Morbidity at bone graft donor sites

The use of rhBMP-2 in interbody fusion cages. Definitive evidence of osteoinduction in humans: a preliminary report

STUDY DESIGN

A prospective randomized controlled human clinical pilot trial.

OBJECTIVES

To determine the feasibility of using rhBMP-2/collagen as a substitute for autogenous bone graft inside interbody fusion cages to achieve arthrodesis in humans.

SUMMARY OF BACKGROUND DATA

Preclinical studies have shown rhBMP-2 to be an effective substitute for autogenous bone graft, but there are no studies to date documenting such efficacy for human spine fusion.

METHODS

Fourteen patients with single-level lumbar degenerative disc disease refractory to nonoperative management were randomized to receive lumbar interbody arthrodesis with a tapered cylindrical threaded fusion cage filled with rhBMP-2/collagen sponge or autogenous iliac crest bone. Patients were evaluated with radiographs, sagittally reformatted computed tomography scans, and Short Form-36 and Oswestry outcome questionnaires.

RESULTS

All 11 patients who received rhBMP-2 were judged by three independent radiologists to have solid fusions (at 6, 12, and 24 months postimplantation), whereas only 2 of the 3 control patients, who received the standard treatment of autogenous iliac crest bone, were deemed to be fused. The Oswestry Disability Questionnaire scores of the rhBMP-2 group improved sooner (after 3 months) than those of the autograft group, with both groups demonstrating similar improvement at 6 months. Short Form 36 scores continued to improve up to 24 months.

CONCLUSION

The arthrodesis was found to occur more reliably in patients treated with rhBMP-2-filled fusion cages than in controls treated with autogenous bone graft, although the sample size was limited. There were no adverse events related to the rhBMP-2 treatment. This study is one of the first to show consistent and unequivocal osteoinduction by a recombinant growth factor in-humans.

Posterolateral and anterior interbody spinal fusion models in the sheep

Posterolateral and anterior interbody spinal arthrodesis is a frequent procedure, but high nonunion rates are reported and harvesting autologous bone graft from the iliac crest significantly increases morbidity. Bone graft substitutes are an alternative, but to date clinical results are not conclusive. Bone substitutes can be organic or inorganic, biologic or synthetic. They can have osteoconductive properties, inductive properties or both. Animal experiments are essential to investigating bone substitutes using biomechanical and histologic methods not available in clinical studies. Few authors reported on instrumented anterior fusion models, but none used the sheep model. In the current study posterolateral and anterior interbody fusion models in sheep are described. Both models used instrumented fusions, applying porous mineral scaffolds, alone or mixed with bone. The surgical techniques are described step-by-step and potential difficulties are highlighted. Preliminary results are reported for the posterolateral fusion model using coralline graft substitutes. The coral granules mixed with locally harvested bone had fusion outcomes similar to pure autologous bone. The graft substitute showed marked resorption between 12 and 20 weeks. All fusions had bone cortex and good trabecular connectivity. Histologic evaluation suggests after 20 weeks nearly the entire surface of the substitute is covered with new bone. Porous mineral bone substitutes mixed with locally harvested autologous bone are thought to be a valid alternative for posterolateral fusions.

Use of allograft bone for posterior spinal fusion in idiopathic scoliosis

Eighty-seven adolescents with idiopathic scoliosis (77 female and 10 male patients) who underwent posterior spinal fusion with instrumentation using only allograft bone for graft material were evaluated retrospectively. The average age at surgery was 14 years 3 months. Each patient had a minimum 2-year followup, with an average of 3 years 5 months followup. The average preoperative curve was 59 degrees thoracic (range, 31 degrees-90 degrees) and 52 degrees lumbar (range, 21 degrees-65 degrees). At followup, the thoracic curve measured an average of 35 degrees and the lumbar curve measured an average of 34 degrees. The average loss of correction from the immediate postoperative period until last followup was 6.5 degrees or 11% in the thoracic curve and 10 degrees or 19% in the lumbar curve. There were seven reoperations; one of these reoperations involved repair of a pseudarthrosis. There was one clinical infection. The typical patient had a 2-ounce allograft at an average cost of $800. The patients' average loss of correction, complication rate, and reoperation rate compare favorably with results reported in other series using autograft bone. The authors of this study showed the ability of allograft bone to produce reliable results with a satisfactory outcome. The potential advantages of using allograft must be weighed against the potential disadvantages before recommending its routine use.

Infected nonunion of the tibia

The treatment of infected nonunited fractures of the tibia using the techniques of Ilizarov was compared with autogenous cancellous bone graft application under a well vascularized soft tissue envelope. There were 10 patients in the Ilizarov group and 17 in the bone graft group. Soft tissue coverage with a free vascularized or a rotational muscle flap was used more frequently among the patients having bone graft (71%) than the Ilizarov group (30%). All 27 patients had bony defects (average, 3.7 cm; range, 1-18 cm). At an average followup of 6 years, 26 patients had a functional limb, and one patient (Ilizarov group) ultimately required a below knee amputation. Three patients in each group required a second plate and bone graft procedure to gain union. Infection persisted in four patients (all in the Ilizarov group). If a well vascularized soft tissue envelope is present (particularly after flap coverage), bone grafting procedures are safe and efficacious. The Ilizarov technique may be best suited for the treatment of very proximal or distal metaphyseal nonunions and nonunions associated with large leg length discrepancies.

Marrow-derived progenitor cell injections enhance new bone formation during distraction

Bilateral femoral distraction was performed in rats to investigate whether injections of marrow-derived mesenchymal progenitor cells could be used to facilitate new bone formation. The cells were isolated from whole marrow of 2-6-month-old Sprague-Dawley rats. One-year-old recipient Sprague-Dawley rats were divided into five experimental groups. Rats in groups I, II, and III received injections of mesenchymal progenitor cells on days 6 (beginning), 12 (middle), and 18 (end of distraction) after surgery, respectively. Those in group IV received injections of serum and carrier gel alone, and those in group V received no injections. Distraction zones were harvested at 36 days and analyzed for new bone volume within the distraction gap by three-dimensional microcomputed tomography. Significant increases in new bone volume were observed for femora injected with marrow-derived progenitor cells compared with contralateral femora and controls (no injection). The timing of the cell injections appeared to have no effect on the experimental outcome. Histologic analyses demonstrated active formation of new trabecular bone with marked osteoblastic activity and osteoid production. No qualitative differences in histologic appearances of new bone among rats in any of the five groups were seen. The results of in vitro lysis assays indicated that donor and recipient rats were not completely syngenic, leaving some doubt as to the reasons for observed increases in new bone formation. Future work will focus on attempting to repeat these experiments in a fully syngenic rat model. This rat distraction model can be used to explore the molecular and cellular behavior of these progenitor cells in a clinically relevant in vivo environment.

Biology of bone grafts

The terminology of bone transplantation is complicated by the various histologic types of bone grafts. A graft moved from one site to another within the same individual is an autograft; the corresponding adjective is autologous or autogenous. An allograft (adjective, allogeneic) is tissue transferred between two genetically different individuals of the same species. A xenograft (adjective, xenogeneic) is tissue from one species implanted into a member of a different species.

Biosynthetic bone grafting

The regeneration of bone remains an elusive yet important goal in the field of orthopaedic surgery. Despite its limitations, autogenous cancellous bone grafting continues to the most effective means by which bone healing is enhanced clinically. Biosynthetic bone grafts currently are being developed as an alternative to autogenous bone grafting. These grafts generally contain one or more of three critical components: (1) osteoprogenitor cells; (2) an osteoconductive matrix; and (3) osteoinductive growth factors. The importance of each of these components based on preclinical data supports their use in biosynthetic bone grafts. The use of growth factors such as bone morphogenetic proteins, transforming growth factor, platelet derived growth factor, and fibroblastic growth factor is reviewed in preclinical long bone defect and spinal fusion models. The use of bone marrow in preclinical and clinical settings is presented with specific emphasis given to the use of bone marrow as a source of osteoprogenitor cells and how the use of these cells can be enhanced with the use of bone morphogenetic protein-2. These data support the concept that although products that contain only one of the three key components of a bone graft may regenerate bone successfully, composites of the three key components will be more successful clinically.

Lumbar spinal fusion using recombinant human bone morphogenetic protein in the canine. A comparison of three dosages and two carriers

STUDY DESIGN

A randomized, prospective and controlled animal study.

OBJECTIVE

To evaluate lumbar spinal fusion using recombinant human bone morphogenetic protein 2 in a canine model.

SUMMARY OF BACKGROUND DATA

Spinal fusion using autogenous bone grafting is associated with donor site morbidity and a nonunion rate of 5% to 35%. The use of recombinant human bone morphogenetic protein 2 as a bone graft substitute would eliminate donor site morbidity and perhaps augment the rate of successful fusion.

METHODS

Mature beagles underwent bilateral paraspinal exposure at L4-L5, followed by transverse process decortication and randomization into one of six groups using differing doses of recombinant human bone morphogenetic protein 2 implanted using either a Type I collagen carrier or a polylactic acid carrier. Two control groups were used: one group without recombinant human bone morphogenetic protein 2 and another group using autogenous rib graft alone.

RESULTS

Groups treated with recombinant human bone morphogenetic protein 2 demonstrated complete fusion in all animals. Animals treated with collagen carrier alone (no recombinant human bone morphogenetic protein 2) demonstrated complete absence of fusion. Successful fusion occurred in one of three canines in the autogenous bone graft group. Fusion masses in the recombinant human bone morphogenetic protein 2 treatment groups were significantly larger in size at 3 months than in the autogenous bone graft group. The collagen carrier was more biocompatible and biodegradable because residual polylactic acid carrier was seen with adjacent multinucleated giant cells. There was no evidence of spinal canal or nerve root encroachment in the recombinant human bone morphogenetic protein 2 treatment groups.

CONCLUSIONS

The use of recombinant human bone morphogenetic protein 2 implanted using a Type I collagen carrier resulted in 100% fusion without adverse effects.

Management of acute odontoid fractures with single-screw anterior fixation

OBJECTIVE

Accepted management strategies for odontoid fractures include external immobilization and surgical stabilization using anterior or posterior approaches. Displaced Type II fractures and rostral Type III fractures are at high risk for nonunion. Anterior fixation of odontoid fractures with a single cortical lag screw is a relatively new technique that combines rigid internal stabilization with preservation of intrinsic C1-C2 motion. We retrospectively reviewed our series of 26 consecutive patients who underwent odontoid screw fixation, to further define the safety and efficacy of the technique.

METHODS

During a 5-year period, 26 patients presented with acute traumatic Type II odontoid fractures. Ten patients were female and 16 were male, with a mean age of 35 years. All patients underwent anterior odontoid screw fixation by the senior surgeon (RWH), within a mean of 3 days after injury. All patients were postoperatively maintained in external orthoses, for a mean of 7.2 weeks, and were monitored with serial clinical and radiographic examinations.

RESULTS

With a mean follow-up period of 30 months, radiographic fusion was documented for 25 of 26 patients (96%). No complications related to the surgical approach were identified, and all patients remained in neurologically stable condition. Two complications (8%) were related to the instrumentation; one patient required external immobilization because of suboptimal screw placement, and one patient required posterior atlantoaxial arthrodesis because of inadequate fracture reduction.

CONCLUSION

Single-screw anterior odontoid fixation was associated with a relatively low complication rate and a high fusion rate in this study. We think that this should be the preferred treatment method for acute Type II odontoid fractures.

Osteoinductive bone graft substitutes for spinal fusion: a basic science summary

An understanding of precise biologic mechanisms at work during spinal fusion healing is just beginning to evolve. Current molecular biology research has shown this process to be multifactorial and extremely complex. With the advent of improved animal models to study the biology of spinal fusion, essential information regarding the basic science behind arthrodesis has advanced knowledge of this process. Moreover, with advances in local gene therapy as well as osteoinductive proteins and osteoinductive carrier matrices, the orthopedic surgeon will soon enter into a new era of biologic manipulation for fusion.

Bone grafting for spinal fusion

At least 250,000 spinal fusions are performed in the United States each year, nearly all requiring implantation of bone graft material. The preferred technique for most of these operations is the transplantation of structured or morcellized autologous corticocancellous bone from the iliac crest. Further, because of the increasing frequency of spinal fusion surgery during the 1990s, arthrodesis of the spine has become the most common reason for autologous bone graft harvest. This article reviews the current clinical status of autogenous bone grafts and alternative materials in spinal fusion surgery.

Enhanced bone regeneration using porcine small intestinal submucosa

Small intestinal submucosa (SIS) is an easily produced material that has been used experimentally for tissue engineering. To evaluate the ability of SIS to facilitate bone growth within a long-bone defect, a segment of the radius was surgically removed in adult, female Sprague-Dawley rats. The defect was either left unfilled or implanted with SIS, demineralized cortical bone (DMCB), or ovalbumin. The defect was evaluated radiographically and histologically after 3, 6, 12, and 24 weeks. Tissue remodeling within the defect was evident by week 3 in SIS- and DMCB-treated rats. Filling was characterized initially by infiltration of mononuclear cells and extracellular material in SIS-implanted rats and multifocal remodeling bone particles and cartilage formation in DMCB-implanted rats. Cartilage was observed as early as 3 weeks and bone as early as 6 weeks in SIS-implanted rats. Filling of the defect arose from multiple foci in DMCB-implanted rats, but was contiguous with and parallel to the ulnar shaft in SIS-implanted rats, suggesting that defect repair by SIS may be conductive rather than inductive. Rats in which the defect was left unfilled demonstrated slow but progressive filling of the defect, characterized by mononuclear cell infiltrates and fibrous extracellular material. In summary, SIS facilitated rapid filling of a long-bone defect. These results suggest that SIS may be useful as a bone repair material.

Use of bone-graft substitutes in distal radius fractures

The development of bone-graft substitutes potentially provides the benefits of bone grafting without the risks of autograft harvest. During the past few years, the US Food and Drug Administration has approved several different types of products. These vary considerably in composition, structural strength, osteoinductive and osteoconductive potential, and mechanisms and rates at which they are resorbed or remodeled. The products now approved for orthopaedic applications in the United States include those based on naturally occurring materials (e.g., demineralized human bone matrix, bovine collagen mineral composites, and processed coralline hydroxyapatite) as well as synthetic materials (e.g., calcium sulfate pellets, bioactive glass, and calcium phosphate cement). Materials in development include variations on available products and a new generation of biologically active materials employing growth factors. Rigorous comparison of the products is difficult, as there are no universally accepted preclinical assays and comparable clinical studies. Despite the limitations of the data now available, controlled studies and anecdotal reports suggest that use of bone-graft substitutes may result in improved treatment outcomes for patients with fractures of the distal radius.

Experimental spinal fusion with use of recombinant human bone morphogenetic protein 2

STUDY DESIGN

Posterolateral lumbar spinal fusion with use of recombinant human bone morphogenetic protein 2 (rhBMP-2) was tested in rabbits by implanting 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 posterolateral spinal fusion in rabbits.

SUMMARY OF BACKGROUND DATA

In animal models, rhBMP-2--impregnated collagen has been successfully used for posterolateral spinal fusion, indicating that it is a potential substitute for the autogenous corticocancellous bone graft currently used most routinely in posterolateral lumbar spinal fusion.

METHODS

Nine rabbits were divided into three equal groups. The bilateral L4-L5 transverse processes were exposed, and collagen strips impregnated with rhBMP-2 (10, 50, or 200 micrograms) were placed on the left transverse processes, and collagen strips alone were inserted on the right. All rabbits were killed 24 weeks after surgery. The implanted sites were assessed for new bone 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 micrograms rhBMP-2). Twelve weeks after implantation, no new bone formation was seen on the right side of all animals. The newly formed bone masses were significantly larger in the 50-microgram and 200-microgram rhBMP-2 groups than in the 10-microgram rhBMP-2 group (P < 0.01), but there was no significant difference between bone formation in the 50-microgram and 200-microgram groups (P = 0.647).

CONCLUSIONS

The rhBMP-2/collagen composite implant was an effective bone graft substitute for achieving posterolateral spinal fusion. When combined with a collagen carrier, the optimal rhBMP-2 dose for achieving posterolateral spinal fusion seemed to be approximately 50 micrograms per segment in rabbits.

Augmentation of distal radius fracture fixation with coralline hydroxyapatite bone graft substitute

We implanted coralline hydroxyapatite bone graft as a substitute for autogenous bone graft to support the reduced articular surface of 21 consecutive patients with distal radius fractures treated with external fixation and K-wires. The purpose of this single-cohort retrospective study was to report the outcomes of treatment with this material, complications associated with its use, and its efficacy in supporting the articular surface reduction. Eighteen patients were available for independent evaluation of motion, subjective outcome analysis, and final radiographic analysis at an average of 35 months after surgery. Wrist motion averaged 90% of the uninjured wrist and grip strength measured 75% of the uninjured side. Results in 17 of the 18 cases were rated as good or excellent by the criteria of Gartland and Werley; 12 by the criteria of Green and O'Brien. Seventeen had good or excellent radiographic results by the modified Lidstrom radiographic scoring system. The average DASH functional/symptom score was 90.3 (maximum, 100). Radiographic parameters were restored to an average of 12 mm radial length, 4 degrees volar tilt, 23 degrees radial inclination, and 0.6 mm positive ulnar variance. Articular reduction was maintained in all patients. A complication related to the use of coral was a 0.5 mm prominence of coralline hydroxyapatite beyond the subchondral line at the radiocarpal joint in 1 patient, which was not present on final radiographs. Coralline hydroxyapatite was effective at maintaining articular surface reduction when used in combination with external fixation and K-wires and had a safety profile comparable to other forms of treatment.

Demineralized bone implants for nonunion fractures, bone cysts, and fibrous lesions

Demineralized bone implants were used to treat eight patients with fracture nonunion, five patients with bone cysts, and eight patients with fibrous lesions. Five of the eight patients with nonunions had had previous unsuccessful attempts at reconstruction. After fixation and implantation with either human or bovine demineralized bone, all eight fractures healed. For those patients with nonunion fractures, mean followup time was 8 years, 5 months, and longest followup was 15 years, 3 months. The cystic lesions in five patients included three typical aneurysmal bone cysts and two recurrent unicameral bone cysts. The aneurysmal bone cysts had excellent healing and bone remodeling. The two unicameral bone cysts were repacked more densely after 1 year and healed. For these patients with bone cysts, the mean followup time was 12 years, 5 months, and longest followup was 15 years, 1 month. The various fibrous lesions in seven of the eight patients were healed within 6 months, with only one requiring repacking. For these patients with fibrous bone lesions, the mean followup time was 9 years, 8 months, and longest followup was 14 years. A biopsy of the lesions in five patients was performed and in two cases showed osteoblasts and new bone around small particles of the implants. These results with long term followup show that allogeneic or xenogeneic demineralized bone implants offer a reasonable alternative for the treatment of typical nonunion fractures, bone cysts, and fibrous lesions of bone.

Characterization of the mechanical and ultrastructural properties of heat-treated cortical bone for use as a bone substitute

Heat-treated bovine cortical bone has been proposed as an alternative to bone grafts and synthetic bone substitutes because it may combine the advantages of allografts (high stiffness and strength) and synthetic materials (abundant supply, reduced risk of rejection and disease transfer). Its mechanical properties and ultrastructure, however, are not well characterized. To address this, we compared the compressive (n = 20, bovine bone) and tensile (n = 26, bovine bone) mechanical properties and the ultrastructure (n = 12, human bone) of intact versus 350 degrees C heat-treated cortical bone. The 350 degrees C heat-treated bone had a mean +/- SD elastic modulus similar to the intact bone for both compression (16.3 +/- 2.2 GPa, pooled; p = 0.68) and tension (16.3 +/- 3.7 GPa, pooled; p = 0.95). It also maintained 63% of the intact strength in compression but only 9% in tension (p < 0.001). Infrared scans and X-ray diffraction patterns showed no differences between the 350 degrees C heat-treated and intact bone but large differences between ashed (700 degrees C) and intact bone. Similarly, heat-treated bone previously has been shown to be biocompatible and osteoconductive. We conclude, therefore, that 350 degrees C heat-treated cortical bone may be an excellent load-bearing bone substitute provided that it is loaded in compression only in vivo and is shown by future work to have acceptable fatigue properties.

Diaphyseal forearm fractures treated with and without bone graft

BACKGROUND

The purpose of this study was to determine whether the acute bone grafting of diaphyseal forearm fractures decreases the incidence of nonunion and reduces the time to union. Although the traditional treatment of comminuted radius and/or ulnar shaft fractures involves bone graft, a recent report called into question this practice.

PATIENTS

A database search was used to identify all acute diaphyseal forearm fractures presenting to an urban Level I trauma center between 1988 and 1996. All radius and/or ulnar shaft fractures, as well as all Monteggia and Galeazzi fracture-dislocations, in patients with closed physes were included. The charts and operative reports were available for 64 diaphyseal forearm fractures in 49 patients. Fifty-six fractures were followed for at least 1 year beyond clinical and radiographic union. The injuries were treated with open reduction and plate fixation by experienced orthopedic traumatologists. All noncomminuted fractures were treated without bone graft. For the comminuted fractures, the decision to use bone graft was left to the discretion of the operating surgeon.

RESULTS

Overall, 55 of 56 fractures (98%) achieved union at a mean of 49 days (range, 19-123 days), with the only nonunion occurring in a patient with a closed, noncomminuted Galeazzi injury. Among the 20 noncomminuted fractures, all of which were treated without bone graft, 19 (95%) achieved union at a mean of 50 days (range, 19-102 days). Among the 36 comminuted fractures, all 25 treated without bone graft achieved fusion at an average of 50 days (range, 20-123 days) and all 11 treated with bone graft achieved union at an average of 45 days (range, 22-67 days). No statistically significant difference in the incidence of nonunion or time to union was noted between fractures that were treated with and without bone graft.

CONCLUSION

Acute bone grafting of diaphyseal forearm fractures did not affect the union rate or the time to union.

Bone graft and bone graft substitutes: a review of current technology and applications

The morbidity associated with autogenous bone graft harvest and the recent concern regarding the transmission of live virus through use of allografts, have been the impetus for research into a variety of materials that could take the place of these standard materials for bone grafting. The positive results reported with various ceramics and/or bone derivatives suggest the possibility of a material with osteoconductive and/or osteoinductive properties for use with or in place of bone graft. This review discusses a variety of bone graft and bone graft substitute materials. Among the osteoconductive materials outlined are the hydroxyapatite and tricalcium phosphate ceramics as well as some reportedly osteoactive polymers. While osteoconduction is a favorable quality, much interest has focussed on the use of osteoinductive or osteogenic materials such as demineralized bone matrix or bone derivatives, that is, BMP, osteogenin, etc. It is increasingly apparent that these materials require a carrier vehicle for optimal expression of osteoactivity. Therefore, the review finishes with a comparison of the various materials suggested for use as carriers.

Knee: role and results of allografts

The vast majority of periprosthetic fractures occur as the result of trauma. There are many predisposing factors for these factors, including osteopenia, neurologic disorders, medications, rheumatoid arthritis, previous arthroplasty, and infection. These same factors also increase the likelihood of fracture comminution, and the presence of poor bone quality makes fixation difficult and prone to failure.

Use of porous hydroxyapatite graft containing recombinant human bone morphogenetic protein-2 for cervical fusion in a caprine model

OBJECT

The efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2) for enhancing anterior cervical spine interbody fusion when added to a porous hydroxyapatite (HA) graft was investigated.

METHODS

Fourteen mature goats underwent three-level anterior discectomies after induction of endotracheal anesthesia. Porous HA grafts that contained 0, 5, and 50 microg of rhBMP-2 were placed concurrently with anterior cervical spine plates to achieve interbody fusion. The fusion rate, radiological findings, biomechanical stiffness, and histological appearance were evaluated in 42 spinal units immediately and again at 4 and 12 weeks after graft and plate placement. At 12 weeks postsurgery, manual testing showed a 100% fusion rate in the spines with HA grafts containing high-dose rhBMP-2; however, only a 50% fusion rate was shown in spines with grafts that contained no or low-dose rhBMP-2. On radiographic and histological studies the process of solid fusion was seen to be more advanced in relation to the use of larger amounts of rhBMP-2. Biomechanical testing demonstrated significantly higher stiffness values for grafts that contained high-dose rhBMP-2 than those without rhBMP-2 in flexion at 4 weeks, as well as in flexion, extension, and lateral bending tests at 12 weeks. Histological analysis demonstrated that rhBMP-2 increased the amount of bone apposition on the surface of the implants and promoted bone formation in the porous structure without increasing the penetration distance.

CONCLUSIONS

Through osteogenesis at the fusion site, the addition of rhBMP-2 to a porous HA ceramic graft enhances the rate of anterior cervical fusion.

The use of recombinant human bone morphogenetic protein 2 (rhBMP-2) to promote spinal fusion in a nonhuman primate anterior interbody fusion model

STUDY DESIGN

A study on the efficacy of recombinant human bone morphogenetic protein 2 (rhBMP-2) in a nonhuman primate anterior interbody fusion model.

OBJECTIVES

To investigate the efficacy of rhBMP-2 with an absorbable collagen sponge carrier to promote spinal fusion in a nonhuman primate anterior interbody fusion model.

SUMMARY OF BACKGROUND DATA

RhBMP-2 is an osteoinductive growth factor capable of inducing new bone formation in vivo. Although dosage studies using rhBMP-2 have been performed on species of lower phylogenetic level, they cannot be extrapolated to the primate. Dosage studies on nonhuman primates are essential before proceeding with human primate application.

METHODS

Six female adult Macaca mulatta (rhesus macaque) monkeys underwent an anterior L7-S1 interbody lumbar fusion. All six sites were assigned randomly to one of two fusion methods: 1) autogenous bone graft within a single freeze-dried smooth cortical dowel allograft cylinder (control) or 2) rhBMP-2-soaked absorbable collagen sponges within a single freeze-dried smooth cortical dowel allograft cylinder also soaked in rhBMP-2. The animals underwent a baseline computed tomography scan followed by 3- and 6-month postoperation scans. Anteroposterior and lateral radiographs of the lumbosacral spine were performed monthly. After the monkeys were killed, the lumbar spine fusion sites were evaluated. Histologic evaluation of all fusion sites was performed.

RESULTS

The three monkeys receiving rhBMP-2-soaked collagen sponges with a freeze-dried allograft demonstrated radiographic signs of fusion as early as 8 weeks. The control animals were slower to reveal new bone formation. The computed tomography scans revealed extensive fusion of the L7-S1 lumbar vertebrae in the group with rhBMP-2. A pseudarthrosis was present in two of the control animals.

CONCLUSIONS

This study was able to document the efficacy of rhBMP-2 with an absorbable collagen sponge carrier and a cortical dowel allograft to promote anterior interbody fusion in a nonhuman primate model at a dose of 0.4 mg per implant site (1.5 mg/mL concentration). The late of new bone formation and fusion with the use of rhBMP-2 and cortical dowel allograft appears to be far superior to that of autogenous cancellous iliac crest graft with cortical dowel allograft.

Bone marrow and recombinant human bone morphogenetic protein-2 in osseous repair

Bone marrow stem cells and recombinant human bone morphogenetic protein-2 each has the capacity to repair osseous defects. Recombinant human bone morphogenetic proteins require the presence of progenitor cells to function. It is hypothesized that a composite graft of recombinant human bone morphogenetic protein-2 and marrow would be synergistic and could result in superior grafting to autogenous bone graft. Syngeneic Lewis rats with a 5-mm critical sized femoral defect were grafted with recombinant human bone morphogenetic protein-2 and marrow, recombinant human bone morphogenetic protein-2, marrow, syngeneic cancellous bone graft, or carrier alone (control). Serial radiographs (3, 6, 9, 12 weeks) and torque testing (12 weeks) were performed. Bone formation and union were determined. The recombinant human bone morphogenetic protein-2 and marrow composite grafts achieved 100% union at 6 weeks. Recombinant human bone morphogenetic protein alone achieved 80% union by week 12. Both groups yielded a higher union rate and superior mechanical properties than did either syngeneic bone graft (38%) or marrow (47%) alone. The superior performance of recombinant human bone morphogenetic protein-2 combined with bone marrow in comparison with each component alone strongly supports a biologic synergism. This experimentation shows the clinical importance of establishing operative site proximity for the osteoinductive factors and responding progenitor cells.

New formulations of demineralized bone matrix as a more effective graft alternative in experimental posterolateral lumbar spine arthrodesis

STUDY DESIGN

A rabbit model of posterolateral intertransverse process spine arthrodesis was used.

OBJECTIVE

To determine the efficacy of two new formulations of demineralized bone matrix.

SUMMARY OF BACKGROUND DATA

The flowable gel form of Grafton (Osteotech, Eatontown, NJ) demineralized bone matrix has been shown to have osteoinductive properties in various models and currently is used clinically as bone graft material in posterolateral lumbar spine arthrodesis. Two new formulations of Grafton, one made of flexible sheets (Flex) and the other made in a malleable consistency (Putty), have improved handling characteristics compared with the gel form.

METHODS

In this study, 108 New Zealand white rabbits underwent bilateral posterolateral intertransverse spine arthrodesis at L5-L6 using autogenous iliac crest bone graft alone (control), one of the new forms of demineralized bone matrix (DBM; made from rabbit bone) alone or in combination with autogenous iliac crest bone. Rabbits were killed 6 weeks after surgery. The lumbar spines were excised, and fusion success or failure was determined by manual palpation and radiography. Specimens also were processed for undecalcified histologic analysis.

RESULTS

Manual palpation of the harvested lumbar spines revealed that the fusion rates of the Flex-DBM/Auto group (9/9, 100%) and Putty-DBM/Auto group (10/10, 100%) were superior (P < 0.01) to those of the Auto/control group (3/9, 33%). As a stand-alone graft substitute, Flex-DBM performed superiorly with a fusion rate of 11/11 (100%) compared with that of Putty-DBM (10/12, 83%) and Gel-DBM (7/12, 58%). The devitalized version of Flex-DBM had a fusion rate of 4/11 (36%), which was comparable with the devitalized Putty-DBM rate of 4/12 (33%). Both were superior (P < 0.05) to the devitalized Gel-DBM rate of 0/12 (0%). More mature fusions with greater amounts of trabecular bone were present radiographically and histologically in rabbits that received all forms of demineralized bone matrix than in those in which autograft was used.

CONCLUSIONS

The new flexible sheet and malleable putty forms of demineralized bone matrix were effective as graft extender and graft enhancer in a model of posterolateral lumbar spine fusion. These newer formulations of Grafton appear to have a greater capacity to form bone than the gel form or autogenous bone graft alone in this model.

Osteogenic protein versus autologous interbody arthrodesis in the sheep thoracic spine. A comparative endoscopic study using the Bagby and Kuslich interbody fusion device

STUDY DESIGN

Using an in vivo interbody arthrodesis model, the efficacy of the Bagby and Kuslich (BAK) device packed with recombinant human osteogenic protein-1 (rhOP-1) was evaluated.

OBJECTIVES

To compare the efficacy of osteogenic protein with that of autograft for interbody arthrodesis, with fusion success based on biomechanical, histologic, and radiographic analyses.

SUMMARY OF BACKGROUND DATA

The use of recombinant human bone morphogenetic proteins (rhBMPs) as osteoinductive bone graft substitutes or expanders has recently gained considerable research interest, particularly when applied in posterolateral arthrodesis. However, whether these results can be extrapolated to a successful interbody spinal arthrodesis remains uncertain.

METHODS

Twelve sheep underwent a multilevel thoracic spinal decompression by thoracoscopic approach. Three noncontiguous destabilization sites (T5-T6, T7-T8, T9-T10) were prepared and randomly treated as follows. Control group treatments were nonsurgical, destabilization alone, and empty BAK. Experimental groups were treated with autograft alone, BAK device packed with autograft, or BAK device packed with rhOP-1. Four months after surgery, interbody fusion status was quantified by biomechanical testing, computed tomography, microradiography, and histomorphometry.

RESULTS

Results of biomechanical analysis showed statistically higher segmental stiffness levels when comparing the control and experimental groups with four of the five testing methods (P < 0.05). Computed tomography and microradiography characterized destabilization alone as producing one fusion in six preparations; the empty BAK, two in six;, autograft alone, four in eight; BAK with autograft, five in eight; and BAK with rhOP-1 group, six in eight-all evidenced by woven trabecular bone spanning the fusion sites. Histomorphometry yielded significantly more trabecular bone formation at the fusion sites in the three experimental groups than in the two control groups (P < 0.05).

CONCLUSIONS

Interbody spinal fusions showing biomechanical and histomorphometric equivalency to autologous fusions have been achieved with rhOP-1. The functional unit stability and histologic osteointegration evidenced by the BAK/rhOP-1 complex shows this interbody arthrodesis technique to be a viable alternative toconventional autologous iliac crest, thereby obviating the need for an iliac crest donor site and associated patient morbidity.

Bone repair techniques, bone graft, and bone graft substitutes

This paper reviews the techniques and materials (bone graft and bone graft substitutes) that currently are used to treat nonunions and bone defects. The techniques reviewed are intramedullary nailing, plating, distraction osteogenesis, and electric stimulation. Bone graft and bone graft substitutes reviewed are as follows: vascularized bone transfers; autogenous bone graft; autogenous bone marrow; dimineralized bone matrix; growth factors; calcium sulphate; calcium phosphates; and allograft. The goal of management of fractures, nonunions, and segmental bony defects, is the return of function as quickly and completely as possible. Techniques and management strategies constantly are evolving to accomplish this goal. This paper reviews the history, indications, and limitations of bone repair techniques, methods of bone grafting, and materials available as bone graft substitutes.

Augmentation of spinal arthrodesis with autologous bone marrow in a rabbit posterolateral spine fusion model

STUDY DESIGN

Posterolateral spinal fusion with autologous bone marrow aspirate in addition to autograft iliac crest bone graft in a rabbit model.

OBJECTIVE

To demonstrate that the addition of autologous bone marrow can have positive effects on bone formation and spinal fusion.

SUMMARY OF BACKGROUND DATA

Bone marrow has been shown to contain osteoprogenitor cells. A number of studies have demonstrated that bone formation is possible with autologous marrow injection into orthotopic sites such as that performed in femur fracture models.

METHODS

A bone paucity model of posterolateral spine fusion was developed. The control animals received 0.8 g of morselized autogenous iliac crest bone graft harvested from a single iliac crest. The graft was mixed with 2 mL of clotted peripheral blood. In the experimental group, 2 mL of bone marrow aspirated from the opposite iliac crest was substituted for the peripheral blood clot. All rabbits were killed at 12 weeks, and the specimens were subjected to evaluation by posteroanterior radiography for the presence of fusion, computed tomography for bone volume, and biomechanical testing for stiffness.

RESULTS

Successful fusion was achieved in 61% of the animals in the experimental group versus 25% in the control group (P < 0.05). The fusion mass in the experimental group had a mean volume of 919 +/- 387 mm3 versus 667 +/- 512 mm3 for the control group, as measured from computed tomography images. The results of the biomechanical testing validated the radiographic scoring system. The stiffness in specimens, graded as having a radiographic score of 4, was significantly greater than in specimens with radiographic scores of 1 and 2.

CONCLUSION

In cases for which an adequate quantity of autogenous bone graft is not available, addition of bone marrow may facilitate greater bone formation and successful fusion.

Segment transport employing intramedullary devices in tibial bone defects following trauma and infection

OBJECTIVES

To compare two different methods of segment transport in posttraumatic and postseptic tibial defects by employing intramedullary tibial nails as the fixation system and to evaluate differences in the complication rate between external fixation and wire towropes as the transport system.

DESIGN

Randomized, prospective, nonblinded study.

SETTING

Level 1 trauma center.

PATIENTS

Thirty patients with posttraumatic or postseptic defects of the tibial shaft were admitted at our center between January 1994 and December 1995. For study purposes, they were divided into two groups with fifteen patients in each.

METHODS

All thirty patients underwent a standardized therapy protocol consisting of three phases: (a) eradication of infection, (b) restoration of soft tissue defects, and (c) bone segment transport. The first two phases were identical for both groups. The third phase was different: in Group A transport of the segment was performed with a combination of intramedullary nail and wire towrope; in Group B the intramedullary nail was combined with an external fixation device. We then evaluated both subjective data (patient comfort, restrictions in physiotherapy) and objective data (mobility of knee and ankle joint, transport time, reoperations, complications) to determine treatment success.

RESULTS

Both methods are useful for segment transport in patients with tibial shaft defects following trauma and infection. The relative transport time was shorter in Group A than in Group B (12.2 versus 13.7 days/centimeter; p = 0.002). Group B also recorded a significantly higher complication rate than did Group A (septic complications, twenty-six versus six events; necessary recorticotomies, four versus zero events).

CONCLUSIONS

An intramedullary nail and wire towrope proves to be a reliable combination for segment transport in tibial defects following trauma and infection and provides a relatively high patient comfort rate and a low complication rate.

The use of coralline hydroxyapatite with bone marrow, autogenous bone graft, or osteoinductive bone protein extract for posterolateral lumbar spine fusion

STUDY DESIGN

A posterolateral lumbar arthrodesis animal model using coralline hydroxyapatite as a bone graft substitute.

OBJECTIVE

To determine the effectiveness of coralline hydroxyapatite as a bone graft substitute for lumbar spine fusion when used with bone marrow, autogenous bone graft, or an osteoinductive bone protein extract.

SUMMARY OF BACKGROUND DATA

Coralline hydroxyapatite is commonly used as a bone graft substitute in metaphysial defects but its use in a more challenging healing environment such as the posterolateral spine remains controversial. There are no published animal studies in which the use of coralline hydroxyapatite has been evaluated in a posterolateral lumbar arthrodesis model.

METHODS

Single-level posterolateral lumbar arthrodesis was performed at L5-L6 in 48 adult New Zealand White rabbits. Rabbits were assigned to one of three groups based on the graft material they received: 3.0 mL coralline hydroxyapatite 1.5 mL plus bone marrow; 1.5 mL coralline hydroxyapatite plus 1.5 mL autogenous iliac crest bone; and, 3.0 mL coralline hydroxyapatite plus 500 micrograms bovine-derived osteoinductive bone protein extract on each side. Rabbits were killed after 2, 5, or 10 weeks, and the spines were excised and evaluated by manual palpation, radiographs, tensile biomechanical testing, and nondecalcified histology.

RESULTS

Fusions were assessed by manual palpation at 5 weeks for comparisons among the three groups of graft materials. The coralline hydroxyapatite used with bone marrow produced no solid fusions (0/14). When combined with an equal amount of autogenous iliac crest bone, coralline hydroxyapatite resulted in solid fusion in 50% (7/14) of the rabbits (P < 0.05). When combined with the osteoinductive growth factor extract, the coralline hydroxyapatite resulted in solid fusion in 100% (11/11) of the rabbits (P < 0.05). The fusion masses in the growth factor group were significantly stronger (1.8 +/- 0.2 vs. 1.3 +/- 0.1; P = 0.02) and stiffer (1.5 +/- 0.2 vs. 1.2 +/- 0.1, P = 0.04) based on tensile testing to failure when normalized to the adjacent unfused level.

CONCLUSION

These data indicate that coralline hydroxyapatite with bone marrow was not an acceptable bone graft substitute for posterolateral spine fusion. When combined with autogenous iliac crest bone graft-coralline hydroxyapatite served as a graft extender yielding results comparable to those obtained with autograft alone. Coralline hydroxyapatite served as an excellent carrier for the bovine osteoinductive bone protein extract yielding superior results to those obtained with autograft or bone marrow.

Modern alternatives and techniques for one-level discectomy and fusion

Monosegmental cervical spondylosis with radiculopathy requiring operative intervention responds well to anterior disc excision and fusion with autograft. However, there is a 20% to 25% morbidity from the donor site. Several new surgical techniques using biomechanical spacers or internal fixation have been developed that can be used with local bone or allograft, thus eliminating donor site morbidity. Surgical outcomes are comparable with those of traditional anterior cervical discectomy and fusion.

Lumbar spine fusion by local gene therapy with a cDNA encoding a novel osteoinductive protein (LMP-1)

STUDY DESIGN

A posterior arthrodesis animal model using local expression of a newly discovered osteoinductive protein delivered in bone marrow cells.

OBJECTIVE

To introduce the concept of local gene therapy and determine its feasibility for achieving lumbar spine fusion using a gene for a novel osteoinductive protein: LIM Mineralization Protein-1 (LMP-1).

SUMMARY OF BACKGROUND DATA

Extensive work is currently underway to improve the healing success and morbidity associated with the gold standard bone-grafting material of autogenous iliac crest. As a result, alternative osteoinductive proteins and new delivery methods warrant investigation. The authors' laboratory recently identified a novel gene that had osteoinductive capacity in vitro and is therefore a candidate for a new in vivo osteoinductive agent.

METHODS

Single-level posterior lumbar and thoracic arthrodesis was attempted in 14 athymic rats. The graft material, which consisted of a devitalized bone matrix (no osteoinductive activity) soaked with 0.75 to 1.5 million bone marrow cells, was inserted with the dorsal spine exposed. In each rat, one site received marrow cells transfected with the cDNA encoding a novel osteoinductive protein. At the other site for a control, the marrow cells were transfected with the reverse copy of the cDNA that did not express any protein. Transfection of marrow cells for 2 hours was accomplished using the mammalian expression vector pCMV2. Rats were killed after 4 weeks, and the spines were evaluated by manual palpation, radiographs, and nondecalcified histology.

RESULTS

In the pivotal experiment, successful spine fusion was obtained in 9/9 (100%) of the sites receiving marrow cells transfected with the active LMP-1 cDNA and in 0/9 (0%) of the sites receiving marrow cells transfected with the reverse (inactive) LMP-1 cDNA. Radiographs and histology confirmed the manual palpation results, demonstrating controlled new bone formation in the carrier and marrow transfected with the active LMP-1 cDNA and essentially no bone induction in the sites treated with marrow cells that did not express the protein.

CONCLUSIONS

These data confirm that local delivery of the novel LMP-1 cDNA using bone marrow cells is feasible in vivo. Furthermore, these results demonstrate that posterior thoracic or lumbar spine fusion can be achieved in rats by local delivery of the LMP-1 cDNA.

In vitro strength comparison of hydroxyapatite cement and polymethylmethacrylate in subchondral defects in caprine femora

Hydroxyapatite cement was investigated in situ for the reconstruction of juxta-articular defects. Polymethylmethacrylate is currently the most commonly used material for the reconstruction of bone defects following the exteriorization and curettage of aggressive benign tumors. In vitro, we compared the effects of hydroxyapatite cement and polymethylmethacrylate in restoring the stiffness of the subchondral plate in a caprine femoral defect model. Ten matched pairs of caprine femora underwent nondestructive compression testing normal to the load-bearing surface. A standardized subchondral defect 12 mm in diameter was created in the medial femoral condyle. Compression testing was repeated to determine the reduction in stiffness caused by the defect. Each femur from each pair was randomly assigned to one of two groups (n=9), and the defects were augmented with either polymethylmethacrylate or hydroxyapatite cement. After 12 hours, compression testing was repeated to determine the subchondral stiffness after augmentation. Compared with intact femora, the defect specimens that were later treated with either polymethylmethacrylate or hydroxyapatite cement exhibited stiffness values of 70 (386+/-107 N/mm) and 59% (343+/-94 N/mm) respectively, which represented a significant reduction in stiffness (p=0.05). Augmentation with polymethylmethacrylate or hydroxyapatite cement restored stiffness by 81 (450+/-111 N/mm) and 71% (413+/-115 N/mm), respectively, of the values of intact specimens. Hydroxyapatite cement restored stiffness significantly (p=0.05) over the stiffness of the nonaugmented defect compared with the stiffness after augmentation with polymethylmethacrylate (p=0.12). Neither polymethylmethacrylate nor hydroxyapatite cement restored stiffness to that of intact femora (p=0.05). In the current detect model, hydroxyapatite cement was comparable with polymethylmethacrylate in restoring subchondral stiffness. Unlike polymethylmethacrylate, however, hydroxyapatite cement has the following advantages: it is osteoconductive, is replaced by host bone, and avoids the potential for thermal necrosis. Hydroxyapatite cement may therefore provide a viable alternative to polymethylmethacrylate for augmentation of juxta-articular and other bone defects.

Optimal selection and preparation of fresh frozen corticocancellous allografts for cervical interbody spinal fusion

STUDY DESIGN

Iliac crest corticocancellous allografts for anterior interbody fusion were harvested from six cadavers. The grafts were cut sequentially from left and right crests and randomly assigned to tricortical or bicortical preparations. Their compression strengths then were determined and compared by matched pair analysis.

OBJECTIVES

To quantify the failure strength of the grafts from different iliac locations and determine the optimal type of preparation of the grafts for anterior interbody fusion.

SUMMARY OF BACKGROUND DATA

Iliac crest corticocancellous autografts and allografts commonly are used for interbody cervical fusions. However, graft strengths for specific sites have not been determined fully.

METHODS

Six paired, fresh frozen, iliac crests were sectioned using a customized miter box into multiple 1-cm-thick grafts 1.5 cm in depth to simulate cervical interbody grafts. The left and right sides of each pair were randomly assigned to tricortical and bicortical preparations. The samples were tested by applying a compressive load to failure using a specialized fixture to simulate vertebral body loading.

RESULTS

The grafts closer to the anterosuperior iliac spine had significantly higher failure loads and failure strengths than those closer to the posterosuperior iliac spine. The strengths of the bicortical grafts were 72 +/- 14% of the strengths of the tricortical grafts (P < 0.001).

CONCLUSIONS

Anterior iliac crest grafts were stronger in compression, even after removal of one cortical surface, than posterior iliac crest grafts.

Combination of bone marrow and TGF-beta1 augment the healing of critical-sized bone defects

A 1.5 cm segmental defect in the radius of rabbits was used to compare healing at sites administered TGF-beta, with or without autologous bone marrow, to autogenous cortical bone graft. The carrier for TGF-beta consisted of tricalcium phosphate (TCP) granules and hetastarch. The efficacy of TGF-beta formulations and bone marrow (BM) was compared to autogenous bone, carrier control, and untreated defect sites. Bone measurements taken at necropsy included the anterior-posterior (AP) diameter and medial to lateral (LAT) diameter of the defect; the AP and LAT diameters of both radii measured 1 cm proximal to the distal epiphysis, and the AP and LAT diameters of the mid-shaft of the femora. The bones from each group were subdivided for either histological evaluation or for mechanical testing. Strength (maximum torque), energy, angle of rotation and stiffness were determined for both the treated and contralateral radii. Results of the radiographic, necropsy, and mechanical data for defects administered 1.0 microgram of TGF-beta1 + BM or autogenous cortical bone were similar and indicated superior healing compared to defects left blank or administered the carrier control with or without bone marrow. Defects administered 1.0 microgram of TGF-beta1 + BM or autogenous cortical bone had high mechanical strength relative to the control groups and were characterized histologically as healed primarily with lamellar bone. The results from the defects left blank or administered carrier control were similar and generally characterized by poor healing or nonunion. This study demonstrated substantial equality of healing between 1.0 microgram of TGF-beta1 + BM and autograft indicating that this formulation could function as a substitute for autologous grafts.

Biologic enhancement of spinal fusion

Scientific advances in the past decade have generated considerable clinical interest in developing biologic tools that may ultimately enhance spinal fusion. This article reviews the current understanding of each of these and other fusion-enhancing tools with particular attention to the results of in vivo animal experimentation and, where available, objective clinical data.

Enhancement of fracture healing with autogenous and allogeneic bone grafts

The factors contributing to a delayed union or nonunion are many. In general they may be divided into three major categories: deficiencies in vascularity and angiogenesis, deficiencies in the robustness of the chondroosseous response, and deficiencies in stability, strain, or physical continuity. Frequently, deficiencies in more than one category are present, thus complicating the approach to therapy. For a bone grafts to enhance fracture healing, it must provide or stimulate that which is deficient. Autogenous fresh cancellous and cortical bone most frequently are used, but other common grafts include allogeneic frozen, freeze dried, or processed allogeneic cortical, corticocancellous and cancellous grafts, and demineralized bone matrix. These grafts have varying capacities to provide active bone formation, to induce bone formation by cells of the surrounding soft tissue, and to serve as a substrate for bone formation. However, the graft cannot exert its biologic activity in isolation, dependent as it is on the surrounding environment for cells to respond to its signals and, in some cases, for blood supply. The mechanical environment of the graft site is also important. Successful graft incorporation requires that an appropriate match must be made between the biologic activity of a bone graft, the condition of the perigraft environment, and the mechanical environment. The task of the clinician who performs a bone grafting procedure for the enhancement of fracture healing is to choose the right graft or combination of grafts for the biologic and mechanical environment into which the graft will be placed.

Proper design of clinical trials for the assessment of bone graft substitutes

To assess the effectiveness and safety of engineered bone graft substitutes proper, clinical trials will need to be performed. Although the randomized placebo controlled prospective clinical trial is the gold standard, clinical trials of this design are difficult to perform in the surgical setting. At this writing, several clinical trials evaluating bone graft materials have been performed, and much was learned toward improving the design of future studies. This article reviews alternatives to the placebo controlled randomized clinical trials in the surgical setting. The importance of long term surveillance is emphasized.

Mesenchymal stem cells in osteobiology and applied bone regeneration

Bone marrow contains a population of rare progenitor cells capable of differentiating into bone, cartilage, muscle, tendon, and other connective tissues. These cells, referred to as MSCs, can be purified and culture expanded from animals and humans. This review summarizes recent experimentation focused on characterizing the cellular aspects of osteogenic differentiation, and exploration of the potential for using autologous stem cell therapy to augment bone repair and regeneration. The authors have completed an array of preclinical studies showing the feasibility and efficacy of MSC based implants to heal large osseous defects. After confirming that syngeneic rat MSCs could heal a critical size segmental defect in the femur, it was established that human MSCs form bone of considerable mechanical integrity when implanted in an osseous defect in an immunocompromised animal. Furthermore, bone repair studies in dogs verify that the technology is transferable to large animals, and that the application of this technology to patients at geographically remote sites is feasible. These studies suggest that by combining MSCs with an appropriate delivery vehicle, it may be possible to offer patients new therapeutic options.

Autologous bone grafting in staged scoliosis surgery. The patient as bone bank

STUDY DESIGN

A prospective clinical study in which autologous rib graft, harvested during the thoracotomy in staged scoliosis correction, is stored within the patient for use during the second stage (posterior intrumentation and fusion).

OBJECTIVE

To determine whether the bone stored by this technique is biologically viable and microbiologically safe.

SUMMARY OF BACKGROUND DATA

To the authors' knowledge, this method of storage of bone has never been described previously.

METHODS

During the first operation, the excised rib was divided into 3-5 cm fragments and stored in a sub-muscular plane adjacent to the posterior elements of the spine before closure. The graft was then retrieved at the second stage. Samples were sent for histologic and microbiologic examination before implantation.

RESULTS

On histologic examination, more than 50% of the osteocytes retained their basophilic staining, indicating that they were viable. In addition, osteoclastic activity was notably absent. There was no significant bacterial contamination of the samples. Clinically, all patients achieved satisfactory bone fusion.

CONCLUSION

Homeostatic equilibrium in humans provides the ideal environment in which bone graft can be stored. There is no increased risk of infection, and the osteogenic potential of the graft is retained.

Maxillary sinus augmentation in the non-human primate: a comparative radiographic and histologic study between recombinant human osteogenic protein-1 and natural bone mineral

The posterior maxilla has traditionally been one of the most difficult areas to successfully place dental implants due to poor bone quality and close approximation to the maxillary sinus. Sinus augmentation procedures have become a viable means of assuring adequate bone for the placement of dental implants in this area. However, with the techniques currently employed, a considerable variation in the quality of bone attained with the sinus augmentation procedure exists. The purpose of this in vivo study was to evaluate the healing response and bone formation stimulated by 3 doses of recombinant human osteogenic protein-1 (rhOP-1), 0.25, 0.6, and 2.5 mg OP-1 per gram of collagen matrix; natural bone mineral; or collagen matrix alone (control) placed in the maxillary sinus of adult chimpanzees. Results were assessed using clinical, histologic, and radiographic techniques. Radiographic analysis of the computed tomography scans taken at 1 week, and 2.5, 4.5, and 6.5 months revealed a more rapid mineralization with the 2.5 mg OP-1/g collagen matrix and natural bone mineral treatment groups. The incremental bone mineral density (BMD) increase for these 2 treatments from 1 week to 2.5 months was over 2.5 times the increase found with the collagen matrix alone; these 2 treatments also had a higher BMD at the most superior slices evaluated when compared to the other 3 groups. Biopsy specimens were taken at 3.5, 5.5, and 7.5 months and for all 5 treatment groups bone formation was observed at all time points in the majority of the specimens. At 7.5 months the 2.5 and 0.6 mg OP-1/g collagen matrix treatment groups had an increase in the percent bone area when compared to the matrix alone control. In conclusion, these results demonstrate that sinus augmentation with natural bone mineral or 2.5 mg OP-1/g collagen matrix induce comparable radiographic and histologic evidence of bone formation and that both of these treatments performed superior to the control group of collagen matrix alone based upon all methods of evaluation.

Use of an osteoinductive biomaterial (rhOP-1) in healing large segmental bone defects

OBJECTIVE

To assess the radiographic, histologic, and mechanical characteristics of new bone formation in large segmental bone defects treated with a new osteoconductive material, recombinant human osteogenic protein-1 (rhOP-1).

DESIGN

In vivo animal study.

INTERVENTION

Sixteen dogs (thirty-two limbs) with an ulna segmental defect (2.5 centimeters) were randomized to three treatment groups: rhOP-1, collagen alone, and no implant.

MAIN OUTCOME MEASUREMENTS

Radiographic evidence of defect healing, mechanical testing (torsional strength) as compared with thirty-one control intact dog ulnas, and histologic analysis.

RESULTS

At twelve weeks, complete radiographic healing was observed in twenty-five of twenty-eight defects (89 percent) treated with rhOP-1. The mechanical strength of the rhOP-1-treated defects at twelve weeks was 65 percent of that of intact ulnas. Histologic analysis revealed that defects treated with rhOP-1 were bridged with lamellar and woven bone that was in continuity with the host bone.

CONCLUSIONS

The results indicate that osteoinductive materials, which have the ability to quickly fill and heal large defects, may have advantages over osteoconductive materials, which are typically used to fill smaller non-load-bearing bone voids.

Postoperative drains at the donor sites of iliac-crest bone grafts. A prospective, randomized study of morbidity at the donor site in patients who had a traumatic injury of the spine

A prospective, randomized study was performed to assess the effectiveness of postoperative closed suction drainage. One hundred and twelve consecutive procedures involving autologous iliac-crest bone graft were performed, from December 29, 1992, to July 1, 1993, following a traumatic injury of the spine in 108 patients. Sixty of the sites from which the bone graft had been obtained were drained with a single large Hemovac device. The drains were maintained for two to five days postoperatively. The remaining fifty-two incisions were closed without a drainage device. All patients were evaluated clinically for problems with wound-healing. The incisions were considered to be healed when they had been asymptomatic for one year. Of eleven patients who had problems with wound-healing, six had been managed with a drain and five had not. The findings of this study do not support the routine use of drainage at the donor sites of iliac-crest bone grafts.

A new modified technique for harvest of calcaneal bone grafts in surgery on the foot and ankle

Reported sites for retrieval of cancellous bone for grafts include the iliac crest, greater trochanter, proximal tibia, and distal tibia. A new lateral technique for retrieval of cancellous bone from the calcaneus is evaluated through anatomic review, quantitative analysis, and retrospective clinical assessment. Of 22 patients managed with this technique over a 2-year period, 17 returned for an evaluation by questionnaire, physical examination, and radiographic follow-up at an average of 7 months after surgery (range, 4-16 months). Complaints/complications were minor: three had minor incisional symptoms, five had medial heel pain (3 caused by plantar fasciitis), and one had unchanged preoperative heel pain secondary to clubfoot deformity. Compared with more extensive bone-grafting procedures, this procedure offers the advantages of bone harvested under local anesthesia using a readily accessible ipsilateral extremity and producing minor complications.

Osseous regeneration in the jaws using demineralized allogenic bone implants

Osseous defects of the jaws following trauma, congenital deformity or pathology may show poor osteogenesis and the affected area may never be completely replaced by bone or will show alveolar height loss. The purpose of the present study was to evaluate the effect of allogenic bone implants (ABI) on the osteogenesis of jaw defects. Fifty-two patients (27 males, 25 females) with cystic lesions of the jaws were randomly divided into two groups: Group A underwent enucleation and packing with adsorbable gelatine sponge. Group B underwent enucleation and grafting with ABI. Both groups were evaluated radiographically. The height of the alveolar process was measured directly on the radiography. The density was measured with a digital densitometer. In Group A, the mandibular height at 6, 12 and 24 months postoperatively was 88%, 80% and 78% of the preoperative heights, respectively. In Group B, the heights were 95%, 93% and 90%, respectively. These differences were significant (P < 0.05-0.01). The density in Group B was significantly greater (P < 0.05-0.01) than in Group A at 6 and 12 months postoperatively. The difference at 24 months was not significant. On the basis of these findings, it can be concluded that ABI grafting of jaw defects enhances osteogenesis and prevents alveolar height loss in the mandible. ABI represent an encouraging alternative to autogenous bone grafting.

Cervical interbody fusion cages. An animal model with and without bone morphogenetic protein

STUDY DESIGN

The Alpine goat model for multilevel anterior cervical discectomy and fusion was used to analyze the use of an intervertebral fusion device to promote an arthrodesis after anterior cervical discectomy. Comparisons were drawn with biomechanical, histologic, and radiographic data.

OBJECTIVES

To analyze the use of an intervertebral fusion device, with and without a bone graft substitute, to promote an arthrodesis anterior cervical discectomy.

SUMMARY OF BACKGROUND DATA

In previous studies, the goat cervical spine has proven to be an excellent model for examining the healing of fusions using bone grafts, instrumentation, or bone substitutes.

METHODS

Three-level anterior cervical dissectomies were performed on 21 mature Alpine goats. Three treatment groups of seven goats each were used. Group I used a standard titanium cervical BAK device filled with autogenous bone graft. Group II used a hydroxyapatite-coated BAK device filled with autogenous bone graft. Group III used a BAK device filled with recombinant human bone morphogenetic protein-2.

RESULTS

Radiographically, no cages became displaced. Lucencies were seen around 3 of the 21 cages in Group 1, 4 cages in Group II, and none in Group III. Fluorochrome analysis revealed that the recombinant human bone morphogenetic protein-2-filled cages had an accelerated rate of bone growth around and through each cage-vertebral body interface at 3 weeks. A successful arthrodesis was also more likely with a recombinant human bone morphogenetic protein-2-filled cage (95%) than the hydroxyapatite-coated (62%) or the standard (48%) cage. Biomechanical stiffness testing did not reveal any statistically significant differences between the three groups. There was a tendency for successfully arthrodesed interspaces to be stiffer than those that were not.

CONCLUSIONS

The use of a threaded intervertebral fusion cage, with or without hydroxyapatite coating, filled with autogenous bone graft provides a fusion rate that is slightly better than those previously reported using autogenous interbody bone grafts with or without plate stabilization. Recombinant human bone morphogenetic protein-2-filled cages resulted in a much higher arthrodesis rate and accelerated bone formation compared with either autogenous bone-filled BAK devices, or autogenous interbody bone grafts with or without plate stabilization.

Bony healing of large cranial and mandibular defects protected from soft-tissue interposition: A comparative study of spontaneous bone regeneration, osteoconduction, and cancellous autografting in dogs

The purpose of this study was to compare spontaneous bone regeneration, osteoconduction, and bone autografting in critical size calvarial and mandibular defects (defects which do not heal spontaneously during the lifetime of the animal) that were protected from soft-tissue interposition. Eighteen adult mongrel dogs underwent osteotomies to create a unilateral 30-mm segmental defect in the midbody of the edentulated right mandible and bilateral 15-mm x 20-mm full-thickness window defects in the parietal bones. The defects were either left empty, implanted with coralline hydroxyapatite (HA) blocks, or autografted with iliac cancellous bone. All defects were protected with a macroporous titanium mesh and the segmental mandibular defects were additionally stabilized by internal plate fixation. Specimens were retrieved after 2 and 4 months and three undecalcified longitudinal central sections including the osteotomy interfaces were prepared from each specimen for histometry and histology. Sections were analyzed for volume fractions of bone, soft tissue, and implant using scanning electron microscopy, backscatter electron imaging and histometric computer software. In the mandibular model, the empty defects exhibited the greatest amount of bone formation after 4 months (47.3 percent), which was greater than the amount of bone in the autografted group (34.8 percent) and significantly greater than the amount of bone within the hydroxyapatite implants (19.0 percent, p < 0.05). In the cranial defects, the autografted specimens demonstrated the greatest volume fraction of bone after 4 months (27.3 percent), which was significantly greater than within both the empty defects (18.2 percent, p < 0.05) and the hydroxyapatite implants (18.2 percent, p < 0.05). New bone formation in the mandibular defects united the cut ends at 4 months regardless of treatment and originated predominantly from the periosteum which remained present only along the alveolar border after surgical closure. In the calvarial defects, periosteum was not preserved and bone regenerated centripetally, originating from the diploë without any evidence of dural osteogenesis. Bone bridging was incomplete in the empty cranial defects at 4 months. In both the mandibular and cranial specimens, new bone at 2 months was a mixture of woven and parallel fibered bone. At 4 months, the new bone had remodeled almost entirely into mature Haversian bone. This study demonstrated a remarkable ability of defect protection with a macroporous protective sheet to facilitate bone regeneration in critical size mandibular and cranial bone defects. When active osteogenic periosteum was present, as in our mandibular model, we concluded that defect protection alone was sufficient to allow for healing even of critical size defects. When periosteum was absent as in our cranial defects, the limited spontaneous bone formation benefited from the added contributions of cancellous grafting and osteoconductive implants, both of which promoted bone bridging across the defects. We suggest that in the future a resorbable macroporous protective sheet would be advantageous in comparison to a titanium mesh to facilitate bone regeneration by preventing soft-tissue prolapse and allowing the migration of mesenchymal cells and the proliferation of blood vessels from the adjacent soft tissues into the bone defect. Finally, this study identified the need to differentiate critical size defects into those with and without defect protection and periosteum.