Hydroxyapatite cement. I. Basic chemistry and histologic properties

The fate of porous hydroxyapatite granules used in facial skeletal augmentation

Facial appearance is largely determined by the morphology of the underlying skeleton. Hydroxyapatite is one of several materials available to enhance projection of the facial skeleton. This study evaluated the long-term maintenance of augmented bony projection when porous hydroxyapatite granules are used on the facial skeleton. Ten female patients aged 28–58 years were studied following aesthetic augmentation of the facial skeleton at 24 sites using porous hydroxyapatite granules. Postoperative CT scans at 3 months served as the baseline measurement and compared with scans taken at 1 and 2 years, with the thickness of the hydroxyapatite measured in axial and coronal planes. Thickness of original bone plus overlay of hydroxyapatite, thickness of the overlying soft tissue, and the overall projection (bone plus soft tissue) were recorded. It was found that 99.7% of the hydroxyapatite was maintained at 2 years, with no statistical difference (t test) from the baseline measurement. The overall projection (bony and soft tissue) was maintained as there was no evidence of native bone resorption or soft tissue atrophy. Radiographic results confirmed that the use of porous hydroxyapatite granules for enhancement of the facial skeleton is not only a predictable procedure, but maintains full bony projection at 2 years.

Office-based injection laryngoplasty in the irradiated larynx

OBJECTIVES/HYPOTHESIS

To review the clinical results of office-based injection laryngoplasty with two different therapeutic materials in patients with vocal fold paralysis and history of radiation therapy to the larynx.

STUDY DESIGN

Retrospective study.

METHODS

Chart review of 11 patients who underwent office-based injection laryngoplasty with calcium hydroxylapatite or micronized Alloderm. All patients had a history of radiation therapy to the neck, with the larynx included in the radiation field. Voice analyses, clinical outcomes, and complications were reviewed. Efficacy of the procedure was evaluated by comparing pre- and postinjection mean phonation time (MPT) results from voice analysis data.

RESULTS

A total of 15 injections were performed in 11 patients with vocal fold paralysis (one females, 10 males, mean age 62 years). Data from voice analyses before and after the procedure were available for nine injections. The MPT was significantly increased among patients undergoing the procedure (P < .05). All procedures were successful, and only one self-limited complication was reported.

CONCLUSIONS

Office-based injection laryngoplasty is a safe procedure with acceptable clinical results in patients with vocal fold paralysis who have a history of radiation therapy to the larynx.

Bioceramics of calcium orthophosphates

A strong interest in use of ceramics for biomedical applications appeared in the late 1960's. Used initially as alternatives to metals in order to increase a biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics, bioactive (or surface reactive) and bioresorbable ones. Furthermore, any type of bioceramics could be porous to provide tissue ingrowth. This review is devoted to bioceramics prepared from calcium orthophosphates, which belong to the categories of bioresorbable and bioactive compounds. During the past 30-40 years, there have been a number of major advances in this field. Namely, after the initial work on development of bioceramics that was tolerated in the physiological environment, emphasis was shifted towards the use of bioceramics that interacted with bones by forming a direct chemical bond. By the structural and compositional control, it became possible to choose whether the bioceramics of calcium orthophosphates was biologically stable once incorporated within the skeletal structure or whether it was resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics, which is able to regenerate bone tissues, has been developed. Current biomedical applications of calcium orthophosphate bioceramics include replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Potential future applications of calcium orthophosphate bioceramics will include drug-delivery systems, as well as they will become effective carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

Calcium hydroxylapatite injection laryngoplasty for the treatment of presbylaryngis: long-term results

OBJECTIVES/HYPOTHESIS

Presbylaryngis is a normal part of the aging process, but many people visit hospitals with communication difficulties. The authors evaluated the efficacy of calcium hydroxylapatite (CaHA) injection laryngoplasty in patients with presbylaryngis.

STUDY DESIGN

Retrospective review.

METHODS

Thirty-three patients with diagnosed presbylaryngis were administered a CaHA injection, and 17 of these patients without other vocal pathologies were included in the analysis. All 17 were male (mean age 65.9 years), mean follow-up duration was 335 days, and all injections were performed through the cricothyroid membrane under local anesthesia in a clinic.

RESULTS

Subjective ratings, perceptual ratings, maximum phonation time, and closed quotients significantly improved after injection, and these improvements persisted without significant change for over 12 months. No major complications were encountered except for transient hematoma, pain, and a foreign body sensation.

CONCLUSIONS

The authors conclude that CaHA injection laryngoplasty offers an effective and safe means of treating presbylaryngis.

The use of Straumann Bone Ceramic in a maxillary sinus floor elevation procedure: a clinical, radiological, histological and histomorphometric evaluation with a 6-month healing period

OBJECTIVES

In this study, we evaluated the quality and quantity of bone formation in maxillary sinus floor elevation procedure using a new fully synthetic biphasic calcium phosphate (BCP) consisting of a mixture of 60% hydroxyapatite and 40% of beta-tricalcium phosphate (Straumann Bone Ceramic).

MATERIAL AND METHODS

A unilateral maxillary sinus floor elevation procedure was performed in six patients using 100% BCP. Biopsy retrieval for histological and histomorphometric analysis was carried out before implant placement after a 6-month healing period.

RESULTS

In this study, the maxillary sinus floor elevation procedure with the use of BCP showed uneventful healing. Radiological evaluation after 6 months showed maintenance of vertical height gained immediately after surgery. Primary stability was achieved with all Straumann SLA dental implants of 4.1 mm diameter and 10 or 12 mm length. The implants appeared to be osseointegrated well after a 3-month healing period. Histological investigation showed no signs of inflammation. Cranial from the native alveolar bone, newly formed mineralized tissue was observed. Also, osteoid islands as well as connective tissue were seen around the BCP particles, cranial from the front of newly formed mineralized tissue. Close bone-to-substitute contact was observed. Histomorphometric analysis showed an average bone volume/total volume (BV/TV) of 27.3% [standard deviation (SD) 4.9], bone surface/total volume (BS/TV) 4.5 mm(2)/mm(3) (SD 1.1), trabecula-thickness (TbTh) 132.1 mum (SD 38.4), osteoid-volume/bone volume (OV/BV) 7.5% (SD 4.3), osteoid surface/bone surface (OS/BS) 41.3% (SD 28.5), osteoid thickness (O.Th) 13.3 mum (SD 4.7) and number of osteoclasts/total area (N.Oc/Tar) 4.4 1/mm (SD 5.7).

CONCLUSIONS

Although a small number of patients were treated, this study provides radiological and histological evidence in humans confirming the suitability of this new BCP for vertical augmentation of the atrophied maxilla by means of a maxillary sinus floor elevation procedure allowing subsequent dental implant placement after a 6-month healing period. The newly formed bone had a trabecular structure and was in intimate contact with the substitute material, outlining the osteoconductive properties of the BCP material. Bone maturation was evident by the presence of lamellar bone.

Vascularized mastoid bone flap cranioplasty after translabyrinthine vestibular schwannoma surgery

OBJECTIVE

We describe a novel technique of cranioplasty using a vascularized mastoid bone flap in patients after translabyrinthine excision of vestibular schwannomas (VS). Postoperative outcomes in terms of pinna and postauricular deformity are evaluated.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary referral center.

RESULTS

Seventeen patients underwent cranioplasty with bone flap after translabyrinthine VS excision. At minimum follow-up of 12 months, none had a cerebrospinal fluid (CSF) leak. The measured pinna projections between the operated and non-operated sides had a mean difference of 0.80 mm (+/-1.70), which is not statistically significant (p > 0.05). The mean depth of the postauricular depressions was 1.38 mm (+/-0.93). Over the same period, 10 patients underwent translabyrinthine VS surgery without cranioplasty. In this group, there was a significant difference of 4.71 mm (+/-1.53) in mean pinna underprojections on the operated sides compared with the non-operated sides. Compared with patients who have undergone cranioplasty, the retroauricular depressions were significantly deeper (p < 0.05) with a mean depth of 2.92 mm (+/-1.21).

CONCLUSIONS

Vascularized mastoid cortical bone flap cranioplasty is a simple and effective technique to ameliorate the pinna and retroauricular deformities after translabyrinthine VS excision without increased surgical cost or the use of alloplastic materials.

Deriving fast setting properties of tetracalcium phosphate/dicalcium phosphate anhydrous bone cement with nanocrystallites on the reactant surfaces

OBJECTIVE

This study attempts to reveal how nanocrystallites on the ceramic surfaces of non-dispersive calcium phosphate cement (nd-CPC) participate in setting processes as compared with conventional CPC (c-CPC).

METHODS

The compositions and morphologies of CPC during the early setting reactions were studied with X-ray diffraction and a scanning transmission electron microscope equipped with an energy dispersive spectroscopy system. The pH values and dispersive properties of CPC during the early setting reactions were investigated as well as the compressive strength of nd-CPC after 24h of immersion with varying liquid to powder ratios.

RESULTS

The mechanical strength of nd-CPC was approximately 60MPa after a 24h immersion in simulate body solution with a P/L ratio between 3.3 and 4.2g/mL. The nanocrystallites on the particle surfaces of nd-CPC were shown to grow rapidly and provided interlocking sites that allowed rapid development of the apatite phase in the cement, and were also shown to be non-dispersive in solution as determined by an injection test of c-CPC.

CONCLUSIONS

The interlocking particles produced by whisker growth on the ceramic particles or new crystallites formed between the ceramic particles caused the cement to be non-dispersive in solution. The particles of reactants with nanocrystallites on surfaces also gave this cement the ability to be shaped easily as a paste during an operation or to be injected into a cavity.

Evaluation of polymethylmethacrylate adhesion: a comparison of direct onlay versus screw anchoring techniques

Polymethylmethacrylate (PMMA) is still the most frequently used alloplastic material for calvarial reconstruction, especially when dealing with large bony defects. It is strong, provides good protection to the underlying cerebral structures, and is stable and minimally reactive. One of the disadvantages of this material is its tendency to become loose over time because of its poor adherence to bone. Onlay miniscrews in improving PMMA's adhesion to bone have been previously proposed. A series of experiments were conducted to evaluate whether placement of screw anchors will significantly improve the adhesion force between the polymer and bony surface.

METHODS

Four fresh-frozen cadaver heads were used for this experiment. The PMMA preparation and setup time strictly followed manufacturer guidelines. Two experimental groups were created: (1) PMMA was placed on the subperiosteal bony surface with increasing surface areas (areas: 1-20 cm2), and (2) a standard area of 16 cm2 PMMA was placed on the bony surface with an increasing number of titanium miniscrews (number of screws: 0-5). The force required to separate the material from the underlying bone was assessed using a digital pull force gauge (Imada DPS-44) through vertical traction. The experiments were undertaken in triplicate; the results were statistically analyzed using Student t test.

RESULTS

Experiment 1: increasing forces were required as the surface area of PMMA application increased (1.2-42.3 N). The most consistent measurements with a low SD were obtained on the 16-cm2 implant, which was chosen for experiment 2. A 16-cm2 area would allow for the placement of up to 5 screws without technical difficulty. Experiment 2: higher forces were needed to detach the material, with increasing screw placement (1, 79; 2, 132.5; 3, 194.2; and 4 and 5, >196.1 N). In 73 of 75 experiments, the screws remained attached to the PMMA after separation. When the PMMA alone on a 16-cm2 surface area was compared with the placement of one or more screws, the force of adhesion significantly increased for all groups (P < 0.01). There was a 2.6x increase in this force with 1 screw, 4.4x with 2, 6.4x with 3, and 6.5x with 4 or more screws. Three or more miniscrews provided sufficient stabilization to anchor an implant firmly in place while resisting large traction forces.

CONCLUSION

Although greater surface areas of PMMA will increase the adhesion force between the polymer and bone, a clinically and statistically significant increase in this force may only be achieved with the use of miniscrews.

Calcium Orthophosphates in Nature, Biology and Medicine

The present overview is intended to point the readers’ attention to the important subject of calcium orthophosphates. These materials are of the special significance because they represent the inorganic part of major normal (bones, teeth and dear antlers) and pathological (i.e. those appearing due to various diseases) calcified tissues of mammals. Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium ortho-phosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and as tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, technical grade calcium orthophosphates are very popular mineral fertilizers. Thus ere calcium orthophosphates are of great significance for humankind and, in this paper, an overview on the current knowledge on this subject is provided.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.

DELAYED EXTRUSION OF HYDROXYAPATITE CEMENT AFTER TRANSPETROSAL RECONSTRUCTION

OBJECTIVE

Use of hydroxyapatite cement has been advocated for closure of transpetrosal defects to decrease the incidence of cerebrospinal fluid leaks. We previously identified delayed extrusion of this cement as a significant complication associated with this closure technique and now update our long-term experience.

METHODS

In our retrospective review, we identified 1231 patients who underwent transpetrosal procedures by our multidisciplinary cranial base team between 1984 and 2005. Of the subgroup of 177 patients who had hydroxyapatite cement used during the closure of the procedure, 13 patients (7.3%) experienced delayed extrusion of hydroxyapatite cement.

RESULTS

Extrusion occurred in 3 patients within 12 months and in 10 patients within 68 to 140 months. Twelve patients presented with draining fistulae and concomitant Staphylococcus aureus infection; 1 patient presented asymptomatically with a large temporal lobe abscess identified on surveillance magnetic resonance imaging. All 13 patients underwent reoperation, including 1 who underwent a second procedure.

CONCLUSION

Delayed extrusion of hydroxyapatite cement resulted in significant morbidity to our patients and often presented in an indolent manner. We recommend serial examination and imaging studies in patients who have had transpetrosal closures with hydroxyapatite cement. Because of the complication rates associated with hydroxyapatite cement, we have discontinued its use.

Next generation calcium phosphate-based biomaterials

It has been close to a century since calcium phosphate materials were first used as bone graft substitutes. Numerous studies conducted in the last two decades have produced a wealth of information on the chemistry, in vitro properties, and biological characteristics of granular calcium phosphates and calcium phosphate cement biomaterials. An in depth analysis of several key areas of calcium phosphate cement properties is presented with the aim of developing strategies that could lead to break-through improvements in the functional efficacies of these materials.

Composite ceramic bone graft substitute in the treatment of locally aggressive benign bone tumours

PURPOSE

To report the use of a composite ceramic bone graft substitute containing calcium sulphate and hydroxyapatite (HA) in the treatment of large expansive osteolytic benign bone tumours.

METHODS

4 women and 9 men aged 8 to 49 (mean, 22) years with aneurysmal bone cysts (n=6) or giant cell tumours (n=7) in the epi- or meta-physeal areas of the lower limbs underwent curettage, phenolisation, and filling with bone graft substitute containing calcium sulphate and HA. The mean tumour size was 38.5 (range, 18-65) ml. The patients were followed up for a mean of 41 (range, 33-52) months. Range of movement, Musculoskeletal Tumor Society Rating Score (MTSRS), and haematological and blood biochemical parameters were measured.

RESULTS

Two patients had recurrence at 7 and 9 months, both progressed to grade-III giant cell tumours. One underwent revision with an iliac crest autograft, whereas the other underwent en bloc excision and prosthetic replacement. The 11 other lesions displayed clinical and radiological consolidation at a mean of 4.6 (range, 3-7) months. No restriction of range of movement was observed, except in the patient undergoing prosthetic replacement. The mean MTSRS was 96% (range, 83-100%) of that expected for normal function. During the follow-up period, haematological and blood biochemical parameters stayed within normal limits.

CONCLUSION

Composite bioceramic osteoconductive grafts, which combine porous HA with calcium sulphate, provide a framework for human osteogenesis and avoid donor-site morbidity (autologous bone graft harvesting). Tumour recurrence remains a major concern especially in young patients, as revision invariably requires removal of additional bone, potentially compromising joint integrity.

Basic research on aw-AC/PLGA composite scaffolds for bone tissue engineering

Recently, it has become important to develop effective material to be used as scaffolds for bone tissue engineering. Therefore, we fabricated new three-dimensional (3D) scaffolds consisting of biodegradable poly(D,L-lactide-co-glycolic acid)(PLGA)(75/25) with anti-washout type AC (aw-AC) particles. The aim of this study was to evaluate this new scaffold concerning its basic properties and biocompatibility. The obtained scaffolds were observed with scanning electron microscopy (SEM), and measured for porosity, shrinkage and biaxial compressive strengths. It was shown that PLGA with aw-AC composite scaffolds (aw-AC/PL) showed a greater strength and stability than PLGA scaffolds (PL). Also, the mass reduction of aw-AC/PL during incubation decreased compared to that of PL. The number of MC3T3-E1 cell in PL and aw-AC/PL was counted at 5 h, 1 week, and 2 weeks after cell seeding. As a result, aw-AC/PL exhibited a superior performance in terms of attachment and proliferation compared to PL. Histologically, aw-AC/PL showed an excellent response toward soft tissues. Therefore, it was shown that aw-AC/PL was more biocompatible than PL. In conclusion, it was strongly suggested that aw-AC/PL was more useful for cell transplantation than PL in bone tissue engineering.

Use of a novel bone graft substitute in peri-articular bone tumours of the knee

We treated three patients with aneurysmal bone cysts and seven with giant cell tumours who presented with a large osteolytic lesion in peri-articular areas of the knee. The patients age ranged from 8 to 49 years (mean 25 years). The average tumour volume was measured at 39.8 cm(3) (range 18 to 65 cm(3)). The tumour cavities were treated with curettage, phenolisation and application of a composite bone graft substitute containing 35% calcium-sulphate hemihydrate and 65% hydroxyapatite granules. All patients were followed up for 4.0 to 5.2 years (mean 4.5 years). Tumour recurrence was noted in two cases. In the remaining patients consolidation of the lesion was considered complete at a mean of 4.5 months (3-6.5 months). During follow-up no deformities developed and no radiological signs of joint degeneration were noted. All patients regained close to normal function, with a mean Musculoskeletal Tumour Society Rating Score of 95.1%. Due to their good osteoconductive abilities, composite synthetic bone graft substitute combining porous hydroxyapatite with calcium-sulphate appears to be an effective alternative to autologous cancellous bone graft in the treatment of large osteolytic lesions in peri-articular areas around the knee joint. They bear major advantages through ubiquitous availability and the avoidance of morbidity associated with iliac crest harvest. Concerns remain as the radio-opaque appearance of the bone graft substitute may potentially delay the detection of tumour recurrence.

New antimicrobials, systemic distribution, and local methods of antimicrobial delivery in horses

The local delivery of antimicrobials is a valuable therapeutic tool with a low morbidity, is practical to use, and is well tolerated by horses. Clinically, its use has allowed equine practitioners to achieve better results when treating musculoskeletal infections, and it represents an extremely useful tool in the practitioner's armamentarium against these types of infections. The technique is indicated to combat orthopedic infections involving bones, joints, physes, tendon sheaths, and foot tissues. Optimal treatment must include other approaches, such as systemic antimicrobial therapy and surgical debridement and lavage, and monitoring of the clinical progression of the patient can help to determine the ideal protocol for each patient.

Comparativein vitro study of the proliferation and growth of human osteoblast-like cells on various biomaterials

In vitro studies about the growth behavior of osteoblasts onto biomaterials is a basic knowledge and a screening method for the development and application of scaffolds in vivo. In this in vitro study human osteoblast-like (HOB) cells were cultured on seven different biomaterials used in dental and craniomaxillofacial surgery, respectively. The tested biomaterials were synthetic biodegradable (MacroPore, Ethisorb, PDS, Beriplast P) and nonbiodegradable polymers (Palacos) as well as calcium phosphate cement (BoneSource) and titanium. The cell proliferation and cell colonization were analyzed by scanning electron microscopy and EZ4U-test. Statistical analysis were performed. HOB-like cells cultivated on Ethisorb showed the highest proliferation rate. The proliferation rate was statistically significant compared with Palacos, MacroPore, and BoneSource. Whereas, Beriplast, PDS, and titanium yielded lower proliferation rates. However, there was no statistically significant difference compared with Palacos, MacroPore, and BoneSource. SEM analysis showed no significant difference in individual cell features and cell colonization. But an infiltration and a growth of HOB-like cells throughout the porous structure of Ethisorb, which is formed by crossing fibers, is a striking different feature (macrotopography). This feature can explain the highest proliferation rate of Ethisorb. The results showed that HOB-like cells appear to be sensitive to substrate composition and topography. Moreover, the basis for further studies with such biomaterial/osteoblast constructs in vivo are provided. Further focusing points are developing techniques to fabricate three-dimensional porous biomaterial/cell constructs, studying the tissue reaction and the bone regeneration of such constructs compared with the use of autologous bone.

Effects of a magnesium adhesive cement on bone stability and healing following a metatarsal osteotomy in horses

OBJECTIVE

To compare biodegradable magnesium phosphate cement (Mg-cement), calcium phosphate cement (Ca-cement), and no cement on bone repair, biocompatibility, and bone adhesive characteristics in vivo in horses.

ANIMALS

8 clinically normal adult horses.

PROCEDURES

Triangular fragments (1-cm-long arms) were created by Y-shaped osteotomy of the second and fourth metatarsal bones (MTII and MTIV, respectively). Fragments were replaced in pairs to compare Mg-cement (MTII, n = 8; MTIV, 8) with Ca-cement (MTIV, 8) or with no cement (MTII, 8). Clinical and radiographic evaluations were performed for 7 weeks, at which time osteotomy sites were harvested for computed tomographic measurement of bone density and callus amount, 3-point mechanical testing, and histologic evaluation of healing pattern and biodegradation.

RESULTS

All horses tolerated the procedure without clinical problems. Radiographically, Mg-cement secured fragments significantly closer to parent bone, compared with Ca-cement or no treatment. Callus amount and bone remodeling and healing were significantly greater with Mg-cement, compared with Ca-cement or no cement. Biomechanical testing results and callus density among treatments were not significantly different. Significantly greater woven bone was observed adjacent to the Mg-cement without foreign body reaction, compared with Ca-cement or no cement. The Mg-cement was not fully degraded and was still adhered to the fragment.

CONCLUSIONS AND CLINICAL RELEVANCE

Both bone cements were biocompatible in horses, and Mg-cement may assist fracture repair by osteogenesis and fragment stabilization. Further studies are warranted on other applications and to define degradation characteristics.

Mechanical and biocompatible influences of chitosan fiber and gelatin on calcium phosphate cement

Calcium phosphate cement (CPC) is a widely used bone substitute in the clinic; however, the low strength of CPC limits its utilization. In this study, we investigated mechanical influences of chitosan fiber combined with gelatin on CPC, and examined the biocompatibility of the new composite with rat bone marrow stromal cells. Compared to the fiber impregnated in phosphate buffered saline (80.5 MPa), our study showed that tensile strength of chitosan fiber increased 106 and 114% with the impregnation of gelatin at the mass fraction 5 and 10%, although this increase was not statistically significant. It was demonstrated by Fourier transform infrared spectroscopy that the characteristic absorption bands of chitosan were changed with the addition of gelatin. The optimal flexural strength enhancement was obtained when CPC was reinforced with fiber at volume fraction of 30% and gelatin at mass fraction of 5% (maximum: 12.31 MPa). The fiber morphology was more compact when the chitosan fibers impregnated with gelatin at mass fraction of 5 or 10% than chitosan alone. The fracture analysis showed that the new CPC-chitosan fiber-gelatin composite presented many remnants of CPC adhered to fibers. Short minimum essential medium extract test showed no cell growth inhibition after the addition of the new composite. Rat bone marrow stromal cells retain the ability to spread and grow on the composite. Our studies demonstrated that the flexural strength is greatly increased by using CPC incorporated with proper ratio of CF and gelatin. More over, the new composite demonstrated biocompatibility in vitro.

Primary pedicle screw augmentation in osteoporotic lumbar vertebrae: biomechanical analysis of pedicle fixation strength

STUDY DESIGN

Pedicle screw pullout testing in osteoporotic and control human cadaveric vertebrae, comparing augmented and control vertebrae.

OBJECTIVE

To compare the pullout strengths of pedicle screws fixed in osteoporotic vertebrae using polymethyl methacrylate delivered by 2 augmentation techniques, a standard transpedicular approach and kyphoplasty type approach.

SUMMARY OF BACKGROUND DATA

Pedicle screw instrumentation of the osteoporotic spine carries an increased risk of screw loosening, pullout, and fixation failure. Osteoporosis is often cited as a contraindication for pedicle screw fixation. Augmentation of the vertebral pedicle and body using polymethyl methacrylate may improve fixation strength and construct survival in the osteoporotic vertebrae. While the utility of polymethyl methacrylate has been demonstrated for salvage of screws that have been pulled out, the effect of the cement technique on pullout strength in osteoporotic vertebrae has not been previously studied.

METHODS

Thirteen osteoporotic and 9 healthy human lumbar vertebrae were tested. All specimens were instrumented with pedicle screws using a uniform technique. Osteoporotic pedicles were augmented with polymethyl methacrylate using either a kyphoplasty type technique or a transpedicular augmentation technique. Screws were tested in a paired testing array, randomly assigning the augmentation techniques to opposite sides of each vertebra. Pullout to failure was performed either primarily or after a 5000-cycle tangential fatigue conditioning exposure. After testing, following screw removal, specimens were cut in the axial plane through the center of the vertebral body to inspect the cement distribution.

RESULTS

Pedicle screws placed in osteoporotic vertebrae had higher pullout loads when augmented with the kyphoplasty technique compared to transpedicular augmentation (1414 +/- 338 versus 756 +/- 300 N, respectively; P < 0.001). An unpaired t test showed that fatigued pedicle screws in osteoporotic vertebrae augmented by kyphoplasty showed higher pullout resistance than those placed in healthy control vertebrae (P = 0.002). Both kyphoplasty type augmentation (P = 0.007) and transpedicular augmentation (P = 0.02) increased pullout loads compared to pedicle screws placed in nonaugmented osteoporotic vertebrae when tested after fatigue cycling.

CONCLUSIONS

Pedicle screw augmentation with polymethyl methacrylate improves the initial fixation strength and fatigue strength of instrumentation in osteoporotic vertebrae. Pedicle screws augmented using the kyphoplasty technique had significantly greater pullout strength than those augmented with transpedicular augmentation technique and those placed in healthy control vertebrae with no augmentation.

Porous polyethylene implants in orbital floor reconstruction

BACKGROUND/PURPOSE

Various alloplastic materials are used in orbital wall reconstruction. This study investigated the outcome of patients treated with porous polyethylene sheet implants in the reconstruction of orbital floor fracture.

METHODS

Twenty-one patients who underwent orbital reconstructions using 0.85-mm porous polyethylene sheets for the repair of orbital floor fracture were included. A transconjunctival approach was used in all patients. The mean duration of postoperative follow-up was 29.7 +/- 12.3 months. Postoperatively, results and complications such as infection and implant extrusion were followed-up on the first day, the first week, monthly for the first 3 months and then every 3-6 months thereafter.

RESULTS

All 21 patients had symptomatic diplopia before surgery. The diplopia resolved in 14 patients and improved in seven patients within the first month after surgery. All patients except one were free from diplopia at follow-up periods exceeding 6 months. Preoperative enophthalmos resolved in four of seven patients and improved in three. None of the patients developed orbital infection, implant exposure or migration, worsening diplopia, infraorbital anesthesia or loss of vision during follow-up.

CONCLUSION

The study demonstrated that porous polyethylene implants in the repair of orbital wall fractures had good results with few complications.

Histological Evaluation of Apatite Cement Containing Atelocollagen

Tissue response to apatite cement (AC) containing atelocollagen (AC (ate)) was evaluated using conventional AC (c-AC) as a control material. At one week, the only difference between AC (ate) and c-AC was found in the soft tissue response. With c-AC, a moderate inflammatory response was exhibited: small particles of c-AC were scattered in the cutaneous tissue and many foreign body giant cells were aggregated around the scattered c-AC, whereas AC (ate) showed only a slight inflammatory response with few foreign body giant cells. In terms of bone tissue response, difference between AC (ate) and c-AC was observed at four weeks. New bone formation was observed along the cement at the edge of the pre-existing cortical bone in both c-AC and AC (ate). However, in the case of AC (ate), more abundant and thicker new bone was formed along the cement in the bone marrow when compared with c-AC.

Characterization of a novel calcium phosphate composite bone cement: flow, setting, and aging properties

The flow, setting, and aging characteristics of a newly developed calcium phosphate/calcium aluminate composite orthopaedic cement were studied. The effect of vibration on the flow of the cement paste was studied and found to greatly enhance placement. The setting times of this cement were dependent on temperature and decreased with increasing temperatures. At 37 degrees C, the working and setting times were 6.3 +/- 0.3 and 12.8 +/- 0.4 minutes, respectively. Hydration and conversion of the cement phases continued while specimens were stored under simulated, physiological conditions. A cumulative increase in mass of 8.23 +/- 0.65% was observed over a 14 month test period. During this time, the cement was found to expand slightly, 0.71 +/- 0.39%. X-ray diffraction was used to characterize the crystalline phases present during hydration and conversion. The calcium aluminate in the cement hydrated and formed calcium aluminate chloride hydrates, while no changes were observed in the beta-tricalcium phosphate during the testing period.

Novel injectable calcium phosphate/chitosan composites for bone substitute materials

In this study, a novel injectable bone substitute material was developed which consists of chitosan, citric acid and glucose solution as the liquid phase, and tricalcium phosphate powder as the solid phase. This material was moldable because of its paste consistency after mixing. We used four groups of cement to investigate the mechanical properties and biocompatibility of the new biomaterial in vitro, which were named group A (10% citric acid), B (15% citric acid), C (20% citric acid) and D (25% citric acid). The setting times of the cements were 5-30 min. X-ray diffraction analysis showed that the products were hydroxyapatite (HA) and dicalcium phosphate anhydrous. When the concentration of citric acid was increased, the compressive strength of specimen increased. Through the simulated body fluid test, we observed the material was bioactive. Group D could induce Ca and P ions to deposit the surface group D quickly. These results indicated that the concentration of citric acid in the liquid component affected the mechanical properties and bioactivity of cements. The cell cultivation test showed that the cytocompatibility of the new biomaterial was good. The method for preparing the novel bone substitute material is simple. The starting material is more readily available and cheaper than HA, poly(methyl methacrylate), and so on. The cement could have good prospects for medical application.

High early strength calcium phosphate bone cement: effects of dicalcium phosphate dihydrate and absorbable fibers

Calcium phosphate cement (CPC) sets in situ to form resorbable hydroxyapatite with chemical and crystallographic similarity to the apatite in human bones, hence it is highly promising for clinical applications. The objective of the present study was to develop a CPC that is fast setting and has high strength in the early stages of implantation. Two approaches were combined to impart high early strength to the cement: the use of dicalcium phosphate dihydrate with a high solubility (which formed the cement CPC(D)) instead of anhydrous dicalcium phosphate (which formed the conventional cement CPC(A)), and the incorporation of absorbable fibers. A 2 x 8 design was tested with two materials (CPC(A) and CPC(D)) and eight levels of cement reaction time: 15 min, 30 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, and 24 h. An absorbable suture fiber was incorporated into cements at 25% volume fraction. The Gilmore needle method measured a hardening time of 15.8 min for CPC(D), five-fold faster than 81.5 min for CPC(A), at a powder:liquid ratio of 3:1. Scanning electron microscopy revealed the formation of nanosized rod-like hydroxyapatite crystals and platelet crystals in the cements. At 30 min, the flexural strength (mean +/- standard deviation; n = 5) was 0 MPa for CPC(A) (the paste did not set), (4.2 +/- 0.3) MPa for CPC(D), and (10.7 +/- 2.4) MPa for CPC(D)-fiber specimens, significantly different from each other (Tukey's at 0.95). The work of fracture (toughness) was increased by two orders of magnitude for the CPC(D)-fiber cement. The high early strength matched the reported strength for cancellous bone and sintered porous hydroxyapatite implants. The composite strength S(c) was correlated to the matrix strength S(m): S(c) = 2.16S(m). In summary, substantial early strength was imparted to a moldable, self-hardening and resorbable hydroxyapatite via two synergistic approaches: dicalcium phosphate dihydrate, and absorbable fibers. The new fast-setting and strong cement may help prevent catastrophic fracture or disintegration in moderate stress-bearing bone repairs.

Analyses of the factors influencing bone graft infection after delayed cranioplasty

BACKGROUND

Several factors influencing bone graft infection after delayed cranioplasty are analyzed in order to reduce the occurrence of infection.

METHODS

For about 10 years, from March 1995 to February 2005, delayed cranioplasty was performed for 206 cases. The cases comprised 124 males and 82 females. Age distribution of the patients ranged from 6 months to 79 years old. The mean postoperative follow-up period was 1834 days. Autogenous bone, which was preserved in 100% ethanol at -20 degrees C and autoclaved before operation, was used in 54 patients. Polymethylmethacrylate (PMMA) was used in 55 patients. Custom-made PMMA was used in 3 patients. Custom-made titanium mesh was used in 77 patients. Custom-made ceramics (Alumina-ceramics 10 cases and hydroxyapatite 7 cases) was used in 17 patients.

FINDINGS

Autoclaved and autogenous bone graft and PMMA have a significantly high rate of graft infection. Titanium mesh has the significantly lowest rate of graft infection. Alumina-ceramic has a merit that it has sufficient strength, however the number of cases using custom-made ceramics including alumina-ceramic was relatively small, and thus we cannot find significant differences in infection rate compared with that of other materials. There was no statistically significant difference in the bone graft infection rate among four categories of preceding diseases; cerebrovascular diseases, head trauma, infectious diseases, and brain tumour.

CONCLUSION

Autoclaved and autogenous bone grafts and PMMA have a significantly higher rate of graft infection. Titanium mesh has the significantly lowest rate of graft infection.

The use of temporal polyethylene implant after temporalis myofascial flap transposition: clinical and radiographic results from its use in 21 patients

PURPOSE

The use of temporalis myofascial flap (TMF) as a pedicled flap in craniofacial reconstructive surgery is well established. The transposition of temporalis muscle results in a large hollowing of the temporal fossa that leaves the patient with a cosmetic impairment. Reconstruction of this donor site deformity is desirable. One of the established reconstructive techniques is the use of a prefabricated porous high-density polyethylene (HDPE) temporal implant. In order to evaluate results from its use, we retrospectively reviewed a series of 21 consecutive patients.

MATERIALS AND METHODS

From October 1999 to October 2004, 21 patients (7 men and 14 women) aged 32 to 85 years (mean, 65) had their surgical defects reconstructed with the use of a TMF. The majority of patients (15 of 21) had squamous cell carcinoma of the maxilla or the maxillary sinus. In 17 patients, the reconstructive procedure was performed simultaneously with the oncological resection, whereas in 4, a secondary reconstruction was performed. In 1 patient, bilateral TMFs were used to cover a total maxillectomy defect. Standard surgical approach was used in all patients during TMF elevation. The temporal defect was reconstructed with the use of a prefabricated sterile HDPE implant (Medpor; Porex Surgical Inc, College Park, GA). Fixation of the implant to the recipient infratemporal fossa was performed with black silk sutures (in 2 patients) or titanium miniscrews (in 19 patients). The manufacturer's instructions for the placement of the implant were followed in all cases. One of the 21 operated patients preoperatively received radiotherapy (RT). Of the remaining 20 patients, 5 underwent postoperative RT.

RESULTS

Eighteen patients are alive and free from disease. One died during the perioperative period from myocardial infarction and 2 more from locoregional recurrence of their disease, 18 and 27 months postoperatively. In all 21 patients, the placement of the Medpor temporal implant was successful and no immediate or perioperative complications resulting from its use were encountered, giving an overall success implantation rate of 100%. Follow-up ranged from 9 to 70 months (mean, 39). The condition of the implant was evaluated with computed tomography in 18 of the 21 patients as part of the standard postoperative assessment. Radiographic results of the recipient site did not reveal any abnormalities. In 7 patients, the contour of the HDPE implant could be manually palpated, and in 3, it could be seen to protrude subcutaneously. Esthetic results were judged satisfactory from all patients. The hemicoronal skin flap healed uneventfully in all patients and did not cause a visible scar even to bald male patients.

CONCLUSIONS

The reconstruction of the temporal defect after TMF transposition with the use of a Medpor temporal implant is an easy and safe method. The implant does not seem to cause any tissue reaction, and long-term functional and esthetic results are excellent. When properly used and the relevant manufacturers' instructions are carefully followed, the success rate of the method is extremely high.

Physicochemical properties of TTCP/DCPA system cement formed in physiological saline solution and its cytotoxicity

In this paper, the physicochemical properties and cytotoxicity of calcium phosphate cement (CPC), prepared by mixing cement powders of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA) with a cement liquid of physiological saline solution, were investigated. The microstructure evolution of various hardened cement bodies and their hydration crystals as a function of immersion time in similar physiological fluids, physiological saline solution (0.9% NaCl), or simulated body fluids (SBF), were also studied. Results show that the setting time of CPC is in the range of 12-15 min, which meets the clinical application demands. We also found that the mean compressive strength of the CPC samples immersed in SBF for 3 days is 104+/-10 MPa which reaches the transverse compressive strength, 106-133 MPa, of human long bone. The results obtained from both the X-ray powder diffraction analyses (XRD) and scanning electron microscopy (SEM) observations indicated that a reinforcing effect of some remaining TTCP particles in the early stages of immersion is mainly responsible for the increase in the initial strength. Although the CPC failed to keep this high level when immersed for a longer time, the initial reinforcing effect of the remaining TTCP particles provides advantages for clinical applications. This would be effective when the material is loaded at the very beginning of the implantation, especially for the material used as a fixation, which requires a certain initial strength in the early stages of the implantation. The cytotoxicity results showed that the relative growth rate (RGR%) of L929 cells on the CPC samples using physiological saline solution as a cement liquid was slightly superior to that of the samples using the 0.5 mol/L phosphate acid solution as the cement liquid. This was most likely caused by the pH difference between the two CPC samples immersed in a DMEM-BFS medium.

Effectiveness of hydroxyapatite-vancomycin bone cement in the treatment of Staphylococcus aureus induced chronic osteomyelitis

In the field of local application of antimicrobials, a number of novel drugs and/or new drug delivery systems have been developed in recent years. The present study aimed to investigate hydroxyapatite cement (HAC) as a carrier for vancomycin in the treatment of chronic osteomyelitis due to Staphylococcus aureus strains with various mechanisms of resistance. The release of vancomycin from standard test cylinders was determined in vitro and the efficacy of the delivery system was measured in vivo using a rabbit model of chronic osteomyelitis. First, powdered HAC was mixed with vancomycin at 80, 160 and 240 mg/g. After hardening, formed cylinders were eluted in phosphate buffer and antibiotic release was measured by agar diffusion. High levels of release (1512+/-318 to 1937+/-336 microg/ml) were obtained for 12 to 20 days depending on the dosage of vancomycin. Additionally, bone infection was induced in the tibia of 30 New Zealand white rabbits by injecting either a methicillin-resistant S. aureus strain (MRSA) or a S. aureus strain with a small colony variant (SCV) phenotype. After 3 weeks (chronic infection), all animals were treated by debridement. Moreover, group 1 (challenged with SCVs) and group 2 (challenged with MRSA) were treated by filling the marrow with HAC alone, whereas in groups 3 (SCVs) and 4 (MRSA) the marrow was filled with HAC/vancomycin (160 mg/g). After 6 weeks all animals were sacrificed. At 3 weeks, pathogens were detected in 24 of 30 animals. All swabs of the control groups, positive for S. aureus on day 21, were also positive on day 42 and S. aureus strains recovered were shown to be clonal to the strains used for induction of osteomyelitis. By contrast, no growth was found in the treatment group following 7 days of incubation in BHI bouillon. HAC/vancomycin-treated animals showed no histological evidence of infection on day 42. In the other groups, different stages of chronic osteomyelitis were found histologically. No local or systemic side effects due to HAC or vancomycin were seen. HAC is an effective carrier material for antibiotic compounds even in refractory infections due to MRSA or S. aureus SCVs.

A Comparison of Resistance to Fracture Among Four Commercially Available Forms of Hydroxyapatite Cement

Hydroxyapatite cement is a relatively new biomaterial that has found widespread use in craniomaxillofacial surgery. Despite its common usage, complication rates as high as 32% have been reported. When failed implants are removed, implant fracture has been cited as a potential cause of failure. The purpose of this study was to evaluate resistance to fracture among 4 commercially available hydroxyapatite cement formulations. The materials tested included Norian Craniofacial Repair System (carbonated apatite cement) (AO North America, Devon, PA), Norian CRS Fast Set Putty (carbonated apatite cement) (AO North America), BoneSource (hydroxyapatite cement) (Stryker Leibinger, Portage, MI), and Mimix (hydroxyapatite cement) (Walter Lorenz Surgical, Inc, Jacksonville, FL). To ensure consistency, all materials were embedded in acrylic wells. Each material was placed into a well 2.54 cm in diameter and 0.953 cm in thickness. The materials were prepared per manufacturer specifications. All materials were incubated at 37.0 degrees C, in 6% CO2, 100% humidity for 36 hours. Using the Bionix MTS Test System, a 12-mm-diameter probe applied incremental force to the center of the disk at a rate of 0.1 mm per second. The transmitted force was measured using a Bionix MTS Axial-Torsional Load Transducer for each disk. The force which resulted in fracture was recorded for each material. Ten disks of each material were processed by this method, for a total of 40 disks. The significance of resistance to fracture for the 4 compounds was analyzed using 1-way analysis of variance with post hoc Scheffe method. Mean fracture force with related P values was plotted for direct comparison of group outcomes. Material type contributed significantly to variance in fracture force for the biomaterials studied. Norian CRS required the greatest mean fracture force (1385 N, SD+/-292 N), followed by Norian CRS Fast Set Putty (1143 N, SD+/-193 N). Mimix required a mean fracture force of 740 N, SD+/-79 N. BoneSource required a mean fracture force of 558 N, SD+/-150 N. Mimix and BoneSource required significantly less force for fracture when compared with Norian CRS and Fast Set Putty (P<0.01). Comparisons of fracture load resistance between 4 commonly used bone substitute materials have not been previously reported. Increasing biomaterial strength may reduce complications resulting from reinjury to cranioplasty sites. In this model, Norian CRS and Norian CRS Fast Set Putty demonstrated a significantly greater resistance to fracture when compared with BoneSource and Mimix.

The Use of Calcium Hydroxylapatite for Nipple Projection After Failed Nipple-Areolar Reconstruction

Numerous studies have shown that the final stage in breast reconstruction, creation of the nipple-areolar complex, correlates highly with patient satisfaction and acceptance of body image. There are many different techniques, including nipple sharing, free-composite grafts, and local "pull-out" flaps, all of which are vulnerable to an unpredictable degree of loss of projection and possible need for reoperation. This leads to problems with symmetry and overbuilding the initial reconstruction with wider-based, larger flaps, which may cause breast-contour changes. We have used calcium hydroxylapatite (Radiesse, Bioform Inc., Franksville, WI) following nipple-areolar reconstruction to maintain or restore projection in selected breast-reconstruction patients. Approximately 0.4-1 mL of calcium hydroxylapatite was injected subdermally using a 27-gauge needle in 6 selected patients. All patients tolerated the office procedure well without the need for local anesthesia. We report initial short-term success, with 100% patient satisfaction, minimal loss of projection, and no complications. Semipermanent injectable soft-tissue fillers such as calcium hydroxylapatite may be useful in selected patients as a simple solution to the difficult problem of the lack of nipple projection following reconstruction.

Use of Mimix hydroxyapatite bone cement for difficult ossicular reconstruction

OBJECTIVE

To describe the advantages of using Mimix hydroxyapatite (HA) bone cement in reconstructing a variety of ossicular chain abnormalities.

STUDY DESIGN AND SETTING

Case series at a tertiary medical center.

RESULTS

Twenty-five cases of HA reconstruction are included in this series (ages 23-74; mean, 47 years). The examples presented include (1) HA as the sole reconstructive material for incus erosion, (2) HA for securing a total or partial ossicular replacement prosthesis, (3) incus augmentation after crimping for revision stapedotomy with incus erosion, (4) HA in primary stapedotomy to fix the crimped prosthesis to an intact incus, and (5) other unique situations. Preoperative and postoperative audiograms were evaluated for 4-tone pure tone average (PTA), speech reception thresholds, word recognition scores, and air-bone gaps (AB gaps). Mean follow-up was 11 months (range 2 to 22 months). The mean PTA improved from 57 dB to 37 dB, whereas the mean AB gaps decreased from 33 dB to 16 dB. There were no cases of infection or extrusion.

CONCLUSIONS

Hydroxyapatite bone cement is an excellent adjunct or alternative to ossiculoplasty with preformed prostheses. Easily malleable, rapidly setting, and rapidly hardening, Mimix is particularly well suited for middle ear work.

SIGNIFICANCE

Definitive fixation with bone cements during difficult ossicular chain reconstruction may ensure a more enduring successful outcome.

Contouring of Cranial Vault Irregularities With Hydroxyapatite Cement: A Clinical and Experimental Investigation

The biocompatible hydroxyapatite cement (HAC) is a welcome alternative to the traditional use of autogenous bone for postoperative corrections of cranial vault irregularities. The authors performed experimental studies to show the safety and osseointegration capacity of HAC on animal models and confirm the osseous replacement without toxic reactions. The purpose of the current study was to analyze the clinical outcome after correction of secondary cranial vault irregularities with HAC. Twenty-one patients were treated for residual cranial frontal bone defects after craniotomy with HAC (Bone Source, Stryker Leibinger GmbH, D-79111 Freiburg, Germany). The average age was 38.5 years (range, 23-57 years). All of the patients were male. The average volume per patient was 53.83 g. The volume implanted ranged from 25 to 125 g; in all cases the dura was covered with bone. Irregularities resulted from sunken bone. The authors' clinical series demonstrates that a satisfactory and aesthetically pleasing result can be achieved in one surgical intervention in patients for surgical correction of postoperative cranial vault irregularities using HAC. It permits osseointegration, which makes it relatively resistant to infection. HAC is easy to apply and shape to suit individual needs. HAC is a welcome alternative to the traditional use of autogenous bone for postoperative corrections of cranial vault irregularities.

Einfluss unterschiedlicher Anr�hrfl�ssigkeiten auf die mechanischen und mikromorphologischen In-vitro-Eigenschaften von Hydroxylapatitzement

AIM

In reconstructive craniofacial surgery a new synthetic hydroxyapatite cement has been used in the last few years. Tetra- and dicalcium phosphates react with either slow setting aqua bidest. or with faster setting sodium monophosphate solution to hydroxyapatite. The aim of this study was to investigate the two mixing fluids of hydroxyapatite for resulting micromorphology, pressure strength, and interactions with fibroblasts.

MATERIAL AND METHODS

Pressure strength tests of hydroxyapatite cement test samples (n=80) were performed after a setting time of 3 and 24 h. The micromorphology of surfaces of the resulting particles was assessed under an electron microscope. In cell cultures L-929 and HEp2 cells were incubated with test samples and cell growth was assessed by light and electron microscopy.

RESULTS

The test samples mixed with sodium monophosphate solution showed statistically significantly higher values of pressure strength. The resulting pressure strength depended on respective mixing fluids, setting time, and pressure of application. In general, test samples mixed with sodium monophosphate solution showed a more load-stable, homogeneous anorganic matrix whereas test samples mixed with aqua bidest. had a porous microarchitecture which was more fragile. In cell culture the porous structure showed disintegration in cell culture medium.

CONCLUSION

To what extent the two mixing liquids of hydroxyapatite cement influence the resorption and bony substitution has to be shown in further studies.

Experimental facial augmentation with hydroxyapatite cement

OBJECTIVE

To study the results of implantation of preformed hydroxyapatite (HA) disks and HA cement in onlay augmentation.

METHODS

In this prospective study involving 16 adult New Zealand rabbits, HA disk and HA cement samples were implanted separately and together along the bony and cartilaginous nasal dorsum as well as over the supraorbital bone. Gross and histologic examinations of the implants were performed at intervals ranging from 3 to 24 months.

RESULTS

There was no evidence of infection, adverse reaction, or implant extrusion in the 15 rabbits surviving the planned period. Grossly, all rabbits had prominent noses and supraorbital regions that were immobile on digital palpation. No measurable change in HA disk height and width was noted but there was a 15% decrease in height and width in the HA cement implant. Microscopically, preformed HA disks were found to be enclosed in a vascularized fibrous capsule. When disks were combined with HA cement, a vascular fibrous capsule was still noted around the implant but there was osteoconversion in the underlying cement layer. Used alone, HA cement underwent both osteoconversion and osteointegration. Neither the preformed HA disk with and without HA cement nor the HA cement alone elicited giant cell reaction or inflammatory changes. The HA cement alone was found to have microscopic fissures at the edges.

CONCLUSION

This animal study suggests that preformed HA implants and HA cement, alone or in combination, can be used to augment the non-stress-bearing craniofacial skeleton.

Frei modellierbare Hydroxylapatit-Kollagen-Komposite zur Sanierung oss�rer Defekte

AIM

In the following study we evaluated the biological response of a new freely moldable bone substitute in an animal model.

MATERIAL AND METHODS

Critically sized defects were created surgically in the lower jaw of ten adult minipigs. The drill defects were filled with hydroxyapatite collagen paste. After observation periods of 1, 3, 6, 12, and 18 months the mandibles were harvested without wound healing defects for histological evaluation of resorption and bone ingrowth with a sawing and grinding technique.

RESULTS

The result of the remodeling process was a complete degradation of hydroxyapatite collagen implants after 12-18 months with reorganization of vital trabeculae oriented in a mature pattern.

CONCLUSION

The hydroxyapatite collagen cement works as an osteoconductor and shows signs of direct osseointegration and resorption.

Vocal fold augmentation with calcium hydroxylapatite

OBJECTIVES

Voice disorders affect more than 3% of the general population. Vocal fold atrophy is a part of the normal aging process, with up to 60% of 60-year-old individuals displaying evidence of glottal insufficiency. A safe, effective, and durable substance for injection augmentation of the vocal folds is not currently available. The purpose of this investigation was to describe our preliminary experience with calcium hydroxylapatite (CaHA) for vocal fold augmentation.

METHODOLOGY

All patients undergoing injection augmentation of the vocal folds with CaHA between January 1, 2002 and June 1, 2003 were prospectively evaluated. Data concerning indications, technique, functional outcome, and complications were collected. In addition, the larynx donated from a woman who underwent vocal fold augmentation with CaHA and subsequently died from terminal cancer was histologically examined.

RESULTS

A total of 39 vocal folds in 23 individuals were injected with CaHA. The mean age of the cohort was 62. Fifty-two percent were male. The indications for augmentation were unilateral vocal fold paralysis (9/23), unilateral vocal fold paresis (5/23), presbylarynx (3/23), Parkinson's (3/23), bilateral vocal fold paresis (2/23), and abductor spasmodic dysphonia (1/20). There were no adverse reactions. All individuals reported improvement on a self-administered disease-specific outcome measure (P < 0.001). The pathology from the donated larynx 3 months after injection revealed intact CaHA spherules in good position with a minimal, monocellular inflammatory reaction to the gel carrier and no evidence of implant rejection.

CONCLUSIONS

Initial experience with vocal fold augmentation using CaHA is promising. Long-term safety and efficacy needs to be established.

In vivo cancellous bone remodeling on a strontium-containing hydroxyapatite (sr-HA) bioactive cement

The purpose of this study was to investigate the in vivo bone response to the strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into the cancellous bone. Sr-HA cement was injected into the iliac crest of rabbits for 1, 3, and 6 months. Active bone formation and remodeling were observed after 1 month. Newly formed bone was observed to grow onto the bone cement after 3 months. Thick osteoid layer with osteoblasts formed along the bone and guided over the bone cement surface reflected the stimulating effect of Sr-HA. From scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thick layer of 70 microm in width, and fusion of Sr-HA with the bone was observed. Blood vessels were found developing in remodeling sites. The affinity of bone on Sr-HA cement was increased from 73.55 +/- 3.50% after 3 months up to 85.15 +/- 2.74% after 6 months (p < 0.01). In contrast to Sr-HA cement, poly(methyl methacrylate) (PMMA) bone cement was neither osteoconductive nor bioresorbable. Results show that the Sr-HA cement is biocompatible and osteoconductive, which is suitable for use in treating osteoporotic vertebral fractures.

Biomaterials in craniofacial reconstruction

Biomaterials have become an integral component of craniofacial reconstruction. Their increasing ease of use, long "shelf-life," and safety enables them to be used effectively and play an important role in reducing operating times. There are various biomaterials currently available and specific usages have been characterized well in the literature. This article reviews different biomaterials that can be used in craniofacial reconstruction,including autogenous bone, methyl methacrylate and hard tissue replacement,hydroxyapatite, porous polyethylene, bioactive glass, and demineralized bone.