Surgical Dislocation of the Adult Hip for Treatment of Femoroacetabular Impingement

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CHAPTER SYNOPSIS

Femoroacetabular impingement is a pathologic condition in which structural abnormalities of the femoral head-neck junction and/or acetabulum result in repetitive abutment between the proximal femur and the acetabular rim, causing labral tears and chondral lesions. Its classification, diagnosis, indication for surgery, surgical techniques, and outcomes are discussed in this chapter.

IMPORTANT POINTS

1

Femoroacetabular impingement can be classified into three types: cam, pincer, and combined.
2

Patients generally have groin pain, a positive impingement test result, and morphologic abnormalities on radiographic images. The pain occasionally is located over the greater trochanter or buttock.
3

Patients with femoroacetabular impingement in the absence of advanced osteoarthritis are candidates for surgical dislocation if they have not responded to nonoperative management.
4

Patients with femoroacetabular impingement and advanced osteoarthritis are contraindicated for the procedure.
5

Preservation of blood supply to the femoral head is critical during the procedure.

CLINICAL/SURGICAL PEARLS

1

Longitudinal lateral incision (Gibson) centered at the anterior border of the greater trochanter allows incision of the fascia lata at the anterior margin of the gluteus maximus muscle and avoids splitting the muscle or compromising its neurovascular supply.
2

Trochanteric osteotomy is performed with the insertions of gluteus medius, gluteus minimus, and vastus lateralis on the trochanteric fragment but lateral to insertions of piriformis and short rotator so the blood supply to the femoral head is preserved.
3

A Z-shaped capsulotomy (right hip) allows adequate exposure of the joint.
4

The intact labral periphery can be detached at its base on the acetabular rim. The degenerated labral base and the osseous overcoverage can be resected down to bleeding bone, and the labrum is then reattached.
5

Any nonspherical portion of the femoral head and the bony prominence of the anterolateral part of the head-neck junction can be removed without violating the blood supply to the femoral head.

CLINICAL/SURGICAL PITFALLS

1

The medial femoral circumflex artery is the primary source of blood flow to the adult femoral head; the short external rotators must be protected to preserve the blood supply of the femoral head.
2

The risk of osteonecrosis of the femoral head is high if the osteotomy is too medial and extends into the base of the neck.
3

The sciatic nerve runs in close proximity to the piriformis muscle and is at risk when the capsular exposure is erroneously performed distal to the piriformis muscle.
4

Iatrogenic injuries of the femoral head cartilage and/or acetabular labrum are possible while performing capsulotomy. The operative extremity should be flexed and externally rotated to give more room for capsulotomy.
5

Excessive resection of the acetabular rim must be avoided because this may lead to undercoverage of the femoral head, causing instability of the hip.
6

Excessive osseous resection at the head-neck junction (more than 30%) mechanically weakens the femoral neck.

INTRODUCTION

Femoroacetabular impingement (FAI) is a pathologic condition in which structural abnormalities of the femoral head-neck junction and/or acetabulum result in repetitive abutment between the proximal femur and the acetabular rim, causing labral tears and chondral lesions. Evidence is growing that FAI eventually leads to osteoarthritis of the hip, particularly in the young adult. In general, the conservative management of FAI is not effective. Arthroscopy has been used alone or combined with other surgical techniques to treat FAI. It provides a minimally invasive approach for diagnostic and therapeutic management of FAI and is particularly useful in the treatment of labral tears, removal of loose bodies, and debridement of minimal morphologic abnormalities of the femoral neck. However, arthroscopic treatment of FAI has many shortcomings. Correcting pincer-type impingement, reconstructing the labrum, and manipulating the instruments inside the hip joint are quite difficult with currently available techniques and surgical tools. Therefore arthroscopic surgery is reserved only for simple cam-type impingements. Osteochondroplasty of the femoral head-neck junction and the acetabular rim through a greater trochanteric flip osteotomy and anterior dislocation of the femoral head has been well studied and established by Ganz et al. Early and mid-term results of surgical dislocation and osteochondroplasty of the hip for FAI have been encouraging. The procedure can reduce pain and improve function. The long-term goal of surgery is to stop or at least slow further development of degenerative joint disease. This chapter focuses on treatment of FAI with the techniques of surgical dislocation and osteochondroplasty through a greater trochanter flip osteotomy.

CLASSIFICATION

FAI can be classified into three types ( Fig. 5-1 ). The cam type presents with an aspheric femoral head-neck contour caused by widening of the femoral neck or a reduction in the head-neck offset. The occurrence of the aspheric nature is a development feature. The aspheric extension of the femoral head has been shown to be covered by hyaline cartilage, and a separation disorder of the epiphyseal growth plate is believed to be responsible for its appearance. This causes repetitive impingement between the proximal femur and the acetabular rim. Osteophytes at the head-neck junction are sequelae of FAI and a sign of advanced degeneration of the hip. Active men in the second and third decades of life typically are most often affected. The current treatment includes the removal of the aspheric extension of the femoral head onto the neck.

The pincer impingement is caused by a localized or global acetabular overcoverage (see Fig. 5-1, C ). Radiographically, this appears as acetabular retroversion or coxa profunda to protrusion. The femoral neck is normal. The increased acetabular coverage limits the range of motion and, as a result, the labrum is caught between the femoral neck and the acetabular rim. Cartilage damage is much less extensive and limited to a narrow strip along the acetabular rim. In general, women in the third and fourth decades of life are most often affected. For the treatment of the pincer impingement the acetabular rim is resected to give the acetabulum a normal depth and orientation with reattachment of the labrum.

Isolated cam or pincer impingement is rare. The combined cam-pincer impingement is the most common form of the disease (see Fig. 5-1, D ). Surgical treatment of this type of FAI is directed at restoring both a more normal femoral head-neck offset and the appropriate acetabular depth and orientation to alleviate femoral abutment against the acetabular rim.

DIAGNOSIS

Clinical Presentation

Active young adults with a history of pain in the groin, especially during combined flexion and internal rotation of the hip, should be suspected of having FAI. The pain initially may be intermittent and may be exacerbated by athletic activities and prolonged sitting. The pain may be referred to the knee. Historically, because of the lack of knowledge of FAI, patients sometimes have been subjected to extensive diagnostic workups and even unnecessary surgical procedures such as inguinal hernia repair, knee scoping, and laparotomy.

Physical Examination

Patients with FAI almost always have a positive impingement test result. The test is performed with the patient in the supine position. The test result is positive if the pain is produced with the hip flexed to approximately 90 degrees while it is internally rotated and adducted. Patient also may have limited range of motion, especially internal rotation and adduction in flexion.

Radiographic Assessment

Standard anteroposterior (AP) view of the pelvis and lateral view of the affected hip should be obtained. The standard AP radiograph has the patient standing and should be symmetric bilaterally so that the coccyx points to the symphysis pubis with a distance of 1 to 2 cm between them. This standard view is critical to assess acetabular version and anterior overcoverage. A positive crossover sign ( Fig. 5-2 ) or coxa profunda on this view indicates pincer-type impingement. The cross-table lateral view with the lower extremity internally rotated 15 degrees is ideal for assessment of cam-type FAI ( Fig. 5-3, A ). This standard view has been reported to best show femoral head-neck asphericity. The anterior offset angle α has been used to identify anterosuperior asphericity at the femoral head-neck junction. The angle α value was reported as 42 degrees in a control group and an average 74.0 degrees in patients with FAI. The method to measure the angle α is simple and has good reproducibility. The legs of the α angle are the femoral neck axis and a line connecting the center of the femoral head with a point where the femoral head extrudes a circle around the femoral head centered on the femoral head center (see Fig. 5-3, B ). The software used for measuring the angle α (ImageJ) can be obtained from the National Institutes of Health website ( http://rsbweb.nih.gov.easyaccess1.lib.cuhk.edu.hk/ij ). Magnetic resonance imaging arthrograms are highly sensitive and specific for diagnosing labral and chondral lesions except for undetached chondral separations. They also are capable of detecting ossification of the labrum, asphericity of the femoral head-neck junction, impingement cysts, and low offset of the femoral neck.

INDICATIONS

Patients with hip pain, a positive impingement test result, radiographic evidence of FAI in the absence of advanced secondary changes to the cartilage, and unsuccessful nonoperative management are recommended for surgical dislocation and osteochondroplasty. FAI can be caused by localized or generalized acetabular overcoverage (retroversion or coxa profunda), a nonspherical femoral head, an insufficiently narrowed head-neck junction, pelvic osteotomies that result in overcorrection, and combined extraarticular and intraarticular impingement. A diagnostic injection of the hip joint is helpful in determining the intraarticular origin of hip pain.

CONTRAINDICATIONS

Patients with FAI and advanced osteoarthritis are contraindicated for the procedure. However, patient age, activity level, and expectations also must be considered. In some circumstances even slight joint space narrowing, if it is indicative of substantial cartilage damage causing pathologic axial loading, will lead to a poor outcome.

SURGICAL TECHNIQUES

The techniques of surgical dislocation have been previously reported. A thorough knowledge of the blood supply in the adult hip is critical to allow safe execution of surgical dislocation of the hip. The deep branch of the medial femoral circumflex artery is the primary source of blood supply to the femoral head ( Fig. 5-4 ). It reaches the greater trochanter just proximal to the quadratus femoris. It then crosses the tendon of the obturator externus posteriorly and continues its course anterior to the superior and inferior gemellus and the obturator internus tendon. It perforates the capsule at the superior margin of the superior gemellus tendon and divides into several terminal branches, the so-called retinacular vessels. Almost 80% of all foramina are located at the posterosuperior head-neck junction. Its course explains why the short external rotators must be protected. During dislocation of the femoral head, the external rotators, especially the obturator externus, protect the medial femoral circumflex artery from stretching or rupture. If the capsulotomy is performed strictly anteriorly, damage to the retinaculum can be avoided.