Osteonecrosis of the Hip

Osteonecrosis of the Hip is a progressive disease that is a result of a loss of circulation of the femoral head results from numerous potential causes.

Osteonecrosis means “dead bone”, formerly it’s referred to as avascular necrosis, the term hip osteonecrosis is now preferred.

20,000 new cases of osteonecrosis of the hip are diagnosed each year in the United States. 18% of all total hip arthroplasties performed in the United States are done for osteonecrosis.

Osteonecrosis generally affects patients in the age of 30-50 years, male is more affected than females. Bilateral osteonecrosis occurs in 80 % of cases.

Risk Factors

Risk factors of developing osteonecrosis of the hip include:

1. Trauma: Trauma results in damage to the medial femoral circumflex artery which is the main blood supply to the femoral head. This leads to the death of cells within the bony matrix.
2. Corticosteroid use
3. Alcohol abuse
4. Smoking
5. Hemoglobinopathies (e.g., sickle cell anemia)
6. Coagulation disorders
7. Myeloproliferative disorders (Gaucher disease, leukemia)
8. Caisson disease
9. Human immunodeficiency virus infection
10. Pregnancy
11. Systemic lupus erythematosus (SLE)

Other risk factors may cause intravascular coagulation:

• Coagulation of the intraosseous microcirculation results in venous thrombosis.
• This leads to arterial occlusion due to the lack of venous outflow.
• The arterial occlusion causes an increase in pressure within the bone which ultimately leads to decreased blood flow to the femoral head and eventual death of the cells.

Once the cells die, the reparative process begins and results in bony collapse and arthritic changes and collapse.

See Also: Hip Joint Osteoarthritis

Classification

Modified Ficat classification for AVN of hip (Steinberg Classification):

Stage	MRI	Bone Scan	Radiographs	Patient Status
0	Positive	Positive	Negative	Asymptomatic
1	Positive	Positive	Negative	Symptomatic
2	Positive	Positive	Positive – No crescent sign	Symptomatic
3	Positive	Positive	Positive – Crescent sign without flattening	Symptomatic
4	Positive	Positive	Positive – Femoral head flattening	Symptomatic
5	Positive	Positive	Joint narrowing and/or acetabular changes	Symptomatic
6	Positive	Positive	Advanced degenerative changes	Symptomatic

Clinical Evaluation

Avascular necrosis symptoms & signs include:

• Patients are typically asymptomatic in early stage.
• Insidious onset of pain in the anterior region of the hip.
• Pain is increased with stairs, inclines, and impact.

Physical Examination:

It is essential to obtain a full, detailed history pertaining to the symptomatology including onset, location of the pain, duration of symptoms, the characteristics of the pain, alleviating and aggravating symptoms, radiation of symptoms, and timing of symptoms.

Examinaion is normal in early stages, while in late stages, hip movements are restricted (especially internal rotation).

Special hip tests include:

• Log Roll test.
• The Stinchfield test.

See Also: Hip Special Tests

Imaging Evaluation:

Radiography Imaging:

Recommended views include pelvis antero-posterior (AP) and lateral radiographs view (Frog-Leg).

Radiographic changes seen in osteonecrosis depend on the stage of the disease. Plain films may appear normal in the early stages, but changes are noted as the disease progresses, such as increased density or lucency in the femoral head.

Crescent sign is visible on plain films (best seen on frog-leg lateral views).

In the end stages of the osteonecrosis of the hip, femoral head collapse occurs, and severe arthritic changes may be seen on both sides of the joint.

MRI:

MRI is the standard imaging modality when radiographs are negative and osteonecrosis of the hip is suspected, because it has high sensitivity (99%) and specificity (99%).

When plain radiographs show changes in only one joint, MRI of the pelvis is indicated, not only to define clearly the extent of the disease in the symptomatic hip but also to evaluate the asymptomatic hip.

MRI Findings in AVN of hip include:

1. “Double density” appearance which appears dark on the T1 sequence and bright on the T2 sequence. 
2. The presence of a bright signal on the T2 sequence indicates bone marrow edema and is predictive of worsening pain and progression of the disease. 

Bone scanning:

Bone scanning can be useful, especially in assessing the status of multiple joints. The uptake of technetium-99m usually is decreased in the very early stage of disease and is variable or increased at a stage when symptoms occur.

AVN Treatment

Non-operative treatment is indicated in pre-collapse of osteonecrosis of the hip (before crescent sign appearing) which is Ficat stages 0-II.

Bisphosphonate treatment for osteonecrosis of the hip will decrease risk for head collapse.

Surgical treatment for osteonecrosis of the hip depends on these major variables:

1. Head collapse (crescent sign).
2. Age (40 or younger).
3. Etiology (reversible or not): Irreversible etiology may include:
   1. Continued steroid use
   2. Idiopathic
   3. Hypercoagulable state
4. Extent of head involvement (by osteonecrosis): Percent of head involved on AP image multiplied by percent head involved on lateral image (e.g., 50% × 50% = 25% volume head involvement).
   1. A – small lesion: less than 15% head involvement.
   2. B – medium lesion: 15% to 30% head involvement.
   3. C – large lesion: greater than 30% head involvement.

Different conditions of surgical treatment:

1. Younger age patient (< 40 years) and crescent sign: Total Hip Arthroplasty is the recommended treatment.
2. Younger age patient (< 40 years) and NO crescent sign:
   • Core decompression: Stimulates a healing response.
   • Vascularized fibular strut.
   • Curettage of necrotic bone and bone grafting through femoral neck trap door.
   • Rotational proximal femoral osteotomy.
3. Age 40 years or older and medium (B) or large (C) lesion: Total Hip Arthroplasty is the recommended treatment.
4. Older than 40 years and small (A) lesion: Best option is core decompression.

Core decompression indications includes:

• No crescent sign.
• Reversible etiology: Patients on chronic steroids have poor results with core decompression.
• Small head lesion (A lesion): Patients with medium and large head lesions frequently collapse.

Vascularized fibular strut indications includes:

• Medium (B) and large (C) lesions
• No crescent sign (preferred)
• Reversible etiology.

References & More

1. Campbel’s Operative Orthopaedics 12th edition Book.
2. Millers Review of Orthopaedics -7th Edition Book.
3. Matthews AH, Davis DD, Fish MJ, et al. Avascular Necrosis. [Updated 2022 Nov 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537007/
4. Sh, Mohammed & Al-Edanny, & Karbala, & Aledanni, Mohammed & Al-Kidney,. (2012). Non Vascularized Bone Graft versus Core Decompression…. Non Vascularized Bone Graft versus Core Decompression in Treatment of Early Stages of Non Traumatic Hip Osteonecrosis. 5.