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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.

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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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Bioglass specimens were implanted in 11 dogs for periods ranging between two and twelve weeks in order to study the short term bonding behaviour of bioglass coated on metal. Metal fibre porous coated specimens without bone growth inducive microlayer were implanted as controls. The conclusions reached pertain to the validity of push out test results, bioglass short term bonding and the effect of the dipping procedure to coat bioglass on metal: 1. It is impossible to compare the bonding effectiveness of bonding materials tested under slightly differing circumstances, and a fortiori at different laboratories, 2. there is no sufficient evidence to establish a difference in bone bonding strength with regard to trabecular bone of bioglass and metal fibre porous coated specimens at 2 and 4 weeks; at 12 weeks, however, a higher interfacial failure shear strength is obtained with the control porous specimens, 3. bone bonding may be hampered by compositional differences arising as a result of the processing of a bioglass on metal coating. Technologically it is, however, possible to exclude this problem.

Forty-five cases of osteosarcoma were studied for transepiphyseal spread of the lesion because of the current interest in local resection and chemotherapy as treatment of this disease. In 17 cases, the epiphyseal plate had closed and all 17 had transepiphyseal extension of the tumor. In 28 cases, the epiphyseal plate was open; 2 1 showed growth or microscopic evidence of transepiphyseal extension of the lesion. The most common method of extension was directly through tile epiphyseal plate along vascular channels, o r less commonly, about the epiphyseal plate beneath the perichondrium and into the epiphysis along the epiphyeal vascular channels. The majority of these extensions were not detectable by either conventional radiography or radioisotope scanning. Local resection with preservation of the epiphysis will, in all likelihood, leave residual disease despite the oft-quoted statement that an open epiphyseal plate is a biologic barrier to the extension of bone tumors.Cancer 41:1526-1537, 1978C osteosarcoma revolves around nonablative surgical resection while relying on adjunctive chemotherapy to suppress or "cure" microresidual disease. T h e justification for such seemingly inadequate surgery has included: better cosmesis, improved function and rehabilitation, ability to maintain one's previous life-style, and in general, to provide better quality of life. 5,10 In this context, preservation of the distal femoral or proximal tibia1 epiphysis is tempting, particularly in light of the commonly held belief that an intact epiphyseal plate is a barrier to sarcomatous spread (Fig. l) Instructor.Accepted for publication July 5, 1977. M A T E R I A L S AND METHODSForty-five cases of osteosarcoma of the distal femur or proximal tibia were available for study. The series was composed of 26 males and 19 females. The average age of the series was 17 (range 8 to 34). Available data included preoperative routine AP and lateral X-rays of the lesion, tomograms, '-Tc or '9Sr bone scan, and regional angiography.The pathologic studies included gross photographs of the bi-valved specimen, specimen X-rays, and celloidin embedded macrosections of the entire lesion. An orthopedic radiologist with no prior knowledge of the point in question (epiphyseal extension) was asked to review the preoperative data and form a n opinion as to involvement of the epiphysis with tumor.The macrosections were carefully studied to determine the incidence and method of transepiphyseal extension of osteosarcoma. Finally, pathologic findings were compared with the radiologists unbiased interpretation of the preoperative studies in attempt to predict transepiphyseal tumor extension. RESULTSOf the 45 cases, 17 had closed epiphyseal plates. I n each of these, direct extension of the tumor was present across the old epiphyseal scar. In 11 of these cases, the epiphyseal scar