New Bioabsorbable Implants for the Fixation of Metaphyseal Bone An Experimental and Clinical Study

The purpose of the present study was to investigate the suitability of bioabsorbable drawn selfreinforced polyglycolide (SR-PGA) and poly-L/DL-lactide 70:30 (SR-PLA70) implants in experimental and clinical fixations of cancellous bone osteotomies, arthrodeses and fractures. The study consists of a set of two experimental and two clinical studies, including 109 experimental animals and 87 patients, respectively. In the experimental studies, the right femora of 77 Wistar rats were osteotomized and fixed with either drawn SR-PGA or SR-PLA70 bioabsorbable pins. Both femora of each rat were taken as specimens at follow up times ranging from 1 to 52 weeks after the operations. Radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies were performed. In the mechanical studies, four pins of SR-PLA70 or SR-PGA were implanted in the dorsal subcutaneous tissue of 32 rats for mechanical testing at 1 – 52 weeks. The clinical studies were prospective randomized studies concerning osteosynthesis with either SR-PLA70 or self-reinforced poly-L-lactide (SR-PLLA) screws. In the third study, 62 ankle fractures were treated using bioabsorbable screws in the fixation. The patients were followed for one year using clinical examination, radiography and Olerud-Molander score. The second clinical study included 25 patients with 32 painful feet with hallux valgus needing proximal osteotomy or arthrodeses of the 1 tarsometatarsal (TMT) joint. The patients were followed up for one year using radiography, clinical examination and hallux-metatarso-interphalangeal scoring (HMIS). The initial flexural strengths of the SR-PGA and SR-PLA70 pins were 270 ± 30 MPa and 214 ± 4.2 MPa, respectively. The initial flexural modulus of the SR-PGA and SR-PLA 70 pins were 13 ± 2 GPa and 6.0 ± 0.5 GPa, respectively. At 3 weeks in vivo, the SR-PGA pins had maintained 50 % of flexural strength and 46 % of modulus of the initial value, whereas SR-PLA70 pins retained 43 % of their flexural strength and 41 % of their modulus compared to the initial value at one year after implantation. In the ankle fractures patients, the SR-PLA70 and SR-PLLA study groups differed significantly only in the mean time of sick leave (SR-PLA70 60 days, SR-PLLA 65 days, p=0,02). At the one year follow-up, syndesmotic ossification was more common in the SR-PLA70 group (5 vs. 1 patient, p=ns.). There were no infections or signs of tissue reactions in either of the study groups. In the hallux valgus patients, 26 of 32 feet were treated with proximal osteotomy of the 1st metatarsal bone, and the other 6 feet with concomitant laxity of the 1st tarsometatarsal (TMT) joint were treated with arthrodesis. At 12 weeks, bony union in 31 out of 32 osteotomies or arthrodeses was seen. At one year, the change of hallux valgus angle was 16° and 16°, and the change of intermetatarsal angle was 8° and 9° in SR-PLA70and SR-PLLA-groups, respectively. HMIS-scores were 90 and 92 accordingly. No signs of tissue reaction were seen during the follow-up time which lasted up to one year. Radiologically, the screw channel had not disappeared in any of the patients in the clinical studies by the one year follow-up. The present investigation showed that the mechanical strength and fixation properties of SR-PGA and SR-PLA70 pins are suitable for fixation of cancellous bone osteotomies in rats. Bioabsorbable SRPLA70and SR-PLLA-screws are suitable in the fixation of ankle fractures, the proximal osteotomy of the 1st metatarsal bone, and TMT joint arthrodesis in the treatment of hallux valgus deformity. National Library of Medicine Classification: QU 98, QY 60.R6, WE 190, WE 880, WE 883 Medical Subject Headings: Absorbable Implants; Ankle Injuries; Bone Screws; Bone Substitutes; Femur; Follow-Up Studies; Fracture Fixation, Internal; Fractures, Bone; Hallux Valgus; Humans; Lactic Acid/analogs & derivatives; Materials Testing; Osteogenesis; Osteotomy; Rats, Wistar; Time Factors; Treatment Outcome S