Limited Open Osteochondroplasty for the Treatment of Anterior Femoroacetabular Impingement

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CHAPTER 29 Limited Open Osteochondroplasty for the Treatment of Anterior Femoroacetabular Impingement

Murat Pekmezci, John C. Clohisy

Introduction

An abnormal relationship of the femur and the acetabulum that is characterized by repetitive abutment of the anterolateral femoral head–neck junction against the acetabular rim–labral complex is called the femoroacetabular impingement syndrome (FAI). Repetitive anterolateral impingement produces acetabular articular cartilage delamination, labral disease, and, eventually, osteoarthritis. To date, there is no prospective data that shows the natural history of untreated hip impingement. However, there are several retrospective case series that analyzed the structural anatomy associated with hip arthritis. These series demonstrated that deformity at the head–neck junction is commonly associated with osteoarthritis and that this may have a causative role in the disease pathogenesis. Currently, many investigators believe that untreated FAI has a poor prognosis and that the joint pathomechanics will lead to labral tears, articular cartilage injury, and progressive joint degeneration.

Pathophysiology

An appropriate relationship between the femoral head–neck junction and the acetabulum is a prerequisite for normal hip function. Normal hip range of motion requires a specific orientation of the acetabulum as well as of the proximal femur. The wide range of motion of normal hip function requires the appropriate orientation of the proximal femur and the acetabulum as well as normal femoral head–neck anatomy. Any deviation from this optimal orientation and alignment of the acetabulum and the femur may result in a decreased range of motion. For example, a decreased head–neck offset (i.e., the distance between the most prominent part of the anterior femoral neck and the articular surface of the anterior femoral head at the widest diameter of the head) results in less clearance between the neck and the bony acetabulum. As a result, the impingement of the femoral neck against the acetabulum and the labrum may occur within the normal range of hip motion. Activities that involve deep hip flexion (e.g., squatting, cycling) may aggravate the symptoms.

FAI has two types that depend on the anatomic location of the abnormality. The abnormality may be on the acetabular side (e.g., acetabular retroversion, coxa profunda) and result in abnormal coverage or overcoverage of the femoral head; this is called pincer-type impingement. If the abnormality is on the femoral side in the form of an aspheric head–neck junction or an abnormal head–neck junction with a decreased head–neck offset (e.g., slipped capital femoral epiphysis, Perthes abnormalities, femoral neck malunions), it is called cam-type impingement. The third type of FAI is a combination of the cam and pincer types of impingements. In all scenarios, the impingement of either the femoral neck or the head–neck junction at the edge of the acetabulum results in repetitive trauma to the labrum. This leads to degenerative tears in the labrum and the disruption of the labrochondral junction, which leads to osteoarthritis of the hip. Although the degeneration starts in the anterolateral joint space, it may also affect the posteroinferior joint space as a result of the levering of the femoral head on the anterior edge of the acetabulum caused by anterior impingement.

Indications

• The surgical strategy presented here has been primarily used for the treatment of cam-type deformities.
• Pincer abnormalities may be addressed with arthroscopic techniques or open procedures.
• Ideal surgical candidates have symptomatic anterior FAI, are well conditioned, are less than 50 years old, and have no or mild secondary osteoarthritis.

History and physical examination

The most common clinical presentation is activity-related groin pain in the young to middle-aged athletic individual. Associated lateral and posterior hip pain is also commonly observed. The symptoms are frequently intermittent, and the intensity ranges from mild to severe. High-demand sport activities that involve running, cutting, pivoting, and repetitive hip flexion (e.g., soccer) frequently exacerabate symptoms. Patients also complain of groin discomfort with prolonged sitting. Mechanical symptoms of locking and catching may also be problematic, and these presumably result from labral disease or unstable articular cartilage flaps. A history of hip trauma, childhood hip disease, and previous surgeries and treatments should be determined. These patients are commonly evaluated by multiple physicians and have been treated for tendonitis and synovitis. However, conservative treatment commonly fails as a result of the persistent structural abnormalities of the joint.

The physical examination starts with an observation of the patient’s gait and sitting posture. Patients with FAI may avoid sitting erect in a chair. These patients may also have an antalgic gait, depending on the extent of the disease, and abductor weakness is common. Previous surgical scars are inspected to clarify the nature of previous procedures and to facilitate preoperative planning. A Trendelenburg test is used to assess abductor strength. During physical examination, the most common finding is the limited internal rotation of the hip, particularly with simultaneous hip flexion. The anterior impingement test is performed by passively flexing (90 degrees to 100 degrees), adducting (10 degrees to 20 degrees), and internally rotating (5 degrees to 20 degrees) the hip. This motion elicits the groin pain by moving the proximal anterolateral part of the femoral neck into contact with the rim of the acetabulum. A positive test can be indicative of anterior FAI. The Patrick test is performed by flexing, externally rotating, and abducting the hip by placing the ipsilateral foot on the contralateral knee. A positive test (i.e., the presence of groin pain) suggests the irritability of the hip joint and intra-articular hip disease. Finally, an examination of the lumbar spine and the entire limb is necessary to eliminate other sources of pain.

Imaging and diagnostic studies

Plain radiographs are the traditional imaging modality for this condition. They can include a standing or supine anteroposterior pelvic view, a cross-table lateral view with 15 degrees of internal rotation, and a Dunn view or a frog-leg lateral view. The rotation and tilt of the pelvic x-ray should be assessed by observing the symmetry of the obturator foramens and the distance of the symphysis pubis to the sacrococcygeal joint, respectively. The normal value for the latter is 47 mm in females and 32 mm in males. Acetabular inclination and femoral head coverage should be evaluated to rule out associated hip dysplasia (i.e., structural instability). Acetabular version can also be assessed by looking for the presence of a crossover sign, which indicates acetabular retroversion. In addition, joint space narrowing, subchondral sclerosis, and periarticular cysts should be noted as indicators of secondary articular degeneration. The cross-table lateral view is helpful to evaluate the femoral head–neck junction. The femoral head–neck offset, the head–neck offset ratio, and alpha angle can be measured with the use of this view. These measurements have been shown to demonstrate abnormal femoral head morphology that is observed with cam-type impingement, and they can also be analyzed with the 45-degree and 90-degree Dunn views or the frog-leg lateral radiograph.

The next step in imaging should be magnetic resonance arthrography. This modality is sensitive for detecting intra-articular abnormalities (e.g., labral tears, chondral defects), and it is also helpful for excluding other diagnoses (e.g., osteonecrosis of the femoral head, stress fracture, neoplasm, infection). When evaluating patients with FAI, a computed tomography scan with three-dimensional reconstruction is informative with regard to the osseous deformity. The contour of the femoral head–neck junction and the extent of the femoral-sided disease can be appreciated in detail. The version of the acetabulum and associated osseous anomalies of the acetabular rim can also be defined.

Finally, diagnostic intra-articular hip injections provide valuable information about the presence or absence of intra-articular disease. Patients with intra-articular hip diseases (e.g., labral tears) usually report significant pain relief after injection. Alternatively, patients who do not have any pain relief should be re-evaluated for other causes of extra-articular hip disease (e.g., abdominal wall hernia, trochanteric bursitis, spinal stenosis).

Surgical treatment

The goal of the surgical treatment of FAI is to restore a more normal bony anatomy while addressing the associated soft-tissue problems (e.g., labral tears, acetabular cartilage lesions). The ideal surgical approach should possess the following properties:

• It should allow the surgeon to accurately visualize and evaluate disease characteristics.
• It should allow the surgeon to accurately reconstruct the structural hip anatomy.
• It should allow the surgeon to accurately treat the associated labral or acetabular cartilage disease.
• It should cause minimal morbidity while achieving these goals.
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