Purpose. We evaluated the clinical and radiographic outcomes of cementless bipolar hemiarthroplasty using rectangular cross-section stem for femoral neck fracture in elderly patients more than 80 years of age with osteoporosis. Material and Methods. 76(cemented 46, cementless 30) bipolar hemiarthroplasties for femur neck fracture were performed in elderly patients more than 80 years old. The mean follow-up period was 4.3 years (2 to 7 years). The Harris hip score at last follow-up and pre-postoperative daily living activity scale according to Kitamura methods were analyzed clinically. The radiological results were assessed using stability of femoral stem and other complications were evaluated. Results: At last follow-up, there were no significant differences of Harris hip score and daily living activity between two groups. Stem loosening and instability were not observed in cementless arthroplasty. There were 18 cases of osseous fixation in radiologic study. There were 1 case of dislocation and 1 case of superficial infection in cemented arthroplasty and 1 case of deep infection in cementless arthroplasty. Conclusion. Cementless bipolar hemiarthroplasty using rectangular cross-section stem for elderly patients with a femoral neck fracture showed satisfactory short-term clinical and radiological results compared to using cement stem

Transforaminal lumbar interbody fusion (TLIF) using an implanted cage is the gold standard surgical treatment for disc diseases such as disc collapse and spinal cord compression, when more conservative medical therapy fails. Titanium (Ti) alloys are widely used implant materials due to their superior biocompatibility and corrosion resistance. A new Ti-6Al-4V TLIF cage concept featuring an I-beam cross-section was recently proposed, with the intent to allow bone graft to be introduced secondary to cage implantation. In designing this cage, we desire a clear pathway for bone graft to be injected into the implant, and perfused into the surrounding intervertebral space as much as possible. Therefore, we have employed shape optimization to maximize this pathway, subject to maintaining stresses below the thresholds for fatigue or yielding. The TLIF I-beam cage (Fig. 1(a)) with an irregular shape was parametrically designed considering a lumbar lordotic angle of 10°, and an insertion angle of 45° through the left or right Kambin's triangles with respect to the sagittal plane. The overall cage dimensions of 30 mm in length, 11 mm in width and 13 mm in height were chosen based on the dimensions of other commercially available cages. The lengths (la, lp) and widths (wa, wp) of the anterior and posterior beams determine the sizes of the cage's middle and posterior windows for bone graft injection and perfusion, so they were considered as the design variables for shape optimization. Five dynamic tests (extension/flexion bending, lateral bending, torsion, compression and shear compression, as shown in Fig. 2(b)) for assessing long term cage durability (10. 7. cycles), as described in ASTM F2077, were simulated in ANSYS 15.0. The multiaxial stress state in the cage was converted to an equivalent uniaxial stress state using the Manson-Mcknight approach, in order to test the cage based on uniaxial fatigue testing data of Ti-6Al-4V. A fatigue factor (K) and a critical stress (σcr) was introduced by slightly modifying Goodman's equation and von Mises yield criterion, such that a cage design within the safety design region on a Haigh diagram (Fig. 2) must satisfy K ≤ 1 and σcr ≤ SY = 875 MPa (Ti-6Al-4V yield strength) simultaneously. After shape optimization, a final design with la = 2.30 mm, lp = 4.33 mm, wa = 1.20 mm, wp = 2.50 mm, was converged upon, which maximized the sizes of the cage's windows, as well as satisfying the fatigue and yield strength requirements. In terms of the strength of the optimal cage design, the fatigue factor (K) under dynamic torsion approaches 1 and the critical stress (σcr) under dynamic lateral bending approaches the yield strength (SY = 875 MPa), indicating that these two loading scenarios are the most dangerous (Table 1). Future work should further validate whether or not the resulting cage design has reached the true global optimum in the feasible design space. Experimental validation of the candidate TLIF I-beam cage design will be a future focus. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Aims. In computer simulations, the shape of the range of motion (ROM) of a stem with a cylindrical neck design will be a perfect cone. However, many modern stems have rectangular/oval-shaped necks. We hypothesized that the rectangular/oval stem neck will affect the shape of the ROM and the prosthetic impingement. Methods. Total hip arthroplasty (THA) motion while standing and sitting was simulated using a MATLAB model (one stem with a cylindrical neck and one stem with a rectangular neck). The primary predictor was the geometry of the neck (cylindrical vs rectangular) and the main outcome was the shape of ROM based on the prosthetic impingement between the neck and the liner. The secondary outcome was the difference in the ROM provided by each neck geometry and the effect of the pelvic tilt on this ROM. Multiple regression was used to analyze the data. Results. The stem with a rectangular neck has increased internal and external rotation with a quatrefoil cross-section compared to a cone in a cylindrical neck. Modification of the cup orientation and pelvic tilt affected the direction of projection of the cone or quatrefoil shape. The mean increase in internal rotation with a rectangular neck was 3.4° (0° to 7.9°; p < 0.001); for external rotation, it was 2.8° (0.5° to 7.8°; p < 0.001). Conclusion. Our study shows the importance of attention to femoral implant design for the assessment of prosthetic impingement. Any universal mathematical model or computer simulation that ignores each stem’s unique neck geometry will provide inaccurate predictions of prosthetic impingement. Cite this article: Bone Joint Res 2021;10(12):780–789

Introduction: Femoral neck (FN) fragility has been attributed to age-related bone loss, with increased loss in women. It has been shown that the mechanical properties of a supporting structure will also change with any alteration to the structure’s dimensions. The purpose of this study was to identify the age-related changes that take place in the morphology of the mid cross-section of the FN, and the implications for its mechanical properties in the different regions around the mid FN cross-section. Materials and Methods: Measurements were taken from peripheral quantitative computed tomogram (pQCT) images of 81 cadaveric femurs (36 F, 45 M). The mid FN cross-section was segmented radially into eight regions and the cortical bone thickness (CT) and change of the centroid position (CP) of the FN cross-section were measured. The age-related effects of the corresponding changes in the proportion of cortical bone and the “resistance to bending” (section modulus, (Z)) were also measured. Results: Four femurs were excluded because there were clear signs of OA being present. The maximum difference in regional CT between men and women, was less than 7% (Female: 3.07 ± 0.108mm; Male: 3.28 ± 0.123 mm (mean ± SEM) p =0.21). However, there were regional differences in CT between the young under fifty, (Un50, n=26) and the old, (Abv50), (ANOVAs for young vs old: CT p = 0.001 t 0.01). These effects were attributable to differences in the inferior region, where there was an increase in thickness of the cortical bone of 27% with senior status (Abv50: 3.44 ± 0.09mm; Und50: 2.70 ± 0.12mm. p = 0001) counter balanced by anterior and posterior loss. There was a corresponding change in CP, the distance of the superior, posterior, and superoposterior regions to the FN cross-section’s centroid, 7.6% (Abv50: 20.88 ± 0.28mm; Und50: 19.40 ± 0.47mm; p = 0.005); 6.7% (Abv50: 14.67 ± 0.2mm; Und50: 13.74 ± 0.32mm; p = 0.01); and 8%(Abv50: 17.95 ± 0.24; Und50: 16.61 ± 0.37), respectively. When these two measurements were combined (CP divided by CT) to provide the Local Buckling Ratio (BLR), where the higher the ratio the more unstable the structure, there were significant differences in superoanterior, 30%(Abv50: 15.8 ± 0.52; Und50: 12.1 ± 0.59;p=0.0001); anterior, 20%(Abv50: 10.1 ± 0.32; Und50: 8.3 ± 0.4; p=0.001); inferior, 35%(Abv50: 4.37 ± 0.14; Und50: 5.8 ± 0.34; p=0.0001); inferoposterior 18%(Abv50 8.6 ± 0.27: Und50: 7.36 ± 0.41; p=0.008); posterior, 29%(Abv50: 14.0 ± 0.33; Und50: 10.8 ± 0.5; p=0.0001) and superoposterior, 14%(Abv50: 14.6 ± 0.3; Und50: 12.8 ± 0.4; p=0.001), regions. There was no significant difference in bending resistance nor in the proportion of cortical bone. Conclusions: A more uniform cortical thickness, seen in the young, would optimise fracture resistance to overloading from unusually loaded directions. Ageing was associated with a thickening of the inferior cortex and thinning of the cortex elsewhere. This effects the location of the area that is least susceptible to the loading forces experienced in stance – that is of the FN mid cross-section’s neutral bending axis – as it will be nearer to the inferior region. Such a change in the morphology will produce deterioration in the FN’s capacity to take a load as shown by the detrimental change in the LBR. This change may indicate that the potential for femoral neck fracture increases with age when load is applied in a direction different to normal stance eg through the greater trochanter

Abstract. Objectives. Bone shape and internal architecture are accepted as optimised to resist joint contact and muscle forces the skeleton is subjected to through daily living and more demanding activities. Finite element studies to predict bone architecture, either using continuum or structural approaches have made assumptions common in structural optimisation, that lead to trabecular bone effectively being modelled as a truss-type structure, with compressive or tensile strains, present due to axial forces driving adaptation. These models are successful in predicting bone fracture, and trends in bone degradation associated with disuse or unloading osteopenia but tend to overpredict bone mineral density reduction compared to clinical observations. Methods. A new structural model of bone adaptation, including both trabeculae (element) cross-section adaptation in response to axial force and biaxial bending moments, and alteration of joint (node) positions within the trabecular network, was developed using a Voronoi space partition to define the initial network. This was compared to results from a structural bone adaptation using a truss-type network generated by connecting each node to its nearest 16 neighbours [1]. Results. Relative density (bone volume divided by total volume) was higher in the predicted structure from the Voronoi network, compared to the truss-type network, with elements close to nodes adapting to resist higher bending moments. Bone promoting strains were found to be spread throughout the Voronoi network in contrast to the truss-type network. Predicted bone degradation in the Voronoi network was lower than in the truss-type network when load cases were removed from the loading envelope. Conclusion. It is hypothesised that bone is optimised for robustness as well as stiffness, with trabecular architecture allowing a wide range of load cases to cause bone promoting strains across the network, reducing the impact of reduced activity or altered loading. 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

Impaction allografting is increasingly used for the treatment of failed total hip replacements. In six human cadaveric femurs the impaction allografting procedure was performed to comprehensively describe the postoperative morphology of impaction allografting. After the procedure, the specimens were sectioned and prepared for histomorphometric analysis. The graft porosity was lowest in Gruen zone four (52%) and highest in Gruen zone one (76%). At the level of Gruen zone six and two, virtually the entire cross-section was filled with bone cement. The presented data will serve as a baseline for future investigations of the impaction allografting. Impaction allografting is an attractive procedure for the treatment of failed total hip replacements. The purpose of this study was to comprehensively describe the morphology of impaction allografting post operatively to form a baseline for further investigations. Three experienced surgeons performed the impaction allografting procedure on six cadaveric femurs. After the procedure, the femurs were cut in 6mm thick transverse sections and processed for histomorphometric analysis. The porosity of the impacted graft was highest proximally in Gruen zone one (76%) and lowest in Gruen zone four (52%). Below the tip of the stem (Gruen zone four), the mean cement penetration was significantly lower compared to the proximal part of the femur. The averaged residual impacted graft layer in Gruen zone six and two was (0.5mm SD 0.4mm) significantly thinner compared with Gruen zone’s one, 7/1, and four. In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer (Figure). Even the simulated lytic defects in this region were filled with the graft cement composite which may not be remodelled by the host bone. The graft porosity was found to be highest proximally and lowest distally. In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer. This investigation will serve as a baseline for future studies of the mechanical and biological processes that make the impaction allografting a successful procedure. Funding: Stryker Howmedica and DePuy for provided implants and instruments. Please contact author for figures and/or diagrams

Traditional procedures for orthopedic total joint replacements have relied upon bone cement to achieve long-term implant fixation. This remains the gold standard in number of procedures including TKR and PKR. In many cases however, implants fixed with cement have proven susceptible to aseptic loosening and 3. rd. body wear concerns. These issues have led to a shift away from cement fixation and towards devices that rely on the natural osteoconductive properties of bone and the ability of porous-coated implants to initiate on-growth and in-growth at the bone interface, leading to more reliable fixation. To facilitate long-term fixation through osseointegration, several mechanical means have been utilized as supplemental mechanism to aid in stabilizing the prostheses. These methods have included integrated keels and bone screws. The intent of these components is to limit implant movement and provide a stable environment for bone ingrowth to occur. Both methods have demonstrated limitations on safety and performance including bone fracture due keel induced stresses, loosening due to inconsistent pressfit of the keel, screw-thread stripping in cancellous bone, head-stripping, screw fracture, screw loosening, and screw pullout. An alternative method of fixation utilizing blade-based anchoring has been developed to overcome these limitations. The bladed-based fixation concept consists of a titanium alloy anchor with a “T-shaped” cross-section and sharped-leading end that can be impacted directly into bone. The profile is configured to have a bladed region on the horizontal crossbar of the “T” for engagement into bone and a solid rail at the other end to mates with a conforming slot on the primary body of the prosthesis. A biased chisel tip is added to the surface of the leading blade edge to draw the bone between the anchor's horizontal surface and surface of the implant, thus generating a compressive force at the bone-to-prothesis interface. The anchoring mechanism has been successfully been integrated into the tibial tray component of a partial knee replacement; an implant component that has a clinical history of revision due to loosening. A detailed investigation into the pulloff strength, wear debris generation, compressive-force properties, and susceptibility to tibial bone fracture was carried out on the anchor technology when integrated in a standard tibial tray of a partial knee replacement. When tested in rigid polyurethane bone foam (Sawbones, Grade 15) the pulloff strength of the construct increased by 360% when utilizing the anchor. The tibial tray and anchor construct were cycled under compressive loading and demonstrated no evidence of interface corrosion or wear debris generation after 1 million cycles. In addition, the anchor mechanism was shown to generate 340N of compressive force at the tibial tray-to-bone interface when evaluated with pressure sensitive film (Fuji Prescale, Medium Grade). Finally, the ultimate compressive load to induce tibial fracture was shown to increase by 17% for the anchored tray as compared to a traditional keeled tray when tested in an anatomic tibial sawbones model; and by 19% when evaluated in human cadaveric tibias. For any figures or tables, please contact authors directly

Despite poly(vinyl alcohol) (PVA) hydrogel-based drug delivery systems have been extensively studied in the last years, so far there is no research investigating hydrogels in microspherical shape. In the present study, hydrogels for drug delivery systems were obtained from different formulations of poly(vinyl alcohol), poly(acrylic acid), ciprofloxacin and hydroxyapatite (Hap) aqueous solutions and shaped into spheres through dripping the solution into liquid nitrogen at extremely low temperatures. Hydrogels were then strengthened by freeze-thaw cycles. Characterisation of the samples produced aimed to evaluate the thermal (DSC), chemical (EDS), morphology (SEM), drug release properties of the hydrogel and to investigate the influence of each compound on PVA and their biocompatibility. Samples were able to maintain a spherical shape after the freeze-thawing cycles, also, cross-section of these samples revealed different internal structures depending on the components incorporated into the PVA, EDS revealed quantities of Ca and P into these hydrogels due to the HAp and the incorporation of drug, poly(acrylic acid) and hydroxyapatite increased both the melting point and the glass transition temperature of PVA. Ciprofloxacin release exhibited a burst release for approximately two hours, then stabilising the drug release to a maximum of 96.82%. PAA has acted as a release retardant and the burst release was significantly delayed. PAA chains helped encapsulating the drug and reinforced the three-dimensional structure of the hydrogel, hampering ciprofloxacin to be delivered, the total of drug release was 92.11%. Cells mortality rate (MTT) shows that PVA substrates is non-toxic for NRK cells after 24 hours of exposure

Introduction. Soft-tissue balancing methods in TKA have evolved from surgeon feel to digital load-sensing tools. Such techniques allow surgeons to assess the soft-tissue envelope after bone cuts, however, these approaches are ‘after-the-fact’ and require soft-tissue release or bony re-cuts to achieve final balance. Recently, a robotic ligament tensioning device has been deployed which characterizes the soft tissue envelope through a continuous range-of-motion after just the initial tibial cut, allowing for virtual femoral resection planning to achieve a targeted gap profile throughout the range of flexion (figure-1). This study reports the first early clinical results and patient reported outcomes (PROMs) associated with this new technique and compares the outcomes with registry data. Methods. Since November 2017, 314 patients were prospectively enrolled and underwent robotic-assisted TKA using this surgical technique (mean age: 66.2 ±8.1; females: 173; BMI: 31.4±5.3). KOOS/WOMAC, UCLA, and HSS-Patient Satisfaction scores were collected pre- and post-operatively. Three, six, and twelve-month assessments were completed by 202, 141, and 63 patients, respectively, and compared to registry data from the Shared Ortech Aggregated Repository (SOAR). SOAR is a TJA PROM repository run by Ortech, an independent clinical data collection entity, and it includes data from thousands of TKAs from a diverse cross-section of participating hospitals, teaching institutions and clinics across the United States and Canada who collect outcomes data. PROMs were compared using a two-tailed t-test for non-equal variance. Results. When comparing the baseline PROM scores, robotic patients had equivalent womac knee stiffness (p=0.58) and UCLA activity scale (p=0.38) scores but slightly higher womac knee pain (p=0.002) and functional scores (p=0.014, figure-2). While all scores improved over time, the rate of improvement was generally greater at 6 months than at three months when comparing the two groups, with statistically higher six-month scores in the robotic group for all categories (p<0.001). Overall patient satisfaction in the RB cohort was 90.3%, 95.0% and 91.8% at 3M, 6M and 1Y, respectively (figure-3). Average length of hospital stay was 1.6 days (±0.8). Surgical complications in this cohort included one infection four months post-op, 6 post-operative knee manipulations, one pulmonary embolism and one wound dehiscence from a fall. Discussion. We postulated that the ability to use gap data prospectively under known loading conditions throughout the knee range-of-motion would allow femoral cut planning that resulted in optimum balance with fewer releases and better long-term results. While the study group patients had slightly higher baseline knee pain and function than registry patients and showed similar net improvements at the three-month mark, study patients showed significantly better improvements in all areas between three months and six months compared to registry data. WOMAC stiffness and UCLA activity scores were equal between the two groups at baseline and significantly improved at three months and six months. Better ligament balance may have significantly contributed to these gains and to the high rates of satisfaction reported in the study patients compared to the historical literature. Limitations to this study include the small number of patients and the lack of a closely matched control group. For any figures or tables, please contact authors directly

Introduction. The osteogenic capability of any biomaterial is governed by a number of critical surface properties such as surface energy, surface potential, and topography. Prior work suggested that the Si-Y-O-N phase(s) present in the form of a thin (<150 nm), interrupted film at the surface of an annealed silicon nitride bioceramic may be responsible for an observed upregulation of osteoblastic activity due to passive surface properties and dissolution of chemical species. In this study high- resolution analytical electron microscopy was utilized to identify the Si-Y-O-N phase present on the annealed silicon nitride surface, and dissolution studies were employed to elucidate mechanisms of the material's favorable cell interactions. Materials and Methods. Si. 3. N. 4. discs (12.7 mm diameter × 1 mm thick) containing Y. 2. O. 3. and Al. 2. O. 3. sintering aids were processed using conventional techniques and subsequently subjected to annealing in a nitrogen atmosphere. Pre-cultured SaOS-2 osteosarcoma cells at a concentration of 5 × 10. 5. cells/ml were seeded onto sterile polished nitrogen-annealed Si. 3. N. 4. discs in an osteogenic medium consisting of DMEM supplemented with about 50 µg/mL ascorbic acid, 10 mM β-glycerol phosphate, 100 mM hydrocortisone, and 10% fetal bovine calf serum. The samples were incubated for up to 7 days at 37°C with two medium replenishments. Transmission electron microscopy (TEM) images were acquired from focused ion beam (FIB)-prepared samples using a Hitachi HF-3300 TEM (300 kV). Scanning transmission electron microscopy (STEM) images were recorded using a Nion UltraSTEM 100 (60 kV). STEM high-angle annular dark-field (HAADF) imaging and energy dispersive X-ray spectroscopy (EDS) analyses were performed on a JEOL JEM2200FS (200 kV) equipped with a third-order CEOS aberration corrector and a Bruker XFlash silicon drift detector. Results. A cross-section of the of the Si. 3. N. 4. /extracellular polymer (ECP) interface is illustrated in Fig. 1(a)∼(b) as a high- angle annular dark field (HAADF) STEM image (a) with and EDS map overlay (b) highlighting locations of Ca, Y, and Si. The underlying Si. 3. N. 4. microstructure is covered by a yttrium-rich intergranular phase (IGP) film. Deposition of cell-derived hydroxyapatite (HAp) occurred directly onto this IGP film. In Fig. 2, a bright field TEM image (electron diffraction pattern inset) shows the interface between the partially-crystalline HAp and the Y-Si-O-N phase, identified as monoclinic yttrium disilicate (i.e., m-Y. 2. Si. 2. O. 7. ) with a 2 atomic% N impurity, at teh atomic scale. Although rapid electron damage of the mineralized ECP was observed, EDS analyses suggested a Ca/P ratio of ∼1.43, along with the incorporation of Si. Conclusions. The osteogenic Si-Y-O-N phase was successfully identified as a minority concentration of Si. 3. N. 4. dissolved into a m-Y. 2. Si. 2. O. 7. matrix. Evidence of the release of (SiO. 4. ). 4−. tetrahedra from this phase into the local biological microenvironment and their incorporation into the cell-derived HAp layer was also observed. Identification of this phase paves the way for ongoing work to understand and optimize this novel biomaterial. For any figures or tables, please contact the authors directly

Purpose. The purpose of this study is to report the results of the first 1000 cases hip arthroplasty using the Bencox. ®. hip stem, the first hip prosthesis developed and manufactured in Korea. Material & Method. This study reviewed 1000 cases retrospectively who underwent arthroplasty using Bencox. ®. hip system. The Bencox. ®. hip stem is the first hip prosthesis developed and manufactured in Korea. This stem have a double-tapered, wedge shape figure with a rectangular-shaped cross-section and specially designed neck shape, which is design to achieve normal stress pattern of the proximal femur and to increase initial stability and to increase range of motion. Surface is treated with MAO (Micro Arc Oxidation) coating. From the first arthroplasty with this system in September 2006, sequentially 1000 arthroplasties were performed by single surgeon until the July 2014. This material included 439 men and 561 female. Average age of patients was 65 year old. Follow up period was average 72.1 month (minimum 34 months to maximum 120 months). 1000 cases consisted of 569 hips in patients with femoral neck or intertrochanteric fracture or subtrochanteric fracture (fracture group), 155 hips in osteoarthritis, 192 hips in patients with osteonecrosis of the femoral head (arthritis group), 84 hips in revision surgery (revision group). Revision cases consisted of 58 hips with aseptic loosening and 26 hips with loosening due to infection sequelae. They were underwent hip arthroplasty using a Bencox. ®. hip stem in combination with Bencox. ®. bipolar cup and Bencox. ®. acetabular cup. Patients in the fracture group usually underwent bipolar hip arthroplasty, and those in the arthritis group and revision group underwent total hip arthroplasty. They were reviewed by medical records, clinically and radiologically. Results. During the follow-up period, there were no cases of revision of the femoral stem. Radiographically, there were no cases of radiolucent line except very proximal part of the stem endosteal bone ongrowth was found in most cases. Postoperative complications such as stem loosening, infection, dislocation, and ceramic breakage were not noted. But periprosthetic fracture was encountered in 7 hips due to slip down. They were treated by open reduction and internal fixation with plate and cables. There were no cases of failure of these treatments. Conclusion. Clinical and radiographic evaluations of hip arthroplasty using the Bencox. ®. hip system showed excellent outcomes with average 72.1 month follow-up in 1000 case

Aims

Although the Fitmore Hip Stem has been on the market for almost 15 years, it is still not well documented in randomized controlled trials. This study compares the Fitmore stem with the CementLeSs (CLS) in several different clinical and radiological aspects. The hypothesis is that there will be no difference in outcome between stems.

Aims

Rotator cuff muscle atrophy and fatty infiltration affect the clinical outcomes of rotator cuff tear patients. However, there is no effective treatment for fatty infiltration at this time. High-intensity interval training (HIIT) helps to activate beige adipose tissue. The goal of this study was to test the role of HIIT in improving muscle quality in a rotator cuff tear model via the β3 adrenergic receptor (β3AR).

Introduction. Up to 60% of total hip arthroplasties (THA) in Asian populations arise from avascular necrosis (AVN), a bone disease that can lead to femoral head collapse. Current diagnostic methods to classify AVN have poor reproducibility and are not reliable in assessing the fracture risk. Femoral heads with an immediate fracture risk should be treated with a THA, conservative treatments are only successful in some cases and cause unnecessary patient suffering if used inappropriately. There is potential to improve the assessment of the fracture risk by using a combination of density-calibrated computed tomographic (QCT) imaging and engineering beam theory. The aim of this study was to validate the novel fracture prediction method against in-vitro compression tests on a series of six human femur specimens. Methods. Six femoral heads from six subjects were tested, a subset (n=3) included a hole drilled into the subchondral area of the femoral head via the femoral neck (University of Leeds, ethical approval MEEC13-002). The simulated lesions provided a method to validate the fracture prediction model with respect of AVN. The femoral heads were then modelled by a beam loaded with a single joint contact load. Material properties were assigned to the beam model from QCT-scans by using a density-modulus relationship. The maximum joint loading at which each bone cross-section was likely to fracture was calculated using a strain based failure criterion. Based on the predicted fracture loads, all six femoral heads (validation set) were classified into two groups, high fracture risk and low fracture risk (Figure 1). Beam theory did not allow for an accurate fracture load to be found because of the geometry of the femoral head. Therefore the predicted fracture loads of each of the six femoral heads was compared to the mean fracture load from twelve previously analysed human femoral heads (reference set) without lesions. The six cemented femurs were compression tested until failure. The subjects with a higher fracture risk were identified using both the experimental and beam tool outputs. Results. The computational tool correctly identified all femoral head samples which fractured at a significantly low load in-vitro (Figure 2). Both samples with a low experimental fracture load had an induced lesion in the subchondral area (Figure 3). Discussion. This study confirmed findings of a previous verification study on a disease models made from porcine femoral heads (Preutenborbeck et al. I-CORS2016). It demonstrated that fracture prediction based on beam theory is a viable tool to predict fracture. The tests confirmed that samples with a lesion in the weight bearing area were more likely to fracture at a low load however not all samples with a lesion fractured with a low load experimentally, indicating that a lesion alone is not a sufficient factor to predict fracture. The developed tool takes both structural and material properties into account when predicting the fracture risk. Therefore it might be superior to current diagnostic methods in this respect and it has the added advantage of being largely automated and therefore removing the majority of user bias. For any figures or tables, please contact the authors directly

Osteoarthritis is one of the most common musculoskeletal diseases. It involves degeneration and loss of articular cartilage, leading to a painful bone on bone articulation during movement. Numerical FEA models exist to predict the mechanical behaviour of degenerated cartilage. One of the limitations of these models arises from the poor validation that can be attained with traditional experimental data. This typically relies on comparison with global mechanical quantities such as total tissue strain, which mask the individual contributions originating from the different layers. In order to improve on this, an experimental method was developed to visualise the through-thickness behaviour of articular cartilage. Four experiments were performed on hemi-cylindrical cartilage plugs, harvested from a porcine femoral head, and immersed in a fluid solution. An Indian ink speckle pattern was applied to the flat surface of each hemi-cylinder. The specimens were equilibrated in 2.5M NaCl solution, transferred to a custom designed testing rig, and a reference image of the tissue cross-section was taken. The solution concentration was then decreased to 0.15M and, predictably, the tissue thickness changed. Images of the tissue cross section were taken every 60s for the duration of the experiment (3600s). All images were analysed using a DIC algorithm (Ncorr open-source 2D digital image correlation matlab program), and documented the strain changes through the tissue thickness as a function of time. The measured total strain in the tissue was consistent with that reported by Lai et al. (1991). However the present technique allows to quantify the strain contribution from any of the tissue layers or sublayer. This poses a significant advantage over traditional methods as resulting information can further the understanding of the factors contributing to the mechanical behaviour of the tissue and provides an ideal platform for validating more and more refined models of tissue behaviour

Stiffness after total knee arthroplasty (TKA) is a common problem occurring between 5% and 30% of patients. Stiffness is defined as limited range of motion (ROM) that affects activities of daily living. A recent International Consensus on definition of stiffness of the knee graded stiffness as mild, moderate or severe (90–100, 70–89, <70, respectively) or an extension deficit (5–10, 11–20, >20). Stiffness can be secondary to an osseous, soft tissue, or prosthetic block to motion. Heterotopic bone or retained posterior osteophytes, abundant fibrotic tissue, oversized components with tight flexion or extension gaps or component malrotation can all limit knee motion. Infection should always be considered in the knee that gradually loses motion. Alternative causes include complex regional pain syndrome and Kinesiophobia that can limit motion without an underlying mechanical cause. The evaluation of knee stiffness radiographs of the knee and cross-section imaging should be performed if component malrotation is considered. A metal suppression MRI assists in quantifying the extent of fibrosis and its location in the anterior or posterior compartment of the knee. Inflammatory markers and joint aspiration as indicated to rule out infection. Arthrofibrosis, or post-surgical fibrosis, is related to abnormal scar formation after surgery that leads to loss of motion. The cause of arthrofibrosis is multifactorial and likely related to genetic host factors. Current research is focusing on molecular signatures that may better identify patients at risk. In addition, therapeutic interventions are being studied that best prevent fibrosis and its recurrence and include the use of anti-inflammatories, corticosteroids, Colchicine, biologic medications (IL-1 inhibitors) and low-dose radiation. Early treatment of the stiff TKA includes physical therapy and manipulation under anesthesia (MUA). MUA performed within 3 months may have the greatest increase in ROM but notable improvement can occur up to 6 months after TKA. After six months, arthroscopic or open surgery is recommended for persistent stiffness. Arthroscopic lysis of adhesions can improve ROM greater than 1 year after index TKA. Average improvement of ROM for both MUA and arthroscopic lysis of adhesions (usually in conjunction with MUA) is approximately 30 degrees. The outcome after open lysis of adhesions are reportedly poor but current adjuvant therapies may improve these clinical outcomes as this addresses the biologic, in addition to the mechanical, basis of fibrosis. Component revision performed for component malposition and stiffness has variable outcomes but a recent study reports a mean increase in ROM of 20 degrees and a modest improvement in overall knee function. The cause of post-operative stiffness after TKA is a complex interplay of the patient, surgeon, and post-operative factors. Correct diagnosis of the underlying cause of the stiff total knee is essential to optimizing treatment outcomes. More research in needed in how to best prevent and treat the biologic risk factors and pathways that contribute to post-surgical fibrosis

In recent years, cementless stems have dominated the North American market. There are several categories of cementless stems, but in the past 20 years, the two most popular designs in the United States have been the extensively coated cylindrical cobalt-chrome (CoCr) stem and the proximally coated tapered titanium stem, which in recent years has become the most common. The 10-year survival for both stem types has been over 95% with a distinction made on factors other than stem survival, including thigh pain, stress shielding, complications of insertion, and ease of revision. Conventional wisdom holds that proximally coated titanium stems have less stress shielding, less thigh pain, and a higher quality clinical result. Recent studies, however, including randomised clinical trials have found that the incidence of thigh pain and clinical result is essentially equivalent between the stem types, however, there is a modest advantage in terms of stress shielding for a tapered titanium stem over an extensively coated CoCr stem. One study utilizing pain drawings did establish that if a CoCr cylindrical stem was utilised, superior clinical results in terms of pain score and pain drawings were obtained with a fully coated versus a proximally coated stem. In spite of the lack of a clinically proven advantage in randomised trials, tapered titanium stems have been favored because of the occasional occurrence of substantial stress shielding, the increased clinical observation of thigh pain severe enough to warrant surgical intervention, ease of use of shorter tapered stems that involve removal of less trochanteric bone and less risk of fracture both at the trochanter and the diaphysis due to the shorter, and greater ease of insertion through more limited approaches, especially anterior approaches. When tapered stems are utilised, there may be an advantage to a more rectangular stem cross-section in patients with type C bone. In spite of the numerous clinical advantages of tapered titanium stems, there still remains a role for more extensively coated cylindrical stems in patients that have had prior surgery of the proximal femur, particularly for a hip fracture, which makes proximal fixation, ingrowth, and immediate mechanical stability difficult to assure consistently. Cement fixation should also be considered in these cases. While the marketplace and the clinical evidence strongly support routine use of tapered titanium proximally coated relatively short stems with angled rather than straight proximal lateral geometry in the vast majority of cases, there still remains a role for more extensively coated cylindrical and for specific indications

Introduction. Oxidation of ultrahigh molecular weight polyethylene (UHMWPE) can lead to failure of implants used in total joints. Cyclic loading is postulated to be one mechanism of in vivo oxidation in UHMWPE components as one previous study has shown [1]. We developed an accelerated aging test that incorporated compressive cyclic loading that the UHMWPE components would be exposed to in vivo. Surgeons are moving towards larger femoral heads in hip arthroplasty and removing less bone in knee arthroplasty necessitating thinner UHMWPE components. We hypothesized that, in this accelerated aging test, thinner UHMWPE components would be more susceptible to oxidation caused by the cyclic loading due to higher stresses in the material. Materials and Methods. All samples tested in this study were Conventional PE: GUR1050 was machined into test specimens, vacuum packaged and gamma sterilized. Test samples were blocks 100 mm × 89 mm in cross-section with 3 different thicknesses: 1 mm, 3 mm, and 10 mm (n=3 each). Three cylinders were cored out of each test sample to serve as controls (Fig 1a) that were physically separated and thereby isolating the oxidation attributable to an applied compressive cyclic load. The controls were placed back into the holes from where they were cored during testing. Compressive loading was administered by a 12.5 mm diameter applicator affixed to a hydraulic test frame (Fig 1b), and all testing was done at 80°C in air. A sinusoidal compressive cyclic stress between 1 and 10 MPa was applied at 5 Hz for 7 days. Microtomed thin films from all samples were analyzed via Fourier Transform Infrared Spectroscopy (FTIR) to quantify oxidation [2] after testing. Oxidation was measured through the thickness of the sample at targeted points along the length from directly underneath the center of the load applicator to 10mm away (Fig 1a). Oxidation was also measured through the thickness of the cylindrical controls. Results. The oxidation profiles of each sample at 0.0mm (Fig 2a) and 3.0mm (Fig 2b) from the center point of load application showed that as one decreases the thickness of the test sample the oxidation levels of the sample increase. Both locations showed increased oxidation over the control samples. Discussion. Cyclic loading increased the rate of oxidation of gamma sterilized UHMWPE. The oxidation also increased with decreasing thickness of the UHMWPE samples. This oxidation could potentially accelerate the long term oxidative instability and could contribute to the delamination failure of tibial inserts. For figures/tables, please contact authors directly.

Aims

When performing revision total hip arthroplasty using diaphyseal-engaging titanium tapered stems (TTS), the recommended 3 to 4 cm of stem-cortical diaphyseal contact may not be available. In challenging cases such as these with only 2 cm of contact, can sufficient axial stability be achieved and what is the benefit of a prophylactic cable? This study sought to determine, first, whether a prophylactic cable allows for sufficient axial stability when the contact length is 2 cm, and second, if differing TTS taper angles (2° vs 3.5°) impact these results.

Aims

Aseptic loosening is the most common cause of failure following cemented total knee arthroplasty (TKA), and has been linked to poor cementation technique. We aimed to develop a consensus on the optimal technique for component cementation in TKA.