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Biomedical subjects

R D Crowninshield

Publications and source records attributed to R D Crowninshield.

At least 19 recordsLinked to original sources
PubMed2001

A low stiffness composite biologically fixed prosthesis.

The current authors addressed the question whether stress-induced adaptive bone remodeling of the proximal femur is a necessary consequence after total hip reconstruction with extensively biologically-fixed femoral components. A novel total hip femoral component was designed to simultaneously achieve stable skeletal fixation, structural durability, and reduced femoral stress shielding. This implant allowed for proximal and distal canal filling, yet was significantly less rigid than all-metallic femoral stems crafted of either cobalt chromium or titanium alloy. A cohort of 366 patients (386 hips) treated at 21 institutions worldwide now have been followed up a mean of 2.4 years postoperatively (range, 3 months-6 years). Two hundred sixty-eight patients have 2 years minimum followup. To date, no femoral implants have failed to achieve bone ingrowth and none have required revision. The implants appear radiographically well-fixed with no progressive radiolucencies or osteolysis. Radiostereometric analysis studies on one subset of patients showed stable initial fixation and minimal stem micromotion. Dual energy xray absorptiometry analysis on another subset of patients revealed excellent periprosthetic bone mineral density retention. Compared with more rigid metal implants, this design shows reduced proximal femoral bone loss secondary to stress-mediated bone resorption.

Absorptiometry, Photon↗
PubMed1998

Cemented femoral component surface finish mechanics.

A cemented femoral component's surface finish may influence implant function through variations in cement adhesion and abrasion properties. Morphologic characterization of historic and current femoral hip prosthesis surface finishes show greater than x 20 range in implant roughness. Early implants typically had relatively smooth surfaces, whereas many of the more recent implants have rougher surface finishes. Smoother implant surfaces have lower cement-metal interface fixation strength, whereas rougher surfaces have greater fixation strength. With interface motion, the smoother surfaces are less abrasive of bone cement, whereas rougher implant surfaces are more abrasive. Because of enhanced bone cement attachment, rougher implant surfaces may have a lower probability of interface motion, while at the same time, a higher debris generation consequence if motion occurs. In contrast, smoother implant surfaces may have a higher probability of interface motion with a lower debris generating consequence of that motion. The prolonged use of cemented total hip replacement may be approached by either extending the duration of implant function after cement-metal interface loosening with smooth surfaced implants or, in contrast, by extending the duration of cement-metal interface adhesion with rougher surfaced implants.

Arthroplasty, Replacement, Hip↗
PubMed1992

Bone ingrowth into a low-modulus composite plastic porous-coated canine femoral component.

Bone ingrowth into low-modulus canine femoral components made of composite plastics and porous coated with titanium fiber mesh was evaluated and compared to that found in femoral components of the same design made of titanium alloy and porous coated with titanium fiber mesh. Both types of components demonstrated extensive bone ingrowth into the porous coatings at 6 weeks and there were no differences in the histologic appearance of the tissue ingrowth in the two groups. The amount of bone that grew into the porous surface, the areal density of bone within the available pore space, and the extent of the prosthesis periphery with bone ingrowth were not significantly varied in the two different components. The results of this study show that adequate fixation of low-modulus composite femoral components porous coated with titanium fiber mesh by bone ingrowth can occur and that further investigation of these materials for femoral components may be warranted.

Animals↗
PubMed1986

The in vivo kinematics of the rheumatoid wrist.

The objectives of this study were to describe the three-dimensional in vivo kinematic behavior of wrists affected by rheumatoid arthritis, to correlate kinematic parameters and two radiographic indices of carpal disease, and to describe the in vivo kinematic behavior of the Swanson Silastic wrist implant. Fifteen normal wrists, 17 rheumatoid wrists, and 7 wrists with Silastic wrist implants were tested using a three-dimensional sonic digitizing system. The motion of the hand segment relative to the forearm segment, corresponding to the positions exhibited during flexion-extension motion (FEM) and radial-ulnar deviation (RUD), was described using the equivalent screw displacement (ESD) concept. The mean magnitudes of ESD rotation for both FEM and RUD were statistically different (p less than 0.05) among the normal, rheumatoid, and implant groups. The remaining ESD parameters (i.e., mean values for the translation, the direction angles of the ESD axis, and the intercepts of this axis with the planes of motion), the minimum separation between the FEM and RUD axes, and the coordinates of the midpoint of this separation were not statistically different (p greater than 0.05) among the normal, rheumatoid, and implant groups. The two radiographic indices (carpal collapse and carpal translation) did not correlate with the magnitude of rotation or with any other ESD parameter.

Adult↗
PubMed1986

Mechanical properties of porous metal total hip prostheses.

The forged condition is the strongest form of the Co-Cr-Mo and Ti-6Al-4V alloys used in orthopaedics. Both the Co-Cr-Mo alloy and the Ti-6Al-4V alloy lose strength when incorporated into porous implants. The strength loss in the Co-Cr-Mo alloy is a generalized condition and is largely a result of the microstructure of these cast and then gravity-sintered prostheses. The greatest fatigue strength achieved throughout these porous Co-Cr-Mo implants is that of the cast alloy. The strength loss in diffusion-bonded, porous titanium-alloyed implants is largely a result of notch sensitivity. This strength loss is not a generalized condition; it is localized on the implant to regions of porous coating attachment. In implant regions apart from the porous coatings, these titanium implants can have the strength of other wrought or forged titanium alloy implants. To achieve a functionally strong implant, porous implant design needs to account for these losses in material strength. Implant strength should be verified experimentally and communicated to the orthopaedic surgeon for assessment of implant adequacy for a particular patient. Patient weight, activity, and life expectancy are important elements in judging the adequacy of an implant's strength.

Alloys↗
PubMed1985

The kinetics of normal and prosthetic wrists.

The purposes of this study were (1) to describe normal wrist kinetics, and (2) to investigate the in-vitro kinetics of four currently available wrist prostheses (Swanson, Meuli, Volz, Hamas). The effective tendon moment arms of the six major wrist muscles were determined through the use of load cells and applied weights. Testing was conducted in a neutral wrist configuration with hand pronation-supination both constrained and unconstrained. The results indicate that each of the muscles studied has a unique set of effective tendon moment arms about the normal wrist as well as about wrists with the implanted prostheses, and that none of the prosthetic wrists studied duplicated normal wrist kinetics.

Humans↗
PubMed1985

Prediction of muscle and joint loads after segmental femur replacement for osteosarcoma.

The authors designed a mathematical model that simulated 28 proximal and distal femoral resections and reconstructions for tumor and then predicted muscle and joint forces during gait and stair climbing. Such models will become increasingly useful as improvements are available, as tumor patient longevity increases, and as the design and manufacture of custom devices become more common. Inertial property changes with surgery were minor and can be ignored for most purposes. For most simulations, physiologically reasonable muscle forces were predicted, suggesting that patients would be able to walk in a normal or near-normal fashion. Large joint and muscle loads were predicted after extensive muscle resections, particularly during stair climbing, suggesting that patients would limp. The quadriceps muscle group was sufficiently strong to allow normal gait with partial excisions. With complete quadriceps excision and transfers, however, high joint loads were predicted. Furthermore, if an endoprosthesis had inherent varus-valgus stability in such cases, the moments to be satisfied by the prosthesis would predispose to high interface stresses and loosening. If, conversely, the endoprosthesis did not have inherent stability, muscle forces in the remaining muscles would be unrealistically high, suggesting that such a patient would limp or require ambulation assists.

Adult↗
PubMed1984

Design sensitivity analysis: a new method for implant design and a comparison with parametric finite element analysis.

A unified theory of structural design sensitivity is proposed to be used in conjunction with the parametric design variation method traditionally used in finite element analyses applied to biomechanics problems. Bone cement strain energy density dependence on cement and stem modulii of elasticity as analyzed with the theory of structural design sensitivity analysis is compared parametrically varied finite element results. Two-dimensional, eight-noded isoparametric and interface finite elements with optimal stresses at Gauss points are employed. Design sensitivity for strain energy density compares well with perturbation of design and reanalysis by finite element techniques.

Hip Prosthesis↗
PubMed1983

Cement strain measurement surrounding loose and well-fixed femoral component stems.

Strain measurement within the cement surrounding stemmed total hip femoral components was accomplished using PMMA encapsulated and embedded strain gauges. Cement strain measurement associated with a well-bonded stem-cement interface and an unbonded stem-cement interface (i.e., loose prosthesis) was performed. The presence of a stem-cement bond was found to reduce proximal cement strain magnitudes while having little effect on distal cement strain magnitudes. The assurance of a stem-cement bond on only the proximal third of the interface was found to have an effect similar to that of a complete stem-cement bond. The results of this experimental investigation confirm the theoretical prediction that the stem-cement bond is important in maintaining the integrity of the cement mantle surrounding a stemmed femoral component.

Biomechanical Phenomena↗
PubMed1983

An analysis of tibial component design in total knee arthroplasty.

An axisymmetric finite element model of the proximal tibia and cemented tibial component subject to nonaxisymmetric loading is presented. Model variations included polyethylene components and steel reinforced polyethylene components both with and without a central fixation post. Central fixation posts of 35 and 70 mm were modeled. A vertically oriented load applied unilaterally to the tibial component was found to generally cause the largest magnitude peak stresses within the various components of the structure. The addition of steel reinforcement to tibial components without central fixation post is predicted to significantly reduce stress levels within the polymethylmethacrylate and underlying cancellous bone. Although to a lesser extent, the addition of a relatively short central fixation post to the steel reinforced tibial component further reduced these stress levels. The longer steel central fixation post can appreciably reduce proximal cement and bone stress levels. The tibial component condylar width is predicted to have little effect on polymethylmethacrylate and cancellous bone stresses, with the exception that proximal tibial cancellous bone compressive stresses are reduced with wide steel reinforced components.

Biomechanical Phenomena↗
PubMed1983

A physiologically based criterion for muscle force predictions on locomotion.

A quantitative method of muscle activity prediction is presented which uses a criterion of maximum endurance of musculoskeletal function and is based on the inversely nonlinear relationship of muscle force and contraction endurance. The results obtained through the use of this method agree more closely with known patterns of muscle activity, as revealed by electromyography, than do those obtained by most linear optimization techniques.

Biomechanical Phenomena↗
PubMed1983

Pathologic ligamentous constraint of the hip.

A mathematic model of the hip capsule and lower extremity musculature was utilized to predict the forces present in the hip ligaments during locomotion. The results demonstrate principles and trends (rather than absolute results) in hip mechanics, the details of which are affected by the associated modeling assumptions. The active stretching of a hip joint capsule tightened by scarring or surgical transfer may appreciably increase the hip contact force. Capsular elements that prevent hip flexion and adduction play a major role in hip contact force exaggeration during common activities. The positive effect of maintaining the hip capsule to reduce total hip component dislocation contrasts with the potential negative effects of restricting joint motion and increasing the joint contact force. Increased joint loading due to capsular restriction may contribute to prosthetic component loosening.

Hip Joint↗
PubMed1983

Roentgenologic results of total hip arthroplasty. A ten-year follow-up study.

A ten-year roentgenologic follow-up study was made of the results of 326 total hip arthroplasties in 256 patients. Seventy-two percent of the living patients are included in the study. Clinical results at ten years were good in 87% of the patients, fair in 7%, and poor in 6%. The incidence of femoral component loosening was 9% at ten years. There was no correlation between femoral component loosening and calcar resorption. The incidence of acetabular component loosening at ten years was 7.9%. Of six hips with calcar resorption greater than 5 mm, three had loose acetabula. Most of these components shown to be loose roentgenologically were clinically asymptomatic. One and one-half percent were revised because of loosening.

Bone Cements↗
PubMed1983

A stress analysis of acetabular reconstruction in protrusio acetabuli.

UNLABELLED: We are reporting the results of a finite-element analysis of acetabular reconstruction for total hip replacement in the presence of protrusio acetabuli. In a protruded acetabulum, cortical bone stresses on the medial part of the pelvic wall increase with medial placement of the acetabular component, while normal placement of the component (more lateral placement) reduces these stresses. Metal backing of a polyethylene acetabular component causes a reduction in the peak cement and trabecular-bone stresses. A metal protrusio ring about only the periphery of the acetabular component increases stress levels within the lateral part of the pelvic cortex and has little effect on stresses in the medial part of the pelvic wall. A complete metal protrusio cup increases stresses in the lateral part of the pelvic cortex while decreasing substantially the stresses in the medial part of the cortex and the trabecular bone. Prosthetic reinforcement of the medial part of the acetabular wall has little effect on stress patterns in the acetabular region. CLINICAL RELEVANCE: The major long-term problem with cemented total hip prostheses is loosening. Loosening is probably related in part to the stress state in the cement and surrounding bone. The protruded acetabulum is particularly difficult to reconstruct in a manner that ensures longevity of the total hip replacement. In patients with protrusio acetabuli, the prosthetic acetabulum should be placed in a normal and not in a protruded position. A metal-backed acetabular component or a complete metal cup incorporated within the cement reduces stress levels within the medial aspect of the pelvic bone and thus may reduce the incidence of loosening.

Acetabulum↗
PubMed1982

An axisymmetric model of acetabular components in total hip arthroplasty.

An axisymmetric finite element model with nonaxisymmetric loading of an acetabular arthroplasty and the surrounding pelvic bone is presented. Model variations include ultra high density polyethylene acetabular components of varying wall thicknesses and metal backed ultra high density polyethylene components. Each of the two component types is modeled as implanted within an acetabulum with intact subchondral bone and within an acetabulum without subchondral bone. Thin wall polyethylene acetabular prostheses are predicted to increase, relative to thick wall components, maximum stresses in the cement-bone composite. Trabecular bone stresses are predicted to increase with the removal of subchondral bone. Stiffer metal-backed acetabular components are predicted to reduce maximum cement and bone stresses and to abridge the effects of altered component wall thickness and of subchondral bone removal.

Acetabulum↗
PubMed1982

The scapholunate ligament.

The effects of scapholunate ligament sectioning on scaphoid and lunate bone three-dimensional kinematics were analyzed using a sonic digitizer method. Carpal bone motions were described using a screw displacement axis concept. After scapholunate ligament sectioning, few significant kinematic changes were observed in the orientation of the screw displacement axes or in carpal bone rotation about the screw displacement axes. The angles between the screw displacement axes of the scaphoid and lunate bones were only minimally affected, indicating that the two bones continued to track well relative to each other. The results indicate that sectioning of the scapholunate ligament does not result in a major disturbance of scaphoid and lunate bone motions.

Biomechanical Phenomena↗
PubMed1982

An in-vivo study of normal wrist kinematics.

The motion of the hand relative to a reference frame embedded in the radius is described using the screw displacement axis (SDA) concept. A three-dimensional sonic digitizer was utilized in a study of the dominant wrist of 15 normal subjects to determine the location and orientation of the SDAs based on the endpoints of flexion-extension motion (FEM) and radial-ulnar deviation (RUD) of the hand. The length of the common perpendicular between the SDAs of FEM and RUD was as large as 6 mm in some individuals; however, in some subjects the FEM SDA was distal of the RUD SDA while in others it was proximal. Considering the group of 15 subjects, the SDAs of FEM and RUD for the normal group nearly intersect in the head of the capitate in the neutrally positioned wrist and forearm.

Biomechanical Phenomena↗