4.2. Methods and techniques

4.2.1.1. Cadaver iliac crest harvest

In study I, bone was trephined from the right and left iliac crests of twenty five freshly-preserved adult cadavers. An open technique was used on the left iliac crest. The overlying soft tissue was dissected free from the bone exposing the entire anterior iliac crest and the medial and lateral cortical walls. This permitted direct visualization of the bone being harvested by the trephine in the cadaver subjects. On the right side, the iliac crest was approached in a closed fashion. A one centimetre stab incision was made through the skin down to periosteum, through which the trephine could access the entire crest by displacing the soft tissues with a funnel shaped retractor. Five consecutive cores of cancellous bone were harvested from each of the open and closed sides using the percutaneous power driven trephine (Osteocore^®, Straumann AG, Waldenberg, Switzerland) (Fig. 2).

The trephine consisted of a pre-cutter used to cut through the periosteum and to score the cortex of the iliac crest. The core drill or actual trephine then drilled and separated a cancellous core from the surrounding bone. The internal diameter of the trephine was 4.0mm and its length was 38mm. It engaged the original recess made by the pre-cutter and was drilled into the bone (Fig. 3).

A hand-held funnel-shaped winged positioner controlled by an assistant was used to stabilize the trephine (Fig. 4). Within the trephine, an internal forceps fractured the core of bone graft away from the iliac crest. An internal plunger was used to push out the core of bone from the trephine (Fig. 5).

The medial and lateral aspects of the right and left iliac crests were dissected and examined for perforations through the cortical plates of the ilium (Fig. 6). The cores were then weighed and their volumes measured.

The safety of the procedure was tested after acquiring the cadaver cancellous cores. Twenty additional sites in 10 cadavers were drilled in such a way as to intentionally perforate the medial cortex of the ilium. These perforations were made with the trephine pushed down maximally into the iliac crest to its length of 38 mm. The area medial to the ilium was then explored and dissected to check for the depth of soft tissue penetration past the medial cortical plate of the ilium. In particular, involvement of the iliacus muscle, peritoneum or peritoneal contents were checked.

4.2.1.2. Patient iliac crest harvest

Following the cadaver study, the trephine was used to harvest bone in a total of 149 patients requiring autologous free grafts for various augmentation procedures: 11 patients in study I, 84 patients in study II, and 54 patients in study III. All the patients underwent bone harvest from an essentially closed anterior approach, using the same motor-driven trephine (Osteocore®, Straumann, A.G., Waldenburg, Switzerland) used in the cadaver subjects from study I. A 0.5 to 1.0 cm stab incision was made through skin and subcutaneous tissue overlying the area between the anterior superior iliac spine (ASIS) and the iliac tubercle (Fig 7).

Limited blunt dissection was directed down to the level of the fascia and periosteum. Tissue overlying the anterior ilium was incised. Care was taken to remain medial to the tensor fascia lata and gluteus medius muscles, and lateral to the iliacus and external abdominal oblique muscles. The same specialized trocar used in the cadaver study, with a serrated edge designed to engage the periosteum, was introduced through the stab incision (Fig 8).

The cancellous core (CC) harvest involved the use of a pre-cutter drill which was inserted through the trocar and used to score the overlying periosteum and cortical crestal bone. Next, a 4 mm diameter core cutter was used to define and withdraw the core of cancellous bone. Up to 8 cores per patient were obtained through the same stab incision. The length of each CC was measured and recorded. The intervening bony septum between each core harvest defect was removed with rongeurs, and the cancellous component of the ilium was further curetted through the stab incision to maximize the harvest (Fig 9). Following irrigation with sterile saline, gelfoam was placed into the core defects and closure proceeded in a layered fashion. No drains were used, but a pressure dressing was applied for 48 hours.

In study III, the first 22 patients were assigned to a corticocancellous block graft cohort (CCBG) and underwent harvesting of corticocancellous block grafts through an anterior medial approach to the ilium. This involved a 6 cm incision beginning 1 cm posterior to the ASIS and 1 cm lateral to the bony prominence. Subcutaneous tissue dissection proceeded with electrocautery through Scarpa’s fascia without progressing through any adjacent muscles. Once the anterior crest was visualized, a midcrestal periosteal incision was made 1 cm posterior to the ASIS and the medial musculature was reflected in a subperiosteal plane. The external oblique abdominal and iliacus muscles were reflected and bone was removed from the area between the tubercle and 1 cm posterior to the ASIS. A 2.5 to 4.5 cm² (mean 3.8 cm²) rectangular subcrestal cortical window was created with a reciprocating saw and cancellous bone was removed with chisels, curettes and gouges (Fig. 10). The surgical site was thoroughly irrigated with sterile saline solution. Gelfoam was placed into the bony defect, and closure was accomplished in layers from deep to superficial, including the musculoperiosteal flap, subcutaneous tissues, dermal layer and skin. A drain was not used in any of the 22 subjects.

4.2.1.3. Cranio-maxillofacial coral-derived granule reconstruction

In study IV, 36 patients requiring augmentation of osseous defects in various parts of the cranio-maxillofacial skeleton were treated with coral granules. The contour defect was identified and outlined at surgery. A solution containing 2 percent lidocaine with epinephrine in a concentration of 1: 100,000 was injected subdermally, but not subperiosteally, in the area of the defect, until the contour defect was completely eliminated by the local anesthetic solution. The volume of the injected solution was measured and recorded. This was assumed to be the volume necessary to produce the desired correction of the osseous defect.

A distant skin incision, placed in a relatively inconspicuous location, was used as an entry to dissect a subperiosteal pocket large enough to eliminate the defect. The size of the periosteal pocket was always dissected so that its borders would precisely correspond to the borders of the contour defect. Inadvertent overextension of the pocket was avoided as this could lead to the spillage of coral granules into areas outside the defect.

The same volume of coral granules as measured with the local anesthetic solution was then introduced into the subperiosteal pocket using a preloaded syringe. The most distant portion of the subperiosteal pocket from the incision was always filled first. Once the pockets were filled external pressure and molding was used to attain the final desired contours, avoiding any edge effects that are commonly found with solid blocks of implanted materials and bone grafts (Fig 11).

4.2.1.4. Dento-alveolar coral-derived granule reconstruction

In study V, a total of 48 single recently edentulated sites in 21 healthy patients were grafted with CDG using a so-called “alveolar preserving technique”. After the injection of 2 ml of 2 percent lidocaine with epinephrine local anaesthetic solution, traumatized or ankylosed teeth were removed from the anterior maxillary or posterior maxillary and or mandibular alveoli. Mucosal advancement flaps, using releasing incisions, were fashioned to cover the extraction socket defects in a tension free closure. Periosteal scoring was used to achieve this in all cases. Care was taken to deposit the CDG into the intact tooth sockets in the alveoli as an inlay graft. Care was taken to try to avoid the spillage of CDG into a subperiosteal location. The wounds were all sutured with 4–0 Vicryl-Rapide^® (Ethicon, Peterborough, Ontario Canada). All patients were instructed to rinse their oral wounds twice daily with a 0.12% chlorhexidine gluconate containing mouth rinse until mucosal healing occurred (Fig 12).

Patients were reassessed post-operatively and seen at 2, 4, 6, 12 weeks, then at 6, 12, 18, 24 months and annually until osseointegrated implant placement. Clinical and radiographic examinations were performed at follow-up visits to check for complications including infection, inflammation, wound dehiscence and resorption. In all cases of maxillary anterior tooth-loss, a maxillary removable appliance was provided to the patients and was inserted at the 4-week post-operative visit. This prosthesis consisted of an acrylic tooth suspended from an acrylic resin occlusal splint and trimmed so that the acrylic was out of contact with the mucosa. The design of this prosthesis avoided any loading of the maxillary anterior edentulous site. No orthodontic retainers or partial dentures were placed in any of the posterior maxillary or mandibular edentulous sites. Space maintenance, when deemed necessary, was accomplished with fixed orthodontic appliances.

Success of the alveolar sparing procedure was defined as the ability to successfully place an osseointegrated dental implant into the xenograft reconstructed site without the need for a revisional bone graft.

Once the cessation of skeletal growth had been identified using serial cephalometric analysis, threaded, machined titanium Brånemark dental implants (Nobel Biocare AB, Goteborg, Sweden) were placed into the reconstructed sites, either into the coral granule-augmented sites, or into subsequently bone graft-augmented sites if the coral granules did not provide enough bone for the placement of a dental implant. The implants were followed annually after their restoration.

4.2.2.1. Cancellous core dimensions

In the cadaver model in study I, the percutaneous power driven trephine was used to obtain 5 cores of corticocancellous bone per cadaver site. The medial and lateral aspects of the right and left iliac crests were surgically explored, dissected and examined for perforations. The cores were then measured and weighed and their volumes were determined.

Another 10 cadavers were then drilled with the trephine in an open approach on one side and a closed approach on the other producing 20 additional sites. An intentional perforation was created at each of the sites by drilling with the motorized trephine to the depth of maximal penetration into the bone of the ilium allowed by the trephine and retractor combination. The medial and lateral aspects of these iliac crests were then explored surgically to check for soft tissue and specifically for peritoneal involvement.

Following this cadaver study, the trephine was used in patients requiring autologous free grafts for various augmentation procedures. The first 40 CC’s were weighed, measured and their volumes were determined for comparative purposes with respect to the cadaveric model.

4.2.2.2. Questionnaire

In study II each subject participated in a follow-up telephone interview in which questions regarding morbidity and patient satisfaction with respect to the anterior iliac crest bone harvest were asked. Morbidity was defined as post-operative pain and/or gait disturbance noted by the patient. To assess overall satisfaction, patients were asked if they would undergo the same procedure again. Post-operative pain and gait disturbance were assessed as both short term (1–14 days post-op), and long term (greater than 6 months post-op) variables.

4.2.2.3. Post-operative clinical examination, gait and discharge criteria

In study III, the following parameters were used to evaluate patient morbidity: number of days to unassisted ambulation, length of hospital stay, and pain scores for both the recipient and the donor sites. Unassisted ambulation was defined as the ability of the patient to get up from bed and walk to the bathroom and hallway outside of their hospital room, without any assistance. Gait was noted to be normal or abnormal if on observation during ambulation, the patient had an obvious disturbance in the rhythm of gait post-operatively. Patients were discharged from hospital once they were clinically stable and able to care for themselves at home. A visual analogue scale was used to grade the subjective hip and maxillofacial pain scores.

4.2.2.4. Visual analogue scale

In study III a 10 cm visual analogue scale was constructed with 1 cm graduations. The label “no pain” was used as an anchor on the left side of the scale at position zero, with the “most severe pain” label used as an anchor on the right side at position 10. The visual analogue scale was used to grade the subjective hip and maxillofacial pain scores daily until the patients were discharged and on day 3 if the patients had been already discharged from hospital.