John H. Phillips

Fixation Effects on Membranous and Endochondral Onlay Bone-graft Resorption

Difficulties arise in the prediction of maintenance of graft volume over time when bone grafts are used for racial contour reconstruction. We hypothesize that graft fixation will decrease movement and lead to decreased resorption. Fixed and nonfixed endochondral (rib) and membranous (skull) onlay bone grafts measuring 30 × 10 × 4 mm were grafted to the mandible bilaterally in 10 adult sheep. Fixation was achieved using the lag-screw technique. Volume measurements using caliper technique were made 20 weeks postoperatively. The volume of graft present at 20 weeks was significantly greater for the fixed bone grafts (p < 0.001): fixed membranous, 85.9 percent; fixed endochondral, 76.2 percent; nonfixed membranous, 55 percent; and non-fixed endochondral, 16.6 percent. The results are explained using biomechanical theories related to the effects of strain. At present, it is suggested by this study that when onlay bone grafts are stabilized, improved results with respect to graft resorption can be expected.

The importance of the zygomatic arch in complex midfacial fracture repair and correction of posttraumatic orbitozygomatic deformities.

Collapse of the zygomatic arch following trauma results in inadequate anteroposterior projection of the zygomatic body and an increase in facial width. Accurate assessment of the position of the zygomatic arch in relation to the cranial base posteriorly and the midface anteriorly is the key to the acute repair of complex midfacial fractures and the secondary reconstruction of posttraumatic deformities of the orbitozygomaticomaxillary complex. Loss of projection of the zygomatic arch may occur with injuries confined to the orbitozygomaticomaxillary region or in association with complex midfacial fractures. A safe anatomic approach to the zygomatic arch allows exact anatomic restoration of the zygomatic arch using miniplates and screws and results in the reconstruction of an outer facial frame with a correct anteroposterior projection and facial width. The zygomatic arch injury is diagnosed using axial CT scanning. Three-hundred and seventeen arches have been exposed through a coronal incision following acute trauma and 47 arches have been exposed in patients requiring late correction of a posttraumatic orbitozygomaticomaxillary deformity. Permanent palsy to the frontal branch of the facial nerve has occurred in one patient following the exact definition of the anatomy of this region.

Fixation Effects on Membranous and Endochondral Onlay Bone Graft Revascularization and Bone Deposition

This paper investigates the relationship between bone resorption, the process of bone revascularization, and graft fixation. Vital staining techniques and microangiography were used to study the extent of graft revascularization of fixed and nonfixed endochondral (rib) and membranous (skull) onlay bone grafts in 20 adult sheep mandibles bilaterally. This assessment was carried out at 2 and 20 weeks postoperatively. Sequential fluorochrome staining was performed to examine the pattern of new bone deposition. Fixation was achieved using the lagscrew technique. At 2 weeks, membranous bone demonstrated a greater area of graft revascularization if fixed than if the graft was not fixed. The opposite result was seen for endochondral grafts, where nonfixed grafts showed a greater area of revascularization than fixed grafts. At 20 weeks, all bone that was present was fully vascularized. The inconsistencies in the results on the relationship between fixation and revascularization for membranous and endochondral grafts in the early stages of healing (2 weeks) suggest that although revascularization is a necessary precondition for bone resorption and deposition, biomechanical and structural factors may be a more satisfactory explanation for the differences observed in the maintenance of bony volume.

Distraction osteogenesis in the irradiated canine mandible.

The potential use of distraction osteogenesis in mandibular reconstruction has been limited by its questionable efficacy in previously radiated bone. We studied five mongrel dogs that had a hemimandible rendered edentulous and underwent a full course of external beam radiation therapy (50 Gy/20 fractions). Six months after completion of radiotherapy, a 2-cm critical-size segmental mandibular defect was created and stabilized with a stainless steel plate. A proximal mandibular transport segment was then formed and an external lengthening apparatus (Orthofix) applied. By means of bifocal distraction osteogenesis, the defects were filled with new bone in a period of 30 days in four of five dogs. Histologic analysis and fluorochrome microscopy confirmed the formation of new cortical bone. Our results suggest that distraction osteogenesis is successful in previously radiated bone and that it may be a simple method of mandibular reconstruction following ablative head and neck surgery. (Plast. Reconstr. Surg. 93: 164, 1994.)

a Contraindication for the Use of Hydroxyapatite Cement in the Pediatric Population

&NA; The authors report on their experience with a particular hydroxyapatite cement in the pediatric population and review cases that elucidate potential limitations of its use in this population. In all patients, the implant was used for recontouring and augmenting the cranial vault. Seven of 15 patients had a direct communication between sinus mucosa and the implant at the time of surgery. Three of the seven patients developed late postoperative inflammatory reactions of the surgical site with delamination of the implant. Each patient required an aggressive irrigation and debridement with removal of the delaminated hydroxyapatite. Pathologic findings showed evidence of a foreign body inflammatory reaction in the tissue, and mixed bacterial flora were identified in all specimens. No late problems with the cement were seen in patients without a communication to the sinuses. Our findings suggest that the use of BoneSource, an essentially nonviable, nonvascularized implant, in areas exposed to bacterial contamination is contraindicated in the pediatric population. BoneSource and other similar hydroxyapatite biomaterials do have a role as implants in the craniofacial skeleton. The indications and contraindications of these substances will need to be further defined for wide acceptance to occur.

Comparison of compression and torque measurements of self-tapping and pretapped screws.

The choice of an internal fixation system for maxillofacial surgery is made difficult because of lack of information with respect to functional load. This study attempted to clarify some of the controversy with respect to maxillofacial use of these implants. Maximal compressive force to torque values were measured in standardized bone thicknesses of 1, 2, 3, and 4 mm. The screws tested were pretapped AO 1.5-, 2.0-, 2.7-, and 3.5-mm rescue screws and self-tapping Luhr, Champy, and AO 1.5- and 2.0-mm screws. Ten measurements were made for each screw type/bone thickness combination using a piezoelectric washer and torque screwdriver. It was apparent that for 1- and 2-mm bone thicknesses the use of self-tapping screws resulted in the highest compression values. In 3- and 4-mm bone thicknesses, pretapped screws offered the highest compression values. As expected, self-tapping screws had the highest torque values on insertion owing to torque loss in cutting the screw threads. The 2.7-mm screw offered no advantage over the 2.0-mm screws in 1- and 2-mm bone thicknesses but resulted in higher compression values in 3- and 4-mm bone thicknesses.

The effect on facial growth of pediatric mandibular fractures.

The incidence of facial fractures in the pediatric population is between 1.4% and 15% of all maxillofacial traumas. Forty-one percent of pediatric facial fractures involve the mandible. No study has commented on the incidence of mandibular fractures that go on to develop growth disturbances leading to asymmetry and malocclusion. A retrospective chart review was carried out that identified and followed 88 children who sustained mandibular fractures and presented to The Hospital for Sick Children in Toronto during the 13-year period from 1980 to 1993. Patient follow-up ranged from 2 to 15 years, and was performed via phone survey and medical/orthodontic chart review. Patients who required orthodontics and orthognathic surgery were identified. Results indicated that a pediatric mandibular fracture does not lead to a higher incidence of orthodontic intervention. Furthermore, children younger than 4 years or older than 12 years rarely require orthognathic surgery to correct facial growth disturbances following mandibular fractures. In contrast, 22% of children age 4 to 7 years, and 17% of children age 8 to 11 years required orthognathic surgery to correct facial growth disturbances following mandibular fractures. Condylar fractures were the most common site of mandibular fracture, and led to facial asymmetry most frequently.

Combined injuries of the cranium and face

The neurosurgeon and plastic surgeon are increasingly called upon to manage the care of patients with combined injuries of the cranium and face. The authors briefly review the pathogenesis and classification of craniofacial fractures and outline historical approaches to them. Current principles of management are then discussed. Experience with 167 patients is presented with emphasis on surgical technique, the sequence of repair and early primary reconstruction. The controversial issue of fontal sinus fracture repair is addressed. The authors favour preservation of the frontal sinus cavity, where possible, and do not obliterate the nasofrontal duct. With injuries to the floor of the sinus, the base of the sinus and frontonasal duct are sealed with bone graft and a vascularised soft tissue flap and the sinus is cranialised. Immediate bone grafts, using split skull or rib, are used to reconstruct areas of bony destruction or loss. Ninety-eight patients required 402 grafts. Immediate bone grafting resulted in few complications and low incidence of secondary deformities needing correction.

Mandibular growth following reconstruction using a free fibula graft in the pediatric facial skeleton.

Background: Mandible reconstruction in the growing facial skeleton is challenging, especially with reconstructions necessitating free vascularized bone grafts. The need for further combined orthodontic-orthognathic intervention at skeletal maturity must be anticipated. The growth potential of these grafts and potential new problems associated with performing a sagittal split osteotomy at skeletal maturity are poorly understood. Methods: A retrospective chart review revealed 11 patients who underwent reconstruction with a free fibula at The Hospital for Sick Children from 1990 to 2000. Radiographic and photographic studies were assessed for long-term growth of the reconstructed mandible, with follow-up ranging from 2 to 12 years. Results: Of the 11 patients who underwent reconstruction with a free fibula, two had surgery at skeletal maturity, two moved out of the country, one died as a result of her malignancy, and one was lost to follow-up. The remaining five patients are being followed by the craniofacial and orthodontic services and have not reached skeletal maturity. Of the two patients who have had orthognathic surgery, the one patient whose reconstruction involved the temporomandibular joint exhibited no growth on the reconstructed side and required a 57-mm advancement on the reconstructed side. The other patient, who had preservation of the temporomandibular joint at the time of reconstruction, required only a 5-mm advancement on the reconstructed side. Both patients had significant surgical complications as a result of the initial reconstructive techniques. Technical modifications necessary at the initial reconstruction became apparent when the authors performed a sagittal split osteotomy on the reconstructed side. Conclusions: Certain technical modifications to the original free fibula reconstructed pediatric mandible should be considered in anticipation of the need for a subsequent bilateral sagittal split at skeletal maturity.

The effects of varying pilot hole size on the holding power of miniscrews and microscrews

Screw failure during insertion is not an uncommon problem, especially with the micro and mini fixation systems. In this study, the holding power of 1-, 1.5-, and 2-mm screws was tested at various simulated bone thicknesses of 1, 2, 3, 4, and 5 mm with an increasing pilot hole size. This was done to ascertain the effects of pilot hole size on screw failure and any subsequent tradeoff with respect to decrease in holding power. For the 1-mm screws, there was no statistically significant decrease in holding power of the screws with increasing pilot hole size that ranged from 70 to 85 percent of the external diameter of the screw. For the 1.5-mm screw, a critical pilot hole size was found to be 1.24 mm (82 percent of the screws external diameter), with no statistically significant decrease in holding power in the 1-, 2-, and 3-mm thickness blocks. For the 2-mm screws, the critical pilot hole size was found to be 1.65 mm (83 percent of the screws external diameter). A statistically significant decrease in holding power was observed after this drill hole size in all thicknesses. Commercially available systems use drill bits that represent approximately 70 to 75 percent of the external diameter of the screw. Our results show that the pilot hole size for the 1-, 1.5-, and 2-mm screws can be increased to 80 to 85 percent of the screws external diameter without losing significant holding power. Therefore, in areas where screw failure is a problem, the pilot hole may be increased to 80 percent of the external diameter of the screw without affecting the holding power of the system.