Femoro-Acetabular-Impingement FAI Hip Pain Explained
Functional Anatomy of the Hip Joint
The hip joint is a very stable ball and socket joint between the head of the femur and the acetabulum of the pelvis. The joint is enclosed by the acetabular labrum and joint capsule which increase joint stability. The main function of the hip joint is to support forces being transferred between the upper limbs, trunk and lower limbs. There are three groups of muscles which all play a role in the complex movement of the hip joint. The role of the deep muscle system is to control the position of the femoral head in the acetabulum as well as contributing to joint stability through a proprioceptive role. The intermediate muscle system controls movement of the pelvis on the femur during weight bearing as well as being secondary stabilisers of the femoral head in the acetabulum. The superficial muscle system is primarily used for force production around the hip joint.
What is FAI?
Femoro-Acetabular-Impingement (FAI) is a defect in the normal mechanics of the hip joint due to abnormal bony contact between the head of the femur and the acetabulum of the pelvis. This abnormal bony contact generally causes pain and discomfort in the anterior/later hip and groin area. Sitting for prolonged periods or activity requiring a large range of motion around the hip such as sports involving kicking actions often cause pain for people with FAI. FAI is more common in a younger active population and over time can lead to damage to the soft tissue structures, labral tears, muscle inhibition, bursitis, tendinopathy and osteo-arthritis.
What causes FAI Hip Pain?
There are two main forms of bony deformity that contribute to FAI Hip Pain either in isolation or in combination with each other. CAM impingement refers to a bony growth on the neck of the femur which butts up against the rim of the acetabulum during hip flexion and internal rotation. Pincer impingement refers to a thickening and widening of the acetabular rim, causing over-coverage of the acetabular rim in relation to the femur which does not allow enough room for the head and neck of the femur to move without making contact with the acetabular rim. Other factors which can contribute to FAI include tight posterior joint capsule, anterior instability and poor or delayed muscle activation of glute min, quadratus femoris and/or illiacus.
Treating FAI Hip Pain
Conservative management of FAI focusses on improving hip joint mechanics and optimising movement by improving muscle activation and strength of glute minimus and quadratus femoris, reducing posterior capsule tightness and strengthening the superficial muscle to a neutral position to avoid excessive anterior movement of the head of femur. In some cases surgical intervention may be necessary to reduce abnormal bony contact between the femur and the acetabulum by debriding the abnormal bony growth through arthroscopic surgery. If surgery is performed, pre-surgery and rehabilitation will focus on maximising hip joint function and addressing the factors outlined above during conservative management.
Written by Jack Hickey
Exercise Physiologist at MD Health Pilates