Cl. Tisdel et al., THE INFLUENCE OF A HYDROXYAPATITE AND TRICALCIUM-PHOSPHATE COATING ONBONE-GROWTH INTO TITANIUM FIBER-METAL IMPLANTS, Journal of bone and joint surgery. American volume, 76A(2), 1994, pp. 159-171
A study was done in rabbits to determine the effect of a hydroxyapatit
e and tricalcium-phosphate. coating on bone growth into titanium fiber
-metal im plants. Titanium fiber rods with a solid titanium core were
implanted bilaterally into the distal aspect of the femora of fifty-fi
ve New Zealand White rabbits. One rod was uncoated and the other rod w
as 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 t
wenty-four weeks after the operation; and studied histologically and h
istomorphometrically. The implants in the remaining twenty rabbits wer
e subjected to pull-out testing to determine the shear strength at the
implant-bone interface at three, six, twelve, and twenty-four weeks a
fter the operation. Histomorphometry revealed significant effects of t
he hydroxyapatite and tricalcium-phosphate coating. When whole-group m
eans (which included all time-points) were compared, it was found that
44 per cent of the perimeter of the hydroxyapatite and tricalcium-pho
sphate-coated implants was covered with bonecompared with 12 per cent
of the perimeter of the uncoated implants. The percentage of the inter
nal surface of the implant that was covered with bone was also signifi
cantly higher in the hydroxyapatite and tricalcium-phosphate-coated im
plants: 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 hydroxyap
atite and tricalcium-phosphate-coated implants: 12 per cent of the ava
ilable pore space in the hydroxyapatite and tricalcium-phosphate-coate
d implants was filled with bone compared with 4 per cent in the uncoat
ed implants. Scanning electron microscopy of the implants, done in bac
kscatter mode, demonstrated apposition of new bone directly on the hyd
roxyapatite and tricalcium-phosphate coating, with variable degrees (a
mounts) of hydroxyapatite and tricalcium-phosphate resorption and new-
bone replacement over time. Bone was never directly apposed to uncoate
d titanium fiber-metal. The pull-out strength of the hydroxyapatite an
d tricalcium-phosphate-coated implants was consistently greater than t
hat of the uncoated implants, at all time-periods. CLINICAL RELEVANCE:
The growth of bone into porous surfaces is compromised by conditions
encountered in the revision of failed total joint prostheses, by osteo
porosis, or by abnormal osseous anatomy. This study suggests that hydr
oxyapatite and tricalcium-phosphate-coated titanium fiber-metal intram
edullary implants have more rapid and voluminous bone ingrowth than do
uncoated implants. The use of this surface to enhance fixation of the
component in unfavorable clinical circumstances (where the ingrowth o
f bone is compromised) may help to improve the functional outcome of t
otal joint replacements.