Osteonecrosis Of The Hip

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)