Femoroacetabular impingement (FAI) is a condition the involves an irregular shape of the bones comprising the hip joint (the femoral head and the acetabulum). The irregularity can result in excessive stress to surrounding tissues, including the labrum. Over time, pain results.
Anatomy and Pathophysiology
The hip is a ball-and-socket joint. The ball is the femoral head, while the socket is part of the pelvis known as the acetabulum. On the surface of the femoral head and the acetabulum, articular cartilage exists and enables a low friction surface for gliding of the joint. The labrum is fibrocartilage that forms a tight seal around the joint, and helping to provide stability.
Types of FAI
- Pincer: impingement due to excessive bone over the normal rim of the acetabulum.
- Cam: impingement due to abnormal shape of the femoral head
- Combined: a mix of pincer and cam type FAI
Physical Examination and Work-up
On examination, pain generally is provoked with special tests, such as the Impingement test, where the knee is brought up towards the chest and inwards toward the opposite shoulder. Additional tests of range of motion, strength and neurovascular examination are also conducted.
X-rays enable evaluate of the joint for signs of osteoarthritis, as well as allow important measurements of the pincer and cam deformities. MRI is best to assess the integrity of the labrum, while CT scans provide more detailed 3-D bony shape and detail.
Management of FAI
Activity modification, rest, physical therapy and injection are often the first line of treatment. Physical therapy focuses on hip and core strengthening, and addresses imbalances. If symptoms do not improve with prescribed non-operative management, surgery may be considered. Most FAI cases are performed arthroscopically with a small camera, called an arthroscope, to view inside the hip. During arthroscopy, the cartilage and labrum are assessed, and treatment is performed based on intra-operative findings. Post-operative rehabilitation is closely guided and important for a successful outcome.