Reconstruction of the temporal contour for traumatic tissue loss using a CAD/CAM-prefabricated titanium implant-case report.

INTRODUCTION: A 16-year-old Arab boy had suffered from a severe head injury including an intracranial haematoma. Despite replantation of the bone flap later on, the cosmetic result was very unfavourable due to partial resorption of the reinserted bone and atrophy of the right temporalis muscle. AIM: For contour reconstruction of both soft and hard tissues the boy was transferred from Saudi Arabia. METHOD: A spiral CT was obtained and the contour was reconstructed using a new algorithm for surface generation. RESULT: The resulting titanium implant was inserted without complications or the need for revision. The cosmetic result was good and corresponded to the preoperative digital planning. CONCLUSION: Techniques of computer-assisted implant prefabrication and surgery may include special algorithms for considering soft tissues including contour deficits of the temporalis muscle.

Performance of functionally graded implants of polylactides and calcium phosphate/calcium carbonate in an ovine model for computer assisted craniectomy and cranioplasty.

Biodegradable functionally graded skull implants on the basis of polylactides and calcium phosphate/calcium carbonate were prepared in an individual mould using a combination of different processing techniques. A geometrically corresponding resection template was designed to enable a craniectomy and cranioplasty with the prepared implant in the same operation. After various preliminary experiments concerning degradation kinetics, pH evolution during degradation, micromorphology, biocompatibility tests in human osteoblast cell cultures and surgery of cadaver heads, a new large-animal model was developed for long-term in vivo studies. In eight 12-months-old sheep, the surgical templates were used to create 4.5 x 5 cm(2) calvarial defects which were then filled with the corresponding degradable implants in the same operation. The animals were sacrificed after 2, 9, 12 and 18 months, and the implants and the surrounding tissues were analysed by computer tomography (CT), macroscopic examination and microscopy. The new animal model proved to be reliable and very suitable for large individual craniectomies and cranioplasties. The formation of new bone from the dural layer of the meninges corresponded well to the degradation of the porous inner layer of the implants whereas the skull contour was stabilised by the compact outer layer over the follow-up period.

Geometrically structured implants for cranial reconstruction made of biodegradable polyesters and calcium phosphate/calcium carbonate.

The aim of this study was the development of a processing pathway for manufacturing of biodegradable skull implants with individual geometry. The implants on the basis of polylactide and calcium phosphate/calcium carbonate were prepared by a combination of hot pressing and gas foaming. On the inside, the implant consists of a macroporous and faster degradable material (poly(D,L-lactide)+CaCO3) to allow the ingrowth of bone cells. The pore size is in the range of 200-400 microm. On the outside, the implant consists of a compact and slower biodegradable material (poly(L-lactide) and calcium phosphate) to ensure mechanical stability and protection. To overcome problems like inflammatory reactions caused by acidic degradation products of polylactide, the polyester was combined with basic filling materials (calcium salts). The filler neutralises the lactic acid produced during polymer degradation and increases the bioactivity of the material. The stabilised pH was demonstrated by long-term in vitro pH studies. Over a time period of 250 d in demineralised water, the pH was in the physiological range. The in vitro biocompatibility was shown by cell cultures with human osteoblasts. A good proliferation of the cells was observed over the whole test period of 4 weeks.

Microsurgical tissue transfer and individual computer-aided designed and manufactured prefabricated titanium implants for complex craniofacial reconstruction.

From 1994 to 2000 187 individual computer-aided designed and manufactured (CAD/CAM) prefabricated titanium skull implants were inserted at 37 clinical centres. Since the processing chain of construction and fabrication of implants has become routine the clinical success totally depends on the condition of the soft tissues at the recipient site. In three patients in our own department with a history of up to 18 surgical interventions, and additional previous irradiation in one case, these conditions were so bad that a microsurgical tissue transfer had to be made before insertion of the implant. A latissimus dorsi free flap with submandibular microsurgical anastomosis had to be used in all three cases. However, the aetiology of the soft tissue deficits differed, and they were at a different tissue level in each case: anterior skull base, subcutaneous temporal area, and frontoparietotemporal skin. This series of patients therefore demonstrates the variability of possible combinations, which also require special timetables and principles of construction of the CAD of the implant. In all cases the cranioplasties were done three to five months after the transfer of the flaps and fulfilled the criteria of greatest precision and the best possible aesthetic outcome with minimal stress for the patients. These applications are surgical strategies for extreme cases but also illustrate the elaborate interdisciplinary approach in Computer Assisted Surgery.