OrthoNet

Osteonecrosis of the Hip

- often in young patients (30-50)
- natural history (we think) is that of progressive collapse (in 80%)
- higher failure rate in these young patients with this diagnosis, even when accounting for age and activity level;
? necrotic bone with altered remodeling?
- pathophysiology is not well understood. Four hypothesis exist - none are particularly solid:
1. Direct cellular mechanisms - death of osteocytes
2. Extraosseous arterial mechanisms - reduction in blood flow to the head
3. Extraosseous venous mechanisms - venous stasis
4. Intraosseous extravascular mechanisms - inflammatory marrow edema
- in truth, the disease is probably multifactorial, and there is a concept of “multiple hits” of multiple insults, superimposed on what might be a genetic susceptibility.

Classification - Ficat Classification - University of Pennsylvania
0 - asymptomatic, normal x-rays - abnormal MRI 0 - asymptomatic, normal x-rays, abnormal MRI
I - normal x-rays I - normal x-rays
II - sclerosis or cystic lesions II - sclerosis or cystic lesions
III - crescent sign with subchondral collapse III - cresent sign only
IV - osteoarthrosis IV - subchondral collapse
V - early arthritis
VI - late arthritis * A, B, C depending on size of lesion
(For any given stage)

Head Preserving Treatment:

Core Decompression
- good results in Ficat I and II; moderate in Ficat III (47% survival)
- probably best for Ficat I and II, small, central lesions in young, non-obese patient not on steroids
- success rate is closer to 20% in post-collapse

Osteotomy
- to move the diseased part of the head into a less weightbearing area
- critical size is 30% or 200o combined necrotic arc angle on AP and lateral - beyond this, don’t try osteotomy!
- probably effective only for Ficat I and II, and very early stage III hips.

Nonvascularized Grafting
- structural grafting through the core decompression track
- cancellous and cortical grafting through femoral neck and head
- osteochondral grafting

Vascularized Grafting
- decompresses the femoral head, provides structural support, removes dead bone, increases vascularization, and provides additional cancellous bone
- in general, best for young patients with early disease (like all the rest)
- patients over 55 are not candidates, as are patients on continued corticosteroids
- still has somewhat limited results in hips with more than 30% head involvement

* in general - when the lesion is >200o combined necrotic angle or greater than 30% head involvement, the head preserving techniques have not been very successful (including vascularized grafting)