Least-squares matrix correlations between stump stresses and prosthesis loads for below-knee amputees

Stump stresses were correlated to prosthesis loads for two unilateral, below-knee amputees over a range of flexion-extension angular adjustments. Normal stresses on the patellar tendon and gastrocnemius were related to the axial force and flexion-extension moment of the prosthesis via a matrix equation. Elements of this matrix, influence factors calculated by least-squares algorithms, identified the contributions of each time-dependent load component acting to produce the time-dependent normal stresses. The flexion-extension angular sensitivity of the way these sagittal plane loads combined to produce normal stresses was included in the matrix equation via a first-order Maclaurin series. Highly favorable correlation coefficients between empirically measured and theoretically predicted stump stresses were calculated. This demonstrated that, in future studies, using an influence-factor matrix holds promise for quantifying sensitivities of normal stresses of the stump to multiple adjustments in prostheses.     

Design of Adjustable Frame-Type Prosthetic Socket for Lower Limb

ObjectivesProsthetic socket is the contact interface between the stump and the prosthesis, and also the interface component that transmits forces from the stump to the prosthesis distal. The current prosthetic socket fit is a major factor affecting rehabilitation, especially with the stump volume fluctuations. The main goal of this article is to design an adjustable frame-type prosthetic socket with constant force to adapt to the stump volume fluctuations.Materials and methodsIn this paper, an adjustable frame-type prosthetic socket with constant force is designed. The constant force device is designed based on the superelasticity of the shape memory alloy for maintaining constant stump-socket interface stress and automatically adapting to certain volume fluctuations. The constant force extrusion performance of this prosthetic socket was verified and optimized by finite element analysis.ResultsThe results suggest that the constant force unit may maintain constant interface stress. According to the optimization results, the shape memory alloy dimensional parameters could be selected according to different requirements.ConclusionThe adjustable frame-type prosthetic socket allows the user to adjust the socket volume through the cable system and has a large heat dissipation area. The constant force unit maintains constant interface stress and automatically adapts to stump volume fluctuations.     

FE-analysis of surface stresses for the tribological system in total hip prostheses]

The implantation of a total hip prosthesis is an operation which is performed frequently due to advanced hip joint damage both in humans and in veterinary medicine in dogs. The long-term result of a hip prosthesis is mainly determined by aseptic loosening of the prosthesis; among other causes, abrasion particles of the tribological pairing are responsible for the loosening. For the analysis of the surface stresses with different tribological pairings, a finite element model was generated which was based on the CAD data of a commercial total hip prosthesis. After transmission of a physiological force in the components of the three tribological pairings ceramic/polyethylene, ceramic/ceramic and metal/polyethylene, stresses were calculated. Stresses in the ceramic/ceramic tribological pairings were conspicuously higher than in the other material pairings. In the future adapted prostheses have to be developed that ensure optimal friction and absorption characteristics of the components.     

3D Traction Stresses Activate Protease-Dependent Invasion of Cancer Cells

Cell invasion and migration that occurs, for example, in cancer metastasis is rooted in the ability of cells to navigate through varying levels of physical constraint exerted by the extracellular matrix. Cancer cells can invade matrices in either a protease-independent or a protease-dependent manner. An emerging critical component that influences the mode of cell invasion is the traction stresses generated by the cells in response to the physicostructural properties of the extracellular matrix. In this study, we have developed a reference-free quantitative assay for measuring three-dimensional (3D) traction stresses generated by cells during the initial stages of invasion into matrices exerting varying levels of mechanical resistance. Our results show that as cells encounter higher mechanical resistance, a larger fraction of them shift to protease-mediated invasion, and this process begins at lower values of cell invasion depth. On the other hand, the compressive stress generated by the cells at the onset of protease-mediated invasion is found to be independent of matrix stiffness, suggesting that 3D traction stress is a key factor in triggering protease-mediated cancer cell invasion. At low 3D compressive traction stresses, cells utilize bleb formation to indent the matrix in a protease independent manner. However, at higher stress values, cells utilize invadopodia-like structures to mediate protease-dependent invasion into the 3D matrix. The critical value of compressive traction stress at the transition from a protease-independent to a protease-dependent mode of invasion is found to be ∼165 Pa.     

Crossover replantation and fillet flap coverage of the stump after ectopic implantation: a case of bilateral leg amputation

A successful case of crossover replantation of the left foot to the stump of the right leg and temporary ectopic implantation of the right amputated foot on the forearm is described. The ectopically implanted right foot was used as a free fillet flap for the late reconstruction of the left leg stump. At the latest follow-up examination, 18 months after the accident, the patient was able to walk independently with a prosthesis on the stump of the left leg. Both the cross-replanted foot and the free filleted foot flap, used for the reconstruction of the left leg stump, have maintained adequate protective sensation. The importance of utilization of amputated parts for functional reconstruction is stressed. Crossover replantations and ectopic implantations should be considered in bilateral amputations for the salvage of at least one extremity.     

A three-dimensional non-linear finite element study of the effect of cement-prosthesis debonding in cemented femoral total hip components.

A three-dimensional non-linear finite element analysis of a cemented femoral component in which the component was partially debonded from the cement mantle was used to assess the effects of debonding on stresses in the cement. Three cases of partial cement-metal debonding were modelled with debonding of the proximal portion of the implant down to a horizontal plane which was 35, 62.5, or 82.5 mm below the prosthesis collar. Each situation was studied under loads simulating both gait and stairclimbing. Also, complete debonding between the implant and the surrounding cement mantle was modeled for loads simulating gait. Under stair climbing loads with partial cement-mental debonding, hoop stresses of 13-18 MPa were observed in the cement at the cement-metal interface at the proximal postero-medial corner of the implant. Similarly, in stair climbing, the maximum principal stresses in the cement were also adjacent to the proximal postero-medial region of the implant. These stresses were compressive and increased from 15 MPa with fully bonded interfaces to 48 MPa with debonding down to 82.5 mm below the prosthesis collar. Under gait loads, complete debonding caused high compressive stresses up to 34.9 MPa in the cement distal to the prosthesis tip. Thus, cement failure subsequent to prosthesis debonding is likely in the proximal region in a partially debonded implant due to stair climbing loads and is likely below the prosthesis tip in a fully debonded implant due to gait loading.     

Three-dimensional finite element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems

Glenoid component loosening is the dominant cause of failure in total shoulder arthroplasty. It is presumed that loosening in the glenoid is caused by high stresses in the cement layer. Several anchorage systems have been designed with the aim of reducing the loosening rate, the two major categories being "keeled" fixation and "pegged" fixation. However, no three-dimensional finite element analysis has been performed to quantify the stresses in the cement or to compare the different glenoid prosthesis anchorage systems. The objective of this study was to determine the stresses in the cement layer and surrounding bone for glenoid replacement components. A three-dimensional model of the scapula was generated using CT data for geometry and material property definition. Keeled and pegged designs were inserted into the glenoid, surrounded by a 1-mm layer of bone cement. A 90 deg arm abduction load with a full muscle and joint load was applied, following van der Helm (1994). Deformations of the prosthesis, stresses in the cement, and stresses in the bone were calculated. Stresses were also calculated for a simulated case of rheumatoid arthritis (RA) in which bone properties were modified to reflect that condition. A maximum principal stress-based failure model was used to predict what quantity of the cement is at risk of failure at the levels of stress computed. The prediction is that 94 percent (pegged prosthesis) and 68 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival in normal bone. In RA bone, however, the situation is reversed where 86 percent (pegged prosthesis) and 99 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival. Bone stresses are shown to be not much affected by the prosthesis design, except at the tip of the central peg or keel. It is concluded that a "pegged" anchorage system is superior for normal bone, whereas a "keeled" anchorage system is superior for RA bone.     

Resultant lower extremity joint moments in below-knee amputees during running stance

Resultant flexion/extension lower extremity joint moments of four below-knee amputees running between 2.5 and 5.7 m s-1 were computed during stance on their intact and prosthetic limbs. All subjects wore patellar tendon-bearing prostheses with either a SACH or Greissinger foot component. During stance on the prosthesis, the resultant hip extensor moment on the amputated side was greater in magnitude and duration than its counterpart on the intact limb during its corresponding stance period. Since the artificial foot was planted on the ground, such a moment may help control knee flexion and promote knee extension of the residual limb. For the three subjects whose knees continued to flex at the beginning of stance, there was a dominant extensor moment about the knee joint during stance on the prosthesis. By contrast, for the fourth subject whose knee remained straight or hyperextended throughout stance on the prosthesis, a flexor moment was dominant.     

Rehabilitation of Patients with Through-knee Amputation

One hundred and one patients with through-knee amputations attending the Manchester limb-fitting centre are reviewed. Most amputations were performed for trauma or vascular disease. The interval from amputation to measurement for the first prosthesis averaged 12 weeks in cases of primary healing, and 21 weeks when healing was delayed. Artificial limbs were successfully fitted to 83%, and only 10% failed to use either a limb or a pylon. Three-quarters of those with outdoor mobility returned to work.Disarticulation through the knee has several advantages over above-knee amputation: in particular, the long end-bearing stump facilitates balance and control of the prosthesis. Disadvantages are a tendency to slow healing of the wound, lack of an internal knee mechanism in the artificial limb, and the bulky appearance of the limb. The results of rehabilitation could be improved by careful selection of patients and attention to operative detail; stump bandaging and exercises; earlier attendance at the limb-fitting centre to be measured for pylon or artificial limb; and improvements in design and production of prostheses.     

Pelvic stresses in vitro--I. Malsizing of endoprostheses

Seven embalmed human cadaveric hemi-pelves have been stripped of all soft tissues except the articular cartilage and instrumented with 25 strain-gauge rosettes on both the medial and lateral surfaces. Loads up to 2.5 kN were applied, without simulated muscle forces, to mimic the line-of-action of the resultant joint-force in a single-legged stance. In this parametric study, endoprostheses were studied at the 'correct' size and in sizes of 1 and 2 mm above and below the correct size. The correct size of endoprosthesis produced similar periacetabular stress data to those obtained with the normal femoral head; however, significant changes in stress on the medial and lateral aspects of the ilium suggested the correctly-sized spherical endoprosthesis had a different moment arm than its anatomical counterpart. Endoprostheses of 1 mm greater than the correct size caused major increases in the magnitude of both periacetabular and medial-wall stresses, while prostheses of +2 mm created dramatic and significant increases in magnitudes of these stresses. Endoprostheses smaller than the correct size caused only small but significant changes in the pattern of stresses up to -2 mm malsizing and, in particular, were associated with the disappearance of all periacetabular tensile stresses; however, stress data on the medial and lateral aspects of the ilium were more closely matched to the 'normal' for this -2 mm of undersizing.     

Treatment of phantom limb pain with combined EMG and thermal biofeedback: a case report

Phantom pain is a frequent consequence of the amputation of an extremity and causes considerable discomfort and disruption of daily activities. This study describes a patient with extreme phantom limb pain following amputation of the right upper limb. The treatment consisted of 6 sessions of EMG biofeedback followed by 6 sessions of temperature biofeedback. The patient did not use a prosthesis and had not received previous treatment for chronic pain. Results demonstrated complete elimination of phantom limb pain after treatment, which was maintained at a 3- and 12-month follow-up. Pain relief covaried with increase in skin temperature at stump and perceptual telescoping (retraction of phantom limb into stump).     

Contact stresses and fatigue life in a knee prosthesis: comparison between in vitro measurements and computational simulations

The evaluation of contact areas and pressures in total knee prosthesis is a key issue to prevent early failure. The first part of this study is based on the hypothesis that the patterns of contact stresses on the tibial insert of a knee prosthesis at different stages of the gait cycle could be an indicator of the wear performances of a knee prosthesis. Contact stresses were calculated for a mobile bearing knee prosthesis by means of finite element method (FEM). Contact areas and stresses were also measured through in vitro tests using Fuji Prescale film in order to support the FEM findings.The second part of this study addresses the long-term structural integrity of metal tibial components in terms of fatigue life by means of experimental tests and FEM simulations. Fatigue experimental evaluations were performed on Cr-Co alloy tibial tray, based on ISO standards. FEM models were used to calculate the stress patterns. The failure risk was estimated with a standard fatigue criterion on the basis of the results obtained from the FEM calculations. Experimental and computational results showed a positive matching.     

Matrix dimensions bias demographic inferences: implications for comparative plant demography

While the wealth of projection matrices in plant demography permits comparative studies, variation in matrix dimensions complicates interspecific comparisons. Collapsing matrices to a common dimension may facilitate such comparisons but may also bias the inferred demographic parameters. Here we examine how matrix dimension affects inferred demographic elasticities and how different collapsing criteria perform. We analyzed 13 x 13 matrices representing nine plant species, collapsing these matrices (i) into even 7 x 7, 5 x 5, 4 x 4, and 3 x 3 matrices and (ii) into 5 x 5 matrices using different criteria. Stasis and fecundity elasticities increased when matrix dimension was reduced, whereas those of progression and retrogression decreased. We suggest a collapsing criterion that minimizes dissimilarities between the original- and collapsed-matrix elasticities and apply it to 66 plant species to study how life span and growth form influence the relationship between matrix dimension and elasticities. Our analysis demonstrates that (i) projection matrix dimension has significant effects on inferred demographic parameters, (ii) there are better-performing methods than previously suggested for standardizing matrix dimension, and (iii) herbaceous perennial projection matrices are particularly sensitive to changes in matrix dimensionality. For comparative demographic studies, we recommend normalizing matrices to a common dimension by collapsing higher classes and leaving the first few classes unaltered.     

Cell-cell mechanical communication through compliant substrates

The role of matrix mechanics on cell behavior is under intense investigation. Cells exert contractile forces on their matrix and the matrix elasticity can alter these forces and cell migratory behavior. However, little is known about the contribution of matrix mechanics and cell-generated forces to stable cell-cell contact and tissue formation. Using matrices of varying stiffness and measurements of endothelial cell migration and traction stresses, we find that cells can detect and respond to substrate strains created by the traction stresses of a neighboring cell, and that this response is dependent on matrix stiffness. Specifically, pairs of endothelial cells display hindered migration on gels with elasticity below 5500 Pa in comparison to individual cells, suggesting these cells sense each other through the matrix. We believe that these results show for the first time that matrix mechanics can foster tissue formation by altering the relative motion between cells, promoting the formation of cell-cell contacts. Moreover, our data indicate that cells have the ability to communicate mechanically through their matrix. These findings are critical for the understanding of cell-cell adhesion during tissue formation and disease progression, and for the design of biomaterials intended to support both cell-matrix and cell-cell adhesion.     

Stress analysis and failure prediction in the proximal femur before and after total hip replacement

An investigation was performed to determine the effects of the presence of two lengths of proximal Müller prosthesis on predicted failure loads, as compared to those for an intact femur. Three-dimensional stresses in a bone/cement/prosthesis system were determined using finite element methods, with both isotropic and transversely isotropic material properties used for the diaphyseal cortex. Significant increases in prosthesis stem stresses were found when the transversely isotropic material properties were employed in the diaphyseal cortex. This leads to the conclusion that accurate anisotropic material properties for bone are essential for precise stress determination and optimum design in prosthetic implants. Failure loads were also predicted for vertical compression and axial torque, similar to available experimental conditions, and were within the range of the experimental failure data found in the literature. The technique developed herein can be used to systematically assess existing as well as future implant designs, taking into account the complex three-dimensional interaction effects of the overall bone/cement/prosthesis system.     

A general model for estimating lower extremity inertial properties of individuals with transtibial amputation

Lower extremity joint moment magnitudes during swing are dependent on the inertial properties of the prosthesis and residual limb of individuals with transtibial amputation (TTA). Often, intact limb inertial properties (INTACT) are used for prosthetic limb values in an inverse dynamics model even though these values overestimate the amputated limb’s inertial properties. The purpose of this study was to use subject-specific (SPECIFIC) measures of prosthesis inertial properties to generate a general model (GENERAL) for estimating TTA prosthesis inertial properties. Subject-specific mass, center of mass, and moment of inertia were determined for the shank and foot segments of the prosthesis (n = 11) using an oscillation technique and reaction board. The GENERAL model was derived from the means of the SPECIFIC model. Mass and segment lengths are required GENERAL model inputs. Comparisons of segment inertial properties and joint moments during walking were made using three inertial models (unique sample; n = 9): (1) SPECIFIC, (2) GENERAL, and (3) INTACT. Prosthetic shank inertial properties were significantly smaller with the SPECIFIC and GENERAL model than the INTACT model, but the SPECIFIC and GENERAL model did not statistically differ. Peak knee and hip joint moments during swing were significantly smaller for the SPECIFIC and GENERAL model compared with the INTACT model and were not significantly different between SPECIFIC and GENERAL models. When subject-specific measures are unavailable, using the GENERAL model produces a better estimate of prosthetic side inertial properties resulting in more accurate joint moment measurements for individuals with TTA than the INTACT model.     

3D collagen cultures under well‐defined dynamic strain: A novel strain device with a porous elastomeric support

The field of mechanobiology has grown tremendously in the past few decades, and it is now well accepted that dynamic stresses and strains can impact cell and tissue organization, cell–cell and cell–matrix communication, matrix remodeling, cell proliferation and apoptosis, cell migration, and many other cell behaviors in both physiological and pathophysiological situations. Natural reconstituted matrices like collagen and fibrin are often used for three‐dimensional (3D) mechanobiology studies because they naturally form fibrous architectures and are rich in cell adhesion sites; however, they are physically weak and typically contain >99% water, making it difficult to apply dynamic stresses to them in a truly 3D context. Here we present a composite matrix and strain device that can support natural matrices within a macroporous elastic structure of polyurethane. We characterize this system both in terms of its mechanical behavior and its ability to support the growth and in vivo‐like behaviors of primary human lung fibroblasts cultured in collagen. The porous polyurethane was created with highly interconnected pores in the hundreds of µm size scale, so that while it did not affect cell behavior in the collagen gel within the pores, it could control the overall elastic behavior of the entire tissue culture system. In this way, a well‐defined dynamic strain could be imposed on the 3D collagen and cells within the collagen for several days (with elastic recoil driven by the polyurethane) without the typical matrix contraction by fibroblasts when cultured in 3D collagen gels. We show lung fibroblast‐to‐myofibroblast differentiation under 30%, 0.1 Hz dynamic strain to validate the model and demonstrate its usefulness for a wide range of tissue engineering applications. Biotechnol. Bioeng. 2009;103: 217–225. © 2008 Wiley Periodicals, Inc.     

Patient-Specific Design and Biomechanical Evaluation of a Novel Bipolar Femoral Hemi-Knee Prosthesis

While total knee replacement is successful, hemiarthroplasty is necessary for some young, obese and active patients who are especially not suitable for unicompartmental or total knee prostheses. Hemiarthroplasty also provides an opportunity for children with bone tumors. The design ofhemiarthroplasty should be patient-specific to reduce contact stress and friction as well as instability, compared to conventional hemi-knee prosthesis. A novel bipolar hemi-knee prosthesis with two flexion stages was developed according to a healthy male＇s knee morphological profile. The motion mode of the bipolar hemi-knee prosthesis was observed through roentgenoscopy in vitro experiment. The biomechanical properties in one gait cycle were evaluated though finite element simulation. The bipolar hemi-knee prosthesis was found to produce knee flexion at two stages through X-ray images. The first stage is the motion from upright posture to a specified 60~ flexion, followed by the second stage of motion subsequently to deep flexion. The finite element simulation results also show that the designed hemi-knee prosthesis has the ability to reduce stresses on the joint contact surfaces. Therefore, it is possible for the bipolar hemi-knee prosthesis to provide better biotribological performances because it can reduce stresses and potentially wear on the opposing contacting surface during a gait cycle, orovidin~ a t~romisin~ treatment strate~v in future Joint renair znd renlneement     

Use of extracellular matrix components for cell culture

Extracellular matrix components when used as a substratum in vitro can greatly influence cell behavior. The response observed is dependent on the type of cell and matrix used. Cells in vitro usually respond best to the matrix components with which they are normally in contact in vivo. More differentiated phenotypes are observed and cells generally survive longer on such matrices. In some cases, the presence of such matrices allows cells to be cultured in the absence of serum and growth factors. As more investigators try the matrices and matrix components described, as well as new components and combinations of them, it is anticipated that improvement in the culture of many cells can be expected.     

Hyaluronan matrices in pathobiological processes

Hyaluronan matrices are ubiquitous in normal and pathological biological processes. This remarkable diversity is related to their unique mechanism of synthesis by hyaluronan synthases. These enzymes are normally activated in the plasma membrane and utilize cytosolic substrates directly to form these large polyanionic glycosaminoglycans, which are extruded directly into the extracellular space. The extracellular matrices that are formed interact with cell surface receptors, notably CD44, that often dictate the biological processes, as described in the accompanying minireviews of this series. This article focuses on the discovery in recent studies that many cell stress responses initiate the synthesis of a monocyte-adhesive hyaluronan extracellular matrix, which forms a central focus for subsequent inflammatory processes that are modulated by the dialogue between the matrix and the inflammatory cells. The mechanisms involve active hyaluronan synthases at the cell membrane when cell stresses occur at physiological levels of glucose. However, dividing cells at hyperglycemic levels of glucose initiate the synthesis of hyaluronan in intracellular compartments, which induces endoplasmic reticulum stress and autophagy, processes that probably contribute greatly to diabetic pathologies.