Femoroacetabular impingement: a review of diagnosis and management

Abstract

Hip pain in adults has traditionally been associated with osteoarthritis in the joint. However, many young patients with hip pain do get referred to orthopaedic surgeons without arthritis. Subtle bony and soft tissues abnormalities can present with hip pain in the active young adult. These abnormalities can lead to premature arthritis. With the improvements in clinical examination for hip impingement, radiological imaging using magnetic resonance arthrography (MRA) and or computed tomograms (CT) Scans, these lesions are being detected early. Though the cause of primary osteoarthritis is unknown, it is suggested that femoro-acetabular impingement (FAI) may be responsible for the progression of the disease in these patients. FAI is a pathological condition leading to abutment between the proximal femur and the acetabular rim. Two different mechanisms are described, although a combination of both is seen in clinical practice. Cam impingement is a result of reduced anterior femoral head neck offset. Pincer lesion is caused by abnormalities on the acetabular side. FAI due to either mechanism can lead to chondral lesions and labral pathology. Patients present with groin pain and investigated with radiographs, CT and MRA. Surgery is the treatment of choice. Open or arthroscopic exploration of the hip is undertaken with bony resection to improve the femoral head neck junction with resection or repair of the damaged labrum. This may involve femoral osteochondroplasty for the cam lesion and acetabular rim resection for pincer lesion. There is no difference in outcome between open and arthroscopic surgery for FAI.

Keywords: Cam; Femoro-aecetabular; Hip; Impingement; Pincer; Young adults.

Fig. 1

Anteroposterior (AP) radiograph showing pistol grip deformity (arrow)

Fig. 2

(a) AP radiograph demonstrating cam lesion. (b) Cross table lateral radiograph showing normal alpha angle and normal head neck offset (left) and increased alpha angle with reduced head neck offset in cam lesion (right). (c) Cross table lateral view demonstrating calculation of the anterior offset ratio (AOR)

Fig. 3

AP (left) and cross table lateral (right) radiographs in a hip with pincer lesion. Note the cross over sign in the AP (coloured lines) and lateral views (arrow). The ischeal spines are prominent in the AP radiograph

Fig. 4 (a & b)

AP radiograph (left) demonstrating measurement of medial proximal femoral angle (MPFA) and the presence of posterior wall sign (middle schematic diagram and right radiograph)

Fig. 5

(a & b) AP radiograph showing a cam deformity with degenerative changes in the hip (left) and coxa profanda socket in the acetabulum (right). (c) Cross table lateral radiographs showing fibrocystic changes at the head neck junction (arrow) indicating dynamic hip impingement (foot print of FAI)

Fig. 6

(a) Coronal sections from magnetic resonance arthrogram (MRA) showing extrusion of radio opaque dye (arrow) at the site of labral tear. (b) Coronal section from magnetic resonance arthrogram (MRA) showing further extravasation of dye (arrow) through the torn labrum

Fig. 7

Three-dimensional reconstruction of Computed Tomography (CT) hip showing pre operative plan with marking of the area in the head neck junction (red circle) to be resected

Fig. 8 (a & b)

CT scans in position of discomfort (CT POD). Note the footprint of FAI in the coronal section with the hip in normal position (left) and dynamic impingement in position of discomfort best demonstrated with 3-D reconstruction of the CT images (right)