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Paul Banaszkiewicz Paul Banaszkiewicz Segment Author

The number of patients identified with FAI has risen rapidly over the past 10 years.For exam canddiates there is a good chance that a patient may be seen as either an intermediate of less likely short case clinical 

Definitions

Acetabular dysplasia
Acetabular dysplasia describes an underdeveloped or shallow, upwardly sloping acetabulum, which may occur with varying degrees of deformity of the proximal femur such as excessive femoral neck anteversion, coxa valga or femoral neck cam deformity. It is an important cause of hip pain, often affecting young women. Symptoms may be experienced for many years before osteoarthritis develops. Patients describe a sharp activity related groin pain that increasingly affects their lifestyle. Symptoms may be exacerbated by rising from a seated position, climbing in or out of a car, going downstairs or sudden rotational movements.


FAI
Femoral acetabular impingement encompasses a spectrum of disease patterns and severity. It is a cause of hip pain, restricted hip motion, labral disease, articular cartilage degeneration and secondary osteoarthritis.
It is recognised as a sequela of common paediatric hip conditions such as Perthes’ disease and SUFE.

Epidemiology

  • The general prevalence of FAI as a clinical diagnosis is estimated to be around 10%
  • FAI manly affects people with a past history of athletic activities requiring extreme of hip flexion and rotation
  • An athelitic patient would generally be someone who took part in sports or exercise for more than 2 hours a day

Types of impingement lesions 

Impingement lesions exist as:

1.     Cam
2.     Pincer
3.     Mixed (cam + pincer)

1.Cam lesion

The cam type of impingement is caused by an overgrowth of the anterior and anterosuperior femoral head-neck junction, leading to an increased peripheral radius of the head entering the acetabulum throughout the range of movement of the hip. The chondral rim of the acetabulum is vulnerable to damage. Predisposing factors include SUFE, mal-union of a femoral neck or head fracture and femoral retroversion.

2 Pincer lesion

Pincer type impingement occurs because of acetabular over-coverage of the femoral head caused by a deep or retroverted acetabulum. A centre-edge angle of>40° is considered diagnostic of pincer impingement. This results in degeneration, ossification and tears of the anterosuperior portion of the labrum as well as a posteroinferior contrecoup pattern of cartilage loss from the femoral head and corresponding acetabulum. Predisposing factors include acetabular protrusio, acetabular retroversion and mal-union of an acetabular fracture.

3 Mixed lesion

The patient presents with clinical features  of both CAM and Pincer involvement

History
Patients present with hip pain that is located in the anterior part of the groin and sometimes the lateral aspect of the hip but without greater trochanter tenderness. The pain can be sharp and catching, worse with sitting and deep flexion. If the pain involves substantial catching or popping, suspect labral pathology. On clinical examination patients demonstrate a painful range of hip movement, particularly internal rotation and positive impingement test.

Examination
The impingement test is performed by placing the patient in the supine position with the hip in 90° flexion and then adducting and internally rotating the hip.

Anterior impingement test 
The anterior impingement test is a sensitive test to reveal intra-articular pathology in particular a torn anterior superior acetabular labrum.
With the patient supine,the hip is flexed to 90°,then adducted and internally rotated.A positive test reproduces the patients pain in the hip or groin.A positive test may sometimes be accompanied by a crepitus,clicking or a popping sesation.
The test compresses the anterior surface of the labrum
 
Posterior Impingement test
The posterior impingement test is helpful in demonstrating any disease between the posterior acetabular wall and femoral neck.
The patient lies supine at the edge of the examination couch with the affected leg dangling.The contralateral leg is held in flexion while the examiner fully extends the affected hip while abducting and externally rotating the leg
nerve by the piriformis muscle
 
FABER test
The FABER test is used to distinguish between pain arising from the sacro-iliac joint and pain arising from the posterior aspect of the hip.It is also a test for posterior impingement.
The patient lies supine,placing the ipsilateral foot on the contralateral knee.This is the so called figure of 4 position.The ipselateral leg is allowed to relax and the leg will be is seen to drop outwards to a variable degree.When this endpoint has been reached,the examiner places one hand on the flexed knee and the other on the ASIS of the contralateral sie and presses gently downwards of the flexed knee.
Increased pain can be elicited but with different localisation for the SIJ and posterior hip
The FABER distance is measured as the vertical distance between the knee and the examination table.

Imaging

A number of hip angles should be measured

1. Lateral centre-edge angle of Wiberg (LCEA). This assess the superolateral coverage of the femoral head or more simply femoral head lateralisation on an AP pelvis radiograph. It is obtained by measuring the angle between two lines: (a) a vertical line through the centre of the femoral head; and (b) a line from the centre of the femoral head to the superolateral aspect of the acetabular sourcil. An angle <20° is diagnostic of dysplasia whereas values above 40° may indicate pincer femoroacetabular impingement (FAI).

2. Anterior centre edge angle of Lequesne (ACEA).This measures anterior dysplasia on the false profile radiographic view that provides a true lateral view of the acetabulum. It is the angle between two lines: (a) a vertical line through the centre of the femoral head; and (b) a line from the centre of the femoral head to the most anterior point of the acetabulum. It is a measure of anterior coverage of the femoral head. An angle <20° is suggestive of anterior subluxation or deficiency.

3. Tönnis angle (acetabular inclination). This measures the angle of the weight-bearing surface or sourcil. It is the angle between two lines: (a) a line from the most inferior point of the acetabular sourcil to the lateral margin of the acetabular sourcil; and (b) a horizontal line running through the most inferior part of the sourcil.

A normal Tönnis angle is between 0° and 10°. A decreased Tönnis angle can lead to a pincer form of FAI whilst an increased Tönnis angle may indicate structural instability.

4. Acetabular angle (of Sharp). This measures acetabular inclination or opening. It measures the intersection between the following two lines: (a) a horizontal line from the inferior aspect of one teardrop to the other; and (b) a line from the inferior aspect of the

CT scan. This will identify early degenerative changes, cysts and acetabular/femoral version. Three-dimensional CT reconstructions can be useful in identifying cam on the anterior femoral neck.

MRI.To evaluate abnormal (bump) head-neck junction and possible labral and chondral pathology

Three-dimensional CT scan.To confirm the diagnosis and define the bony lesion

MRI arthrogram. To detect chondral/labral pathology and extracapsular abnormalities such as avascular necrosis.

Non-operative

This can be used for those patients who have primary lesion of FAI but have not yet developed any labral tear or chondral damage.
Activity modification
Reducing activities that aggravate pain such as running, martial arts,triathlons , etc. may help reduce  pain experienced.
NSAIDS (non-steroidal anti-inflammatory drugs)
Physiotherapy is usually not helpful

Operative

Diagnostic local anaesthetic hip injection with examination under anaesthesia (EUA) to confirm the intra-articular origin of pain
Hip arthroscopy 
PAO

  • The mainstay of surgical management is the Ganz periacetabular osteotomy (PAO). The acetabulum is reoriented to enhance coverage of the femoral head. The aim of surgery is to achieve congruity, stabilise the hip joint, medialize the hip joint center and to reduce contact pressures. This will relieve pain, improve function and prevent further overload of the labrum, cartilage and soft tissues, thereby delaying the onset of osteoarthritis.
  • Advantages include posterior column remains intact leaving the pelvis stable and allowing immediate partial weight-bearing, minimal internal fixation, extensive mobilization of the acetabular fragment is possible, the blood supply of the acetabulum is unaffected and the dimensions of the true pelvis are maintained.
  • Indications include:

-Symptomatic acetabular dysplasia with persistent pain
-A centre edge angle of <25°
-A congruent hip joint
-Maintained range of motion with hip flexion>110°
-Preoperative osteoarthritis corresponding to Tonnis grades 0-1

Arthroscopy 

Hip arthroscopy for management of chondro/labral pathology and excision of a cam impingement lesion. Occasionally when hip arthroscopy is used to treat labral pathology this may lead to a worsening of symptoms, as the stabilising effect of the labrum may be lost.

Surgical hip dislocation 

  • This allows the surgeon to directly visualise the femoral head and acetabulum
  • Ganz  technique is popular

Risks
The procedure is invasivve and does carry with it a number of possible complications including 

  • Trochanteric non-union 
  • Sciatic nerve injury
  • Heterotopic ossification 
  • AVN rare

Peri-acetabular osteotomy 

During surgery, the acetabulum is re-oriented  in order to improve the coverage of the lateral and anterior part of the femoral head.
The aim is to achieve congruity, to stabilize the hip joint, to medialize the hip joint centre and to reduce contact pressures.
 
Complications
Complications divided into minor and major:
Minor include lateral femoral cutaneous nerve dysesthesia, delayed union and heterotopic ossification
Major include injury to major vessels or nerves, arterial thrombosis. unintended extension of the osteotomy into the joint or through the posterior column and infection
Obesity has recently been shown to increase the risk of a serious complication by a factor of 10
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References

  • 1. Matsuda DK. Acute iatrogenic dislocation following hip impingement arthroscopic surgery. Arthroscopy 2009;25(4):400–4
  • 2. Ganz R et al. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulkum without the risk of avascular necrosis. J Bone Joint Surg Br 2001;83(8):1119–24