The characterisation of gait patterns of people with multiple sclerosis.

BACKGROUND: There are relatively few reports describing gait patterns in multiple sclerosis (MS) and most are confined to the analysis of temporal distance parameters with some assessment of joint range of motion. The aim of this study was to perform a biomechanical characterisation of gait patterns among people with MS across a wide range of severity of ambulatory impairment. METHODS: Sixteen patients with MS were recruited for this study. Initially, the spasticity of lower limb muscle groups was measured and ambulatory ability was graded. Patients were then placed in two groups based on the level of severity of ambulatory ability. Kinematic, kinetic and EMG gait data from both MS groups were then compared to a control group of 10 healthy subjects. RESULTS: Patients with MS in both groups were found to walk with reduced gait speed, reduced maximum hip and knee extension, ankle plantarflexion angle and propulsive force compared to the control group. In general, the same gait impairments were found in both MS groups compared to the control group, and were greater for the more severely affected MS patient group. INTERPRETATION: This study highlights typical gait patterns of people with MS and provides an indication of common pathways in the degeneration of ambulatory ability as a consequence of disease progression. This information should enable improved clinical treatment of ambulation, as well as the prescription, or even design, of appropriate assistive devices.

Ambulatory rehabilitation in multiple sclerosis.

Multiple sclerosis (MS) is an autoimmunogenic disease involving demyelination within the central nervous system. Many of the typical impairments associated with MS can affect gait patterns. With walking ability being one of the most decisive factors when assessing quality of life and independent living, this review focuses on matters, which are considered of significance for maintaining and supporting ambulation. This article is an attempt to describe current research and available interventions that the caring healthcare professional can avail of and to review the present trends in research to further these available options. Evidence-based rehabilitation techniques are of interest in the care of patients with MS, given the various existing modalities of treatment. In this review, we summarise the primary factors affecting ambulation and highlight available treatment methods. We review studies that have attempted to characterise gait deficits within this patient population. Finally, as ambulatory rehabilitation requires multidisciplinary interventions, we examine approaches, which may serve to support and maintain ambulation within this patient group for as long as possible.

Analysis of the mechanical behavior of a titanium scaffold with a repeating unit-cell substructure.

Titanium scaffolds with controlled microarchitecture have been developed for load bearing orthopedic applications. The controlled microarchitecture refers to a repeating array of unit-cells, composed of sintered titanium powder, which make up the scaffold structure. The objective of this current research was to characterize the mechanical performance of three scaffolds with increasing porosity, using finite element analysis (FEA) and to compare the results with experimental data. Scaffolds were scanned using microcomputed tomography and FEA models were generated from the resulting computer models. Macroscale and unit-cell models of the scaffolds were created. The material properties of the sintered titanium powders were first evaluated in mechanical tests and the data used in the FEA. The macroscale and unit-cell FEA models proved to be a good predictor of Young's modulus and yield strength. Although macroscale models showed similar failure patterns and an expected trend in UCS, strain at UCS did not compare well with experimental data. Since a rapid prototyping method was used to create the scaffolds, the original CAD geometries of the scaffold were also evaluated using FEA but they did not reflect the mechanical properties of the physical scaffolds. This indicates that at present, determining the actual geometry of the scaffold through computed tomography imaging is important. Finally, a fatigue analysis was performed on the scaffold to simulate the loading conditions it would experience as a spinal interbody fusion device.

Porous titanium scaffolds fabricated using a rapid prototyping and powder metallurgy technique.

One of the main issues in orthopaedic implant design is the fabrication of scaffolds that closely mimic the biomechanical properties of the surrounding bone. This research reports on a multi-stage rapid prototyping technique that was successfully developed to produce porous titanium scaffolds with fully interconnected pore networks and reproducible porosity and pore size. The scaffolds' porous characteristics were governed by a sacrificial wax template, fabricated using a commercial 3D-printer. Powder metallurgy processes were employed to generate the titanium scaffolds by filling around the wax template with titanium slurry. In the attempt to optimise the powder metallurgy technique, variations in slurry concentration, compaction pressure and sintering temperature were investigated. By altering the wax design template, pore sizes ranging from 200 to 400 microm were achieved. Scaffolds with porosities of 66.8 +/- 3.6% revealed compression strengths of 104.4+/-22.5 MPa in the axial direction and 23.5 +/- 9.6 MPa in the transverse direction demonstrating their anisotropic nature. Scaffold topography was characterised using scanning electron microscopy and microcomputed tomography. Three-dimensional reconstruction enabled the main architectural parameters such as pore size, interconnecting porosity, level of anisotropy and level of structural disorder to be determined. The titanium scaffolds were compared to their intended designs, as governed by their sacrificial wax templates. Although discrepancies in architectural parameters existed between the intended and the actual scaffolds, overall the results indicate that the porous titanium scaffolds have the properties to be potentially employed in orthopaedic applications.

Stress distribution in the intervertebral disc correlates with strength distribution in subdiscal trabecular bone in the porcine lumbar spine.

BACKGROUND: It is understood that an interdependence of properties exists between the intervertebral disc and the subdiscal trabecular bone. Determining the biomechanics of this relationship is important in the development of novel spinal implants and instruments. The aim of this study was to analyze this relationship for the porcine lumbar spine and to compare it with that of the human spine. METHODS: The stress distribution within the intervertebral disc of 10 porcine lumbar (L4/L5) motion segments was recorded using a 1.5mm needle pressure transducer. For dynamic loading a specialized testing rig was developed to apply flexion/extension and medial/lateral bending while intervertebral disc stress was simultaneously recorded. The regional variation in mechanical properties of trabecular bone was also examined for an additional 10 porcine (L5) vertebral bodies. For compressive testing of the subdiscal bone, columns were prepared using a low speed cutting saw and subjected to axial compression. FINDINGS: Under pure compressive loading, stress levels within the intervertebral disc were relatively uniform. However, during asymmetric loading large peak stresses were evident in the periphery of the intervertebral disc in areas underlying the annulus fibrosus. The mechanical properties of trabecular bone demonstrated regional variations within the vertebral body. The ratio of compressive yield strength of bone underlying the outer annulus fibrosus to that of bone underlying the nucleus pulposus averaged 1.36. INTERPRETATION: Although the effects of stress distribution and bone mass adaptation cannot be directly related, it is probable that peak stresses arising in the annulus fibrosus during asymmetric loading provide greater stimuli for the underlying bone to undergo adaptive remodeling to withstand the greater forces experienced. Findings of intervertebral stress distribution and strength distribution of subdiscal trabecular bone for the porcine spine may aid in the development of strategies for preclinical animal testing of spinal implants.

Fabrication methods of porous metals for use in orthopaedic applications.

Implant stability is not only a function of strength but also depends on the fixation established with surrounding tissues [Robertson DM, Pierre L, Chahal R. Preliminary observations of bone ingrowth into porous materials. J Biomed Mater Res 1976;10:335-44]. In the past, such stability was primarily achieved using screws and bone cements. However, more recently, improved fixation can be achieved by bone tissue growing into and through a porous matrix of metal, bonding in this way the implant to the bone host. Another potentially valuable property of porous materials is their low elastic modulus. Depending on the porosity, moduli can even be tailored to match the modulus of bone closer than solid metals can, thus reducing the problems associated with stress shielding. Finally, extensive body fluid transport through the porous scaffold matrix is possible, which can trigger bone ingrowth, if substantial pore interconnectivity is established [Cameron HU, Macnab I, Pilliar RM. A porous metal system for joint replacement surgery. Int J Artif Organs 1978;1:104-9; Head WC, Bauk DJ, Emerson Jr RH. Titanium as the material of choice for cementless femoral components in total hip arthroplasty. Clin Orthop 1995;85-90]. Over the years, a variety of fabrication processes have been developed, resulting in porous implant substrates that can address unresolved clinical problems. The advantages of metals exhibiting surface or bulk porosity have led researchers to conduct systematic research aimed at clarifying the fundamental aspects of interactions between porous metals and hard tissue. This review summarises all known methods for fabricating such porous metallic scaffolds.

Pressure distribution at the seating interface of custom-molded wheelchair seats: effect of various materials.

OBJECTIVE: To identify which of 4 materials has the most favorable pressure distribution when used in custom-molded seats (CMSs) to assist clinicians in providing appropriate seating for wheelchair-bound individuals who are prone to develop pressure ulcers. DESIGN: Repeated-interface pressure measurements for all materials, followed by statistical analysis. SETTING: The general community and referral centers. PARTICIPANTS: Seven subjects, 5 with cerebral palsy, 1 with Schilder's disease, and 1 with postmeningitis effects. All subjects were seated in a CMS and had spinal deformities. INTERVENTIONS: Viscoelastic polyurethane foams (Pudgee, Sunmate) and gels (Floam trade mark, Jay) were used as inserts in the CMSs. Evazote foam was used as a control material. MAIN OUTCOME MEASURES: Pressure readings were taken at the seat interface with pneumatic pressure sensors and the Talley Pressure Monitor. Peak pressure readings, mean pressure ratio, and peak pressure ratio for the different materials were compared. RESULTS: Foams, Sunmate in particular, produced lower peak-interface pressures and also showed better pressure distribution than did gels. CONCLUSION: Foams are the preferred insert material with CMSs when increased tissue breakdown risk is present.