M. J. Kallioinen

Consolidation of craniotomy lines after resorbable polylactide and titanium plating : A comparative experimental study in sheep

&NA; The consolidation process of craniotomy lines in a skeletally immature large mammal was studied. A traditional narrow titanium miniplate was compared with a 0.5‐mm‐thick, 12‐mm‐wide absorbable punched self‐reinforced poly‐L‐lactide (SR‐PLLA) plate, both fixed with titanium miniscrews over bilateral parietal 2.5‐mm‐wide stable transosseous craniotomies on nine female sheep (16 to 20 months old). After 6, 12, 20, 52, and 104 weeks, cross‐sectional histology, histomorphometry, and oxytetracycline chloride fluorescence studies were done to compare the healing process of the craniotomy lines and to study the biocompatibility and the degradation process of the SR‐PLLA plate. The consolidation pattern supported the principle of guided tissue regeneration: under the wide, resorbable plate osseous bridging proceeded evenly throughout the line, whereas titanium plating led to bulky, uneven growth in the bone margins. All SR‐PLLA‐plated osteotomy lines had healed completely by 20 weeks, whereas none of the titanium‐plated lines had consolidated during a follow‐up of 1 year. The nonossified gaps were filled with dense connective tissue. Histomorphometric analysis showed that osseous bridging proceeded significantly faster on the resorbable plate side compared with the titanium side (p < 0.001). The osteoid surface fraction over the total trabecular surface was highest at 6 weeks, being 63 percent on the SR‐PLLA side and only 36 percent on the titanium side. The oxytetracycline chloride fluorescence studies confirmed these findings. After 52 weeks, there was no osteoid or oxytetracycline chloride fluorescence left as a sign of terminated ossification, even in the nonconsolidated titanium sides. Microscopic cracking of the plate was evident at 12 to 20 weeks, and the first signs of active resorption were present at 52 weeks. After 2 years, the plate had disappeared and tiny polylactide particles were being actively resorbed. The biocompatibility of SR‐PLLA and titanium was good, and no adverse cellular reactions to these materials were noted, except a clinical foreign body reaction caused by loosened titanium miniscrews. A densely punched, 0.5‐mm‐thick self‐reinforced PLLA plate seems to retain its integrity for a sufficiently long time to complete osseous healing of a 2.5‐mm‐wide craniotomy line in the sheep calvarial area. A thin, wide fixation plate enables superior healing, especially in osseous defects. The degradation process of the SR‐PLLA plate begins within 1 year and is far advanced after 2 years. By using absorbable SR‐PLLA fixation plates instead of metallic plates, a subsequent operation for the removal of the implants can be avoided. SR‐PLLA devices could thus be a potential additive or even alternative to metallic implants in craniofacial surgery. (Plast. Reconstr. Surg. 101: 123, 1998.)

Development of the neurocranium after transsutural fixing by new, resorbable poly-L-lactide miniplates. A comparison to fixing with the common titanium miniplates.

SummaryThe right coronal sutures of twelve (12) newborn rabbits were fixed with commercially available, self-reinforced poly-L-lactide miniplates, with eight (8) rabbits sham treated with titanium miniplate fixation as reference experiments, in order to demonstrate the possible effects on skull growth. After six (6) months follow-up, both types of plate were detected to have caused a similar asymmetry in the neurocranium. Therefore, in our opinion, fixing across growing sutures, even with the new biodegradable devices, should be avoided.

Histopathological and immunohistochemical changes in neurosurgically resected epileptic foci.

SummaryNeurosurgical resection of an epileptic focus was performed in eleven patients suffering from drug resistant focal epilepsy. The clinical result was favourable in nine cases and corresponds to the earlier results. The routinely processed biopsy specimens obtained from the brain resections were stained with haematoxylin-eosin and with specific antisera to GFAP, S-100, NSE, laminin, and fibronectin using the peroxidase-antiperoxidase technique. The main pathological finding was gliosis in eight cases, neuronal degeneration in two cases, and a vascular malformation in one case. The anti-GFAP as a specific marker of astrocytes made the astroglial proliferation clearly visible, demonstrating an astroglial scar in four cases and a moderately to strongly increased amount of astroglial cells in another four cases. Anti-S-100 and anti-fibronectin are not as specific markers. They stained both neurones and glial cells with comparable results to that of anti-GFAP but with a lower specificity and sensitivity. Anti-NSE showed decreased amounts of neurones in most of the heavily gliotic lesions and also stained glial cells in some cases. Anti-laminin stained the pial and vascular basement membranes and revealed an increased vasculature in two cases.From these results, it appeares that GFAP immunostaining is a highly demonstrative means for the visualization of astrogliosis in epileptic lesions and may be of help in identifying slight focal changes. An exact demonstration of neuronal loss or other neuronal changes still waits for a more specific marker then NSE. A favourable clinical outcome after neurosurgery seems to be associated with the patients showing a clearly gliotic brain lesion in one temporal lobe.

Bone tissue engineering: treatment of cranial bone defects in rabbits using self-reinforced poly-L,D-lactide 96/4 sheets.

This study is one of a series in which the authors evaluate various absorbable sheets to guide bone regeneration in cranial bone defects. The aim was to evaluate the use of self-reinforced poly-L,D-lactide 96/4 (SR-PLA96) sheets for cranial bone tissue engineering in experimental defects in rabbits. Square defects of 10 × 10 mm were created in the right parietal bone. SR-PLA96 implants (15 × 15 mm) were used to cover these defects in 12 New Zealand White rabbits. Similar defects were created in the left parietal bone, but no sheets were used (controls). The rabbits were killed after 6, 24, or 48 weeks. Histology and histomorphometry were used to evaluate healing of the defects. Defects covered with SR-PLA96 sheets showed more abundant bone formation than control (non-covered) defects. At 6 weeks, the defects were occupied mainly by fibrous tissue. At 24 weeks, healing with bone formation was more obvious in the covered defects. At 48 weeks, bone completely bridged defects covered with SR-PLA96 sheets, and incomplete bridging was seen in non-covered control defects. Hence, bone tissue engineering in experimental cranial bone defects in rabbits can be achieved using SR-PLA96 sheets to guide bone regeneration.

Tissue engineering of bone in muscle by using free periosteal grafts with a self-reinforced polyglycolide membrane scaffold. An experimental study in growing rabbits

Abstract For tissue engineering of predesigned rectangular bone from free tibial and calvarial periosteal grafts, using self-reinforced polyglycolide membrane (SR-PGA) as a scaffold, fourteen growing New Zealand White rabbits were used. In twelve animals, free tibial and calvarial periosteal grafts wrapped around membranes and grafts without membranes were implanted in muscle. In two control animals membranes only were implanted. Follow-up periods were 6 and 12 weeks. Bone formation and tissue reactions were evaluated macroscopically and histologically. Tibial grafts produced bone more often than calvarial grafts (11/12 vs. 5/12). At 6 weeks mature rectangular bone was obtained from tibial grafts with membranes, whereas none was obtained from calvarial grafts with membranes. At 12 weeks, bone ossicles obtained from both types of graft with membranes were clearly smaller than at 6 weeks and the rectangular form was lost. SR-PGA membrane can be used as a scaffold to obtain predesigned rectangular bone from free tibial periosteal grafts in growing rabbits. Transplantation should be performed before resorption occurs.

Polylactide and polyglycolic acid-reinforced coralline hydroxy-apatite for the reconstruction of cranial bone defects in the rabbit

SummaryThe possibility of using coralline hydroxy-apatite in combination with polylactide and polyglcycolic acid instead of a bone graft in the skull region is examinated. Coralline hydroxy-apatite blocks strengthened with a membrane made of a combination of polylactide and polyglycolic acid were inserted into bony defects created in 12 rabbit skulls. The blocks were observed during a follow-up of 12 months. They became fixed to the surrounding bone and no adverse effects or harmful reactions in the nearby tissues could be detected.

Poly-L-lactic acid plate for covering of small cranial bone holes: an experimental study in rabbits

Abstract Cranioplasty was performed on 13 adult New Zealand white rabbits to investigate the potential of poly-L-lactic acid (PLLA) plates for cover of small cranial bone holes. Two holes of 5 mm in diameter were drilled through the parietal bone, one on each side of the skull. One was covered with a self-reinforced polylactide (SR-PLLA) plate while the other one was left empty, with only the periosteum covering. The results were analysed by taking X-rays and samples for histological examination 3, 6, 24 and 48 weeks postoperatively. There were no special radiological findings. Histologically, new bone formation was clearly seen on the implant side at 24 and 48 weeks after the operation, while there was only a slight reaction on the control side in the same rabbit. We conclude that SR-PLLA appears to enhance the healing of cranial bone.

Remodelling of rabbit rib cartilages with perichondrial flaps and biodegradable implants

Remodelling of rib cartilages using the regenerative potential of perichondrium and self-reinforced polyglycolic acid (SR-PGA) implants was studied in eight growing rabbits. The 5th rib cartilage was resected subperichondrially on both sides and a 10 × 1.1-mm SR-PGA rod was placed inside the perichondrium on one side while the other served as a control. In one-half of the cases the perichondrium was used as a vascularized flap while in the other half it was used as a non-vascularized flap. Samples were taken 6 weeks postoperatively. Neocartilage formation was observed from vascularized as well as non-vascularized flaps.

A new method for the creation and measurement of experimental craniosynostosis

Craniosynostosis is described as a condition in which the premature closure of one or more cranial sutures is exposed as a skull deformity alone or accompanied by neurological disturbances. According to previous research it seemed possible to create an experimental model for investigating the disease by simply resecting a suture in a newborn rabbit. We resected 16 coronal sutures in 16 newborn rabbits and had the skulls investigated for shape and histology up to 6 months of age. A clear deformity at the cranial vault could be detected. The fused site of th suturectomy later on presented a suture-like structure which was macroscopically distinct from a normal skull suture. The procedure is thus established, first, for investigating procedures for treating craniosynostosis in the growing skull, and, secondly, for studying the pathophysiology of craniosynostosis.

Stabilization of anterior thoracoplasty with a resorbable, self-reinforced poly-l-lactic acid rod: an experimental study in rabbits

Thoracoplasty using a self-reinforced, poly-l-lactic acid (SR-PLLA) rod was performed on 14 growing rabbits. The 4th–6th rib cartilages were resected subperichondrially on both sides, preserving the perichondrium, and a transverse sternotomy was performed between the levels of the 3rd and 4th ribs. The caudal part of the sternum was depressed, creating an experimental pectus excavatum, and fixed in this position using a 2 × 30 mm SR-PLLA rod placed trasversally on the sternum and fixed laterally between the 4th and 5th ribs on both sides. A CT examination was performed on each rabbit postoperatively and before killing. Samples were taken 1, 6, and 12 months after the operation. Both CT and clinical findings showed that the experimentally created pectus excavatum had maintained well throughout the experimental period. Regeneration of the resected rib cartilages was observed in every rabbit.