FEMOROACETABULAR IMPINGEMENT
WHAT IS FAI?
Femoroacetabular Impingement (FAI) syndrome describes the pain and/or functional limitation caused when there is an excess of bone growth in the “ball and socket” joint of the hip. There are three types of FAI morphology that are seen;
1. CAM – A bony growth on the anterior/superior neck of femur (ball) which impacts on the rim of the acetabulum (socket).
2. PINCER – An excess of bone coverage of the acetabulum over the femoral head, or retroversion (tilted backward) of the acetabulum that will impact on the femoral head.
3. MIXED – Some individuals will have both Cam and Pincer presentations.
DIAGNOSIS OF FAI
A Cam or Pincer lesion picked up on imaging does NOT form a diagnosis of FAI. FAI refers to the pain and pathology that occurs when the Cam or Pincer lesion impinges on structures, such as the labrum (cartilage on the edge of the acetabulum to deepen the socket). Many individuals have positive imaging findings without symptoms, and can live with this bony morphology without any pain or limitation through their life.
The Warwick Agreement on femoroacetabular impingement syndrome: an international consensus statement, published in 2016, states that for an individual to be diagnosed with FAI Syndrome they must have;
1. Positive imaging findings
2. Symptoms of hip or groin pain
3. Signs of FAI, including physical impairments and positive impingement tests.
The most useful imaging to measure the bony morphology is a plain X-Ray (AP Pelvis and Dunn 45 view), where the radiologist will determine the alpha angle. An alpha angle >60deg is diagnosed as a Cam lesion, with larger alpha angles associated with greater risk of hip osteoarthritis (OA). To measure other associated pathology in the hip, such as tearing of the labrum or degeneration of the surface covering of the bone (chondral layer), an MRI may be ordered by your physio or GP.
SYMPTOMS OF FAI
A study by Heerey et al (2016) found that 100% of subjects had pain in the groin region and approximately half with also have posterior hip pain.
The pain felt is most likely coming from a damaged labrum, which contains nociceptors (pain receptors). Pain may also be due to chronic inflammation (synovitis) if there is damage to the cartilage, suggesting early OA. The actual bone to bone impact may also be causing pain due to damage of the subchondral bone structure.
Other symptoms that patients may report about their hip include;
· Clicking
· Catching
· Locking
· Stiffness
· Restricted range of movement
· Sense of hip giving way
SIGNS OF FAI
Special Test - FADIR
Although commonly used in clinical practice, the FADIR test (Flexion, Adduction and Internal Rotation) of the hip has been found to be a good test to rule out people as not having FAI, but is not a good test to rule people in as having FAI (i.e. There is a high risk of false positives).
Special Test - FABER
The FABER test (Flexion, Abduction and External Rotation) has been shown to have a high degree of both false negative and false positive results (i.e. Is not that good a test for determining if the hip pain is due to FAI).
Special Test – Flexion & IR with overpressure
The Flexion and Internal Rotation with overpressure test is good at excluding people as not having FAI (i.e. If this test does not reproduce the clients pain unlikely they will have FAI), but again it has a high risk of false positives meaning it is a poor to fair test to rule people in as having FAI.
Physical Impairments
An individual with FAI may present with the following physical impairments;
1. Reduced hip muscle strength
2. Reduced functional task performance (e.g. Hopping, jumping, landing, cutting/change of direction)
3. Increased impingement in single leg squat
4. Reduced trunk endurance
5. Alterations in gait and running biomechanics
6. Reduced range of movement of the hip joint
TREATMENT FOR FAI
Physiotherapy
Physiotherapy can assist with manual techniques such as massage and joint mobilisation. A comprehensive rehabilitation program focusing on strengthening deep posterior muscles of the hip (obturator internus, superior and inferior gemelli, quadratus femoris) will help to reduce the force on the anterior/superior femoral head. Exercises to target the mid and outer gluteal muscles (gluteus minimus, medius and maximus) will also help to reduce anterior hip force.
Surgery
Surgery for FAI Syndrome should be the last option if conservative management fails to improve functional outcomes. There is currently no level 1 evidence for hip arthroscopy in FAI, however if symptoms and functional limitations do not improve, a referral to an orthopaedic surgeon may be recommended to consider debridement of the hip joint. This surgery does not necessarily mean the individual will be pain free after, as there is considerable rehabilitation that is required post-op. Any strengthening and control work that has been done before should not be considered a waste of time, as this will assist in recovery. Patients should understand also that surgery does not mean they will not require a total hip replacement in future, as FAI is now considered to be on the continuum of hip osteoarthritis, i.e. arthritic changes are likely to have already developed.
REFERENCES
Griffen DR, et al. (2016) The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome): an international consensus statement. British Journal of Sports Medicine; 50:1169-1176
Heerey J, et al. (2017) What is the location and distribution of pain in femoroacetabular impingement using a novel and quantitative method? Journal of Science and Medicine in Sport; 20:e90