Polylactide screws in the fixation of olecranon osteotomies. A mechanical study in sheep

Effect of a bioabsorbable, super-high molecular weight poly-D,L-lactic acid plate containing recombinant human bone morphogenetic protein-2 for fracture healing

The aim of this study was to investigate the effect of a bioabsorbable, super-high molecular weight poly-D,L-lactic acid (PDLLA) plate exhibiting the sustained release of recombinant human bone morphogenetic protein-2 (rhBMP-2) (PDLLA-rhBMP-2) on the treatment of fracture with internal fixation. A total of 32 New Zealand rabbits were randomly allocated to one of four groups (2, 4, 8 and 12 weeks), and a 2.5-mm middle ulnar osteotomy was performed bilaterally. The right side (experimental side) was fixed internally with PDLLA-rhBMP-2, and the left side (control side) was fixed with a normal PDLLA plate. At 2, 4, 8 and 12 weeks after surgery, the gross pathology of the ulnas was examined and radiographic, histological and computer image analyses were performed. The results demonstrated that the ulna fractures were fixed stably with the two bioactive plates at 2, 4, 8 and 12 weeks after surgery. At the 8-week time-point, 7 rabbits exhibited good healing at the osteotomy site on the experimental side. At 12 weeks after surgery, 8 rabbits exhibited good healing at the osteotomy site on both sides, but the experimental side showed enhanced compatibility between the plates and surrounding tissue, faster bone formation, a greater bone regeneration mass and better medullary canal structure compared with the control side. In conclusion, PPLLA-rhBMP-2 may be effectively used to treat fracture or nonunion at a non-weight-bearing site.

Biodegradable Materials in Arthroscopy

The use of biodegradable materials as implants has revolutionized the way medicine is practiced today. This review provides a general description of salient biodegradable polymeric materials currently used in arthroscopy. These materials include polyglycolic acid, self-reinforced polyglycolic acid, poly-L-lactic acid, self-reinforced polylactic-L-acid, poly-D-L-lactic acid, copolymer of poly-D-L-lactic acid polyglycolic acid, and polyglyconate. The mechanical strength, degradation properties, and widespread use of these materials, especially in the knee and shoulder, are discussed individually. Also discussed are the relatively few complications that are related to these materials' arthroscopic use. Future directions in biodegradable materials, including smart polymers, are also considered. In the future, novel techniques to identify the ideal polymer for a particular application will need to be developed to minimize the risk for implant complications.

Assessment of Carbon Fibre Composite Fracture Fixation Plate Using Finite Element Analysis

In the internal fixation of fractured bone by means of bone-plates fastened to the bone on its tensile surface, an on-going concern has been the excessive stress shielding of the bone by the excessively-stiff stainless-steel plate. The compressive stress shielding at the fracture-interface immediately after fracture-fixation delays callus formation and bone healing. Likewise, the tensile stress shielding in the layer of bone underneath the plate can cause osteoporosis and decrease in tensile strength of this layer. In this study a novel forearm internal fracture fixation plate made from short carbon fibre reinforced plastic (CFRP) was used in an attempt to address the problem. Accordingly, it has been possible to analyse the stress distribution in the composite plates using finite-element modelling. A three-dimensional, quarter-symmetric finite element model was generated for the plate system. The stress state in the underlying bone was examined for several loading conditions. Based on the analytical results the composite plate system is likely to reduce stress-shielding effects at the fracture site when subjected to bending and torsional loads. The design of the plate was further optimised by reducing the width around the innermost holes.

Histological study on sinus lift grafting by Fisiograft and Bio-Oss

The work aims to provide a histological investigation of Fisiograft, a PLA/PGA copolymer, used as filler for bone defects in humans. The study was performed on biopsies of sinus lifts where Bio-Oss and Fisiograft gel were applied as graft material. Bone regeneration was satisfactory in all sinus lifts, even when Fisiograft was applied alone. Due to remarkable osteoclast activity, Bio-Oss granules were cleared from the majority of biopsy cores. At histology, Fisiograft gel appeared as globes enveloped by fibroblasts, displaying an epithelial-like cell appearance. Due to its solubility in solvents, undegraded Fisiograft (recorded for 7 months or more) did not stain whereas degraded Fisiograft stained positive. The loose connective tissue, that surrounded Fisiograft and bone contained isolated mastocytes. Bone grew inside the loose connective and often reached the surface of Fisiograft by intervening cells. The results seem to indicate that Fisiograft may be considered both a polymer useful for fastening bone substitutes inside a defect and in addition a material capable of prompting bone regeneration, with or without the use of a bone substitute. In addition to space-former and space-maintainer functions, Fisiograft shows potential bone stimulation function, which may be labelled as osteopromotive capability.

Pre-clinical in vivo evaluation of orthopaedic bioabsorbable devices

The presence of bioabsorbable materials in orthopaedics has grown significantly over the past two decades with applications in fracture fixation, bone replacement, cartilage repair, meniscal repair, fixation of ligaments, and drug delivery. Numerous biocompatible, biodegradable polymers are now available for both experimental and clinical use. Not surprisingly, there have been a wealth of studies investigating the biomechanical properties, biocompatibility, degradation characteristics, osteoconductivity, potential toxicity, and histologic effects of various materials. Promising results have been reported in the areas of fracture fixation, ligament repair, and drug delivery. In this article we review the pre-clinical in vivo testing of bioabsorbable devices with particular emphasis on implants used for these applications.

Fixation of osteotomies using bioabsorbable screws in the canine femur

The purpose of this study was to compare the healing properties of femoral osteotomies fixed by bioabsorbable screws (20:80 polyglycolic copolylactic acid copolymer) to standard stainless steel screws of a similar design in a dog femoral model. Two osteotomies were used, the trephine osteotomy (10 mm diameter) in the metaphyseal lateral femoral condyle and in the femoral diaphysis, and a unilateral osteotomy in the lateral femoral condyle. Two months after the trephine osteotomies, the femurs that contained the polymer screws were not significantly different in mechanical strength from the femurs treated with the stainless steel screws, either in the diaphyseal or metaphyseal model. There was no histological difference in bone healing between the metallic and polymer screws for all periods (2, 9, and 17 months). There was no adverse inflammatory response to the polymeric or metallic screws. By month 17, the polymer screws were resorbed completely. All the diaphyseal screw tracks had healed with bone and areas of remodeling were evident in two specimens. For the femoral condyle osteotomy model at 2 months, the polymer screws were present and intact, and all osteotomies healed with no evidence of inflammation. By 9 months, only one specimen had polymeric material left in the screw track. At 15 months, the screw tracks still were present but no evidence of any polymer remained. The tracks were filled with fibrous and adipose connective tissue. All osteotomies stabilized with either bioabsorbable polymer screws or stainless steel screws did heal satisfactorily without any complications, inflammation, or osteolysis. The polyglycolic polylactic acid copolymer may have a clinical role as a bioabsorbable material without the concerns for the osteolysis, foreign body reaction, and sterile abscess formation that have occurred with bioabsorbable fixation methods in the past.

Comparison of the tissue response to absorbable self-reinforced polylactide screws and metallic screws in the fixation of cancellous bone osteotomies: an experimental study on the rabbit distal femur

The availability of absorbable fracture-fixation devices for clinical use calls for better knowledge of the reaction of bone tissue to absorbable polyester implants as compared with similar metallic devices. To examine and compare the tissue response to biodegradable and metallic screws within cancellous bone, a transverse transcondylar osteotomy of the distal femur was fixed with absorbable self-reinforced polylevolactide screws in 35 rabbits and with stainless-steel screws in 35 rabbits. New bone formation and consolidation of the osteotomy were examined histologically, histomorphometrically, and microradiographically within standardized sample fields 1, 3, 6, 12, 24, 36, and 48 weeks postoperatively. The intact contralateral femur served as the control. A vigorous osteoconductive response to the polylevolactide screws was observed at 3 weeks postoperatively, and the osteoid surface fraction was significantly higher in all follow-ups than in the contralateral femora. In the femora with metallic screws, new bone formation was seen 3, 6, and 12 weeks postoperatively, but at 24, 36, and 48 weeks the osteoid surface fraction did not differ significantly from that of the intact control femora. The total bone area was significantly larger in the femora with self-reinforced polylevolactide screws than in the control bone 6-48 weeks postoperatively; in the femora with metallic screws, this was found only at 6 and 12 weeks. After 48 weeks, the femora fixed with metallic screws had statistically smaller total bone area than the intact control femora. Solid bone union was seen in 84% of the osteotomies in the self-reinforced polylevolactide group and in 76% of those in the metallic group after 3 weeks or more. No signs of degradation of the self-reinforced polyleuolactide implant and only a mild foreign-body reaction with no accumulations of inflammatory cells to either self-reinforced polylevolactide or metallic screws were observed during the follow-up period. Both types of screws seemed to induce an osteostimulatory response around their threads. This phenomenon was transient for metallic screws but lasted for at least 48 weeks for self-reinforced polylevolactide screws. The polylevolactide screw does not seem to cause osteopenia at the implantation site. The fixation properties of both self-reinforced polylevolactide screws and metallic screws appear to be sufficient for the fixation of small fragments of cancellous bone.

Comparison of the fixation of subcapital femoral neck osteotomies with absorbable self-reinforced poly-L-lactide lag-screws or metallic screws in sheep

Seven subcapital femoral osteotomies of adult sheep were each fixed with two absorbable self-reinforced poly-L-lactide lag-screws, and seven other osteotomies were each fixed with two metallic cancellous bone screws. At 3 and 12 weeks, radiographs were taken and callus formation, displacement, and union were evaluated. At 12 weeks, the animals were killed and strength measurements were carried out. According to the radiographs, union was achieved in six of seven osteotomies in both groups, while after 3 weeks one fixation in both the group treated with absorbable screws and the group treated with metallic screws had failed. There were no statistical differences between the groups with respect to callus formation or displacement. Regarding the strength of the osteotomized bones, at 12 weeks there were no statistically significant differences in the load-carrying capacity between the bones fixed with self-reinforced poly-L-lactide screws and those fixed with metallic screws. These results showed that self-reinforced poly-L-lactide screws, which have been used successfully in fractures and osteotomies in cancellous bone, are strong enough to support this more demanding fixation of weight-bearing bones.

Comparison of bioabsorbable pins and Kirschner wires in the fixation of chevron osteotomies for hallux valgus

A retrospective review of the medical records and radiographs of 32 consecutive patients, totaling 52 extremities with chevron osteotomies for hallux valgus, was conducted to compare K wire fixation with absorbable (poly-p-dioxanone) pin fixation. Each group comprised 21 feet, with a mean clinical follow-up of 35.6 months (25.6-50.5 months) in the K wire group and 23.1 months (13.7-28.8 months) in the absorbable pin group. Demographics as well as final clinical follow-up scores (hallux-metatarsophalangeal-interphalangeal scale and visual analogue scores) were similar in both groups. Postoperative hallux valgus and intermetatarsal angles were similar in both groups. No complications, such as osteolysis for inflammatory sinus formation, occurred in the absorbable pin group. Two patients in the K wire group had a malunited osteotomy and two patients had a retained K wire at final follow-up. Our experience suggests that poly-p-dioxanone pins are at least as effective as K wires, and the previous reports of inflammatory sinus formation and osteolysis are not a significant concern in the fixation of chevron osteotomies for hallux valgus.

Finite element stress analysis of a hybrid fracture fixation plate

Metal plates are commonly used in the operative treatment of bone fractures. Rigid metal plates stabilize the fracture site, maintain good contact between bone fragments and allow early weight bearing and patient mobility. However, treatment with rigid metal plates can cause localized bone atrophy due to stress-shielding and interference with blood circulation, and the weakened bone can refracture after plate removal. A hybrid bone plate system that combines the torsional and bending rigidity of a metal plate with the axial compliance of a polymer insert has been designed. A three-dimensional, quarter-symmetric finite element model was generated for a canine femur diaphysis plated with this metal/polymer hybrid design. A model with a standard metal fixation plate was also generated for comparison purposes. The stress state in the underlying bone was examined for several loading conditions taken from published in vivo studies. The finite element model was used to study the performance of biodegradable polymer inserts in the plate system. The flexible plate reduced stress-shielding effects at the fracture site when subjected to an axial load. The bending strength of the plate was not compromised by the addition of the polymer inserts. Biodegradable inserts further enhanced the performance of the new plate design, transferring less of the axial load to the plate as the inserts broke down.

Biocompatibility study of as-polymerized poly(L-lactide) in rats using a cage implant system

To evaluate the biocompatibility of in vitro predegraded as polymerized poly(L-lactide) (PLLA), a cage implant system was used to investigate white cell and enzyme concentrations with time. The use of a cage permits in a serial fashion a quantitative and qualitative measurement of exudate components formed around an implant. Subcutaneously in rats, caped cages manufactured from stainless-steel mesh were implanted with in vitro predegraded, as-polymerized PLLA, as-polymerized PLLA cylinders, and empty cages serving as controls. In vitro predegradation was used to simulate the degradation products of long-term in vitro degradation. Predegraded PLLA particles were obtained by in vitro hydrolysis at elevated temperatures. The first 7 days of implantation were characterized by an acute inflammatory reaction; the exudate extracted from the cages showed predominantly neutrophils for all types of implants. After day 7, there was a more chronic inflammatory reaction with predominantly macrophages and lymphocytes. There were no significant differences in the total leukocyte concentration or macrophage concentration for any of the cages in the period from 10-21 days. Extracellular enzyme activity also did not show any significant differences among the three types of cages. A possible explanation for the absence of any significant differences could be that the in vitro predegraded particles were sieved before implantation, thus eliminating all small particles (< 70 microns) that are probably mandatory to provoke an increased cellular reaction.