Superimposition of maximal stress and necrosis areas at the top of the femoral head in hip aseptic osteonecrosis.

INTRODUCTION: Recent reports described possible mechanical factors in the development and aggravation of osteonecrosis of the femoral head (OFH), but these have yet to be confirmed on dedicated mechanical study. We therefore developed a 3D finite element model based on in-vivo data from patients with incipient OFH, with a view to determining whether the necrosis area was superimposed on the maximal stress area on the femoral head. HYPOTHESIS: The location of the necrosis area is determined by stress on the femoral head. MATERIAL AND METHOD: All patients from the rheumatology department with early stage OFH in our center were investigated. Analysis of CT scans showed stress distribution on the head by 3D finite elements models, enabling determination of necrosis volume within the maximal stress area and of the percentage intersection of necrosis within the stress area (%I n/s: necrosis volume in stress area divided by total stress area volume and multiplied by 100) and of stress within the necrosis area (%I s/n: stress volume in necrosis area divided by total necrosis area volume and multiplied by 100). RESULTS: Nineteen of the 161 patients assessed retrospectively for the period between 2006 and 2015 had incipient unilateral OFH, 10 of whom (4 right, 6 left) had CT scans of sufficient quality for inclusion. Mean age was 52 years (range, 37-81 years). Mean maximal stress was 1.63MPa, mean maximal exported stress volume was 2,236.9 mm3 and mean necrosis volume 6,291.1 mm3. Mean %I n/s was 83% and mean %I s/n 35%, with no significant differences according to gender, age, side or stress volume. There was a strong inverse correlation between necrosis volume and %I s/n (R2=-0.92) and a strong direct correlation between exported stress volume and %I s/n (R2=0.55). %I s/n was greater in small necrosis (<7,000mm3). CONCLUSION: OFH seems to develop within the maximal stress area on the femoral head. The present results need confirmation by larger-scale studies. We consider it essential to take account of these mechanical parameters to reduce failure rates in conservative treatment of OFH. LEVEL OF EVIDENCE: IV.

Popliteal artery thrombosis complicating posterior tibial exostosis in a 35-year-old male.

Chronic popliteal artery thrombosis complicating tibial exostosis has never been described as far as we know. Here, we report the case of a 35-year-old male patient complaining of intermittent claudication over the previous 4 months, without history of trauma or hereditary multiple exostoses. Clinical examination found no popliteal or distal pulses. The diagnosis was confirmed based on CT angiography showing distinct blockage of the contrast product over an exostosis on the posterior side of the proximal tibia. Treatment consisted of removing the exostosis and then bypassing the popliteal artery with a reversed autogenous venous graft.