**9. Current operative methods of frontal sinus management**

According to the clinical presentation of the fractures, treatment can range from reconstruction of the sinus walls to obliteration or cranialization. The degree of the displacement of the facture and the involvement of FSOT and/or the brain will determine the type of management of the fracture.

#### **9.1. Reconstruction of frontal sinus**

Common treatment for simple FS fracture without FSOT involvement requires adequate surgical exposure, an anatomic reduction and plating. Frontal sinus function and anatomy can be preserved this way in the majority of cases. [1]

#### *9.1.1. Open methods*

The surgical approach is usually through coronal incision or alternatively through existing lacerations if access is adequate. [37] After complete exposure of the fracture it is necessary to remove fragments of the anterior sinus wall to gain unobstructed access and to be able to evaluate integrity of posterior sinus wall, FSOT and sinus mucosa. In case of comminuted fracture with multiple fragments these can be lifted using periosteal elevator or small bone hook. Reduction of noncomminuted, compressed fractures can be challenging. When the convex surface of the frontal bone is fractured, it goes through a compression phase before it becomes concave. Fracture reduction requires enough force to pull the bone fragments back through the compression phase. [38] It may be necessary to remove bone from fracture line using cutting burr and widen it to gain enough space and relieve pressure for lifting of impacted fragment. It can be helpful to place a screw in the depressed segment, grasp it with a heavy hemostat, and pull upward - technique similar to use of Carrol-Girard screw for zygoma reduction. It is important to record orientation of removed fragments to prevent confusion during reassembly. Placing the fragments atop a drawing of the fracture will help to maintain the anatomic orientation of each fragment. Damaged or diseased mucosa of sinus should be removed as well as mucosa covering mobilized fragments, but intact mucosa should be left undisturbed.

FSOT can be visually evaluated and if there is doubt about its patency, it can be tested by application of flurescein or diluted methylene blue followed by inspection of nasal contents. Any suspicion of blockage of FSOT as evidenced by preoperative imaging studies or by intraoperative inspection and testing warrants treatment by sinus obliteration. Sinus preser‐ vation with duct reconstruction with the help of drainage tube or stent has been attempted in the past [39-41]. Unfortunately, a rate of stenosis of the duct following stent removal can be as high as 30%. [28] Recently there has been tendency to preserve and reconstruct sinuses despite injuries of FSOT with the help of endoscopic sinus surgery (ESS). [42]The final step is reas‐ sembly of fragments and reconstruction of anterior sinus wall using microplates or miniplates. Small gaps (4 to 10 mm) can be reconstructed with titanium mesh (Figure 9). [38]

stent has been attempted in the past [39‐41]. Unfortunately, a rate of stenosis of the duct following stent removal can be as high as 30%. [28] Recently there has been tendency to preserve and reconstruct sinuses despite injuries of FSOT with the help of endoscopic sinus surgery (ESS).

miniplates. Small gaps (4 to 10 mm) can be reconstructed with

titanium mesh (**Figure 9**). [38] **Figure 9. Fracture of FS with displacement of fragment into left orbit. Figure 9.** Fracture of FS with displacement of fragment into left orbit. Fragment is impinging on levator palpebrae su‐ perioris and displacing the globe. Reconstruction of orbital roof with titanium mesh after removal of the fragment.

**globe. Reconstruction of orbital roof with titanium mesh after removal of**

#### **Fragment is impinging on levator palpebrae superioris and displacing the** *9.1.2. Endoscopic methods*

**9. Current operative methods of frontal sinus management**

fracture.

*9.1.1. Open methods*

be left undisturbed.

**9.1. Reconstruction of frontal sinus**

be preserved this way in the majority of cases. [1]

448 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

According to the clinical presentation of the fractures, treatment can range from reconstruction of the sinus walls to obliteration or cranialization. The degree of the displacement of the facture and the involvement of FSOT and/or the brain will determine the type of management of the

Common treatment for simple FS fracture without FSOT involvement requires adequate surgical exposure, an anatomic reduction and plating. Frontal sinus function and anatomy can

The surgical approach is usually through coronal incision or alternatively through existing lacerations if access is adequate. [37] After complete exposure of the fracture it is necessary to remove fragments of the anterior sinus wall to gain unobstructed access and to be able to evaluate integrity of posterior sinus wall, FSOT and sinus mucosa. In case of comminuted fracture with multiple fragments these can be lifted using periosteal elevator or small bone hook. Reduction of noncomminuted, compressed fractures can be challenging. When the convex surface of the frontal bone is fractured, it goes through a compression phase before it becomes concave. Fracture reduction requires enough force to pull the bone fragments back through the compression phase. [38] It may be necessary to remove bone from fracture line using cutting burr and widen it to gain enough space and relieve pressure for lifting of impacted fragment. It can be helpful to place a screw in the depressed segment, grasp it with a heavy hemostat, and pull upward - technique similar to use of Carrol-Girard screw for zygoma reduction. It is important to record orientation of removed fragments to prevent confusion during reassembly. Placing the fragments atop a drawing of the fracture will help to maintain the anatomic orientation of each fragment. Damaged or diseased mucosa of sinus should be removed as well as mucosa covering mobilized fragments, but intact mucosa should

FSOT can be visually evaluated and if there is doubt about its patency, it can be tested by application of flurescein or diluted methylene blue followed by inspection of nasal contents. Any suspicion of blockage of FSOT as evidenced by preoperative imaging studies or by intraoperative inspection and testing warrants treatment by sinus obliteration. Sinus preser‐ vation with duct reconstruction with the help of drainage tube or stent has been attempted in the past [39-41]. Unfortunately, a rate of stenosis of the duct following stent removal can be as high as 30%. [28] Recently there has been tendency to preserve and reconstruct sinuses despite injuries of FSOT with the help of endoscopic sinus surgery (ESS). [42]The final step is reas‐ sembly of fragments and reconstruction of anterior sinus wall using microplates or miniplates.

Small gaps (4 to 10 mm) can be reconstructed with titanium mesh (Figure 9). [38]

**the fragment. 8.1.2 Endoscopic methods** Throughout all surgical fields, less invasive approaches have been employed to decrease the potential morbidity of traditional open procedures. Endoscopic procedures and their applications for management of FS fractures allow for more conservative management and sinus preservation in selected Throughout all surgical fields, less invasive approaches have been employed to decrease the potential morbidity of traditional open procedures. Endoscopic procedures and their appli‐ cations for management of FS fractures allow for more conservative management and sinus preservation in selected patients. [43] Trephination and endoscopic visualization of FS can be useful to assess the frontal recess as well as the extent of any posterior table injury. Skin incision is placed midway between the medial canthus and the glabella and a small cutting burr is used to open a 4- to 5-mm frontal sinusotomy. The posterior table and nasofrontal recess can be examined with a 0-degree and/or 30-degree endoscope. A Valsalva maneuver can assist with the diagnosis of a CSF leak. [44, 45]

patients. [43] Trephination and endoscopic visualization of FS can be useful to assess the frontal recess as well as the extent of any posterior table injury. Skin incision is placed midway between the medial canthus and the glabella and a small cutting burr is used to open a 4‐ to 5‐mm frontal sinusotomy. *Shumrick* reported on endoscopic reduction of FS fractures on 19 patients. The author's technique is similar endoscopic forehead lifting, with one central and two lateral hairline incisions. The forehead soft tissues are elevated subperiosteally, and the fractures are visual‐ ized by means of a 30-degree endoscope. An attempt is made to elevate the fragments with endoscopic elevators. However, it is usually necessary to approach the fragments directly through small forehead incisions (preferably hidden in the brow). The fractures are elevated using percutaneous nerve hooks, or by drilling into the fragments and grabbing them with threaded Steinmann pins. With gentle retraction, the fragments often elevate into a reduced position and are stable without the need for rigid fixation. Residual surface irregularities can be camouflaged with patches of Vicryl mesh. In four patients endoscopic fracture repair was unsuccessful, the fracture segments were unstable. These cases were converted to an open approach with coronal incisions and rigid fixation. The described technique is appropriate only for anterior wall FS fractures that have several large segments without extensive com‐ minution. [44]

Alternative technique of endoscopic transnasal reduction in combination with balloon support has also been reported. [45]

Endoscopic technique can also be used for camouflage of cosmetic deformity resulting from untreated depressed anterior table FS fractures above the orbital rim. The repair is performed 2 to 4 months after the injury when all forehead swelling has resolved. A 3-5 cm parasagittal working incision should be placed above the fracture, 3 cm behind the hairline and carried through the periosteum onto bone. A 1-2 cm subperiosteal endoscope incision is then placed at the same height, 6 cm medial to the working incision. Using an endoscopic brow lift elevator and external palpation, subperiosteal dissection is performed down to the level of the fracture and the periosteum is carefully elevated over the defect. Once the limits of the fracture have been visualized, alloplastic implant is fitted to the defect and fixed with self-drilling screws transcutaneously. [38]

Another usage of endoscopic surgery is reestablishing of patency of compromised FSOT. The endoscopic surgery can be either part of primary FS management or can be kept in reserve for delayed FSOT recanalization, should the obstruction develop or not resolve postoperatively. [42, 45]

#### **9.2. Obliteration of the frontal sinus**

The principle of FS obliteration is turning it into self-contained cavity devoid completely of mucosa, including microscopic remnants and extensions into pits of Breschet, and filling it by choice of material, or leaving it empty for spontaneous ossification. After gaining satisfactory access through some of the above mentioned surgical approaches, the anterior wall of sinus is removed and preserved for later reconstruction. This can be achieved by careful removal of fractured fragments. It is important to record orientation of removed fragments to prevent confusion during reassembly. Placing the fragments atop a drawing of the fracture will help to maintain the anatomic orientation of each fragment. With incomplete fractures, it is often necessary to remove the intact remainder of the anterior table or to perform formal frontal sinusotomy. To keep the bone cut within the confine of FS and prevent violation of intracranial space, it is necessary to mark the extent of the sinus. This can be done using pre-prepared sterilized film cut out or tin template based on posteroanterior skull x-ray in Caldwell projection with the patient placed 1.8 meters (6 feet) from the x-ray tube. [46] Alternatively, one tine of a two-pronged instrument, like tweezers, artery forceps or bipolar cautery can be placed through defect or trephination on each side of the anterior table. The internal tine is then used to probe the periphery of the sinus, while the outer tine is used to mark its outline. Another technique involves trans-illumination with a light source inserted into a fracture line. [38] Intraoperative navigation is the most accurate but requires specialized equipment. Sometimes it is possible to preserve contralateral FS if the contralateral sinus is not injured and the interlining septum remains intact. After the limits of the sinus have been defined, mini‐ plates can be pre-applied, spanning the osteotomy site. This allows accurate re-approximation of the bone fragments at the end of the procedure. During osteotomy, a burr or a saw should be angled toward the sinus cavity to avoid intracranial penetration. Care should be taken to avoid obliteration of the predrilled miniplate holes while performing the osteotomy. After complete exposure of the sinus, integrity of the posterior table is evaluated. If it is stable and free of large defects, sinus obliteration is acceptable. All sinus mucosa must be meticulously removed from all walls of the sinus. This applies also to temporarily removed fractured or osteotomized segments of anterior sinus wall. Inner walls of FS are reduced with a large cutting burr and smaller diamond burrs, as the surgeon proceeds deeper into the sinus. Access to the peripheral extensions of the sinus, especially above the orbital roofs, can be extremely difficult in patients with pronounced pneumatization. Special attention must be paid to the scalloped areas deep in the sinus. If the orbital roof has significant convexity, it may be necessary to remove a portion of the roof to gain access the posterior sinus mucosa. After complete removal of the sinus mucosa, the mucosa of the FS infundibulum is elevated and inverted into the frontal recess. A small temporalis muscle or pericranium plug is then placed over the FSOT to obliterate it. It can be held in place by packed oxycellulose (Surgicel®) or fibrin glue. Finally two bone chips obtained from the calvarium can be inserted to complete isolation of FS from the nasal cavity. [, 38] The FSOT can be further secured using the pedicled pericranial flap, which is rotated into the sinus. The rest of the sinus is packed with autologous or alloplastic material and anterior wall of FS is reassembled and stabilized with titanium miniplates. A number of autogenous and alloplastic materials have been used as fillers in FS obliteration.

only for anterior wall FS fractures that have several large segments without extensive com‐

Alternative technique of endoscopic transnasal reduction in combination with balloon support

Endoscopic technique can also be used for camouflage of cosmetic deformity resulting from untreated depressed anterior table FS fractures above the orbital rim. The repair is performed 2 to 4 months after the injury when all forehead swelling has resolved. A 3-5 cm parasagittal working incision should be placed above the fracture, 3 cm behind the hairline and carried through the periosteum onto bone. A 1-2 cm subperiosteal endoscope incision is then placed at the same height, 6 cm medial to the working incision. Using an endoscopic brow lift elevator and external palpation, subperiosteal dissection is performed down to the level of the fracture and the periosteum is carefully elevated over the defect. Once the limits of the fracture have been visualized, alloplastic implant is fitted to the defect and fixed with self-drilling screws

Another usage of endoscopic surgery is reestablishing of patency of compromised FSOT. The endoscopic surgery can be either part of primary FS management or can be kept in reserve for delayed FSOT recanalization, should the obstruction develop or not resolve postoperatively.

The principle of FS obliteration is turning it into self-contained cavity devoid completely of mucosa, including microscopic remnants and extensions into pits of Breschet, and filling it by choice of material, or leaving it empty for spontaneous ossification. After gaining satisfactory access through some of the above mentioned surgical approaches, the anterior wall of sinus is removed and preserved for later reconstruction. This can be achieved by careful removal of fractured fragments. It is important to record orientation of removed fragments to prevent confusion during reassembly. Placing the fragments atop a drawing of the fracture will help to maintain the anatomic orientation of each fragment. With incomplete fractures, it is often necessary to remove the intact remainder of the anterior table or to perform formal frontal sinusotomy. To keep the bone cut within the confine of FS and prevent violation of intracranial space, it is necessary to mark the extent of the sinus. This can be done using pre-prepared sterilized film cut out or tin template based on posteroanterior skull x-ray in Caldwell projection with the patient placed 1.8 meters (6 feet) from the x-ray tube. [46] Alternatively, one tine of a two-pronged instrument, like tweezers, artery forceps or bipolar cautery can be placed through defect or trephination on each side of the anterior table. The internal tine is then used to probe the periphery of the sinus, while the outer tine is used to mark its outline. Another technique involves trans-illumination with a light source inserted into a fracture line. [38] Intraoperative navigation is the most accurate but requires specialized equipment. Sometimes it is possible to preserve contralateral FS if the contralateral sinus is not injured and the interlining septum remains intact. After the limits of the sinus have been defined, mini‐ plates can be pre-applied, spanning the osteotomy site. This allows accurate re-approximation of the bone fragments at the end of the procedure. During osteotomy, a burr or a saw should

minution. [44]

has also been reported. [45]

450 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

transcutaneously. [38]

**9.2. Obliteration of the frontal sinus**

[42, 45]

**Autogenous fat** is probably the most widely used and has the longest tradition [47]. The advantages of fat grafts include ease of harvest, minimal donor site morbidity, ample available volume, and favorable handling characteristics. However, complication rate was reported as high as 18% [48]. Magnetic resonance study 24 months post-operatively found vital fatty tissue in only 6 out of 11 cases of obliteration of FS via an osteoplastic approach. Fatty necrosis occurred five times; whereas in four cases a transformation into granulation tissue and in one case into connective tissue could be seen [49].The harvest of the fat is performed using sterile technique: the surgeon will rescrub and a separate set of instruments that have not come in contact with the infected field is used. A transverse incision is made in the left lower abdominal quadrant, and subcutaneous fat is removed. Alternatively, a periumbilical incision can also be made. Bleeding is controlled using monopolar cautery, but excessive cauterization should be avoided because it may harm the fat cells and result in graft failure. Drainage of the abdomen is usually not necessary. [46]

**Autogenous muscle** graft harvested from temporalis muscle has advantage of being located within the operative field and being available in adequate volume. Like autogenous fat graft, this nonvascularized graft undergoes necrosis and eventual replacement by fibrous tissue. Donor site morbidity, including temporal hollowing and trismus, is unacceptable. [37]

**Autogenous bone** graft for FS obliteration was first described in 1969 [50]. Since then, cancellous bone grafts, most often harvested from the ilium, have been widely used as a filler material. Cancellous bone promotes re-ossification from both the periphery of the defect and centrally. The main contributions of the grafts are their osteoconductive properties and osteoinductive factors that are released from them during the process of resorption. [51] Another advantage of cancellous bone over adipose or muscle tissue for obliteration is that it [53].

is easier to distinguish radiographically in postoperative period between resorption, infection, and mucocele formation.[13,37] The greatest disadvantage to the use of cancellous bone grafts lies with the potential donor site morbidity. [52] Much more comfortable and safer is to harvest bone chips from adjacent calvarium. It can be done using bone scraper. In case the harvested amount of bone is not sufficient for filling of a large sinus, it can be augmented by admixture of bone substitute such as demineralized bone matrix (Figure 10) [53]. and mucocele formation.[13,37] The greatest disadvantage to the use of cancellous bone grafts lies with the potential donor site morbidity. [52] Much more comfortable and safer is to harvest bone chips from adjacent calvarium. It can be done using bone scraper. In case the harvested amount of bone is not sufficient for filling of a large sinus, it can be augmented by admixture of bone substitute such as demineralized bone matrix (**Figure 10**)

radiographically in postoperative period between resorption, infection,

**Figure 10. Fracture of left FS with minimal defect in posterior sinus wall Figure 10.** Fracture of left FS with minimal defect in posterior sinus wall and displacement of supraorbital rim. Recon‐ struction with titanium mesh and obliteration of the left FS with small pericranial flap.

**and displacement of supraorbital rim. Reconstruction with titanium mesh and obliteration of the left FS with small pericranial flap. Pericranial flap** has been widely used in anterior cranial fossa repair, reconstruction of the middle third of face defects, full-thickness scalp defects, and orbital defects. It is composed of the skull periosteum and the subgaleal fascia. The anteriorly based flap receives its blood supply from the supraorbital and supratrochlear arteries. Branches of the superficial temporal artery supply the laterally based flap. In contrast to all other avascular grafts used for sinus obliteration, the anteriorly based pericranial flap is composed of a well-vascularized tissue. The high vascularity makes this flap less prone to infections and turns it into an ideal method for obliteration of an infected cavity in a contaminated surgical field. [54]

is easier to distinguish radiographically in postoperative period between resorption, infection, and mucocele formation.[13,37] The greatest disadvantage to the use of cancellous bone grafts lies with the potential donor site morbidity. [52] Much more comfortable and safer is to harvest bone chips from adjacent calvarium. It can be done using bone scraper. In case the harvested amount of bone is not sufficient for filling of a large sinus, it can be augmented by admixture

radiographically in postoperative period between resorption, infection, and mucocele formation.[13,37] The greatest disadvantage to the use of cancellous bone grafts lies with the potential donor site morbidity. [52] Much more comfortable and safer is to harvest bone chips from adjacent calvarium. It can be done using bone scraper. In case the harvested amount of bone is not sufficient for filling of a large sinus, it can be augmented by admixture of bone substitute such as demineralized bone matrix (**Figure 10**)

**Figure 10. Fracture of left FS with minimal defect in posterior sinus wall and displacement of supraorbital rim. Reconstruction with titanium mesh**

**Figure 10.** Fracture of left FS with minimal defect in posterior sinus wall and displacement of supraorbital rim. Recon‐

**Pericranial flap** has been widely used in anterior cranial fossa repair, reconstruction of the middle third of face defects, full-thickness scalp defects, and orbital defects. It is composed of the skull periosteum and the subgaleal fascia. The anteriorly based flap receives its blood supply from the supraorbital and supratrochlear arteries. Branches of the superficial temporal

**and obliteration of the left FS with small pericranial flap.**

struction with titanium mesh and obliteration of the left FS with small pericranial flap.

of bone substitute such as demineralized bone matrix (Figure 10) [53].

452 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

[53].

**Allografts** like lyophilized cartilage [55] have the advantage of unlimited availability and lack of donor site morbidity. They are easy to handle, well adaptable to the defect, and thus reduce the operative time. Nevertheless, a failure in revascularization or subsequent osseointegration may occur, with associated risk of infection and extrusion [56]. Allogenic transplantation may be associated with increased risk of transmitting such diseases as hepatitis, AIDS or bovine spongiform encephalopathy.

**Alloplastic materials.***Methyl methacrylate* has been widely used alloplastic material since its introduction in 1940. It is well tolerated by soft tissues and has a density similar to bone, low thermal conductivity, and acceptable strength. However, the material produces a significant exothermic reaction during polymerization and foreign body reaction has been noted when it is polymerized in contact with tissue. [57]

**Hydroxyapatite** is a nonceramic calcium phosphate substance (*BoneSource, Stryker Leibinger*). It has osteoconductive properties, may be contoured to a defect, adheres to adjacent bone, has the ability to resist mucosal ingrowth, is resistant to infection, and is gradually replaced by native bone without a loss of volume. It has been investigated in experimental and clinical frontal sinus obliteration, but no long term observation results were reported [58]. Currently the use of hydroxyapatite cement in FS is not recommended. Significant problems related to material failure have been reported. [37]

**Glass-ionomer cement** is a hybrid glass polymer composite consisting of inorganic glass particles in an insoluble hydrogel matrix and bonded by ionic cross-links, hydrogen bridges, and chain entanglements. It is widely used in dentistry and also has been used in frontal sinus reconstruction [59]. However, because of severe complications after using glass ionomer cement next to dura mater this material has been taken off the market. [51]

**Proplast**, a polytetrafluoroethylene (*Teflon*) polymer with vitreous carbon fibers with pore sizes of 200 to 500 µm, is extremely porous to body fluids. Fibrous tissue ingrowth occurs rapidly and acts to mechanically stabilize the material. The material can cause a mild foreign body reaction. [51, 60]

**Glass ceramic***(bioactive glass)* has proved biocompatible, non-toxic and bone conducting material for occlusion of bone cavities. Total accurate obliteration of the sinus is achieved with different sizes of granules and blocks. Uneventful recovery and clinical outcome were seen in 92% of patients. Histopathological samples revealed a healing process progressing from the fibrous tissue phase to bone formation with scattered fibrous tissue and granule remnants. Bone produced by replacement of material was similar to natural frontal bone. Microbiologic cultures obtained with histological samples revealed no growth of bacteria. [61, 62]

**Spontaneous obliteration** was reported long ago by Samoilenko (1913), who found oblitera‐ tion by osteofibrous ingrowth in an experimental study on cats and dogs. His results were confirmed by later experimental studies that found subsequent replacement of obliterated FSs by cancellous bone to a variable degree. [51] Because FS after removal of all of its mucosa and occluding the nasofrontal duct is nothing more than an isolated bone cavity, it is not irrational to expect its gradual ossification. [63]

#### **9.3. Cranialization of the frontal sinus**

Cranialization is the most radical method of FS management. It can be considered an extension of obliteration procedure with complete removal of the posterior table. In effect, it increases the volume of anterior cranial fossa at the expense of cranialized FS, and the brain is allowed to expand into this additional extradural dead space. Because intracranial space is entered, and there is a possibility of encountering dura and brain injury, cranialization should always be performed in cooperation with a neurosurgeon. The approach to FS cranialization should be as a rule performed via a coronal incision. This approach provides wide access to the entire upper facial skeleton, allowing repair of associated naso-orbito-ethmoid fractures. Further‐ more, it allows dissection of a pericranial flap and harvesting of split calvarial bone grafts when necessary. [32] Maintaining integrity of the pericranial flap is critical for isolation of expanded intracranial space from FSOT and ethmoid cells.

Cranialization can be achieved either through sinusotomy as described in previous segment dealing with FS obliteration [13], or through frontal craniotomy. The choice is usually de‐ pendent on the degree of brain damage and preference of the neurosurgeon. [39]

In the former case, once access to the posterior table has been achieved, this is removed carefully in pieces with a rongeur. Larger pieces are saved in moist gauze for possible use replacing defects in the anterior table, instead of separately harvested bone grafts. When the dura is exposed, any adherent posterior table bone fragments should be carefully dissected off. The brain should be gently retracted and the remaining posterior table bone is then removed using straight and angled (Kerrison) rongeurs. Small overhangs at the periphery of the sinus should be smoothed completely, using a cutting burrs and the posterior table edge should be made flush with the anterior sinus walls, floor, and anterior cranial fossa. [32]

In most cases cranialization is performed through frontal craniotomy. This will allow thorough evaluation and repair of dural lacerations, immediate reconstruction of the orbital roof, medial orbital wall, or naso-orbito-ethmoidal fractures. [37] If a craniotomy has been performed, the portions of the posterior table associated with the craniotomy bone flap can be removed easily and safely, working on a sterile side table. [32] Also split calvarial bone grafts can be harvested from inner compacta of the craniotomy bone flap. Care should be taken during craniotomy to maintain the integrity of the cribriform plate and to avoid injury to the sagittal sinus. Once all the sinus mucosa and the posterior bony table have been removed the nonviable bone, soft tissue or damaged brain, are debrided and dural lacerations repaired. The next step is a reconstruction of the orbital roof, naso-orbital-ethmoid complex, or cribriform plate/fovea ethmoidalis, as necessary. Establishing a secure barrier between the cranial fossa and the nose is mandatory to prevent CSF leak and meningitis, but also to prevent ascending regrowth of the sinonasal mucosa with late mucocele. The frontal recess and FSOT are occluded as previously described in FS obliteration. Pericranial flap is sutured as far back as possible to the cranial base dura over the anterior cranial fossa to provide additional isolating layer of vascularized tissue. Because the wide pedicle of this flap will prevent the access to supraorbital rims, glabella and nasal skeleton, osteosynthesis of these parts must be completed first. A small bony defect (slit) must be left between supraorbital rims and inferior margin of repositioned craniotomy flap to prevent compression and ischemia of the pericranial flap. After reposition‐ ing of craniotomy flap the anterior table of FS is reconstructed as described in FS reconstruction section previously (Figure 11).

**Figure 11. Severe comminuted fracture involving anterior cranial fossa, supraorbital rims and naso‐orbito‐ethmoidal complex. Nasal dorsum, Figure 11.** Severe comminuted fracture involving anterior cranial fossa, supraorbital rims and naso-orbito-ethmoidal complex. Nasal dorsum, supraorbital rims and glabella are reconstructed with bone grafts harvested from inner corti‐ calis of craniotomy flap. Pericranial flap covers anterior cranial fossa.

**supraorbital rims and glabella are reconstructed with bone grafts**

#### **harvested from inner corticalis of craniotomy flap. Pericranial flap covers anterior cranial fossa. 10. Indications and treatment algorithms**

**9. Indications and treatment algorithms Injured FS can be managed in four basic ways**: 1‐observation, 2‐ **Injured FS can be managed in four basic ways**: 1-observation, 2-exploration and fracture reduction without or with internal fixation, 3- obliteration and 4-cranialization. [13] The choice of method is dependent on following factors:

Other circumstances important for treatment planning are associated facial injuries, patient's general health condition, expected compliance and availability for follow‐up, as well as availability of specialized services that could help in solving complications, namely endoscopic sinus surgery.

e) Presence or absence of CSF leak. f) Associated neurological injuries

confirmed by later experimental studies that found subsequent replacement of obliterated FSs by cancellous bone to a variable degree. [51] Because FS after removal of all of its mucosa and occluding the nasofrontal duct is nothing more than an isolated bone cavity, it is not irrational

Cranialization is the most radical method of FS management. It can be considered an extension of obliteration procedure with complete removal of the posterior table. In effect, it increases the volume of anterior cranial fossa at the expense of cranialized FS, and the brain is allowed to expand into this additional extradural dead space. Because intracranial space is entered, and there is a possibility of encountering dura and brain injury, cranialization should always be performed in cooperation with a neurosurgeon. The approach to FS cranialization should be as a rule performed via a coronal incision. This approach provides wide access to the entire upper facial skeleton, allowing repair of associated naso-orbito-ethmoid fractures. Further‐ more, it allows dissection of a pericranial flap and harvesting of split calvarial bone grafts when necessary. [32] Maintaining integrity of the pericranial flap is critical for isolation of expanded

Cranialization can be achieved either through sinusotomy as described in previous segment dealing with FS obliteration [13], or through frontal craniotomy. The choice is usually de‐

In the former case, once access to the posterior table has been achieved, this is removed carefully in pieces with a rongeur. Larger pieces are saved in moist gauze for possible use replacing defects in the anterior table, instead of separately harvested bone grafts. When the dura is exposed, any adherent posterior table bone fragments should be carefully dissected off. The brain should be gently retracted and the remaining posterior table bone is then removed using straight and angled (Kerrison) rongeurs. Small overhangs at the periphery of the sinus should be smoothed completely, using a cutting burrs and the posterior table edge should be made flush with the anterior sinus walls, floor, and anterior cranial fossa. [32]

In most cases cranialization is performed through frontal craniotomy. This will allow thorough evaluation and repair of dural lacerations, immediate reconstruction of the orbital roof, medial orbital wall, or naso-orbito-ethmoidal fractures. [37] If a craniotomy has been performed, the portions of the posterior table associated with the craniotomy bone flap can be removed easily and safely, working on a sterile side table. [32] Also split calvarial bone grafts can be harvested from inner compacta of the craniotomy bone flap. Care should be taken during craniotomy to maintain the integrity of the cribriform plate and to avoid injury to the sagittal sinus. Once all the sinus mucosa and the posterior bony table have been removed the nonviable bone, soft tissue or damaged brain, are debrided and dural lacerations repaired. The next step is a reconstruction of the orbital roof, naso-orbital-ethmoid complex, or cribriform plate/fovea ethmoidalis, as necessary. Establishing a secure barrier between the cranial fossa and the nose is mandatory to prevent CSF leak and meningitis, but also to prevent ascending regrowth of the sinonasal mucosa with late mucocele. The frontal recess and FSOT are occluded as previously described in FS obliteration. Pericranial flap is sutured as far back as possible to

pendent on the degree of brain damage and preference of the neurosurgeon. [39]

to expect its gradual ossification. [63]

454 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

**9.3. Cranialization of the frontal sinus**

intracranial space from FSOT and ethmoid cells.

### **f.** Associated neurological injuries

Other circumstances important for treatment planning are associated facial injuries, patient's general health condition, expected compliance and availability for follow-up, as well as availability of specialized services that could help in solving complications, namely endoscopic sinus surgery.

Degree and combination of anterior and posterior table, with or without FSOT involvement, would best help to determine the management protocol for FSFs, from observation to surgery [28, 38].

Improvement in diagnostic imaging, especially introduction of CT, and surgical technology has led to a wide variety of philosophies, protocols, and procedures. There is no universal agreement as to how the best achieve treatment goals, and no consensus on when surgical intervention is indicated. The choice of surgical method largely depends on the extent of the injury, the status of the FSOT and presence or absence of CSF leak. [63, 64] Most surgeons agree that nondisplaced fractures should be treated non-operatively. Management of patients with more complex injuries remains controversial. Many of the previously published reports are of poor quality (level 4 evidence) and represent retrospective case series consisting of highly censored samples with little reference given to exclusion or inclusion criteria. Additionally, most previous reports fail to include patients who were treated non-operatively, so little is known about the outcome of these patients or the relative frequency of procedures in the context of a population of trauma patients. [1]

#### **10.1. Anterior table fractures without FSOT involvement**

Nondisplaced or minimally displaced (less 2 mm) anterior table fractures can be observed. The risk of an aesthetic deformity increases with the degree of displacement (>2 mm). An endo‐ scopic repair or repair through alternative skin incision may be indicated in this patient population. However, many authors found it to be technically challenging.

Another option is to assess the degree of deformity after all facial edema has resolved. At this point, the patient can make an informed decision as to whether he/she desires surgical intervention, which can be endoscopic camouflage. A significant number of patients will opt for no surgical intervention. [27]

More complex anterior table fractures and those extending below the orbital rim may require open reduction using a coronal incision. The presence of improperly reduced bone segments, comminuted sequestrae, foreign bodies, devitalized and torn sinus mucosa expose the patient to a greater risk of infectious complications. [39] Reconstruction of the anterior wall using miniplates is a procedure virtually free of significant complications when the FSOT is patent.

#### **10.2. Anterior table fractures with FSOT involvement**

This is the point, where controversy about appropriate treatment of FS injuries begins. The traditional treatment for FS fractures with FSOT involvement is obliteration followed by anterior table reconstruction. [23,64] Some authors are not only strong proponents of obliter‐ ation, but employ this method also for some cases on nondisplaced anterior table fractures with FSOT involvement and even cranialize patients with nondisplaced and displaced fractures with FSOT involvement. [65]

On the other hand, the advancement in endoscopic surgery of frontal recess and modern imaging has enabled sinus preservation as a viable alternative to FS obliteration in cases with suspected FSOT involvement in the fracture. High-resolution, thin-section CT with sagittal reformatting may evaluate the involvement and severity of injury of the FSOT preoperatively and help in planning of its management. Sinus preservation may apply for displaced anterior wall FS fractures, even with concomitant minimally displaced posterior wall fractures, and without significant intracranial injury or persistent CSF leak. [28]

*Thong and Lee* [42] reported on primary endoscopic management. Patients with depressed anterior table FS fractures that involved FSOT were managed by ORIF via a coronal incision plus endoscopic fronto-ethmoidectomy with removal of any obstructing bony fragments, and insertion of a stent into the fronto-ethmoidal recess. Middle meatal nasal packs were left in situ for 1 week and patients were discharged home with prophylactic antibiotics. Frontal stents were removed after 1 month. Patients were followed up by regular endoscopic surveillance and CT scans were performed annually. There were no complications.

*Smith at al.* [45] treated 14 patients with FS and concurrent facial fractures. Seven patients were included in the modified treatment algorithm. Postoperatively, 5 patients had spontaneous FS ventilation. Two patients, both of whom had naso-orbito-ethmoid fractures, had persistent FSOT obstruction. These patients were successfully managed with an endoscopic FS proce‐ dure. The decision to repair, obliterate, or cranialize the sinus is often made intraoperatively, based on the extent of FSOT obstruction found during the procedure. [37]

#### **10.3. Posterior table fractures**

**f.** Associated neurological injuries

456 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

context of a population of trauma patients. [1]

for no surgical intervention. [27]

**10.1. Anterior table fractures without FSOT involvement**

**10.2. Anterior table fractures with FSOT involvement**

sinus surgery.

[28, 38].

Other circumstances important for treatment planning are associated facial injuries, patient's general health condition, expected compliance and availability for follow-up, as well as availability of specialized services that could help in solving complications, namely endoscopic

Degree and combination of anterior and posterior table, with or without FSOT involvement, would best help to determine the management protocol for FSFs, from observation to surgery

Improvement in diagnostic imaging, especially introduction of CT, and surgical technology has led to a wide variety of philosophies, protocols, and procedures. There is no universal agreement as to how the best achieve treatment goals, and no consensus on when surgical intervention is indicated. The choice of surgical method largely depends on the extent of the injury, the status of the FSOT and presence or absence of CSF leak. [63, 64] Most surgeons agree that nondisplaced fractures should be treated non-operatively. Management of patients with more complex injuries remains controversial. Many of the previously published reports are of poor quality (level 4 evidence) and represent retrospective case series consisting of highly censored samples with little reference given to exclusion or inclusion criteria. Additionally, most previous reports fail to include patients who were treated non-operatively, so little is known about the outcome of these patients or the relative frequency of procedures in the

Nondisplaced or minimally displaced (less 2 mm) anterior table fractures can be observed. The risk of an aesthetic deformity increases with the degree of displacement (>2 mm). An endo‐ scopic repair or repair through alternative skin incision may be indicated in this patient

Another option is to assess the degree of deformity after all facial edema has resolved. At this point, the patient can make an informed decision as to whether he/she desires surgical intervention, which can be endoscopic camouflage. A significant number of patients will opt

More complex anterior table fractures and those extending below the orbital rim may require open reduction using a coronal incision. The presence of improperly reduced bone segments, comminuted sequestrae, foreign bodies, devitalized and torn sinus mucosa expose the patient to a greater risk of infectious complications. [39] Reconstruction of the anterior wall using miniplates is a procedure virtually free of significant complications when the FSOT is patent.

This is the point, where controversy about appropriate treatment of FS injuries begins. The traditional treatment for FS fractures with FSOT involvement is obliteration followed by anterior table reconstruction. [23,64] Some authors are not only strong proponents of obliter‐

population. However, many authors found it to be technically challenging.

The primary decision criteria for surgical intervention are the degree of fracture displacement and the presence of a CSF leak. Traditionally as a rule of thumb, a width of the posterior table displacement is considered significant. [14, 32]

#### *10.3.1. Fractures without significant displacement*

Patients with posterior table displacement less than one table width and no CSF leak may be observed. Long-term follow-up with repeat CT scans at 2 months and 1 year is appropriate to rule out mucocele formation. If a CSF leak is present at time of injury, 1 week of observation is indicated; 50% will resolve spontaneously. The methods of conservative treatment include complete bed rest with oral acetazolamide 250 mg every 8 hours, prescription of laxatives and prophylactic antibiotics, and avoidance of breath holding and straining. Acetazolamide is a carbonic anhydrase inhibitor and is intended to reduce CSF secretion. Laxatives are given to prevent increases in intracranial pressure caused by constipation, and antibiotics to prevent infection. CSF drainage can be performed if the patient has intracranial infection or rapid leakage. Persistent leak openings in the posterior wall of the frontal sinus warrant repair via craniotomy. CT cisternography facilitate highly accurate preoperative localization of the fistula. [66] fistula. [66]craniotomy. CT cisternography facilitate highly accurate preoperative localization of the fistula. [66]

#### *10.3.2. Fractures with significant displacement 10.3.2. Fractures with significant displacement 10.3.2. Fractures with significant displacement*

Patients with posterior table displacement greater than one table width, no CSF leak, and only mild comminution should be considered for sinus obliteration. More severe injuries, with a frank CSF leak and/or moderate to severe comminution, will likely require removal of posterior table bone to repair the dural tear. If the injury or surgical repair results in disruption of more than 25 to 30% of the posterior table, sinus cranialization should be considered. [32] Patients with posterior table displacement greater than one table width, no CSF leak, and only mild comminution should be considered for sinus obliteration. More severe injuries, with a frank CSF leak and/or moderate to severe comminution, will likely require removal of posterior table bone to repair the dural tear. If the injury or surgical repair results in disruption of more than 25 to 30% of the posterior table, sinus cranialization should be considered. [32] Patients with posterior table displacement greater than one table width, no CSF leak, and only mild comminution should be considered for sinus obliteration. More severe injuries, with a frank CSF leak and/or moderate to severe comminution, will likely require removal of posterior table bone to repair the dural tear. If the injury or surgical repair results in disruption of more than 25 to 30% of the posterior table, sinus cranialization should be considered. [32]

#### **10.4. Treatment algorithms 10.4. Treatment algorithms 10.4. Treatment algorithms**

In an effort to optimize functional and cosmetic outcomes in complex clinical situations, while minimizing serious short- and long-term sequelae, algorithms were developed to determine which patients should receive operative intervention and which frontal sinus procedure is most appropriate in a given case. Following are examples of such algorithms placing emphasis on different aspects of FSF characteristics: In an effort to optimize functional and cosmetic outcomes in complex clinical situations, while minimizing serious short- and long-term sequelae, algorithms were developed to determine which patients should receive operative intervention and which frontal sinus procedure is most appropriate in a given case. Following are examples of such algorithms placing emphasis on different aspects of FSF characteristics: In an effort to optimize functional and cosmetic outcomes in complex clinical situations, while minimizing serious short- and long-term sequelae, algorithms were developed to determine which patients should receive operative intervention and which frontal sinus procedure is most appropriate in a given case. Following are examples of such algorithms placing emphasis on different aspects of FSF characteristics: It seems to be obvious that all these algorithms are to some extent simplified. To develop

It seems to be obvious that all these algorithms are to some extent simplified. To develop algorithm taking into account all possible characteristics and circumstances would probably result in a too -complicated diagram. It seems to be obvious that all these algorithms are to some extent simplified. To develop algorithm taking into account all possible characteristics and circumstances would probably result in a too -complicated diagram. algorithm taking into account all possible characteristics and circumstances would probably result in a too -complicated diagram.

**Cranialization**

**obliteration**

According to Chen et al., 2006 [64] According to Chen et al., 2006 [64]

**Sinus preservation**  Contemporary Management of Frontal Sinus Injuries and Frontal Bone Fractures http://dx.doi.org/10.5772/59096 459 Contemporary Management of Frontal Sinus Injuries and Frontal Bone Fractures 25 Contemporary Management of Frontal Sinus Injuries and Frontal Bone Fractures 25

> **Cranialize and repair anterior table**

**Observation Reconstruction**

**Repair NOE repair anterior table**

**table**  According to Bell et al., 2007 [37] According to Bell et al., 2007 [37] According to Bell et al., 2007 [37]

**Cranialize Repair**

**anterior**

craniotomy. CT cisternography facilitate highly accurate preoperative localization of the

craniotomy. CT cisternography facilitate highly accurate preoperative localization of the

Patients with posterior table displacement greater than one table width, no CSF leak, and only mild comminution should be considered for sinus obliteration. More severe injuries, with a frank CSF leak and/or moderate to severe comminution, will likely require removal of posterior table bone to repair the dural tear. If the injury or surgical repair results in disruption of more

Patients with posterior table displacement greater than one table width, no CSF leak, and only mild comminution should be considered for sinus obliteration. More severe injuries, with a frank CSF leak and/or moderate to severe comminution, will likely require removal of posterior table bone to repair the dural tear. If the injury or surgical repair results in disruption of more

Patients with posterior table displacement greater than one table width, no CSF leak, and only mild comminution should be considered for sinus obliteration. More severe injuries, with a frank CSF leak and/or moderate to severe comminution, will likely require removal of posterior table bone to repair the dural tear. If the injury or surgical repair results in disruption of more

In an effort to optimize functional and cosmetic outcomes in complex clinical situations, while minimizing serious short- and long-term sequelae, algorithms were developed to determine which patients should receive operative intervention and which frontal sinus procedure is most appropriate in a given case. Following are examples of such algorithms placing emphasis

In an effort to optimize functional and cosmetic outcomes in complex clinical situations, while minimizing serious short- and long-term sequelae, algorithms were developed to determine which patients should receive operative intervention and which frontal sinus procedure is most appropriate in a given case. Following are examples of such algorithms placing emphasis

In an effort to optimize functional and cosmetic outcomes in complex clinical situations, while minimizing serious short- and long-term sequelae, algorithms were developed to determine which patients should receive operative intervention and which frontal sinus procedure is most appropriate in a given case. Following are examples of such algorithms placing emphasis

It seems to be obvious that all these algorithms are to some extent simplified. To develop algorithm taking into account all possible characteristics and circumstances would probably

It seems to be obvious that all these algorithms are to some extent simplified. To develop algorithm taking into account all possible characteristics and circumstances would probably

It seems to be obvious that all these algorithms are to some extent simplified. To develop algorithm taking into account all possible characteristics and circumstances would probably

**FS fracture**

**No CSF leak CSF leak**

**Observe 7 days**

**Resolved Persistent**

**Cranialization**

**FSOT involved**

**ORIF of anterior table Sinus obliteration**

than 25 to 30% of the posterior table, sinus cranialization should be considered. [32]

than 25 to 30% of the posterior table, sinus cranialization should be considered. [32]

than 25 to 30% of the posterior table, sinus cranialization should be considered. [32]

fistula. [66]

fistula. [66]

fistula. [66]

24

*10.3.2. Fractures with significant displacement*

*10.3.2. Fractures with significant displacement*

*10.3.2. Fractures with significant displacement*

458 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

24 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

on different aspects of FSF characteristics:

on different aspects of FSF characteristics:

on different aspects of FSF characteristics:

result in a too -complicated diagram.

result in a too -complicated diagram.

result in a too -complicated diagram.

**FSOT not involved**

**ORIF of anterior table Sinus preservation**

According to Chen et al., 2006 [64]

According to Chen et al., 2006 [64]

**10.4. Treatment algorithms**

**10.4. Treatment algorithms**

**10.4. Treatment algorithms**

According to Rodriguez at al., 2008 [65] According to Rodriguez at al., 2008 [65]

According to Rodriguez at al., 2008 [65]

#### **11. Complications of frontal sinus fractures 11. Complications of frontal sinus fractures** Frontal sinus fractures carry a risk of complications, which can be characterized as early or

**11. Complications of frontal sinus fractures**

Frontal sinus fractures carry a risk of complications, which can be characterized as early or late. Complication rates for patients with FS fractures range from 10% to 17%. [67] The most Frontal sinus fractures carry a risk of complications, which can be characterized as early or late. Complication rates for patients with FS fractures range from 10% to 17%. [67] The most late. Complication rates for patients with FS fractures range from 10% to 17%. [67] The most serious are early infectious complications that can endanger patient's life. There is a greater urgency of operative treatment in cases where intracranial infection can develop through potential communication of the neurocranium with the non-sterile sinuses. Bellamy et al. [68] found that delay in repair beyond 48 hours was associated with a greater than fourfold increased risk of serious infection, even when controlling for clinical and statistical confound‐ ers. However, FS fracture patients often present with other, more severe intracranial and bodily injuries. Thus, definitive management is often delayed until the patient's neurologic and medical condition has stabilized. Several additional factors are associated with serious infection, among them use of an external cerebrospinal fluid drainage catheter and soft-tissue infection that predisposes to deeper infection in these patients.

The recommendation of 7-days waiting period for management of persistent CSF leaks was borne out of historical studies that predate the modern research. According to recent opinion, there is no evidence to support 7 days as a particularly important threshold for cerebrospinal fluid leak management to prevent intracranial infection. [68]

The efficacy of antibiotic prophylaxis, especially beyond the perioperative period, in frontal sinus and skull base injury remains unclear. The risks of antibiotic use, evolving drug resis‐ tances and associated patient and epidemiologic costs require careful evaluation. To date, there is no standard of care for postoperative antibiotic administration, though many surgeons continue to administer antibiotics beyond the immediate perioperative period.[68] A variety of adverse events can occur after fixation of a frontal sinus fracture, such as frontal sinusitis, mucocele, mucopyocele, cerebrospinal fluid leakage, deformity, hardware infection, head‐ ache, and chronic pain in the area of the injury.[67] Potentially life threatening late complica‐ tions include thrombosis of the cavernous sinus, encephalitis, mucopyocele, or brain abscess. [21] In the literature there is no consensus regarding the follow-up. Because of the possible long period after trauma until complications, namely mucocele, develops, some advise to continue to follow these patients for a lifetime. Others suggest a follow-up period of 5 or 7 years. [26]


2.5.2. Bone Properties

The biomechanical behavior of bone is extremely complex due to its anisotropic and viscoelastic nature. However, it exhibits elastic behavior under usual mechanical conditions. The femur being a long bone, the analysis was performed considering the transversely isotropic properties of cortical bone and, according to the literature [53], it has been assumed that the trabecular bone presents a large-scale isotropy. Bone properties were estimated using the apparent density (*ρapp*), which was obtained employing the "Segment Statistics" tool of 3D Slicer® [18] and considering its relationship with the Hounsfield units (HU). Rho et al. [54] determined a linear relationship between HU and apparent density for the proximal femur:

$$
\rho\_{app} = 131/1000 + 1.067 \text{Hll} / 1000 \text{[g/cm}^3] \tag{16}
$$

The Young's modulus of cortical bone in the longitudinal direction (*Ez*,*cortical*) and the stiffness of trabecular one (*Etrabecular*) were estimated using the equation described by Keyak et al. [55] and rectified by Schileo et al. [56]:

$$E\_{z,overall} = E\_{trabeam} = 14.900 \left( 0.6 \rho\_{app} \right)^{1.86} \text{[MPa]} \tag{17}$$

In addition, the Young's modulus (*Ex*, *Ey*) and shear modulus (*Gyz*, *Gzx*) in the transverse direction, for cortical bone, were calculated using Pithioux's laws [57]:

$$E\_x = E\_y = 0.6E\_z \tag{18}$$

$$\mathbf{G}\_{yz} = \mathbf{G}\_{z\mathbf{x}} = \mathbf{0}.\mathbf{25E}\_{z} \tag{19}$$

Poisson's coefficients in the longitudinal (*νyz*, *νzx*) and transverse (*νxy*) directions of cortical bone were obtained from the literature, being 0.25 and 0.4, respectively [58]; the value of 0.3 for the Poisson's coefficient (*ν*) of trabecular bone was taken from experimental data [59]. The shear modulus in the longitudinal direction (*Gxy*) of cortical bone [60,61] and the shear modulus (*G*) of trabecular bone were obtained from the following equations:

$$G\_{xy} = \frac{E\_x}{2\left(1 + \upsilon\_{xy}\right)}\tag{20}$$

$$G = \frac{E}{2(1+\nu)}\tag{21}$$

Table 1 summarizes the physical and mechanical properties of both bones for GC1 and GC2.

**Table 1.** Physical and mechanical properties of the cortical and trabecular bone of each geometric case.


**Spatial Communication Activity in Wireless Sensor Networks Based on Migrated Base Stations**

Jan Nikodem, Marek Woda and Maciej Nikodem

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50078


**6. Conclusions**

In this paper, a fault feature extraction of the rolling bearing signal under strong noise background is studied by using the combination of VMD optimized with information entropy and RobustICA. The conclusions were as follows.

(1) Although VMD can analyze the signal in the frequency domain, the effect is limited by the impact of modal component *k* and penalty factor *α*. This study used information entropy to optimize VMD to set initialization parameters. Compared with the way of setting parameters by experience, this method can search for a better combination of VMD parameters. This method can overcome the problems of modal aliasing and endpoint effect caused by impact component and noise interference in traditional EMD, LMD and EEMD, and has a good processing effect on the extraction of fault characteristic frequency of nonstationary and nonlinear signals. It can extract fault features more accurately. Compared with the traditional method, the experimental results show that this method can highlight the fault characteristic frequency and distinguish the fault.

(2) In this experiment, a typical simulation signal model is selected and Gaussian white noise is added on this basis to simulate the periodic impact signal caused by bearing fault under the condition of noise interference. Then, a signal component screening criterion based on correlation coefficient and kurtosis is established, and the optimal signal component is used to construct the observation signal channel of RobustICAalgorithm, so as to achieve the purpose of noise reduction.Through the in-depth analysis of the constructed simulation signal and the collected signal of the actual rolling bearing, it can be seen that compared with the traditional methods based on LMD–RobustICA, EMD–RobustICA, and EEMD–RobustICA, the method proposed in this paper can obtain better evaluation results of noise-reduction index, and the time–domain waveform of the signal after noise reduction is very similar to the waveform of the original signal.

(3) By comparing and analyzing the envelope demodulation results obtained by different methods, it can be seen that after the envelope spectrum analysis using the method proposed in this paper, the amplitude of fault characteristic frequency has been enhanced, and the surrounding interference will not affect the identification of fault fundamental frequency and frequency doubling, which is more convenient for fault diagnosis and analysis.

As an effective adaptive signal processing method, VMD has achieved good results in the field of fault diagnosis. However, the relevant parameters of this method need to be set in advance. In the process of parameter optimization, there is no theoretical basis for the definition of parameter search range. Therefore, in the next work, we will conduct in-depth research and further improve the parameter optimization method of VMD method.

**Author Contributions:** Conceptualization, J.Y.; Data curation, J.Y. and C.Z.; Formal analysis, C.Z. and X.L.; Funding acquisition, J.Y.; Methodology, J.Y.; Resources, J.Y.; Writing—original draft, J.Y.; Writing—review and editing, J.Y., C.Z., and X.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the Scientific research fund project of Baoshan University (Grant No. ZKMS202101), Special Basic Cooperative Research Programs of Yunnan Provincial Undergraduate Universities' Association (Grant No. 202001BA070001-109), collaborative education project of industry university cooperation of the Ministry of Education (Grant No.<PHONE_NUMBER>26), 10th batches of Baoshan young and middle-aged leaders training project in academic and technical (Grant No. 202109), and the Ph.D. research startup foundation of Yunnan Normal University (Grant No.01000205020503131).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data used to support the findings of this study are available from the corresponding author upon request.

**Conflicts of Interest:** The authors declare that they have no conflict of interest.