Bioabsorbable osteosynthetic implants of ultra high strength poly-L-lactide. A clinical study

Use of biomaterials in scaphoid fracture fixation, a systematic review

BACKGROUND

Scaphoid fractures account for 60-70% carpal injury. Due to limited vascular supply achieving adequate reduction and healing is important to avoid complications including avascular necrosis. Recent technological advances have led to renewed vigour in bioabsorbable material research to develop devices which could be used without the need for removal and complications including stress shielding and suboptimal imaging.

METHODS

A systematic search of databases including PubMed, Ovid Medline, and Google Scholar databases was made to identify studies related to the use of bioabsorbable materials in scaphoid fixation and postoperative patient outcomes. PRISMA guidelines were utilised for this review.

FINDINGS

Initial search results yielded 852 studies. 124 studies were screened, with 79 patients across 7 studies included in this review. Poly-L-Lactic acid derivatives were the most common biomaterial for scaphoid fixation, with magnesium and polyglycolide also used. Levels of evidence for studies ranged between III-IV. Analysis demonstrated mixed findings with generally comparable outcomes to conventional alloy-based screws.

INTERPRETATION

Development in bioabsorbable materials is ongoing, however there remains a dearth in data regarding their use in the scaphoid. Further research is needed to establish the efficacy and applicability of bioabsorbable devices in the scaphoid bone.

Bone Regeneration Capacity of Newly Developed Uncalcined/Unsintered Hydroxyapatite and Poly-l-lactide-co-glycolide Sheet in Maxillofacial Surgery: An In Vivo Study

Uncalcined/unsintered hydroxyapatite and poly-l-lactide-co-glycolide (u-HA/PLLA/PGA) is a new bioresorbable nanomaterial with superior characteristics compared with current bioresorbable materials, including appropriate mechanical properties, outstanding bioactive/osteoconductive features, and remarkably shorter resorption time. Nevertheless, the bone regeneration characteristics of this nanomaterial have not been evaluated in maxillofacial reconstructive surgery. In this study, we used a rat mandible model to assess the bone regeneration ability of u-HA/PLLA/PGA material, compared with uncalcined/unsintered hydroxyapatite and poly-l-lactide acid (u-HA/PLLA) material, which has demonstrated excellent bone regenerative ability. A 4-mm-diameter defect was created at the mandibular angle area in 28 Sprague Dawley male rats. The rats were divided into three groups: u-HA/PLLA/PGA (u-HA/PLLA/PGA graft + defect), u-HA/PLLA (u-HA/PLLA graft + defect), and sham control (defect alone). At 1, 3, 8, and 16 weeks after surgeries, the rats were sacrificed and assessed by micro-computed tomography, histological analysis with hematoxylin and eosin staining, and immunohistochemical analyses. The results confirmed that the accelerated bone bioactive/regenerative osteoconduction of u-HA/PLLA/PGA was comparable with that of u-HA/PLLA in the rat mandible model. Furthermore, this new regenerative nanomaterial was able to more rapidly induce bone formation in the early stage and had great potential for further clinical applications in maxillofacial reconstructive surgery.

Mathematical modeling of oxygen release from hyperbarically loaded polymers

Polymer-based scaffolds are used extensively in the field of regenerative medicine. These biomaterials may induce therapeutic responses through modulating a wound microenvironment with or without the addition of cells. It has long been known that oxygen is a crucial component of the microenvironment that influences cellular and physiological processes such as metabolism, proliferation, differentiation, matrix deposition, phagocytic killing, and wound healing. Consequently, several studies have investigated the potential for using oxygen-eluting biomaterials to regulate the oxygen tension within a wound microenvironment and to tune the regenerative response. We recently demonstrated that hyperbarically loaded polymers could be used as oxygen delivery devices for biomedical uses. To further develop this strategy, it is important to quantitatively characterize the spatiotemporal oxygen diffusion profile from scaffolds. Here, we use analytical and numerical solutions to describe the profiles of oxygen diffusion from hyperbarically loaded polymers as a function of different scaffold geometries, material compositions, and ambient temperatures. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 2018 © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2751, 2019.

Bioresorption and degradation of biomaterials

The human body is a composite structure, completely constructed of biodegradable materials. This allows the cells of the body to remove and replace old or defective tissue with new material. Consequently, artificial resorbable biomaterials have been developed for application in regenerative medicine. We discuss here advantages and disadvantages of these bioresorbable materials for medical applications and give an overview of typically used metals, ceramics and polymers. Methods for the quantification of bioresorption in vitro and in vivo are described. The next challenge will be to better understand the interface between cell and material and to use this knowledge for the design of “intelligent” materials that can instruct the cells to build specific tissue geometries and degrade in the process.

Tissue restoration after implantation of polyglycolide, polydioxanone, polylevolactide, and metallic pins in cortical bone: an experimental study in rabbits

We performed qualitative and histoquantitative investigations of tissue restoration after implanting polyglycolide (PGA), polydioxanone (PDS), polylevolactide (PLLA), and stainless steel pins in the intramedullary canal of rabbit femurs. The effect of bioabsorbable devices on healing of a cortical bone defect was also assessed. The cortical bone defect was created in the right femur of 80 rabbits. Bioabsorbable and metallic pins in 60 and two metallic pins alone were implanted in 20 intramedullary canals; 80 left femurs served as intact controls. Follow-up times were 3, 6, 12, 24, and 52 weeks. At all time points, collagenous connective tissue, including bone trabeculae, surrounded the implant at the tissue-implant interface, replacing hematopoiesis and fat of the intramedullary canal. The groups did not differ in the area and trabecular bone area fraction of the resulting callus. Residual fragments of PGA and PDS were observed at 24 weeks, and complete degradation occurred within 52 weeks. PGA, PDS, PLLA, and metallic implants induced a bony and fibrous walling-off response in the intramedullary cavity. No inflammation was observed. Complete tissue restoration did not occur within the follow-up, even after complete degradation of PGA and PDS, which had shorter degradation times than PLLA. The cortical bone healing effect was not different between bioabsorbable pins and metallic wires. Thus, these polymers had no specific osteostimulatory or osteoinhibitory properties compared to stainless steel. Within the follow-up period, there were no significant differences in biocompatibility between the implants and no adverse inflammatory foreign-body reactions.

Long-term results of cemented total hip arthroplasty for dysplasia, with structural autograft fixed with poly-L-lactic acid screws

This study reviewed a series of cemented total hip arthroplasty (THA) for dysplasia, with structural autograft fixed with poly-L-lactic acid screws. Grafted bone union was confirmed radiologically in every case, and there were no cases of early collapse or extravasation of grafted bone. Kaplan-Meier survivorship analysis of socket revision, radiologic loosening of the socket, and the appearance of a radiolucent line greater than 1 mm in the graft-socket interface as the end points indicated survival rates of 99%, 97.1%, and 63.5% at 10 years and 96.6%, 90.2%, and 56.1% at 15 years, respectively. The results of this study indicated that poly-L-lactic acid screws are safe and useful for the fixation of acetabular bone graft concomitant to cemented THA with a careful rehabilitation program.

Tissue response to polyglycolide, polydioxanone, polylevolactide, and metallic pins in cancellous bone: An experimental study on rabbits

The purpose of this study was to investigate, qualitatively and histoquantitatively, the tissue response of rabbit femur cancellous bone to polyglycolide (PGA), polydioxanone (PDS), polylevolactide (PLLA), and stainless steel pins under identical conditions. Eighty knees in 50 rabbits were operated on by inserting bioabsorbable pins (PGA, PDS, or PLLA) together with metallic Kirschner wire in 60, and two metallic Kirschner wires alone in 20 knees, while 20 knees served as intact controls. Follow-up times were 3, 6, 12, 24, and 52 weeks. Cancellous bone tissue response to implants was studied using histological, histomorphometrical, microradiographical, and oxytetracycline fluorescence methods. Residual fragments of PGA and PDS were seen at 24 weeks. Complete degradation of these polymers had taken place before 52 weeks. No signs of degradation of the PLLA pins were observed within the entire follow-up period. The osteoid formation surfaces at tissue implant-interface were statistically larger in all test groups as compared to intact controls. The number of macrophages at tissue implant-interfaces increased in all bioabsorbable implant specimens until 6 weeks, and with PGA until 12 weeks. No differences in the osseous response emerged when comparing groups of bioabsorbable implants with each other or with stainless steel group. Bioabsorbable pins and metallic Kirschner wires evoked an osteoconductive response in the cancellous bone surrounding implant, but the response intensity between implants displayed no differences. This suggests a simple, nonspecific walling-off new-bone front type of response. Consequently, the polymers possessed no specific osteostimulatory or osteoinhibitory properties. Within the follow-up, no significant differences in biocompatibility between the implants appeared, and no frank inflammatory foreign-body reactions occurred. The small-volume pins obviously did not exceed the local tissue tolerance and clearing capacity of the bone.

Fixation with poly-L-lactide screws in hip osteotomies

The purpose of our study was to investigate the bone union rates and complication rates, including breakage of screws, infection, and osteolysis, in hip osteotomies using poly-L-lactic screws. We prospectively followed up 111 hips in 100 patients using conventional radiography, in which 81 rotational acetabular osteotomies, 26 Chiari pelvic osteotomies, and four Sugioka's transtrochanteric osteotomies were performed. The mean age of the patients at the time of surgery was 34 years, and the mean followup was 5.4 years. Eighty-one osteotomized acetabula and 98 osteotomized greater trochanters were fixed using poly-L-lactic screws. These hips were compared with 64 hips in 58 patients using metallic screws. Bone union was achieved in 80 of the 81 acetabular osteotomies, except in one hip with postoperative deep infection. Proximal displacement of the greater trochanter because of poly-L-lactic screw breakage occurred in six (6%) hips. None of the metallic screws broke. Osteolysis occurred in one hip with a trochanteric osteotomy using poly-L-lactic screws. Poly-L-lactic screws are suitable to transfix the osteotomized acetabulum, but there is some risk of fracture when used to reattach an osteotomized greater trochanter. Complete bone ingrowth in the screw channels cannot be expected for several years after insertion. Osteolysis is a possible complication.

LEVEL OF EVIDENCE

Therapeutic study, Level II (prospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Ectopic bone formation around the poly-L-lactide screw head in rotational acetabular osteotomy for hip dysplasia

Ectopic bone formation around the poly-L-lactide (PLLA) screw head in eccentric rotational acetabular osteotomy for hip dysplasia was investigated. A total of 174 hips in 165 patients with hip dysplasia were consecutively treated with eccentric rotational acetabular osteotomy. Average age at the time of operation was 37 years. Acetabular fragments of 123 patients (132 hips) were fixed by Kirschner wires (K-wire group), and 42 hips in 42 patients were fixed with PLLA screws (PLLA group). There was no statistically significant difference between the backgrounds of the two groups. All patients were evaluated clinically and radiologically. In the K-wire group, ectopic bone formation of class 2 was observed in only 1 hip. In the PLLA group, ectopic bone formation of class 3 in 1 hip and class 2 in 3 hips was observed around the screw head 3 months postoperatively, and all hips but 1 showed class 2 at final follow-up. One hip with class 3 at 1 year developed marked reduction of range of motion, and this patient complained of moderate hip pain and stiffness. PLLA screws significantly enhanced ectopic bone formation around the screw head in eccentric rotational acetabular osteotomy.

Tissue restoration after resorption of polyglycolide and poly-laevo-lactic acid screws

Despite worldwide clinical use of bio-absorbable devices for internal fixation in orthopaedic surgery, the degradation behaviour and tissue replacement of these implants are not fully understood. In a long-term experimental study, we have determined the patterns of tissue restoration 36 and 54 months after implantation of polyglycolic acid and poly-laevo-lactic acid screws in the distal femur of the rabbit. After 36 months in the polyglycolic acid group the specimens showed no remaining polymer and loose connective tissue occupied 80% of the screw track. Tissue restoration remained poor at 54 months, the amounts of trabecular bone and haematopoietic elements being significantly lower than those in the intact control group. The amount of trabecular bone within the screw track at 54 months in the polyglycolic acid group was less than in the empty drill holes (p = 0.04). In the poly-laevo-lactic acid group, polymeric material was present in abundance after 54 months, occupying 60% of the cross-section of the core area of the screw track. When using absorbable internal fixation implants we should recognise that the degradation of the devices will probably not be accompanied by the restoration of normal trabecular bone.

Use of bioabsorbable osteofixation devices in the hand

Bioabsorbable internal fixation by means of pins, tacks, screws and miniplates offers an alternative to metallic osteofixation for the stabilization of small bone fractures, osteotomies, ligament injuries and fusions in the hand. The advantages of using them include avoidance of metallic-implant-related long-term complications and a secondary removal operation. Currently the most commonly used devices are made of poly L-lactide (PLLA) and copolymers of polylactides (P(L/DL)LA) and polyglycolide (PLGA). In areas of mechanical stress, the use of ultra-high-strength self-reinforced devices is recommended. Biomechanical studies on fresh frozen bones have shown that the fixation rigidity achieved with self-reinforced devices approaches that of metallic osteofixation methods. The reliability of modern implants has been confirmed in several experimental and clinical studies.

Tissue response to poly-L-lactide acid-polyglycolic acid absorbable screws in autogenous bone grafts: a histologic morphological analysis

OBJECTIVES

To evaluate the local bone condition of autogenous chin grafts in contact with resorbable polymers fixation devices.

MATERIAL AND METHODS

Seven patients presenting severe maxillary and mandibular atrophy underwent alveolar ridge reconstruction with autogenous chin grafts fixed with conventional metallic screws, who received poly L-lactide acid-polyglycolic acid and titanium test screws for histological evaluation after 4 months of implantation.

RESULTS

Viable bone tissue could be seen in the specimens related to titanium test screws, with no signs of bone resorption or inflammation. A thick layer of fibrous connective tissue was observed between the resorbable test screws and bone tissue, which presented a few areas of resorption.

CONCLUSION

There are no contraindications of both materials for use as fixation devices in autogenous bone grafts. However, care must be taken when using absorbable screws in a period of 4 months, which can interfere with the sequence of the treatment with endosseous dental implants.

Mechanical evaluation of novel spinal interbody fusion cages made of bioactive, resorbable composites

Osteoconductive and totally bioresorbable spinal/cervical interbody fusion cages were fabricated from a forged composite of raw particulate hydroxyapatite/poly L-lactide (u-HA/PLLA) with an u-HA 40wt% fraction (F-u-HA 40). The mechanical strengths of three types of cages, designed for open-box, screw and cylinder constructs, were compared with those of existing metal and carbon-fiber/polymer cages. Compressive strengths of these composite cages surpassed those of existing metal and carbon-fiber cages. Fatigue resistance to alternate and static compressive loading persisted for longer than the minimum period (6 months) necessary for spinal devices in simulated body fluid (SBF) at 37 degrees C. These novel interbody fusion cages await clinical application in humans.

Composite poly(lactide)/hydroxylapatite screws for fixation of osteochondral osteotomies. A morphometric, histologic and radiographic study in sheep

The aim of this study was to evaluate the healing of an osteochondral fragment created in the distal sheep femur in response to fixation with a biodegradable polylactide/hydroxylapatite composite screw. Poly(L-lactide) screws were used for comparison. At follow-up times of 4 and 8 weeks, the specimens were examined with standard radiography and computed tomography, as well as with macro- and micro-histomorphometry. The intact contralateral femur served as a control. Only minimal signs of degradation of the polymer could be seen in the histologic specimens. At 8 weeks, nearly all osteotomies had healed completely and an association between implant type and delayed osteotomy healing was found. The width of the repair tissue at the tissue-implant interface was 250 +/- 48 microm, representing a clear transition zone of newly formed trabecular bone separating the implant from the surrounding plexiform bone. This study showed that large polylactide implants which are buffered with hydroxylapatite show benign tissue responses and good implant osteointegration. The osteotomy healing in a weight-bearing osteochondral fragment model in sheep utilizing a composite polylactide/hydroxylapatite screw was equivalent to a similar polylactide screw implant, indicating that hydroxylapatite-buffered screw implants could be used for similar indications in current clinical use.

The long-term behavior of poly-L-lactide screws in a minipig fracture model: preliminary report

The long-term degradation tissue response to poly-L-lactide (PLLA) screw was investigated for a minipig tibia fracture. As a bone-fracture model, three PLLA screws per animal were used to fix a tibia that had been subjected to a crank-shaped osteotomy. A total of 12 nine-month-old male minipigs were used. In time period from 1 month to 3 years, clinical, radiographic, and pathological studies were conducted. On macroscopic examination, no clear granuloma or fistula formation was noted for 3 years. On microscopic examination, no osteoclasts or giant cells were detected around the screws during the 3 years postoperatively. A substantial degradation of PLLA screw was observed between 2 and 3 years. At 3 years only slight residual breakdown products were found in macrophages. On electric microscopic examination, numerous degraded polymers were seen in a small number of macrophages around the screws. In this model, fixation of tibia fractures using PLLA screws was not associated with any side effects, and was safe and useful for up to 3 years.

Polyhydroxyalkanonate derivatives in current clinical applications and trials

Polyhydroxyalkanonate is a typical biodegradable material, which is permitted for use in the medical and pharmaceutical fields. For its biodegradability, biocompatibility, and toxicological safety, the majority of products practically used are composed of homo-polymers of poly(lactic acid), poly(glycolic acid), and poly(epsilon-caprolactone) and their co-polymers. On the market, suture strings are still the main usage. The needs of biodegradable materials have been being gradually increased by the development of drug delivery systems, tissue engineering, and regenerative medicine. Some types of formulation, that is, mono-fibers, twisted fibers, films, fabrics, sponges, and injectable particles are developed to match each purpose. This article reviews the current clinical applications and trials of polyhydroxyalcanonate products.

Osteosynthesis in digital replantation using bioabsorbable rods

There are several fixation techniques for osteosynthesis in digital replantation. Kirschner wire fixation is used commonly but the wires protrude and disturb mobilization. Moreover, it requires removal. Since February 1995, the authors have been using a bioabsorbable rod made of poly-L-lactide as an intramedullary nail for osteosynthesis in digital replantation. The advantages of this technique include the absence of protruding hardware that would require removal and technical simplicity. This method has been applied for 15 arthrodeses (12 distal interphalangeal joints, 1 proximal interphalangeal joint, and 2 interphalangeal joints of the thumb) and for 11 diaphysis fractures (5 proximal, 5 middle, and 1 distal phalanx). All patients were observed until there was clinical and radiographic evidence of fusion (average interval to fusion, 8.4 wk). Bone resorption occurred in one patient. There were no cases of nonunion or infection. Poly-L-lactide rod fixation is a simple and effective technique.

The application of bioimplants in the management of chronic osteomyelitis

The management of musculoskeletal infections is an increasing challenge to clinicians. Bioimplants provide a unique system for skeletal specific drug delivery. Antibiotic-impregnated beads and spacers can be used to treat chronic osteomyelitis and deep soft-tissue infections locally with higher antibiotic concentrations, while avoiding potential systemic side effects.

Influence of bioresorbable, unsintered hydroxyapatite/poly-L-lactide composite films on spinal cord, nerve roots, and epidural space

The effect of forged unsintered hydroxyapatite/poly-L-lactide (u-HA/PLLA) composite films on spinal cord and nerve roots and its degradation behavior and osteoconductivity in epidural space were compared with those of calcined HA (c-HA)/PLLA and unfilled PLLA films. Partial laminectomy was performed on 20 rabbits, and u-HA/PLLA and PLLA films were implanted in the intervertebral space. Total laminectomy was performed on 30 rabbits to implant u-HA/PLLA, c-HA/PLLA, and PLLA films in both epidural and subcutaneous spaces. For up to 50 weeks, there were no histological changes in the spinal cord or nerve root, and no inflammatory cell infiltration into the epidural space around the films. The rate of decrease in viscosity average molecular weight of both composite films was initially higher than that of PLLA but eventually became lower, although there was no difference in the degradation behavior of the three films in either the epidural or subcutaneous spaces after 50 weeks. Scanning electron microscopic and energy-dispersive X-ray analysis indicated calcium phosphate deposits on the surface of composite films with new bone formation from 4 weeks. The u-HA/PLLA composite film therefore has good biocompatibility, osteoconductivity, and fast primary degradation rate, which may prove compatible with application to spinal surgery.

Effect of filler content on mechanical and dynamic mechanical properties of particulate biphasic calcium phosphate--polylactide composites

A bioabsorbable self-reinforced polylactide/biphasic calcium phosphate (BCP) composite is being developed for fracture fixation plates. One manufacturing route is to produce preimpregnated sheets by pulling polylactide (PLA) fibres through a suspension of BCP filler in a PLA solution and compression moulding the prepreg to the desired shape. To aid understanding of the process, interactions between the matrix and filler were investigated. Composite films containing 0-0.25 volume fraction filler, produced by solvent casting, were analysed using SEM, tensile testing and dynamic mechanical analysis (DMA). Homogeneous films could be made, although some particle agglomeration was seen at higher filler volume fractions. As the filler content increased, the failure strain decreased due to a reduction in the amount of ductile polymer present and the ultimate tensile strength (UTS) decreased because of agglomeration and void formation at higher filler content. The matrix glass transition temperature increased due to polymer chain adsorption and immobilization onto the BCP particles. Complex damping mechanisms, such as particle-particle agglomeration, may exist at the higher BCP volume fractions.

Bioabsorbable rods in Salter's osteotomy

Salter's innominate osteotomy is a commonly used procedure in the treatment of developmental dysplasia of the hip. The graft is usually fixed with two K-wires that are removed surgically 6 weeks later. The use of bioabsorbable rods to fix the graft saves patients further surgery for removal of wires and ensures a better scar. This paper reports for the first time the successful use of bioabsorbable self-reinforced polyglycolic acid rods for fixing the graft of Salter's innominate osteotomy in the treatment of developmental dysplasia of the hip, and describes the suggested operative technique for their use.

Bioresorbable devices made of forged composites of hydroxyapatite (HA) particles and poly L-lactide (PLLA). Part II: practical properties of miniscrews and miniplates

Miniscrews and miniplates made of forged composites composed of raw hydroxyapatite (u-HA) particles (particle size 0.2-20 microm, averaging 3.0 microm, Ca/p = 1.69 and containing CO3(2-)) and a poly L-lactide (PLLA, Mv: about 180 kDa, containing residual 0.05 wt% lactide) with osteological bioactivity such as direct bonding to bone and osteoconductivity, total resorbability and radiopacity were examined for various mechanical properties in order to evaluate their usefulness for cranio-, oral and maxillo-facial as well as plastic and reconstructive surgeries with PLLA-only or titanium devices. The composites containing u-HA particles at 30wt% for miniscrews and 40wt% for miniplates were selected based on total mechanical strengths and bioactivity, respectively. It was found that the composite devices generally had slightly different mechanical properties than forged PLLA-only devices of which strengths are ranked the highest among the reinforced PLLA-only ones that having been used in many clinical cases to date, in spite of their approximate 2 or 3 times lower absolute strengths than those of titanium ones. However, a remarkable distinction that makes the composite miniplates stand above the titanium ones was confirmed on their fatigue resistance to alternate bendings such that they retained 70% of their initial strength even after 60 times without revealing any damage, whereas the metallic devices fully broke off at only 8 times. This behavior was similar to that of forged PLLA-only devices but is unique as composites made of organic polymers divided by inorganic particles. In addition, profile plates such as L-, T-, X, T, C-, Mesh-, Box-, and Barhole types which were processed by forging twice exhibited nearly directional isotropy in strength and could be deformed in situ at ordinary temperatures to adjust their shapes along the surface undulations of the skull, mandible, maxilla, zygomatic bone and the like without thermoforming and did not return to their original shapes inside an alive body due to the high PLLA's Tg (65 degrees C) over an alive body temperature (37 degrees C). Since it had already been confirmed in previous papers that these stiff and tough composites have the osteological bioactivity which is missing from both PLLA-only and titanium ones, and radiopacity which is wanting in PLLA-only ones, these various small and thin screws and plates have conclusively less objectionable practicality for use in oral-maxillo and craniofacial as well as plastic and reconstructive surgeries.

Enhancement of chondrogenic differentiation of human articular chondrocytes by biodegradable polymers

Biodegradable polymers are attractive candidates for chondrocyte embedding and transplantation in cartilage tissue engineering. In an attempt to determine the effects of a variety of biodegradable materials on cartilage proliferation and extracellular matrix production, poly-L-lactic acid (PLLA) with a molecular weight of 5,000, polyglycolic acid (PGA) with a molecular weight of 3,000, and copolymer of poly(L-lactic acid-glycolic acid) 50:50 (PLGA) with a molecular weight of 5,000, were dissolved in DMSO and added into the medium for 4 weeks in in vitro high-density micromass culture of multiplied human articular chondrocytes (HAC). PLLA with a molecular weight of 270,000 (PLAO3) was used as thin film. Cell proliferation and differentiation in these biomaterials were compared with tissue culture polystyrene (TCPS) as a control. Alamar blue and alcian blue staining were carried out to determine the chondrocyte proliferation and differentiation, respectively. Samples exposed to these biomaterials promoted cell proliferation in the range of 86-105% of the control proliferation, and a slight but significant increase in cell proliferation was noted only in the culture exposed to PLGA. The sample exposed to PGA elicited a significant 3.7-fold higher (p < 0.01) cell differentiation than controls and was significantly higher than that of the samples exposed to PLLA, PLAO3, and PLGA. After 4 weeks of culture, the cell differentiation from most to least was in the following order PGA > PLAO3 > PLGA = PLLA > Cont. = DMSO. Chondrocyte differentiation of the samples exposed to various biomaterials were significantly higher compared with controls. Thus, serially passage chondrocytes are competent for cell growth and quantifiable matrix production, and biodegradable polymers, especially PGA, hold promise as suitable substrates for scaffolding materials for human cartilage tissue engineering.

Response of articular cartilage and subchondral bone to internal fixation devices made of poly-L-lactide: a histomorphometric and microradiographic study on rabbits

To study the tissue response of articular cartilage and subchondral bone to biodegradable fixation devices, pins and rods made of poly-L-lactide with a fibers-in-matrix texture were implanted through the articular surface of the intercondylar portion of the distal rabbit femur. The initial raw material viscosity average molecular weight of the polymer was 660,000. One pin or screw was implanted per animal. The pins were cylindrical and measured 4.5 mm in transverse diameter. The screws had a core diameter of 3.2 mm and an outer diameter of 4.5 mm. At insertion, the implants were cut flush with the articular surface. After follow-up times of 36 and 48 weeks, the specimens were examined histomorphometrically and microradiographically. The intact contralateral femur served as a control for comparison. No signs of erosion or degradation of the polymer could be seen in the specimens. A brim of reparative tissue was formed at the entrance of the implant channel. The width of the reparative tissue from the tissue-implant boundary towards the center of the entrance hole varied greatly between the specimens, from 30 to 950 microm. In most specimens this bridging tissue consisted of undifferentiated mesenchymal tissue. Only two out of 24 specimens showed a near-normal metachromatic toluidine-blue staining of the matrix. Degenerative chondrocyte clustering occurred in the pre-existing cartilage within a 400 microm wide zone from the tissue-implant interface into the recipient tissues. Some new-bone formation was seen to envelop the implant in all specimens, but the fractional osteoid formation surface of the trabeculae showed a value significantly higher than that of the intact control side only in the screw-implanted 36-week specimens. Because of the long degradation time of poly-L-lactide, the restoration process of the articular cartilage was slow, and with regard to the quality and quantity of the reparative tissue, very variable. Large implants made of poly-L-lactide may not be suitable for insertion through intra-articular surfaces.

Clinical biocompatibility of biodegradable orthopaedic implants for internal fixation: a review

When the polymeric material reaches the final stages of its degradation process, biodegradable orthopaedic fixation devices elicit a local foreign-body reaction. In most cases, the symptoms of this tissue response are subclinical and pass unnoticed, but in some patients a clinically manifest inflammatory foreign-body reaction ensues. Mild clinical reactions consist of a painful erythematous papule, those of medium severity show a sinus discharging polymeric debris for up to 6 months, and in the patients affected by a severe reaction, extensive osteolytic lesions may develop at the implant tracks. The histopathologic picture is that of a non-specific foreign-body reaction. For implants made of polyglycolide, the average incidence of the manifest reactions is 5%. When slow-degrading polymers are used, the incidence is lower. The tissue responses to polyglycolide manifest themselves 11 weeks after surgery, on an average, whereas foreign-body reactions to devices made of poly-L-lactide can emerge as late as 4 or 5 yr after the original fracture fixation operation. A poorly vascularized bone section, use of a quinone dye as an additive in the polymer, and an implant geometry with large surface area each seems to be associated with an increased risk of the occurrence of a foreign-body reaction. Yet in majority of the patients affected, no known individual marker of high risk is present. Some recent laboratory experiments indicate that it may be possible to diminish the risk of an adverse tissue response by incorporating alkaline salts or antibodies to inflammatory mediators in the implants. The results of in vitro and animal experiments, however, cannot always be directly extrapolated to humans. Only large-scale long-term clinical research will ultimately show which physico-chemical characteristics of a biodegradable orthopaedic implant provide the optimal clinical biocompatibility.

Bone bonding ability of a new biodegradable composite for internal fixation of bone fractures

Hydroxyapatite particles and poly(L-lactide) composites for internal fixation of bone fractures have been developed based on the hypothesis that incorporation of hydroxyapatite particles in a poly(L-lactide) matrix might enhance bone bonding. This study evaluated the bone bonding ability of these biodegradable composites. Two types of hydroxyapatite and poly(L-lactide) composite were used in this study: calcined hydroxyapatite/poly(L-lactide) and uncalcined hydroxyapatite/poly(L-lactide). Rectangular plates (2 x 10 x 15 mm) of each composite or poly(L-lactide) were implanted into the metaphysis of the tibiae of 33 male rabbits, and the failure load was measured by conducting a detaching test 8, 16, and 25 weeks after implantation. The failure loads of calcined hydroxyapatite/poly(L-lactide), uncalcined hydroxyapatite/poly(L-lactide), and poly(L-lactide), respectively, were 13.60, 13.95, and 0.46 N at 8 weeks; 29.84, 24.09, and 2.86 N at 16 weeks; and 25.50, 29.67, and 2.43 N at 25 weeks. Histologic observation revealed that the composites formed direct contact with the bone. The results in this study indicate that the composites improved the strength of the interface between bone and plate. This improved interfacial strength lead to a substantial decrease in the frequency of implant loosening in the treatment of fractured bones by internal fixation.

Biodegradation behavior of ultra-high-strength hydroxyapatite/poly (L-lactide) composite rods for internal fixation of bone fractures

The purpose of this study was to investigate the biodegradation behavior of the ultra-high-strength hydroxyapatite/poly(L-lactide) (HA/PLLA) composite rods for fracture repair. Two kinds of composite materials were used in this study: u-HA/PLLA. which contained 30% by weight of uncalcined HA as reinforcing particles, and c-HA/PLLA, which contained 30% by weight of calcined HA as reinforcing particles. These composite rods were implanted in the subcutis and in the medullary cavities of rabbits. The specimens were removed at specific intervals between 2 and 52 weeks and the mechanical strength was measured for the rods in the subcutis, and the molecular weight and crystallinity were measured for the rods in both the subcutis and medullary cavities. The rod surfaces were examined using a scanning electron microscope (SEM). The specimens were examined histologically by light microscopy. The bending strength of the composites implanted in the subcutis was maintained at more than 200 M Pa at 25 weeks and at 150 MPa at 52 weeks. The molecular weight dropped to 45% of the initial values at 8 weeks and to approximately 10% at 52 weeks. Significant differences in the molecular weight were seen between c-HA/PLLA and u-HA/PLLA, with u-HA/PLLA showing a faster rate of decrease than c-HA/PLLA after 8 weeks. SEM demonstrated that HA particles disappeared increasingly from the rod surfaces over time and that the spaces left by these HA particles formed many pores in the composite surfaces at 52 weeks. Histologically, a fibrous tissue layer was formed around the composite rod from 4 weeks in the subcutis and in the diaphyseal area of the medullary canal. This became more mature over time. Bony tissue contact to the composites without fibrous tissue layers was seen in the metaphyseal area of the medullary canal. During the experimental period, there were no inflammatory cells such as mono- or multi-nuclear phagocytes. Although further long-term studies for degradation are needed, the composites have promising mechanical strength and no adverse tissue reaction for use as fracture-fixation devices during the experimental periods.

Bonding behavior of ultrahigh strength unsintered hydroxyapatite particles/poly(L-lactide) composites to surface of tibial cortex in rabbits

Unsintered hydroxyapatite particles/poly(L-lactide) (u-HA/PLLA) composites with an initial bending strength of up to 270 MPa were developed based on the hypothesis that inclusion of u-HA particles in a PLLA matrix might enhance bone bonding. The purpose of this study was to examine the bonding strength and behavior of these u-HA/PLLA composites on the surface of the bone cortex. Composites containing 30 (u-HA30), 40 (u-HA40), or 50 wt % (u-HA50) of fine u-HA particles (3-microm average particle size) were prepared. Semicolumnar plates of these composites and control PLLA plates were fixed with metal screws to the surface of both proximal tibial cortices in 45 rabbits. The loads required to detach the plates from the bone cortex surface, defined as the bonding strengths, were measured at 4, 8, and 25 weeks after implantation. Bonding strengths in the u-HA30 group at 8 weeks and in the u-HA40 and u-HA50 groups at each postimplantation time were significantly greater than in the PLLA group (post hoc test using Fisher's protected least significant difference method). At each postimplantation time histological examinations revealed direct contact between the bone and the u-HA/PLLA composite plates without any intervening fibrous tissue. There was no evidence of any inflammatory or foreign-body response in any group throughout the follow-up periods. The results of this study suggest that the biodegradable PLLA fixation plates amended with u-HA particles could be functionally superior to PLLA plates without particles.

Delayed aseptic swelling after fixation of talar neck fracture with a biodegradable poly-L-lactide rod: case reports

A 63-year-old woman complained of acute swelling and pain in her ankle at 15 months, after fixation of a talar neck fracture with poly-L-lactide rods. Roentgenographic and laboratory data revealed no abnormalities, but T1-weighted magnetic resonance imaging showed a diffuse area of low intensity in the talus. After nonweightbearing for 1 month, local findings had disappeared and the area of low intensity shown by magnetic resonance imaging had decreased without surgical treatment. Although there have been some reports of aseptic swelling or synovitis after fixation of a fracture with polyglycolide rods or screws, there has been no report of such cases with poly-L-lactide rods or screws.

Biomechanical evaluation of translaminar facet joint fixation. A comparative study of poly-L-lactide pins, screws, and pedicle fixation

STUDY DESIGN

Nine sheep cadaveric spines were used in this acute postoperative model.

OBJECTIVES

To compare the biomechanical performance of translaminar facet joint fixation techique with that of cortical screws and bioabsorbable poly-L-lactide pins and with that of rigid pedicle screw fixation in the lumbar spine.

SUMMARY OF BACKGROUND DATA

Among numerous posterior spine fixation techniques, pedicle screw fixation has been reported to be the most rigid construct and to provide high fusion rate. Translaminar facet joint screw fixation is an alternative to pedicle screw fixation and is the lowest profile construct that achieves stabilization. The authors have developed a new concept involving application of bioabsorbable poly-L-lactide pins to translaminar facet joint fixation. Degradation in the stiffness of the implants with time may be advantageous for fusion mass remodeling.

METHODS

A total of nine sheep L2-L6 cadaveric spines were used. Each intact spine was nondestructively tested in flexion-extension bending (+/- 5-Nm peak bending moment with 100-N axial compression) on a modified testing machine. Loads were applied for 10-second periods using sinusoid waveforms. After testing the intact spine, bilateral fenestration was performed between L4 and L5 and the medial aspect of the facet capsule was resected. The L4-L5 functional spinal unit was than stabilized by five methods: translaminar facet joint fixation with smooth poly-L-lactide pins; translaminar facet joint fixation with cortical screws; pedicle screw fixation with the Texas Scottish Rite Hospital system; and without instrumentation, in that order. Linear displacement of L4 inferior and L5 superior articular processes in the sagittal plain (delta facet) and L4-L5 intervertebral rotation in the sagittal plain (theta sagittal) were measured by the extensometers mounted to the spine. Ranges of motion (delta facet and theta sagittal), neutral zones, linear elastic zone stiffness, and the total energy absorption during the load-unload cycle (hysteresis) were calculated.

RESULTS

By resecting the facet joint capsules and ligamentum flavum, delta facet and theta sagittal were not increased significantly, whereas the increase of neutral zones and hysteresis were statistically significant. Compared with the intact spine, delta facet was significantly reduced to 41% of normal with translaminar facet joint fixation with poly-L-lactide pins, to 9% with translaminar facet joint fixation with screws, and to 11% with the Texas Scottish Rite Hospital system. Neutral zones of delta facet showed a similar pattern, and these differences were significant. Regarding linear elastic zone stiffness, translaminar facet joint fixation with screws provided a stiffer construct than did pedicle screw fixation in the flexion loading mode, whereas pedicle screw fixation yielded higher values for stiffness in extension loading. Translaminar facet joint fixation with poly-L-lactide pins increased linear elastic zone stiffness in extension loading, but the increase was less than was achieved with the other constructs.

CONCLUSIONS

The facet joint is the only true articulation in the lumbosacral spine. It is logical to fix this part directly to achieve spine fixation. Translaminar facet joint fixation with screws show similar biomechanical performance to pedicle screw fixation. Translaminar facet joint fixation with poly-L-lactide pins is significantly less stiff than either type of screw fixation, but it also restricts the facet joint and intervertebral motions significantly when compared with the intact spine.

Bioabsorbable polymers: materials technology and surgical applications

Biostable and bioabsorbable biomaterials are used to manufacture implants for supporting, replacement, augmentation and guiding of growth of tissues. Bioabsorbable implants are a better choice for applications where only the temporary presence of the implant is needed. Because of bioabsorption of such implants, there is no need for a removal operation after healing of the tissue and the risks of implant related, long-term complications are eliminated or strongly reduced. Reinforcing of bioabsorbable materials is necessary in order to develop strong and safe, small implants for fixation of bone fractures and connective tissue damage. Self-reinforced bioabsorbable polymeric implants have been used so far extensively in the treatment of traumas of the musculoskeletal system.

MR imaging of biodegradable polylevolactide osteosynthesis devices in the ankle

OBJECTIVE

To assess the feasibility of magnetic resonance (MR) imaging in the postoperative follow-up after internal fracture fixation using biodegradable polylevolactide (PLLA) plugs and to investigate the MR characteristics of these devices.

STUDY DESIGN AND METHODS

MR findings in ten patients with displaced malleolar fractures treated by internal fixation using absorbable PLLA plugs were evaluated after three different postoperative periods. The average postoperative follow-up time was thirty months for four patients, forty-two months for another four patients, and fifty-one months for the remaining two patients.

RESULTS

On T1-weighted coronal images, the geometry of the PLLA plug was clearly visible in all cases, without signs of fatigue failure or absorption. The host-to-tissue area between the deployed two fins of the plug showed higher signal intensity than the surrounding cancellous bone on fat-saturated proton density (PD) and turbo inversion recovery (tIR) images. This area had signal intensity similar to articular cartilage on T1-weighted coronal images. In none of the cases could any fluid accumulation be seen around the plug. In all ten cases, a thin rim with signal intensity similar to the area between the deployed fins was detected around the PLLA plug on fat-saturated axial PD images. On fat-saturated T2 and tIR sequences, this rim was less clearly detectable in all cases. No differences in the signal intensity or geometry of the PLLA plug on the MR images emerged between the three patient groups with mean follow-ups of thirty, forty-two, and fifty-one months. No artifacts produced by the implants were seen on any of the MR images. A biopsy specimen obtained at a reoperation necessary seventeen months postoperatively showed no signs of degradation of the PLLA plug.

CONCLUSIONS

MR imaging can visualize PLLA implants within bone. It also shows, without artifacts, the tissue interaction between the artificial biodegradable material and bone tissue in humans.

In vivo monitoring of the degradation process of bioresorbable polymeric implants using magnetic resonance imaging

The degradation of a bioresorbable poly(L-lactide) osteosynthesis plug after fixation of a transferred coracoid bone block using the Bristow-Latarjet procedure was examined by means of magnetic resonance (MR) imaging. There were 15 patients with a mean follow-up time of 38 months (range 34-42 months). The gross geometry of the biomaterial plug remained unaltered on the MR images. The bone marrow signal reached the implant surfaces in all cases, and no signs of liquid phase around the implant could be discerned. The implants themselves were visible as homogeneous low signal intensity (SI) black linear structures when compared to the surrounding bone, which had a much higher SI. The mean implant SI was 18.2 (s.d. +/- 6.6), that of the scapular bone 48.9 (s.d. +/- 14.3) and that of the background 4.3 (s.d. +/- 1.5). The SI of a newly manufactured intact implant was 5.7. Serial plain radiographs showed no decreased bone density or focal osteolytic lesions around the poly(L-lactide) expansion plug. The implant channel was discernible on most of the radiographs and a sclerotic rim was detected to outline the implant profile in some of the projections of plain radiographs at each follow-up examination. Computer tomography scans on five patients 3 years postoperatively also revealed a discernible implant channel outlined with a sclerotic rim. The radiographic appearance of the radiolucent implant channel did not change over the follow-up period. Summarizing the present findings, MR imaging seems to be able to visualize poly(L-lactide) implants within the bone. Actually, at present it is the only method available to study the degradation process of implants made of this polymer in humans. No signs of degradation of or of an osteolytic foreign-body reaction to poly(L-lactide) at the host tissue-implant interface could be observed within the follow-up times of this study.

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.

Fixation of osteotomies of the distal femur with absorbable, self-reinforced, poly-L-lactide plates. An experimental study on rabbits

Osteotomies of the distal femur were fixed with two self-reinforced poly-L-lactic acid (SR-PLLA) plates and metallic screws placed through the plates on each side of the femur in 23 adult rabbits. They were followed-up after 3, 6, 12 and 24 weeks. After killing, radiological, histological, microradiographic and oxytetracycline fluorescence studies were performed. Except for one histologically confirmed fibrotic non-union at 24 weeks, the osteotomies healed, including one involving a rabbit which had suffered an ipsilateral femoral shaft fracture of unknown cause. No malformations were observed, and the macroscopically detected swelling was a normal postoperative reaction. This study showed that SR-PLLA plates implanted on both sides on the bone are suitable for the fixation of weight-bearing cancellous bone osteotomies in rabbits.

A simple and secure anchoring system for Caspari's transglenoid multiple suture technique using a biodegradable poly-l-lactic acid button

To manage a difficulty in tying sutures over the infraspinatus fascia when using Caspari's transglenoid multiple suture technique, we developed a new anchoring system using a biodegradable poly-L-lactic acid (PLLA) button and investigated its clinical efficacy in 28 patients who were followed-up for more than 2 years postoperatively (mean, 26.5 months). Twenty-four patients had Bankart lesions and 4 had detachment of the superior glenoid labrum. The mean age at operation was 22.1 years. The PLLA button measured 8 x 8 x 1.2 mm and had two holes. After multiple sutures were inserted by the routine Caspari technique (mean, 7.3 sutures), the sutures were divided into 2 bundles, passed through the holes in the button, and tied over it on the posterior scapular neck under traction. The arm was immobilized in a Velpeau bandage for 3 weeks after Bankart repair and for 1 to 2 weeks after superior labral repair. The results of Bankart repair were excellent in 13 patients, good in 7, and poor in 4 according to Rowe's rating scale (success rate, 83%), while the outcome of superior labral repair was excellent in 3 and good in 1 according to our own criteria. All 4 patients who showed a poor outcome were contact athletes who developed resubluxation postoperatively. There were no complications, but transient damages to the suprascapular nerve occurred in 2 patients. In conclusion, the PLLA button provided simple and secure suture fixation for the Caspari technique.

Enhancement of bone formation by drawn poly(L-lactide)

Poly(L-lactide) (PLLA) was molded into films and rods, and drawn in the longitudinal direction to endow them with piezoelectricity. The piezoelectric constants of PLLA films increased with the draw ratio and, after passing a maximum at a draw ratio around 5, decreased. PLLA samples with a draw ratio 5 underwent fibrilization. The PLLA rods were intramedullarily implanted in the cut tibiae of cats for internal fixation up to 8 weeks. Fracture healing was clearly promoted with increased callus formation as the draw ratio of the PLLA rod increased, whereas the undrawn PLLA as well as a polyethylene control rod had no effect on callus formation, or rather, retarded it. This finding strongly suggests that the promotion of fracture healing by fixation with drawn PLLA can be ascribed to the piezoelectric current generated by the strains accompanying leg movement.

Bioabsorbable rods and pins for fixation of metacarpophalangeal arthrodesis of the thumb

We report results on the use of bioabsorbable pins and intramedullary rods made of high-molecular-weight polylactic acid in both experimental and clinical conditions. In the experimental study, bioabsorbable rods were implanted in rabbit femora. Histologic assessment on nondecalcified bone showed that resorption of the material began at 4 months after implantation and gradually fragmented over a period of 3 years. In 12 patients 13 metacarpophalangeal joints of the thumb were arthrodesed by using one bioabsorbable intramedullary rod with one or two oblique pins. All joints fused within 6 to 8 weeks. During that period there was no sign of inflammation, and there were no nonunions. Postoperative magnetic resonance imaging assessment was done in all rabbits and eight patients. This modality is a useful tool in postoperative evaluation of the position and shape of the rod but is not sufficiently sensitive to assess the presence of local inflammation and the rate of resorption of the rods.