Alexander Tschakaloff

Congenital bilateral coronal suture synostosis in a rabbit and craniofacial growth comparisons with experimental models.

Experimental rabbit models of postnatal coronal suture (CS) synostosis have helped make significant contributions towards the understanding and surgical management of human congenital craniosynostosis. The present study compares craniofacial growth patterns in animals with experimental CS immobilization and in a rabbit born in our laboratory with congenital CS synostosis. The study sample consisted of 10 sham controls, 14 experimental animals with bilateral CS immobilization, and one animal with congenital, bilateral CS synostosis. At 1.5 weeks of age, all animals had amalgam markers placed on either side of the frontonasal, coronal, and anterior lambdoid sutures. At this time, the experimental animals had bilateral CS immobilization using methyl-methacrylate. Serial lateral head x-rays were taken at 1.5, 6, 12, and 18 weeks of age. Results revealed that by 1.5 weeks of age the congenital animal already exhibited changes in the cranial vault, cranial base, midface, and orthocephalic cranial base angles compared to controls. By 6 weeks of age, animals with experimental immobilization showed compensatory growth patterns similar to the congenital animal, particularly at the calvarial sutures and upper midface. This pattern continued through 18 weeks. Results showed that experimental, postnatal CS immobilization produced similar craniofacial growth patterns to those observed for our single congenital animal, but to a lesser degree, and therefore validates, in part, findings from experimental rabbit models of synostosis.

Degradation kinetics of biodegradable DL-polylactic acid biodegradable implants depending on the site of implantation

A recently developed biodegradable system made of DL-polylactic acid (DL-PLA) for internal fixation of non-weight-bearing bones of the craniofacial skeleton was investigated. The plates were used for rigid fixation of experimental nasal bone fractures in 20 New Zealand white rabbits. In addition, prebent plates were placed in subcutaneous pockets in the backs of the animals. The material was removed after 7, 14, 28, and 42 days, and bending angles, plate stability, molecular weights (MW), and histologic analyses were studied. A significant decrease of MW over time and a difference in MW loss, showing a faster degradation subcutaneously, were observed. Plate stability did not decrease during the interval of 6 weeks, but a loss of bending angle was found in all prebent implants. This effect was caused by memory of DL-PLA. The results suggest that memory of biodegradable materials should be investigated before clinical application and that degradation rates differ according to the site of implantation.

Coronal suture response to distraction osteogenesis in rabbits with delayed-onset craniosynostosis.

Recent studies have identified a subpopulation of persons with craniosynostosis who exhibit progressive or delayed-onset synostosis and mild cranial vault deformities. These persons may be good candidates for nonextirpation distraction osteogenesis. The present studies were designed to determine force-displacement parameters and assess the effects of distraction osteogenesis on coronal suture growth and morphologic characteristics in a rabbit model with congenital, delayed-onset craniosynostosis. Data were collected from a total of 178 rabbits: 71 normal controls; 16 normal controls with distraction; 72 with delayed-onset coronal suture synostosis; and 19 with delayed-onset coronal suture synostosis and distraction. At 10 days of age, all rabbits had amalgam markers placed on both sides of the coronal suture. In the force-displacement study, force-displacement distractors were placed across the coronal suture and distracted acutely for 1.0 mm at 42 days of age. Force-displacement curves for the coronal suture were best described by a third-order polynomial regression equation for both normal and synostosed groups. Significant differences (P < 0.05) were found in the mean force necessary to distract a normal suture 1 mm in distance (13.72 kg) compared with a suture with delayed-onset synostosis (48.39 kg). A significant (P < 0.05) relationship was also found between the extent of synostosis and the distractive force in rabbits with delayed-onset synostosis. In the distraction study, internal distractors were fixed across the coronal suture at 25 days of age and percutaneously and intermittently activated at an average of 0.11 mm/day for 42 days (4.54 mm total). Serial radiographs were taken at 10, 25, 42, and 84 days of age. Results revealed that rabbits with delayed-onset synostosis and distraction had significantly (P < 0.01) more coronal suture growth rates compared with rabbits with delayed-onset synostosis and no distraction. Coronal sutures were harvested at 84 days of age for qualitative histologic examination. Normal, distracted coronal sutures showed widened sutural ligaments and thin, active osteogenic fronts. In contrast, distracted coronal sutures from rabbits with delayed-onset synostosis showed narrowed sutural ligaments, thickened and blunt osteogenic fronts, and increased collagen and bony matrix deposition compared with controls. Results suggest that distraction osteogenesis without corticotomy may be a treatment alternative in persons with progressive, delayed-onset synostosis. However, these preliminary data also suggest that distractive forces may accelerate or stimulate osteogenesis differentially in persons with craniosynostosis, possibly through an underlying genetic disorder of bone and cytokine regulation. These differential osteogenic responses to distraction, if validated clinically, will need to be taken into account when planning distraction rate and rhythm protocols for patients with craniosynostosis.

Internal Calvarial Bone Distraction in Rabbits with Delayed-Onset Coronal Suture Synostosis

&NA; Recent studies have identified a subpopulation of craniosynostotic individuals who exhibit progressive or delayed‐onset synostosis and mild craniofacial growth abnormalities. These individuals may be good candidates for nonextirpation, distraction osteogenesis therapy. The present study was designed to test this hypothesis by using internal calvarial bone distraction in a rabbit model with familial delayed‐onset craniosynostosis. Data were collected from 159 rabbits: 71 normal controls, 72 with delayed‐onset coronal suture synostosis, 8 with delayed‐onset coronal suture synostosis and coronal suturectomy, and 8 with delayed‐onset coronal suture synostosis and distraction. At 10 days of age, all rabbits had amalgam markers placed on both sides of the frontonasal, coronal, and anterior lambdoidal sutures. At 25 days of age, correction was accomplished through either a 5‐mm‐wide suturectomy or distraction osteogenesis. An internal distraction appliance was fixed to the frontal and parietal bones and percutaneously and intermittently activated at an average of 0.10 mm/day for 42 days (4.11 mm total). Serial radiographs were taken at 10, 25, 42, and 84 days of age. Results revealed that rabbits with delayed‐onset synostosis had significantly (p < 0.01) reduced coronal suture growth rates (0.04 mm/day) compared with the other three groups (0.07 mm/day). Rabbits with suturectomy and rabbits with distraction showed similar coronal suture responses. However, from 42 to 84 days of age, rabbits with distraction showed reduced growth at the vault sutures and abnormal growth patterns in cranial vault width, cranial vault shape, and cranial base angulation compared with the other three groups. Results demonstrated that, although the normal coronal suture growth rate was maintained in rabbits with delayed‐onset synostosis using intermittent distraction osteogenesis, normal adult craniofacial structure was not achieved. Such anomalous growth was probably a result of altered growth vectors and compressive forces at adjacent sutures during distraction. These findings suggest that distraction osteogenesis without corticotomy may be a treatment alternative in individuals with progressive, delayed‐onset synostosis, but that internal appliances that generate low‐level, continuous distractive forces should be investigated and developed. (Plast. Reconstr. Surg. 102: 1109, 1998.)

Internal Calvarial Bone Distraction in Rabbits with Experimental Coronal Suture Immobilization

Correction of craniosynostosis involves removal of the coronal suture to allow for expansion of the developing brain and normal craniofacial growth. Frequently, however, the site reossifies, restricts growth, and requires additional surgery. The present study was designed to assess the effects of an internal, subperiosteal calvarial distractor on suturectomy site patency and compensatory craniofacial growth changes in an experimental rabbit model of coronal suture synostosis. In the present study, 43 1 1/2-week-old rabbits were used. Amalgam markers were placed across the frontonasal, coronal, and anterior lambdoidal sutures in all animals. Twenty-nine rabbits underwent bilateral coronal suture immobilization using methyl methacrylate. Fourteen rabbits were left untreated and served as sham controls. At 6 weeks of age, the immobilized rabbits were divided into three groups: (1) immobilized (controls), (2) suturectomy, and (3) suturectomy and distraction. The distractors were activated percutaneously at an average of 0.6 mm/week for 5 weeks (3 mm total). Lateral head radiographs were taken at 1 1/2, 6, 12, and 18 weeks of age. Results revealed that, by 6 weeks of age, animals with coronal suture immobilization exhibited significantly (p < 0.01) reduced growth across the coronal suture, resulting in shorter and inferiorly rotated cranial vaults compared with sham controls. By 12 weeks of age, rabbits with distraction returned to normal (sham control) coronal suture marker separation, whereas rabbits with immobilized sutures and suturectomy only showed significantly reduced marker distances. Rabbits with distraction also exhibited greater anterior cranial base lengths compared with the other experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Memory of Dl-polylactic Acid Biodegradable Plates

Biodegradable plates and screws have many advantages over metal plates and screws. Plates were injection-molded and made of DL-polylactic acid. Four-hole plates were bent with the use of a heated tip to angles of 30, 45, and 60 degrees. They were inserted in the subcutaneous space in the back of rabbits. After 2 weeks, the plates straightened, suggesting that the plates had a memory. The results were confirmed by similar in vitro investigations. The in vitro experiment was repeated with tempering of the plates. The plates were heated to a temperature of 200°C for 45 seconds, cooled, and then again heated to 200°C for 40 seconds. This process resulted in loss of memory of the plates. After 4 weeks, there was a change of the bending angle of less than 2.5 degrees.

Alternative Knochenersatzmaterialien zur präoperativen Fertigung individueller CAD/CAM-Schädelimplantate

Hintergrund. Die Verfahrenskette zur präoperativen Fertigung individueller CAD/CAM-Schädelimplantate ist auf den Werkstoff Titan zugeschnitten und optimiert, erlaubt jedoch grundsätzlich auch die Verarbeitung anderer Materialien. Verarbeitung anderer Materialien. Der Einsatz von Poly-(D,L-lactid) (PDLLA) als Implantatwerkstoff für individuelle Schädelimplantate wurde an einem adulten, formalinfixierten Schafkopf untersucht. Zum einzeitigen operativen Vorgehen wurde neben einem herkömmlichen Titanimplantat eine korrespondierende Sägeschablone aus Aluminium geplant und mittels computergesteuerter Fräsmaschine gefertigt. Die Herstellung einer Hohlform aus Teflon zur Fertigung eines PDLLA-Implantats mit dem CO2-Begasungsverfahren für denselben Defekt erlaubte die kritische Gegenüberstellung beider Implantatwerkstoffe. Dabei zeigte sich bezüglich Passgenauigkeit und Praktikabilität bei der Herstellung die grundsätzlich problemlose Verarbeitung des PDLLA bei Überlegenheit des Titans in Bezug auf die erreichte Präzision. Diskussion. Zielsetzung gegenwärtiger Forschungsvorhaben ist die Herstellung eines gradierten Werkstoffs aus Polylactid, Polyglycolid, Calciumphosphat und ggf. osteoinduktiven Proteinen in Verbindung mit der individuellen Formgebung durch die oben beschriebene Verfahrenskette, da die hohen Anforderungen an einen idealen Implantatwerkstoff von einem Werkstoff allein nicht erbracht werden können. Background. The preoperative manufacturing of individual skull implants using computer aided design (CAD) and computer aided manufacturing (CAM) is based on the use of titanium, although the use of other materials is also potentially possible. The use of other materials. The use of poly(D,L-lactide) (PDLLA) as an implant material was investigated using an adult, formalin fixed sheeps head with a complex frontolateral defect. A standard individual titanium implant as well as a resection template made of aluminium were milled in order to allow bone resection and reconstruction within one operation. A mould was made of Teflon for the fabrication of the PDLLA implant using carbon dioxide at high pressure. This procedure allowed a critical comparison to be made of both implant materials and showed that the production of a biodegradable PDLLA implant is possible. At present the titanium implant is superior to the PDLLA implant, as PDLLA settled with slightly larger dimensions than the mould, although the structure itself was exact. Discussion. The goal of the present research is the fabrication of a functionally graded material made of polylactide, polyglycolide, calcium phosphate and osteoinductive proteins using existing technology, which will meet all of the requirements for stability, resorption kinetics, biocompatibility, radiotranslucence and osteogenic potency of an ideal implant material.

ALTERNATIVES KNOCHENERSATZVERFAHREN - SYNTHESE VON CAD/CAM UND TISSUE ENGINEERING

Die an der Ruhr-Universität Bochum im Rahmen eines interdisziplinären Forschungsprojekts entwickelte Verfahrenskette zur präoperativen Herstellung individueller CAD/CAM-Schädelimplantate basierend auf CTDaten des Patienten ist klinisch bisher auf den Werkstoff Titan zugeschnitten. Das Verfahren, das bereits in über 160 Fällen angewendet wurde und dessen besonderes Merkmal die geschlossene, rechnerinterne Führung der Patientendaten ist, erlaubt jedoch grundsätzlich auch die Verarbeitung anderer Materialien durch Fräsen oder in der Hohlform [1]. Resorbierbare Materialien, die bereits als Osteosynthesematerialien klinisch eingesetzt werden, können als Trägersubstanzen für osteoinduktive Proteine bei vorhersagbarer Resorption und gleichzeitiger Freisetzung der osteoinduktiven Proteine eine Knochenapposition ermöglichen. Hier ist insbesondere das Polylactid zu nennen [3]. Um die Praktikabilität bezüglich der Verarbeitung des Polylactids als Knochenersatzmaterial bei Defekten im Bereich der Schädelkalotte in Form eines präoperativ individuell gefertigten Implantats zu untersuchen und mit der herkömmlichen, etablierten Methode unter Verwendung von Titan zu vergleichen, wurde ein erster Vorversuch durchgeführt.