Biomechanical analysis for primary stability of shoulder arthrodesis in different resection situations.

BACKGROUND: Only very few publications dealing with shoulder arthrodesis after bone resection procedures and no biomechanical studies are available. The presented biomechanical analysis should ascertain the type of arthrodesis with the highest primary stability in different bone loss situations. METHODS: On 24 fresh cadaveric shoulder specimens three different bone loss situations were investigated under the stress of abduction, adduction, anteversion and retroversion without destruction by the use of a material testing machine. In each of the testings a 16-hole reconstruction plate was used and compared to arthrodesis with an additional dorsal 6-hole plate. FINDINGS: The primary stability of shoulder arthrodesis with a 16-hole reconstruction plate after humeral head resection could be increased significantly if an additional dorsal plate was used. However, no significant improvement with the additional plate was detected after resection of the acromion. Of all investigated forms, arthrodesis after humeral head resection with additional plate showed the highest and arthrodesis after humeral head resection without additional plate showed the lowest force values. The mean values for forces achieved in abduction and adduction were considerably higher than those in anteversion and retroversion. INTERPRETATION: There are no consistent specifications of arthrodesis techniques after resection situation available, thus the presented biomechanical testings give important information about the most stable form of arthrodesis in different types of bone loss. These findings provide an opportunity to minimize complications such as pseudarthrosis for a satisfying clinical outcome.

A system for engineering an osteochondral construct in the shape of an articular surface: preliminary results.

A tissue-engineered articular condyle could provide a new alternative approach to joint replacement. This study describes progress made towards engineering an articular condyle in vitro using human bone marrow stromal cells (hBMSCs) in a biphasic matrix. hBMSCs were transferred to a rat collagen-I hydrogel which was then pressed onto a bovine cancellous bone matrix. The gel/cell suspensions, each at a density of approximately 5 x 10(5)cells/ml containing fourth passage cells pressed into an adult human tibial condyle form using CT scan based moulds. The osteochondral constructs fabricated in vitro were stimulated in a bioreactor using cyclic compression and continuous perfusion. Penetration and cell distribution were demonstrated as homogeneous and cells were found to be viable after gel compression. The filamentous structure of the collagen fibres was more dense and homogeneous using compression. Mechanical tests showed a significant enhancement of primary matrix stability after initial compression. Stiffness was not observed to increase significantly over 7 days under loading in a bioreactor. The successful integration of mechanical stimulation in the tissue engineering process leads to an improvement in the structural and biomechanical properties of these tissues and offers new possibilities in the management of joint injuries and degenerative diseases. Remarkably, the stiffness was enhanced in our setting after initial compression of the construct in the glass cylinder without observing a negative influence on cell viability. Further studies need to clarify the influence of compression and various mechanical and hydrostatic stress patterns over different periods of time.

Tissue engineering of heart valves: biomechanical and morphological properties of decellularized heart valves.

BACKGROUND AND AIM OF THE STUDY: Biological scaffolds are widely used in the process of cardiac valve tissue engineering. Scaffold characteristics are decisive for valve durability. Herein, the influence of three different decellularization protocols on the morphological and biomechanical properties of porcine pulmonary valve conduits was evaluated. METHODS: Pulmonary valve conduits were decellularized with 1% sodium deoxycholate (SD), 1% sodium dodecylsulfate (SDS), or 0.05% trypsin/0.02% EDTA. The degree of decellularization and morphological integrity of the treated pulmonary valve cusp, wall and myocardial cuff were analyzed with hematoxylin and eosin staining, Movat-Pentachrome staining, electron microscopy, and DNA assay. The conservation of extracellular matrix (ECM) proteins was evaluated by immunohistochemical staining against collagens I and IV, and laminin. The biomechanical properties of the obtained scaffolds were evaluated using uniaxial tension tests. Native grafts served as controls. RESULTS: All treatments resulted in complete decellularization of the cusp, whereas only SD and SDS treatments were able to remove completely all cells from the pulmonary valve wall and subvalvular myocardial cuff. The morphological integrity and preservation of ECM proteins was clearly superior in both detergent-treated groups. Enzyme treatment resulted in destruction of the basement membrane. Wall longitudinal tension parameters (stiffness, elasticity modulus, ultimate force; stress and strain) were significantly inferior in the trypsin/EDTA group (p < 0.05). No significant differences were observed between detergent-treated and native samples. The results of transversal tension parameters were comparable in all groups. CONCLUSION: Both, SD and SDS treatment of the pulmonary valve may better preserve the morphological and biomechanical properties of the scaffold than the chosen enzymatic treatment. In the authors' opinion, detergent-based decellularization should be used in preference to enzyme treatment in the tissue engineering of heart valves.

Primary stability of shoulder arthrodesis using cannulated cancellous screws.

There are no biomechanical studies available concerned with the primary stability of shoulder arthrodesis. The aim of our biomechanical investigations was to ascertain a minimal material combination with high primary stability for shoulder arthrodesis. For that purpose, the primary stability of 6 different forms of screw arthrodesis was investigated under the stress of abduction, adduction, anteversion, and retroversion. The mean values of the screw arthrodeses were compared with those of a 16-hole plate arthrodesis. All tests were carried out on 24 human specimens without destruction by use of a materials testing machine. The most stable form of screw arthrodesis for the load directions of abduction, adduction, anteversion, and retroversion results from a specific configuration of screws comprising 3 horizontal humeroglenoid screws and 3 vertical acromiohumeral screws (318.5 +/- 99.0 N). For three forms of arthrodesis, each with 3 humerus-glenoid screws (299.9 +/- 95.4 N), no significant difference (P = .530) was found compared with a 16-hole plate arthrodesis (293.4 +/- 89.3 N). The plate arthrodeses only achieved higher power values on abduction and adduction stress in comparison with screw arthrodesis with 3 humerus-glenoid screws. The difference was insignificant. Because arthrodesis with 3 humerus-glenoid screws was significantly more stable on stress of anteversion and retroversion, this particular screw arthrodesis is considered superior to plate arthrodeses. The use of the most stable form of screw arthrodesis may reduce nonunion.

Risk evaluation of thermal injury to the cervical spine during intradiscal laser application in vitro.

OBJECTIVE: We aimed to investigate temperature distribution during laser and its possible thermal damage to the neurovascular structures. BACKGROUND DATA: Percutaneous laser disc decompression (PLDD) is now being performed as a minimally invasive intradiscal technique for the operative therapy of non-sequestered herniated cervical discs. As yet, no experimental basic research has been reported with regard to temperature rise and distribution in the cervical region during laser radiation. MATERIALS AND METHODS: An in vitro laser procedure was performed on human cervical intervertebral discs under standardized conditions. A thermo-camera was used to monitor in real-time the zones sensitive to temperature increase. RESULTS: Average intervertebral disc volume was 2000 mm3. With a total energy conduction of 600 Joules, a temperature increase of around 30 degrees C was shown with an initial temperature of 28 degrees C at the posterior longitudinal ligament lying immediately in front of the myelon. The defect volume was less than 1% of the total intervertebral disc volume. CONCLUSION: If, during laser application, the total amount of conducted energy is too high, with an unfavorable position of the fibers in the intervertebral space, there is a risk of thermal damage to the spinal cord and nerve roots.