Surgical resection and reconstruction after resection of tumors involving the sacropelvic region

Objectives Surgical management of the tumors in the sacropelvic region is a challenging field of spine surgery because of the complex local anatomy and biomechanics. Recent development in anesthesia and intensive care has allowed us to perform extended surgeries focused on the en bloc resection of sacropelvic tumors. Various techniques for the resection and for the reconstruction were published in the last decade. Methods Sacropelvic tumor resection techniques and methods for the biomechanical and soft-tissue reconstruction are reviewed in this paper. Results Literature data is based on case reports and case-series. Several different techniques were developed for the lumbopelvic stabilization after sacropelvic tumor resection according to three different reconstruction principles (spinopelvic fixation, posterior pelvic ring fixation, anterior spinal column fixation); however, long term follow up data and comparative studies of the different techniques are still missing. Soft-tissue reconstruction can be performed according to an algorithm depending on the surgical approach, but relatively high complication rates are reported with all reconstruction strategies. The clinical outcome of such surgeries should ideally be evaluated in three dimensions; surgical-, oncological-, and functional outcomes. The last, and most important step of the presurgical planning procedure is a careful presentation of the surgical goals and risks to the patient, who must provide a fully informed consent before surgery can proceed. Discussion Sacropelvic tumors are rare conditions. In the last decade, growing evidence was published on resection and reconstruction techniques for these tumors; however, experience at most medical centers is limited by the low case-number. Formation of international expert groups and initiation of multicenter studies is strongly encouraged to produce a high level of evidence in this special field of spine surgery

Surgical treatment of primary malignant tumors of the sacrum

Objectives The objective of the authors was to provide an up-to-date review about the epidemiology, diagnosis and surgical management of the malignant primary sacral tumors. Methods A PubMed search was conducted using a combination of the following items: (("Spinal Neoplasms"[Mesh]) AND "Sacrum"[Mesh]) NOT ("Metastasis" OR "Metastases" OR "Benign"). The literature review and the author's own surgical experiences were used to assess the current treatment strategies of the malignant sacral tumors. Results Twenty case series were identified, which studies discuss in detail the surgical strategies, the postoperative complications, the functional and onclolgic outcome, the recurrence free and the disease specific survival of this rare patient category. Discussion Sacral tumors are rare pathologies. Their management generates a complex medical problem, as they usually are diagnosed in advanced stages with extended dimensions involving the sacral nerves and surrounding organs. The evaluation and complex treatment of these rare tumors require a multidisciplinary approach, optimally at institutions with comprehensive care and experience. Although conventional oncologic therapeutic methods should be used as neoadjuvant or adjuvant therapies in certain histological types, en bloc resection with wide surgical margins is essential for long-term local oncologic control. This is often technically difficult to achieve, as just a few centers in the world perform sacral tumor surgeries on a regular basis, and have enough wide experience. Therefore international cooperation and organization of multicenter tumor registries are essential to develop evidence based treatment protocols

Biomechanical evaluation of vertebroplasty and kyphoplasty by uniaxial compressive test

In vertebroplasty, by injecting cement into the fractured osteoporotic vertebra, the cement can leak into the surrounding soft tissues. To avoid this injurious side-effect, in kyphoplasty a suitable place is previously prepared for the cement, by an inflated and removed balloon. In this study the biomechanical evaluation of vertebroplasty and kyphoplasty is presented by comparing the strength, stiffness and deformability of post-operated vertebrae by using uniaxial compressive mechanical test. As for conclusion, mechanical properties following vertebroplasty are more sensitive to initial bone density than after kyphoplasty, however, both techniques give practically the same failure load, vertebroplasty yields larger stiffness and smaller compressive deformability.  DOI: 10.17489/biohun/2013/1/3

Biomechanical evaluation of interbody devices by using mechanical compressive test: PEEK spacers versus PMMA cement spacers

If spine degenerations are accompanied by osteoporosis, the traditional PEEK spacers can strongly subside into the irregularly deformed endplates and vertebrae following surgical stabilization. To avoid implant subsidence, a new technique is developed where bone cement is applied as interbody device along the vertebra-implant interface. In this study, the mechanical comparison of the traditional PEEK and the new PMMA cement spacers are presented based on uniaxial compression tests. It was concluded that in osteoporotic spine the cement spacers provide better contact along the irregularly deformed endplates, and stronger vertebra-implant interface leading to enhanced stability of lumbar interbody fixation. In the case of PMMA cages, the failure deformation of segments is almost the half of that of the PEEK spacers, while the stiffness of them is more than two times larger. In strongly osteoporotic cases, a more evenly distributed cement pattern results in smaller stress concentrations and greater strength which may decrease the risk of subsidence. DOI: 10.17489/biohun/2013/1/2

Biomechanical evaluation of two different vertebral interbody devices by using QCT-based case-specific nonlinear finite element models

Interbody devices are widely used to replace the degenerated discs of the spine. For this purpose, a novel methodology uses cement instead of conventional spacers, which is hypothesized to provide smoother transition of forces, lower risk of bone tissue damage, thus smaller subsidence, reduced risk of further pathological deformations and other complications. This new treatment approach has been compared with the conventional method experimentally by mechanical loading of human vertebral motion segments treated with either of these. The present study aimed at complementing the that work with finite element analysis and, by performing in silico mechanical testing of QCT-based case specific models incorporating the elasto-plastic behavior of bone, providing better understanding of experimental results, in particular, the differences between the two sample groups equipped with the different spacer types. This report presents the applied numerical methodology as well as the first results, which are in line with the experimental ones. Besides providing deeper insight into the experimental outcomes, these models are expected to provide a basis for virtual parameter analysis studies, which may help to optimize the surgical procedure. DOI: 10.17489/biohun/2013/1/2

Taylor teszt modellezése a Johnson-Cook anyagmodell alkalmazásával: a hőmérséklet hatása

Az extrém nagy alakváltozási sebességű mechanikai anyagvizsgálat egyik legegyszerűbben végrehajtható módja a Taylor-teszt. Egyszerűsége ellenére igen komplex az alakváltozás lefolyása és eloszlása a próbatestben. A próbatest alakváltozását végeselemes módszerrel vizsgáltuk, ahol anyagmodellnek a Johnson-Cook modellt választottuk. Vizsgáltuk a hőmérséklet hatását egy réz próbatest deformációjára három különböző sebességű becsapódás esetén

LOAD HISTORY AND STRUCTURE ANALYSIS OF UTILITY VEHICLES

Due to statistics 90\% of the damages can be attributed to material fatigue in the scope of mechanical engineering. We can reduce the risk of damage - among others - by adequate dimensioning methods. Which method is applied, the knowledge of the load history is absolutely indispensable. One of the possible analysis of the load history when we set different stress levels, and the numbers are counted, when the load history is crossing these preset values. These numbers are used for lifetime estimation. The authors are suggesting a method for the determination of the expectable values of the stress level crossing numbers