Revision surgeries for orthopaedic infections are done in two stages – one surgery to implant an antibiotic spacer to clear the infection and another to install a permanent implant. A permanent porous implant, that can be loaded with antibiotics and allow for single-stage revision surgery, will benefit patients and save healthcare resources. Gyroid structures can be constructed with high porosity, without stress concentrations that can develop in other period porous structures [1] [2]. The purpose of this research is to compare the resulting bone and prosthesis stress distributions when porous versus solid stems are implanted into three proximal humeri with varying bone densities, using finite element models (FEM).

Porous humeral stems were constructed in a gyroid structure at porosities of 60%, 70%, and 80% using computer-aided design (CAD) software. These CAD models were analyzed using FEM (Abaqus) to look at the stress distributions within the proximal humerus and the stem components with loads and boundary conditions representing the arm actively maintained at 120˚ of flexion. The stem was assumed to be made of titanium (Ti6Al4V). Three different bone densities were investigated, representing a healthy, an osteopenic, and an osteoporotic humerus, with an average bone shape created using a statistical shape and density model (SSDM) based on 75 cadaveric shoulders (57 males and 18 females, 73 12 years) [3]. The Young's moduli (E) of the cortical and trabecular bones were defined on an element-by-element basis, with a minimum allowable E of 15 MPa. The Von Mises stress distributions in the bone and the stems were compared between different stem scenarios for each bone density model.

A preliminary analysis shows an increase in stress values at the proximal-lateral region of the humerus when using the porous stems compared to the solid stem, which becomes more prominent as bone density decreases. With the exception of a few mesh dependent singularities, all three porous stems show stress distributions below the fatigue strength of Ti-6Al-4V (410 MPa) for this loading scenario when employed in the osteopenic and osteoporotic humeri [4]. The 80% porosity stem had a single strut exceeding the fatigue strength when employed in the healthy bone.

The results of this study indicate that the more compliant nature of the porous stem geometries may allow for better load transmission through the proximal humeral bone, better matching the stress distributions of the intact bone and possibly mitigating stress-shielding effects. Importantly, this study also indicates that these porous stems have adequate strength for long-term use, as none were predicted to have catastrophic failure under the physiologically-relevant loads. Although these results are limited to a single boney geometry, it is based on the average shape of 75 shoulders and different bone densities are considered. Future work could leverage the shape model for probabilistic models that could explore the effect of stem porosity across a broader population. The development of these models are instrumental in determining if these structures are a viable solution to combatting orthopaedic implant infections.

Equilibrative nucleoside transporter 1 (ENT1) transfers nucleosides, such as adenosine, across plasma membranes. We reported previously that mice lacking ENT1 (ENT1-KO) exhibit progressive ectopic calcification of spinal tissues, including the annulus fibrosus (AF) of intervertebral discs (J Bone Miner Res 28:1135–49, 2013, Bone 90:37–49, 2016). Our purpose was twofold: (1) to compare ectopic calcifications in ENT1-KO mice with those in human DISH, and (2) to investigate the molecular pathways underlying pathological calcification in ENT1-KO mice.

Studies were performed with age-matched wild-type (WT) and ENT1-KO mice, as well as human cadaveric vertebral columns meeting radiographic criteria for DISH. Mouse and human specimens were scanned using high-resolution, micro-computed tomography (micro-CT). As well, some samples were decalcified and processed for histological assessment. Calcified lesions in selected specimens were examined using energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). To investigate molecular changes associated with ectopic calcification, we isolated AF tissue from thoracic intervertebral discs of WT and ENT1-KO mice. Tissues were then subjected to transcriptomic and proteomic analyses.

Micro-CT of ENT1-KO mice revealed ectopic calcification of spinal tissues, first appearing in the cervical-thoracic region and extending caudally with advancing age. Histological examination of calcified lesions in mice revealed accumulations of amorphous, eosinophilic, acellular material in paraspinal ligaments and entheses, intervertebral discs, mandibular symphysis, and sternocostal articulations. There was no evidence of inflammation associated with these lesions. EDX of calcified lesions revealed a high content of calcium and phosphorus in a molar ratio of ∼1.6, with hydroxyapatite detected by micro-XRD. Ten human cadaveric spines (three females and seven males, mean age 81 years) that met radiographic criteria for DISH were analysed in detail by micro-CT. Remarkable heterogeneity in the density and morphology of ectopic calcifications was observed. Analyses of calcifications by EDX and XRD again yielded a calcium/phosphorus ratio of ∼1.6 and a crystalline diffraction pattern matching hydroxyapatite. Histological examination of human lesions revealed regions of mature ossification and other areas of irregular amorphous calcification that resembled lesions in ENT1-KO mice. Microarray analysis of AF tissue from WT and ENT1-KO mice showed extensive dysregulation of transcription in affected tissues. Cell cycle-associated transcripts were the most affected, including the E2f family of transcription factors and proliferating cell nuclear antigen. In addition, expression of genes involved in the regulation of mineralization and bone development were dysregulated. Proteomic analyses confirmed transcriptomic changes and revealed alterations in known modulators of biomineralization such as matrix Gla-protein.

Many of the characteristics of ectopic calcification in ENT1-KO mice resemble those of DISH in humans. Human lesions were found to be heterogeneous with regions of pathological ossification and amorphous calcification, the latter resembling lesions in the mouse model. Our studies of the molecular events associated with ectopic calcification in ENT1-KO mice may provide insights into the pathogenesis of DISH in humans. ENT1-KO mice may also be useful for evaluating therapeutics for the prevention of ectopic calcification in DISH and related disorders.

Introduction

Infections affect 1–3% of Total Knee Arthroplasty (TKA) patients with severe ramifications to mobility. Unfortunately, reinfection rates are high (∼15%) suggesting improved diagnostics are required. A common strategy to treat TKA infection in North America is the two-stage revision procedure involving the installation of a temporary spacer in the joint while the infection is treated for 6–12 weeks before permanent revision. Subdermal temperature increases during infection by 1–4°C providing a potential indicator for when the infection has been cleared. We propose an implantable temperature sensor integrated into a tibial spacer for telemetric use. We hypothesized that suitable sensing performance for infection monitoring regarding precision and relative accuracy can be attained using a low power, compact, analog sensor with <0.1ºC resolution.

Purpose: Accurate acetabular cup positioning is essential to successful total hip arthroplasty (THA). Intra-operative navigation of the acetabular component can optimize positioning, but often necessitates registration of the pelvis in the supine position. The majority of surgeons use the lateral position, however, which hides commonly employed registration landmarks. The purpose of this study was to identify novel anatomical landmarks for use in navigated THA from the lateral approach.

Method: We identified 156 patients that underwent pelvic CT scans for non-orthopaedic reasons from which 60 patients (mean age 62 years; 30 males, 30 females) were included in the study. CT scans were analyzed with sophisticated software (region grow, isosurface creation, and geometry overlay features). Saved coordinates from each scan were inputted into the program MATLAB (Mathworks, Natick, MA), v7.0, on a Macintosh-based workstation. A code was created to be able to calculate the normal vector for both planes and then calculate the angle formed between the normal vectors. The anterior plane (pubic tubercle (PT) and anterior superior iliac spine (ASIS)) was defined in addition to a series of lateral planes by retaining the ipsilateral PT and ASIS from the anterior plane, plus a variable third landmark. Angles obtained were those between the anterior and lateral planes. Angle conversions between the planes were analyzed using a paired t-test with a p-value of < 0.05 accepted as significant.

Results: The list of landmarks acquired included those used for supine registration (PT and ASIS) in addition to: posterior superior iliac spine (PSIS); posterior inferior iliac spine, (PIIS); ischial tuberosity (IT); tuber-culum of the iliac crest (TIC); and a line drawn along the outer lip of the iliac crest. The angle between the anterior plane and the novel lateral planes did not show a significant level of variance for two of the proposed lateral planes (P< 0.05).

Conclusion: An imageless navigation system in THA that can be accurately employed in the lateral position will benefit many surgeons. The invariance in angle calculations for the lateral planes calculated using the PSIS and the TIC suggest that they could be novel pelvic landmarks for lateral plane registration.

Purpose: Osteoarthritis (OA) is a complex disease process affecting both articular cartilage and underlying bone. An emphasis has been placed on understanding changes in articular cartilage that occur with disease progression, but comparatively little work has been done to understand changes in subchondral bone. The purpose of this study was to evaluate the architectural changes that occur in underlying osteoarthritic bone and to determine their relation to the stages of arthroscopic disease progression.

Methods: Three cadaver knees were evaluated and graded arthroscopically using the Marshall grading system. Representative bone plugs were then extracted from each compartment. Twenty-eight plugs were extracted and imaged using microcomputed tomography (microCT) scanner developed at the Robart’s Research Institute. Volumetric data for each plug biopsy was obtained in 20 minutes of scan time at an isotropic resolution of 68 μm voxels. The data acquired was analyzed using the GE Health Care Scan Control software and reconstruction utility. Subchondral bone thickness bone mineral density (BMD), trabecular thickness (TT), trabecular separation (TS), and structure model index (SMI) were collected and compared in the medial, lateral and patellofemoral compartments of the knees.

Results: No statistical difference was found in any of the parameters when compared with advancing arthroscopic disease progression. When the data was pooled into normal and osteoarthritic specimens, BMD was found to be significantly decreased (p < 0.05) in osteoarthritic bone. A decrease in BVF and an increase in SMI approached significance in osteoarthritic bone.

Conclusions: Further investigation is required for a complete understanding of the architectural changes that occur in subchondral bone with disease progression. A better understanding of OA would have clinical implications in primary and secondary disease prevention. Funding: Other Education Grant