Jyrki Kilpikari

BIODEGRADABLE IMPLANTS IN FRACTURE FIXATION: EARLY RESULTS OF TREATMENT OF FRACTURES OF THE ANKLE

Biodegradable polylactide-glycolide copolymer implants for fracture fixation were developed and tested in rabbits. In a prospective clinical study 44 patients with a displaced fracture of the ankle were randomly allocated to two groups; one was treated with conventional metallic implants and the other with the biodegradable implants. There were no differences between the two groups in the early results, but the biodegradable fixation method is advantageous because the removal procedure associated with metallic implants is avoided.

Strength and strength retention vitro, of absorbable, self-reinforced polyglycolide (PGA) rods for fracture fixation

The initial shear strength and changes in flexural strength of self-reinforced, absorbable polyglycolide (PGA) composite rods, submerged in distilled water (at 37 degrees C) for a period of 6 wk, were investigated. The recently developed self-reinforced absorbable material consists of an absorbable polymeric matrix reinforced with fibres of the same polymer. The initial shear strength of self-reinforced cylindrical PGA rods with a diameter of 3.2 mm was 250 MPa and the initial flexural strength of the rods was 370 MPa. During the first week of immersion the level of flexural strength decreased very little i.e. to 320 MPa. The loss of flexural strength increased after 1 wk immersion. However, after 3 wk it was 90 MPa. After 5 wk the flexural strength decreased to the level of strength of cancellous bone i.e. 10-20 MPa. The gamma-irradiation of the PGA rods (total dosage 2.5 Mrad) decreased the initial bending strength to 300 MPa but the hydrolytic behaviour of the rods was not changed. The in vitro strength and the strength retention of self-reinforced PGA rods are clearly better than the corresponding values for self-reinforced glycolide/lactide copolymer rods which we developed recently. Self-reinforced PGA rods are now used routinely in Helsinki University Central Hospital in the treatment of certain types of cancellous bone fracture.

The effects of fibre reinforcement and gold plating on the flexural and tensile strength of PGA/PLA copolymer materials in vitro

Changes in the flexural and/or tensile strength of plates and rods made of PGA/PLA copolymer submerged in water for a period of 4 wk were investigated. During this time, the effects of PGA/PLA fibre self-reinforcement, carbon fibre reinforcement and gold plating on tensile and/or flexural strength were examined. The results were used for evaluation of the surgical applications of PGA/PLA copolymer and its composites. The initial tensile strength of non-reinforced material was 45 Mpa and its flexural strength was 150 MPa: the flexural strength of self-reinforced material was 265 MPa. The tensile strength of carbon fibre reinforced material was 90 MPa and its flexural strength 190 MPa. The initial strengths of plated and unplated samples were the same but plating delayed the loss of the mechanical strength of carbon fibre reinforced samples. After 4 wk the flexural strength of self-reinforced and carbon fibre reinforced samples was decreased to the level of cancellous bone (10-20 MPa) while the flexural strength of non-reinforced samples was below that level (less than or equal to 5 MPa). The results suggested that self-reinforced PGA/PLA composites may be used for the treatment of fractures in cancellous bone. Positive animal experiments led to clinical studies in vivo. These studies showed that there was no difference in outcome between 2 groups of patients with displaced fractures of the ankle treated with metallic implants or PGA/PLA fibre self-reinforced implants, respectively. Self-reinforced biodegradable implants are now used routinely in Helsinki University Central Hospital.

Fixation of experimental osteotomies of the distal femur of rabbits with biodegradable material

SummaryOsteotomies of the distal femur in 19 rabbits were operatively fixed with totally biodegradable implants. Radiographic, histological, microradiographic, and oxytetracycline-labeling studies showing healing of the osteotomy within 6 weeks. The fixation proved stable sufficiently during healing of the osteotomized bone. The osteotomies united without delay and malalignment did not occur, although no external support was used and the rabbits were allowed to walk freely after the operation. Successful use of the biodegradable fixation developed in the present study was reported recently for the treatment of fractures of the ankle.

Biodegradable fixation of rabbit osteotomies

Osteotomies of the tibial diaphysis were operatively fixed with biodegradable implants in 44 rabbits. Polyglycolic acid (PGA)/polylactic acid (PLA) copolymer implants reinforced with 7 per cent carbon fibre and overlaid with gold were used in 24 rabbits. Poly-beta-hydroxy butyric acid (PHBA) with carbon fibre reinforcement and gold surfacing were used in 20 rabbits. No external support was used. Unsatisfactory results were achieved with the PGA/PLA copolymer implants. Better results were achieved in 15 out of 20 rabbits whose osteotomies were fixed with carbon fibre-reinforced PHBA implants.

Experimental fixation of bone cement and composite resins to bone.

SummaryThe aim of this study was to ascertain whether the use of liquid acrylic resin or NeoCryl XK-53 acrylic emulsion or etching of the bone surface with phosphoric acid or the application of both these methods would improve the bonding of CMW bone cement or Concise and Silar composite resin to bone. The test materials were applied to fresh cortical bovine bone. Their bonding capacity was measured by the Instron Universal Testing Machine. The surfaces of the test materials and the bone surfaces were examined by means of optic microscope or scanning electron microscope. The bonding strength of the bone cement and composite resins as such were found to be of the same magnitude. A three- to five-fold improvement was obtained with liquid acrylic intermediary material. Acid etching impaired the bonding.ZusammenfassungDas Ziel dieser Untersuchung war, herauszufinden, ob der Gebrauch von füissigen zusammengesetzten Acryl-Harzen oder von NeoCryl XK-53 Acryl-Emulsionen oder von Ätzung der Knochenoberfläche mit Phosphorsäure oder die Anwendung von beiden Methoden die Fixierung des Knochenzements CMW oder der zusammengesetzten Harze Concise und Silar verbessern wurde. Die untersuchten Materialien wurden an frischen corticalen Rinderknochen angebracht. Die Fixierungskapazität wurde mit dem Universal-Gerät Instron fur Material-tests gemessen. Die Oberflächen des Testmaterials und des Knochens wurden mit Hilfe eines optischen oder Raster-Elektronenmikroskops untersucht. Die Resultate bewiesen, daß sich der Knochenzement wie die zusammengesetzten Harze an dem Knochen fixierten. Das als Zwischenstoff verwendete flüssige Acryl verbesserte die Haftfahigkeit um das 3–5fache. Die Ätzungen mit Säure verschlechterte die Häftfahigkeit.

Fixation of experimental osteotomy of the distal femur with biodegradable thread in rabbits.

A distal femoral osteotomy on 24 rabbits was fixed with biodegradable polyglycolic acid (PGA) thread pulled through drill holes made on both sides of the osteotomy. Follow-up times were one, three, six, 12 and 24 weeks. The distal part of each femur was removed, fixed in alcohol, embedded in methylmethacrylate, sawed to 80 microns thick for oxytetracycline (OTC)-labeling studies and microradiography, and sectioned at 5 microns for histologic studies. As judged by histologic microradiographic, and OTC-labeling studies, 19 of 24 osteotomies were healing normally; after six weeks of follow-up examination, union of 11 of 14 osteotomies was observed on radiographs. On the basis of the present study, PGA threads may be promising for the fixation of osteotomies of the metaphyseal cancellous bone in rabbits.