SYMPOSIUM

REPAIR PROCESSES IN FEMORAL HEAD OSTEONECROSIS: HISTOMORPHOLOGY CORRELATED TO MR-IMAGING

Hanns PLENK Jr, MD¹, Martina GSTETTNER, BSc, Karl GROSSSCHMIDT, PhD, Martin BREITENSEHER, MD², Michael URBAN, MD³, and Siegfried HOFMANN, MD^1,4

1. Bone & Biomaterials Research, Institute for Histology & Embryology, University of Vienna, AUSTRIA;
2. MR-Institute, University Clinic for Radiology, Vienna, AUSTRIA;
3. Institute for Radiology, Danube Hospital, Vienna, AUSTRIA;
4. Department of Orthopaedics, LKH Stolzalpe, AUSTRIA

ABSTRACT (278)

Not only size and position of the necrotic lesion, but also different repair processes affect the clinical course of non-traumatic avascular femoral head osteonecrosis (ON). For the present study, 14 femoral heads had been retrieved at total hip arthroplasty after either core decompression treatment in ARCO-stage II (n=7, after 5 to 63 months), or conservative treatment (n=7, for 2 to 45 months) from 13 male patients (age 25 to 70 years), diagnosed with ARCO-stages II to IV femoral head ON and followed by magnetic resonance tomography (MR) and other imaging. In order to determine repair types, features of coronal MR-images were correlated with light microscopy of corresponding coronal undecalcified sections and microradiographs.

In 5 heads repair of necrotic bone and marrow tissues stayed up to 63 months restricted to the reactive interface, only producing the diagnostic osteosclerotic rim with adjacent hypervascularity (=limited repair). In 5 heads predominant resorption of necrotic bone led within 2 to 50 months to femoral head breakdown (=destructive repair). Core decompression had not always reached the necrotic area, reduced accompanying bone marrow edema and delayed disease progress, but could not improve repair. In 4 heads reparative bone formation had started from subchondral fractures and/or the reactive interface, definitely reducing the size of the necrotic area (=reconstructive repair). In these cases disease progressed slowly up to 45 months, irrespective of treatments, but risk factor elimination seemed beneficial.

While ON with limited repair can be identified, the similar signal changes of destructive and reconstructive repair, particularly in the reactive interface, cannot be distinguished on MR-images alone. New therapeutic concepts should promote reconstructive repair and guide it to sufficient "creeping substitution" of femoral head ON.

Key Words: Femoral head osteonecrosis - Repair processes - MR-imaging - Histomorphology.