Objectives. Bioresorbable orthopaedic devices with calcium phosphate (CaP) fillers are commercially available on the assumption that increased calcium (Ca) locally drives new bone formation, but the clinical benefits are unknown. Electron beam (EB) irradiation of polymer devices has been shown to enhance the release of Ca. The aims of this study were to: 1) establish the biological safety of EB surface-modified bioresorbable devices; 2) test the release kinetics of CaP from a polymer device; and 3) establish any subsequent beneficial effects on bone repair in vivo. Methods. ActivaScrew Interference (Bioretec Ltd, Tampere, Finland) and poly(L-lactide-co-glycolide) (PLGA) orthopaedic screws containing 10 wt% β-tricalcium phosphate (β-TCP) underwent EB treatment. In vitro degradation over 36 weeks was investigated by recording mass loss, pH change, and Ca release. Implant performance was investigated in vivo over 36 weeks using a lapine femoral condyle model. Bone growth and osteoclast activity were assessed by histology and enzyme histochemistry. Results. Calcium release doubled in the EB-treated group before returning to a level seen in untreated samples at 28 weeks. Extensive bone growth was observed around the perimeter of all implant types, along with limited osteoclastic activity. No statistically significant differences between comparative groups was identified. Conclusion. The higher than normal dose of EB used for surface modification did not adversely affect tissue response around implants in vivo. Surprisingly, incorporation of β-TCP and the subsequent accelerated release of Ca had no significant effect on in vivo implant performance, calling into question the clinical evidence base for these commercially available devices. Cite this article: I. Palmer, S. A. Clarke, F. J Buchanan. Enhanced release of calcium phosphate additives from bioresorbable orthopaedic devices using irradiation technology is non-beneficial in a rabbit model: An animal study. Bone Joint Res 2019;8:266–274. DOI: 10.1302/2046-3758.86.BJR-2018-0224.R2

Abstract. Objectives. Osteoporotic fractures tend to be more challenging than fractures in healthy bone and the efficacy of metal screw fixation decreases with decreasing bone mineral density making it more difficult for such screws to gain purchase. This leads to increased complication rates such as malunion, non-union and implant failure (1). Bioresorbable polymer devices have seen clinical success in fracture fixation and are a promising alternative for metallic devices but are rarely used in the osteoporotic population. To address this, we are developing a system that may allow osteoporotic patients to avail of bioresorbable devices (2) but it is important to establish if patients have any reservations about having a plastic resorbable device instead of a metal one. Therefore the aim of this study was to explore the acceptability of bioresorbable fracture fixation devices to people with osteoporosis. Methods. A cross sectional descriptive study was conducted in a UK wide population using convenience sampling. An online survey comprising nine survey questions and nine demographic questions was developed in Microsoft Teams and tested for face validity in a small pilot study (n=6). Following amendments and ethical approval, the survey was distributed by the Royal Osteoporosis Society on their website and social media platforms. People were invited to take part if they lived in the UK, were over 18 years old and had been diagnosed with osteoporosis. The survey was open for three weeks in May 2023. Responses were analysed using descriptive statistics. Results. There were 112 responses. Eight participants had not been diagnosed with osteoporosis and therefore did not meet the study criteria. Of the remaining 104, 102 were female and 2 were male and 102 were white (2 chose not to disclose their ethnicity). The majority of participants were aged 55–64 (34.6%) or 65–74 (37.5%), were college/university educated (38.5%) and had previously sustained a fragility fracture (52.9%). Only 3.9% of participants had heard of bioresorbable fracture fixation devices compared to 62.5% for metal devices. Most people were unsure if they would trust one type of device over the other (58.7%) and would ask for more information if their surgeon were to suggest using a bioresorbable device to fix their fracture (61.5%). The most commonly reported concerns were about device safety and efficacy: toxicity of the degradation products and the device breaking down too early before the fracture had healed. Two participants cited environmental concerns about increased use of plastics as a reason they would decline such a device. Conclusions. As expected, participants had little to no knowledge of bioresorbable polymer fixation devices. In general, they were willing to be guided by their surgeon but would require supporting information on the safety and efficacy of their long-term use. The results of this study show that it will be important to have relevant and understandable information to give patients when recommending these devices as treatments to ensure and support a shared-decision approach to patient care. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction. In recent years, there has been a growing interest in bioresorbable metals. Orthopaedic components made from these materials do not require removal by secondary surgery, and offer superior load bearing capability compared to the existing biodegradable polymers. Research on bioresorbable metals have largely focused on alloys based on a subset of the Mg-Zn-Ca ternary system [1, 2], which are pre-existing elements inside the human body. Cytocompatibility assessments of these alloys have reported no signs of inflammation or adverse cellular reactions [2-4]. Rather than designing for longevity, bioresorbable metals rely on their tendency to corrode in a controlled manner. Hence, controlling their corrosion rates is of utmost importance. In the present work, we have explored the effect of compositional variation on the properties of the Mg-Zn-Ca amorphous metals. Subsequent characterisations are performed to assess their suitability as a bioresorbable material. Materials and Methods. A mixture of pure elements and master alloys, namely magnesium, zinc, calcium, and Mg-Ca master alloy, were melted in an induction furnace, followed by injection casting to produce the amorphous metallic samples. Pure magnesium (crystalline) was also used in the subsequent characterisation tests for comparison. The thermophysical properties of the as-cast amorphous metals were characterized using x-ray diffraction (XRD) and differential scanning calorimetry (DSC). The biocorrosion performance was assessed by a combination of immersion, potentiodynamic polarisation (PDP) and hydrogen evolution studies. These tests were conducted in cell media, with a sodium bicarbonate buffer, at 37°C and pH 7.4 in a humidified CO. 2. atmosphere. Results and Discussion. A range of amorphous metal compositions, from Mg-rich to Ca-rich, were successfully produced. XRD confirmed that the alloys were amorphous. Subsequent characterisation tests revealed that minor alterations in composition were not detrimental to thermophysical properties; however, the critical casting size and corrosion rates were much more sensitive to alloy chemistry. In comparison, the Mg-rich alloys have superior corrosion resistance, whereas the Ca-rich alloys have improved thermophysical properties, thereby allowing them to undertake more complex thermoplastic forming processes. Conclusion. We have successfully produced amorphous metals with a range of corrosion resistance and thermophysical properties. The combination of biocompatible elements, superior corrosion resistance and reduced hydrogen evolution, make these amorphous metals more suitable for use as bioresorbable orthopaedic components than their crystalline counterparts. Acknowledgements. The authors would like to thank the Australian Research Council (ARC) for partial funding of this work via the ARC Centre of Excellence for Design in Light Metals (CE0561574)

Research in orthopaedics is now moving away from permanent metallic implants, and looking towards the use of bioresorbable polymers (e.g. PLLA, PGA and related co-polymers) that, when implanted into the injured site, bioresorb as the tissue heals. However, reports of a delayed inflammatory reponse occurring in the late stages of polymer degradation has limited the wide scale use of these polymers. Few studies assess the long-term biocompatibility of these polymers and with an increasing market for bioresorbable materials it is anticipated that this will be a future issue. This work aims to develop a predictive tool that can be used to assess the delayed inflammatory response of poly(D,L-lactide-co-glycolide) (PDLGA) using in vitro tests. An elevated temperature accelerated test (47. o. C) was developed and utilitised to induce predetermined amounts of degradation in PDLGA. This was used to mimic a range of clinically relevant in vivo implantation times up to 5–6 months. All pre-degradion work was performed under sterile conditions, in PBS solution. At predetermined time intervals, indicators of late stage inflammation will be assessed using an MTT cytotoxicity assay, an inflammation antibody array and an ELISA analysis for inflammatory factors, with mouse L929 fibroblasts, RAW264.7 and primary BMDM macrophages. It is hypothosised that at the later degradation time intervals signs of inflammatory factors will be observed. The methodologies developed in this work can be applied to the optimisation of polymer degradation profiles to minimise late-stage inflammatory repsonse and identification of beneficial additives in this regard

Introduction: Accelerated rehabilitation programs following ACL reconstruction require adequate fixation strength. Staple fixation of grafts outside the tibial tunnel has been shown to have fixation strength comparable to interference screws. The use of bioresorbable polymer implants has potentially significant advantages especially if revision is required. The purpose of this study was to evaluate a new bioresorbable fixation staple using an ovine model. Materials and Methods: Forty-eight mature sheep underwent unilateral cranial cruciate ligament (CrCl) reconstruction. The reconstruction comprised a loop of superficial digital flexor tendon (autograft) joined to a prosthetic ligament (LK-15). Femoral fixation was by endobutton. Tibial fixation of the LK-15 was with either a new Poly-L-lactic acid (PLLA) staple (Zimmer Japan/Gunze Ltd.) or a Cobalt-chrome (CoCr) staple. Biomechanical and histological responses were evaluated at 0, 6, 12 and 24 weeks. Results: At all times post-reconstruction there were no significant differences between staple types for construct strength or stiffness (p> 0.05). The staple was not the site of reconstruction failure, and there were no adverse tissue reactions, for either staple type. Fibrous tissue was more often found at the interface of the CoCr staple. Conclusions: The PLLA staple performed biomechanically as well as the metal staple for tibial fixation of cruciate ligament reconstructions. There were no significant observable adverse histological responses over the time intervals examined

Purpose: This work revealed the advantages of percutaneous suture of the Achilles tendon using an improved technique with entirely resorbable material. Material and methods: Thirty cases of subcutaneous tears were operated on two to ten days after the accident (range 24 hr – 7 weeks). We used a 4-thread resorbable V-suture anchored in the calcaneum and, after blocking the ankle in the equine position, on the proximal fragment using two bioresorbable buttons. Postoperatively, immediate weight bearing was progressive using an adjustable and removable orthesis. Active-passive rehabilitation was initiated immediately. The material was left in place indefinitely and was resorbed after three months. Results: We followed these patients for 24 – 8 months. Wound healing was excellent and material tolerance was exceptional (only one complaint of transient calcaneal pain). Objective outcome was comparable with that obtained with conventional suture, with a significant reduction in the risk of skin and neurological complications. There were no cases of recurrent tears. CT and MRI controls confirmed the early healing, the quality of the tendon repair, and material resorption within the expected delay. Subjective outcome was excellent. Discussion: While the results obtained in this series are comparable to those with prior percutaneous techniques, the important improvement was the very significant reduction in skin and neurological complications often reported in other series. It is also noteworthy that there were no recurrent tears. The advantages are even more remarkable compared with surgery. The greater solidity authorises very rapid rehabilitation, similar to protocols advocated for nonoperative care. The limitations on indications appear to be tears seen after three weeks and true calcaneal de-insertions. Conclusion: This technique improves patient comfort and follow-up while allowing safer rehabilitation

This prospective randomized multicenter study compares two methods of bone defect treatment in tibial plateau fractures: a bioresorbable calcium phosphate paste (Alpha-BSM) that hardens at body temperature to give structural support versus Autogenous iliac bone graft (AIBG). One hundred and eighteen patients were enrolled with a 2:1 randomization, Alpha-BSM to AIBG. There was a significant increased rate of non-graft related adverse affects and a higher rate of late articular subsidence (three to nine month period) in the AIBG group. A bioresorbable calcium phosphate material is recommended in preference to the gold standard of AIBG for bone defects in tibial plateau fractures. This prospective randomized multicenter study was undertaken to compare two methods of bone defect treatment: a bioresorbable calcium phosphate paste (Alpha-BSM –DePuy, Warsaw, IN) that hardens at body temperature to give structural support and is gradually resorbed by a cell-mediated bone regenerating mechanism versus Autogenous iliac bone graft (AIBG). One hundred and eighteen adult acute closed tibial plateau fractures, Schatzker grade two to six were enrolled prospectively from thirteen study sites in North America from 1999 to 2002. Randomization occurred at surgery with a FDA recommendation of a 2–1 ratio, Alpha BSM (seventy-eight fractures) to AIBG (forty fractures). Only internal fixation with standard plate and screw constructs was permitted. Follow-up included standard radiographs and functional studies at one year, with a radiologist providing independent radiographic review. The two groups exhibited no significant differences in randomization as to age, sex, race, fracture patterns or fracture healing. There was however, a significant increased rate of non-graft related adverse affects in the AIBG group. There was an unexpected significant finding of a higher rate of late articular subsidence in the three to nine month period in the AIBG group. Recommendations for the use of AIBG for bone defects in tibial plateau fractures should be discouraged in favor of bioresorbable calcium phosphate material with the properties of Alpha BSM. We believe further randomized studies using AIBG as a control group for bone defect support of articular fractures are unjustified. A bioresorbable calcium phosphate material is recommended in preference to the gold standard of AIBG for bone defects in tibial plateau fractures. Funding: DePuy, Warsaw, IN

Purpose: The aim of this work was to evaluate the short- and long-term biocompatibility, tolerance and tissue response after implantation of an intersomatic bioresorbabled lumbar cage (Phusiline®). Material and methods: Eighteen sheep were operated on in 1999; three animals were sacrificed for study at three, six, nine and twelve months after implantation. The cage was placed between two lumbar vertebrae and filled and covered with cancellous bone. Cerebrospinal fluid, lateroaortic lymph nodes, liver, spleen and kidney samples were taken after sacrifice. The spinal segment from L1 to S1 was removed with the surrounding ligaments and muscles for radiography, MRI, and CT scan. Histology sections were stained with Paragon. The pathology examination included: bone and cell density, degree of tissue differentiation in contact with the implant, remodeling and consolidation of the fusion, implant resorption and associated reactions. An epifluorescence study was performed to assess bone apposition. Reaction of tissue in contact with the implant or far from the implant (laterovertebral muscles, paravetebral lymph nodes, liver, kidney, spleen) were qualified histologically. Results: At three months, there was no evidence of implant resorption; there was active formation of new bone around the implant. Implant resorption and osteointegration had started at six months and bone remodeling around the implant was increased. There were signs of bone fusion within and around the cage. Spondylodesis was effective at nine months with bone apposition. Implant resorption continued. Spondylodesis was confirmed. After nine and twelve months implantation, there was no sign of local or general intolerance. Degradation of the implants was visible after one month and appeared to be most marked at 12 months. Approximately 30% of the initial surfaced area of the implants had been resorbed at 12 months. Conclusion: One year after implantation, the implant had not induced any sign of local intolerance (no sign of inflammation, necrosis, osteolysis). Fusion occurred within and around the case. This study will be pursued (two groups of three animals will be sacrificed at 24 and 36 months) and should confirm the long-term effectiveness of this technique

Different 3D printing techniques for orthopaedic ceramic implants fabrication were compared. Stereolithography of calcium-phosphate slurries makes possible to achieve pre-determined pore size (50 mkm and more) and porosity of 70–80%. For the first time ceramic implants based on double calcium alkali metal phosphates (rhenanites) with given architecture serving good osteoconductivity as well as high resorptivity and strength (up to 10 MPa) were obtained. Development of biomaterials based on calcium phosphates for orthopaedics is an important area of modern materials science. Chemical, physical and mechanical compatibility of this materials is a primary goal for this field. An ideal implant should gradually dissolve and be replaced by the new bone tissue in the patience body. Bone is a multilevel organic/inorganic composite and the main inorganic compound is hydroxyapatite (HA, Ca. 10. (PO. 4. ). 6. (OH). 2. ). Due to this, biomaterials based on HA are widely used, along with biomaterials based on tricalcium phosphate (TCP, Ca. 3. (PO. 4. ). 2. ); however, low solubility of HA (lowest soluble phosphate) as well as TCP does not meet all of the requirements that biomaterials should have. In this work decreasing of the crystal lattice energy approach was used as a strategy of improving the solubility. Modifying the chemical composition by replacing Ca. 2+. cation in the TCP structure by a singly charged alkali metal cation leads to structural changes from TCP to CaMPO. 4. (M=Na, K) – rhenanite. This work focuses on using double calcium alkali metal phosphates Ca. (3 – x). М. 2x. (PO. 4. ). 2. (x = 0–1, М = Na, K) as bioresorbable osteoconductive ceramic implant. Additive manufacturing techniques are the most competitive technology which has been applied in the medical field for the direct or indirect construction of scaffolds and hard or soft tissues. Different techniques were used to prepare ceramics with given structure based on double calcium alkali metals phosphates to improve its osteoconductive properties. High resolution stereolithography (SLA) of ceramic photocurable resins has a great potential in fabrication of high quality complex shaped ceramics. For the first time ceramic implants based on double calcium alkali metal phosphates (rhenanites) with pre-determined pore size (50 mkm and more) and porosity of 70–80% were obtained. Given architecture of scaffold is serving a good osteoconductivity as well as a high resorptivity and strength (up to 10 MPa). High resolution SLA can be easily used for fabrication of a small size implants (3mm in diameter/height or less) for in vivo experiments, and it can be freely used to fit any shade in osteoconductive properties of ceramic materials designed for bone grafting. Russian Science Foundation supported this study under Grant No. 14-19-00752. The authors acknowledge partial support from Lomonosov Moscow State University Program of Development

Objectives: Advances in biomedical engineering have led to a thorough understanding of the body’s own capacity for ACL healing if provided the correct impetus—a long-term bioresorbable graft scaffold that anticipates the defect site’s biological and mechanical requirements. We hypothesize that by providing a structural scaffold which anticipates ACL repair mechanisms, “engineered” autologous ligament with excellent functional integrity can be developed by the body itself. This study evaluated the SeriACL™ graft, a non-mammalian derived long-term bioresorbable multi-bundled silk-based implant, for ACL replacement in a goat model at 3, 6 and 12 months post-operatively. Methods: The ACL of 43 goats was replaced with the SeriACL graft in an arthroscopically assisted procedure. The ACL was excised, a guide pin driven into the femur and 6mm diameter antegrade drilling performed. The tibial tunnel was drilled under direct visualization. The SeriACL, designed to mimic hamstring grafts, was anchored around a post on the femur. The graft was tensioned to 50N and cycled 30x before tibial fixation with a staple and sutures around a post. Animals were clinically, mechanically and histomorphometrically evaluated at 3, 6 and 12 months. Results: The SeriACL graft or surgical procedure did not induce early signs of acute inflammation, swelling or initial scar formation as indicated by rapidly declining scores for pain and knee size. All animals were weight bearing at 3, 6 and 12 months, with 95% returning to normal gait by 6 months. Lachmann showed the majority of knees were clinically stable at all points. Range of motion assessment indicated the knees maintained a normal range flexion and extension at all points. No gross cartilaginous damage, synovitis or particulate debris in lymph nodes was observed at any time point. Organized collagen and aligned fibroblasts in a crimp pattern were observed in the periphery of the ligament structure, adjacent to and attached to the remaining SeriACL device at all necropsy times. Collagen development throughout the graft and bone tunnels increased with time. Conversely, inflammation and device mass loss decreased with time. Fluoroscopy indicated no abnormal bone tunnel findings. Total plasma IgG levels did not increase from pre-surgery levels at any time. AP laxity indicated joint stability at all time points. Implant abrasion was observed to varying extents yet mechanical testing revealed tissue development supported increased load bearing over time. Conclusions: Results clearly demonstrate the potential of a scaffold-first strategy in engineering viable autologous ACL tissue that may serve over the patient’s life time. The SeriACL graft supported autologous development of a mechanically robust, biologically viable ligament which stabilized the joint over a 12 mo period. Mechanical, clinical and histological results indicated the safety of the SeriACL with initial indications of efficacy. Thus, the implant may offer the potential of an ACL replacement graft without the deleterious side-effects associated with donor-site morbidity and allogenic and xenogenic grafts

These results support the use of an injectable, in situ hardening calcium phosphate paste to prevent the early loss of calcaneal height and maintain a more anatomic calcaneal reduction. The purpose of this prospective randomized controlled trial was to determine whether ORIF plus an injectable bioresorbable calcium phosphate paste (_-BSM) is superior or inferior to ORIF alone in the treatment of calcaneal bone voids encountered after operative treatment of displaced intraarticular fractures of the calcaneus. Forty-four patients (forty-eight displaced intraarticular calcaneal fractures necessitating operative fixation) presenting to a Level One trauma center were enrolled into the study and randomized 1:1 to receive ORIF and injection of _-BSM or ORIF alone. All patients had a standardized ORIF thru a lateral approach by a single surgeon (R.B.). The primary outcome measure was the maintenance of post- operative Bohler’s angle at six weeks, three months, and six months. Other outcome measures included the SF-36 and LEM (Lower Extremity Measure) Score at six months. Five patients with seven calcaneal fractures were lost to follow up leaving thirty-nine patients with forty-one calcaneal fractures (85%) for analysis. Twenty-one were randomized into the ORIF and _-BSM group and twenty into the ORIF alone group. There was no statistical difference between the two groups with regard to age, sex, mechanism of injury, initial Bohler’s angle, or type of fracture. There was no difference between the groups in the degree of collapse of Bohler’s angle at six weeks and three months when compared to initial post-operative values. However, at six months the mean collapse of the _-BSM and ORIF group was 5.6° and ORIF alone was 10.6°. This was statistically significant (p< 0.01). Funding: Industry supported: DePuy, a Johnson & Johnson Company. Analysis and data collection performed independently

Summary Statement. A resorbable and biocompatible polymer-based scaffold was used for the proliferation and delivery of adipose derived stromal cells, as well as delivery of a cell growth/differentiation promoting factor for improved tendon defect regeneration. Introduction. Surgeons perform thousands of direct tendon repairs annually. Repaired tendons fail to return to normal function following injury, and thus require continued efforts to improve patient outcomes. The ability to produce regenerate tendon tissue with properties equal to pre-injured tendon could lead to improved treatment outcomes. The aim of this study was to investigate in vivo tendon regeneration using a biodegradable polymer for the delivery of adipose derived stromal cells (ADSCs) and a polypeptide, growth/differentiation factor-5/(GDF-5), in a tendon gap model. Patients & Methods. Female Fischer 344 rats underwent unilateral Achilles tenotomies. Defects were left un-repaired (Group 1-control), bridged using electrospun 65:35 polylactide-co-glycolide (PLAGA) tubular scaffolds (Group 2), PLAGA/ADSCs (Group 3), or PLAGA/GDF-5 (Group 4) scaffold composites. The plantaris was left intact. Operative limbs were immobilised for 10–14 days, followed by unrestricted activity. The rats were sacrificed at 4 weeks or 8 weeks after surgery, and tendons were assessed with histological, biochemical, and mechanical analyses. Results. PLAGA, PLAGA/ADSCs, and PLAGA/GDF-5 groups showed increased collagen I gene expression at both the 4 and 8 week time points (p<0.05). Tenomodulin (Tnmd) is the mature tendon phenotype marker unique to tendon tissue. Both the PLAGA/ADSCs and PLAGA/GDF-5 groups demonstrated increased tenomodulin expression at 4 and 8 weeks (p<0.05). Ultimate tensile load strength was improved in all PLAGA groups (2, 3, and 4) versus the control. Both composite groups (2 and 3) showed improved collagen deposition, as indicated by increased Collagen Area Fraction (CAF), approaching that of normal tendon at 8 weeks (p<0.05). Scaffold resorption was evident at 4 weeks, with complete replacement of the polymer with regenerate tissue and minimal gap formation at 8 weeks without evidence of an adverse inflammatory reaction. Defects bridged using the scaffold seeded with ADSCs showed improved collagen organization and increased modulus of elasticity compared with controls as well as properties approaching those of native tendon. Discussion/Conclusions. These results demonstrate that a tubular bioresorbable scaffold can promote extracellular matrix synthesis and organization, and the formation of neo-tendinous tissue; as well as serve as a carrier of adipose stromal cells and growth factors that are effective for tendon regeneration. Cells, growth factors and synthetic biomaterial polymers may be combined as a paradigm for regenerative engineering thereby serving as promising options for improved treatments of tendon injuries and potentially improving patient outcomes

Objective: The high incidence of retear following primary rotator cuff tendon (RCT) repair necessitates new strategies for tendon footprint augmentation. This study’s objective was to evaluate the SeriCuff™, a non-mammalian derived silk-based long-term bioresorbable implant, for RCT footprint reinforcement. The study aimed to characterize the device when overlaid on the infraspinatus tendon footprint of sheep in a RCT repair model. The technique was not targeted for the repair of massive RCT defects but advocated as a preventive measure to cuff reruptures in mid-to-large cuff tears, avoiding the need for surgical revision. Methods: Bilateral surgeries were performed on each of 10 sheep during a single surgical session. The right shoulder of each animal was implanted with SeriCuff and the left shoulder was used as an operated control. The superficial layer of the infraspinatus tendon was removed and feathered for a distance of 1 cm. The remaining footprint was bluntly dissected from the humeral head with the exception of a thin band of the superior portion of the infraspinatus tendon. The footprint was approximated, 3 suture anchors placed equi-distantly along the edge of the full thickness region of the tendon and the tendon sutured to the anchors with a modified Mason-Allen stitch. Two additional anchors were placed along the lateral edge of the tendon in the right shoulder. The SeriCuff device was positioned over the 5 anchors and sutured in place using a single suture at each location (Fig 1B). In the left shoulder, no device was implanted and a second row of anchors was not used. Animals were allowed to ambulate immediately post-op with unrestrained motion for the duration of the study. All animals were necropsied at 3 mos and evaluated histologically (N=4) and mechanically (N=6). Samples designated for mechanical analysis were dissected leaving only the infraspinatus tendon and muscle attached to the humorous. The tendon was pulled to failure at a rate of 500 mm/min with the sample positioned such that the longitudinal axis of the tendon was collinear with the applied load. Results: The animals were able to ambulate following surgery with return to normal gait at an average of 6 days post-operatively. Pain scores diminished with time throughout the first two weeks. Mechanical analysis indicated an average 42% increase in repair strength of the SeriCuff reinforced repair as compared to the contralateral control at 3 months. The SeriCuff device supported the formation of Sharpy’s fibers in the remodeling tendon tissue. Conclusions: The addition of SeriCuff helped to reestablish the tendon footprint resulting in significantly increased repair strength 3 most post-op and therefore may have applications in reducing the high incidence of primary repair failure

Objectives. We hypothesise that a long-term bioresorbable hydrophilic silkworm silk device, the SeriACL(tm) scaffold, can support the development and remodelling of native functional ligament tissue if designed to anticipate the remodelling curve of an ACL graft. This study evaluated the SeriACL scaffold for ACL replacement in a goat model at 3, 6 and 12 months. Methods. The ACL of 43 goats was replaced in an arthroscopically assisted procedure. The ACL was excised, a guide pin driven into the femur and 6mm diameter antegrade drilling performed. The tibial tunnel was drilled under direct visualisation. The graft was anchored around a post on the femur, tensioned to 50N and cycled 30x before tibial fixation with a staple and sutures around a post. Animals were clinically, mechanically and histologically evaluated. Results. The SeriACL graft did not induce acute inflammation, swelling or initial scar formation as indicated by rapidly declining pain and knee size scores. All animals were weight bearing at 3, 6 and 12 months, with 95% returning to normal gait by 6 months. Lachman showed the majority of knees were clinically stable with a normal range of motion at all times. No gross cartilaginous damage, synovitis or particulate debris in lymph nodes was observed. Collagen development throughout the graft and bone tunnels increased with time. Conversely, inflammation and device mass decreased with time. Fluoroscopy indicated no abnormal bone tunnel findings. Total IgG levels did not increase from pre-surgery levels. AP laxity indicated joint stability at all times. Implant abrasion was observed to varying extents yet mechanical testing revealed tissue development supported increased load bearing over time. Conclusions. The SeriACL graft supported autologous development of a mechanically robust, biologically viable ligament which stabilised the goat joint over a 12 month period. Mechanical, clinical and histological results indicated SeriACL graft safety with initial indications of efficacy

Aims: The purpose of this in-vitro study is to understand the mechanical behaviour of a fracture plate incorporating biodegradable inserts. Methods: A new, innovative fracture plate design incorporating biodegradable inserts was tested. These plates allow for micromotion during the union phase, which allows for increased healing. Resorption of the inserts over time works to decrease stress shielding during the remodelling phase. Two separate bone models were used to simulate a fracture during both the union phase of healing and the remodelling phase. This plate, termed an axially compressible plate (ACP) was mounted to the bone models in four different conþgurations. On the model simulating the union phase, stiffness and micromotion were measured using an LVDT for bending and an extensometer for compression. With the model simulating the remodelling phase, strain was measured on the bone model using a strain gage mounted directly below the plate midpoint.

Conclusions: The results show that during the union phase, the ACP should allow for micromotion, which increases with successive loss of inserts. Results also show that during the remodelling phase, the loss of inserts increases the amount of strain in bone and thus decreases stress shielding.

Objectives. Osteochondral injuries, if not treated adequately, often lead to severe osteoarthritis. Possible treatment options include refixation of the fragment or replacement therapies such as Pridie drilling, microfracture or osteochondral grafts, all of which have certain disadvantages. Only refixation of the fragment can produce a smooth and resilient joint surface. The aim of this study was the evaluation of an ultrasound-activated bioresorbable pin for the refixation of osteochondral fragments under physiological conditions. Methods. In 16 Merino sheep, specific osteochondral fragments of the medial femoral condyle were produced and refixed with one of conventional bioresorbable pins, titanium screws or ultrasound-activated pins. Macro- and microscopic scoring was undertaken after three months. . Results. The healing ratio with ultrasound-activated pins was higher than with conventional pins. No negative heat effect on cartilage has been shown. Conclusion. As the material is bioresorbable, no further surgery is required to remove the implant. MRI imaging is not compromised, as it is with implanted screws. The use of bioresorbable pins using ultrasound is a promising technology for the refixation of osteochondral fractures

Introduction. Cerament, a bioresorbable hydroxyapatite and calcium sulfate cement, is known to be used as a bone-graft substitute in traumatic bone defect cases. However, its use in open fractures has not previously been studied. Materials and Methods. Retrospective, single-centre review of cases between November 2016 and February 2021. Open fractures were categorised according to the Orthopaedic Trauma Society classification (OTS). Cases were assessed for union, time to union, and associated post-operative complications. Results. Twenty-four patients were identified. Fifteen cases were classified as OTS simple open fractures, and nine cases were complex open fractures requiring soft tissue reconstruction. Four cases were lost to follow-up. Four cases had limited follow-up beyond 6 months but showed evidence of progressive radiographic union. Of the remaining 16 cases, eight cases (50%) went on to union with a mean time to union of 6.7 months (5 to 12 months). Persistent non-union remained in six cases (38%). Two cases required return to theatre due to an infected skin graft and wound dehiscence respectively. One case had the complication of persistent weeping of Cerament from the wound. This self-resolved within two weeks. Limitations of this case series include the lack of complete follow-up in eight patients (33%) and the lack of patient reported outcome measures. Conclusions. Cerament can be a useful adjunct in managing open fractures. However, it should be noted there is a high rate of non-union which may be reflective of the significant morbidity associated with open fractures with structural bone defects

Aim. Implant-associated osteomyelitis is a devastating complication with poor outcomes following treatment, especially when caused by antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). A large animal model of a two-stage revision to treat MRSA implant-associated osteomyelitis has been developed to assess novel treatments. A bioresorbable, thermo-responsive hyaluronan hydrogel (THH) loaded with antibiotics has been developed and our aim was to investigate it´s in vivo efficacy as a local antibiotic carrier compared to the current standard of care i.e. antibiotic-loaded polymethylmethacrylate (PMMA) bone cement. Method. 12 female, 2 to 4 year old, Swiss Alpine Sheep were inoculated with MRSA at the time of intramedullary nail insertion in the tibia to develop chronic osteomyelitis. After 8 weeks sheep received a 2-stage revision protocol, with local and systemic antibiotics. Group 1 received the gold standard clinical treatment: systemic vancomycin (2 weeks) followed by rifampicin plus trimethoprim/sulfamethoxazole (4 weeks), and local gentamicin/vancomycin via PMMA. Group 2 received local gentamicin/vancomycin delivered via THH at both revision surgeries and identical systemic therapy to group 1. Sheep were euthanized 2 weeks following completion of antibiotic therapy. At euthanasia, soft tissue, bone, and sonicate fluid from the hardware was collected for quantitative bacteriology. Results. Sheep tolerated the surgeries and both local and systemic antibiotics well. Gold standard of care successfully treated 3/6 sheep with a total of 10/30 culture-positive samples. All 6 sheep receiving antibiotic-loaded THH were successfully treated with 0/30 culture-positive samples, p=0.0008 gold-standard vs. hydrogel (Fisher's Exact). Conclusions. The clinical gold standard treatment was successful in 50% of sheep, consistent with outcomes reported in the literature treating MRSA infection. The antibiotic-loaded THH clearly outperformed the gold standard in this model. Superior efficacy of the THH is likely due to 1) the ability to administer local antibiotics at the both revision surgies due to the bioresorbable nature of the hydrogel, and 2) complete antibiotic release compared to bone cement, which is known to retain antibiotics. Our results highlight the potential of local delivered, biodegradable systems for antibiotics for eradicating implant-related infection caused by antibiotic-resistant pathogens. Acknowledgement. Funding provided by AO Trauma

Background. Bioresorbable materials offer the potential of developing fracture fixation plates with similar properties to bone thereby minimising the “stress shielding” associated with metal plates and obviating the need for implant removal. Phosphate glass fibre reinforced (PGF)-polylactic acid (PLA) composites are bioresorbable and have demonstrated sufficient retention of mechanical properties to enable load bearing applications. Aim. To determine the potential in vivo “stress shielding” effects of a novel PGF reinforced PLA composite plate in an animal model. Methods. Twenty five NZW rabbits underwent application of the composite plate to the intact right tibia. They were divided into 5 groups corresponding to the time points from surgery to sacrifice −2, 6, 12, 26 and 52 weeks. Outcomes included radiographs, NanoCT imaging, histological assessment and mechanical testing of the retrieved plated tibia and opposite control tibia. Results. Plate integrity was retained up to 26 weeks on radiographs and scanning electron microscopy (SEM). The mechanical properties of the plated bones were equivalent or greater than the control bones at each time point although the relative improvement in mechanical properties diminished with time. Nano CT imaging and SEM revealed bone remodelling with cortical thinning beneath the composite plate which progressed as the duration of implantation increased. Discussion. The bone-composite plate construct retained its mechanical properties compared to the control bone despite thinning of the cortex beneath the plate. More importantly, this work suggests that fracture fixation systems with equivalent mechanical properties to bone may still induce a “stress shielding” response

Background. Bioresorbable materials offer the potential of developing fracture fixation plates with similar mechanical properties to bone thereby minimizing stress shielding and obviating the need for implant removal. Aim. To determine the in vivo degradation profile of a novel phosphate glass fibre composite bioresorbable plate and effects on the underlying bone. Methods. Twenty five NZW rabbits underwent application of the plate to the intact right tibia. They were divided into 5 groups corresponding to the time points from surgery to sacrifice −2, 6, 12, 26 and 52 weeks. Outcomes included radiographs, nanoCT imaging, scanning electron microscopy (SEM) and mechanical testing of the plated bone and the opposite unplated tibia at each time point. Results. At sacrifice, plate integrity was retained up to 12 weeks with no evidence of macroscopic inflammation. The mean load to failure of the plated bones expressed as a percentage of the opposite unplated bones was 179, 174, 172 and 115% after implantation for 2, 6, 12 and 26 weeks respectively. The flexural stiffness of the plated bones expressed as a percentage of the opposite bones revealed a mean increase of 245, 317, 205 and 110% at 2, 6, 12 and 26 weeks respectively. Although radiographs did not reveal any evidence of structural changes in the bones, NanoCT and SEM analysis revealed early porosity and progressive thinning of the cortex beneath the implant. However, bone formation around the plate progressed up to 26 weeks with improved cross sectional area characteristics of the plated bone compared to the control bone. Discussion. Cortical changes beneath the plate would indicate that stress shielding may occur even in plates with similar mechanical characteristics to bone. However, this is only one part of the adaptive response of the bone which overall maintains the mechanical properties of the plated bone