Understanding Femoroacetabular Impingement (FAI)
Do you experience a pinching pain in the front of your hip when you squat, ride your bike, or sit for a long period of time?
While there are many causes of hip and groin pain, one of the most common causes of this specific pinching sensation is “Hip Impingement”, which is also referred to as “Femoroacetabular Impingement” or FAI for short.
What is Femoroacetabular Impingement?
Femoroacetabular Impingement (FAI) is a condition that is characterized by pain in the front of the hip and/or groin when the hip is flexed upwards towards the torso.
The pain is produced when the femoral head (upper portion of the femur bone) and the acetabulum (cup-shaped bone on the pelvis) move closer together and the soft tissues (specifically the labrum) of the hip become pinched causing pain and stiffness within the hip.
If left untreated, FAI can lead to tearing of the labrum and increase the rate at which degenerative/arthritic changes develop within the hip joint.
How do I know if I have FAI?
We use 3 tests to determine if the pain our patients are experiencing is coming from the hip joint and could fall under the diagnosis of FAI.
C-Sign
Log Roll Test
Flexion-Adduction-Internal Rotation (FADIR) Test
Here’s a quick video detailing these 3 tests:
If at least two of these three tests reproduce pain in the hip it’s likely that you have FAI.
In order to better understand FAI and how we approach treatment for this type of condition it’s important to dive into the anatomy of the hip joint.
Hip Joint Anatomy
The hip joint, as we mentioned above, is made up of the femoral head and the acetabulum of the pelvis.
The labrum is located on the rim of the acetabulum, which helps to provide stability to the hip joint secondary to the joint capsule that envelopes the hip joint itself.
The picture below shows demonstrates the anatomy:
Image Source: https://orthoinfo.aaos.org/globalassets/figures/a00571f01.jpg
It’s also important to recognize the normal variations in hip anatomy. For example, the natural anatomic position of the femur within the acetabulum can be either “retroverted” or “anteverted”.
Hip retroversion is when the hip joint orientation is rotated slightly posterior (backward) relative to the horizontal axis of the pelvis.
Hip anteversion is when the hip joint orientation is rotated slightly anterior (forward) relative to the horizontal axis of the pelvis.
Retroversion and anteversion are demonstrated in the image below:
The reason that these normal variations are important to consider is that their “neutral” hip positions may look off from what would be considered neutral for the majority of people.
We need to ensure that we take an approach to treatment that incorporates these natural variations in normal anatomy.
What causes FAI?
Causes of FAI fall under two main categories:
Anatomical Hip Joint Deformity (Cam & Pincer Deformities)
Functional Movement Patterns (Muscular Imbalances)
These categories are not mutually exclusive, so being able to understand how they contribute to the development of FAI helps us in terms of approaching treatment for these types of complaints.
Let’s dive into the two main anatomical deformities that occur and contribute to the development of FAI, which are Cam and Pincer deformities.
What is a “Cam” deformity?
Typically, the femoral head (topmost portion of the femur) is smooth, round, and fits congruently within the cup-shaped acetabulum of the pelvis.
A “Cam” deformity is characterized by enlargement of a portion of the femoral head, most commonly the superior (upper) portion of the femoral head, that causes pinching of the soft tissues of the hip when the hip is flexed or abducted (raised to the side) as it runs into the outer portion of the acetabulum.
What is a “Pincer” deformity?
A “Pincer” deformity is characterized by enlargement of the acetabulum such that it covers more of the femoral head that also causes pinching of the soft tissues of the hip when the hip is flexed or abducted.
Cam and Pincer deformities can exist both exclusively and in combination with each other, which is why imaging (X-Ray, MRI, and/or CT) can be helpful in further evaluation of chronic hip impingement.
Below is an image demonstrating both Cam and Pincer deformities, as well as what a combination looks like:
Image Source: https://orthoinfo.aaos.org/link/2849dd42979a4a0ab837c7fd3a84d437.aspx
However, because the hip is a joint and joints are made to move… it’s important to understand the functional components that contribute to FAI!
Functional Movement Patterns of FAI:
Understanding the underlying anatomy of the hip is crucial to understanding how that joint moves in context of its anatomy.
To further break this down let’s talk about how the position of our feet (our stance) as well as control of the pelvis relative to the femur can change symptoms of FAI.
Foot Stance and FAI:
Simply put, mobile joints like the hip function best when the ball (femoral head) is centered within the socket (acetabulum).
By “stance”, we’re referring to the position of the feet as they relate to the hips/pelvis. If someone has any degree of retroversion within their hip they’re more likely to have a wider stance with some level of external rotation (turning out) of their feet.
Alternatively, if someone has any degree of anteversion within their hip they’re more likely to have a narrow stance with some level of internal rotation (turning in) of their feet.
Finding the correct stance for one’s own anatomy helps to keep the joint centered and allows for the most amount of range of motion in flexion, thus helping to prevent pinching of the soft tissues.
Pelvic Positioning and FAI:
The position of the pelvis also influences the position of the hip joint as a whole.
Anterior tilting of the pelvis (rocking the pelvis forward) brings the anterior (front) portion of the acetabulum towards the femoral head, thus leaving less room within the joint for the hip to flex upwards.
Posterior tilting of the pelvis (rocking the pelvis backward) brings the anterior (front) portion of the acetabulum away from the femoral head, thus leaving more room within the joint for the hip to flex upwards.
Limiting anterior pelvic tilting, and sometimes encouraging a posterior pelvic tilt, can help to place the joint in a better position by freeing up space for the femoral head to move within the acetabulum and thus prevent the pinching pain associated with FAI.
Here’s a quick video that demonstrates this concept:
Muscular Imbalances and FAI:
There are numerous muscles that have insertions on the femur and pelvis that help to control movement and provide stability to the hip joint.
For the sake of simplicity, we’re going to focus on the patterns we see most commonly with FAI.
First, the core plays a major role in maintaining pelvic stability during hip flexion. The ability to brace the core helps to maintain pelvic position and prevent excessive anterior pelvic tilting during hip flexion (like when squatting).
Excessive recruitment of the lumbar extensors, vs co-contraction of the lumbar and core musculature) can cause anterior pelvic tilting and contribute to FAI.
Second, the gluteal muscles play an important role in keeping the femoral head centered within the acetabulum. In hip flexion, the external rotators and abductors help to allow for controlled rotation of the femur while the internal rotators, adductors, and hip extensors act as stabilizers during this movement.
Excessive recruitment of the hip flexors paired with a lack of recruitment of the hip rotators and hip extensors can also cause instability of the hip in flexion and cause forward migration of the femoral head within the joint that contributes to hip impingement.
While that may seem complex, the key here is to recognize that symptoms of FAI develop both from anatomical variations and the way in which we move the hip.
As a result, successful conservative care for FAI involves taking both structure and function into consideration!
Are you experiencing pinching pain in your hip? We’re here to help!
Follow this link to book an appointment today: https://momentachiropractic.janeapp.com/
