Temporary Protective Shoulder Implants for Revision Surgery with Bone Glenoid Grafting.

This article describes the development of a temporary protective glenoid prosthesis placed between the augmentation and humeral head prosthesis during the healing phase of shoulder prosthesis revision with necessary reconstruction of the bony structure of the glenoid. The glenoid protection prosthesis ensures the fixation of the augmentation material and protects the screws from contact with the metallic humeral head prosthesis. Another approach of the development is a reduction of the resorption of the augmentation by targeted mechanical stimulation of the tissue. The aim should be to achieve significantly improved conditions for the implantation of a new glenoid component at the end of the healing phase of the augmentation material in comparison to the current standard method. The development of the protective prosthesis was carried out according to specific needs and includes the collection of requirements and boundary conditions, the design and technical detailing of the implant, the verification of the development results as well as the validation of the design. For the verification, FEM simulations (Finite Element Analysis) were performed to estimate the mechanical stability in advance. Mechanical tests to confirm the stability and abrasion behavior have been carried out and confirm the suitability of the protective implant. The result of the present work is the detailed technical design of two variants of a glenoid protective prosthesis "GlenoProtect" for use in revision procedures on shoulder joints-with large-volume defects on the glenoid-treated by arthroplasty and the necessity of augmenting the glenoid, including a description of the surgical procedure for implantation.

Multi-patient finite element simulation of keeled versus pegged glenoid implant designs in shoulder arthroplasty.

This study investigates the mechanical behaviour of keeled and pegged implant designs used in shoulder arthroplasty for the first time using multiple 3D models. Thus, this study should provide valuable insights into the preferable use of either of these two controversial implant designs. Three-dimensional models of a scapula were derived from the CT scans of five patients, and an inter-patient-specific finite element analysis with special attention to bone density and boundary conditions was carried out. A distinct decrease in the investigated parameters was evident with the pegged implant in all of the patients, specifically for the implant and the bone cement. The relevance of the stress reduction within the bone is minor, whereas the reduction in the stress of the bone cement contributes to an increase in the bone cement survival. The particular construction of the pegged implant provides better stability and therefore supports bone ingrowth. The large variations between the patients show the necessity of patient-specific simulations and the use of multiple models to derive valuable results. In the conducted inter-patient-specific FEA, the pegged glenoid implants were found to exhibit superior behaviour compared with keeled implants. The results confirm the general clinical findings and demonstrate the FEA as a valuable tool in prosthetic and orthopaedic problems.

A Bone Sample Containing a Bone Graft Substitute Analyzed by Correlating Density Information Obtained by X-ray Micro Tomography with Compositional Information Obtained by Raman Microscopy.

The ability of bone graft substitutes to promote new bone formation has been increasingly used in the medical field to repair skeletal defects or to replace missing bone in a broad range of applications in dentistry and orthopedics. A common way to assess such materials is via micro computed tomography (µ-CT), through the density information content provided by the absorption of X-rays. Information on the chemical composition of a material can be obtained via Raman spectroscopy. By investigating a bone sample from miniature pigs containing the bone graft substitute Bio Oss®, we pursued the target of assessing to what extent the density information gained by µ-CT imaging matches the chemical information content provided by Raman spectroscopic imaging. Raman images and Raman correlation maps of the investigated sample were used in order to generate a Raman based segmented image by means of an agglomerative, hierarchical cluster analysis. The resulting segments, showing chemically related areas, were subsequently compared with the µ-CT image by means of a one-way ANOVA. We found out that to a certain extent typical gray-level values (and the related histograms) in the µ-CT image can be reliably related to specific segments within the image resulting from the cluster analysis.

Need for CT-based bone density modelling in finite element analysis of a shoulder arthroplasty revealed through a novel method for result analysis.

Treatment of common pathologies of the shoulder complex, such as rheumatoid arthritis and osteoporosis, is usually performed by total shoulder arthroplasty (TSA). Survival of the glenoid component is still a problem in TSA, whereas the humeral component is rarely subject to failure. To set up a finite element analysis (FEA) for simulation of a TSA in order to gain insight into the mechanical behaviour of a glenoid implant, the modelling procedure and the application of boundary conditions are of major importance because the computed result strongly depends upon the accuracy and sense of realism of the model. The goal of this study was to show the influence on glenoid stress distribution of a patient-specific bone density distribution compared with a homogenous bone density distribution for the purpose of generating a valid model in future FEA studies of the shoulder complex. Detailed information on the integration of bone density properties using existing numerical models as well as the applied boundary conditions is provided. A novel approach involving statistical analysis of values derived from an FEA is demonstrated using a cumulative distribution function. The results show well the mechanically superior behaviour of a realistic bone density distribution and therefore emphasise the necessity for patient-specific simulations in biomechanical and medical simulations.

Quality improvement in preoperative assessment by implementation of an electronic decision support tool.

OBJECTIVES: To evaluate the impact of the electronic decision support (eDS) tool 'PReOPerative evaluation' (PROP) on guideline adherence in preoperative assessment in statutory health care in Salzburg, Austria. MATERIALS AND METHODS: The evaluation was designed as a non-randomized controlled trial with a historical control group (CG). In 2007, we consecutively recruited 1363 patients admitted for elective surgery, and evaluated the preoperative assessment. In 2008, PROP was implemented and available online. In 2009 we recruited 1148 patients preoperatively assessed using PROP (294 outpatients, 854 hospital sector). Our analysis includes full blood count, liver function tests, coagulation parameters, electrolytes, ECG, and chest x-ray. RESULTS: The number of tests/patient without indication was 3.39 in the CG vs 0.60 in the intervention group (IG) (p<0.001). 97.8% (CG) vs 31.5% (IG) received at least one unnecessary test. However, we also observed an increase in recommended tests not performed/patient (0.05±0.27 (CG) vs 0.55±1.00 (IG), p<0.001). 4.2% (CG) vs 30.1% (IG) missed at least one necessary test. The guideline adherence (correctly tested/not tested) improved distinctively for all tests (1.6% (CG) vs 49.3% (IG), p<0.001). DISCUSSION: PROP reduced the number of unnecessary tests/patient by 2.79 which implied a reduction of patients' burden, and a relevant cut in unnecessary costs. However, the advantage in specificity caused an increase in the number of patients incorrectly not tested. Further research is required regarding the impact of PROP on perioperative outcomes.

Sinus elevation with a cortical bone graft block: a patient-specific three-dimensional finite element study.

PURPOSE: The aim of the present study was to perform a finite element (FE) analysis of a modified sinus elevation procedure involving additional implantation of a cortical bone graft block for stabilization of an implant. A secondary aim was to compare the modified sinus augmentation with the standard technique and to determine whether the FE model to replace a dental implant can be simplified into a cylinder without compromising the accuracy of the outcome. MATERIALS AND METHODS: Based on computed tomography data, three-dimensional FE models of half of a maxilla were created. A basic model was generated to analyze a conventional sinus elevation procedure and another was created for the modified version, which involved insertion of a cortical bone graft block. Two implant models were used in the premolar region: a typical threaded endosseous dental implant and a simplified 4 x 10-mm cylinder. Occlusal loads were applied in axial, mediotrusive, and laterotrusive directions, and perfect bonding was assumed to be present at all interfaces. RESULTS: The maximum von Mises stresses were significantly lower for the sinus graft models with added cortical bone than for the conventional sinus elevation under all types of loads. No significant difference was observed between the use of threaded implants and the simplified implant cylinders. CONCLUSION: The addition of a cortical bone graft may be a useful approach to decrease stresses around implants placed into the grafted sinus.