Introduction

Osteonecrosis of the femoral head, which is also known as avascular necrosis, describes the clinical picture that is observed after the death of bone marrow and osteocytes. Resorption of the dead bone marrow and subchondral tissue leads to the generation of weaker tissue. The newly formed bone is prone to both fracture and collapse, and this may cause pain and decreased function of the hip joint. Without intervention, the disease process usually leads to articular cartilage destruction and resulting osteoarthritis. Osteonecrosis is most often seen in individuals who are 40 years old or younger, with approximately 10,000 to 20,000 new cases identified in the United States each year.

Trauma is the most common cause of osteonecrosis, but it can also be classified as atraumatic, in which the cause is not well defined. Traumatic osteonecrosis is seen when the blood supply of the femoral head and neck is disrupted as a result of trauma to the joint. This may occur after femoral head and neck fracture, hip dislocation, or both. Some atraumatic conditions (e.g., Caisson disease, sickle cell disease, myeloproliferative diseases, coagulation disorders) may directly cause osteonecrosis via the impairment of blood supply to the bone. However, most cases of atraumatic osteonecrosis have unknown causes, although they have numerous associated risk factors, including corticosteroid use, alcohol abuse, smoking, systemic lupus erythematosus, chronic renal disease, inflammatory bowel disease, human immunodeficiency virus infection, and hypertension. Some individuals may also have a genetic predisposition for osteonecrosis.

Various treatment methods have been used in an attempt to alleviate the symptoms or to slow the progression of the disease, including nonoperative (e.g., limited weight bearing, medication) and operative modalities (e.g., core decompression, bone grafting, osteotomies, hip arthroplasty). Nonvascularized bone grafting is a surgical technique that attempts to remove necrotic bone, to increase the amount of viable bone present in the femoral head for remodeling, and to provide support to decrease damage to the articular cartilage. In this chapter, we will describe the basic science of osteonecrosis as well as the indications, diagnostic methods, surgical techniques, rehabilitation, results, and complications of nonvascularized bone grafting for the treatment of osteonecrosis of the femoral head.

Basic science

In patients with traumatic osteonecrosis, the initial insult is a decrease in the blood supply that is caused by the disruption of the blood vessel. Bone marrow death follows within 12 hours of vascular compromise. The event that precipitates atraumatic osteonecrosis is less well defined, in part because of the lack of knowledge of the causes of this disease. Some causes are believed to incorporate the combined effects of metabolic factors, mechanical stresses, local factors that affect blood supply, and increased intraosseous pressure. Corticosteroid use and excessive alcohol intake are associated with the majority of cases.

The pathologic disease course that occurs after the initial insult is similar for both traumatic and atraumatic osteonecrosis. Reperfusion initiates a cascade of local metabolic factors that cause demineralization and trabecular thinning. Despite attempts to replace dead bone and repair weak bone, subchondral fractures occur. The resulting lack of mechanical support for the articular cartilage leads to altered joint mechanics and the degeneration of the hip joint.

Indications

As with other treatment modalities, the successful employment of bone grafting is most dependent on the stage of the disease. Several classification systems, including the Ficat and Steinberg systems, have been used to define various stages of tissue involvement, as shown in Table 30-1. The goal of bone grafting is to preserve the structure of the bone and the articular cartilage, so the procedure is most useful during precollapse stages (Ficat and Steinberg stages I and II), especially when less than 30% of the femoral head is involved. Bone grafting may also be used for a limited number of patients who have smaller Ficat stage III lesions if the articular cartilage is mostly intact.

Table 30–1 Descriptions of the stages of two widely used systems for classifying osteonecrosis of the femoral head

* The University of Pennsylvania stages I-V are further subclassified into three grades: Grade A = mild, involving less than 15% of the femoral head. Grade B = moderate, involving 15 to 30% of the femoral head. Grade C = severe, involving greater than 30% of the femoral head. In Stage V, the grade is determined by averaging the extent of involvement of the femoral head and the acetabulum.

History and physical examination

Patients who have osteonecrosis of the femoral head often present in a similar manner to patients who have other hip diseases (e.g., osteoarthritis), except that patients with osteonecrosis are frequently 40 years old or younger. The most common symptom of osteonecrosis is groin pain, which often occurs with weight bearing or other activity. Patients may describe the feeling of a groin pull (i.e., a sudden loss of hip stability) or groin fullness. Some patients who have an advanced stage of osteonecrosis may experience a sudden change in their ambulatory status. The physician should understand the risk factors for this disease. Patients may have a history of corticosteroid or alcohol use. Corticosteroid doses of more than 2 g of prednisone in 3 months or analogous doses of other steroids are generally associated with osteonecrosis. Alcohol exhibits a clear relationship with osteonecrosis, with higher doses of alcohol being associated with an increased risk of osteonecrosis. Other important risk factors include chronic conditions (e.g., systemic lupus erythematosus, renal disease) and immunocompromising conditions (e.g., human immunodeficiency virus, previous organ transplantation).

During the physical examination, pain is reproduced with passive as well as active internal rotation of the leg. The patient will point to the groin as the area of maximum pain, but he or she occasionally may point to the lateral trochanteric region, which may signify referred discomfort. Patients may be unable to fully bear weight on the affected extremity because of the pain. It is important to routinely perform a straight-leg raise and contralateral straight-leg raise to ensure that the cause of the pain is not the lumbar region.

Imaging and diagnostic studies

When evaluating a patient who has hip pain, several imaging studies may facilitate the diagnosis of osteonecrosis, including plain radiographs, bone scans, and magnetic resonance imaging (MRI). Currently, the standard diagnostic studies include plain radiographs followed by MRI. Plain radiographs should include an anteroposterior pelvic view to include the contralateral hip as a comparison and a cross-table lateral view of the affected hip. The presence of sclerosis, cystic changes, a crescent sign, or collapse on the plain radiographs may indicate the presence of osteonecrosis. The MRI is the current gold standard for the diagnosis of osteonecrosis; it is considered to be 98% to 99% sensitive and specific for the condition, and it also allows for the quantification of the size of the necrotic segment on both the sagittal and coronal axes.

Surgical technique