Kimmo Vihtonen

Bioabsorbable fixation in orthopaedic surgery and traumatology

Bioabsorbable internal fixation devices were introduced clinically in the treatment of fractures and osteotomies of the extremities at the Department of Orthopaedics and Traumatology, Helsinki University, in 1984. Since November 5, 1984, a total of 3200 patients were managed using bone or ligament fixation devices made of self-reinforced (matrix and fibres of the same polymer) bioabsorbable alpha-hydroxy polyesters. The devices used included cylindrical rods, screws, tacks, plugs, arrows, and wires. The most common indication for the use of bioabsorbable implants was the displaced malleolar fracture of the ankle. Transphyseal fixation with small-diameter, mainly polyglycolide pins was used in children. The postoperative clinical course was uneventful in more than 90% of the patients. The complications included bacterial wound infection in 4% and failure of fixation in 4%. In one-fifth of the latter cases, however, re-operation was not necessary. The occurrence of non-infectious foreign-body reactions two to three months postoperatively has been observed in 2% of the patients operated in the last few years with polyglycolide implants but none of the patients managed with polylactide implants. This inflammatory tissue response often required aspiration with a needle but did not influence the functional or radiologic result of the treatment. Owing to the biodegradability of these internal fixation devices, implant removal procedures were avoided. This results in financial benefits and psychological advantages. Bioabsorbable implants can also be used in open fractures and infection operations.

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.

Ankle fractures treated using biodegradable internal fixation.

In order to reduce the resources needed for the removal of metallic fixation devices in fracture treatment, absorbable implants of biodegradable synthetic polymers were developed using self-reinforced lactide-glycolide copolymer and polyglycolide. In a prospective study 102 patients with displaced unimalleolar or bimalleolar fractures of the ankle were managed using internal fixation devices consisting of cylindrical biodegradable implants 3.2 or 4.5 mm in diameter and 50 or 70 mm in length. After open reduction of the fracture a channel was drilled from the tip of the malleolus into the cancellous bone through the fracture surfaces. A biodegradable rod of the same diameter was then tapped into the drill channel to fix the fracture. Postoperatively, the ankle was immobilized by a plaster cast for six weeks. An anatomic initial reduction was achieved in 93 patients (91%). A slight secondary displacement occurred in four patients. In six patients a sinus formation yielding remnants of the degrading implant was seen two to four months after the operation. This minor complication did not influence the union of the fracture or functional recovery. At the one-year follow-up examination there was no change in the ability to participate in sports and other physical activities in 89 patients (87%). The biodegradable fixation method is now the routine approach of the department in treating displaced unimalleolar and bimalleolar ankle fractures. New clinical applications for the implants are under trial.

Biodegradable internal fixation for malleolar fractures. A prospective randomised trial

Fifty-six patients with displaced malleolar fractures had open reduction and fixation of the fracture fragments using, by random selection, either biodegradable implants or metal AO plates and screws. The cylindrical biodegradable implants were made of polylactide-glycolide copolymer (polyglactin 910). The complications, radiographic results and functional recovery were studied prospectively. After follow-up of at least one year, no significant differences emerged in the complication rate or in the results of treatment between the two methods of fixation. Because of the advantage of avoiding the need to remove metal fixation after union, we now use biodegradable internal fixation routinely to treat displaced malleolar fractures.

Self-reinforced absorbable screws in the fixation of displaced ankle fractures: a prospective clinical study of 152 patients.

Summary The series consisted of 152 patients with ankle fractures treated between May 1987 and August 1989 using absorbable screws of self-reinforced polyglycolide 3.4 mm in inner diameter and 25–70 mm in length. The mean follow-up time was 2 years, 5 months (range, 1 year, 7 months-3 years, 10 months). After open reduction, a channel was drilled through the fracture surfaces and the fragments were fixed with one absorbable screw or screws. A plaster cast was used postoperatively. At 1-year follow-up observation, the radiographical result was anatomical in 93.3% of 104 patients with unimalleolar and bimalleolar ankle fractures (Weber A or B) and in 80.5% of 41 severe ankle fractures. Seven patients were unavailable for follow-up observation. Two reoperations were performed because of primary or secondary failure of fixation. In all unimalleolar and bimalleolar fractures and in 95.1% of severe ankle fractures the functional recovery score was at least satisfactory. Sinus formation as a sign of tissue reaction was observed in 10 patients 2–6 months postoperatively, but this did not influence the healing of the fracture or the functional recovery. This report is the first extensive publication on the clinical use of absorbable screws.

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.

Bioabsorbable implants in orthopaedics

Bioabsorbable devices are the best alternative to metals for the internal fixation of fractures, osteotomies, arthrodeses, and ligament injuries because, during the healing process, bioabsorbable devices maintain the fixation, decompose gradually, and the stresses are transferred gradually to the healing tissue so that no stress shielding will occur. Bioabsorbale surgical devices do not require a removal operation, and so may reduce the total cost when compared to metallic devices. This review deals with the bioabsorbable synthetic polyglycolide (PGA), polyactide (PLA), and polydioxanone (PDS) polymeric devices in skeletal fixation, based mainly on our own investigations and experience, in over 3000 operations since 1985.1