Study Design. Posterolateral lumbar spinal fusion with use of recombinant h
uman bone morphogenetic protein 2 (rhBMP-P) was tested in rabbits by implan
ting composites of rhBMP-2 and collagen carrier.
Objectives. To examine the bone-formation-inducing activity of rhBMP-2 and
find the optimal amount of rhBMP to add to a collagen carrier to constitute
bone-formation-inducing implants to be substituted for bone graft in poste
rolateral spinal fusion in rabbits.
Summary of Background Data. In animal models, rhBMP-2-impregnated collagen
has been successfully used for posterolateral spinal fusion, indicating tha
t it is a potential substitute for the autogenous corticocancellous bone gr
aft currently used most routinely in posterolateral lumbar spinal fusion.
Methods. Nine rabbits were divided into three equal groups. The bilateral L
4-L5 transverse processes were exposed, and collagen strips impregnated wit
h rhBMP-2 (10, 50, or 200 mu g) were placed on the left transverse processe
s, and collagen strips alone were inserted on the right. All rabbits were k
illed 24 weeks after surgery. The implanted sites were assessed for new bon
e formation and bony fusion by radiography and histologic examination.
Results. New bone formation was noted in intertransverse spaces on the left
side of all rabbits except one (10 mu g rhBMP-2). Twelve weeks after impla
ntation, no new bone formation was seen on the right side of all animals. T
he newly formed bone masses were significantly larger in the 50-mu g and 20
0-mu g rhBMP-2 groups than in the 10-mu g rhBMP-2 group (P < 0.01), but the
re was no significant difference between bone formation in the 50-mu g and
200-mu g groups (P = 0.647).
Conclusions. The rhBMP-2/collagen composite implant was an effective bone g
raft substitute for achieving posterolateral spinal fusion. When combined w
ith a collagen carrier, the optimal rhBMP-2 dose for achieving posterolater
al spinal fusion seemed to be approximately 50 mu g per segment in rabbits.