Osteoarthritis of the ankle after foreign-body reaction to absorbable pins and screws: a three- to nine-year follow-up study

Dorsal Metatarsal Closed Wedge Osteotomy in the Treatment of Freiberg's Disease: A Prospective Observational Study

The aim of this study was to prospectively evaluate the clinical and radiological results of dorsal metatarsal closed wedge osteotomy and headless screw fixation in the surgical treatment of Freiberg's disease.Thirty-four patients who were treated with dorsal metatarsal closed wedge osteotomy (DMCWO) for Freiberg's disease between February 2018 and March 2022 were included in the study. Patients were staged according to the classification system described by Smillie. Clinical outcomes were evaluated using the American Orthopedic Foot and Ankle Society's (AOFAS) lesser metatarsophalangeal-interphalangeal scale, the visual analog scale (VAS), the range of motion (ROM) of the metatarsophalangeal (MTP) joint, and a subjective patient satisfaction questionnaire. For radiological evaluation, the amount of preoperative shortening of the involved metatarsal, the amount of metatarsal shortening developed after osteotomy, and radiological recovery times were recorded.Thirty-two (94.1%) of the patients were female, and two (5.9%) were male. The average postoperative follow-up period for patients was 33.7 months (range: 24 months to 41 months). The mean AOFAS scores increased from 53.24 to 86.26 (p < 0.01). The mean VAS scores decreased from 8.59 to 1.79, and it was observed that the patients' pain improved significantly (p < 0.01). The mean ROM of the MTP joint increased from 48.76 degrees to 70.76 degrees (p < 0.01). An average of 2.5 mm (range 1 mm to 4.1 mm) of shortening of the metatarsal length developed postoperatively (p < 0.01). Arthrosis developed in 1 case (2.9%), and transfer metatarsalgia developed in 2 cases (5.8%).DMCWO is an effective treatment for both the early and advanced stages of symptomatic Freiberg's disease, leading to high patient satisfaction.

A Narrative Review of u-HA/PLLA, a Bioactive Resorbable Reconstruction Material: Applications in Oral and Maxillofacial Surgery

The advent of bioresorbable materials to overcome limitations and replace traditional bone-reconstruction titanium-plate systems for bone fixation, thus achieving greater efficiency and safety in medical and dental applications, has ushered in a new era in biomaterial development. Because of its bioactive osteoconductive ability and biocompatibility, the forged composite of uncalcined/unsintered hydroxyapatite and poly L-lactic acid (u-HA/PLLA) has attracted considerable interest from researchers in bone tissue engineering, as well as from clinicians, particularly for applications in maxillofacial reconstructive surgery. Thus, various in vitro studies, in vivo studies, and clinical trials have been conducted to investigate the feasibility and weaknesses of this biomaterial in oral and maxillofacial surgery. Various technical improvements have been proposed to optimize its advantages and limit its disadvantages. This narrative review presents an up-to-date, comprehensive review of u-HA/PLLA, a bioactive osteoconductive and bioresorbable bone-reconstruction and -fixation material, in the context of oral and maxillofacial surgery, notably maxillofacial trauma, orthognathic surgery, and maxillofacial reconstruction. It simultaneously introduces new trends in the development of bioresorbable materials that could used in this field. Various studies have shown the superiority of u-HA/PLLA, a third-generation bioresorbable biomaterial with high mechanical strength, biocompatibility, and bioactive osteoconductivity, compared to other bioresorbable materials. Future developments may focus on controlling its bioactivity and biodegradation rate and enhancing its mechanical strength.

[Research progress of interphalangeal arthrodesis]

OBJECTIVE

To review the research progress of interphalangeal arthrodesis in the treatment of interphalangeal joint deformity.

METHODS

The literature about interphalangeal arthrodesis at home and abroad was extensively consulted, and the indications, fusion methods, fixation methods, complications, and so on were summarized and analysed.

RESULTS

The indications of interphalangeal arthrodesis are hammer toe, claw toe, and mallet toe. From the different forms of fusion surface, fusion methods include end-to-end, peg-in-hole, conical reamer type, and V-shape arthrodesis. There are three kinds of fixation methods: Kirschner wire fixation, stainless-steel wire suture fixation, and intramedullary fixation, and there are many kinds of intramedullary fixation. The complications of interphalangeal arthrodesis include vascular injury, fixation related complications, and postoperative complications.

CONCLUSION

Interphalangeal arthrodesis is a good way to correct some deformities of toes, but the incidence of various complications can not be ignored, and there is still a lack of clinical research on interphalangeal arthrodesis.

Assessment of Hedgehog Signaling Pathway Activation for Craniofacial Bone Regeneration in a Critical-Sized Rat Mandibular Defect

Importance

Osseous craniofacial defects are currently reconstructed with bone grafting, rigid fixation, free tissue transfer, and/or recombinant human bone morphogenetic protein 2. Although these treatment options often have good outcomes, they are associated with substantial morbidity, and many patients are not candidates for free tissue transfer.

Objective

To assess whether polysaccharide-based scaffold (PS) constructs that are cross-linked with smoothened agonist (SAG), vascular endothelial growth factor (VEGF), and bone morphogenetic protein 6 (BMP-6) would substantially increase bone regeneration.

Design, Setting, and Participants

This animal model study was conducted at the University of Virginia School of Medicine Cui Laboratory from March 1, 2017, to June 30, 2017. Thirty-three 10-week-old female Lewis rats were acquired for the study. Bilateral nonsegmental critical-sized defects were created in the angle of rat mandibles. The defects were either left untreated or filled with 1 of the 9 PSs. The rats were killed after 8 weeks, and bone regeneration was evaluated using microcomputed tomographic imaging and mechanical testing. Analysis of variance testing was used to compare the treatment groups.

Main Outcomes and Measures

Blinded analysis and computer analysis of the microcomputed tomographic images were used to assess bone regeneration.

Results

In the 33 female Lewis rats, minimal healing was observed in the untreated mandibles. Addition of SAG was associated with increases in bone regeneration and bone density in all treatment groups, and maximum bone healing was seen in the group with BMP-6, VEGF, and SAG cross-linked to PS. For each of the 5 no scaffold group vs BMP-6, VEGF, and SAG cross-linked to PS group comparisons, mean defect bone regeneration was 4.14% (95% CI, 0.94%-7.33%) vs 66.19% (95% CI, 54.47%-77.90%); mean bone volume, 14.52 mm3 (95% CI, 13.07-15.97 mm3) vs 20.87 mm3 (95% CI, 14.73- 27.01 mm3); mean bone surface, 68.97 mm2 (95% CI, 60.08-77.85 mm2) vs 96.77 mm2 (95% CI, 76.11-117.43 mm2); mean ratio of bone volume to total volume, 0.11 (95% CI, 0.10-0.11) vs 0.15 (95% CI, 0.10-0.19); and mean connectivity density 0.03 (95% CI, 0.02-0.05) vs 0.32 (95% CI, 0.25-0.38). On mechanical testing, mandibles with untreated defects broke with less force than control mandibles in which no defect was made, although this force did not reach statistical significance. No significant difference in force to fracture was observed among the treatment groups.

Conclusions and Relevance

In this rat model study, activation of the hedgehog signaling pathway using smoothened agonist was associated with increased craniofacial bone regeneration compared with growth factors alone, including US Food and Drug Administration-approved recombinant human bone morphogenetic protein 2. Pharmaceuticals that target this pathway may offer a new reconstructive option for bony craniofacial defects as well as nonunion and delayed healing fractures.

Level of Evidence

NA.

Generational Biodegradable and Regenerative Polyphosphazene Polymers and their Blends with Poly (lactic-co-glycolic acid)

New fields such as regenerative engineering have driven the design of advanced biomaterials with a wide range of properties. Regenerative engineering is a multidisciplinary approach that integrates the fields of advanced materials science and engineering, stem cell science, physics, developmental biology, and clinical translation for the regeneration of complex tissues. The complexity and demands of this innovative approach have motivated the synthesis of new polymeric materials that can be customized to meet application-specific needs. Polyphosphazene polymers represent this fundamental change and are gaining renewed interest as biomaterials due to their outstanding synthetic flexibility, neutral bioactivity (buffering degradation products), and tunable properties across the range. Polyphosphazenes are a unique class of polymers composed of an inorganic backbone with alternating phosphorus and nitrogen atoms. Each phosphorus atom bears two substituents, with a wide variety of side groups available for property optimization. Polyphosphazenes have been investigated as potential biomaterials for regenerative engineering. Polyphosphazenes for use in regenerative applications have evolved as a class to include different generations of degradable polymers. The first generation of polyphosphazenes for tissue regeneration entailed the use of hydrolytically active side groups such as imidazole, lactate, glycolate, glucosyl, or glyceryl groups. These side groups were selected based on their ability to sensitize the polymer backbone to hydrolysis, which allowed them to break down into non-toxic small molecules that could be metabolized or excreted. The second generation of degradable polyphosphazenes developed consisted of polymers with amino acid ester side groups. When blended with poly (lactic acid-co-glycolic acid) (PLGA), the feasibility of neutralizing acidic degradation products of PLGA was demonstrated. The blends formed were mostly partially miscible. The desire to improve miscibility led to the design of the third generation of degradable polyphosphazenes by incorporating dipeptide side groups which impart significant hydrogen bonding capability to the polymer for the formation of completely miscible polyphosphazene-PLGA blends. Blend system of the dipeptide-based polyphosphazene and PLGA exhibit a unique degradation behavior that allows the formation of interconnected porous structures upon degradation. These inherent pore-forming properties have distinguished degradable polyphosphazenes as a potentially important class of biomaterials for further study. The design considerations and strategies for the different generations of degradable polyphosphazenes and future directions are discussed.

Degradation and interaction with bone of magnesium alloy WE43 implants: A long-term follow-up in vivo rat tibia study

The aim of this in vivo study was to examine the degradation and biocompatibility of the WE43 magnesium alloy containing magnesium yttrium, rare earth elements, and zirconium over a one-year long-term follow-up period. Additionally, we compared anodized WE43 implants with monolithic ones and clarified the effect of the anodization. WE43 cylindrical implants with and without anodization (length, 10 mm; diameter, 0.3 mm) were transplanted into the rat tibia. In both groups, the development of corrosion and the change in implant volume were evaluated by in vivo micro-computed tomography until 12 months, and the bone tissue reaction was observed histologically. In the monolithic WE43 implants, hydrogen gas was evident until 14 days and the volume loss was 36.3% after 12 months. In the anodized WE43 implants, the development of hydrogen gas was inhibited and the volume loss was 27.7% after 12 months. The anodized WE43 implants showed a significantly slower corrosion process in the early phase. Therefore, these implants may require a prolonged period to degrade completely and may even resist complete degradation. At one year post surgery, bone maturation progressed and lamellar bone structure developed around the implant in both groups. In conclusion, the WE43 implants showed good long-term stability and biocompatibility in bone tissue.

Treatment of Lateral Tibial Condylar Fractures Using Bioactive, Bioresorbable Forged Composites of Raw Particulate Unsintered Hydroxyapatite/Poly-L-Lactide Screws

Forged composites of raw particulate unsintered hydroxyapatite/poly-L-lactide (F-u-HA/PLLA) devices possess high mechanical strength, bioactivity, and radio-opacity. The aim of this study was to assess the efficacy of F-u-HA/PLLA screws in the treatment of lateral tibial condylar fractures. From January 2005 to December 2010, a total of 7 patients with displaced closed lateral tibial condylar fractures (Schatzker type II) were treated using F-u-HA/PLLA screws. Open reduction and internal fixation was performed using 2 or 3 F-u-HA/PLLA screws. After surgery, weight bearing was not allowed for 6 weeks. Range of motion exercise was initiated after removal of the plaster splint. Radiographs were evaluated for fracture healing, joint depression, and the radioopacity of F-u-HA/PLLA screws. Clinical outcomes and postoperative complications were also assessed. Average follow-up was 44 months. All fractures were successfully healed. Average values for joint depression were 4.7 mm (range, 2-9 mm) preoperatively, 0.4 mm (range, 0-1 mm) postoperatively, and 0.4 mm (range, 0-1 mm) at final follow-up. Whole shadows of F-u-HA/PLLA screws were observed during the follow-up period. Breakage of screws, osteolysis, and a radiolucent zone around the screws were not observed at final follow-up. Average knee flexion and extension were 134° (range, 110° to 150°) and -1° (range, -10° to 0°), respectively. No patient had wound infection, late aseptic tissue response, or foreign body reaction postoperatively. None of the patients reported pain at final follow-up. These results suggest that F-u-HA/PLLA screws could be an alternative option for the treatment of lateral tibial condylar fractures. [Orthopedics. 2018; 41(3):e365-e368.].

Micro-Nanostructures of Cellulose-Collagen for Critical Sized Bone Defect Healing

Bone tissue engineering strategies utilize biodegradable polymeric matrices alone or in combination with cells and factors to provide mechanical support to bone, while promoting cell proliferation, differentiation, and tissue ingrowth. The performance of mechanically competent, micro-nanostructured polymeric matrices, in combination with bone marrow stromal cells (BMSCs), is evaluated in a critical sized bone defect. Cellulose acetate (CA) is used to fabricate a porous microstructured matrix. Type I collagen is then allowed to self-assemble on these microstructures to create a natural polymer-based, micro-nanostructured matrix (CAc). Poly (lactic-co-glycolic acid) matrices with identical microstructures serve as controls. Significantly higher number of implanted host cells are distributed in the natural polymer based micro-nanostructures with greater bone density and more uniform cell distribution. Additionally, a twofold increase in collagen content is observed with natural polymer based scaffolds. This study establishes the benefits of natural polymer derived micro-nanostructures in combination with donor derived BMSCs to repair and regenerate critical sized bone defects. Natural polymer based materials with mechanically competent micro-nanostructures may serve as an alternative material platform for bone regeneration.

Bioabsorbable self-retaining PLA/nano-sized β-TCP cervical spine interbody fusion cage in goat models: an in vivo study

STUDY DESIGN

This is an experimental animal study.

OBJECTIVE

The objective of this study was to compare an anterior cervical discectomy and interbody fusion of a novel polylactide/nano-sized β-tricalcium phosphate (PLA/nβ-TCP) bioabsorbable self-retaining cervical fusion cage (BCFC) with an autologous bone graft and polyetheretherketone (PEEK) cages.

BACKGROUND

Although PLA cervical cages have potential advantages compared with traditional materials, they are not currently routinely used in spine surgery because of undesirable effects such as the lack of osteoconductivity and osteolysis around the implant. This study involved the manufacturing of a bioabsorbable cage from PLA/nβ-TCP that was then used as a device for anterior cervical discectomy and fusion (ACDF) on a goat cervical spine fusion model.

MATERIALS AND METHODS

Eighteen goats underwent C3/C4 discectomy and were randomly divided into three groups based on the following methods: Group A (n=6), an autologous bone graft; Group B (n=6), PEEK cage filled with an autologous graft; and Group C (n=6), BCFC filled with an autologous iliac bone. Radiography was performed preoperatively and postoperatively and at 1, 4, 8, and 12 weeks after the operation. Disc space height (DSH) was measured at the same time. After 12 weeks, the fused segments were harvested and evaluated with functional radiographic views, biomechanical testing, and histological analyses.

RESULTS

Over a 12-week period, the BCFC and PEEK cage groups exhibited significantly higher DSH values than the bone graft group. Additionally, the BCFC group yielded a significantly lower range of motion in axial rotation than both the autologous bone graft and PEEK cage groups. A histologic evaluation revealed an increased intervertebral bone volume/total volume ratio and better interbody fusion in the BCFC group than in the other groups.

CONCLUSION

The BCFC device exhibited better results than the autologous bone graft and PEEK cages in single-level ACDF models in vivo. This device may be a potential alternative to the current PEEK cages.

Application of bioabsorbable screw fixation for anterior cervical decompression and bone grafting

OBJECTIVES

To examine the application of bioabsorbable screws for anterior cervical decompression and bone grafting fixation and to study their clinical effects in the treatment of cervical spondylosis.

METHODS

From March 2007 to September 2012, 56 patients, 36 males and 20 females (38-79 years old, average 58.3±9.47 years), underwent a novel operation. Grafts were fixed by bioabsorbable screws (PLLA, 2.7 mm in diameter) after anterior decompression. The bioabsorbable screws were inserted from the midline of the graft bone to the bone surface of the upper and lower vertebrae at 45 degree angles. Patients were evaluated post-operatively to observe the improvement of symptoms and evaluate the fusion of the bone. The Japanese Orthopaedic Association (JOA) score was used to evaluate the recovery of neurological functions.

RESULTS

All screws were successfully inserted, with no broken screws. The rate of symptom improvement was 87.5%. All of the grafts fused well with no extrusion. The average time for graft fusion was 3.8±0.55 months (range 3-5 months). Three-dimensional reconstruction of CT scans demonstrated that the grafts fused with adjacent vertebrae well and that the screws were absorbed as predicted. The MRI findings showed that the cerebrospinal fluid was unobstructed. No obvious complications appeared in any of the follow-up evaluations.

CONCLUSIONS

Cervical spondylosis with one- or two-level involvement can be effectively treated by anterior decompression and bone grafting with bioabsorbable screw fixation. This operative method is safe and can avoid the complications induced by metal implants.

Collagen nanofibril self-assembly on a natural polymeric material for the osteoinduction of stem cells in vitro and biocompatibility in vivo

This manuscript reports the characterization of molecularly self-assembled collagen nanofibers on a natural polymeric microporous structure and their ability to support stem cell differentiation in vitro and host tissue response in vivo.

Intramedullary Fixation System for the Treatment of Hammertoe Deformity

Hammertoe is one of the most common foot deformities. Arthrodesis or arthroplasty of the proximal interphalangeal joint using temporary Kirschner wire fixation is the most widespread method of surgical stabilization. However, this type of fixation is associated with some potential complications that can be obviated if percutaneous fixation is avoided. The purpose of the present study was to prospectively collect clinical and radiographic outcomes of operative correction of hammertoe deformity using a permanently implanted 1-piece intramedullary device. A total of 29 patients with 60 painful, rigid hammertoes were prospectively enrolled, clinically and radiographically examined, operatively treated, then followed and re-examined. The outcomes were measured in terms of the American Orthopaedic Foot and Ankle Society lesser toe and visual analog pain scores. After ≥18 months of follow-up, the incidence of fusion with satisfactory radiographic alignment was 85% (51 of 60 toes). One toe (1.67%) developed early postoperative implant failure because of dislocation of the device, there were no cases of infection, and the mean American Orthopaedic Foot and Ankle Society lesser toe score was 87.4 ± 1.3 and the mean visual analog scale pain score was 1.78 ± 0.94. Twenty-five patients (86.21%) stated that they had no symptoms in the involved toes after surgery, and 4 (13.8%) experienced occasional pain, 2 (6.9%) of whom reported limitations of recreational activities and 2 (6.9%) reported persistent swelling without activity limitations. All the patients stated that they would undergo the surgery again if they had the same preoperative condition.

Bioabsorbable fish scale for the internal fixation of fracture: a preliminary study

Fish scales, which consist of type I collagen and hydroxyapatite (HA), were used to fabricate a bioabsorbable bone pin in this study. Fresh fish scales were decellularized and characterized to provide higher biocompatibility. The mechanical properties of fish scales were tested, and the microstructure of an acellular fish scale was examined. The growth curve of a myoblastic cell line (C2C12), which was cultured on the acellular fish scales, implied biocompatibility in vitro, and the morphology of the cells cultured on the scales was observed using scanning electron microscopy (SEM). A bone pin made of decellularized fish scales was used for the internal fixation of femur fractures in New Zealand rabbits. Periodic X-ray evaluations were obtained, and histologic examinations were performed postoperatively. The present results show good cell growth on decellularized fish scales, implying great biocompatibility in vitro. Using SEM, the cell morphology revealed great adhesion on a native, layered collagen structure. The Young's modulus was 332 ± 50.4 MPa and the tensile strength was 34.4 ± 6.9 MPa for the decellularized fish scales. Animal studies revealed that a fish-scale-derived bone pin improved the healing of bone fractures and degraded with time. After an 8-week implantation, the bone pin integrated with the adjacent tissue, and new extracellular matrix was synthesized around the implant. Our results proved that fish-scale-derived bone pins are a promising implant material for bone healing and clinical applications.

Biomechanical Evaluation of Plate Versus Lag Screw Only Fixation of Distal Fibula Fractures

Traditional fixation of unstable Orthopaedic Trauma Association type B/C ankle fractures consists of a lag screw and a lateral or posterolateral neutralization plate. Several studies have demonstrated the clinical success of lag screw only fixation; however, to date no biomechanical comparison of the different constructs has been performed. The purpose of the present study was to evaluate the biomechanical strength of these different constructs. Osteotomies were created in 40 Sawbones(®) distal fibulas and reduced using 1 bicortical 3.5-mm stainless steel lag screw, 2 bicortical 3.5-mm lag screws, 3 bicortical 3.5-mm lag screws, or a single 3.5-mm lag screw coupled with a stainless steel neutralization plate with 3 proximal cortical and 3 distal cancellous screws. The constructs were tested to determine the stiffness in lateral bending and rotation and failure torque. No significant differences in lateral bending or rotational stiffness were detected between the osteotomies fixed with 3 lag screws and a plate. Constructs fixed with 1 lag screw were weaker for both lateral bending and rotational stiffness. Osteotomies fixed with 2 lag screws were weaker in lateral bending only. No significant differences were found in the failure torque. Compared with lag screw only fixation, plate fixation requires larger incisions and increased costs and is more likely to require follow-up surgery. Despite the published clinical success of treating simple Orthopaedic Trauma Association B/C fractures with lag screw only fixation, many surgeons still have concerns about stability. For noncomminuted, long oblique distal fibula fractures, lag screw only fixation techniques offer construct stiffness similar to that of traditional plate and lag screw fixation.

Application of calcium phosphate materials in dentistry

Calcium phosphate materials are similar to bone in composition and in having bioactive and osteoconductive properties. Calcium phosphate materials in different forms, as cements, composites, and coatings, are used in many medical and dental applications. This paper reviews the applications of these materials in dentistry. It presents a brief history, dental applications, and methods for improving their mechanical properties. Notable research is highlighted regarding (1) application of calcium phosphate into various fields in dentistry; (2) improving mechanical properties of calcium phosphate; (3) biomimetic process and functionally graded materials. This paper deals with most common types of the calcium phosphate materials such as hydroxyapatite and tricalcium phosphate which are currently used in dental and medical fields.

Absorbable implants versus metal implants for the treatment of ankle fractures: A meta-analysis

This meta-analysis was performed to evaluate the efficiency and the safety of absorbable implants. Five major electronic databases (PubMed, Embase, Cochrane Library, SinoMed and Wanfang Data) were systematically searched for randomized controlled trials (RCTs) from their establishment to November 2012. Studies on absorbable implants and metal implants for ankle fractures were selected. The meta-analysis was performed using RevMan 5.1. Ten studies with 762 patients were included and analyzed. Compared with metal implants, absorbable implants used for the internal fixation of ankle fractures produce similar radiographic and functional outcomes (P= 0.52). Normally, removal of the internal fixation is unnecessary (P<0.0001) and the incidence of palpable implants is lower (P=0.02) for absorbable implants. No statistically significant difference was observed between the two groups with regard to foreign body reactions (P=0.07), infection (P= 0.69), osteoarthritis (P= 0.39), pain (P= 0.06), refracture (P=0.67), skin necrosis (P=0.99), deep vein thrombosis (P=0.21) and nerve injury (P=0.94). Absorbable implants used in ankle fractures rarely require reoperation and result in similar functional outcomes and complications compared with metal implants. These characteristics make them efficient and reasonably safe for the treatment of ankle fractures.

Ligament regeneration using an absorbable stent-shaped poly-L-lactic acid scaffold in a rabbit model

PURPOSE

Ligaments are frequently damaged in sports activities and trauma, and severe ligament injury can lead to joint instability and osteoarthritis. In this study, we aimed to regenerate the medial collateral ligament (MCL) using an absorbable stent-shaped poly-L-lactic acid (PLLA) scaffold in a rabbit model to examine the biocompatibility and mechanical properties.

METHODS

Twenty-three Japanese white rabbits were used in this study. MCL defects were surgically created in the knee joints and then reconstructed using stent-shaped PLLA scaffolds. As controls, flexor digitorum longus (FDL) tendons were implanted into the contralateral knees. Seven rabbits were sacrificed at three time points, conducted four, eight and 16 weeks after the operation. The regenerated tissues were histologically evaluated using fibre alignment scoring, morphology of fibroblast scoring and immunohistochemical analysis of types I and III collagen. The regenerated tissues were also biomechanically evaluated by measuring the ultimate failure load and stiffness.

RESULTS

At four weeks post-operation, spindle-shaped cells were observed on the inside of the scaffolds. At eight weeks, maturation of the regenerated tissues and collagen fibre alignment parallel to the ligaments was observed. At 16 weeks, the fibre alignment had become denser. The fibre alignment and morphology of fibroblast scores significantly increased in a time-dependent manner. Expression of type I collagen was more strongly observed in the scaffold group at eight and 16 weeks post-operation than at four weeks. Type III collagen was also observed at four, eight and 16 weeks post-operation. A thin layer of fibrocartilage was observed at the ligament-bone junction at eight and 16 weeks. The ultimate failure load of the scaffold group was 46.7 ± 20.7 N, 66.5 ± 11.0 N and 74.3 ± 11.5 N at four, eight and 16 weeks post-operation, respectively. There was no statistical difference between the normal MCL and the scaffold group at 16 weeks post-operation.

CONCLUSIONS

The stent-shaped PLLA scaffold allowed for MCL regeneration with type I collagen expression and fibrocartilage formation and resulted in sufficient mechanical function.

Foreign-body reaction and osteolysis induced by an intraosseous poly-L-lactic Acid suture anchor in the wrist: case report

Polyglycolic acid and poly-L-lactic acid have become popular choices for bioabsorbable anchor fixation in the hand and wrist. We report a case of osteolysis, synovitis, and chondral erosion secondary to a poly-L-lactic acid suture anchor in the wrist.

Local antibiotic therapy in osteomyelitis

The local delivery of antibiotics in the treatment of osteomyelitis has been used safely and effectively for decades. Multiple methods of drug delivery have been developed for the purposes of both infection treatment and prophylaxis. The mainstay of treatment in this application over the past 20 years has been non-biodegradable polymethylmethacrylate, which has the advantages of excellent elution characteristics and structural support properties. Biodegradable materials such as calcium sulfate and bone graft substitutes have been used more recently for this purpose. Other biodegradable implants, including synthetic polymers, are not yet approved for use but have demonstrated potential in laboratory investigations. Antibiotic-impregnated metal, a recent development, holds great promise in the treatment and prophylaxis of osteomyelitis in the years to come.

Osteoconductive properties of poly(96L/4D-lactide)/beta-tricalcium phosphate in long term animal model

The objective of this study was to determine the effect of calcium phosphate mineral content on the bone in-growth at the expense of composite of co-polylactide polymer charged with 2 different ratios of β-TCP granules (10 and 24 w-% of β-TCP). The evaluation was realized in a long term rabbit bone model. After 24, 48 and 76 weeks, the implants were examined by micro CT, scanning electron microscopy (SEM) using backscattered electron (BSE) and light microscopy (polarized and blue light microscopy). No foreign body reaction was detected during the 76 weeks follow-up in any of the test samples. Polymer hydrolysis began at approximately 24 weeks, by 76 weeks, the pure polymer implant had begun to release P(96L/4D)LA particles and show signs of peripheral localized bone resorption. A decrease in the amount of CaP was noticed between 24 and 76 weeks in both 10 wt-% and 24 wt-% β-TCP/P(96L/4D)LA composites. The study showed that the highest bone in-growth was with 24 wt-% β-TCP/P(96L/4D)LA composite. Bone in-growth and mineralization were evident for the composites associated with specific peripheral bone architecture. Fluorescent labelling demonstrated high bone in-growth and remodeling at the interface, while for pure co-polymer no bone remodeling or bone activity was maintained after 48 weeks. The study demonstrated the positive effect of calcium phosphate content into P(96L/4D)LA. This kind of composite is a suitable resorbable osteoconductive matrix, which provides long term stability required for ligament fixation device.

Intraosseous foreign body granuloma in rotator cuff repair with bioabsorbable suture anchor

Biodegradable implants lead to problems such as cyst formation, soft-tissue inflammation, loose implant fragments or local osteolysis. This report represents the first published case of an intraosseous foreign body granuloma in the humeral head after arthroscopic rotator cuff tear fixation with a poly-L: -lactide (PLLA) suture anchor. A 48-year-old female patient presented with pain in her right shoulder. A refixation of her right supraspinatus tendon with a biodegradable suture anchor was performed 11 months ago at an external hospital. Laboratory tests showed normal values for C-reactive protein, leukocytes and the erythrocyte sedimentation rate. No signs of infection or instability were noted. The visual analogue scale (VAS) was 8, the simple shoulder test (SST) was 4 and the American shoulder and elbow surgeons score (ASES) was 44. Plain radiographs showed high lucency in the area of the tuberculum majus. MRI showed an intra- and extraosseous mass surrounded by fluid in this area. Surgical care involved arthroscopic debridement and removal of the suture anchor. Histological examination revealed a foreign body granuloma. At the 18-month follow-up the patient was nearly pain-free. The VAS was 2, SST was 10 and ASES was 88. Foreign body granulomas are a well known but rarely described complication that arises after the use of biodegradable suture anchors in shoulder surgery. Every patient presenting with shoulder pain after usage of a biodegradable fixation material should be evaluated closely. Orthopaedic surgeons should be aware of the possibility of delayed foreign body reactions, especially after using PLLA anchors.

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.

Dipeptide-based polyphosphazene and polyester blends for bone tissue engineering

Polyphosphazene-polyester blends are attractive materials for bone tissue engineering applications due to their controllable degradation pattern with non-toxic and neutral pH degradation products. In our ongoing quest for an ideal completely miscible polyphosphazene-polyester blend system, we report synthesis and characterization of a mixed-substituent biodegradable polyphosphazene poly[(glycine ethyl glycinato)(1)(phenyl phenoxy)(1)phosphazene] (PNGEG/PhPh) and its blends with a polyester. Two dipeptide-based blends namely 25:75 (Matrix1) and 50:50 (Matrix2) were produced at two different weight ratios of PNGEG/PhPh to poly(lactic acid-glycolic acid) (PLAGA). Blend miscibility was confirmed by differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy. Both blends resulted in higher tensile modulus and strength than the polyester. The blends showed a degradation rate in the order of Matrix2 Collapse

Key Words

• polyphosphazenes
• poly(lactic acid-glycolic acid)
• polymeric blends
• biodegradation
• biocompatibility
• bone tissue engineering

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MESH Headings

• Animals
• Bone Substitutes/chemistry
• Bone Substitutes/metabolism
• Cell Proliferation
• Cells, Cultured
• Dipeptides/chemistry
• Dipeptides/metabolism
• Glycolates/chemistry
• Lactic Acid
• Male
• Materials Testing
• Organophosphorus Compounds/chemistry
• Organophosphorus Compounds/metabolism
• Osteoblasts/cytology
• Osteoblasts/metabolism
• Polyesters/chemistry
• Polyesters/metabolism
• Polyglycolic Acid
• Polylactic Acid-Polyglycolic Acid Copolymer
• Polymers/chemistry
• Polymers/metabolism
• Rats
• Rats, Sprague-Dawley
• Tissue Engineering/methods
• Tissue Scaffolds/chemistry

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Grants

• R01 AR052536 NIAMS NIH HHS
• R01 EB004051 NIBIB NIH HHS

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Affiliation(s)

Meng Deng Department of Orthopaedic Surgery, University of Connecticut, Farmington, Connecticut 06030 Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia 22904
Lakshmi S. Nair Department of Orthopaedic Surgery, University of Connecticut, Farmington, Connecticut 06030 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269
Syam P. Nukavarapu Department of Orthopaedic Surgery, University of Connecticut, Farmington, Connecticut 06030 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269
Tao Jiang Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia 22904
William A. Kanner Department of Pathology, University of Virginia, Charlottesville, Virginia 22903
Xudong Li Department of Orthopeadic Surgery, University of Virginia, Charlottesville, Virginia 22908
Sangamesh G. Kumbar Department of Orthopaedic Surgery, University of Connecticut, Farmington, Connecticut 06030 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269
Arlin L. Weikel Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
Nicholas R. Krogman Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
Harry R. Allcock Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
Cato T. Laurencin Department of Orthopaedic Surgery, University of Connecticut, Farmington, Connecticut 06030 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269

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Collaborators Collapse

Time-dependent failure in load-bearing polymers: a potential hazard in structural applications of polylactides

With their excellent biocompatibility and relatively high mechanical strength, polylactides are attractive candidates for application in load-bearing, resorbable implants. Pre-clinical studies provided a proof of principle for polylactide cages as temporary constructs to facilitate spinal fusion, and several cages already made it to the market. However, also failures have been reported: clinical studies reported considerable amounts of subsidence with lumbar spinal fusion cages, and in an in vivo goat study, polylactide spinal cages failed after only three months of implantation, although mechanical testing had predicted sufficient strength for at least eight months. The failures appear to be related to the long-term performance of polylactides under static loading conditions, a phenomenon which is common to all glassy polymers and finds its origin in stress-activated molecular mobility leading to plastic flow. This paper reviews the mechanical properties and deformation kinetics of amorphous polylactides. Compression tests were performed with various strain rates, and static stress experiments were done to determine time-to failure. Pure PLLA appeared to have a higher yield strength than its co-polymers with D: -lactide, but the kinetic behaviour of the polymers was the same: an excellent short-term strength at higher loading rates, but lifetime under static stress is rather poor. As spinal implants need to maintain mechanical integrity for a period of at least six months, this has serious implications for the clinical application of amorphous polylactides in load bearing situations. It is recommended that standards for mechanical testing of implants made of polymers be revised in order to consider this typical time-dependent behaviour.

Time-dependent failure of amorphous polylactides in static loading conditions

Polylactides are commonly praised for their excellent mechanical properties (e.g. a high modulus and yield strength). In combination with their bioresorbability and biocompatibility, they are considered prime candidates for application in load-bearing biomedical implants. Unfortunately, however, their long-term performance under static load is far from impressive. In a previous in vivo study on degradable polylactide spinal cages in a goat model it was observed that, although short-term mechanical and real-time degradation experiments predicted otherwise, the implants failed prematurely under the specified loads. In this study we demonstrate that this premature failure is attributed to the time-dependent character of the material used. The phenomenon is common to all polymers, and finds its origin in stress-activated segmental molecular mobility leading to a steady rate of plastic flow. The stress-dependence of this flow-rate is well captured by Eyring's theory of absolute rates, as demonstrated on three amorphous polylactides of different stereoregularity.We show that the kinetics of the three materials are comparable and can be well described using the proposed modeling framework. The main conclusion is that knowledge of the instantaneous strength of a polymeric material is insufficient to predict its long-term performance.

Biodegradable Polymers in Bone Tissue Engineering

The use of degradable polymers in medicine largely started around the mid 20^th century with their initial use as in vivo resorbing sutures. Thorough knowledge on this topic as been gained since then and the potential applications for these polymers were, and still are, rapidly expanding. After improving the properties of lactic acid-based polymers, these were no longer studied only from a scientific point of view, but also for their use in bone surgery in the 1990s. Unfortunately, after implanting these polymers, different foreign body reactions ranging from the presence of white blood cells to sterile sinuses with resorption of the original tissue were observed. This led to the misconception that degradable polymers would, in all cases, lead to inflammation and/or osteolysis at the implantation site. Nowadays, we have accumulated substantial knowledge on the issue of biocompatibility of biodegradable polymers and are able to tailor these polymers for specific applications and thereby strongly reduce the occurrence of adverse tissue reactions. However, the major issue of biofunctionality, when mechanical adaptation is taken into account, has hitherto been largely unrecognized. A thorough understanding of how to improve the biofunctionality, comprising biomechanical stability, but also visualization and sterilization of the material, together with the avoidance of fibrotic tissue formation and foreign body reactions, may greatly enhance the applicability and safety of degradable polymers in a wide area of tissue engineering applications. This review will address our current understanding of these biofunctionality factors, and will subsequently discuss the pitfalls remaining and potential solutions to solve these problems.

Biomechanical evaluation of plate osteosynthesis of distal fibula fractures with biodegradable devices

BACKGROUND

This study compared fixation with a titanium one-third tubular plate and one lag-screw vs. fixation with biodegradable plates with one lag-screw applied with two different plate-screw patterns.

MATERIALS AND METHODS

Ten pairs of fibulas were osteotomied, plated (titanium plate with one lag screw vs. absorbable 2/8 plate-screws crossing vs. 0/8 plate-screws crossing the osteotomy gap). and tested in torsion and bending to obtain stiffness and neutral-zone (NZ) data. Tests were performed using 5 load cycles. No load to failure was performed. Biodegradation was simulated by 6 week immersion in phosphate-buffered saline after which the testing protocol was repeated. The specimens were then loaded with 100 N in bending.

RESULTS

Post-implantation, there were no significant differences, in torsion and bending, regarding the NZ or the stiffness, between the 2/8 biodegradable plate and the titanium plate. The 0/8 pattern performed significantly less well in terms of stiffness and NZ in the initial torsion test, and significantly less well in terms of stiffness in the initial bending test. After 6 weeks' immersion, all biodegradable constructs showed a significantly larger NZ and significantly reduced bending and torsional stiffness. When loaded with 100 N, four of the six 0/8 osteosyntheses failed. There were no significant differences between the 2/8 pattern and the titanium plates.

CONCLUSION

In a model of a Weber-B fracture, the use of a 2/8 biodegradable plate construct initially did not differ statistically to that obtained with a one-third tubular titanium plate. After immersion the 2/8 construct withstood some physiological load.

CLINICAL RELEVANCE

For the fixation of ankle fractures with a biodegradable plate of the type employed in this study, the use of fracture-gap-crossing screws is recommended.

Miscibility and in vitro osteocompatibility of biodegradable blends of poly[(ethyl alanato) (p-phenyl phenoxy) phosphazene] and poly(lactic acid-glycolic acid)

Previously we demonstrated the ability of ethyl glycinato substituted polyphosphazenes to neutralize the acidic degradation products and control the degradation rate of poly(lactic acid-glycolic acid) (PLAGA) by blending. In this study, blends of high strength poly[(50% ethyl alanato) (50% p-phenyl phenoxy) phosphazene] (PNEA(50)PhPh(50)) and 85:15 PLAGA were prepared using a mutual solvent approach. Three different solvents, methylene chloride (MC), chloroform (CF) and tetrahydrofuran (THF) were studied to investigate solvent effects on blend miscibility. Three different blends were then fabricated at various weight ratios namely 25:75 (BLEND25), 50:50 (BLEND50), and 75:25 (BLEND75) using THF as the mutual solvent. The miscibility of the blends was evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). Among these, BLEND25 was miscible while BLEND50 and BLEND75 were partially miscible. Furthermore, BLEND25 formed apatite layers on its surface as evidenced in a biomimetic study performed. These novel blends showed cell adhesion and proliferation comparable to PLAGA. However, the PNEA(50)PhPh(50) component in the blends was able to increase the phenotypic expression and mineralized matrix synthesis of the primary rat osteoblasts (PRO) in vitro. Blends of high strength PNEA(50)PhPh(50) and 85:15 PLAGA are promising biomaterials for a variety of musculoskeletal applications.

Treatment of Freiberg disease with intra-articular dorsal wedge osteotomy and absorbable pin fixation

BACKGROUND

The purpose of this study was to evaluate the outcome of intra-articular dorsal wedge osteotomy and absorbable pin fixation for the treatment of Freiberg disease.

METHODS

From January of 1997, to July of 2003, 12 patients with symptomatic Freiberg disease had intra-articular dorsal wedge osteotomy through the affected metatarsal head fixed with absorbable polyglycolide pins. All 12 patients were women with an average age of 36 (range 16 to 59) years. The Smillie stage of necrosis ranged from II to V. Active range-of-motion exercise was allowed after 4 weeks of short-leg walking cast wear, and weightbearing on the forefoot was allowed after radiographic union was achieved. The mean followup was 45 (range 22 to 84) months.

RESULTS

Radiographically, solid healing of all osteotomies was observed at an average of 10 (range 8 to 16) weeks. There was no evidence of displacement, osteolysis, sinus formation, or progression of osteonecrosis at final followup. Pain measurement on a visual analog scale had improved significantly from an average of 8.0 to 2.3 (p<0.05). The range of motion of the metatarsophalangeal joint increased by a mean of 26 (range 5 to 60) degrees. All patients were satisfied with the results and would have the surgery again.

CONCLUSIONS

In patients with Freiberg disease, intra-articular dorsal wedge osteotomy restores congruity of the metatarsophalangeal joint, and fixation with absorbable pins provides adequate fixation and avoids a second procedure for implant removal.

Locally delivered TGF-beta1 and IGF-1 enhance the fixation of titanium implants: a study in dogs

BACKGROUND

Osteogenic growth factors have been suggested to enhance the fixation of implants used in joint replacement. We examined the effect of locally delivered transforming growth factor-beta1 and insulin-like growth factor-1 in a biodegradable poly (D, L-lactide) coating.

MATERIAL AND METHODS

In a paired study using 9 dogs, unloaded titanium implants surrounded by a 1-mm gap were inserted into the proximal humerus. The growth factors were incorporated in a poly (D, L-lactide) coating at a 1% (w/w) ratio of TGF-beta1 and a 5% (w/w) ratio of IGF-1. Control implants were uncoated. After 4 weeks, the implants were evaluated by mechanical push-out test and by histomorphometry.

RESULTS

A twofold increase was seen in mechanical fixation (strength, stiffness, energy absorption) for the growth factor-treated implants (p = 0.04). Similar results were seen in histomorphometry, as bone ongrowth was 2.5 times higher (p = 0.02), and gap healing was 30-110% higher (p = 0.04) for the growth factor-treated implants than for the control implants. Ongrowth of fibrous tissue was eliminated by the treatment.

INTERPRETATION

TGF-beta-1 and IGF-1, locally delivered in a biodegradable poly(D,L-lactide) coating, enhance the mechanical fixation and osseointegration of titanium implants in cancellous bone, and no fibrous tissue is produced in the growth factor treated implants.

Less is more: lag screw only fixation of lateral malleolar fractures

Displaced fractures of the lateral malleolus are typically treated with plate osteosynthesis with or without the use of lag screws, and immobilisation in a plaster cast for up to 6 weeks. Fixation through a smaller incision with less metal, such as lag screw only fixation, would theoretically lead to decreased infection rates and less irritation caused by hardware. The purpose of this study was to evaluate the benefits and success of lag screw only fixation of the lateral malleolus in non-comminuted oblique fractures of the lateral malleolus. A total of 25 patients who had non-comminuted unstable oblique fractures of their lateral malleolus that had been surgically fixed with lag screws only were retrospectively evaluated. All patients were younger than 60 years of age. Evaluation of the success of fixation, complications, resultant mobility and patient satisfaction was based on information gathered from chart reviews, X-ray findings and a standardised questionnaire based on the AOFAS Foot and Ankle Outcomes Questionnaire. These results were compared to an age-matched group of 25 consecutive patients treated with plate osteosynthesis. Of the 25 patients fixed with lag screws, nine had an unstable fracture of the lateral malleolus only, ten were bimalleolar fractures and six were trimalleolar. Eighteen patients were treated with two lag screws, and seven were treated with three lag screws. The bi- and trimalleolar fractures were treated with standard partially threaded cancellous screws. None of the lag screw-only group lost reduction. There were no documented wound infections in the lag screw group as compared to three deep infections in the plate group. Lag screw-only patients reported no palpable hardware as compared to 50% of the plate group. AOFAS scores at a mean of 12 months post-operative were similar in both groups. Lag screw only fixation of the lateral malleolus is a safe and effective method that has a number of advantages over plate osteosynthesis, in particular less soft tissue dissection, less prominent, symptomatic and palpable hardware and a reduced requirement for secondary surgical removal.

Long-term magnetic resonance imaging evaluation of bioresorbable anterior cervical plate resorption following fusion for degenerative and traumatic disk disruption

STUDY DESIGN

A retrospective magnetic resonance imaging (MRI) review of a series of patients who underwent a single-level anterior cervical discectomy and fusion followed by anterior plate stabilization using an anterior cervical resorbable mesh plate and screw system.

OBJECTIVE

MRI evaluation of the long-term implant resorption properties of a bioresorbable anterior cervical plate and the adjacent peri-implant soft tissue environment.

SUMMARY OF BACKGROUND DATA

The use of bioresorbable anterior cervical plates for immediate cervical stabilization following an anterior cervical discectomy and fusion presents several distinct advantages over metallic instrumentation. Bioresorbable polymers may diminish, by their resorbability, implant-related complications such as loosening, migration, and failure of instrumentation, as well as stress shielding of the underlying fusion. Information on the intermediate and long-term bony and soft tissue reaction to the resorption byproducts of these biomaterials is limited.

METHODS

There were 9 consecutive patients who underwent single-level anterior cervical decompression and fusion using allograft cortical bone, followed by bioresorbable polylactide anterior mesh plate and screw fixation. Following institutional review board approval, 5 of the 9 patients agreed to postoperative MRI assessment of the peri-implant area. An independent radiologist then characterized implant degradation, and the presence of soft tissue inflammation and swelling during the resorption phase of the bioresorbable plate.

RESULTS

At an average follow-up of 32 months, MRI assessment showed no evidence of soft tissue swelling or inflammation related to the resorption of a bioresorbable anterior plate in any of the 5 patients. In addition, none of the patients complained of any dysphagia or phonation difficulties.

CONCLUSIONS

Based on MRI assessment, these devices, at more than 2-year follow-up, did not indicate any local chronic inflammation or swelling resulting from their degradation. Clinical symptoms of dysphagia or dysarthria, a common reported problem following anterior cervical spine procedures, were not observed in any patient.

Evaluation of biodegradable polyesters modified by type II collagen and Arg-Gly-Asp as tissue engineering scaffolding materials for cartilage regeneration

Synthetic biodegradable polyesters poly(L-lactide) (PLLA) and poly(D,L-lactide-coglycolide) (PLGA) (50:50) modified by porcine type II collagen and an Arg-Gly-Asp (RGD)-containing protein were evaluated as scaffolds for cartilage regeneration in this study. Cytocompatibility of the polymer films was tested using immortalized chondrocytes. Neocartilage formation in vitro on cell-seeded scaffolds was further examined using primary porcine chondrocytes. The inflammatory response of the scaffolds was evaluated subcutaneously in rats. A pilot animal study was conducted, in which rabbit allogeneic chondrocyte-seeded scaffolds were implanted to repair the defected rabbit knee cartilage. The results demonstrated that PLGA as well as its blends with PLLA had better cell growth than pure PLLA, and that type II collagen enhanced, but RGD inhibited cell proliferation. Scaffolds made of blended PLLA/PLGA had larger dynamic compressive modulus compared to scaffolds made of PLLA or PLGA single polymer. Chondrocyte-seeded scaffolds modified by type II collagen without RGD had the greater number of cells as well as higher glycosaminoglycan (GAG) and collagen contents compared to scaffolds without type II collagen modification or scaffolds further modified with RDG. Type II collagen modification prevented infiltration by host tissue and capsule formation. Unmodified PLLA and PLLA/PLGA constructs demonstrated persisting inflammatory response after 6 months, while all type II collagen-modified PLLA/PLGA constructs showed complete repair and no inflammation. Partial or full repair was observed after 2 months of postimplantation in type II collagen-modified PLLA/PLGA constructs, with equal cellularity and 75-80% matrix contents of a normal rabbit articular cartilage. It was concluded that PLLA/PLGA blended scaffolds modified by type II collagen were a potential tissue engineering scaffold for cartilage regeneration.

Long-term tissue response to bioabsorbable poly-L-lactide and metallic screws: an experimental study

Late, clinically manifest, adverse inflammatory reactions have sometimes occurred after the use of slowly degrading bioabsorbable poly-l-lactide (PLLA) devices in clinical series of bone fixation. In this study, long-term tissue response to bioabsorbable fracture fixation screws made of poly-l-lactide and to similar metallic screws in cancellous bone was examined and compared with intact bone. The postoperative evaluation of the rabbit femora was performed by using plain radiography, microradiography, histology, histomorphometry, and oxytetracycline labeling studies. The follow-up times were 36 and 51 months in groups of 15 and 14 rabbits, respectively. A walling-off response by formation of trabecular bone which outlined the screw profile was observed in the PLLA and metallic groups both. Connective tissue between this bone front and the implant was seen only in the PLLA group. There was no difference in the thickness of the layer between the two follow-up groups. Between the surgically handled femora and the intact control bone, there was no statistically significant difference in the amount of trabecular bone. The osteoid formation activity in the tissue-implant interface showed no differences between the groups. However, active osteoblasts were visible only in the PLLA group. The amount of birefringent PLLA material diminished between the 36-month and the 51-month follow-up groups. Within the follow-up times of this study, both the PLLA screws and the metallic screws were rather inert. Also, long-term walling-off was a typical response to both PLLA and metallic screws in cancellous bone. PLLA screws did not evoke any osteostimulatory reaction over the long-term follow-up. The findings clearly demonstrated that the overall degradation process of PLLA was very slow and accompanied by fibrous tissue formation. Macrophage activity seemed to be related to the slow degradation process of PLLA and might be associated with the formation of connective tissue replacing the original implant. The results of this study showed no significant differences between the bioabsorbable PLLA screws and the metallic screws in biocompatibility, and no signs of inflammatory foreign-body reactions occurred during the follow-up.

Deleterious tissue reaction to an alkylene bis(dilactoyl)-methacrylate bone adhesive in long-term follow up after screw augmentation in an ovine model

Biomaterials are designed to support orthopedic surgeons and once implanted they will help the body to heal itself. In this way one of the most attractive substances are biomaterials that allow gluing of bone fragments and implant fixation. Although no bone adhesive is established for practical use in clinical practice yet, there is evidence in vitro and in vivo that a new class of bone adhesives based on alkylene bis(dilactoyl)-methacrylates may meet the requirements to bridge the gap between bench and bedside. The purpose of this experimental study was to investigate the long-term biocompatibility as well as the integration in the remodeling process of a new polymer of this group of substances that was used for both fragment adaptation and implant fixation in a large-scale animal model. In 24 sheep the lateral tibial condyle was osteotomized and refixed by three cortical screws. In 12 of them overdrilling the bone thread of one screw was performed to simulate the poor mechanical properties of osteoporotic bone and the polymer was used in this setting for screw augmentation, furthermore the osteotomy surface was covered with polymer before osteosynthesis to analyze the influence of the material on bone healing. In the other 12 sheep that served as controls osteosynthesis was performed without a polymer. All animals were permitted to walk immediately after surgery under full weight bearing conditions. Six animals of the polymer group and six animals of the control group were analyzed after 6 weeks and 6 months, respectively. Bone healing and implant integration was evaluated by contact X-rays, histology and histomorphometric quantification. After 6 weeks integrity of the healing bone in the polymer group was preserved as compared to the controls, albeit signs of prolonged aseptic inflammation were observed in the polymer group, which is in line with previous reports. In sharp contrast after 6 months, extensive tissue destruction was observed in all animals of the polymer group that was attributed to a massive foreign body reaction at the histological level. These long-term results suggest that (i) short-term observation not always allow valid conclusions regarding the biocompatibility of biomaterials, (ii) that biocompatibility might vary between species, and (iii) that the polymer used in this setting, although previously attributed to be a good candidate for clinical use in patients, does not meet the necessary criteria and tremendously interferes with the physiology of skeletal repair.

MRI study of bioabsorbable poly-L-lactic acid devices used for fixation of fracture and osteotomies

BACKGROUND

The overall clinical results of bioabsorbable fixation devices made of poly-L-lactic acid (PLLA) used for fixation of fractures, bone grafting, and osteotomies have been favorable. However, clinical studies demonstrated no sign of normal bony architecture restored after surgery, although implant channels had been filled with fibrous tissue. The purpose of the present retrospective study was to examine the extent of structural changes in PLLA devices (PLLA-Ds) for fixation of rotational acetabular osteotomies and displaced malleolar ankle fractures using magnetic resonance imaging (MRI).

METHODS

Altogether, 14 patients with osteoarthritis of hip joints and 15 with displaced malleolar ankle fractures were operated on using PLLA-D (NEOFIX). Of these patients, 22 were finally enrolled in the study, and the period from operation to the time of the study ranged from 17 to 78 months. The postoperative radiographic findings were evaluated for union, and changes around the implant holes were classified as sclerosis, resorption, or no change. MRI was carried out to estimate changes in the PLLA-Ds.

RESULTS

Bone union was obtained in all cases; clinical complications such as infection, joint effusion, soft tissue irritation due to PLLA-D deviation, and motion pain in the joints were not observed. The MRI study suggested that water content in PLLA-D increased mainly due to biodegradation and that implants were not replaced by bony tissue.

CONCLUSIONS

The PLLA-Ds were degraded but were not replaced by bony tissue during the observation period. Considering these findings and the assumption that in bony tissues mechanical strength of PLLA-D decreases with time, attention should be paid to mechanical insufficiency, which may occur when the cross-sectional area of a PLLA-D extends beyond the cross-sectional area of the osteosynthesis site.

Biological performance of a new β-TCP/PLLA composite material for applications in spine surgery:In vitro andin vivo studies

The objective of this research was to carry out an in vitro and in vivo study of the biological performance of PLLA/beta-TCP composite materials, to estimate the scope of their potential applications in bone surgery. Samples with increasing beta-TCP (0-60% w/w) contents were processed by injection molding. The in vitro study consisted of an evaluation of inflammatory potential by assaying the IL-1alpha secreted by monocytes, and then cell proliferation (counting) and phenotype expression (PAL and I collagen) in human osteogenous cells. The in vivo study was carried out using cylindrical implants of composite materials composed of composite materials containing 0 or 60% beta-TCP and pure beta-TCP, respectively. The implants were inserted in femoral sites in rabbits, using the Kathagen protocol. Each animal received a 60% implant, with either a 0 or a 100% implant in the contralateral femur, so that the materials could be compared with one another. Five animals were examined for each material and implantation period, giving a total of 30 animals. This study showed that adding increasing percentages of beta-TCP to a lactic acid polymer matrix stimulated the proliferation of human osteogenous cells and synthesis of the extracellular bone matrix in a dose-dependent manner. In vivo results indicate that, in comparison with pure PLA, tricalcium phosphate-containing composite materials had faster degradation kinetics, caused less inflammatory reaction, and promoted contact osteogenesis. The composite material containing 60% beta-TCP demonstrated a similar performance to pure tricalcium phosphate bone grafts in terms of osteogenesis, and is apparently compatible with the production of intra-osseous implants for situations representing high levels of mechanical strain.

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.

Bone repair in the twenty-first century: biology, chemistry or engineering?

Increases in reconstructive orthopaedic surgery, such as total hip replacement and spinal fusion, resulting from advances in surgical practice and the ageing population, have lead to a demand for bone graft that far exceeds supply. Consequently, a number of synthetic bone-graft substitutes (BGSs) have been developed with mixed success and surgical acceptance. Skeletal tissue regeneration requires the interaction of three basic elements: cells, growth factors (GFs) and a permissive scaffold. This can be achieved by pre-loading a synthetic scaffold with GFs or pre-expanded cells; however, a 'simpler' approach is to design intrinsic 'osteoinductivity' into your BGS, i.e. the capability to recruit and stimulate the patient's own GFs and stem cells. Through investigation of the mechanisms controlling bone repair in BGSs, linking interactions between the local chemical and physical environment, scientists are currently developing osteoinductive materials that can stimulate bone regeneration through control of the scaffold chemistry and structure. Moreover, this body of research is providing the foundations for future generations of BGSs and bone-repair therapies and may ultimately contribute towards improving the quality of life through maintenance of the skeleton and reversal of disease states, as opposed to the mending of broken bones that we currently practice. Will we be able to grow our own bones in a bioreactor for use as autologous graft materials in the future? Could surgery be limited to accidental trauma cases, with greater restoration of function through biochemical or gene therapies? The technology and research probes necessary to this task are currently being developed with the advent of nanotechnology, genomics and proteomics: are we about to embark on a chemical revolution in medicine? This paper aims to discuss some of the current thinking on the mechanisms behind bioactivity and biocompatibility in bone and how a fuller understanding of the interactions between cells and the materials used today could bring about completely new approaches for the treatment of bone fracture and disease tomorrow.