Microsporidia (Encephalitozoon cuniculi) in Patients with Degenerative Hip and Knee Disease, Czech Republic.

Total joint arthroplasty is a commonly used surgical procedure in orthopedics. Revision surgeries are required in >10% of patients mainly because of prosthetic joint infection caused by bacteria or aseptic implant loosening caused by chronic inflammation. Encephalitozoon cuniculi is a microsporidium, an obligate intracellular parasite, capable of exploiting migrating proinflammatory immune cells for dissemination within the host. We used molecular detection methods to evaluate the incidence of E. cuniculi among patients who had total hip or knee arthroplasty revision. Out of 49 patients, E. cuniculi genotypes I, II, or III were confirmed in joint samples from 3 men and 2 women who had implant loosening. Understanding the risks associated with the presence of microsporidia in periprosthetic joint infections is essential for proper management of arthroplasty. Furthermore, E. cuniculi should be considered a potential contributing cause of joint inflammation and arthrosis.

Detection of Total Hip Replacement Loosening Based on Structure-Borne Sound: Influence of the Position of the Sensor on the Hip Stem.

Accurate detection of implant loosening is crucial for early intervention in total hip replacements, but current imaging methods lack sensitivity and specificity. Vibration methods, already successful in dentistry, represent a promising approach. In order to detect loosening of the total hip replacement, excitation and measurement should be performed intracorporeally to minimize the influence of soft tissue on damping of the signals. However, only implants with a single sensor intracorporeally integrated into the implant for detecting vibrations have been presented in the literature. Considering different mode shapes, the sensor's position on the implant is assumed to influence the signals. In the work at hand, the influence of the position of the sensor on the recording of the vibrations on the implant was investigated. For this purpose, a simplified test setup was created with a titanium rod implanted in a cylinder of artificial cancellous bone. Mechanical stimulation via an exciter attached to the rod was recorded by three accelerometers at varying positions along the titanium rod. Three states of peri-implant loosening within the bone stock were simulated by extracting the bone material around the titanium rod, and different markers were analyzed to distinguish between these states of loosening. In addition, a modal analysis was performed using the finite element method to analyze the mode shapes. Distinct differences in the signals recorded by the acceleration sensors within defects highlight the influence of sensor position on mode detection and natural frequencies. Thus, using multiple sensors could be advantageous in accurately detecting all modes and determining the implant loosening state more precisely.

Influence of sportive activity on functional and radiographic outcomes following reverse total shoulder arthroplasty: a comparative study.

BACKGROUND: The purpose of the present study was to compare the functional and radiographic outcomes following reverse total shoulder arthroplasty (RTSA) in a senior athletic and non-athletic population. MATERIAL AND METHODS: In this retrospective cohort study, patients who underwent RTSA between 06/2013 and 04/2018 at a single institution were included. Minimum follow-up was 2 years. A standardized questionnaire was utilized for assessment of patients' pre- and postoperative physical fitness and sportive activity. Patients who resumed at least one sport were assigned to the athletic group, while patients who ceased participating in sports were assigned to the non-athletic group. Postoperative clinical outcome measures included the Constant score (CS), American Shoulder and Elbow Surgeons (ASES) score, Simple Shoulder Test (SST), and visual analog scale (VAS) for pain. Active shoulder range of motion (ROM) and abduction strength were assessed. Radiographic evaluation was based on a standardized core set of parameters for radiographic monitoring of patients following shoulder arthroplasty. RESULTS: Sixty-one of 71 patients (85.9%; mean age: 72.1 ± 6.6 years) were available for clinical and radiographic follow-up at a mean of 47.1 ± 18.1 months. Thirty-four patients (55.7%) were assigned to the athletic group and 27 patients (44.3%) to the non-athletic group. The athletic group demonstrated significantly better results for CS (P = 0.002), ASES score (P = 0.001), SST (P = 0.001), VAS (P = 0.022), active external rotation (P = 0.045) and abduction strength (P = 0.016) compared to the non-athletic group. The overall rate of return to sport was 78.0% at an average of 5.3 ± 3.6 months postoperatively. Incomplete radiolucent lines (RLL) around the humeral component were found significantly more frequently in the athletic group compared to the non-athletic group (P = 0.019), whereas the occurrence of complete RLLs around the implant components was similar (P = 0.382). Scapular notching was observed in 18 patients (52.9%) of the athletic group and 12 patients (44.9%) of the non-athletic group (P = 0.51). The overall rate for revision surgery was 8.2%, while postoperative complications were encountered in 3.3% of cases. CONCLUSION: At mid-term follow-up, the athletic population demonstrated significantly better clinical results following RTSA without a higher rate of implant loosening and scapular notching when compared to non-athletic patients. However, incomplete radiolucency around the humeral component was observed significantly more often in the athletic group. LEVEL OF EVIDENCE: III.

Mechanical loading releases osteoclastogenesis-modulating factors through stimulation of the P2X7 receptor in hematopoietic progenitor cells.

Mechanical instability of bone implants stimulate osteoclast differentiation and peri-implant bone loss, leading to prosthetic loosening. It is unclear which cells at the periprosthetic interface transduce mechanical signals into a biochemical response, and subsequently facilitate bone loss. We hypothesized that mechanical overloading of hematopoietic bone marrow progenitor cells, which are located near to the inserted bone implants, stimulates the release of osteoclast-inducing soluble factors. Using a novel in vitro model to apply mechanical overloading, we found that hematopoietic progenitor cells released adenosine triphosphate (ATP) after only 2 min of mechanical loading. The released ATP interacts with its specific receptor P2X7 to stimulate the release of unknown soluble factors that inhibit (physiological loading) or promote (supraphysiological loading) the differentiation of multinucleated osteoclasts derived from bone marrow cultures. Inhibition of ATP-receptor P2X7 by Brilliant Blue G completely abolished the overloading-induced stimulation of osteoclast formation. Likewise, stimulation of P2X7 receptor on hematopoietic cells by BzATP enhanced the release of osteoclastogenesis-stimulating signaling molecules to a similar extent as supraphysiological loading. Supraphysiological loading affected neither gene expression of inflammatory markers involved in aseptic implant loosening (e.g., interleukin-1ß (IL-1ß), IL-6, tumor necrosis factor-α, and PTGES2) nor expression of the osteoclast modulators receptor activator of nuclear factor κ-Β ligand and osteoprotegerin. Our findings suggest that murine hematopoietic progenitor cells are a potential key player in local mechanical loading-induced bone implant loosening via the ATP/P2X7-axis. Our approach identifies potential therapeutic targets to prevent prosthetic loosening.

Impact of Periprosthetic Fibroblast-Like Cells on Osteoclastogenesis in Co-Culture with Peripheral Blood Mononuclear Cells Varies Depending on Culture System.

Co-culture studies investigating the role of periprosthetic fibroblasts (PPFs) in inflammatory osteoclastogenesis reveal contrary results, partly showing an osteoprotective function of fibroblasts and high OPG expression in monolayer. These data disagree with molecular analyses of original periosteolytic tissues. In order to find a more reliable model, PPFs were co-cultivated with peripheral blood mononuclear cells (PBMCs) in a transwell system and compared to conventional monolayer cultures. The gene expression of key regulators of osteoclastogenesis (macrophage colony-stimulating factor (MCSF), receptor activator of NF-κB ligand (RANK-L), osteoprotegerin (OPG), and tumor necrosis factor alpha (TNFα)) as well as the ability of bone resorption were analyzed. In monolayer co-cultures, PPFs executed an osteoprotective function with high OPG-expression, low RANK-L/OPG ratios, and a resulting inhibition of osteolysis even in the presence of MCSF and RANK-L. For transwell co-cultures, profound changes in gene expression, with a more than hundredfold decrease of OPG and a significant upregulation of TNFα were observed. In conclusion, we were able to show that a change of culture conditions towards a transwell system resulted in a considerably more osteoclastogenic gene expression profile, being closer to findings in original periosteolytic tissues. This study therefore presents an interesting approach for a more reliable in vitro model to examine the role of fibroblasts in periprosthetic osteoclastogenesis in the future.

[Hounsfield units as a measure of bone density-applications in spine surgery]. / "Hounsfield units" als Maß für die Knochendichte ­ Anwendungsmöglichkeiten in der Wirbelsäulenchirurgie.

Despite today's good diagnostic and therapeutic options for osteoporosis, the number of unidentified cases is very high and therapy is therefore usually inadequate. Frequently, the diagnosis of osteoporosis is made only after the occurrence of a fracture. The reason for this, apart from the costs incurred as well as the additional radiation exposure of the diagnostics, is certainly the limited availability of dual energy X­ray absorptiometry (DEXA) as well as quantitative computed tomography (q-CT). In search of an alternative technique, Hounsfield units (HU) of the clinical CT examination proved to be ground-breaking: the results of previous investigations demonstrated a reliable correlation between the T values of the DEXA measurement and the HU of the same vertebral body. Due to the widespread use of clinical CT scans of the thorax and the abdomen for a variety of indications, it is expected that the number of unidentified cases of osteoporosis can be significantly reduced-without additional costs and radiation exposure associated with osteoporosis screening. In addition to osteoporosis diagnostics, the calculated HU may also provide better preoperative planning as well as predicting the further course of the disease. Thus, the risk for vertebral body fractures, screw loosening and cage sintering after ventral fusion operations can be sufficiently predicted. In this way, preoperative modifications to the surgical procedure can be made to reduce the risk of implant failure.

Pedicle screw loosening is correlated to chronic subclinical deep implant infection: a retrospective database analysis.

PURPOSE: Spinal fusion is used for treatment of spinal deformities, degeneration, infection, malignancy, and trauma. Reduction of motion enables osseous fusion and permanent stabilization of segments, compromised by loosening of the pedicle screws (PS). Deep implant infection, biomechanical, and chemical mechanisms are suspected reasons for loosening of PS. Study objective was to investigate the frequency and impact of deep implant infection on PS loosening. METHODS: Intraoperative infection screening from wound and explanted material sonication was performed during revision surgeries following dorsal stabilization. Case history events and factors, which might promote implant infections, were included in this retrospective survey. RESULTS: 110 cases of spinal metal explantation were included. In 29.1% of revision cases, infection screening identified a germ, most commonly Staphylococcus (53.1%) and Propionibacterium (40.6%) genus. Patients screened positive had a significant higher number of previous spinal operations and radiologic loosening of screws. Patients revised for adjacent segment failure had a significantly lower rate of positive infection screening than patients revised for directly implant associated reasons. Removal of implants that revealed positive screening effected significant pain relief. CONCLUSIONS: Chronic implant infection seems to play a role in PS loosening and ongoing pain, causing revision surgery after spinal fusion. Screw loosening and multiple prior spinal operations should be suspicious for implant infection after spinal fusion when it comes to revision surgery. These slides can be retrieved under Electronic Supplementary Material.

Evaluation of the success and complication rates of self-drilling orthodontic mini-implants.

AIMS: Orthodontic mini-implants are important devices for successful anchorage management in orthodontics; however, the survival of these devices depends on several clinical factors. The aim of our study was to calculate the success and complication rates of orthodontic mini-implants. MATERIALS AND METHODS: In this retrospective study, patients of our orthodontic department were enrolled, getting overall 59 orthodontic mini-implants during their orthodontic treatment in a 2-year period. Every patient had one or more of the 1.6 mm × 8 mm in size self-drilling mini-implants (Jeil Dual Top Anchor System, Jeil Medical Corp., Seoul, Korea). Screw loading was performed immediately after insertions, keeping tension forces under 150 g. Soft tissue and bone infections, implant mobility and screw loss, implant fracture, and neighboring tooth injury were registered. Relationships between variables were tested using the Chi-square test for statistical significance. RESULTS: The success rate of the orthodontic mini-implants was 89.8% in this study while the average loading period was 8.1 months. Soft-tissue infections varied between 6.3% and 33.3% of the cases while screw mobility varied between 3.1% and 20.8% of the cases regarding the anatomic localization. Screw mobility was significantly more frequent in the buccal fold than in the palate (P = 0.034). Screw mobility was significantly more frequent in the buccal fold than in the palate (P = 0.034) and screw mobility was found more frequently in case of intrusions than by extrusions (P = 0.036). CONCLUSIONS: The overall success rate of mini-implants was found acceptable in this study, however, screw mobility in the buccal fold showed a high incidence, suggesting the thorough consideration of the immediate loading by buccal mini-implants.

Pharmacokinetic and Biodistribution Studies of HPMA Copolymer Conjugates in an Aseptic Implant Loosening Mouse Model.

N-(2-Hydroxypropyl) methacrylamide (HPMA) copolymers were previously found to represent a versatile delivery platform for the early detection and intervention of orthopedic implant loosening. In this article, we evaluated the impact of different structural parameters of the HPMA copolymeric system (e.g., molecular weight (MW), drug content) to its pharmacokinetics and biodistribution (PK/BD) profile. Using 125I, Alexa Fluor 488, and IRDye 800 CW-labeled HPMA copolymer-dexamethasone (P-Dex) conjugates with different MW and dexamethasone (Dex) contents, we found the MW to be the predominant impact factor on the PK/BD profiles of P-Dex, with Dex content as a secondary impact factor. In gamma counter-based PK/BD studies, increased MW of P-Dex reduced elimination, leading to lower clearance, longer half-life, and higher systemic exposure (AUC and MRT). In the semiquantitative live animal optical imaging evaluation, the distribution of P-Dex to the peri-implant inflammatory lesion increased when MW was increased. This result was further confirmed by FACS analyses of cells isolated from peri-implant regions after systemic administration of Alexa Fluor 488-labeled P-Dex. Since the in vitro cell culture study suggested that the internalization of P-Dex by macrophages is generally independent of P-Dex's MW and Dex content, the impact of the MW and Dex content on its PK/BD profile was most likely exerted at physiological and pathophysiological levels rather than at the cellular level. In both gamma counter-based PK/BD analyses and semiquantitative optical imaging analyses, P-Dex with 6 wt % Dex content showed fast clearance. Dynamic light scattering analyses unexpectedly revealed significant molecular aggregation of P-Dex at this Dex content level. The underlining mechanisms of the aggregation and fast in vivo clearance of the P-Dex warrant further investigation.

Radiographic interpretation of carpometacarpal arthroplasty: correlation between radiographic loosening and clinical outcome.

OBJECTIVE: To assess the radiographic appearance and interpretation of loosening in patients following first carpometacarpal joint pyrohemisphere arthroplasty. MATERIALS AND METHODS: A retrospective review over a 6-year period was performed identifying patients with first carpometacarpal pyrohemisphere implants. All postoperative radiographs were reviewed and compared with clinical information. Loosening was defined as greater than 1 mm of periprosthetic lucency or increasing lucency on serial studies. Adverse clinical outcome was defined as infection, complex regional pain syndrome, subluxation or an inability to return to activities of daily living. Statistical analysis included Cohen's Kappa coefficient to measure inter-reader agreement for radiographic interpretation and the agreement between radiographic loosening and an undesired or adverse clinical outcome. RESULTS: Thirty-one implants in 26 patients were reviewed. A total of 73 postoperative radiographs were reviewed. The mean age of the study subjects was 58 years. The mean radiographic follow-up was 13 months (range: 1-56). All arthroplasties were performed for osteoarthritis. Only one repeat surgery was performed. There was good agreement amongst readers with regard to radiographic interpretation, but the strength of agreement between radiographic loosening and adverse clinical outcome was poor. The sensitivity of radiography in predicting an adverse clinical outcome was 63%, specificity 65%, positive predictive value 39%, and negative predictive value 83%. CONCLUSION: Although radiography may be useful in the correct clinical context, it should not be utilized as the sole predictor of adverse clinical outcomes following carpometacarpal arthroplasty.

Long-term analysis of revision reverse shoulder arthroplasty using cemented long stems.

BACKGROUND: Revision of failed shoulder arthroplasty is often associated with poor results and a high rate of complications. Significant humeral bone loss after removal of long stems poses a considerable surgical challenge. Therefore, the aim of our study was the evaluation of the clinical and radiologic outcome of cemented long-stem humeral components in revision reverse shoulder arthroplasty with a minimum 5 years' follow-up. METHODS: Between June 2001 and June 2009, revision reverse shoulder arthroplasty using long-stem cemented humeral components was performed in 124 patients. Mean age at time of surgery was 69.6 years (range, 42-87 years). Complete clinical and radiographic data were available in 50 patients at a mean of 7 years (range, 5-11.6 years). Postoperative radiographs were evaluated for radiolucent lines, implant migration, fracture, and glenoid notching. RESULTS: The mean Constant score improved from 11.1 points (range, 0-27 points) to 39.5 points (range, 14-73 points) at the latest follow-up. Progressive humeral radiolucency was present in 24 patients, including 6 patients demonstrating complete loosening or progressive distal migration of the humeral stem. We noted an overall of 12 additional complications in 8 patients, necessitating revision surgery in 16. CONCLUSION: The use of long-stem humeral components is a beneficial treatment in revision reverse shoulder arthroplasty. Nevertheless, the high percentage of patients with humeral loosening is concerning. Modular cementless revision stems that are adapted to the distal humeral medullary canal and additional distal screw and cable fixation might enhance durable distal fixation in case of advanced bone loss.

Spatial mapping of humeral head bone density.

BACKGROUND: Short-stem humeral replacements achieve fixation by anchoring to the metaphyseal trabecular bone. Fixing the implant in high-density bone can provide strong fixation and reduce the risk of loosening. However, there is a lack of data mapping the bone density distribution in the proximal humerus. The aim of the study was to investigate the bone density in proximal humerus. METHODS: Eight computed tomography scans of healthy cadaveric humeri were used to map bone density distribution in the humeral head. The proximal humeral head was divided into 12 slices parallel to the humeral anatomic neck. Each slice was then divided into 4 concentric circles. The slices below the anatomic neck, where short-stem implants have their fixation features, were further divided into radial sectors. The average bone density for each of these regions was calculated, and regions of interest were compared using a repeated-measures analysis of variance with significance set at P < .05. RESULTS: Average apparent bone density was found to decrease from proximal to distal regions, with the majority of higher bone density proximal to the anatomic neck of the humerus (P < .05). Below the anatomic neck, bone density increases from central to peripheral regions, where cortical bone eventually occupies the space (P < .05). In distal slices below the anatomic neck, a higher bone density distribution in the medial calcar region was also observed. CONCLUSION: This study indicates that it is advantageous with respect to implant fixation to preserve some bone above the anatomic neck and epiphyseal plate and to use the denser bone at the periphery.

Anterior approach for total hip arthroplasty conversion of hip fusion.

PURPOSE: Hip fusion conversion has shown mixed results, in particular a higher rate of failure than primary total hip replacement. Conversion is usually carried out by a lateral approach. METHODS: We reported a series of 37 hip fusion conversions performed by an anterior approach. Clinical and radiographic outcomes of this unusual approach were reported at eight years of follow up. RESULTS: At eight years of follow up, survivorship was 86. 6 % (IC 95 %: 62.4-95.7 %). Sixteen patients reported good relief of the pre-operative back spine or knee pain. PMA score was significantly improved. Two implant aseptic loosenings needing revision surgery were reported. CONCLUSION: The anterior approach seemed to be as good as the other hip approaches for hip fusion conversion to total hip replacement.

Systemically administered zoledronic acid activates locally implanted synthetic hydroxyapatite particles enhancing peri-implant bone formation: A regenerative medicine approach to improve fracture fixation.

Fracture fixation in an ageing population is challenging and fixation failure increases mortality and societal costs. We report a novel fracture fixation treatment by applying a hydroxyapatite (HA) based biomaterial at the bone-implant interface and biologically activating the biomaterial by systemic administration of a bisphosphonate (zoledronic acid, ZA). We first used an animal model of implant integration and applied a calcium sulphate (CaS)/HA biomaterial around a metallic screw in the tibia of osteoporotic rats. Using systemic ZA administration at 2-weeks post-surgery, we demonstrated that the implant surrounded by HA particles showed significantly higher peri­implant bone formation compared to the unaugmented implants at 6-weeks. We then evaluated the optimal timing (day 1, 3, 7 and 14) of ZA administration to achieve a robust effect on peri­implant bone formation. Using fluorescent ZA, we demonstrated that the uptake of ZA in the CaS/HA material was the highest at 3- and 7-days post-implantation and the uptake kinetics had a profound effect on the eventual peri­implant bone formation. We furthered our concept in a feasibility study on trochanteric fracture patients randomized to either CaS/HA augmentation or no augmentation followed by systemic ZA treatment. Radiographically, the CaS/HA group showed signs of increased peri­implant bone formation compared with the controls. Finally, apart from HA, we demonstrated that the concept of biologically activating a ceramic material by ZA could also be applied to ß-tricalcium phosphate. This novel approach for fracture treatment that enhances immediate and long-term fracture fixation in osteoporotic bone could potentially reduce reoperations, morbidity and mortality. STATEMENT OF SIGNIFICANCE: • Fracture fixation in an ageing population is challenging. Biomaterial-based augmentation of fracture fixation devices has been attempted but lack of satisfactory biological response limits their widespread use. • We report the biological activation of locally implanted microparticulate hydroxyapatite (HA) particles placed around an implant by systemic administration of the bisphosphonate zoledronic acid (ZA). The biological activation of HA by ZA enhances peri­implant bone formation. •Timing of ZA administration after HA implantation is critical for optimal ZA uptake and consequently determines the extent of peri­implant bone formation. • We translate the developed concept from small animal models of implant integration to a proof-of-concept clinical study on osteoporotic trochanteric fracture patients. • ZA based biological activation can also be applied to other calcium phosphate biomaterials.

Infection Microenvironment-Responsive Coating on Titanium Surfaces for On-Demand Release of Therapeutic Gas and Antibiotic.

Aseptic loosening and bacterial infection pose significant challenges in the clinical application of titanium (Ti) orthopedic implants, which are primarily caused by insufficient osseointegration and bacterial contamination. To address these issues, a responsive coating on Ti surface is constructed, which achieves enhanced osseointegration and infection elimination by on-demand release of therapeutic gas hydrogen sulfide (H2S) and antibiotic. TiO2 nanotubes (TNT) are anodized on the Ti surface to enhance its bioactivity and serve as reservoirs for the antibiotic. An infection microenvironment-responsive macromolecular H2S donor layer is coated on top of TNT to inhibit premature leakage of antibiotic. This layer exhibits a sustained release of low-dosage H2S, which is capable of promoting the osteogenic differentiation and migration of cells. Moreover, the compactness of the macromolecular H2S donor layer could be broken by bacterial invasion, leading to rapid antibiotic release thus preventing infection. In vitro antibacterial experiments validates significant antibacterial activity of the coating against both Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Crucially, this coating effectively suppresses implant-associated infection with 98.7% antibacterial efficiency in a rat femoral bone defect model, mitigates inflammation at the defect site and promotes osseointegration of the Ti orthopedic implant.

Revision surgery of reverse shoulder arthroplasty.

BACKGROUND: There is limited knowledge regarding revision of reverse shoulder arthroplasty (RSA). This study assesses reasons for failure in RSA and evaluates the outcomes of revision RSA. MATERIALS AND METHODS: Between 1997 and 2009, 37 patients with RSA had revision surgery. Clinical and radiologic examinations performed preoperatively and at 3 months, at 6 months, and then annually postoperatively were analyzed retrospectively. Patients were reviewed with a minimum 2-year follow-up. RESULTS: The most common causes for RSA revision were prosthetic instability (48%); humeral loosening, derotation, or fracture (21%); and infection (19%). Only 2 patients (3%) had to be reoperated on for glenoid loosening. More than 1 re-intervention was performed in 11 patients (30%) because of recurrence of the same complication or appearance of a new complication. Underestimation of humeral shortening and excessive medialization were common causes of recurrent prosthetic instability. Proximal humeral bone loss was found to be a cause for humeral loosening or derotation. Previous surgery was found as a potential cause of low-grade infection. At a mean follow-up of 34 months, 32 patients (86%) had retained the RSA whereas 2 patients (6%) had undergone conversion to humeral hemiarthroplasty and 3 (8%) to a resection arthroplasty. The mean Constant score in patients who retained the RSA increased from 19 points before revision to 47 points at last follow-up (P < .001). CONCLUSIONS: Even if revision may lead to several procedures in the same patient, preservation or replacement of the RSA is largely possible, allowing for a functional shoulder. Full-length scaled radiographs of both humeri are recommended to properly assess humeral shortening and excessive medialization before revision.

Capacitive stimulation-sensing system for instrumented bone implants: Finite element model to predict the electric stimuli delivered to the interface.

BACKGROUND: Prevalence of orthopaedic replacements are increasing around the world. The main cause of revision remains associated to the interface loosening. In this work, a computational study using the Finite element method was developed to predict the electric field stimuli delivered to trabecular bone structures, as well as to predict the sensing ability to detect different bone-implant interface scenarios. METHODS: Three finite element models were developed: two simplified models, including a Gyroid TMP structure, and a realistic model based on microCT scan of a trabecular bone from sheep vertebra. Simulations were performed using a co-surface capacitive technology for stimulating and sensing bone-implant interfaces. Different fixation scenarios were considered, namely by establishing bone-stimulator gap sizes up to 1 mm (from fixation to massive loosening scenario). Electrodes were excited with sinusoidal and square electric signals up to 10V voltage and 64kHz frequency. RESULTS: Simplification of bone geometry resulted in significant electric stimuli differences compared to the realistic bone geometry. Realistic modelling allowed to observe that, in the fixation scenario, the electric field stimuli decreased 85% from the sensor interface to a parallel plane 2 mm apart from such interface. A significant influence of the bone-stimulator distance on the electric stimuli was found: the electric stimuli magnitudes varied in the range between 0.38 V/mm (fixation scenario) and 4.8 mV/mm (massive loosening scenario) for voltages up to 10V. Strong frequency-dependent behaviours were also observed in the electric stimuli: their magnitudes can reach 106-fold decreases when the excitation frequency is decreased from 32 kHz to 14 Hz CONCLUSION: This study points out the inability of our two simplified models to predict the electric stimulation provided to different bone-implant interface scenarios. Results highlight that co-surface stimulators can deliver osteogenic electric stimuli along trabecular bone structures, ensuring low electric power excitations. Moreover, realistic models strongly enhance the sensing predictability of the bone-implant fixation states. These new and significant evidences provide a strong support to integrate co-surface capacitive into bioelectronic implants for both therapeutic and sensing operations.

Metallosis with spinal implant loosening after spinal instrumentation: A case report.

BACKGROUND: Spinal metallosis is a rare complication following spinal instrumentation whereby an inflammatory response to the metal implants results in the development of granulomatous tissue. CASE SUMMARY: We describe the case of a 78-year-old woman who had recurrence of back pain 5 years after lumbar spine posterior decompression and instrumented fusion. Lumbar spine radiographs showed hardware loosening and magnetic resonance imaging showed adjacent segment disease. Revision surgery revealed evidence of metallosis intraoperatively. CONCLUSION: Spinal metallosis can present several years after instrumentation. Radiography and computed tomography may demonstrate hardware loosening secondary to metallosis. Blood metal concentrations associated with spinal metallosis have yet to be established. Hence, metallosis is still an intraoperative and histopathological diagnosis. The presence of metallosis after spinal instrumentation likely indicates a more complex underlying problem: Pseudarthrosis, failure to address sagittal balance, infection, and cross-threading of set screws. Hence, identifying metallosis is important, but initiating treatment promptly for symptomatic implant loosening is of greater paramount.

Nail-stem construct method for periprosthetic humeral fractures with recalcitrant nonunion after total elbow arthroplasty: A surgical technique.

Objectives: The objective of this study was to describe the surgical technique using an innovative nail-stem construct in treatment of periprosthetic humeral fractures with recalcitrant nonunion after total elbow arthroplasty (TEA). Materials and Methods: Patients diagnosed with humeral recalcitrant nonunion in periprosthetic fractures and stem loosening after TEA were retrospectively recruited between 2018 and 2019. The demographic data and related clinical outcomes were recorded. We use a cutting length of the nail pushing into the humeral canal and then pull back distally to dock the tip of the humeral stem. The cement was packed into the humeral canal, and the periprosthetic bone defect was impacting with harvested allograft chip. Results: Patient age, gender, lesion site, number of previous surgeries, and the time period from the primary TEA to the nail-stem reconstruction were allocated. Moreover, the range of motion, degree of elbow stability, and level of pain were evaluated for each patient following this procedure. All the four patients achieved an optimal range of motion and secure stability with painless elbow at final follow-up. Conclusion: Our proposed nail-stem construct with double allogenous bone plate is a feasible alternative for revisional TEA in patients with implant loosening, periprosthetic humeral fractures, and recalcitrant nonunion.