| ABSTRACT: |
STUDY DESIGN. Twenty sheep underwent anterior
lumbar interbody fusions with either a threaded titanium interbody fusion
device (cage, n = 8), autogenous iliac crest dowel graft (autograft, n =
6), or interbody decortication only (sham, n = 6). Two sheep had misplaced
cages and were excluded. Sheep were killed after 6 months. OBJECTIVES. To
determine whether this model is useful for examining the distractive and
fixation properties of interbody fusion cages. SUMMARY OF BACKGROUND DATA.
Interbody fusion cages are used in anterior lumbar interbody fusion procedures
to provide immediate intersegmental fixation and to distract and preserve
interbody height. The process of physiologic anchorage by bone ingrowth
into such devices is under investigation. METHODS. Sheep were radiographed
immediately after surgery and 2, 4, and 6 months after surgery. Interbody
distraction and angulation were measured with a digital photo image analyzer
at each time point. After the sheep were killed, stiffness to flexion, extension,
and lateral bending moments were measured. Twelve untreated cadaver spines
were also tested for comparison. RESULTS. After surgery, interbody distraction
successfully occurred in cage and autograft-implanted sites. Loss of interbody
height ensued, however, in all groups during the first 2 months. Percentage
loss of height was lowest in cage sites. By 6 months, only cage sites remained
distracted beyond normal. Fusions in all groups were stiffer than untreated
spines. Autograft sites were stiffer than cage sites to lateral bending.
Sham sites were stiffer than cage and autograft sites to flexion, but this
likely resulted from complete intervertebral collapse. CONCLUSION. Despite
early subsidence, interbody fusion cages successfully distracted and preserved
interbody spaces. This model is useful for investigating methods of improving
distraction and stabilization. |