The cause of subchondral bone cysts in osteoarthrosis: a finite element analysis.

BACKGROUND

The etiology of subchondral bone cysts in arthrotic joints is unclear.

MATERIALS AND METHODS

We used two-dimensional finite element analysis to evaluate the hypothesis that subchondral bone cysts in the osteoarthrotic hip joint may be the result of microfractures caused by localized cartilage defects or a thinned layer of cartilage. We evaluated the equivalent bone stress (von Mises (VM) stress) in the cancellous bone as an indicator of potential microfractures and further development of cystic lesions.

RESULTS

Cartilage defects induced stress peaks in the subchondral bone. This peak stress distribution corresponded to the clinical observation of development of acetabular and femoral subchondral cysts in a "kissing" position. A femoral subchondral bone cyst induced a stress peak at the corresponding acetabular site, whereas subchondral acetabular cysts did not increase stress in the femoral head. Acetabular cysts showed an increased level of stress at the lateral and medial border of the lesion which was much higher than the stress levels in the femoral head, indicating a tendency to faster growth.

INTERPRETATION

Our study supports the theory that stress-induced bone resorption may cause development of subchondral bone cysts in osteoarthrosis.