Modern bone substitutes with emphasis on calcium phosphate ceramics and osteoinductors

Custom-made Hydroxyapatite Cranioplasty: Radiological and Histological Evidence of Bone-Biomaterial Osteointegration in Five Patients

Custom-made cranial implants facilitate the surgical reconstruction of destructive pathologies of the skull or extensive demolitive skull surgery. Customized cranioplasty allows for an immediate restoration of the functional integrity of the cranial defect (restitutio ad integrum), with excellent functional and esthetic outcome and a quick, safe, and simple procedure. In this context, bioceramics like hydroxyapatite (HA) claim high biocompatibility and bone-binding capability. The osteoconductive properties of the HA have been reported in animal models and humans. The purpose of this study is to demonstrate with radiological and histological examination and how HA prosthesis may integrate after their implantation showing data related to five patients that needed primary HA cranial reconstruction with secondary removal after few years. The histological examination showed neo-formed lamellar/trabecular bone tissue fragments accompanied by the amorphous reticular tissue (HA prosthesis) revealing diffuse ossification sites in all included cases.

Use of "custom made" porous hydroxyapatite implants for cranioplasty: postoperative analysis of complications in 1549 patients

Background:

Cranioplasty is a surgical intervention aimed at reestablishing the integrity of skull defects, and should be considered the conclusion of a surgical act that began with bone flap removal. Autologous bone is still considered the treatment of choice for cranioplasty. An alternative choice is bioceramic porous hydroxyapatite (HA) as it is one of the materials that meets and comes closest to the biomimetic characteristics of bone.

Methods:

The authors analyzed the clinical charts, compiled by the neurosurgeon, of all patients treated with custom-made porous HA devices (Custom Bone Service Fin-Ceramica, Faenza) from which epidemiological and pathological data as well as material-related complications were extrapolated.

Results:

From November 1997 to December 2010, 1549 patients underwent cranioplasty with the implantation of 1608 custom-made porous HA devices. HA was used in 53.8% of patients for decompressive craniectomy after trauma or intracranial hemorrhage, while the remaining cases were for treated for comminuted fracture, cutaneous or osseous resection, cranial malformation, autologous bone reabsorption or infection or rejection of previously implanted material. The incidence of adverse events in patients treated for cranioplasty, as first line treatment was 4.78% (56 events/1171 patients), and 5.02%, (19 events/378 patients) at second line.

Conclusion:

This study demonstrates that HA is a safe and effective material, is well tolerated in both adult and pediatric patients, and meets the requirements necessary to repair craniolacunia.

New approaches in layer by layer synthesis of collagen/hydroxyapatite composite materials

The aim of this work was to increase our understanding of collagen (COLL)/ hydroxyapatite (HA) composite materials; more specifically, we focused on the study of the influence of the precursorconcentrations over the final content of deposited HA. We found that the increase of the precursor concentrations led to better mineralization (on the basis of the content of deposited mineral phase). Regardless of the precursor concentrations, the content of the deposited amount was found to increase with the increase of the number of deposited layers. Quantification of the mineral phase amount was achieved by gravimetric determination. Based on the determined deposition equation the number of layers can be easily determined in order to obtain composite materials with desired content of mineral phase.

[HAC-titanium as an implant for interbody fusion in spinal canal stenosis of the cervical spine. Six-year clinical trial]

A total of 102 patients were operated on in 134 levels because of an isolated spondylotic cervical stenosis in 6 years. A titanium implant coated with hydroxyapatite ceramic (HAC) was inserted. The average age of the patients was 53 years. The final clinical and radiological follow-up was performed after 15 months. The functional outcome was classified as good to excellent (Odoms's score) in 83.8% of the patients. Implant-related complications requiring revision surgery included two dislocated dowels and one vertebral collapse in a bisegmental operation. After 6 weeks beginning of bony growth around the implant was seen in 38% of all inserted titanium cages on roentgenograms. A complete solid bony incorporation was shown in 91.2% of the fused segments after 6 months and in 96% after 12 months or at follow-up, respectively. These results illustrate the efficacy of the easy to handle HAC titanium implant, demonstrating that this technique achieves good clinical outcome with the same complication rate as comparable techniques.

Ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2-loaded porous β-tricalcium phosphate in mice

The present study investigated the ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded porous beta-tricalcium phosphate (beta-TCP) in mice. The porous beta-TCP with 50 microg of rhBMP-2 (n = 25) and porous beta-TCP (control group, n = 25) were implanted into muscle pouches in the right and left thigh of 28-day-old mice (n = 25), respectively. At every time point (3, 7, 14, 21 and 28 days after implantation), five mice were euthanized and the histological examinations of implantation sites were performed. In addition, the alkaline phosphatase (ALP) activity was also quantitatively analyzed. For the rhBMP-2-loaded group, blood vessel formation and immature cartilage was observed within the porous beta-TCP 3 days after implantation. Mature cartilage was observed 7 days after implantation of rhBMP-2-loaded porous beta-TCP. Newly formed woven bone, lamellar bone as well as marrow were observed 14 and 21 days after implantation of the rhBMP-2-loaded porous beta-TCP. Lamellar bone and marrow were observed 28 days after implantation of the rhBMP-2-loaded porous beta-TCP. For the control group, no bone or cartilage was observed at all time points. However, multinucleated giant cells and fibrous tissues were observed in the control group at 7 and 28 days after implantation, respectively. At 21 and 28 days after implantation, porous beta-TCP was observed to fragment indicating early degradation of the porous beta-TCP in both groups. In addition, ALP was observed to be significantly higher in the rhBMP-2-loaded beta-TCP as compared to the control beta-TCP. It was concluded from this study that the rhBMP-2-loaded porous beta-TCP induced blood vessel and ectopic bone formation.

Osteoinduction by a collagen mineral composite combined with isologous bone marrow in a subcutaneous rat model

In a subcutaneous implant rat model, Collagraft alone (n=8), Collagraft plus isologous bone marrow (n=8), and marrow alone (n=8) were evaluated. Twelve rats were euthanized at 11 days and 12 at 21 days. Explants were evaluated histologically for evidence of bone formation, and osteogenic activity was determined by an assay for alkaline phosphatase. Histological bone formation was absent in all groups at 11 days. At 21 days, in the Collagraft alone and bone marrow alone groups, no bone induction was noted. In contrast, 21-day specimens from the Collagraft plus bone marrow group showed newly formed bone. Alkaline phosphatase activity was negligible (<0.05 units/mg) in all 11-day specimens. Activity in Collagraft plus bone marrow specimens at 21 days (0.38 units/mg) was significantly higher than any other group (P<.001 for all comparisons). This study demonstrates that Collagraft plus bone marrow is an osteoinductive matrix.

Size-adjustable titanium plate for reconstruction of the sella turcica. Technical note

A size-adjustable plate constructed of pure titanium is proposed for use in the reconstruction of the sella turcica. The plate is composed of two semicircular pieces that are connected by a hinge located at the top of the plate. Using an applicator, the plate is inserted into the sella turcica in a closed position. The same applicator is then used to open and secure the plate. The titanium causes minimal ferromagnetic artifacts on postoperative magnetic resonance imaging. Preliminary findings indicate a possible clinical use for this plate in the reconstruction of the sella turcica when no suitable piece of bone is available.

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.