Biomechanical and Histologic Evaluation of the Norian Craniofacial Repair System and Norian Craniofacial Repair System Fast Set Putty in the Long-Term Reconstruction of Full-Thickness Skull Defects in a Sheep Model:

Utilization of carbonated calcium phosphate cement for contouring cranioplasty in patients with syndromic craniosynostosis

PURPOSE

Carbonated calcium phosphate (CCP) cement is an alloplastic material which has been increasingly utilized for cranioplasty reconstruction; however, there is a paucity of data investigating its use in patients with syndromic craniosynostosis. The purpose of this study was to characterize our institutional experience with CCP cement for secondary contouring cranioplasty in these patients to establish safety and aesthetic efficacy.

METHODS

Patients with syndromic craniosynostosis undergoing cranioplasty with CCP cement from 2009 to 2022 were retrospectively reviewed for prior medical and surgical history, cranioplasty size, cement usage, and postoperative complications. Aesthetic ratings of the forehead region were quantified using the Whitaker scoring system at three timepoints: preoperative (T1), < 6 months postoperative (T2), and > 1 year postoperative (T3).

RESULTS

Twenty-one patients were included. Age at surgery was 16.2 ± 2.8 years, forehead cranioplasty area was 135 ± 112 cm², and mass of cement was 17.2 ± 7.8 g. Patients were followed for 3.0 ± 3.1 years. Whitaker scores decreased from 1.9 ± 0.4 at T1 to 1.4 ± 0.5 at T2 (p = 0.005). Whitaker scores at T2 and T3 were not significantly different (p = 0.720). Two infectious complications (9.5%) were noted, one at 4.5 months postoperatively and the other at 23 months, both requiring operative removal of CCP cement.

CONCLUSION

Our results suggest that aesthetic forehead ratings improve after CCP contouring cranioplasty and that the improvement is sustained in medium-term follow-up. Complications were uncommon, suggesting that CCP is relatively safe though longer-term follow-up is needed before reaching definitive conclusions.

Histological Processing of CAD/CAM Titanium Scaffold after Long-Term Failure in Cranioplasty

Cranioplasty is a frequently performed procedure after craniectomy and includes several techniques with different materials. Due to high overall complication rates, alloplastic implants are removed in many cases. Lack of implant material osseointegration is often assumed as a reason for failure, but no study has proven this in cranioplasty. This study histologically evaluates the osteointegration of a computer-aided design and computer-aided manufacturing (CAD/CAM) titanium scaffold with an open mesh structure used for cranioplasty. A CAD/CAM titanium scaffold was removed due to late soft tissue complications 7.6 years after cranioplasty. The histological analyses involved the preparation of non-decalcified slices from the scaffold’s inner and outer sides as well as a light-microscopic evaluation, including the quantification of the bone that had formed over the years. Within the scaffold pores, vital connective tissue with both blood vessels and nerves was found. Exclusive bone formation only occurred at the edges of the implant, covering 0.21% of the skin-facing outer surface area. The inner scaffold surface, facing towards the brain, did not show any mineralization at all. Although conventional alloplastic materials for cranioplasty reduce surgery time and provide good esthetic results while mechanically protecting the underlying structures, a lack of adequate stimuli could explain the limited bone formation found. CAD/CAM porous titanium scaffolds alone insufficiently osseointegrate in such large bone defects of the skull. Future research should investigate alternative routes that enable long-term osteointegration in order to reduce complication rates after cranioplasty. Opportunities could be found in mechano-biologically optimized scaffolds, material modifications, surface coatings, or other routes to sustain bone formation.

Analysis of the Osteogenic Effects of Biomaterials Using Numerical Simulation

We describe the development of an optimization algorithm for determining the effects of different properties of implanted biomaterials on bone growth, based on the finite element method and bone self-optimization theory. The rate of osteogenesis and the bone density distribution of the implanted biomaterials were quantitatively analyzed. Using the proposed algorithm, a femur with implanted biodegradable biomaterials was simulated, and the osteogenic effects of different materials were measured. Simulation experiments mainly considered variations in the elastic modulus (20–3000 MPa) and degradation period (10, 20, and 30 days) for the implanted biodegradable biomaterials. Based on our algorithm, the osteogenic effects of the materials were optimal when the elastic modulus was 1000 MPa and the degradation period was 20 days. The simulation results for the metaphyseal bone of the left femur were compared with micro-CT images from rats with defective femurs, which demonstrated the effectiveness of the algorithm. The proposed method was effective for optimization of the bone structure and is expected to have applications in matching appropriate bones and biomaterials. These results provide important insights into the development of implanted biomaterials for both clinical medicine and materials science.

The expansile properties of kryptonite relating to cranioplasty

BACKGROUND AND PURPOSE

Since 2009, a synthetic material known as kryptonite has become increasingly utilized during cranioplasty to repair bony defects. It provides bone-like strength and adhesive properties that make it a suitable replacement for bone. However, applications have been observed in the immediate postoperative period that demonstrates an increase in its original volume, giving rise to irregularities in the cranial surface.

METHODS

Ten kryptonite samples were reconstituted and allowed to polymerize according to the manufacturer's directions. The kryptonite samples were molded into a cylindrical shape, and they were immersed in 10 graduated cylinders filled with normal saline. Measurements of the rise in saline relative to baseline were taken at 0, 10, 20, 30, 40, 50, and 60 minutes, and then hourly through 5 hours, with the final measurement recorded at 24 hours.

RESULTS

The mean expansion of kryptonite was approximately 49% with an SD of 22%. The bulk of the expansion occurred within the first 2 hours, after which the rate tended to plateau for the remaining 22 hours.

CONCLUSIONS

Kryptonite has been touted as an excellent alternative for repairing contour abnormalities manifested in cranioplasty. Given the unpredictability of its expansile properties, the surgeon must take this variability into careful consideration when planning the desired surgical outcome. The results of the current study were communicated with the manufacture. Immediately thereafter, the manufacturer withdrew the product from the US market and is no longer Food and Drug Administration approved for cranioplasty.

Synchronization of calcium sulphate cement degradation and new bone formation is improved by external mechanical regulation

A major challenge faced in the bone materials of weight-bearing without internal fixture support is the mismatch of material degradation and new bone formation, leading to weakening or even failure of the overall bony structure. This study demonstrated in the rat femur model that calcium sulphate cement degradation and new bone formation could be better synchronized by external mechanical force. An ascending force in line with calcium sulphate cement degradation could achieve bone healing in 37 days with ultimate load to failure of 87.00 ± 7.30 N, similar to that of intact femur (80.46 ± 2.79 N, p = 0.369). In contrast, the healing process under either a constant force or no force illustrated significant residual defect volumes of 1.47 ± 0.44 and 4.08 ± 0.89 mm(3) (p < 0.001), and weaker ultimate loads to failure of 69.56 ± 4.74 and 59.17 ± 7.48 N, respectively (p < 0.001). Our results suggest that the mechanical regulation approach deserves further investigation and may potentially offer a clinical strategy to improve synchronization.

Plastic surgeons and the management of trauma: from the JFK assassination to the Boston Marathon bombing

The fiftieth anniversary of the death by assassination of President John Kennedy is an opportunity to pay homage to his memory and also reflect on the important role plastic surgeons have played in the management of trauma. That reflection included a hypothetical scenario, a discussion of the surgical treatment of Kennedy (if he survived) and Governor Connally. The scenario describes the management of cranioplasty in the presence of scalp soft-tissue contracture, reconstruction of the proximal trachea, reconstitution of the abdominal wall, and restoration of a combined radius and soft-tissue defect. The development of diagnostic and therapeutic advances over the past 50 years in the care of maxillofacial trauma is described, including the evolution of imaging, timing of surgery, and operative techniques. Finally, contemporary measures of triage in situations involving mass casualties, as in the Boston Marathon bombings, complete the dedication to President Kennedy.

A review of reconstructive materials for use in craniofacial surgery bone fixation materials, bone substitutes, and distractors

Over the last 40 years, craniofacial surgery, in general, and surgery for craniosynostosis, in particular, has witnessed the introduction of a number of new materials for use in operations involving the cranial vault. Some of these materials have proven quite useful over time, while others have failed to meet their stated objectives. In this review, the more popular implant materials are analyzed, and their relative merits and drawbacks are discussed. Craniofacial surgery in the pediatric population has its own unique limitations, quite different from the adult population and those issues are reviewed as well.

Mineralization Potential of Electrospun PDO-Hydroxyapatite-Fibrinogen Blended Scaffolds

The current bone autograft procedure for cleft palate repair presents several disadvantages such as limited availability, additional invasive surgery, and donor site morbidity. The present preliminary study evaluates the mineralization potential of electrospun polydioxanone:nano-hydroxyapatite : fibrinogen (PDO : nHA : Fg) blended scaffolds in different simulated body fluids (SBF). Scaffolds were fabricated by blending PDO : nHA : Fg in the following percent by weight ratios: 100 : 0 : 0, 50 : 25 : 25, 50 : 50 : 0, 50 : 0 : 50, 0 : 0 : 100, and 0 : 50 : 50. Samples were immersed in (conventional (c), revised (r), ionic (i), and modified (m)) SBF for 5 and 14 days to induce mineralization. Scaffolds were characterized before and after mineralization via scanning electron microscopy, Alizarin Red-based assay, and modified burnout test. The addition of Fg resulted in scaffolds with smaller fiber diameters. Fg containing scaffolds also induced sheet-like mineralization while individual fiber mineralization was noticed in its absence. Mineralized electrospun Fg scaffolds without PDO were not mechanically stable after 5 days in SBF, but had superior mineralization capabilities which produced a thick bone-like mineral (BLM) layer throughout the scaffolds. 50 : 50 : 0 scaffolds incubated in either r-SBF for 5 days or c-SBF for 14 days produced scaffolds with high mineral content and individual-mineralized fibers. These mineralized scaffolds were still porous and will be further optimized as an effective bone substitute in future studies.

Review of bone substitutes

Bone substitutes are being increasingly used in craniofacial surgery and craniomaxillofacial trauma. We will review the history of the biomaterials and describe the ideal characteristics of bone substitutes, with a specific emphasis on craniofacial reconstruction. Some of the most commonly used bone substitutes are discussed in more depth, such as calcium phosphate and hydroxyapatite ceramics and cements, bioactive glass, and polymer products. Areas of active research and future directions include tissue engineering, with an increasing emphasis on bioactivity of the implant.

Controversies in skull reconstruction

In the early 1980s, it was shown that bone from the skull (membranous bone) maintained its volume to a significantly greater extent than bone from the rib and iliac crest regions (endochondral bone). However, the reason for this enhanced volume maintenance was not clarified for many years. On the basis of this enhanced volume maintenance, cranial bone became the ideal autogenous graft of choice for hard tissue repair. In the ensuing years, the current authors performed a large number of autogenous split skull cranial bone cranioplasties with significant success. However, the lure of an off-the-shelf material that obviates bone harvest remained. From 1995 to 2005, the senior author performed 20 full-thickness skull defect cranioplasty corrections using calcium phosphate cement (Norian Craniofacial Repair System; Synthes, Inc, West Chester, PA; Stryker-Leibinger, Kalamazoo, MI). Of these full-thickness defects, 16 were large (arbitrarily defined as greater than 25 cm2). In this paper, we report our long-term major and minor complication rates using this material. Because of our high, long-term complication rate (38%), we believe this material is contraindicated for large, full-thickness, skull defects (>25 cm2) and we have returned to autogenous cranial bone as the criterion standard for reconstruction in such patients.

Complications of hydroxyapatite bone cement in secondary pediatric craniofacial reconstruction

Hydroxyapatite cement has become a popular alternative to bone grafts in reconstructing the calvarium. Although animal studies have shown promising results with use of hydroxyapatite, human clinical studies have shown mixed results including significant rates of infection. This is a retrospective chart review during a 7-year period (1997-2003) of 20 patients who underwent secondary forehead cranioplasty with hydroxyapatite cement (Norian Craniofacial Reconstruction System). Basic demographics including age, sex, and diagnosis were identified. Characteristics of the defects were recorded including size, location, and depth (full versus partial thickness). The volume of hydroxyapatite and any adjunctive procedures were identified. The postoperative course was analyzed for length of follow-up and the presence of infections.Twenty patients were identified in which Norian had been used and 3 patients were lost to follow-up. Secondary forehead asymmetry was the most common presentation. The mean volume of hydroxyapatite used was 24.4 mL. All patients had initially acceptable aesthetic results. Of the 17 patients, 10 (59%) ultimately had infectious complications. Infection occurred on a mean of 17.3 months after surgery (range, 4 mo to 4 y), and the mean amount of hydroxyapatite used was 32.5 mL (infections) versus 14.3 mL (no infections). Of the 10 patients with complications, 9 required surgical debridement and subsequent delayed reconstruction. Although hydroxyapatite cement can yield excellent aesthetic results, its use in secondary reconstruction has yielded unacceptably high infection rates leading to discontinuation of its use in this patient population.

Biomaterials for craniofacial reconstruction

Biomaterials for reconstruction of bony defects of the skull comprise of osteosynthetic materials applied after osteotomies or traumatic fractures and materials to fill bony defects which result from malformation, trauma or tumor resections. Other applications concern functional augmentations for dental implants or aesthetic augmentations in the facial region. For ostheosynthesis, mini- and microplates made from titanium alloys provide major advantages concerning biocompatibility, stability and individual fitting to the implant bed. The necessity of removing asymptomatic plates and screws after fracture healing is still a controversial issue. Risks and costs of secondary surgery for removal face a low rate of complications (due to corrosion products) when the material remains in situ. Resorbable osteosynthesis systems have similar mechanical stability and are especially useful in the growing skull. The huge variety of biomaterials for the reconstruction of bony defects makes it difficult to decide which material is adequate for which indication and for which site. The optimal biomaterial that meets every requirement (e.g. biocompatibility, stability, intraoperative fitting, product safety, low costs etc.) does not exist. The different material types are (autogenic) bone and many alloplastics such as metals (mainly titanium), ceramics, plastics and composites. Future developments aim to improve physical and biological properties, especially regarding surface interactions. To date, tissue engineered bone is far from routine clinical application.

Calcium phosphate cements in skull reconstruction: a meta-analysis

BACKGROUND

This work addresses the controversy regarding the indications and results of calcium phosphate cements in skull reconstruction through a meta-analysis of the published literature.

METHODS

A PubMed search for articles reporting the use of calcium phosphate cements for skull reconstruction was performed. Data collected included age, volume of cement, defect size, material used, length of follow-up, placement in communication with paranasal sinuses or in irradiated fields, and complications.

RESULTS

Nineteen articles met the authors' inclusion criteria. The mean rates of complications were as follows: total complications, 13 percent (range, 0 to 62 percent); major complications, 9 percent (range, 0 to 62 percent); minor complications, 2 percent (range, 0 to 5 percent); infection, 5 percent (range, 0 to 22 percent); reoperation, 14 percent (range, 0 to 62 percent); and secondary surgery for contour correction, 1 percent (range, 0 to 12 percent). There was significant heterogeneity in the estimated rate of total and major complications, infection, and reoperation (p < 0.001), but minor complications and secondary contour correction had less heterogeneity (p = 0.58 and p = 0.78, respectively). Radiotherapy and communication with the paranasal sinuses significantly increased the complication rate (p < 0.05). Duration between surgery and complications averaged 17.5 months (range, 1 to 89 months).

CONCLUSIONS

When mean complication rate and complication range of calcium phosphate cements in our meta-analysis were compared with previous large cranioplasty studies using methylmethacrylate or autogenous bone, calcium phosphate fared no better, and sometimes fared worse, than these other modalities. Calcium phosphate, therefore, should only be used selectively, and prospective long-term studies are needed to further refine its role in skull reconstruction.

Single-stage implantation in the atrophic alveolar ridge of the mandible with the Norian skeletal repair system

Dental implants have played a part in rehabilitation of the jaws for more than 40 years, but in some cases they alone are inadequate because of extreme alveolar resorption. Correction may necessitate a two-stage procedure with additional interventions. We have made a preliminary study of the use of the Norian skeletal repair system (SRS), a carbonated calcium phosphate bone cement used to augment the alveolar ridge as a single-stage procedure, with the placement of implants. Ten edentulous patients with insufficient vertical bone in the interforaminal area were treated. After a horizontal osteotomy and crestal mobilisation of the alveolar ridge, implants were placed through the crestal part and fixed in the basal part of the mandible. Norian SRS was used to fill the gap created. The prostheses were inserted 3 months later. Forty implants were inserted. The follow up period was 60 months, and no fractures or dislocations developed. One of the implants was lost and there was one wound dehiscence, but no surgical intervention or revision was necessary. Radiographs showed good consolidation of the bony structure in all cases. We have described a reliable, single-stage procedure for augmentation and implantation in a highly atrophic alveolar crest. A 98% survival is comparable with those of other techniques. Further clinical trials are necessary to replicate these promising results.

The challenge of establishing preclinical models for segmental bone defect research

A considerable number of international research groups as well as commercial entities work on the development of new bone grafting materials, carriers, growth factors and specifically tissue-engineered constructs for bone regeneration. They are strongly interested in evaluating their concepts in highly reproducible large segmental defects in preclinical and large animal models. To allow comparison between different studies and their outcomes, it is essential that animal models, fixation devices, surgical procedures and methods of taking measurements are well standardized to produce reliable data pools and act as a base for further directions to orthopaedic and tissue engineering developments, specifically translation into the clinic. In this leading opinion paper, we aim to review and critically discuss the different large animal bone defect models reported in the literature. We conclude that most publications provide only rudimentary information on how to establish relevant preclinical segmental bone defects in large animals. Hence, we express our opinion on methodologies to establish preclinical critically sized, segmental bone defect models used in past research with reference to surgical techniques, fixation methods and postoperative management focusing on tibial fracture and segmental defect models.