osteonecrosis of the femoral head

Osteonecrosis of the femoral head is a disease of impaired osseous blood flow to the femoral head.

Commonly affect people between 30-60 yrs old.

Osteonecrosis as a diagnosis represent 5-12% of all Total hip replacements (THR) performed.

Etiological classification

Mainly can be divided into traumatic and non-traumatic.

Traumatic osteonecrosis

This is associated with mechanical interruption of the circulation to the femoral head.

This could be due to:

Fracture neck of femur. Prevalence range from 15 – 50% depending on the type of fracture. Time until reduction and the accuracy of reduction  plays an important role.

Hip joint dislocation. Incidence range from 10 – 25%. The duration of dislocation affect the increase the chance of osteonecrosis. More than 12 hrs of dislocation double the chance of osteonecrosis.

Non- traumatic osteonecrosis

Several pathologies have been reported to be associated with this type of osteonecrosis.

The main three types are:

Alcohol intake, steroid related (10 – 30%) and idiopathic. Other less common associations are; SLE, vasculitis, hemoglobinopathies, dysbarisms (caisson disease), Gaucher disease, intraosseous lipid deposition, hypersensitivity reactions, Shwartzman reaction, and conditions associated with thromboplastin release including pregnancy, malignant tumors, HIV, Cushing disease and inflammatory bowel disease.

Steroid and osteonecrosis

The dose of corticosteroids necessary to induce osteonecrosis is not known, however it was found that daily intake of more than 20 mg of corticosteroids even for a short duration increases the risk of development of osteonecrosis.

Dose has been expressed as mean daily dose, peak dose, cumulative dose, and duration of exposure. Several studies has been made to test all these factors and it was found that the mean daily or peak dose, rather than the cumulative dose or duration of therapy, appeared to be associated with osteonecrosis.

The risk of osteonecrosis associated with corticosteroids is high in patients undergoing renal transplantation Etiology possibly because of an association of underlying mineralization defects and structural weakening of the cancellous bone. 4 fold increase in the rate of osteonecrosis for every 10 mg per day increase in mean daily dose has been shown in some studies.

Alcohol and osteonecrosis

Excessive alcohol intake has been identified as an etiologic factor in osteonecrosis. In some studies it has been shown consuming more than 400 ml of alcohol per week increase the risk of osteonecrosis by 9 folds.

Hemoglobinopathies and osteonecrosis

The prevalence of osteonecrosis in this population varies from 4% to 20%.

Pathophysiology

How does osteonecrosis occur?? The secret lays in the vulnerable microcirculation of the femoral head.

There are 3 main ways to impair this circulation. First is by direct vascular interruption such as in trauma, second by intravascular occlusion to the blood vessels either by thrombotic occlusion such as in the case of hemoglobinopathies or by fat emboli such as in the case of alcohol or steroids, third is by extravascular compression to the blood vessels such as in the case of intraosseous hypertension due to Cushing syndrome.

The reduction of the blood supply leads to decrease in the delivery of O2 to the osteocytes. Osteocyte necrosis occurs after two to three hours of ischemia, however osteocyte death is only observed histologically after 24-72 hrs. Adipocyte necrosis and necrosis of hematopoietic marrow occur before osteocyte necrosis.

Direct osteocyte death could occur as a result of irradiation and chemotherapy.

Diagnosis

Early diagnosis leads to better outcome.  High index of suspicion is essential. Pain is deep in the groin, this is the commonest symptom, and signs can be unremarkable however pain signs could be like pain with flexion and internal rotation, antalgic gate, decreased range of movement and clicking in the hip at later stages when the fragment is collapsed.

Investigation

Plane radiographs are still the first step in making the diagnosis so anteroposterior and frog lateral of both hips is a useful test. Crescent sign and subchondral cyst formation may present later on in the disease.

MRI is becoming the second standard test for suspicion of osteonecrosis. MRI is 99% sensitive and specific for diagnosing the condition. A single-density line on the T1-weighted image demarcates the normal ischemic bone interface, and a double-density line on the T2-weighted image represents the hypervascular granulation tissue.

Bone scan used to be more commonly used however they are 25%-45%% false negative.

Ct scan can identify collapse of the femoral head however it is less commonly used due to high dose of irradiation.

Other tests such as functional evaluation of bone, which involves direct measurements of marrow pressure, venography, and biopsy, are rarely used.

Differential diagnosis (DDX)

Transient osteoporosis

Classification

The goal of any classification system is to give an idea about the treatment and prognosis.

Ficat originally developed a four-stage classification system based on radiographic changes

Many other classification systems have been described such as Marcus classification and the university of Pennsylvania classification, however Ficat classification remains the most relevant classification with regards to planning treatment. Roughly speaking according to the Ficat classification, osteonecrosis could be divided into pre-collapse (stage I and II Ficat), or post collapse (stage III and IV Ficat).

Treatment

Depending on the stage of osteonecrosis weather it is pre- or post collapse of the femoral head.

Core decompression

This is the commonest operation used to treat early stages (pre-collapse) of osteonecrosis.

Originally this procedure was performed by Ficat to obtain tissue histological specimens to confirm that patients actually had osteonecrosis of the femoral head then he started using this technique as therapeutic procedure since decompression of the femoral head allowed the intraosseous pressure to return to normal and that would restore normal vascular flow and subsequently elevates pain.

Several surgical techniques are used to perform core decompression, such as using single core tract, others make multiple core holes. There is a general agreement that this procedure is done under fluoroscopic guidance allowing anteroposterior and lateral views. The patient is positioned on a traction table. The guide wire should be inserted just proximal to the lesser trochanter to reduce the chance of forming a stressor riser at the femoral neck shaft junction. The guide wire should be aimed at the area of the osteonecrosis.

Postoperative care should include protective weight bearing for minimum of six weeks.

Core decompression seems to be more effective than symptomatic treatment. The best results are achieved when osteonecrosis is diagnosed and treated early.

Good prognosis points are treatment pre-collapse, treating smaller lesion and when there is a sclerotic rim.

Free vascularized fibular graft

This technique hasn’t shown any significant advantage over simple core decompression.

The rationale for management of osteonecrosis of the femoral head with a free vascularized fibular graft is based on five principles: decompression of the femoral head, removal of the necrotic bone, replacement with fresh autogenous cancellous bone, support of the subchondral bone with a viable strong bone strut, and revascularization and osteogenesis of the femoral head.

Free vascularized fibular graft is regarded as a major procedure with significant tissue dissection and relatively high complication rate to the donor site as well as to the proximal femur. Furthermore the effect on the potential future total hip replacement is unknown.

Post operatively the patient should be non-weight bearing on the leg for minimum of six weeks followed by another six weeks of protective weight bearing.

Osteotomies

There are several types of osteotomies have been described. The aim of performing an osteotomy is based on the biomechanical effect of removing the necrotic part of the femoral head from the weight-bearing area of the hip joint.

Osteotomies are not widely used to treat osteonecrosis of the femoral head because the outcomes have been variable and it is difficult to convert failed cases to a total hip replacement due to the significant alteration to the shape of the proximal femur.

Non-vascularized bone graft

This could be either a structural core graft through the lateral cortex similar entry to the vascularized bone graft, a graft through a window in the femoral neck or a trap door grafting technique where a bone graft is inserted through an opening made in the cartilage of the head by creating a flap then removing the necrotic bone, bone graft then reinserting the flap back where it belong.

There is no consensus regarding the indications for non-vascularized bone grafting. Proponents of these procedures recommend them for hips with <2 mm of femoral head depression or those in which core decompression has failed and there is no acetabular involvement. The procedures that utilize either a window in the femoral neck or elevation of a flap of cartilage require extensive surgical dissection.

Hemi- resurfacing arthroplasty

This technique maybe useful in young patients with pre-collapse extensive osteonecrosis of the femoral head, or with head collapse without acetabular involvement.

Advantages of this procedure include: The damaged cartilage on the femoral head is removed, femoral head and neck bone stock is preserved and revision to a subsequent total hip arthroplasty is not complicated. However, this procedure fell out of favor as a result of the advances in total hip arthroplasty that increased longevity and durability. Patient should be warned that the pain relief might not be as good as the results with total hip arthroplasty.

Total hip arthroplasty

This procedure is the single treatment with the highest likelihood of providing excellent early pain relief and a good functional outcome. The main indications for total hip arthroplasty are: osteonecrosis of the femoral head and associated advanced secondary degenerative arthritis and an older or low demand patient with extensive involvement or collapse of the femoral head as well as sufficient symptoms to justify total hip arthroplasty. The main contraindications are young patients with early- stage osteonecrosis of the femoral head for whom treatment options that save the femoral head are available and patients at excessively high risk for complications of total hip arthroplasty.

The over all treatment goals are to achieve pain relief with patient own joint for as long as possible. Simply for early stages (pre-collapse) the best treatment option is to do core decompression unless there is extensive involvement of the femoral head >30% where the success of core decompression is less likely, then arthroplasty is considered to have better results. In late stages (post collapse) the best option of treatment is total hip replacement.

Osteonecrosis of the femoral head remain a difficult condition to treat because of lack of full understanding of the cause of the condition and because it affect relatively young patients.