Quantitative comparison of volume maintenance between inlay and onlay bone grafts in the craniofacial skeleton.

BACKGROUND: Nonvascularized autologous bone grafts are the criterion standard in craniofacial reconstruction for bony defects involving the craniofacial skeleton. The authors have previously demonstrated that graft microarchitecture is the major determinant of volume maintenance for both inlay and onlay bone grafts following transplantation. This study performs a head-to-head quantitative analysis of volume maintenance between inlay and onlay bone grafts in the craniofacial skeleton using a rabbit model to comparatively determine their resorptive kinetics over time. METHODS: Fifty rabbits were divided randomly into six experimental groups: 3-week inlay, 3-week onlay, 8-week inlay, 8-week onlay, 16-week inlay, and 16-week onlay. Cortical bone from the lateral mandible and both cortical and cancellous bone from the ilium were harvested from each animal and placed either in or on the cranium. All bone grafts underwent micro-computed tomographic analysis at 3, 8, and 16 weeks. RESULTS: All bone graft types in the inlay position increased their volume over time, with the greatest increase in endochondral cancellous bone. All bone graft types in the onlay position decreased their volume over time, with the greatest decrease in endochondral cancellous bone. Inlay bone grafts demonstrated increased volume compared with onlay bone grafts of identical embryologic origin and microarchitecture at all time points (p < 0.05). CONCLUSIONS: Inlay bone grafts, irrespective of their embryologic origin, consistently display less resorption over time compared with onlay bone grafts in the craniofacial skeleton. Both inlay and onlay bone grafts are driven by the local mechanical environment to recapitulate the recipient bed.

The use of a bovine collagen construct for reconstruction of full-thickness scalp defects in the elderly patient with cutaneous malignancy.

Full-thickness defects of the scalp following cancer resection are reconstructive challenges when bone is exposed. Local, regional, and/or free tissue transfer have all been described for reconstruction when the pericranium is exposed. We examined the surgical outcomes from 23 patients who underwent placement of bovine collagen constructs. Thereafter, delayed skin grafting was performed. The average age of the patients was 70 years. All patients had one of the following: melanoma (n = 13) squamous cell carcinoma (n = 5), angiosarcoma (n = 2), basal cell carcinoma (n = 1), spindle cell carcinoma (n = 1), or malignant pilar tumor (n = 1). The average defect size was 51 cm, with a range of 9 cm to 169 cm. Average time between bovine construct placement and skin grafting was 30 days. Histologic studies demonstrated persistence of the construct and infiltration of nascent fibroblasts. Six patients had delayed healing due to microabscesses in the constructs. All wounds eventually healed. In the elderly, this is a simple method to treat full-thickness scalp defects.

Volume maintenance of inlay bone grafts in the craniofacial skeleton.

Although the clinical use of inlay bone grafts is widespread in craniofacial surgery, the dynamics of inlay bone grafting to the craniofacial skeleton have never been well characterized. Previous work demonstrated that volume maintenance of bone grafts in the onlay position is a consequence of their microarchitectural features, rather than their embryological origins. The purpose of this study was to investigate whether the properties determining the volume maintenance of bone grafts in the onlay position in the craniofacial skeleton could be extended to bone grafts in the inlay position. It was hypothesized that volume maintenance of an inlay bone graft could be better explained on the basis of the microarchitectural features of the graft (cortical versus cancellous composition), rather than its embryological origin (membranous versus endochondral), and that the primary determinant of bone graft behavior is the interaction between the microarchitectural features of the bone graft and the local mechanical environment in which the bone graft is placed. Cortical and cancellous bone grafts were harvested from the iliac crest (endochondral origin) of 25 New Zealand white rabbits, and cortical bone was harvested from the mandible (membranous origin) of each rabbit. Four 7-mm trephine holes were made in the cranium of each rabbit, posterior to the coronal suture. Each defect was filled with endochondral cortical bone, endochondral cancellous bone, or membranous cortical bone or was left as an ungrafted control specimen. Animals were killed at 3, 8, or 16 weeks. Crania were subjected to micro-computed tomographic and histological assessments. Micro-computed tomographic analysis demonstrated significant increases in actual bone volume from time 0 to the time of death for all types of grafts. Cortical bone demonstrated significant increases in space-occupying volume at all time points. By 16 weeks, no statistically significant difference in either the actual bone volume or the space-occupying volume according to graft type could be detected. There was no resorption of the inlay bone grafts; in fact, all bone types exhibited increased volume. Cancellous bone demonstrated the greatest capacity to increase actual bone volume. All bone graft types seemed to reach a steady-state bone volume, as if controlled by a local regulator. The regulator is likely the local mechanical environment in which the grafts were placed, as corroborated by the findings that the bone grafts seemed to recapitulate the characteristics of the bone in which they were placed, rather than maintaining their native characteristics.

Unique rodent model of distraction osteogenesis of the mandible.

Despite the increasing use of distraction osteogenesis (DO) of the mandible, the molecular mechanisms regulating new bone formation during DO remain poorly understood. The purposes of this study were (1) to establish a unique rodent model of DO capable of outlining parameters for new bone formation at the distraction site and (2) to determine a critical-size defect to differentiate osteogenesis resulting from distraction from conventional fracture healing at the osteotomy site. Adult Sprague-Dawley rats were fitted successfully with this newly developed distraction device. Analyses demonstrated that the device could distract the rat mandible reliably to 5.1 mm with complete union. Acute intersegmental gaps of 2 mm resulted in complete bony union in a manner consistent with fracture healing, whereas 3-mm acute gaps resulted in varying degrees of bony union. Acute intersegmental gaps of 5.1 mm invariably resulted in fibrous nonunion. In summary, the authors have developed a rodent model of DO of the mandible. Their distraction protocols resulted successfully in advancement to 5.1 mm with bony consolidation. Notable fracture healing occurred at immediate intersegmental spaces as large as 3 mm. A gap of 5.1 mm was sufficient to act as a critical-size defect, resulting consistently in fibrous nonunion. These findings validate the effectiveness of this distraction device and establish the critical-size defect of a rat mandible at more than 3 mm. This novel model of DO provides an effective method of examining fundamental mechanisms responsible for new bone formation in the craniofacial skeleton.

Intrafocal pinning of distal radius fractures: a simplified approach.

Distal radius fractures are not often treated by plastic surgeons. At the authors' institution, plastic surgery manages half of all traumas below the elbow, including distal radius and forearm fractures. This opportunity gives the residents a unique perspective for comprehensive training in treating upper extremity injuries. Because a distal radius fracture is the most common fracture of the upper extremity, the authors describe the use of intrafocal pinning as a simple and effective approach in the treatment of extra-articular distal radius fractures (Colles' fractures). They conducted a prospective study of 18 patients with Colles' fractures treated sequentially at their institution from 1998 to 2001 using this technique. They measured ulnar variance and palmar tilt of the distal radius at the time of injury, after closed reduction, immediately postoperatively, and 11 weeks postoperatively. Acceptable distal radius reduction aims to achieve at least neutral ulnar variance and 0-deg palmar tilt. Compared with closed reduction, they achieved superior anatomic reduction with intrafocal pinning: ulnar variance, +2.6 mm vs. -1.4 mm; palmar tilt, -13.3 deg vs. +2.1 deg). These results were stable at the 11-week follow-up. Intrafocal pinning is a valuable tool in the management of Colles' fractures. It is simple to perform and to teach, and it produces results that are superior to closed reduction alone.