The Journal of Bone and Joint Surgery, Vol 76, Issue 2 159-171, Copyright © 1994 by Journal of Bone and Joint Surgery, Inc
The influence of a hydroxyapatite and tricalcium-phosphate coating on bone growth into titanium fiber-metal implants
CL Tisdel, VM Goldberg, JA Parr, JS Bensusan, LS Staikoff and S Stevenson
Department of Orthopaedics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
A study was done in rabbits to determine the effect of a hydroxyapatite and
tricalcium-phosphate coating on bone growth into titanium fiber-metal
implants. Titanium fiber rods with a solid titanium core were implanted
bilaterally into the distal aspect of the femora of fifty-five New Zealand
White rabbits. One rod was uncoated and the other rod was surface-coated
with hydroxyapatite and tricalcium phosphate by the plasma-spray technique.
Thirty-five rabbits were labeled sequentially with fluorochromes; killed at
one, two, three, four, six, twelve, or twenty-four weeks after the
operation; and studied histologically and histomorphometrically. The
implants in the remaining twenty rabbits were subjected to pull-out testing
to determine the shear strength at the implant-bone interface at three,
six, twelve, and twenty-four weeks after the operation. Histomorphometry
revealed significant effects of the hydroxyapatite and tricalcium-phosphate
coating. When whole-group means (which included all time-points) were
compared, it was found that 44 per cent of the perimeter of the
hydroxyapatite and tricalcium-phosphate-coated implants was covered with
bone compared with 12 per cent of the perimeter of the uncoated implants.
The percentage of the internal surface of the implant that was covered with
bone was also significantly higher in the hydroxyapatite and
tricalcium-phosphate-coated implants: 27 per cent of the internal surface
of the coated implants was covered compared with 8 per cent in the uncoated
implants. The amount of bone in the pores of the implants was also higher
in the hydroxyapatite and tricalcium-phosphate-coated implants: 12 per cent
of the available pore space in the hydroxyapatite and
tricalcium-phosphate-coated implants was filled with bone compared with 4
per cent in the uncoated implants. Scanning electron microscopy of the
implants, done in backscatter mode, demonstrated apposition of new bone
directly on the hydroxyapatite and tricalcium-phosphate coating, with
variable degrees (amounts) of hydroxyapatite and tricalcium-phosphate
resorption and new-bone replacement over time. Bone was never directly
apposed to uncoated titanium fiber-metal. The pull-out strength of the
hydroxyapatite and tricalcium-phosphate-coated implants was consistently
greater than that of the uncoated implants, at all time-periods.
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