Hip Avascular necrosis

1-Causes:

-The most common cause is cortico-steroid.

-Then, trauma, alcoholism and sickle cell disease.

- Bilaterality is very common in avascular necrosis, so if you did
 x ray for one hip which revealed avascular necrosis while the other hip appeared normal you must do MRI to the other one to see if there is early avascular necrosis not seen in x ray.


-If x ray revealed presence of bilateral avascular necrosis, no needs to do MRI.


-If coronal T1 is normal, the case is normal

2-X-Ray findings:

-Contour irregularities and fissures.
-Areas of bone sclerosis and porosis.
-Structural collapse.
-Osteo-arthritic changes.

D.D.from osteo-arthrtis:

-No osteophytes.
-No joint space narrowing especially in the superior lateral area of the joint space.
-By using bone scan where in case of avascular necrosis the lesion appears photopenic while in osteo-arthrtis appears hot.

3-CT findings:

 -Contour irregularities and fissures.
-Areas of bone sclerosis and porosis.
-Structural collapse.
-Osteo-arthritic changes.

4-MRI Findings:

-Staging of avascular necrosis

Stage 1: Bone marrow edema + no line.
Patch of low intensity in T1 and high intensity in T2.

Stage 2: Normal marrow + line separating dead from normal bone.
Here the dead and normal bones have the intensity in T1(high)&T2(intermediate) as fat.

Stage 3: If the dead bone becomes as fluid.
Here, the dead bone is hypo intense in T1 and hyper intense in T2.

Stage 4: If the dead bone is sclerotic.
Here, the dead bone is hypo intense in both T1&T2.

5-Factors affecting prognosis of operation:

-The size and location of the lesion will affect the prognosis.
-Lesion<25% of the weight bearing area of the femoral head responds well to core compression.
-Medially and centrally located lesion has a better prognosis.