Skeletal fixation of permanent implants by new methods such as fixation by mechanical interlocking of bone with porous prosthetic coatings or chemical bonding with bioactive materials shows growing potential. This paper reports on the resulting skeletal fixation of a combined porous and bioactive material. Metal plugs with a porous metal fiber coating impregnated with hydroxyapatite were implanted for 2, 4, and 12 weeks and were compared to the parent porous, nonbioactive, metal fiber material. Statistical analysis of the interfacial failure shear stress, as obtained by mechanical testing, shows there is a marked influence of hydroxyapatite impregnation on the rate of bone ingrowth and the strength of the interfacial bond the few weeks following surgery. Microscopical examination reveals that the apparent stimulation of bone ingrowth into the surface pores of the implant is the reason for the increased rate of bond formation. The results are of particular clinical interest: with an increased rate of bone ingrowth, weight bearing might be allowed much earlier, thus reducing the recuperation period.
Careful study of 40 cases of osteosarcoma without evidence of multifocal disease, pulmonary metastasis, or history of exposure to predisposing factors has given histologic evidence of microscopic foci of osteosarcoma separate from the primary focus of osteogenic sarcoma. These "skip" lesions are to all pathologic examination completely separate from the primary focus of osteogenic sarcoma. They are more often found proximal to the primary, both intraosseously and transarticularly. Histologically, these "skips" represent areas of osteosarcoma which in many cases are a less-differentiated form of the tumor. The natural history of such tumors with "skips" following ablative surgery is an increased incidence of local recurrence and subsequent pulmonary metastases. Following open biopsy which demonstrated osteosarcoma, a hip disarticulation was performed. At dissection of the specimen, the tumor was found to involve the distal epiphysis and metaphysis and extend proximally to the junction of the distal and middle thirds of the diaphysis. A 1-cm diameter cortical lesion resembling a "blister)' was found at the junction of the proximal and middle thirds of the diaphysis 18 cm above the margin of the primary lesion (Fig. 1A and B). There was no gross or microscopic connection between this and the primary lesion in the distal femur. Histologically, this lesion appeared to be a separate focus of osteogenic sarcoma. Review of the literature at that time revealed several discussions of the entities known as multicentric osteosarcoma and/or metastatic osteosarcoma. 1*69g-11,16
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