Radiographic and pathological stages of the changes at the bone-cement interface: an in-vivo experimental study.

Introduction: Chemical and physical effects of cementation cause radiographic and histological changes at bone-cement interface. These changes can be of interest in the assessment of the residual lesions and subsequent recurrences after local resection and cementation of local aggressive tumours.

Aim: The aim of the study was to evaluate the evolution and determine the stages of the changes that occur at the bone-cement interface after cementation of cavitary lesions.

Material And Methods: We operated on 16 hind legs of 8 sheep (Ovies Aries) under general anaesthesia (Xylasin HCl, Ketamin HCl and Forane). A bone cavity of 12 cm(3) was produced by curettage of the distal femoral condyle and was filled with cement. Control radiographs were taken at 2 days; 3, 6 and 12 weeks, and again at 6 months. One sheep each time was killed after second day and sixth month and two sheep each time after the third, sixth and 12th week and the specimens underwent pathological examination.

Results: After the first 3 weeks, a reactive fibrous membrane was detected on pathological examinations. This membrane consisted of granulation tissue, necrotic bone and bone marrow, which were replaced gradually by fibrous tissue. The radiographic revelation of this fibrous membrane was a radiolucent zone of 0.5-1.5 mm at 3 weeks. A Sclerotic rim appeared around this radiolucent zone at 6 weeks. With new bone formation the fibrous membrane disappeared at 3 months. This was seen on radiographs as the replacement of the radiolucent zone by a sclerotic ring of 0.5-2 mm. This sclerotic ring disappeared at 6 months, when a diffuse sclerosis and cortical bone thickening was detected on radiographs.

Discussion: According to our findings we suggest to consider the pathological processes at the bone-cement interface in 3 phases: (1) Reactive phase (first 3 weeks); (2) Resorption phase (3-6 weeks), and (3) Formation phase (6 weeks to 6 months). We have distinguished five different radiographic stages: Stage 1-Early stage with no apparent zone (first 3 weeks); Stage 2-Radiolucent zone (3-6 weeks); Stage 3-Radiolucent zone with a sclerotic rime (6 weeks to 3 months); Stage 4-sclerotic ring (after 3 months) and Stage 5-Diffuse cortical thickening (after 6 months). Determining the phases of tissue reaction after cementation and its radiographic revelation will ease the diagnosis of residual lesions and subsequent recurrences after local resection and cementation of local aggressive tumors.