa should be lateral to the ilio-issue line. So here in red is the femoral head, and here is the ilio, here is the floor of the acetabular fossa. Both of these should be lateral to this ilio-issue line, which is shown here in the dashed red. When you have a condition where you have increased acetabular depth, it either can be coxa profunda or acetabular protrusio, and these are very interrelated conditions. Coxa profunda is defined as having an acetabular fossa that is medial to the ilio-issue line. This often is resulting from results in mild symptoms. In some cases, it can cause more severe symptoms of FAI. Acetabular protrusio, on the other hand, is when the femoral head is more medial to the ilio-issue line, resulting in progressive severe degeneration of the hip. Visually speaking, dysplasia is often something to evaluate very carefully. The tonus angle is when the sorcial and the horizontal are measured, and that angle should be less than 10 degrees. Otherwise, it is considered a dysplastic hip. A more vertical tonus angle is a sign of dysplasia, and that's why that's greater than 10 degrees is considered a dysplastic. The lateral center of jangle is probably the most widely used dysplasia measurement, and that's when you take the vertical of the femoral head and intersect that with a line crossing the lateral-most point on the acetabulum, and specifically the lateral-most point of the sorcial or the weight-bearing portion. Anything less than 20 degrees is considered dysplastic. 20 to 25 degrees is borderline hip dysplasia, and greater than 25 degrees is more normal, is normal. The thing with dysplasia, if you have an undercover shallow acetabulum, it increases your risk of osteoarthritis, and these are also poor predictors for patients undergoing hip arthroscopy. In general, a lateral center of jangle of less than 20, an anterior center of jangle of less than 15, or a break in Shenton's line indicates a lateralized femur, which are poor predictors for hip arthroscopy. On the femoral side, the CAM lesion is typically measured with a specific lateral femoral neck view called the Dunn lateral, and the reason for this is an AP radiograph often will miss the CAM lesion because the x-rays are not able to adequately project perpendicular to the bony pathology. Here's a CAM deformity and how we measure the alpha angle. So this is a Dunn lateral x-ray view, which is a slightly lateralized position of the hip, and basically you circumscribe a circle onto the femoral head and then measure the angle with which the bony pathology becomes tangential to that perfect circle on the femoral head. Normal is 42 degrees. A CAM lesion is considered anything greater than 50 or 55 degrees. This does have poor inter-observer reliability as shown in various studies. On the advanced imaging side, MRIs and MR arthrograms are often very useful in terms of helping understand which patients have labral pathologies. Typically, an MR arthrogram often is most sensitive for assessing for labral tears, detached labral tears, as well as capsular defects, especially in revision settings. A plain MRI, in many cases, is actually the best test for assessing for cartilage pathology and is more sensitive for viewing cartilage lesions, bony subcontinental bone edema, and other marrow-occupying pathologies. On the CT side, a CT scan with 3D reconstruction is often very helpful for preoperative planning, especially in patients with very severe types of femoroacetabular impingement, as well as os acetabuli and other bony pathologies. CT scans also can be useful for assessing femoral neck version and other bony measurements in a three-dimensional level. So, as I mentioned, MRIs are useful for labral tears, articular cartilage lesions. They're very sensitive and specific for this. And then CT scans are useful for bony anatomy and S-heb or femoral neck roadmaps. Hip arthroscopy is a great procedure, but patient selection is paramount. One of the best pearls that I can impart is that serial x-rays on older patients often saves you a lot of trouble. Here's a case of a 59-year-old patient who's referred from a nearby physical therapy clinic for six months of pain after hip arthroscopy. She's failed quite a bit of conservative measures. When you look at her x-rays, she does look dysplastic, but she does have some decent joint space that is present. However, two months later, if you get a repeat x-ray, you see complete loss of joint space, indicating that the osteoarthritic process is not just mechanical, but it's also biochemical in nature. In this individual, there were certain degenerative enzymes that were degrading the cartilage, causing more thinning to progress. And without getting serial radiographs in this high-risk degenerative patient, we would have missed the pathology and made a significant surgical decision-making error. Ben Dome did a very nice study a few years ago where he reviewed his first 200 cases as well as the last 200 cases that he had done. He noted that the first group that he did hip arthroscopy on had significantly more arthritic changes, 37% versus 21% with regards to tonus grade one, than the second group. Not surprisingly, the second group had a greater proportion of patients that achieved the minimally clinically important difference and patient acceptable symptomatic state. So this indicates that the more patients that you isolate with less degenerative conditions, the better they will do. So that's why serial x-rays are very important to get and making sure that you focus on tonus grade zero. Always assess joint space on standing AP radiographs. Ideally, you want greater than three millimeters of joint space with no subchondral cysts. And this is specifically the distance that you're trying to measure digitally on your x-ray. In summary, proper diagnosis and patient selection is key. Always assess for dysplasia using proper x-rays. Get serial radiographs on older patients with questionable early osteoarthritis. It'll save you a lot of trouble. And advanced imaging is helpful, but it's not as helpful as plain radiographs. Thank you very much. We wish you all the best in your future practice, and please feel free to reach out to me if there are any questions.

FAI Hip Imaging

hip impingement

cam and pincer lesions

osteoarthritis

hip arthroscopy