Bone grafts from extraoral sites
Today, due to the rapid developments in oral implantology, patients have very high expectations for the outcome of implant-supported functional and esthetic restorations, even in cases of severe atrophy or alveolar ridge defects. It is therefore important, in addition to the planned prosthetic rehabilitation, to select the most appropriate augmentation procedure. Even in cases of extreme bone atrophy, high security and predictability are recommended to achieve a successful ridge reconstruction without the risk of harm to further anatomical structures due to complications.
Severe jaw atrophy can be the result of periodontal disease that has not been treated successfully or not been treated at all. In a situation where chronic infection is present over many years, the alveolar bone is sometimes resorbed up until the apex of the teeth. Severe bone atrophy, especially in the maxilla, also occurs in cases of a poorly adapted full prosthesis due to unphysiologic loading with the remaining dentition in the opposite jaw.29 Large bony defects in the oral cavity can be due to traumatic injuries and can also result from surgical resections of malignant tumors with safety margins. Failed implants with or without augmentation procedures usually lead to a severe bony and soft tissue defect, sometimes with the loss of adjacent teeth.14 This is very difficult to treat due to scar tissue formation and the reduced regeneration capacity of the recipient site.
In all these cases, reconstruction of the alveolar crest requires a large amount of bone that cannot be harvested from intraoral sites without the risk of injuring various anatomical structures. In such situations, bone harvesting from extraoral sites offers the possibility of harvesting the necessary bone volume to reconstruct these defects.
The different extraoral donor sites that are available and applied for bone grafting in the oral cavity are the tibia,21 calvaria,50 and the iliac crest, the last being the most frequently used.35 Calvaria bone grafts have a very pronounced cortical structure. They are similar to bone grafts harvested from the retromolar area of the mandible and should be prepared in a similar way. If the harvesting is correctly performed, this donor area is associated with low morbidity. An intensive and detailed explanation should be provided to patients in order to alleviate any fears they may have concerning the harvesting procedure. The tibia21 can easily deliver a significant amount of cancellous bone; however, harvesting corticocancellous bone from this area in large amounts is related to an increased morbidity rate. Bone grafts from the iliac crest are still the most frequently used for the treatment of extended vertical and horizontal bony defects requiring a large 3D reconstrution.12,47
This chapter presents detailed discussions about the calvaria, tibia, and iliac crest as extraoral bone harvesting sites.
5.2 Bone harvesting from the calvaria
Harvesting monocortical bone plates from the calvaria for the reconstruction of the orbital bone wall was first reported in 1929 by Dandy.7 This technique is still used today for the treatment of difficult orbital floor fractures.22 The application of such a procedure is especially appropriate for maxillofacial surgery, since the harvesting area is in proximity to the recipient site50 (Fig 5-1). In 1982, Tessier presented a systematic description of the various methods for harvesting and grafting parietal bone for craniofacial reconstructions.48 Since then, many other studies have been performed, and authors have reported about the advantage of this approach.6,17,50 Tulasne reported about the use of calvaria bone blocks and bone chips for sinus and alveolar ridge augmentation.16,17,30,33,34,42,45,46,50–52 This technique is used today in different centers and is recommended by many authors as an alternative to bone grafts from the iliac crest.3,17,45
Bone removal in the area of the skull should always be carried out in the hair-bearing portion of the scalp. Upon harvesting bone from the parietal part of the skull, only the external cortical layer should be removed in order to maintain sufficient protection of the brain that is guaranteed by the inner cortical structure.49 This approach also minimizes the risks of opening the dura mater.
In the following paragraph, a clinical case is presented in which the technique of harvesting bone from the calvaria as it was described by Vinci53 is elucidated.
5.2.1 Patient preparation
Patients receive perioperative antibiotic prophylaxis with amoxicillin and clavulanic acid (2 g/day for 10 days). The surgery is performed under general anesthesia.
The hair and scalp are washed three times with a disinfecting solution (Cutasept; Bode Chemie, Hamburg, Germany) and dried each time with sterile gauze to achieve the best possible reduction of the bacterial load. Depending on the hair length, different incisions of the scalp can be performed: In cases of long hair (more than 10 cm), the hypothetical incision line should be traced with a felt-tip pen and the hair should be tied together in two strands very close to the incision. In short hair (less than 10 cm), the incision line can be outlined directly in the surgical area, wherein the hair is divided with a sterilized comb and then fixed with Vaseline or an antimicrobial gel (Fig 5-2a). In exceptional cases, the area can be shaved along the incision line to a width of 5 mm. As tape cannot be fixed to the hair, it is important that the surrounding areas are thoroughly cleaned and disinfected in order to prevent infection. The donor area of the skull is strictly prepared as a separate surgical area to the recipient region so that no cross-contamination of the scalp occurs within the oral cavity.
5.2.2 Surgical procedure
The area of the incision line is infiltrated with refrigerated physiological solution, providing good local hemostasis without requiring any vascoconstrictor drug, and at the same time helping to elevate the scalp from the underlying bone. The incision should always be made with a scalpel and not electrosurgically to avoid damage to the hair follicles and prevent postoperative alopecia. The incision should be a minimum length of 10 cm (Fig 5-2b), to generate an appropriate overview of the skull cortex. In patients with little or no hair, the incision should be made along one of the present wrinkles. The scalp can then be detached from the underlying pericranium, widely exposing the bone surface.
Depending on the quantity of bone to be harvested, the exposed area must remain at least 2 cm from the median line and not extend beyond the insertion of the temporal muscle. In the anterior direction, the exposed area must remain behind the coronal suture, since the two bone tables in the suture areas are fused together without cancellous bone in between, which makes harvesting extremely difficult. This is important in order to avoid the danger of exposing the dura mater.53
The limits of the first strip are fixed using a 2-mm round bur (Fig 5-2c). To determine the base of the traced line, care must be taken to stop the drilling procedure once a resistance to advancement of the bur occurs, with slight bleeding. This osteotomy can also be performed using piezoelectric devices, which is much more time consuming. After finishing the osteotomy of the first strip, the monocortical bone plate should be carefully lifted using a hammer and an angulated chisel. If the bone graft does not mobilize immediately, the preparation should be continued in order to avoid damaging the inner structures by a forceful mobilization (Fig 5-2d). Once the first graft has been harvested, the procedure to remove other blocks becomes easier. Depending on the scope of the planned augmentation, multiple segments can be dissected and removed from the skull (Fig 5-2e).
After the removal of the cortical plates, cancellous bone can be collected to be used as filling material in the gaps of the reconstructed crest.23 It is advisable to complete the removal of bone with a reduction of the existing sharp bone edges by using a bone scraper (Fig 5-2f and g). Due to the severe bleeding that will occur, it is recommended to fill the donor site with collagen fleece. The wound closure is performed with subcutaneous and multilayer sutures in the connective tissue of the scalp to perform a tension-free and completely tight wound closure (Fig 5-2h and i). To avoid hematoma, a compression bandage is applied, which should remain in place for 24 h56 (Fig 5-2j).
5.2.3 Possible complications
Some authors have reported extremely rare complications after bone harvesting from the calvaria.8,10,17,49 Besides the classic complications of hematoma formation and very rare local infection in the surgical field, exposure of the dura mater during the harvesting procedure may occur without any patient impairment in about 10% of cases.20,27 The exposed areas of the dura mater should be augmented again with the existing bone material in order to protect the dura mater with bone under the scalp. If damage to the dura mater occurs, with leakage of cerebrospinal fluid, a neurosurgical intervention is necessary to cover the leak.
Due to the risk of hair loss, electrocoagulation in direct contact with hair follicles should be avoided.
Extradural, subdural, and intracerebral hematomas are described as a very rare complication (in the range of less than 0.02%). However, these are classified as extremely rare and are surgeon dependent, so that it can be assumed that the removal of calvarial bone is a good and safe treatment option.27 The transplanted bone shows good long-term results (Fig 5-3a to e).17
5.3 Bone harvesting from the tibia
Harvesting of a bone graft from the tibia head for grafting procedures in alveolar cleft patients was described as early as 1914.9 However, this method differs significantly from the techniques used today for the purposes of oral implant rehabilitation.21,26
The benefits of harvesting cancellous bone from the proximal tibia are that it is a relatively simple surgical procedure, especially in obese patients where iliac crest harvesting is more difficult, and that it is possible to obtain a sufficient amount of extraoral bone grafts without great discomfort or hospitalization but with rapid mobilization of the patient.26,32 The proximal tibia is also an ideal donor site for obtaining a substantial volume of cancellous bone. Experimental anatomical studies have shown that up to 15 ml of cancellous bone can be harvested from this site with a very low complication rate, and the complications that do occur are mainly minor wound infections or hematomas.18,32
Surgically, the tibia can be accessed via the lateral, medial or caudal approach, the medial approach being the most appropriate because no muscle attachment or origin is found at the medial condyle at the height of, or slightly cranially to, the tibial tuberosity (Fig 5-4). With this approach, and in contrast to the lateral one, no ligaments or onsets of the movement muscles need to be mobilized. Therefore, immediately under the skin, the front surface of the medial condyle can be accessed in an extremely uncomplicated manner in order to harvest bone.5,21 Both a monocortical block and sufficient cancellous bone can be harvested from this site. Caudally, the sartorius, gracilis, and semitendinosus muscles are attached to this bone surface in a common tendinous plate (pes anserinus). Part of pes anserinus may serve as a proximal pedicle for a bony lid in the case of an osteoplastic harvesting technique (see Fig 5-4).
In the following paragraph, the technique of harvesting bone from the tibia is presented as it was described by Jakse.21
Spongiosa is especially suited for the augmentation of multiple-wall bone defects because it does not have a stability of its own, as is the case with a cortico-spongeous bone block graft. Since it is mainly spongiosa that is harvested from the head of the tibia, tibial bone grafting has also been successfully introduced as the primary approach in treating cleft palate patients.
The indication for harvesting cancellous bone from the tibia is well suited for highly extended maxillary sinuses, where an augmentation with a mixture of heterologous material and cancellous bone from the area of the tibia can be performed.19,28,39 Due to the reduced availability of monocortical bone, harvesting from the tibia is not suitable for absolute alveolar ridge augmentation in the vertical and horizontal dimensions.
5.3.2 Patient preparation
Patients receive perioperative antibiotic coverage with amoxicillin and clavulanic acid (1.2 g/day for 10 days). The surgery is usually performed under local anesthesia.
Absolutely sterile conditions are a prerequisite for a tibial bone harvest. Patients are placed in a flat position. The leg from which the bone is to be harvested should be in a slight supine position and slightly bent at the knee joint. The operation site must be disinfected and covered with surgical drapes.
The anatomical structures to be operated on and the planned incision are marked with sterile methylene blue. Important anatomical markers are the articular cavity, the tibial tuberosity, and the medial margin of the tibia. There is an expansive bone surface limited by these structures under the skin, which is easily palpable. On this surface, the incision is marked according to the oblique tension lines of the skin from a cranial medial position in a caudal lateral direction. The surgical access should be at least 20 mm below the joint cavity of the knee. The incision is approximately 20- to 30-mm long. The distal end point is situated at the level of the lower margin of the tibial tuberosity (Fig 5-5a).
Local anesthesia is administered with one to two carpules of mepivacaine 3% without a vasoconstrictor (e.g. Scandonest 3%; Septodont, Saint-Maur-des-Fosses Cedex, France). The first application of local anesthetic is administered in the area of the medial tibial condyle (Fig 5-5b). In this way, an anesthetic block in the supply area of the infrapatellar branch of the saphenous nerve is achieved, and after waiting a short period of time, an infiltration anesthetic can be administered relatively painlessly into the skin and the periosteum in the area of the surgical intervention.
5.3.3 Surgical procedure
The incision is carried out according to the planned direction and dimensions. The preparation reaches right up to the pes anserinus. The skin and subcutaneous tissue are held apart with a wound retractor so that the donor site can be clearly seen (Fig 5-5c). To achieve a clearly visible bone harvest area, a bony lid is prepared that remains medially pedicled to the pes anserinus (Fig 5-5d to g).
First incisions are drawn through the pes anserinus, corresponding to the shape and dimensions of the planned bony lid. The pes anserinus must not be severed along the medial length of the planned bony lid; in this way, the bony lid remains attached to the pes anserinus like a trapdoor. The most caudal corner point of the bony lid should be at the level of the tibial tuberosity, while the most cranial corner point should be at least 20 mm below the knee joint surface. The corner points of the bony lid are marked using a small bur. When perforating the cortical bone, the surgeon can estimate its thickness. At the sides, it is best to cut out the bony lid using a micro bone saw in an oblique direction toward the marrow, so that a stable repositioning of the lid is possible. A bone chisel is applied on the lateral side of the bony lid and is driven slightly deeper. With the help of careful lever movements, the bony lid can be lifted medially (like a trapdoor) and be held in an open position by means of a small hook.
With the help of a large spoon-shaped excavator, sufficient quantities of spongiosa can be harvested from the head of the tibia that is clearly visible through the cortical window (Fig 5-5h). While carrying out the cancellous bone harvest, at least 20 mm of bone should be left cranially to the joint surface in order to preserve the mechanical stability of the head of the tibia. For a bilateral sinus floor elevation, approximately 10 ml of compressed cancellous bone is harvested. The harvested spongiosa should be stored at room temperature in physiological sodium chloride or sterile Ringer’s solution for no longer than 2 h. Following the spongiosa harvest, the bony lid is reposed and stabilized to the periosteum by means of resorbable sutures (Fig 5-5i).
This is followed by a two-layer wound closure, with the skin being sewn intracutaneously (Fig 5-5j). Immediately after the bone harvest, the augmentative procedure is carried out intraorally.
5.3.4 Postoperative care
Postoperatively, a tight pressure bandage is applied (Fig 5-5k). This intervention is usually carried out in an outpatient situation. A postoperative inpatient hospital stay for a spongiosa harvest is not necessary.
Patients must continue to take the administered antibiotic orally. In addition, it is recommended to prescribe an antiphlogistic and analgesic medication (diclofenac 50 mg 3×1). The antiphlogistic–analgesic therapy is commenced immediately after the surgery and is recommended for at least 3 days, after which it can be taken on demand, if necessary.
Weight can be put on the leg that has been operated on immediately afterwards. Patients can and should move around as usual and can even engage in sports from the second postoperative week onwards. However, exercises and activities that especially strain the knee joint should be avoided for 3 months.
The first wound check is carried out on the first postoperative day, when the pressure bandage is removed. The wound is cleansed, and a simple adhesive strapping is applied. Patients may wear a compression stocking for 2 weeks to prevent thrombosis.
Since sutures are generally carried out intracutaneously using resorbable material, their removal in the area of the donor region is not necessary.
The last routine check-up is carried out 7 days after the intervention during the removal of the intraoral sutures.
5.3.5 Complications and postoperative morbidity
The expected morbidity and the risk of complications is relatively low. The complication rate is described as less than 2%,1,26 and these are essentially minor complications such as bleeding, swelling, bruising or temporary paresthesia.
Fractures after tibial bone harvesting are relatively rare and are usually caused by an invasive surgical procedure.18