Biomaterials for reconstruction of the internal orbit

Biomaterials and implants for orbital floor repair

Treatment of orbital floor fractures and defects is often a complex issue. Repair of these injuries essentially aims to restore the continuity of the orbital floor and to provide an adequate support to the orbital content. Several materials and implants have been proposed over the years for orbital floor reconstruction, in the hope of achieving the best clinical outcome for the patient. Autografts have been traditionally considered as the "gold standard" choice due to the absence of an adverse immunological response, but they are available in limited amounts and carry the need for extra surgery. In order to overcome the drawbacks related to autografts, researchers' and surgeons' attention has been progressively attracted by alloplastic materials, which can be commercially produced and easily tailored to fit a wide range of specific clinical needs. In this review the advantages and limitations of the various biomaterials proposed and tested for orbital floor repair are critically examined and discussed. Criteria and guidelines for optimal material/implant choice, as well as future research directions, are also presented, in an attempt to understand whether an ideal biomaterial already exists or a truly functional implant will eventually materialise in the next few years.

Mechanical Properties of Orbital Fat and Its Encapsulating Connective Tissue

There is an increasing need to understand the mechanical properties of human orbital fat and its encapsulating connective tissue (OFCT), but such knowledge is not available in the current literature. The purpose of the present study is to examine the mechanical properties of the OFCT. From 5 pairs of 76- to 92-year-old Caucasian human eyes and 33 5- to 7-month-old porcine eyes, 5 human and 11 porcine OFCT samples were dissected at the posterior pole or adjacent to the pole in the vertical, horizontal, and radial directions. Sample dimensions were fixed or measured. Tensile tests were performed on the samples in body-temperature saline. The stress-strain relationship was first approximately linear and then became nonlinear. The linear, the neo-Hookean, and the Mooney–Rivlin constants are reported in Tables 1 and 2. No statistical difference was found among their properties in the different directions in either the human or the porcine samples. Statistical differences were found between the human and the porcine material constants in the horizontal and radial directions. Among our material models, only the Mooney–Rivlin model was able to capture the mechanical properties of the OFCT in large deformation properly. The Mooney–Rivlin model was especially adaptive to the human data. This is the first time the mechanical properties of the human and porcine OFCT have been examined in the literature. We believe our data will provide valuable information to others regarding designing implant biomaterials in orbital treatments and developing computer models to study orbital biomechanics.

[Function-retaining reconstruction after orbital trauma]

Precise anatomical reconstruction of extensive orbital fractures is a challenging procedure for surgeons. Computer-assisted technologies, anatomical preformed implants and the possibility of acquiring 3D images using cone beam computed tomography are considered as the new standards. In this short review these applications are presented.

Biomaterials in skull base surgery

Reconstruction materials and techniques for the base of the skull have undergone rapid developments and differentiation in recent years. While mostly autotransplants, collagens or resorbable alloplastic materials are preferred for duraplasties, pronounced organ-specific differences can be observed in the reconstruction of hard tissues. The use of polymethylmethacryl bone cement, once wide-spread, has decreased greatly due to the release of toxic monomers. Bony autotransplants are still used primarily for smaller skull-base defects, intraoperatively formable titanium nets may be also used for larger fronto- or laterobasal reconstructions of bony defects. Defects in visible areas are increasingly closed with preformed titanium or ceramic implants, which are planned and fitted to the individual patient using preoperative CT imaging. At the skull base, this applies especially to reconstructions of the frontal sinus. For extensive reconstructions of the orbita, titanium nets and non-resorbable plastics have proven valuable; in closing smaller defects especially of the orbital floor, resorbable implants based on Polyglactin 901 are also used.

Use of titanium mesh for reconstruction of extensive defects in fronto-orbito-ethmoidal fracture

Traumatic injuries treatment of the fronto-naso-orbito-ethmoidal region has been one of the most challenging treatments within maxillofacial surgery, particularly of extensive orbital defects, very common in this type of pathologic condition. A 48-year-old man involved in a car collision presented an extensive bilateral fracture of the orbit medial wall, nasal bones, the nasal septum, and the frontal anterior table. The clinical and tomographic findings concluded the diagnosis of a maxilla and fronto-naso-orbito-ethmoidal fracture. Among the variety of biomaterials, the titanium mesh was elected because of the extension and magnitude of the bone defect, obtaining this way esthetic and functional results with better prognosis.

Bone regeneration using a bone morphogenetic protein-2 saturated slow-release gelatin hydrogel sheet: evaluation in a canine orbital floor fracture model

Bone regeneration methods using bone inductive cytokines show promise, however, due to early diffusion and absorption of single applications of these cytokines, the bone inductive effects are limited. In this study, such a system was applied, using gelatin hydrogel as a carrier to slowly release (bone morphogenetic proteins) BMP-2 over a relatively long period in vivo. By coupling this slow-release system with a biodegradable copolymer, this composite was evaluated by grafting into bone defect sites of a canine orbital floor fracture model. Radio-iodinated BMP-2 incorporated into the gelatin hydrogel carrier and subcutaneously implanted into nude mice showed a similar slow release (approximately, 60% at 3 days and 80% at 14 days) as the radiolabeled hydrogel carrier alone. In contrast, greater than 90% of fluid-injected BMP-2 was lost in the injection site within the first 8 hours. Using a dog model of orbital floor fracture, a complex of BMP-2-saturated gelatin hydrogel and a polylactide-based biodegradable copolymer was implanted into the orbital bone defect. Bone structural analysis, using radiography, histologic examination, and microfocus CT, showed greatly enhanced new bone formation and defect healing at 5 weeks in comparison to implanted biodegradable copolymer directly saturated with the same amount of BMP-2 (no slow-release hydrogel carrier). A trabecular structure resembling that normal bone tissue was restored in the new bone tissue generated by the slow-release constructs. Thus study demonstrates the potential of slow-release BMP-2 for bone healing of difficult defects.

Biomimetic coatings for bone tissue engineering of critical-sized defects

The repair of critical-sized bone defects is still challenging in the fields of implantology, maxillofacial surgery and orthopaedics. Current therapies such as autografts and allografts are associated with various limitations. Cytokine-based bone tissue engineering has been attracting increasing attention. Bone-inducing agents have been locally injected to stimulate the native bone-formation activity, but without much success. The reason is that these drugs must be delivered slowly and at a low concentration to be effective. This then mimics the natural method of cytokine release. For this purpose, a suitable vehicle was developed, the so-called biomimetic coating, which can be deposited on metal implants as well as on biomaterials. Materials that are currently used to fill bony defects cannot by themselves trigger bone formation. Therefore, biological functionalization of such materials by the biomimetic method resulted in a novel biomimetic coating onto different biomaterials. Bone morphogenetic protein 2 (BMP-2)-incorporated biomimetic coating can be a solution for a large bone defect repair in the fields of dental implantology, maxillofacial surgery and orthopaedics. Here, we review the performance of the biomimetic coating both in vitro and in vivo.

Treatment with individual orbital wall implants in humans - 1-Year ophthalmologic evaluation

BACKGROUND

In 2009 a method of creating individual, patient specific orbital wall implants using rapid prototyping (RP) was shown in a preliminary human study. That study showed that it is financially viable to produce anatomical models and that this technology could be used in the repair of orbital floor fractures.

MATERIALS AND METHODS

In this study, 24 consecutive subjects who had sustained orbital fractures (14 males, 6 females) without any coexisting central nervous system or globe injury were assessed post-operatively. The first series of 12 patients, recruited during the period 2005-2006, were treated with classical method (CM) of forming titanium mesh by manual manipulation, based on individual subjective assessment of the extent and shape of damaged orbital walls. The following 12 cases, recruited between 2007 and 2008, were treated with patient specific titanium mesh implants designed with an RP method. Early (2 weeks) and late (12 months) follow-up was performed. Patients were evaluated by binocular single vision (BSV) test and an assessment of eye globe motility.

RESULTS

The superiority of the RP treatment method over CM was shown on the basis of early results when BSV loss area and reduction of vertical visual disparity (VVD) in upgaze were considered. Better outcomes for the RP group were confirmed in the late follow-up results which showed a reduction of BSV loss area, correction of primary globe position and a very significant improvement in upgaze.

CONCLUSIONS

One-year post-operatively, functional assessment of pre-bent individual implants of the orbital wall has shown the technique to be a predictable reconstruction method. Nevertheless longer follow-up and an increase in the number of cases treated are required for the full evaluation of the technique.

Options in orbital floor reconstruction in blowout fractures: a review of ten cases

OBJECTIVE

The purpose of this case series was to assess the aesthetic and functional outcome of orbital floor reconstruction performed with calvarial bone graft, titanium mesh or prolene mesh.

METHODS

Ten cases of orbital blowout fractures treated at our centre from October 2006 to July 2008 were considered for this study. Clinical examination, patient satisfaction and radiographic investigations were used to assess repaired fractures.

RESULTS

Prolene mesh was used in four cases, titanium mesh was used in four cases and calvarial graft used in two cases. Nine patients had significant improvement in their esthetic appearance. Symmetry was restored in all cases. All ten cases had a noticeable improvement in the function. Of total ten cases six had diplopia, three recovered completely during the six months after the surgery. Three cases showed improvement later. All ten cases with enopthalmos recovered completely. Of the nine patients with infraorbital numbness, all recovered completely during the six months following surgery. One patient where the reconstruction was done with calvarial bone graft showed mild discrepancy in the ocular level.

CONCLUSION

For small, linear defects measuring less than 2cm with enopthalmos and restricted ocular movements, prolene mesh (four cases) was used. For larger defects and impure blowout fractures involving the infraorbital rim, calvarial graft (two cases) or titanium mesh (four cases) was used. The outcome of surgery with all three materials was satisfactory. No postoperative complications were seen except for mild hypoglobus in a case reconstructed with calvarial graft. All three materials, calvarial graft, titanium mesh, prolene mesh, have the potential to be useful reconstructive materials in orbital floor blowout fractures.

Medial orbital wall reconstruction with swine bone cortex

Fractures of the medial orbital wall can be isolated or associated with other orbital defects arising from maxillofacial fractures. However, a medial orbital wall defect results in a relative increase of the orbital volume. The decision regarding surgical intervention in the management of medial orbital wall fractures is influenced by a variety of factors, including the presence and severity of restricted ocular motility, the degree of enophthalmos, the estimated fracture size, and the clinical judgment of the surgeon; however, untreated medial orbital wall fractures can result in secondary enophthalmos. The aim of this study was to describe our experience with deantigenated swine bone cortex for the reconstruction of the fractured medial orbital wall.

Reconstruction of orbital wall defects: critical review of 72 patients

Between January 1996 and December 2001, 72 out of 354 patients were included in a retrospective study analysing the outcome of repaired orbital wall defects. Selection was dependent on the availability of pre and postoperative CT scans and on ophthalmologic examination. In particular, orthoptical assessment was performed up to 1 year after operation. In 72 patients, 83 orbital wall defects were analysed and allocated to one of five categories. Accuracy and type of reconstruction were assessed in unilateral orbital wall defects (n=61) and compared with functional outcome. Reconstruction was performed by using PDS membrane (39%), calvarian bone (13%), titanium mesh (7%) or a combination of these materials (37%). Postoperatively, 91% of the patients had normal vision without double images within 20 degrees at every gaze. Accuracy of reconstruction correlated with severity of orbital injury and functional outcome. Functional outcome between category II and III fractures showed no significant difference. The medial margin of the lateral infraorbital fissure being preserved (category II fracture) facilitates reconstruction technically. Accuracy of orbital reconstruction is one important factor to obtain best functional outcome, but other determinants like displacement and/or atrophy of intramuscular cone fat should be considered.

Densification and Microstructural Behaviour on the Sintering of Blended Elemental Ti-35Nb-7Zr-5Ta Alloy

Beta titanium alloys, e.g., are now the main target for medical materials. Ti-35Nb-7Zr- 5Ta alloy were manufactured by blended elemental (BE) powder method, which appears to be one of the most promising technique for titanium parts production at reduced cost. The process employs hydrided powders as raw materials with low production costs and oxygen content. Among the titanium alloys recently developed, Ti-35Nb-7Zr-5Ta is distinguished for presenting low modulus of elasticity, high mechanical resistance and superior biocompatibility. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering among 800 at 1500 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. In this work, an alternative blending technique (with planetary mill) was used. The samples presented a good densification and a totally β-type microstructure, with complete dissolution of alloying elements in the titanium matrix with the temperature increase with low pore content.

Anatomical 3-dimensional Pre-bent Titanium Implant for Orbital Floor Fractures

PURPOSE

This cadaver study evaluates the use of pre-bent 3-dimensional titanium mesh implants for orbital floor and medial wall reconstruction.

DESIGN

Nonrandomized comparative study.

PARTICIPANTS

Eight human cadaveric heads (n = 16 orbits).

METHODS

Transcutaneous incisions were used to expose both orbital floors in each cadaveric head. Unilateral orbital floor and medial wall fractures were generated in each specimen. The contralateral orbit remained uninjured. The fractures then were repaired with pre-bent titanium mesh fan plates molded from aluminum templates presenting different sizes. The templates were generated from topographical computed tomography (CT) data previously obtained from normal subjects. The accuracy of orbital reconstruction was evaluated with postoperative CT scans.

MAIN OUTCOME MEASURES

The mean value of the distances between the implant and the bony orbit was evaluated.

RESULTS

The mean distance between all 16 plates and their respective orbital floors/medial walls was 0.81+/-0.74 mm. Mean values were 0.68+/-0.63 mm for the unfractured side and 0.93+/-0.82 mm for the fractured side. No significant differences were found between orbits when evaluated for side of injury, gender, or size of defect.

CONCLUSION

Pre-bent 3-dimensional titanium mesh implants provide accurate reconstruction of orbital floor and medial orbital wall fractures. The mean implant error was <1 mm for all orbits studied.

Bioresorbable poly-L/DL-lactide (P[L/DL]LA 70/30) plates are reliable for repairing large inferior orbital wall bony defects: a pilot study

PURPOSE

The purpose of this study was to share our clinical experience on the use of bioresorbable poly-L/DL-lactide implants (P[L/DL]LA) 70/30 (PolyMax; Synthes, Oberdorf, Switzerland) to repair, large (> or =2 cm2), inferior orbital wall defects and to evaluate whether P(L/DL)LA 70/30 implants adequately support the orbital soft tissue contents.

PATIENTS AND METHODS

Thirteen patients who suffered orbital blowout fractures, with > or =2 cm2 bony defects in the inferior orbital wall, took part in the study. The inferior orbital wall was explored via subconjunctival approach. After repositioning of orbital content, each inferior orbital wall was reconstructed using a round plate of P(L/DL)LA 70/30. Computed tomography and magnetic resonance imaging coronal sections were undertaken before the operation and 2 and 36 weeks postoperatively.

RESULTS

The magnetic resonance imaging studies showed no abnormal tissue foreign body reactions in the orbital region. The material showed adequate strength to stabilize bone segments during the critical period of bone healing. The bone healing seems to take place along the bone fragments. The clinical outcome was excellent in 11 of the 13 cases (85%). At the end of the study, only one patient had mild enophthalmos.

CONCLUSIONS

Bioresorbable P(L/DL)LA 70/30 implants are safe and reliable for the repair of large defects (> or =2 cm2) in the inferior orbital wall. It seems that this is the first reported biodegradable material, in the literature, to promote bone healing along the bone fragments of the inferior orbital wall.