Mechanical Characterization of the Soft Tissues of a Native Human Knee： A Pilot Study

The importance of ligaments in providing joint stability and the incidence of injuries, dictates a need to increase their structural and mechanical properties understanding. Additionally, one of the challenges in the orthopedic industry is to design TKA （total knee arthroplasty） aiming to be soft-tissues friendly. This requires a priori knowledge of physiological knee function, in which the passive stability is achieved and guaranteed by the complex envelope of soft tissues around the joint. Therefore, the knowledge of the mechanical behavior of knee ligaments is fundamental. For this reason, our study aims to define and apply in a pilot study, an ad-hoc methodology to mechanically characterize ligaments of native human knees. The cruciate and collateral ligaments from a fresh frozen cadaver leg were accurately harvested. Each ligament was independently tested during a tensile test at different strain rates, simulating different deformation speeds during gait. Moreover, additional tensile tests until failure were also performed. Axial force and deformation were continuously recorded during each test. Results show that each ligament exhibited own typical non-linear, speed-related behavior. High repeatability in the results is observed among the different repeated tests confirming the robustness of the used methodology. This information will be helpful for clinicians, engineers and researchers to improve the biomechanical knowledge about knee, to develop better implants and to be able to improve the currently available numerical models of the human knee.

Three-dimensional analysis of the gap space under forearm casts

Purpose:Secondary displacement represents a frequent complication of conservative treatment of fractures,particularly of the distal radius.The gap space between skin and cast may lead to a certain degree movements and this increased mobility might favor redisplacement.The aim of this study was to develop a new 3D method,to measure the gap space in all 3 geometrical planes,and to validate this new technique in a clinical setting of distal radius fractures.Methods:This study applies 3D imaging to measure the space between plaster and skin as a potential factor of secondary displacement and therefore the failure of conservative treatment.We developed and validated a new methodology to analyze and compare different forearm casts made of plaster of Paris and fiberglass.An unpaired t-test was performed to document differences between the investigated parameters between plaster of Paris and fiberglass casts.The significance level was set at p<0.05.Results:In a series of 15 cases,we found the width of the gap space to average 4 mm,being slightly inferior on the radial side.Comparing the two different casting materials,plaster of Paris and fiberglass,we found a significantly larger variance of space under casts made of the first material(p=0.39).A roughness analysis showed also a markedly significantly higher irregularity of the undersurface of plaster of Paris as compared with fiberglass.Conclusion:This study allows for a better understanding of the nature of the"gap space"between cast and skin and will contribute to develop and improve new immobilization techniques and materials.