Femoroacetabular Impingement (FAI)
Updated: May 18
What is it?
Femoroacetabular impingement (FAI) is an anatomical mismatch between the head of the femur and the acetabulum creating abnormal friction in the socket, causing damage to the labrum cartilage. FAI is one of many potential causes of labral injury. Femoroacetabular impingement is the leading cause for undiagnosed and misdiagnosed hip pain in patients under the age of fifty.
FAI is sub-classified as cam, pincer, and combined.
Cam impingement: is caused by a loss of the normal femoral head-neck offset. This means the femoral head and proximal neck of the femur are not the shape they should be.
Pincer impingement results for cartilage overdevelopment on the acetabulum or acetabular rim. Pincer-type impingement is also seen in hypermobile patients without a morphologic abnormality of the acetabulum.
Combined impingement is the most common form of FAI and is responsible for between 72-80% of all FAI cases.
Regardless of morphology, hips with FAI undergo repetitive end range of motion restrictions.
Most patients with FAI are young and physically active. Although morphologic abnormalities are often present bilaterally, symptoms are usually unilateral.
Complaints typically have an insidious onset, within the anterior hip or groin pain. The pain is usually described as dull and achy. Symptoms usually get worse with prolonged sitting, stair climbing, or stressful activity - which includes work or sports that require hip flexion and rotation. In the acute phase pain is only exacerbated by provocative activities, but continued impingement may lead to significant pain that affects all activities of daily living.
Patients often report limited range of motion along with possible popping or clicking. Continued cartilage damage may lead to a more painful form of popping and clicking.
FAI patients often demonstrate abnormal hip movement patterns while walking and squatting. Patients with cam impingement exhibit altered hip joint mechanics during the low-demand activity of walking; these alterations can affect load transmission, and contribute to pain, tissue damage, and osteoarthritis.
Hip flexor tightness is common in FAI patients. Clinical evaluation of cam-type FAI characteristically demonstrates painfully limited hip flexion and internal rotation.
Relying on clinical evaluation alone may be inadequate, the diagnosis of femoroacetabular impingement may require plain film or advanced imaging.
An MRI may be necessary to identify the morphologic abnormalities associated with pincer FAI, but should be reserved for only the cases that require additional detail, for example a definitive diagnosis or surgical planning.
Early identification and treatment of FAI may help prevent premature degenerative change.
Research shows and supports conservative care before surgery for management of FAI. Conservative management consists of patient education, activity restriction, proprioceptive training, manual therapy, and stability/strengthening.
Patients should attempt to maintain physical conditioning while avoiding activities that aggravate symptoms. Patients should be advised to limit activity that predispose them to repetitive impingement, particularly hip flexion and internal rotation. Patients should avoid squats in early stages due to pain with this exercise.
Manipulation of the lumbar spine and sacroiliac joints may be appropriate for pain management. Passive hip mobilizations and distraction may help improve hip mobility, especially in the presence of osteoarthritis. However, clinicians should avoid aggressive hip mobilizations and manipulation, as these movements could exacerbate the problem. Clinicians should also avoid stretching exercises or passive range of motion exercises, which are contraindicated and counterproductive.
Ignoring the prevalent functional deficits and gait imbalances associated with FAI patients leads to premature degeneration.
Core and hip (specifically the glutes) strengthening are key components in the conservative management of FAI.
A systematic review concluded that surgical intervention for FAI is not superior to conservative care in the short and medium- term. Patients who fail a trail of conservative care may require surgical intervention to limit progressive degeneration. Clinicians should not delay a surgical consultation for unresponsive or recalcitrant cases.