The spackling paste made from mixing the biologic and nonbiologic agents.
Photograph demonstrates the wide coverage of the mixture onto the defect site.
Six-month postoperative outcome showed good defect coverage.
Axial CT scan showed strong mineralization of bone and defect coverage in 5-mm units.
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Arnaoutakis D, Bahrami A, Cohn JE, Smith JE. Cranioplasty Using a Mixture of Biologic and Nonbiologic Agents. JAMA Facial Plast Surg. 2018;20(1):9–13. doi:10.1001/jamafacial.2017.0437
Can the combination of biologic autologous bone and nonbiologic allograft materials for defect coverage in cranioplasty provide favorable outcomes and limit the occurrence of complications?
In this medical records review that included 26 patients, successful mineralization following primary cranioplasty was shown to be achieved in all but 1 patient with a modified technique. Comparable to previous studies, the rate of infection was 11% and loss rate was 4%.
This unique technique for incorporating both biologic autologous bone and nonbiologic allograft materials for complex defect coverage in cranioplasty is favorable, with satisfactory aesthetic outcomes and limited postoperative complications.
A surgeon faces challenges with cranioplasty techniques to achieve a successful result with relatively few complications.
To describe a unique technique for incorporating both biologic autologous bone and nonbiologic allograft materials for defect coverage in cranioplasty with favorable outcomes and low occurrence of complications.
Design, Setting, and Participants
A retrospective medical records review of all 26 patients who underwent primary cranioplasty procedure with a modified technique between January 2011 and December 2015 at a high-volume head and neck oncologic reconstructive practice was conducted; data analysis was also performed during that period. After several years of experience with traditional cranioplasty maneuvers, the modified technique has evolved to incorporate both autologous bone grafts and alloplastic materials in the formation of a shapeable on-lay material. Data were collected on demographics, need for cranioplasty, materials used, outcomes, and risk factors.
Main Outcomes and Measures
Rates of infection, hematoma, flap loss or resorption, cerebrospinal fluid leak, hardware exposure or malfunction, and repeated reconstruction.
Of the 26 patients, 21 (81%) were men; mean (SD) age was 65.8 (14.3) years. Eight (31%) patients had a history of diabetes, 4 (15%) patients were receiving immunosuppressive drugs, and 5 (19%) patients were active smokers at the time of surgery. Neoplasia was the most common cause of the calvarial defect seen, responsible for 20 of 28 (71%) operative defects and necessitated procedures. All but 1 patient achieved successful mineralization following primary cranioplasty with the modified technique; this success was verified based on physical examination and follow-up imaging. Complications were rare and involved only 3 patients who developed postoperative infection; 1 (4%) of these patients lost the integrity of the cranioplasty. Thus, the rate of infection was 11% and loss rate was 4%. Preoperative and postoperative radiotherapy appeared to have no bearing on graft survival.
Conclusions and Relevance
The results using a unique technique for incorporating both biologic autologous bone and nonbiologic allograft materials for defect coverage in cranioplasty are favorable, with satisfactory aesthetic outcomes and limited postoperative complications.
Level of Evidence
The primary function of the skull serves to house and protect the brain as well as other important components of the central nervous system. Cranioplasty is the surgical intervention to repair any cranial defects that may leave the brain susceptible to injury, thereby reestablishing anatomic boundaries between intracranial and extracranial structures.1 Such defects may result from trauma, neoplasm, congenital malformation, postdecompressive craniectomy performed for traumatic brain injury, or cerebral infarction with imminent intracranial hypertension.2,3 The goal of cranioplasty is not only to provide cosmetic restoration, but also to provide relief from physiologic and psychosocial damage.
Autologous bone remains the most common material used for reconstruction of skull defects and possesses several ideal characteristics, such as strength, biocompatibility, and an ability to achieve a favorable contour. However, in recent years, several studies have demonstrated that the use of autologous bone results in bony resorption, donor-site morbidity, and difficulties in reshaping.4,5 In certain situations, the original bone flap may need to be discarded and consideration then given to alternative means, such as alloplastic material.
Throughout the history of cranioplasty, many different types of materials have been used, including polymethyl methacrylate, hydroxyapatite cement, carbon fiber–reinforced polymer, and titanium.6,7 However, the traditional drawback of alloplastic materials includes their susceptibility to infection and higher likelihood of extrusion. With evolving biomedical technology, newer materials are available to equip a surgeon’s armamentarium. Herein, we describe a novel cranioplasty technique incorporating both biologic and nonbiologic agents and present our outcomes with this technique over a 4-year period.
We reviewed the medical records of all patients who underwent a cranioplasty procedure using our modified approach by the senior author (J.E.S.) between January 2011 and December 2015; data analysis was also performed during that period. A total of 26 patients were included. Clinical data were obtained by examination of progress notes, operative reports, discharge summaries, and clinic notes. Data also were collected on demographics, causes, materials used, outcomes, and risk factors. Causes were categorized as neoplasia, neurologic intervention, or other medical need. Variables included smoking history, previous or posttreatment radiotherapy, history of diabetes or immunosuppression, and size of defect. Outcomes were reported as rates of infection, hematoma, flap loss or resorption, cerebrospinal fluid leak, hardware exposure or malfunction, and repeated reconstruction. The medical records review was approved by Baylor Scott & White All Saints Medical Center; all patients provided written informed consent.
After years of experience with traditional cranioplasty maneuvers, our modified technique has evolved to incorporate both autologous bone grafts and alloplastic materials in the formation of a shapeable on-lay material. Approximately 20 cm3 of corticocancellous bone graft, either from the iliac crest or anterior tibial area, are harvested in the usual manner and then ground (Stryker Bone Mill; Stryker). Added to the crushed bone graft are a bone allograft (Trinity Evolution; Orthofix), 2.8 mL of bone morphogenetic protein, 100 g of acellular dermal matrix powder, 8 mL of platelet-rich plasma, and 10 × 10 cm2 of 0.25-mm thickness L-polylactic acid sheeting (Synthes) that is also ground to small bits using the Stryker Bone Mill. All components are mixed in a sterile specimen container until all additives are dispersed equally.
The dura is repaired or protected as necessary prior to the cranioplasty. The mixture is then spackled on the defect and shaped into the correct size, shape, and thickness for the defect. Local vascularized rotational or microvascular free flaps are used for coverage; skin grafts are often harvested to repair the secondary defect site. Prior to closure of the defect, Hyperflex HD (Cisco) or another acellular dermal substitute is placed between the flap and the cranioplasty material.
Between 2011 and 2015, 26 patients underwent primary cranioplasty with our modified technique. Two patients developed a second defect site, increasing the total to 28 procedures. The mean defect size for this study was 58.9 cm2. The patient group included 21 (81%) men, with a mean (SD) age of 65.8 (14.3) years (range, 42-99 years). Eight patients had a history of diabetes, 4 patients were receiving immunosuppressive drugs, and 5 patients were active smokers at the time of surgery (Table).
In our high-volume head and neck oncologic reconstructive practice, neoplasia was the most common cause of calvarial defect seen, responsible for 20 of 28 (71%) operative defects and necessitated procedures. Ten patients presented for reconstruction following primary radiotherapy to the head and neck, and 14 patients required postoperative radiotherapy as an adjunctive treatment option for cancer. One patient was referred to our practice for chronic osteomyelitis after craniectomy.
All patients achieved successful mineralization following primary cranioplasty with our modified technique (Figure 1). This result was verified based on physical examination (Figure 2 and Figure 3) and follow-up imaging (Figure 4). Eight patients required free-tissue transfer to close the cutaneous defect; otherwise, scalp rotational and other forms of advancement flaps were utilized. Complications were rare and involved only 3 patients who developed postoperative infection; of these, only 1 patient lost the integrity of the cranioplasty. Thus, the rate of infection was 11%, and loss rate was 4%. Preoperative and postoperative radiotherapy seemed to have no bearing on graft survival in this study. Other studies have shown infection rates of 10.3% to 26.4%8-10 and loss rates for cranioplasty between 5.6% and 8.7%.8,11
Cranioplasty can be performed as a primary or secondary procedure depending on the duration, severity, and location of the defect. It is undertaken most often following traumatic injuries; however, in our practice, cranioplasty is most commonly required for reconstruction following neoplasia. In children younger than 3 years, growing skull fractures and congenital anomalies remain common needs for cranioplasty. Contraindications to performing cranioplasty include hydrocephalus, infection, and brain swelling. In certain instances, waiting to perform cranioplasty may be warranted to prevent the development of devitalized autograft or allograft infections.
A fundamental tenet of reconstructive surgery remains the concept of replacing missing structures with those most similar to them.12 For select patients, reconstruction of full-thickness scalp defects can be successfully achieved with a dermal regeneration template or outer table calvarial decortication and surface grafting. Yet, prior scalp radiotherapy, which many of our patients received, indicates probable failure for using these techniques.13,14 As such, cranioplasty surgeons still favor autologous bone grafts for reconstruction of small- to medium-sized defects with viable donor sites. Vascularized bone flaps have been shown to be of particular benefit in settings of previous infection or irradiation.15 The most common source of autografts is either the iliac crest or tibia, but can also be derived from the calvarium or rib.16 The major advantages of osteoplastic reconstruction include less risk of infection, predictable harvest sites, and use of the patient’s own tissue. Drawbacks include possible resorption, loss of contour, and availability of sufficient graft material (ie, bone).17
Allograft materials include polymethyl methacrylate, ceramics, hydroxyapatite, carbon fiber–reinforced polymer, and titanium. An ideal cranioplasty material should possess several properties18: (1) easy to shape, (2) resistant to heat or cold, (3) ready to use, (4) inexpensive, and (5) resistant to infection.
Although polymethyl methacrylate is common and economically viable, it often leads to poor cosmetic outcomes, because it poorly integrates into surrounding tissues. The osteoinductive potency of hydroxyapatite makes it desirable for use in cranioplasty; however, its associated high infection rate and lack of ability to bind to surrounding bone because of dural pulsations has limited its popularity and sidelined its use mostly as an adjunctive material to refine contour over preexisting bone.19 Ceramic materials often have too much volume and are difficult to attach to the adjacent bone. Titanium is the preferred alloplastic material for most surgeons because it is readily available, has excellent rigidity, is easily molded, and has an inert nature; however, it can become easily exposed after adjunctive radiotherapy.20
In addition to cranioplasty material, consideration must be given to soft-tissue coverage. When available, primary closure of the wound without tension from the natural pliable vascularized tissue is preferred. Primary closure is given special attention in alloplastic reconstructions where this tissue serves as a barrier to infection and extrusion. When local flaps are not adequate for tissue coverage, the reconstructive ladder must be climbed toward microvascular free tissue transfer, including anterolateral thigh, radial forearm, or latissimus dorsi flaps.21
The future of cranioplasty likely rests in the field of tissue engineering, which integrates viable cells and biochemical factors to serve biologic functions.22 Growth factors form a core of growth factor–mediated tissue engineering. For example, bone morphologic proteins play an integral role in the regulation of cellular behavior, including proliferation and differentiation, during development. Bone morphologic proteins can regulate processes such as embryogenesis and fracture healing and can promote bone production.23 Scaffolds for bone engineering aim to serve as a template analogous to the extracellular matrix of bone. Scaffolds should possess the capacity to support cellular adhesion and proliferation. Synthetic polymers offer tighter control over the production process and may demonstrate more reproducible outcomes in production. An additional advantage of synthetic polymers is how they can be readily manipulated to change mechanical properties, such as degradation rate and porosity.24
Trinity Evolution is an allograft composed of cancellous bone with viable osteogenic and osteoprogenitor cells retained within the matrix. Both types of cells provide an osteoconductive scaffold and reliable number of viable cells within the bone matrix. Platelets in platelet-rich plasma release growth factors and cytokines that stimulate bone and soft-tissue healing. These proteins include platelet-derived growth factor, transforming growth factor-β, and vascular endothelial growth factor,25 which serve the function of being chemotactic for stem cells and endothelial cells and leads to increased collagen production, vascular permeability, and angiogenesis. The crushed polylactic acid plates serve as the scaffold for the solution and are thought to allow vascular ingrowth and cellular adhesion from 1 component to the next.26
Each element of our mixture provides a unique feature essential to successful cranioplasty. A similar approach has been successfully used to reconstruct a posttraumatic maxillary ridge with a radial forearm free flap and allogeneic avascular bone graft augmented with bone morphologic proteins and bone marrow aspirate concentrate.27 A polylactic acid mesh was used as a containment unit for the bone graft. The mean defect size for this study was 58.9 cm2. By adding other products to the corticocancellous bone obtained from the patient, we increase the volume of product that can be applied to the defect and decrease the amount of native bone that is needed.
Our results are favorable, with satisfactory aesthetic outcomes and limited postoperative complications. Two cases of infection involved patients with poorly controlled diabetes, and the third case occurred in a patient receiving immunosuppressive medication. No episodes of cerebrospinal fluid leak occurred, and no flap revision was needed. Although incorporating the adjunct nonbiologic adjunct materials incurs added cost to the procedure, we believe this increased cost is validated by improved primary aesthetic contouring and decreased number of secondary operations compared with isolated bone grafts.28
Limitations of our study include the retrospective nature as well as the small sample size. Long-term studies will be needed to assess bony resorption over time.
Although advancements in cranioplasty have been achieved over time to allow aesthetic and predictable outcomes, there is still a relatively high incidence of complications. Patients with a history of infection or irradiation are at particular risk for poor outcomes. We have described a unique technique for incorporating both biologic autologous bone and nonbiologic allograft materials for defect coverage in cranioplasty with favorable outcomes.
Accepted for Publication: March 5, 2017.
Corresponding Author: Demetri Arnaoutakis, MD, Division of Facial Plastic and Reconstructive Surgery, Department of Otolaryngology—Head & Neck Surgery, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390 (email@example.com).
Published Online: November 2, 2017. doi:10.1001/jamafacial.2017.0437
Author Contributions: Drs Arnaoutakis and Smith had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: All authors.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: All authors.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Arnaoutakis, Bahrami, Cohn.
Administrative, technical, or material support: Smith.
Study supervision: Smith.
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient depicted in Figure 3 for granting permission to publish this information.
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