The effects of EHDP on regenerating trabecular bone using in vivo microscopic, light and electron microscopic, and electron microprobe techniques.

Metallic chambers were implanted into the proximal tibiae of rabbits to permit microscopic examination of living bone in situ. The bone repair process secondary to the injury produced during installation of the chamber, was visualized. Six to 8 weeks after implantation, osteoid and/or bone could be seen. The effects of various doses of disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP) on the repair and regeneration processes following chamber implantation were studied. Data from various techniques indicated that: (1) following low dose EHDP (0.25 mg/kg/day) chambers contained bone tissue morphologically and ultrastructurally indistinguishable from controls; and (2) with higher doses of EHDP (2.5 or 10 mg/kg/day) chamber contained spicules of normal osteoid, osteoblasts and osteocytes, but were devoid of osteoclasts. The effects of the various regimes of EHDP also were assessed on regenerated, trabecular bone contained within the tibia chambers three months after implantation of the chambers. Data from various methods of analysis supported the following conclusions: (1) the low dose of EHDP (0.25 mg/kg/day) had no toxic effects on the trabecular bone within the chambers but there appeared to be an increase in bone formation as compared to saline control; (2) higher doses of EHDP (2.5 or 10mg/kg/day) were not toxic to bone cells but thick osteoid seams formed on the trabecular bone within the chambers. No osteoclasts were found associated with the bone apparently due to the coverage of bone surfaces by osteoid seams; and (3) osteoid which accumulated after EHDP treatment of 2.5 mg/kg/day for 2 months remained uncalcified for as long as 2 months following withdrawal of EHDP administration. The results showed the value of tibial chamber for examining microscopically living bone in situ and demonstrated the inhibitory effect of EHDP on mineralization of newly formed osteoid and a lack of effect on bone cells.