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Chapter 45 Osteonecrosis

Manual of Rheumatology and Outpatient Orthopedic Disorders

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Chapter 45 Osteonecrosis

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Theresa Colosi and John H. Healey

Definition
Etiology
Diagnosis
Treatment
Summary

I. Definition

Osteonecrosis (ON) is defined as the death in situ of a segment of bone from lack of circulation. Dead bone refers to dead cells, which include osteocytes in addition to the hematopoietic and fatty marrow cells within bone. Circulatory injury that compromises cell viability can secondarily jeopardize the structural integrity of bone. Bone has a rich blood supply, but it varies widely depending on the site. Certain locations are more susceptible to ON. The most common location for ON is the femoral head. Other relatively common locations include the distal femur, proximal humerus, and talus. ON usually affects adults less than 50 years old. This discussion pertains essentially to primary ON of the femoral head. Secondary ON also occurs. Areas of ON complicate osteoarthritis of the hip in 25% of cases.

II. Etiology

1. Four mechanisms of circulatory compromise of bone are recognized and one or more may play a significant role in a given patient:
   1. Mechanical disruption (e.g., traumatic fracture/dislocation or stress fracture).
   2. Arterial occlusion (e.g., embolism, sickle cells, invasion by Gaucher cells or fat, or nitrogen bubbles caisson disease).
   3. Injury to or pressure on an intact artery (e.g., vasculitis, radiation injury, vasospasm).
   4. Venous outflow occlusion (e.g., when venous pressure exceeds arterial pressure by any mechanism). This mechanism may, in fact, be the final common pathway of the other three mechanisms. ON may have a traumatic or an atraumatic cause. Traumatic ON occurs after injury to a bone with a vulnerable blood supplyfor example, femoral head ON after hip dislocation or proximal humerus ON after proximal humerus fracture. Most cases of atraumatic ON are idiopathic or are associated with corticosteroid administration or ethanol abuse. The exact cause is unclear, although fat embolism and local clotting are probable mechanisms (Fig. 45-1).
      
      

      
      

      FIG. 45-1. Mechanisms of ischemic necrosis of bone.

      
      
      
2. Corticosteroid administration is a significant cause of ON because of its widespread use in a variety of diseases, including systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, nephrotic syndrome, lymphoma and other myelogenous diseases, respiratory disease, and central nervous system disorders. In systemic lupus erythematosus, a high average daily dose (over 16.6 mg) and pulse therapy are considered important predictors for the development of ON.
3. Ethanol abuse also presents a clear dose-response relationship: consumption of more than 400 cc weekly results in a 10-fold greater risk for ON. Fat emboli from alcohol-induced fatty liver, increased blood cortisol levels, and altered lipid metabolism are all proposed mechanisms of ON in alcoholics.
4. Smoking is also a risk factor; smokers have a fourfold to fivefold greater risk for ON.
5. Atraumatic causes of ON are:
   1. Dysbaria ( decompression sickness or caisson disease), radiation therapy, and pregnancy . Decompression may precipitate ON if nitrogen bubbles, which may come out of solution subsequent to a rapid drop in barometric pressure, occlude arterioles.
   2. Radiation. Radiation therapy may cause ON as a result of capillary injury and vasculitis. Theories on the mechanism of ON in pregnancy include venous congestion and the well-known phenomenon of hypercoagulability of pregnancy.
   3. Hypercoagulability. A high incidence of coagulopathy exists in patients with ON. In a recent study, 26 patients with newly diagnosed ON of the femoral head underwent evaluation with a detailed coagulopathy profile. The proteins involved in thrombophilia and hypofibrinolysisboth of which may result in an increased incidence of thrombiwere studied. Eighty-three percent of these patients had a defined coagulopathy. Significant findings included high plasminogen activator inhibitor activity, low stimulated plasminogen activator activity, and high anti-cardiolipin immunoglobulin G.
   4. Association with osteoporosis. In addition to coagulopathy, high- turnover osteoporosis or even osteomalacia may coexist with ON. In a histomorphometry study of transiliac bone specimens from 77 patients, investigators found a common profile: reduction in trabecular bone volume and osteoid seam thickness , in calcification rate, and in tetracycline-labeled surfaces. Total resorption surfaces were increased. These changes suggest a significant decrease in osteoblastic appositional rate and bone formation rate at the cell and tissue level. This decrease in appositional rate could explain a defect in healing of microfractures, which would facilitate the formation of subchondral fractures.

III. Diagnosis. One makes the diagnosis of ON on the basis of history, physical examination, and radiologic studies.

1. A careful history should seek out the risk factors discussed previously.
2. Physical examination findings may range from subtle (groin pain only) to significant (reduction in range of motion and pronounced antalgic gait).
3. Appropriate radiologic studies include plain radiographs, bone scan, and magnetic resonance images (MRI). Results of these studies subsequently allow staging of the disease and provide guidelines to treatment. A currently used staging system is that of the University of Pennsylvania (Table 45-1). The importance of the system is that it incorporates the type and extent of radiologic and pathologic changes. The Japanese Investigation Committee for Avascular Necrosis of the Femoral Head also recently developed a classification system; it is based on plain anteroposterior radiographic findings and is used to predict prognosis and, thus, choose treatment.

   
   

   Table 45-1. Steinberg-University of Pennsylvania staging system of osteonecrosis of the hip

   
   
   
4. Histology continues to be the standard for the definitive diagnosis of ON. Initially after vascular compromise, no histologic changes occur. Then examination of the marrow reveals death of hematopoietic cells, capillary endothelial cells, and lipocytes. Osteocytes shrink to produce the empty lacunae that are characteristic of dead bone. These early necrotic changes are associated with increased interstitial water, which produces a marrow abnormality detectable on MRI.
5. Osseous repair processes represent an integral part of the pathology of ON. Initially, reactive hyperemia and fibrous repair occur in the adjacent bone. New vessels from the adjacent fibrous repair tissue revascularize the leading edge of necrotic bone. Primitive mesenchymal cells, which subsequently differentiate into osteoblasts and osteoclasts, coexist with the new vessels. Appositional bone is deposited on existing dead trabeculae, which creates an osteosclerotic area radiographically. Creeping substitution subsequently removes the necrotic tissue. The histologic appearance in cortical bone is described as cutting cones.
6. The features of ON are a composite of both necrotizing and reparative processes. When resorption progresses faster than formation of new bone, the bone becomes weak. Standard mechanical forces can then fracture the vulnerable bone. On radiographs, the subchondral radiolucent line representing collapsed cancellous trabeculae beneath an intact articular surface is known as the crescent sign. Subsequent segmental collapse of the articular surface, femoral head deformity, and joint incongruity lead to the development of secondary osteoarthritis.

IV. Treatment. The treatment of ON depends on the etiology, stage, and extent of the lesion. In the appropriate patient, avoidance of inciting factors such as steroid therapy, alchohol, and trauma is recommended. For patients with very early disease whose evaluation suggests synovitis, treatment consists of nonsteroidal antiinflammatory medications and resting the affected hip by allowing only toe-touch weight bearing . Osteoporosis may respond to calcium, vitamin D, or antiresorptive therapy (e.g., bisphosphonates or calcitonin). For patients in an early stage of disease (i.e., before subchondral collapse has occurred), core decompression represents the best option for pain relief and prevention of progression to collapse and then to total hip arthroplasty. Core decompression is a surgical procedure in which the surgeon uses a cannulated device or drill to remove a core of bone from the femoral head and neck. Core decompression can help delay total hip arthroplasty significantlyon average, almost 10 years for patients with symptoms and normal radiographic findings, almost 5 years for patients with early radiographic changes ( cystic and sclerotic lesions), and even 3 years for patients with structural failure of the femoral head (subchondral radiolucency with fracture or deformity of the femoral head). For patients who have progressed to an advanced stage of ON, total hip arthroplasty is the standard treatment.

V. Summary. ON is bone death secondary to circulatory compromise. The exact etiology is unclear, although several theories exist. ON may progress to a loss of bone structural integrity and thus damage the adjacent joint. The diagnosis is based on history and determination of important risk factors, physical examination findings, and radiologic studies, including plain radiographs and MRI. The treatment is based on the stage and extent of disease.

Bibliography

Arlot ME, et al. Bone histology in adults with aseptic necrosis. J Bone Joint Surg 1983;65-A:1319.

Favus MJ, ed. Primer on the metabolic diseases and disorders of mineral metabolism, 3rd ed. Washington, D.C.: American Society for Bone and Mineral Research, 1996.

Jones LC, et al. Coagulopathies associated with osteonecrosis of the femoral head. Presented at the 44th Annual Meeting of the Orthopedic Research Society, March 1619, 1998, New Orleans, LA.

Ohzono K, et al. The fate of nontraumatic avascular necrosis of the femoral head: a radiologic classification to formulate prognosis. Clin Orthop 1992;277:73.

Simon SR, ed. Orthopedic basic science. Rosemont, IL: American Academy of Orthopedic Surgery, 1994;279.

Steinberg ME, Hayken GD, Steinberg DR. A quantitative system for staging avascular necrosis. J Bone Joint Surg 1995;77-B:34.

Urbaniak JR, Jones JP, eds. Osteonecrosis: etiology, diagnosis, and treatment. Rosemont, IL: American Academy of Orthopedic Surgery, 1997.

Books@Ovid
Copyright 2000 by Lippincott Williams & Wilkins
Stephen A. Paget, M.D., Allan Gibofsky, M.D., J.D. and John F. Beary, III, M.D.
Manual of Rheumatology and Outpatient Orthopedic Disorders

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