The Journal of Bone and Joint Surgery, Vol 73, Issue 1 115-123, Copyright © 1991 by Journal of Bone and Joint Surgery, Inc
The effect of a stiff spinal implant on the bone-mineral content of the lumbar spine in dogs
KR Smith, TR Hunt, MA Asher, HC Anderson, WL Carson and RG Robinson
Department of Pathology, University of Kansas Medical Center, Kansas City 66103.
The response of canine lumbar vertebral bone to the application of a stiff
transpedicular screw-plate implant from the third to the fifth lumbar
vertebra, without arthrodesis, was investigated. Five groups of six dogs
each were studied: dogs that had not had an operation (control group); dogs
that had had a sham operation, with survival periods of three and six
months; and dogs that had received an implant, with survival periods of
three and six months. The results were the same in specimens from the
control group and the group that had had a sham operation. In the groups
that had received an implant, dual-photon absorptiometry revealed an
insignificant decrease in bone-mineral content at the bypassed fourth
lumbar segment (17 per cent at three months and 12 per cent at six months).
When the data for the three and six-month intervals were pooled, the mean
decrease in bone-mineral content of 14 per cent was significant.
Histomorphic study yielded similar results; the mean decrease in
bone-mineral content for the pooled three and six-month specimens was
significant (16 per cent). Losses were similar for the ventral and dorsal
columns. Histomorphometric analysis also showed a significant (13 per cent)
loss of bone-mineral content at the adjacent caudad (sixth lumbar) vertebra
for the pooled three and six-month groups. The results of the methods of
analysis of loss of bone-mineral content correlated strongly. Under these
experimental conditions, a stiff spinal implant caused loss of bone-mineral
content of the bypassed vertebral segment, although the loss was less than
anticipated and did not increase between three and six months.