Matti Mero

The effect of trauma to the lower femoral epiphyseal plate. An experimental study in rabbits

Forty-four rabbits were operated on when five weeks old; in one group a 2 mm drill-hole was made in the intercondylar portion of the right femur across the central portion of the growth plate up to the diaphysis, while in the other group a similar drill-hole of 3.2 mm was made. At 3, 6, 12 and 24 weeks after operation, specimens from the growth plates of both femora were analysed using radiographic, microradiographic, histological and histomorphometric techniques. It was found that destruction of 7% of the cross-sectional area of the growth plate caused permanent growth disturbance and shortening of the femur.

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.

Comparison of in vitro hydrolysis, subcutaneous and intramedullary implantation to evaluate the strength retention of absorbable osteosynthesis implants

To evaluate the behaviour of mechanical properties of absorbable osteosynthesis implants in vivo, the strength retention of self-reinforced polyglycolide rods in distilled water at 37 degrees C in the subcutis and femoral medullary cavity of the rabbit was investigated. The self-reinforced polyglycolide rods lost their strength significantly faster in vivo than in vitro. The strength loss of the self-reinforced polyglycolide rods was only slightly faster in the medullary cavity than in the subcutis. As the removal of the implants from the medullary cavity became difficult 5-6 wk after implantation, it is suggested that subcutaneous implantation would be a suitable method to evaluate the strength retention of absorbable osteosynthesis implants.

Biodegradable self-reinforced polyglycolide (SR-PGA) composite rods coated with slowly biodegradable polymers for fracture fixation: strength and strength retention in vitro and in vivo

Abstract The strength retention of coated and uncoated self-reinforced polyglycolide (SR-PGA) rods was evaluated after immersion in distilled water at 37°C and after implantation in the subcutis of rabbit. Slowly biodegradable coatings improved only the in-vitro strength retention of SR-PGA osteosynthesis implants. In the in-vivo environment the rods lost their strength in 5–6 weeks, and there was no significant difference in the strength retention between coated and uncoated rods. The SR-PGA rods lost their strength considerably faster in vivo than in vitro.

The effect of a penetrating biodegradable implant on the growth plate. An experimental study on growing rabbits with special reference to polydioxanone.

This study examined the fate of a biodegradable polydioxanone (PDS) implant in growing bone in rabbits. In 20 immature rabbits, a PDS rod 2.0 mm in diameter and 25 mm in length was driven into a drill hole of equal bore in the intercondylar portion of the right femur across the central portion of the growth plate. In another 25 immature rabbits, a PDS rod 3.2 mm in diameter and 25 mm in length was driven into a corresponding drill hole using the same technique. The follow-up intervals were three, six, 12, 24, and 36 weeks. The distal femoral growth plates of both femora were analyzed by roentgenographic, microroentgenographic, oxytetracycline-fluorescence, histologic, and histomorphometric studies. Histomorphometric studies showed clear changes at the site of injury and appeared to be an excellent means of providing an exact numerical description of the different cellular areas of the growth plate in experimental studies. A transphyseal PDS implant 2.0 mm in diameter did not cause any permanent growth disturbance of the femur in a growing rabbit. An implant 3.2 mm in diameter caused a growth disturbance similar to a drill hole of equal bore.

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.

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.

Healing of physeal fracture after fixation with biodegradable self-reinforced polyglycolic acid pins. An experimental study on growing rabbits

Physeal fractures occur at a frequency of 15% of all long bone fractures in children. Undisturbed continued bone growth is the main goal of the treatment of these fractures. After the operative reduction and fixation, whenever needed, a second operation for the removal of the pins is inevitable. The purpose of this study was to develop a biodegradable fixation device for transphyseal fracture fixation, abolishing the need of removal operation. Epiphyseal separation of the distal femoral physis was made on the right side in 18 five-week-old rabbits. The fixation of the physeal fracture was made with two self-reinforced polyglycolic acid (SR-PGA) pins 1mm in nominal diameter and 25mm in length. The follow-up times were 3, 6, 12, 24, and 28 weeks. The distal femoral growth-plate of both femurs was analyzed by radiographic, microradiographic, oxytetracycline-fluorescence, histological and histomorphometric studies. Histomorphometric studies showed normal features of growth. Two growth-plate-penetrating transcondylar SR-PGA implants, of 1mm in diameter, provided sufficient stability for the fixation of a distal femoral physeal fracture in a growing rabbit, and did not cause any growth disturbance.

The effect of a diagonally placed penetrating biodegradable implant on the epiphyseal plate. An experimental study on growing rabbits with special regard to polydioxanone

Abstract Forty rabbits, five weeks of age, were operated on. In 20 rabbits an oblique drill hole of 3.2mm in diameter was made at an angle of 60° to the growth plate of the right distal femur. In the other 20 rabbits a polydioxanone rod was driven in a similar drill hole. The follow-up times were three, six, 12, and 24 weeks. The distal femoral growth plates of both femurs were analyzed by radiographic, microradiographic, oxytetracycline-fluorescence, histological and histomorphometric studies. Histomorphometric studies served as an excellent means of an exact numerical description of the different cellular areas of the growth plate in experimental studies. An oblique drill hole resulted in permanent growth retardation and varus deformity of the femur in growing rabbit. A diagonally placed PDS-implant caused a similar growth retardation but did not cause any varus deformity. Internal fixation of physeal fractures with biodegradable pins with no need of implant removal appears as an exciting prospect. The fixation device should possess suitable mechanical properties to provide a safe aid for fixation and still be sufficiently flexible to permit uneventful healing process. The pressure of growth was able to break the PDS implant. Further studies are needed for development of biodegradable fixation of physeal fractures.