The outcome of biphasic calcium phosphate bone substitute in a medial opening wedge high tibial osteotomy.

BACKGROUND: Our objective was to assess clinical and radiological findings following a medial opening wedge high tibial osteotomy using a biphasic calcium phosphate (BCP) synthetic bone substitute, designed as a wedge with two differing zones of density. The in-vivo behaviour of this type of bone substitute over time is currently unknown. HYPOTHESIS: Our hypothesis was that BCP synthetic bone would facilitate bone union and undergo replacement with host bone over the study period. PATIENTS AND METHODS: Fifteen sequential patients were followed prospectively for minimum 4-years post-operatively. All patients were evaluated clinically using patient reported outcome measures and radiologically to evaluate alignment with maintenance of the osteotomy correction, and bone union with expected BCP dissolution. RESULTS: All patients had good clinical scores with no reported complications at 4 years. In all cases there were radiographic findings of bone union with consolidation and no loss of correction. However the graft remained densely radiopaque at final follow-up. DISCUSSIONS: This study demonstrates that a BCP graft in combination with a locking plate for a medial opening wedge HTO allows early weight-bearing, maintains correction and provides good clinical outcomes. Whilst higher densities of BCP are strong, they do not resorb fully, remaining radiographically visible. This may have implications for the performance of a future knee arthroplasty and caution should therefore be taken.

Biphasic calcium phosphates bioceramics (HA/TCP): Concept, physicochemical properties and the impact of standardization of study protocols in biomaterials research.

Biphasic calcium phosphates (BCP) bioceramics have become the materials of choice in various orthopedic and maxillofacial bone repair procedures. One of their main advantages is their biodegradation rate that can be modified by changing the proportional ratio of the composition phases. For enhanced bone tissue regeneration, the bioactivity of BCP should be increased by optimizing their physicochemical properties. To date, the ideal physicochemical properties of BCP for bone applications have not been defined. This is mostly related to lack of standard study protocols in biomaterial science especially with regards to their characterizations and clinical applications. In this paper we provided a review on BCP and their physicochemical properties relevant to clinical applications. In addition, we summarized the available literature on their use in animal models and evaluated the influences of different composition ratios on bone healing. Controversies in literature with regards to ideal composition ratio of BCP have also been discussed in detail. We illustrated the discrepancies in study protocols among researchers in animal studies and emphasized the need to develop and follow a set of generally accepted standardized guidelines. Finally; we provided general recommendations for future pre-clinical studies that allow better standardization of study protocols. This will allow better comparison and contrast of newly developed bone substitute biomaterials that help further progress in the field of biomaterial science.

Anterior cervical fusion with polyetheretherketone (PEEK) cages in the treatment of degenerative disc disease. Preliminary observations in 36 consecutive cases with a minimum 12-month follow-up.

STUDY DESIGN: Retrospective analysis of 36 cases of degenerative disc disease treated by interbody fusion with polyetheretherketone (PEEK) cages. OBJECTIVE: To determine the safety and efficiency of PEEK cages for anterior cervical fusion (ACF). SUMMARY OF BACKGROUND DATA: ACF with autologous bone has been reported since over 50 years ago. The recent development of cages housing materials inducing osteogenesis simplifies the technique of interbody fusion. The main purposes of bone substitutes for ACF are immediate biomechanical support, osteo-integration of the graft, and elimination of local side effects at the donor site. This report shows our results using PEEK cages. MATERIALS AND METHODS: During an 18-month period, 36 consecutive patients had cervical fusions at 43 levels between C3 and C7. All operations involved one or two disc spaces for degenerative disc disease. We implanted all disc spaces with PEEK cages (Stryker Corporation, Kalamazoo, MI) containing granulated coralline hydroxylapatite (Pro-Osteon 200, Interpore Cross International, Irvine, CA) or deantigenated pig bone in a gel solution (Gen-Os, Tecnoss, Torino, Italy). RESULTS: About 97% of patients had a good to excellent outcome; the result in one myelopathic patient was fair. The cervical fusion rate was 16.7% at 3 months, 61.1% at 6 months, and 100% at one year. CONCLUSIONS: PEEK cages appear to be safe and efficient for ACF. In order to confirm our preliminary impressions studies on larger series with long term follow-up are warranted.

Hydroxyapatite implants--a new trend in enucleation and orbital reconstructive surgery.

As treatment modalities evolve in ophthalmology one must assess and re-evaluate current methods of therapy in the care and treatment of the patient facing the loss of an eye. With the advent of Hydroxyapatite Orbital Implants, new challenges face the ophthalmic nurse in caring for the patient undergoing enucleation and reconstructive surgery. Integrated orbital implants are used to replace the volume of the orbit when the eye is removed due to enucleation, evisceration, or as secondary orbital implants. Various materials have been used in the past to replace orbital volume, with the most common being silicone or polymethylmethacrylate. Hydroxyapatite is a new orbital implant material which has unique interconnected porous matrix derived from marine corals with a mineral composition similar to bone. This orbital implant undergoes fibrovascular ingrowth by the patient's own tissue, becoming truly integrated and less likely to reject, migrate or extrude. The hydroxyapatite implant may be inserted with a variety of surgical techniques, all of which are more complex than standard enucleation implant techniques and have special considerations for the ophthalmic registered nurse.

Hydroxyapatite orbital implants: indications for use and nursing considerations.

1. An orbital implant made of coralline hydroxyapatite is available as an enucleation, evisceration, or secondary orbital implant. This material is naturally occurring, nontoxic, nonallergenic, biocompatible, and resistant to infection. 2. Special nursing considerations, beginning with meticulous aseptic technique, are necessitated by the special preparation of the hydroxyapatite sphere for implantation. It is important to assess the patient's understanding of the surgical procedure, postoperative care regimen, and the importance of keeping follow-up appointments. 3. Coralline hydroxyapatite orbital implants undergo fibrovascular ingrowth, making them truly integrated orbital implants. Unique possibilities for prosthetic rehabilitation provide a significant improvement over previously available enucleation implants.

A study on the surface strain distribution on the hydroxyapatite-implanted canine tibia: a preliminary report.

It has been said by many investigators that hydroxyapatite ceramics may be prospective bone substitute materials. Its mechanical brittleness and strength has been the most serious consideration. In the present article a study has been done using animal experiments, the changes of surface strain at the hydroxyapatite implantation site of long-bone when the compressive stress is applied in the direction of long axis, in order to clarify the mechanical behaviors of hydroxyapatite living bone complex. The nonimplanted side was used as the control. Results revealed that the hydroxyapatite living bone complex has been proven to have sufficient flexibility such that it shows no hysteresis in stress versus strain relation up to 200 kg of applied load. The strain distribution pattern on the HA-implanted bone is quite similar to that of the nonimplanted one. This characteristic also suggests that it has normal skeletal function.

[Determination of standards for hydroxyapatite as bone substitute]. / Normbestimmungen für Hydroxylapatit als Knochenersatz.

Hydroxyapatite ceramic for surgical implants is a material that meets the ASTM F 1185-88 standard. A standard defines specifications for the manufacturer, in particular in the area of quality control. A standard like this provides the necessary basis for clinical use, but only the approval of the public health department provides a fully adequate basis for broader application.

Biomechanical optimization of a model particulate composite for orthopaedic applications.

Particulate composites are a potential solution to the need for an injectable, biocompatible, resorbable material that could be used to reinforce fractures and defects in bone and temporarily to stabilize porous ingrowth prostheses. We have developed a model system for producing and testing particulate composites to determine if mechanical properties suitable for orthopaedic applications can be achieved. The experiments used bovine cortical bone and various forms of hydroxyapatite for the particulate phase and a collagen and particulate reinforce gelatin-resorcinol-formaldehyde (G-R-F) adhesive for the matrix phase. Using unconfined compression testing, we measured the effects of variation in particulate type, size, shape, and volume fraction on the material properties of the particulate composites. We found that compressive strengths greater than 10 MPa and compressive moduli greater than 100 MPa could be achieved in this model system. Rough and irregular particulates exhibited higher compressive strengths and moduli than smooth and spherical particulates. Mechanical properties were largely independent of particulate size in the range of 125-850 microns diameter. This model system suggests that, with the development of new biocompatible matrix materials, particulate composites with mechanical properties suitable for orthopaedic applications can be achieved.

Scintigraphic studies to evaluate stability of ceramics (hydroxyapatite) in bone replacement.

In this study, the suitability of a radionuclide bone imaging technique was examined in cases of hydroxyapatite implants for segmental replacements of long bones. The radionuclide bone imaging technique, using [99mTc]MDP was applied to estimate osseous changes at the sites of the hydroxyapatite implants up to 2 yr after their implantation in an animal experimental model. The results were correlated with histological and radiographical findings at the same time. The radionuclide bone imaging with technetium proved to be a useful method to estimate the intensity of osseous changes after bone replacement by a hydroxyapatite implant. It proved to be more sensitive than radiography. The differences in elasticity of the implanted material and adjacent bone may cause an increase of radionuclide uptake at the site of the implant 2 yr after implantation. These osseous changes cannot be detected by standard histological and radiographical methods but could be detected by radionuclide bone imaging. It is submitted that the radionuclide bone imaging is a noninvasive, sensitive, and useful method for the estimation of osseous changes in sites of long term bone implants.

Model system for studying colonization and growth of bacteria on a hydroxyapatite surface.

A model system for the study of bacterial colonization and growth on a hydroxyapatite (HT) surface is described. Hydroxyapatite was crystallized over the surface of porous glass beads. Chemical analysis of the product showed that the ratio of Ca2+/P042- was indistinguishable from that of commercial HT powder. X-ray diffraction analysis supported the conclusion that the product was HT. A system employing [14C]polyethylene glycol, which selectively adsorbs to the glass surface of the beads, was developed to determine the amount of glass surface covered by HT. Over 90% of the glass surface could be covered by our method. The product, HT beads, consisted of approximately 20% (dry weight) HT. The HT beads possess several properties which make them potentially useful for studying microbial adherence, growth, and interactions. These include: (i) chemical similarity to the tooth surface, (ii) large surface area, and (iii) high density. We also describe a method for direct measurement of the microbial mass of cells growing on beads. The method entails immobilizing a sample on a membrane filter (Millipore), staining it with amido black dye, and eluting the dye for spectrophotometric measurement. Streptococcus mutans served as the test organism. For free-growing bacteria the values measured with the filter assay were directly proportional to cell number, with a value of 1 mug of "protein" corresponding to about 1.5 X 10(6) colony-forming units, determined by viable count. For bacteria colonizing the beads, 1 mug of protein corresponded to about 2 X 10(7) colony-forming units on the beads during logarithmic growth. As the culture approached stationary phase, the efficiency of the assay decreased. These data indicate that multiple random samples, taken at a given time, are representative of the entire culture.