What is femoroacetabular impingement (FAI)?
Femoro-acetabular impingement (FAI) is a disease of the hip joint in which pain is caused by the femoral neck striking the acetabular cup. Bony abnormalities are often found at the transition from the femoral head to the femoral neck (cam impingement, cam impingement) or at the acetabulum (biting forceps or pincer impingement).
What are the causes?
Possible causes of cam impingement may be bony attachments (bump) at the head-femoral neck junction or malhealed diseases in childhood and adolescence (e.g., Perthes disease, epipyseolysis capitis femoris). Causes of pincer impingement may be congenital (e.g., retroversion of the acetabulum, protrusio acetabuli) or acquired (e.g., degenerative attachments).
Fig. 1: Typical cam impingement with missing contour of the head-neck junction.
Fig.2: A typical pincer impingement with retroversion of the acetabulum (white=anterior acetabular cup, gray= posterior acetabular cup).
What exactly is so critical about it?
In both cases, mechanical problems are caused by the head-neck transition of the femoral neck striking the anterior glenoid cup, which can then damage both the joint lip (labrum) and, in the course, the articular cartilage. In many cases, this results in early joint arthrosis.
Fig.3: Cam impingement (A) or pincer impingement (B) causes the femoral neck to strike the acetabular cup.
And how exactly does an impingement at the hip feels like?
Affected patients often report pain in the groin, which can occur, for example, when sitting for a long period of time or during sports (e.g., hurdlers, volleyball). Classically, the bony pathology does not improve with conservative treatment measures, so that patients often report frustrating physiotherapy treatments.
How to diagnose a FAI?
In the diagnosis of a so-called femoro-acetabular impingement (FAI), both clinical and further diagnostics play a guiding role.
It is noticeable that the patient experiences increased pain especially when the hip joint is flexed with simultaneous internal rotation and spreading of the leg (anterior impingement test). This involves pressing the head-femoral neck junction against the anterior acetabular cup. In the case of malpositions, full and smooth movement of the hip joint is not possible. This test can also provide information about possible damage to the labrum.
How do imaging techniques help?
X-ray images of the affected joint provide an indication of bony malpositions. Furthermore, magnetic resonance imaging (MRI) with injection of a contrast medium into the joint (MR arthrography) is an important additional examination that can detect further pathologies and possible consequential damage before surgery, whereupon the surgical intervention can be planned precisely.
How to operate a FAI?
Arthroscopic therapy procedures are predominantly used in the treatment of femoroacetabular impingement. Through 2-4 small skin incisions and using special instruments, bony attachments are removed so that the hip joint can continue to move fully in all three directions without causing mechanical problems and pain.
Fig.4: Arthroscopic removal of a cam impingement with repositioning of the head-neck junction.
When is minimally invasive surgery recommended?
More extensive, dorsally extending bony pathologies sometimes require a minimally invasive open approach (MIS, keyhole surgery), as some pathology is very difficult to treat by an arthroscopic approach.Some special cases sometimes implicate a dislocation of the hip joint in order to perform adequate treatment.
How many days do you have to spend in the clinic?
The duration of the hospital stay depends on the type of surgical procedure and can last between three to seven days. Likewise, mobilization and activity depends on the procedure and the extent of the surgery, so each patient receives an individualized physiotherapy and physiotherapy exercise program for further outpatient treatment.