Jm. Toth et al., EVALUATION OF POROUS BIPHASIC CALCIUM-PHOSPHATE CERAMICS FOR ANTERIORCERVICAL INTERBODY FUSION IN A CAPRINE MODEL, Spine (Philadelphia, Pa. 1976), 20(20), 1995, pp. 2203-2210
Study Design. This study compared the efficacy of characterized 50/50
hydroxyapatite/beta-tricalcium phosphate ceramics of 30%, 50%, and 70%
porosity and autograft to promote interbody spinal fusion at C2-C3 an
d C5-C6 in 24 goats: 12 at 3 months and 12 at 6 months. Objectives. Ra
diographs, histology, dual energy x-ray absorptiometry analysis, and b
iomechanical testing were used to evaluate the ability of the 30%, 50%
, and 70% porous 50/50 hydroxyapatite/beta-tricalcium phosphate cerami
cs and autograft to promote cervical interbody fusion. Summary of Back
ground Data. The conundrum in the use of calcium phosphates for interb
ody fusion is what porosity is most effective to promote ingrowth yet
strong enough to resist compressive stresses found in the spine? It is
known that the ability for bone ingrowth increases and the compressiv
e strength decreases as porosity of the ceramic is increased. Dense ce
ramics remain intact but may be surrounded by fibrous tissue. Porous c
eramics have good ingrowth but may fracture. Methods. Radiographs were
evaluated for fusion Methods. Radiographs were evaluated for fusion a
cid fracture or collapse of the ceramics or autograft. Dual energy x-r
ay absorptiometry was used to evaluate the fusion mass. Treated motion
segments underwent biomechanical testing to quantify the flexibility
of the segment. Undecalcified and decalcified histologic analysis were
performed to evaluate the presence or absence of a bony union. Result
s, Thirty percent, 50%, and 70% porous ceramics had better radiographi
c fusion scores than the autograft at 3 and 6 months. Incidence of cer
amic fracture did not increase with porosity and was equivalent to the
collapse of autograft, although ceramics maintained disc height when
fracture occurred. No statistically significant differences were found
between autograft and the porous ceramics with biomechanical testing
and peri-implant bone mineral density values as measured by dual energ
y x-ray absorptiometry. At 3 months, histologic analysis showed a unio
n rate of 0% for autograft and 30% porous ceramic, 67% for 50% porous
ceramic, and 83% for 70% porous ceramic. At 6 months, the union rate w
as 67% for the 30%, 50% and 70% porous ceramics and 50% for autograft.
Conclusions. Thirty percent, 50%, and 70% porous ceramics performed e
qual to or better than autogenous bone after 3 and 6 months. There may
be promise for the use of 50/50 hydroxyapatite/beta-tricalcium phosph
ate in spine surgery as the need to harvest autograft from the iliac c
rest is obviated, and complications and cost associated with the harve
st are avoided.