IntroductionDespite modern fixation techniques, pseudarthrosis is a major cause of failure in the surgical treatment of idiopathic scoliosis. To avoid this, dorsal spondylodesis requires the use of large quantities of bone graft. Autologous bone graft from spinal process and iliac crest often provides insufficient quantities. In addition, morbidity after harvesting bone from the pelvis is considerable [1,7].Allograft bone from bone banks carries known risks of bacterial contamination and viral transmission [2,5].Because of these problems, there is an increasing interest in biodegradable osteoconductive ceramic bone graft substitutes. These materials must fulfil certain properties [1,13]: compatibility with surrounding tissues, chemical stability in body fluids, compatibility of mechanical and physical properties, ability to be produced in functional shapes and to withstand the sterilization process, reasonable cost of manufacture and reliable quality control.Abstract The aim of this study is to evaluate the ability of β-tricalcium phosphate (TCP) in granular form to achieve dorsal spondylodesis in adolescent idiopathic scoliosis (AIS). Twenty-eight patients underwent surgical correction and were followed up for 13±8 (range 6-33) months. Posterolateral grafting was performed, using either autograft bone mixed with allograft bone (n=19; "bone group") or autograft bone mixed with 25 g TCP (n=9; "TCP group"). Patients were followed by clinical examination, X-rays and computed tomographic (CT) scans to measure bone mineral density. Fusion involved 12±1 (range 10-14) vertebrae. The segments were fused after 6±1 months in both groups according to the radiographs. No pseudarthrosis was observed. Bone mineral density was 430±111 (range 273-629) mg/cm 3 in the TCP group versus 337±134 (range 130-669) mg/cm 3 in the bone group. Resorption of TCP was complete on the radiographs after 8±2 (range 6-10) months. Based upon the results of this small preliminary study, the use of TCP appears to be a valuable alternative to allografts for application in the spine, even when large amounts of bone are needed.

Harvesting autologous bone graft from the iliac crest is associated with considerable secondary morbidity. Bone graft substitutes such as porous ceramics are increasingly used for spinal surgery. This paper presents the results of an animal study in which β-tricalcium phosphate (β-TCP) bone substitutes were used for anterior spinal surgery in sheep and baboons. The presented baboon study also investigated the effect of impregnating the ceramic material with transforming growth factor (TGF). In the first study, using the sheep model, a stand-alone instrumented anterior fusion was performed. The animals were randomized into three treatment groups: autologous bone, β-TCP granules, and sham group. The results were analyzed biomechanically and histologically at three survival intervals: 8, 16 and 32 weeks. An additional animal group was added later, with ceramic pre-filled implants. In the second study, a baboon model was used to assess the osteointegration of a 15-mm-diameter porous β-TCP block into the vertebral body. The experiment was partially motivated by a new surgical procedure proposed for local bone graft harvest. Three treatment groups were used: β-TCP plug, β-TCP plug impregnated with TGF-β3, and a sham group with empty defect. The evaluation for all animals included computer tomograms at 3 and 6 months, as well as histology at 6 months. In the sheep model, the mechanical evaluation failed to demonstrate differences between treatment groups. This was because massive anterior bone bridges formed in almost all the animals, masking the effects of individual treatments. Histologically, β-TCP was shown to be a good osteoconductor. While multiple signs of implant micromotion were documented, pre-filling the cages markedly improved the histological fusion outcomes. In the baboon study, the β-TCP plugs were completely osteointegrated at 6 months. For the group that used ceramic plugs impregnated with TGF-β3, no incremental advantage was seen as a result of this particular application. However, TGF-β3 is a potent growth factor at a very low dose. Not only does it speed up the ceramic material resorption, but it is also responsible for massive regional new bone formation. More experiments are required to better understand the biological effects of this growth factor in relation to bone formation, and to be able to take clinical advantage of them.Keywords Tricalcium phosphate · Bone substitute · Transforming growth factor β · Interbody spinal fusion · Anterior surgery · Sheep · Baboon ORIGINAL ARTICLE Eur Spine J (2001) 10 : S132-S140

The combination of beta-TCP and bone marrow has superior osteopromotive properties to venous blood or concentrated mononuclear cells and can be used effectively as a substitute to iliac crest graft.

Harvesting autologous bone graft from the iliac crest is associated with considerable secondary morbidity. Bone graft substitutes such as porous ceramics are increasingly used for spinal surgery. This paper presents the results of an animal study in which β-tricalcium phosphate (β-TCP) bone substitutes were used for anterior spinal surgery in sheep and baboons. The presented baboon study also investigated the effect of impregnating the ceramic material with transforming growth factor (TGF). In the first study, using the sheep model, a stand-alone instrumented anterior fusion was performed. The animals were randomized into three treatment groups: autologous bone, β-TCP granules, and sham group. The results were analyzed biomechanically and histologically at three survival intervals: 8, 16 and 32 weeks. An additional animal group was added later, with ceramic pre-filled implants. In the second study, a baboon model was used to assess the osteointegration of a 15-mm-diameter porous β-TCP block into the vertebral body. The experiment was partially motivated by a new surgical procedure proposed for local bone graft harvest. Three treatment groups were used: β-TCP plug, β-TCP plug impregnated with TGF-β3, and a sham group with empty defect. The evaluation for all animals included computer tomograms at 3 and 6 months, as well as histology at 6 months. In the sheep model, the mechanical evaluation failed to demonstrate differences between treatment groups. This was because massive anterior bone bridges formed in almost all the animals, masking the effects of individual treatments. Histologically, β-TCP was shown to be a good osteoconductor. While multiple signs of implant micromotion were documented, pre-filling the cages markedly improved the histological fusion outcomes. In the baboon study, the β-TCP plugs were completely osteointegrated at 6 months. For the group that used ceramic plugs impregnated with TGF-β3, no incremental advantage was seen as a result of this particular application. However, TGF-β3 is a potent growth factor at a very low dose. Not only does it speed up the ceramic material resorption, but it is also responsible for massive regional new bone formation. More experiments are required to better understand the biological effects of this growth factor in relation to bone formation, and to be able to take clinical advantage of them.Keywords Tricalcium phosphate · Bone substitute · Transforming growth factor β · Interbody spinal fusion · Anterior surgery · Sheep · Baboon ORIGINAL ARTICLE Eur Spine J (2001) 10 : S132-S140