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

Biocompatibility and degradation comparisons of four biodegradable copolymeric osteosynthesis systems used in maxillofacial surgery: A goat model with four years follow-up

Applying biodegradable osteosyntheses avoids the disadvantages of titanium osteosyntheses. However, foreign-body reactions remain a major concern and evidence of complete resorption is lacking. This study compared the physico-chemical properties, histological response and radiographs of four copolymeric biodegradable osteosynthesis systems in a goat model with 48-months follow-up. The systems were implanted subperiosteally in both tibia and radius of 12 Dutch White goats. The BioSorb FX [poly(70LLA-co-30DLLA)], Inion CPS [poly([70–78.5]LLA-co-[16–24]DLLA-co-4TMC)], SonicWeld Rx [poly(DLLA)], LactoSorb [poly(82LLA-co-18GA)] systems and a negative control were randomly implanted in each extremity. Samples were assessed at 6-, 12-, 18-, 24-, 36-, and 48-month follow-up. Surface topography was performed using scanning electron microscopy (SEM). Differential scanning calorimetry and gel permeation chromatography were performed on initial and explanted samples. Histological sections were systematically assessed by two blinded researchers using (polarized) light microscopy, SEM and energy-dispersive X-ray analysis. The SonicWeld Rx system was amorphous while the others were semi-crystalline. Foreign-body reactions were not observed during the complete follow-up. The SonicWeld Rx and LactoSorb systems reached bone percentages of negative controls after 18 months while the BioSorb Fx and Inion CPS systems reached these levels after 36 months. The SonicWeld Rx system showed the most predictable degradation profile. All the biodegradable systems were safe to use and well-tolerated (i.e., complete implant replacement by bone, no clinical or histological foreign body reactions, no [sterile] abscess formation, no re-interventions needed), but nanoscale residual polymeric fragments were observed at every system's assessment.

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Foreign-body reactions are a major concern of biodegradable osteosyntheses.

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Amorphous poly(DLLA) showed the most predictable degradation profile.

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Nanoscale residual polymeric fragments could still be observed after 4 years.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Bioabsorbable magnesium versus standard titanium compression screws for fixation of distal metatarsal osteotomies - 3 year results of a randomized clinical trial

BACKGROUND

For the treatment of hallux valgus commonly distal metatarsal osteotomies are performed. Persistent problems due to the hardware and the necessity of hardware removal has led to the development of absorbable implants. To overcome the limitations of formerly used materials for biodegradable implants, recently magnesium has been introduced as a novel implant material. This is the first study showing mid-term clinical and radiological (MRI) data after using magnesium implants for fixation of distal metatarsal osteotomies.

MATERIAL AND METHODS

26 patients with symptomatic hallux valgus were included in the study. They were randomly selected to be treated with a magnesium or standard titanium screw for fixation of a modified distal metatarsal osteotomy. The patients had a standardized clinical follow up and MRI investigation 3 years' post-surgery. The clinical tests included the range of motion of the MTP 1, the AOFAS, FAAM and SF-36 scores. Further on the pain was evaluated on a VAS.

RESULTS

Eight patients of the magnesium group and 6 of the titanium group had a full clinical and MRI follow up 3 years postoperatively. One patient was lost to follow-up. All other patients could be interviewed, but denied full study participation. There was a significant improvement for all tested clinical scores (AOFAS, SF-36, FAAM, Pain-NRS) from pre-to postoperative investigation, but no statistically relevant difference between the groups. Magnesium implants showed significantly less artifacts in the MRI, no implant related cysts were found and the implant was under degradation three years postoperatively.

CONCLUSION

In this study, bioabsorbable magnesium implants showed comparable clinical results to titanium standard implants 3 years after distal modified metatarsal osteotomy and were more suitable for radiologic analysis.

LEVEL OF EVIDENCE

2.

Establishment of a Segmental Femoral Critical-size Defect Model in Mice Stabilized by Plate Osteosynthesis

The use of tissue-engineered bone constructs is an appealing strategy to overcome drawbacks of autografts for the treatment of massive bone defects. As a model organism, the mouse has already been widely used in bone-related research. Large diaphyseal bone defect models in mice, however, are sparse and often use bone fixation which fills the bone marrow cavity and does not provide optimal mechanical stability. The objectives of the current study were to develop a critical-size, segmental, femoral defect in nude mice. A 3.5-mm mid-diaphyseal femoral ostectomy (approximately 25% of the femur length) was performed using a dedicated jig, and was stabilized with an anterior located locking plate and 4 locking screws. The bone defect was subsequently either left empty or filled with a bone substitute (syngenic bone graft or coralline scaffold). Bone healing was monitored noninvasively using radiography and in vivo micro-computed-tomography and was subsequently assessed by ex vivo micro-computed-tomography and undecalcified histology after animal sacrifice, 10 weeks postoperatively. The recovery of all mice was excellent, a full-weight-bearing was observed within one day following the surgical procedure. Furthermore, stable bone fixation and consistent fixation of the implanted materials were achieved in all animals tested throughout the study. When the bone defects were left empty, non-union was consistently obtained. In contrast, when the bone defects were filled with syngenic bone grafts, bone union was always observed. When the bone defects were filled with coralline scaffolds, newly-formed bone was observed in the interface between bone resection edges and the scaffold, as well as within a short distance within the scaffold.

The present model describes a reproducible critical-size femoral defect stabilized by plate osteosynthesis with low morbidity in mice. The new load-bearing segmental bone defect model could be useful for studying the underlying mechanisms in bone regeneration pertinent to orthopaedic applications.

[Biocompatibility of polylactic acid-absorbable root post film]

OBJECTIVE

To study the biocompatibility of the polylactic acid (PLA)-absorbable root post film prepared by solvent evaporation film.

METHODS

The PLA post film-leaching liquor was prepared by the solvent evaporation of PLA root post films, and its biocompatibility was measured. Sources of human gingival fibroblasts (HGF) were cultivated in vitro and identified initially by the immunohistochemistry method. The toxicity reaction, survival rate, and morphological change of HGF incubated in PLA post film-leaching liquor were observed and tested by morphological observation, 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay, and flow cytometry. The HGF were implanted on the PLA post film and observed by 4',6-diamidino-2-phenylindole staining. After implanting the PLA post film, the surrounding subcutaneous tissue of SD rats and the implants were removed from the back of the rats in the 1st, 4th, 8th, and 12th weeks to observe the general condition of the incisions. The organization was given the hematoxylin-eosin (HE) stain to find the organization condition of local tissue inflammation and foreign body reaction through the infiltration degree of inflammatory fibroblasts.

RESULTS

The effects of the PLA post film-leaching liquor on the proliferation of HGF and fibroblast toxicity were insignificant. The living fibroblast rate was similar to the normal control group. The HGF were able to grow on the PLA film. The results of the organization general observation and HE staining of the rats were similar to the results for the control group, which met all the demands made by biological safety.

CONCLUSIONS

The PLA-absorbable root post film prepared by the solvent evaporation film has good biocompatibility and can be used for further clinical research.

The Effect of Local Delivery Doxycycline and Alendronate on Bone Repair

The aim of the present study was to investigate the local effect of 10% doxycycline and 1% alendronate combined with poly(lactic-co-glycolic acid) (PLGA) on bone repair. Thirty rats were divided into three groups, as follows: control group (CG), drug group (DG), and vehicle-PLGA group (VG). Bone defect was created in the right femur and filled with the following: blood clot (CG); PLGA gel, 10% doxycycline and 1% alendronate (DG); or vehicle-PLGA (VG). The animals were euthanized 7 or 15 days after surgery. Bone density, bone matrix and number of osteoclasts were quantified. At 7 days, the findings showed increased density in DG (177.75 ± 76.5) compared with CG (80.37 ± 27.4), but no difference compared with VG (147.1 ± 41.5); no statistical difference in bone neoformation CG (25.6 ± 4.8), VG (27.8 ± 4), and DG (18.9 ± 7.8); and decrease osteoclasts in DG (4.6 ± 1.9) compared with CG (26.7 ± 7.4) and VG (17.3 ± 2.7). At 15 days, DG (405.1 ± 63.1) presented higher density than CG (213.2 ± 60.9) and VG (283.4 ± 85.8); there was a significant increase in percentage of bone neoformation in DG (31.5 ± 4.2) compared with CG (23 ± 4), but no difference compared with VG (25.1 ± 2.9). There was a decreased number of osteoclasts in DG (20.7 ± 4.7) and VG (29.5 ± 5.4) compared with CG (40 ± 9.4). The results suggest that the association of 10% doxycycline and 1% alendronate with PLGA-accelerated bone repair.

A systemic study on key parameters affecting nanocomposite coatings on magnesium substrates

Nanocomposite coatings offer multiple functions simultaneously to improve the interfacial properties of magnesium (Mg) alloys for skeletal implant applications, e.g., controlling the degradation rate of Mg substrates, improving bone cell functions, and providing drug delivery capability. However, the effective service time of nanocomposite coatings may be limited due to their early delamination from the Mg-based substrates. Therefore, the objective of this study was to address the delamination issue of nanocomposite coatings, improve the coating properties for reducing the degradation of Mg-based substrates, and thus improve their cytocompatibility with bone marrow derived mesenchymal stem cells (BMSCs). The surface conditions of the substrates, polymer component type of the nanocomposite coatings, and post-deposition processing are the key parameters that contribute to the efficacy of the nanocomposite coatings in regulating substrate degradation and bone cell responses. Specifically, the effects of metallic surface versus alkaline heat-treated hydroxide surface of the substrates on coating quality were investigated. For the nanocomposite coatings, nanophase hydroxyapatite (nHA) was dispersed in three types of biodegradable polymers, i.e., poly(lactic-co-glycolic acid) (PLGA), poly(l-lactic acid) (PLLA), or poly(caprolactone) (PCL) to determine which polymer component could provide integrated properties for slowest Mg degradation. The nanocomposite coatings with or without post-deposition processing, i.e., melting, annealing, were compared to determine which processing route improved the properties of the nanocomposite coatings most significantly. The results showed that optimizing the coating processes addressed the delamination issue. The melted then annealed nHA/PCL coating on the metallic Mg substrates showed the slowest degradation and the best coating adhesion, among all the combinations of conditions studied; and, it improved the adhesion density of BMSCs. This study elucidated the key parameters for optimizing nanocomposite coatings on Mg-based substrates for skeletal implant applications, and provided rational design guidelines for the nanocomposite coatings on Mg alloys for potential clinical translation of biodegradable Mg-based implants.

STATEMENT OF SIGNIFICANCE

This manuscript describes the systemic optimization of nanocomposite coatings to control the degradation and bioactivity of magnesium for skeletal implant applications. The key parameters influencing the integrity and functions of the nanocomposite coatings on magnesium were identified, guidelines for the optimization of the coatings were established, and the benefits of coating optimization were demonstrated through reduced magnesium degradation and increased bone marrow derived mesenchymal stem cell (BMSC) adhesion in vitro. The guidelines developed in this manuscript are valuable for the biometal field to improve the design of bioresorbable implants and devices, which will advance the clinical translation of magnesium-based implants.

Tissue response after implantation of pure titanium and bioresorbable screws in scapula with postoperative irradiation: an experimental study on rats

OBJECTIVE

The study focuses on the comparison of tissue reaction to titanium and bioresorbable implants with and without postoperative irradiation on an animal model.

MATERIALS AND METHODS

Thirty-nine LEW/W rats were randomly assigned to experimental or control groups. One titanium and one bioresorbable screw (poly-L-lactide [PLLA] and L- and D-lactide poly-L/D-lactide [PDLLA]) were implanted into the left scapulas of 24 rats. Half of them received 30 Gy to the operation site and the other half received 42 Gy. In the control groups, 3 rats received 30 Gy, and 6 rats received 42 Gy to the scapula area without operation; and 6 rats had implants inserted as in the experimental group, but received no postoperative irradiation. The scapulas were removed 14 or 30 days after irradiation and a histologic analysis was performed.

RESULTS

The host tissue reaction to titanium and PLLA-PDLLA screws without postoperative irradiation was of similar intensity. In irradiated animals, the inflammatory tissue reaction was more evident around the titanium screws than around the bioresorbable screws, irrespective of the radiation dose and of the time that elapsed from the irradiation. The reaction was more evident on the 14th day than on the 30th day after the last radiation dose (70 and 86 days after surgery, respectively). The intensity of the inflammatory tissue reaction, irrespective of the implant type, was more intense in the group irradiated with 42 Gy.

CONCLUSIONS

PLLA-PDLLA implants appear to cause less tissue reaction after irradiation and could be safer reconstructive devices than titanium implants for patients undergoing surgery and adjuvant radiotherapy for cancer.

Vancomycin containing PLLA/β-TCP controls experimental osteomyelitis in vivo

Background

Implant-related osteomyelitis (IRO) is recently controlled with local antibiotic delivery systems to overcome conventional therapy disadvantages. In vivo evaluation of such systems is however too little.

Questions/purposes

We asked whether vancomycin (V)-containing poly-l-lactic acid/β-tricalcium phosphate (PLLA/β-TCP) composites control experimental IRO and promote bone healing in vivo.

Methods

Fifty-six rats were distributed to five groups in this longitudinal controlled study. Experimental IRO was established at tibiae by injecting methicillin-resistant Staphylococcus aureus (MRSA) suspensions with titanium particles in 32 rats. Vancomycin-free PLLA/β-TCP composites were implanted into the normal and infected tibiae, whereas V-PLLA/β-TCP composites and coated (C)-V-PLLA/β-TCP composites were implanted into IRO sites. Sham-operated tibiae established the control group. Radiological and histological scores were quantified with microbiological findings on weeks 1 and 6.

Results

IRO is resolved in the CV- and the V-PLLA/β-TCP groups but not in the PLLA/β-TCP group. MRSA was not isolated in the CV- and the V-PLLA/β-TCP groups at all times whereas the bacteria were present in the PLLA/β-TCP group. Radiological signs secondary to infection are improved from 10.9 ± 0.9 to 3.0 ± 0.3 in the V-PLLA/β-TCP group but remained constant in the PLLA/β-TCP group. Histology scores are improved from 24.7 ± 6.5 to 17.6 ± 4.8 and from 27.6 ± 7.9 to 32.4 ± 8.9 in the CV-PLLA/β-TCP and the V-PLLA/β-TCP groups, respectively. New bone was formed in all the PLLA/β-TCP group at weeks 1 and 6.

Conclusions

CV- and V-PLLA/β-TCP composites controlled experimental IRO and promoted bone healing.

Clinical relevance

CV- and V-PLLA/β-TCP composites have the potential of controlling experimental IRO and promoting bone healing.

Changes of procollagen type III N-terminal propeptide (PIIINP) concentrations during healing of mandible fractures treated with biodegradable and titanium fixations

PURPOSE

The aims of the study were to evaluate procollagen type III N-terminal propeptide (PIIINP) concentrations in blood serum of males in the course of normal healing of mandible fractures, and to determine the correlations between kinetic changes of PIIINP, stages of fracture healing and the applied treatment.

MATERIAL AND METHODS

We collected blood serum samples from 43 male patients aged between 20 and 30 years, treated for mandible fractures. The patients were divided into 2 groups depending on the type of osteosynthesis used for immobilization of the fragments. Group I (n=10) consisted of patients whose reduced bone fragments were fixed with biodegradable fixations, while group II (n=33) included patients with titanium osteosynthesis devices. The control group (n=25) consisted of healthy males at the same age. PIIINP concentrations were determined with the radioimmunological method (RIA).

RESULTS

We found a significant increase in PIIINP concentrations in both study groups (I and II) at defined stages of mandible fracture healing. Differences were noticed in the dynamics of the increase depending on the type of applied osteosynthesis devices.

CONCLUSION

The results point to the fact that the injury and/or mandible fracture increase the collagen type III metabolism and its dynamics depends on the type of the used bone fixation.

Do newer-generation bioabsorbable screws become incorporated into bone at two years after ACL reconstruction with patellar tendon graft?: A cohort study

BACKGROUND

Bioabsorbable interference screws are used frequently for graft fixation in ACL (anterior cruciate ligament) reconstruction. The resorption properties of many available screws that are marketed as bioabsorbable are not well defined. The CALAXO (Smith & Nephew Endoscopy) and MILAGRO (DePuy Synthes) bioabsorbable screws contain polymers of poly(lactic-co-glycolic acid) (PLGA) plus additives to encourage osseointegration over time. The purpose of this study was to evaluate radiographic and magnetic resonance imaging (MRI) properties and compare patient-reported outcomes at a minimum of two years of follow-up after ACL reconstruction using CALAXO or MILAGRO bioabsorbable interference screws.

METHODS

A cohort of patients who underwent ACL reconstruction in which the fixation used was either CALAXO or MILAGRO screws returned for repeat radiographs for evaluation of tunnel widening, repeat MRI for evaluation of graft integrity and screw breakdown, and completion of the pain and symptom items of the KOOS (Knee injury and Osteoarthritis Outcome Score) questionnaire.

RESULTS

At a mean of three years (range, 2.5 to 4.0 years) after surgery, thirty-one patients with sixty-two CALAXO screws and thirty-six patients with seventy-two MILAGRO screws returned for repeat evaluation. Two blinded, independent reviewers found no significant differences between the two screw types when comparing radiographs for tibial or femoral tunnel widening or MRIs for graft integrity, tibial and femoral foreign body reactions, or femoral screw degradation. Both reviewers found a significant difference between the two screw types when comparing tibial screw degradation properties (p < 0.01). All analyzed CALAXO screws were rated as partially intact or degraded; the MILAGRO screws were more likely to be rated as intact. No significant differences were noted between the two screw types when comparing the two KOOS subscales.

CONCLUSIONS

CALAXO screws in the tibial tunnel were more likely to be rated as degraded or partially degraded compared with MILAGRO screws at a mean of three years after implantation for ACL reconstruction. Although these newer-generation bioabsorbable screws were designed to promote osseointegration, no tunnel narrowing was noted, and in the majority of cases the remains of the screws were present at approximately three years.

Short-term and long-term effects of orthopedic biodegradable implants

Presently, orthopedic and oral/maxillofacial implants represent a combined $2.8 billion market, a figure expected to experience significant and continued growth. Although traditional permanent implants have been proved clinically efficacious, they are also associated with several drawbacks, including secondary revision and removal surgeries. Non-permanent, biodegradable implants offer a promising alternative for patients, as they provide temporary support and degrade at a rate matching tissue formation, and thus, eliminate the need for secondary surgeries. These implants have been in clinical use for nearly 25 years, competing directly with, or maybe even exceeding, the performance of permanent implants. The initial implantation of biodegradable materials, as with permanent materials, mounts an acute host inflammatory response. Over time, the implant degradation profile and possible degradation product toxicity mediate long-term biodegradable implant-induced inflammation. However, unlike permanent implants, this inflammation is likely to cease once the material disappears. Implant-mediated inflammation is a critical determinant for implant success. Thus, for the development of a proactive biodegradable implant that has the ability to promote optimal bone regeneration and minimal detrimental inflammation, a thorough understanding of short- and long-term inflammatory events is required. Here, we discuss an array of biodegradable orthopedic implants, their associated short- and long- term inflammatory effects, and methods to mediate these inflammatory events.

A novel murine femoral segmental critical-sized defect model stabilized by plate osteosynthesis for bone tissue engineering purposes

Mouse models are invaluable tools for mechanistic and efficacy studies of the healing process of large bone defects resulting in atrophic nonunions, a severe medical problem and a financial health-care-related burden. Models of atrophic nonunions are usually achieved by providing a highly stable biomechanical environment. For this purpose, external fixators have been investigated, but plate osteosynthesis, despite its high clinical relevance, has not yet been considered in mice. We hereby proposed and investigated the use of an internal osteosynthesis for stabilizing large bone defects. To this aim, a 3.5-mm-long segmental bone defect was induced in the mid-shaft of the femur using a Gigli saw and a jig. Bone fixation was performed using a titanium microlocking plate with four locking screws. The bone defect was either left empty or filled with a syngenic bone graft or filled with a coralline scaffold. Healing was monitored using radiographs. The healing process was further assessed using microcomputed tomography and histology 10 weeks after surgery. With the exception of one mouse that died during the surgical procedure, no complications were observed. A stable and reproducible bone fixation as well as a reproducible fixation of the implanted materials with full weight bearing was obtained in all animals tested. Nonunion was consistently observed in the group in which the defects were left empty. Bone union was obtained with the syngenic bone grafts, providing evidence that, although such defects were of critical size, bone healing was possible when the gold-standard material was used to fill the defect. Although new bone formation was greater in the coralline scaffold group than in the left-empty animal group, it remained limited and localized close to the bony edges, a consequence of the critical size of such bone defect. Our study established a reproducible, clinically relevant, femoral, atrophic nonunion, critical-sized defect, low morbidity mouse model. The present study was successful in designing and testing in a small animal model, a novel surgical method for the assessment of bone repair; this model has the potential to facilitate investigations of the molecular and cellular events involved in bone regeneration in load-bearing, segmental-bone defects.

Bone screws have advantages in repair of experimental osteochondral fragments

BACKGROUND

Cartilage defects are created on intraarticular osteochondral fragments at the entrance holes of fixation devices when these fragments are fixed to the original sites. Conventional fixation devices hinder repair of these defects and there is a latent risk of secondary osteoarthritis. We therefore developed a novel fixation device system consisting of bone screws made of cortical bone for osteochondral fragments to improve repair of these surface defects.

QUESTIONS/PURPOSES

We asked whether bone screws had advantages over poly-L-lactic acid (PLLA) screws in terms of (1) gross assessment of the surface, (2) volume and histologic quality of the repair tissue, and (3) biomechanical assessment of the tissue stiffness.

METHODS

We examined gross morphology, microCT, histology, and stiffness of the repaired tissue with PLLA (n = 32) and bone (n = 32) screws in a rabbit model of osteochondral fracture, compared with normal controls (n = 16).

RESULTS

Gross morphology and histology revealed better quality with bone screws than with PLLA screws. Mean repaired volumes in microCT were 70.6% ± 14% with bone screws and 50.3% ± 15% with PLLA screws. Average stiffness values for PLLA screws, bone screws, and normal cartilage were 1.67 ± 0.54 N/mm, 2.63 ± 0.42 N/mm, and 3.15 ± 0.49 N/mm, respectively.

CONCLUSIONS

Our results show better repaired tissue was observed for quality and quantity when chondral fractures were treated with bone screws than when treated with PLLA screws.

CLINICAL RELEVANCE

Bone screws made of cortical bone may have applications in clinical situations for the fixation of intraarticular osteochondral fragments.

Early Stage Foreign Body Reaction against Biodegradable Polymer Scaffolds Affects Tissue Regeneration during the Autologous Transplantation of Tissue-Engineered Cartilage in the Canine Model

To overcome the weak points of the present cartilage regenerative medicine, we applied a porous scaffold for the production of tissue-engineered cartilage with a greater firmness and a 3D structure. We combined the porous scaffolds with atelocollagen to retain the cells within the porous body. We conducted canine autologous chondrocyte transplants using biodegradable poly-l-lactic acid (PLLA) or poly-dl-lactic- co-glycolic acid (PLGA) polymer scaffolds, and morphologically and biochemically evaluated the time course changes of the transplants. The histological findings showed that the tissue-engineered constructs using PLLA contained abundant cartilage 1, 2, and 6 months after transplantation. However, the PLGA constructs did not possess cartilage and could not maintain their shapes. Biochemical measurement of the proteoglycan and type II collagen also supported the superiority of PLLA. The biodegradation of PLGA progressed much faster than that of PLLA, and the PLGA had almost disappeared by 2 months. The degraded products of PLGA may evoke a more severe tissue reaction at this early stage of transplantation than PLLA. The PLLA scaffolds were suitable for cartilage tissue engineering under immunocompetent conditions, because of the retarded degradation properties and the decrease in the severe tissue reactions during the early stage of transplantation.

Osteolysis after rotator cuff repair with bioabsorbable anchors

PURPOSE

The current study was designed to evaluate the rate of osteolysis and the clinical and functional outcomes in patients who underwent mini-open rotator cuff repairs using first generation bioabsorbable suture anchors. Our hypothesis was that patients with osteolysis noted on post-repair MRI would have an accompanying decrease in functional and clinical patient outcomes when compared with patients who did not have osteolysis evident on post-repair MRI.

TYPE OF STUDY

Clinical retrospective study.

METHODS

Between September 2000 and May 2004, 76 patients were repaired using first generation Bio-Corkscrew suture anchors (Arthrex, Naples, FL). 30 patients were available for complete follow-up evaluation. The mean follow-up time was 36 months (range 24-58). Patients were assessed with the Constant-Murley Score, radiographs and magnetic resonance imaging (MRI). Post-operative strength was measured using an Isokinetic Cybex-Dynamometer. 14 patients had osteolysis evident on MRI (Group A) while 16 patients did not have osteolysis on MRI (Group B).

RESULTS

In both groups, a total of 70 bio-anchors were used. 22 anchors showed osteolytic changes on MRI (Group A). Concerning ROM, there was no statistical difference in both groups. The Constant-Score was statistically not different in both groups A (92.4) and B (83.7). On MRI-scans, there were repair failures in both groups (A, 2 reruptures; B, 3 reruptures).

CONCLUSIONS

Although, we found a high rate of osteolysis after rotator cuff repair with bioabsorbable anchors, these results did not change the clinical outcomes after rotator cuff repair. Recurrent tears were not significantly different in both groups and are comparable to rerupture rates in prior studies. More studies are needed to verify the effect of osteolysis over the long term.

Optimizing Injectable Poly-L-Lactic Acid Administration for Soft Tissue Augmentation: The Rationale for Three Treatment Sessions

BACKGROUND

The availability and variety of different injectable modalities has led to a dramatic increase in soft tissue augmentation procedures in recent years. Injectable poly-L-lactic acid (PLLA) is a synthetic, biodegradable polymer device approved in the United States for use in immunocompetent patients as a single regimen of up to four treatment sessions for correction of shallow to deep nasolabial fold contour deficiencies and other facial wrinkles. Injectable PLLA is also approved for restoration and/or correction of signs of facial fat loss (lipoatrophy) in individuals with HIV.

METHODS

The present article provides an overview of previous studies with injectable PLLA, and specifically focuses on the number of recommended treatment sessions and intervals between treatment sessions. The authors also provide two case studies to support their recommendations for an average of three treatment sessions.

RESULTS

Although the specific mechanisms remain hypothetical, injections of PLLA are believed to cause a cascade of cellular events that lead to collagen repair and subsequent restoration of facial volume. Because the development of a response to injectable PLLA is gradual and its duration of effect is long lasting, sufficient time between treatment sessions should be allocated to avoid overcorrection.

CONCLUSION

Studies of injectable PLLA support the hypothesized mode of operation, and the experience and clinical recommendations of the authors that suggest that three treatment sessions are an optimal regimen for use of injectable PLLA in the majority of patients.

Progressive osteolysis of the radius after distal biceps tendon repair with the bioabsorbable screw

BACKGROUND

Several complications have been reported with the use of the PLLA (poly-L-Lactide) bioabsorbable screw in orthopedic surgery. The hypothesis was that the use of a bioabsorbable screw in distal biceps tenodesis results in significant osteolysis of the radial bone. The correlation between osteolysis and functional and clinical outcomes was also studied.

METHODS

All consecutive patients who underwent anatomic repair of the distal biceps tendon with a bioabsorbable screw were included. From the x-ray taken immediately after the surgery, the ratio between the volume of the bone tunnel and the volume of the radius bone section was measured. This relation was calculated at different follow-up periods to obtain the percentage of tunnel enlargement over time. Complications, as well as functional and clinical outcomes, were also assessed. Mayo Elbow Performance Score (MEPS), the quick-Disability Arm Shoulder Hand (DASH), and the Short-Form 12 (SF-12) were used.

RESULTS

Nineteen consecutive patients were available for follow-up. The average initial relative volume occupied by the screw tunnel was 49% of the bone section and increased to 61% at the last follow-up at an average of 22 months (range, 3-62 months). Eight of the 19 patients presented postoperative complications. There was only 1 case of complete bone filling of the tunnel, which was observed at a 5-year and 2-months follow-up. There was no significant correlation between the volume of bone resorption and functional and clinical outcomes.

DISCUSSION

No correlation was found between the volume of bone tunnel and the functional outcome. However, the results indicate that the use of a bioabsorbable screw in distal biceps tendon repair results in significant bone osteolysis.

Is the etiology of pretibial cyst formation after absorbable interference screw use related to a foreign body reaction?

BACKGROUND

Arthroscopically assisted anterior cruciate ligament reconstruction using a bioabsorbable tibial fixation screw is occasionally complicated by pretibial cyst formation. The few case reports describing pretibial cyst formation noted several graft types and fixation techniques, making it difficult to establish one etiology. Some literature suggests cysts form from communication between the joint and pretibial area leading to extravasation of joint fluid, maturing into a cyst. We propose the development of cysts after PLLA screw use may be related to a foreign body reaction.

QUESTIONS/PURPOSES

We propose this foreign body reaction (1) relates to the biochemical breakdown of bioabsorbable materials; and (2) differs from cystic formations resulting from joint communication.

METHODS

We retrospectively reviewed seven patients who developed pretibial cysts at least 2 years after original primary ACL reconstruction surgery. MRI was used to visualize the extent of cystic formation. Cysts were treated by débridement with specimens sent for histologic analysis. Cyst appearance had a 3-year incidence of 5%.

RESULTS

No cyst had an infectious etiology. In all cases, the tibial screw outline was present on MRI, although intraoperatively, the screw was substantially decomposed. Grafts were well incorporated and none of the knees demonstrated anterior laxity. Histologically, cyst material contained fragments of PLLA surrounded by foamy histiocytes, suggesting a foreign body reaction. No cysts recurred.

CONCLUSIONS

Tibial cysts occur in a subset of patients undergoing ACL reconstruction using a bioabsorbable PLLA interference screw. We suspect they arise from a foreign body response to the screw breakdown. Removal is well tolerated.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Effects of a pediatric physeal slide-traction plate on fracture healing: an experimental study in a goat model

BACKGROUND

It has been an intractable issue for the orthopaedic surgeons to treat pediatric epiphyseal injury and surrounding bone fracture using Kirschner wires and screws, etc. Earlier research has indicated that pediatric physeal slide-traction plate (PPSP) can fix bone fracture without restricting growth. However, it is not clear whether this material can be clinically used to treat pediatric epiphyseal injury and surrounding bone fracture.

METHODS

The PPSP and standard plate (SP) were designed to configure to the femoral condyle. Twelve premature female goats were enrolled in this study. Fracture models were successfully established on goats, on which the right femurs were fixed with SP, and the left femurs were fixed with PPSP. Radiographic analysis and biomechanical tests were done at 4 and 8 weeks after surgery.

RESULTS

The callus gray density increased with time going on in each group, at the same postoperational time point, the PPSP group was higher than that of the SP group. The difference between PPSP group and SP group was statistically significant at the same stage (P<0.01). The biomechanical tests showed that the PPSP group was stronger than the SP group in anticompression, antibending, and antitorsion at the same stage (P<0.05). In addition, it was shown through the radiographic analysis that PPSP extended accordingly as the epiphyseal plate grows, and the epiphyseal morphology was considered normal all the time. However, epiphyseal premature closure and angular deformity were observed in the samples of the SP group.

CONCLUSIONS

PPSP contributed greatly to healing of bone fracture with increased callus density and callus strength in the early stage, and did not restrict the growth of the epiphyseal plate. It may be clinically applied in the treatment of pediatric epiphyseal injury and surrounding bone fracture in the future.

LEVEL OF EVIDENCE

Therapeutic level II.

Augmentation of bone defect healing using a new biocomposite scaffold: an in vivo study in sheep

Previous studies support resorbable biocomposites made of poly(L-lactic acid) (PLA) and beta-tricalcium phosphate (TCP) produced by supercritical gas foaming as a suitable scaffold for tissue engineering. The present study was undertaken to demonstrate the biocompatibility and osteoconductive properties of such a scaffold in a large animal cancellous bone model. The biocomposite (PLA/TCP) was compared with a currently used beta-TCP bone substitute (ChronOS, Dr. Robert Mathys Foundation), representing a positive control, and empty defects, representing a negative control. Ten defects were created in sheep cancellous bone, three in the distal femur and two in the proximal tibia of each hind limb, with diameters of 5 mm and depths of 15 mm. New bone in-growth (osteoconductivity) and biocompatibility were evaluated using microcomputed tomography and histology at 2, 4 and 12 months after surgery. The in vivo study was validated by the positive control (good bone formation with ChronOS) and the negative control (no healing with the empty defect). A major finding of this study was incorporation of the biocomposite in bone after 12 months. Bone in-growth was observed in the biocomposite scaffold, including its central part. Despite initial fibrous tissue formation observed at 2 and 4 months, but not at 12 months, this initial fibrous tissue does not preclude long-term application of the biocomposite, as demonstrated by its osteointegration after 12 months, as well as the absence of chronic or long-term inflammation at this time point.

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.

Comparison of bioabsorbable versus metallic implant fixation for physeal and epiphyseal fractures of the distal tibia

BACKGROUND

Transepiphyseal screw fixation of displaced distal tibial epiphyseal fractures is the most common method of treatment for these intraarticular injuries. Recent literature indicates that retained transepiphyseal metallic screws cause an increase in ankle joint contact pressure, thus favoring screw removal. Our hypothesis is that bioabsorbable screw fixation is an alternative to metallic fixation, which offers similar results without the need for screw removal.

METHODS

This is a retrospective review of distal tibial epiphyseal ankle fractures treated with screw fixation. Two groups, those treated with bioabsorbable screw fixation (group B, n = 24) and those with metallic screw fixation (group M, n = 26), were compared (t test) for differences in clinical and radiographic outcomes.

RESULTS

Analysis of demographic data revealed no significant differences between groups for sex, ethnicity, age, and height. Group B was significantly heavier than group M (67.4 vs 55.6 kg; P = 0.0496). Each group had a similar number of Salter-Harris types III and IV medial malleolus fractures and transitional fracture types. There was no significant difference between groups in the time from injury to fixation or in operative time. Radiographically, there were no nonunions in either group, and at final follow-up, 1 patient in group B had distal tibial joint line irregularity versus 3 in group M. Clinically, there were no significant differences between groups in time to full weight bearing or time to full activities.There were fewer complications in group B. A single case of loss of reduction requiring revision fixation occurred in each group. There was one documented growth arrest in group M and 2 suspected growth arrests in each group. Two patients in group M were successfully treated for a superficial wound infection with oral antibiotics. Fourteen patients in group M underwent planned screw removal.

CONCLUSIONS

Bioabsorbable screw fixation can be used for distal tibial epiphyseal fractures with no increase in operative time, nonunion rate, number of unplanned secondary surgeries, or other complications. The use of bioabsorbable screws eliminates the need for epiphyseal screw removal. A prospective randomized study is planned to eliminate the potential selection bias and to standardize clinical and radiographic follow-up.

LEVEL OF EVIDENCE

Level III, case-control study.

Tibial fixation of bone-patellar tendon-bone grafts in anterior cruciate ligament reconstruction: a cadaveric study of bovine bone screw and biodegradable interference screw

BACKGROUND

The use of interference screw fixation for bone-patellar tendon-bone grafts in anterior cruciate ligament fixation is well established. No previous study has compared bovine bone screws and biodegradable interference screws or demonstrated their efficacy for requirements associated with early rehabilitation.

HYPOTHESIS

There is no difference in tension loss and pull-out strength between bovine bone screws and biodegradable interference screws.

STUDY DESIGN

Controlled laboratory study.

METHODS

Anterior cruciate ligament reconstructions with bone-patellar tendon-bone allografts were performed in 40 human tibiae from 20 donors. A bovine bone screw and a polylevolactide interference screw were used for tibial fixation in each pair. A cyclic testing protocol with varying magnitude and orientation of the graft loading was developed. Cyclic tests were performed at 1 Hz for 5000 cycles with a peak force of 200 N applied to the graft. Survival rate and postcyclic-test pull-out strength were compared.

RESULTS

Fifteen of 20 reconstructions fixed with bovine bone screws and 17 of 20 fixed with biodegradable screws reached 5000 cycles. Graft tension drop after the 5000 cycles averaged 19.7 N ( +/- 12.9) for bovine bone screws and 18.9 N ( +/- 16.3) for biodegradable screws. There were no significant differences in tension loss and pull-out strength between the 2 types of screws.

CONCLUSION

Bovine bone screws are comparable to biodegradable interference screws in providing stable tibial fixation in anterior cruciate ligament reconstruction using bone-patellar tendon-bone allografts.

CLINICAL RELEVANCE

The use of bovine bone screws may be comparable to the popular biodegradable interference screws used for anterior cruciate ligament reconstruction in postsurgery rehabilitation.

Bioabsorbable fixation for Mitchell's bunionectomy osteotomy

Although bioabsorbable pins have been used to successfully stabilize a wide range of osteotomies, to date there have been not published studies describing the results of their use for fixation of first metatarsal osteotomies in Mitchell's bunionectomy. The purpose of this retrospective investigation of 78 first metatarsal osteotomies was to evaluate the effectiveness of polydioxanone bioabsorbable pin fixation of the first metatarsal osteotomy in Mitchell's bunionectomy. The mean length of the first metatarsal preoperatively was 6.65 +/- 0.42 cm, and postoperatively it was 6.31 +/- 0.57 cm (P < .0001). The mean first IMA preoperatively was 17.59 degrees +/- 3.51 degrees , and postoperatively it was 9.91 degrees +/- 2.58 degrees (P < .0001). The mean HVA preoperatively was 29.74 degrees +/- 4.70 degrees , and postoperatively it was 12.89 degrees +/- 4.26 degrees (P < .0001). The average time to bony union was 6.01 +/- 0.61 weeks. There were 5 (6.41%) superficial wound infections that resolved with oral antibiotics, 1 (1.28%) deep-seated infection requiring surgical debridement, and 2 (2.56%) patients complained of transfer metatarsalgia. Five (6.41%) patients displayed persistent localized translucency at some portion of the osteotomy site on postoperative radiographs, and there were no cases of progressive osteolysis. In this series there were no complications related to pin fracture or failure of osteotomy fixation. Based on the results observed in this study, it appears that the use of polydioxanone bioabsorbable pins provides satisfactory stabilization of the first metatarsal osteotomy in Mitchell's bunionectomy, and was not associated with any serious complications.

LEVEL OF CLINICAL EVIDENCE

2.

Effects of oxygen plasma treatment on adipose-derived human mesenchymal stem cell adherence to poly(L-lactic acid) scaffolds

Plasma treatment of substrate surfaces can be utilized to improve adhesion of cells to tissue-engineered scaffolds. The purpose of this study was to enhance cell adhesion to non-woven poly(L-lactic acid) (PLLA) scaffolds using oxygen plasma treatment to increase surface hydroxyl groups and thereby enhance substrate hydrophilicity. It was hypothesized that oxygen plasma treatment would increase the number of adipose-derived human mesenchymal stem cells (hMSCs) that adhered to melt-blown, non-woven PLLA scaffolds without affecting cell viability. The number of cells that adhered to the oxygen plasma-treated (10 min at 100 W) or untreated PLLA scaffolds was assessed at 2, 4, 8, 12, 24 and 48 h post-seeding via DNA analysis. Cell viability and morphology were also assessed at 2, 4, 8, 12 and 24 h post-seeding via a live/dead assay and hematoxylin staining, respectively. Oxygen plasma treatment decreased the contact angle of water from 75.6 degrees to 58.2 degrees , indicating an increase in the surface hydrophilicity of PLLA. The results of the DNA analysis indicated that there was an increased number of hMSCs on oxygen plasma treated scaffolds for two of the three donors. In addition, oxygen plasma treatment promoted a more even distribution of hMSCs throughout the scaffold and enhanced cell spreading at earlier time points without altering cell viability. This early induction of cell spreading and the uniform distribution of cells, in turn, may increase future proliferation and differentiation of hMSCs under conditions that simulate the microenvironment in vivo.

Comparison of bioabsorbable pins and nails in the fixation of adult osteochondritis dissecans fragments of the knee: an outcome of 30 knees

BACKGROUND

The optimal device for the fixation of osteochondritis dissecans fragments of the knee remains controversial and lacks long-term results.

PURPOSE

To review a group of young adults with osteochondritis dissecans of the knee treated with arthroscopic fixation of the fragment using bioabsorbable pins and nails and to examine the medium-term outcome of the fixation via magnetic resonance imaging and clinical evaluation.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Twenty-eight patients (30 knees) with osteochondritis dissecans of the knee were treated with arthroscopic fixation using bioabsorbable, self-reinforced poly-L-lactide pins and nails. All patients were young adult males with closed physes. The average follow-up time was 5.4 years (range, 3-12). At follow-up, magnetic resonance imaging studies were used to evaluate subchondral bone healing, and the outcome was evaluated by the Kujala score.

RESULTS

The functional results were excellent or good for 73% of the patients in the nail group versus 35% in the pin group. The lesions treated were large, with an average size of 447 mm(2), affecting the weightbearing area in the majority of the patients. On magnetic resonance imaging, incomplete bone consolidation was predominant in the pin group.

CONCLUSIONS

Arthroscopic fixation with bioabsorbable nails seems to be a suitable method of repair for osteochondritis dissecans of the adult knee and appears to be superior to arthroscopic fixation with bioabsorbable pins.

In vivo micro-CT scanning of a rabbit distal femur: repeatability and reproducibility

Before in vivo micro-CT scanning can be used to investigate femoral trabecular microarchitecture over time in rabbits, its repeatability and reproducibility must be demonstrated. To accomplish this, both distal femurs of two 6-month-old New Zealand white rabbits were scanned five times each in 1 day under different conditions (repeatability). Scanning was done at 28 microm isotropic voxel size to produce five image stacks of each femur. Three operators then followed a standard image processing protocol (reproducibility) to isolate two separate cubes from each anterior femoral condyle [total n = (8 cube sites)(5 scans)(3 operators) = 120]. Bone volume fraction (BV/TV) of the eight different cube sites (sample) ranged from 0.408 to 0.501 (mean: 0.453); trabecular thickness (Tb.Th) ranged from 158.1 to 185.5 microm (mean: 168.6 microm); and trabecular separation (Tb.Sp) ranged from 179.4 to 233.1 microm (mean: 204.7 microm). Using ANOVA and the variance component method, the total process variation was +/- 14.1% of the mean BV/TV of 0.453. The sample variation was +/- 13.9% (p < 0.001), the repeatability was +/- 2.1% (p < 0.001), and the reproducibility was +/- 0.1% (p > 0.05). Results were similar for Tb.Th and Tb.Sp. Though the contribution due to repeatability was statistically significant for each of the three indices, the natural sample differences were far greater than differences caused by repeated scanning under different conditions or by different operators processing the images. These findings suggest that in vivo micro-CT scanning of rabbit distal femurs was repeatable and reproducible and can be used with confidence to measure differences in trabecular bone microarchitecture at a single location in a longitudinal study design.