6.1. General comments

Both techniques of harvesting autogenous bone in the form of cancellous cores (CC) from the iliac crest, and the treatment of cranio-maxillofacial or dento-alveolar bony defects with coral-derived granules (CDG) as a bone graft substitute, are safe and successful techniques. They present opportunities for the reduction of morbidity in the osseous reconstruction of the cranio-maxillofacial skeleton. The harvesting of CC reduces potential morbidity by using a minimally invasive surgical technique. The use of CDG eliminates the need for a donor site totally and the accompanying morbidity. The results of the five studies support these two observations.

In study I, the well-documented morbidity associated with open iliac crest bone graft harvesting was the driving force to find a less invasive harvesting technique (Cocklin 1971, Marx & Morales 1988, Tayapongsak et al. 1994, de la Torre et al. 1999, Seiler & Johnson 2000). Trephines have a long history of application in bone biopsy harvesting for the diagnosis of metabolic bone diseases and for research purposes (Malluche & Fauguere 1986). These biopsy techniques require atraumatic sampling without the destruction of bone. The potentially gentle nature of this method makes such a technique attractive for bone graft harvesting as the harvested bone is viable for grafting purposes. Ultimately, if successful, such a method could change an in-hospital procedure requiring admission to a technique used on an outpatient basis.

The initial goal of this series of studies was to establish the safety of these techniques. A graduated method was chosen, beginning in study I with cadaver observations. Despite the fact that perforations are possible with any trephination technique, the nature of these perforations had not been previously documented in other studies (Smirnov & Baranov 1971, Johnson et al. 1997, Faugere & Malluche 1983, Caddy & Reid 1985, McGurk et al. 1993, Altman & Blenkisopp 1994, Billmire & Rotatori 1994).

Once the safety of the technique had been determined, the technique was applied in vivo in the form of a retrospective study to determine complication rates and patient satisfaction in study II. Finally the technique was compared with an existing routine method of bone harvesting, the open approach to the iliac crest. A prospective format with strictly defined outcome measures allowed the comparison of morbidity parameters that were not previously available in other trephine studies (Johnson et al. 1997, Duncan et al. 1980, Faugere & Malluche 1983, McGurk et al. 1993, Billmire & Rotatori 1994, Habal 1995).

With respect to CDG, the material was successful in reducing donor site morbidity within the strictly defined applications used in studies IV and V. Previous experience with this material in the cranio-maxillofacial skeleton and dento-alveolar region was scant with no reports on outcome measures of morbidity and few meaningful insights on whether this type of treatment was successful (Chiroff et al. 1975, Levet & Jost 1983, Guillemin et al. 1987, Issahakian et al. 1987b, Robier et al. 1987, Besins & Philipe 1988, Brasnu et al. 1988, Issahakian & Ouhayoun 1988, Levet et al. 1988, Roux et al. 1988a,b, Ouhayoun et al. 1991, Yukna & Yukna 1998). Therefore a strict definition of a successful outcome was developed for a narrow but well defined clinical scenario in the dento-alveolar region, in study V.

These studies I through V examine a large number of independent variables with a relatively small population. There were a total of 253 subjects of whom 196 participated in anterior iliac crest bone graft harvesting. A total of 849 CC’s of autogenous bone were harvested from these subjects. Using CDG, a total of 57 patients received augmentations to parts of their cranio-maxillofacial skeletons. The advantage of these studies is that the entry criteria were narrow and that the same surgeon-investigator supervised the majority of surgical procedures and follow-up visits.

None-the-less there exists with the trephine harvesting technique, the risk of perforation of the medial or lateral cortices of the ilium with the possibility of increased morbidity due to intramuscular haematoma. The other more major risk involves the possibility of peritoneal involvement. The results of intentional perforation of the medial cortex of the ilium in the cadaver subjects, perforating the medial cortex, to the fullest depth allowed by the instrumentation used in the study, showed that it was impossible to engage any of the peritoneal contents. When the donor sites were surgically explored after the intentional perforations, only the periosteum of the ilium or the iliacus muscle was noted to be involved in these intentional maximal perforations. The experience in vivo with living patients confirmed this, as there were no clinically evident peritoneum-related complications following harvesting post-operatively. This is in contradistinction to other studies, which used different approaches and instrumentation than used in the present study. There were previous reports of fracture of the ilium (Duncan et al. 1980), avulsion of the anterior superior iliac spine (Stellon et al. 1985) and a case of pneumoperitoneum (Williams & Ford 1986). None of these major complications were observed in the study population using the current trephining technique.

Morbidity is consistently lower with CC trephine harvesting than with open CCBG harvesting at the anterior iliac crest. Patients with CC harvests ambulate sooner, are discharged from hospital more quickly and have lower pain scores at the donor site than do patients who undergo open CCBG harvests.

CDG seem to result in stable augmentation with few complications attributable to the use of this xenograft. The issue of material migration and ectopic placement of the material into more superficial layers of the wound must be addressed surgically at the time of placement of the material.