Effect of Anatomical Sites On the Mechanical Properties of Spinal Dura Subjected to Biaxial Stretching

The spinal cord is encased by spinal meninges called the pia, arachnoid, and dura maters. Among these membranes, the dura mater is the thick and outermost layer and is the toughest and strongest. Thus, mechanical failure of the dura mater can lead to spontaneous cerebrospinal fluid leaks or hypovolemia, resulting in a complication or exacerbation of unfavorable symptoms involved in a mild traumatic brain injury. To develop protective equipment that can help prevent such injuries, accurate characterization of the spinal dura mater is required, especially regarding the mechanical properties at different anatomical sites. In this study, we used an equiload biaxial tensile tester to investigate the mechanical properties of porcine meningeal dura mater along the whole length of the spine. The resultant strain of the dorsal side was greater than that of the ventral side (P < 0.01), while the circumferential direction was significantly stiffer than the longitudinal direction (P < 0.01) at lower strains regardless of the spinal level. We also found that the material stiffness progressively increased from the cervical level to the thoracolumbar level at lower strains, which implies that the dura mater inherently possesses structurally preferred features or functions because the neck requires sufficient flexibility for daily activities. Further, Young's modulus was significantly less on the dorsal side than on the ventral side at higher strains (P < 0.05), suggesting that the dorsal side is readily elongated by spinal flexion even within the range of physiological motion.

Design and Modeling of a Parallel Continuum Manipulator for Trunk Motion Rehabilitation

The objective of the present work is to develop a device for training the trunk balance and motion during the early stage of rehabilitation of patients who have suffered a stroke. It is coupled to a standing frame and is based on a parallel continuum manipulator where a wearable jacket is moved by four flexible limbs actuated by rotary motors, achieving the translation and rotation required in the trunk to perform a given exercise. The flexible limbs act as a natural mechanical filter in such a way that a smooth physiological motion is achieved, and it feels less intimidating to the patient. After measuring the kinematic requirements, a model has been developed to design the system. A prototype has been built and a preliminary experimental validation has been done where the jacket generates translation coupled to a rotation around the anteroposterior, medio-lateral and longitudinal axis. The measurements of the motors torque and the force sensors located in the flexible limbs have been compared with the simulations from the model. The results prove that the prototype can accomplish the motions required for the rehabilitation task, although further work is still required to control the interaction with the patient and improve the performance of the device.

Imaging coronary plaques using 3D motion-compensated [18F]NaF PET/MR

Background Cardiac PET has recently found novel applications in coronary atherosclerosis imaging using [18F]NaF as a radiotracer, highlighting vulnerable plaques. However, the resulting uptakes are relatively small, and cardiac motion and respiration-induced movement of the heart can impair the reconstructed images due to motion blurring and attenuation correction mismatches. This study aimed to apply an MR-based motion compensation framework to [18F]NaF data yielding high-resolution motion-compensated PET and MR images. Methods Free-breathing 3-dimensional Dixon MR data were acquired, retrospectively binned into multiple respiratory and cardiac motion states, and split into fat and water fraction using a model-based reconstruction framework. From the dynamic MR reconstructions, both a non-rigid cardiorespiratory motion model and a motion-resolved attenuation map were generated and applied to the PET data to improve image quality. The approach was tested in 10 patients and focal tracer hotspots were evaluated concerning their target-to-background ratio, contrast-to-background ratio, and their diameter. Results MR-based motion models were successfully applied to compensate for physiological motion in both PET and MR. Target-to-background ratios of identified plaques improved by 7 ± 7%, contrast-to-background ratios by 26 ± 38%, and the plaque diameter decreased by −22 ± 18%. MR-based dynamic attenuation correction strongly reduced attenuation correction artefacts and was not affected by stent-related signal voids in the underlying MR reconstructions. Conclusions The MR-based motion correction framework presented here can improve the target-to-background, contrast-to-background, and width of focal tracer hotspots in the coronary system. The dynamic attenuation correction could effectively mitigate the risk of attenuation correction artefacts in the coronaries at the lung-soft tissue boundary. In combination, this could enable a more reproducible and reliable plaque localisation.

Correction to: In cervical arthroplasty, only prosthesis with flexible biomechanical properties should be used for achieving a near-physiological motion pattern

An amendment to this paper has been published and can be accessed via the original article.

In cervical arthroplasty, only prosthesis with flexible biomechanical properties should be used for achieving a near-physiological motion pattern

Background In cervical arthroplasty, qualitative motion analysis generally investigates the position of the center of rotation (COR) before and after surgery. But is the pre-op COR suitable as reference? We believe that only a comparison against healthy individuals can answer whether a physiological motion pattern has been achieved. The aim of our study was to examine how the COR for flexion/extension after insertion of 3 biomechanically completely different types of disc prostheses compares to healthy volunteers, and whether and how prosthesis design contributes to a more natural or maybe even worse motion pattern. Methods In 15 healthy volunteers, MRI in flexion and in extension was taken, and the coordinates for the CORs (COR-HV) from C3 to C7 were determined. Then pre- and post-op flexion/extension x-rays from 30 patients with a one-level disc prosthesis underwent analysis for determination of COR from C3 to C7; 10 patients who received a Bryan, a Prestige STLP, or a Discover prosthesis were chosen, respectively. Change of post-op COR position was investigated in relation to the COR-HV. Results The pre-operative COR is not congruent with the COR found in healthy subjects and therefore cannot be used as reference for investigation whether a disc prosthesis resembles natural motion. However, the comparison with healthy individuals shows that prosthesis insertion can change the coordinates of the COR to any direction in all levels from C3/4 to C6/7 regardless of the operated segment. Prostheses with flexible biomechanical properties can contribute to shift the COR toward normal, but devices with unphysiological biomechanical design, like fixed ball socket designs, for instance, can make the motion pattern even worse. Conclusions Even if the small cohorts in our study do not allow strong conclusions, it seems that in cervical arthroplasty, the biomechanical concept of the prosthesis has a significant impact whether a near-physiological motion pattern can be achieved or not. As it is a rumor but not scientifically proven that prosthesis design has no influence on clinical outcome, surgeons should only choose devices with flexible biomechanical properties for disc replacement.

In Cervical Arthroplasty Only Prostheses with Flexible Biomechanical Properties Should be Used for Achieving a Near-Physiological Motion Pattern

Background: In cervical arthroplasty, qualitative motion analysis generally investigates the position of the Center of Rotation (COR) before and after surgery. But is the prae-op COR suitable as reference? We believe that only a comparison against healthy individuals can answer whether a physiological motion pattern has been achieved. The aim of our study was to examine how the COR for flexion / extension after insertion of 3 biomechanically completely different types of disc prostheses compares to healthy volunteers, and whether and how prosthesis design contributes to a more natural or maybe even worse motion pattern.Methods: In 15 healthy volunteers MRI in flexion and in extension was taken, and the coordinates for the CORs (COR-HV) from C3 to C7 were determined. Then prae- and post-op flexion-/extension x-rays from 30 patients with a one-level disc prosthesis underwent analysis for determination of COR from C3 to C7; 10 patients who received a Bryan-, a Prestige STLP- or a Discover prosthesis were chosen, respectively. Change of post-op COR position was investigated in relation to the COR-HV.Results: The pre-operative COR is not congruent with the COR found in healthy subjects and therefore cannot be used as reference for investigation whether a disc prosthesis resembles natural motion. However, the comparison with healthy individuals shows that Prosthesis-insertion can change the coordinates of the COR to any direction in all levels from C3/4 to C6/7 regardless of the operated segment. Prostheses with flexible biomechanical properties can contribute to shift the COR towards normal, but devices with unphysiological biomechanical design, like fixed ball-socket designs, for instance, can make the motion pattern even worse.Conclusions: Even if the small cohorts in our study do not allow strong conclusions, it seems that in cervical arthroplasty, the biomechanical concept of the prosthesis has a significant impact whether a near-physiological motion pattern can be achieved or not. As it is rumor but not scientifically proofed that prosthesis-design has no influence on clinical outcome, surgeons should only choose devices with flexible biomechanical properties for disc replacement.

In Cervical Arthroplasty Only Prostheses With Flexible Biomechanical Properties Should Be Used for Achieving a Near-physiological Motion Pattern

Background:In cervical arthroplasty, qualitative motion analysis generally investigates the position of the Center of Rotation (COR) before and after surgery.But is the prae-op COR suitable as reference? We believe that only a comparison against healthy individuals can answer whether a physiological motion pattern has been achieved. The aim of our study was to examine how the COR for flexion / extension after insertion of 3 biomechanically completely different types of disc prosthesescompares to healthy volunteers,and whether and how prosthesis design contributes to a more natural or maybe even worse motion pattern.Methods: In 15 healthy volunteers MRI in flexion and in extension was taken, and the coordinates for the CORs (COR-HV) from C3 to C7 were determined.Thenprae- and post-op flexion-/extension x-rays from 30 patients with a one-level disc prosthesis underwent analysis for determination of COR from C3 to C7; 10 patients who received a Bryan-, a Prestige STLP- or a Discover prosthesis were chosen, respectively. Change of post-op COR position wasinvestigated in relation to the COR-HV.Results:The pre-operative COR is not congruent with the COR found in healthy subjects and therefore cannot be used as reference for investigation whether a disc prosthesis resembles natural motion. However, the comparison with healthy individuals shows that Prosthesis-insertion can change the coordinates of the COR to any direction in all levels from C3/4 to C6/7 regardless of the operated segment. Prostheses with flexible biomechanical properties can contribute to shift the COR towards normal, but devices with unphysiological biomechanical design, like fixed ball-socket designs, for instance, can make the motion pattern even worse.Conclusions: In cervical arthroplasty, the biomechanical concept of the prosthesis has a significant impact whether a near-physiological motion pattern can be achieved or not.As it is rumor but not scientifically proofed that prosthesis-design has no influence on clinical outcome, surgeons should only choose devices with flexible biomechanical properties for disc replacement.