Friday, October 23, 2009

Femoroacetabular Impingement

Femoroacetabular impingement

▪ The presence of aberrant morphology involving the proximal femur and/or the acetabulum results in abnormal contact between the femoral neck and the acetabular rim during terminal motion of the hip.
▪ Ganz described two types of FAI: cam impingement and pincer impingement.
▪ Cam impingement: Cam impingement occurs when an abnormally shaped (ie, nonspherical) femoral head with increased radius is jammed into the acetabulum during normal motion, especially flexion. The prominence on the femoral neck is forced into the acetabulum and results in tearing of the labrum and/or its avulsion from the rim.
▪ The pincer impingement: is the result of abnormal contact between the acetabular rim and the femoral neck. The femoral head in this situation may be normal, and the abutment is mostly a result of overcoverage of the femoral head in conditions such as coxa profunda or acetabular retroversion.
▪ Both mechanisms lead to cartilage wear and eventually osteoarthritis

clinical features

▪ Presents in active young adults with slow onset of groin pain that may start after a minor trauma
▪ Hip or groin pain on prolonged standing or sitting or athletic activities.
▪ Anteroposterior impingement test(fig a). The patient is placed supine with the hip in 90° of flexion. Internal rotation of the hip and adduction recreates the symptoms.
▪ Posteroinferior impingement test(fig b) is performed by having the patient lie supine on the edge of the bed and having the legs hang free from the end of the bed in order to produce maximum hip extension. External rotation with the hip in extension that gives rise to severe, deep-seated groin pain is indicative of posteroinferior impingement


Following X-rays are required ,

1. True AP view of pelvis- A true X-ray is one in which the coccyx points toward the symphysis pubis with a distance of 1 to 2 cm between them
2. Cross table lateral view with hip in 10 deg of Internal Rotation.
3. Dunn View- An anteroposterior radiograph of the hip in neutral rotation, 20deg of abduction, and 90deg of flexion.

Differentiating b/n Cam and Pincer type impingement is important as the treatment varies.

Common Features-Pitt’s pit - Fibrocystic changes at the femoral head-neck junction
seen on X-ray but more clear in CT/MRI scan - 91% specific & positive predictive value of 71%

Features of Pincer Impingement- True AP View of Pelvis , ,
a Retroverted Acetabulum,
1.The Crossover sign- Anterior wall of the acetabulum crossing the posterior

2. The Posterior Wall sign- Center of the femoral head lying lateral to the
posterior wall.

3. The Ischial Sign- Ischial spine projecting into the pelvic cavity on
the AP pelvic radiograph.

b. Coxa Profunda:

1. The medial wall of the acetabulum lies on or medial to the ilioischial line.

2. Protrusio, which represents the more severe form of coxa profunda, is
diagnosed when the femoral head crosses the ilioischial line.

Features of Cam type Impingement- Cross Table Lateral/ Dunn View,
1. Asphericity of femoral head.

2. Alpha Angle > 50.5 degrees ( The angle between the axis of the neck and
the point where the bone of the head-neck junction crosses outside the
radius of curvature of the head)

3. The Head-Neck Offset Ratio measured by dividing the anterior offset by the femoral head diameter)

Non operative Treatment:
▪ NSAIDs, activity modification, restriction of athletic activities

Surgical Dislocation of the Hip (Ganz et al)
▪ Involves dislocation of the hip, with preservation of the blood supply to the femoral head, and femoroacetabular osteoplasty
▪ After crossing the obturator externus muscle posteriorly, the MFCA runs anteriorly toward the short rotators and crosses the femoral neck anteriorly to become the retinacular vessels penetrating the femoral neck
▪ Preservation of the short posterior rotators of the hip ensures that the MFCA is not damaged during surgical dislocation of the hip.
▪ Involves a trochanteric flip osteotomy through a lateral incision and a lazy S–shaped capsulotomy
▪ Osteoplasty of the femoral neck is then carried out.
▪ The torn labrum is débrided, and osteotomy is performed of the acetabular rim to remove the chondral lesion
▪ The remaining labrum is reattached using nonabsorbable anchor sutures.

Hip arthroscopy:
▪ Is both diagnostic as well as therapeutic
▪ Maybe useful for simple cam type impingement.
▪ The disadvantage of hip arthroscopy is in the fact that, it is difficult to address posterior labral lesions, inability to guide the extent of resection of the femoral neck prominence and inadequate treatment of an associated chondral lesion

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