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Biomedical subjects

R D Crowninshield

Publications and source records attributed to R D Crowninshield.

35 records · Page 2Linked to original sources
PubMed1982

A model of lower extremity muscular anatomy.

The mathematical prediction of muscle and joint force requires a quantitative knowledge of muscle origins and insertions. A model is presented based upon marking the origins and insertions in three cadavers (six limbs). Right-to-left biological variations and/or making errors are sometimes significant, but they rarely result in moment arm calculation variations of greater than 20 percent and usually the variations are less than 10 percent. The muscle origin and insertion differences between small and large cadavers is great, as would be expected, and the use of single specimen or average data will result in large errors in muscle force predictions. A scaling scheme is presented which substantially reduces those errors. The inherent limitations of developing a straight line muscle model include: 1) right-to-left biological variations and/or marking errors; 2) difficulties in establishing "effective" origins or insertions when the locations of the actual origin or insertion do not accurately reflect muscle function; and 3) intersubject variability which cannot be accounted for by simple scaling schemes.

Female↗
PubMed1982

The three-dimensional rotational behaviors of the carpal bones.

The rotational behaviors of the carpal bones of ten fresh cadaver forearms were determined using a three-dimensional sonic digitizer, as the hands were passively moved through planar constrained motions. Changing forearm orientation from supination to pronation results in an increase in the magnitudes of extension of the proximal and distal carpal row bones and a reduction in the magnitudes of flexion of the distal carpal row bones. The included angles between each carpal bone screw displacement axis (SDA) and third metacarpal SDA for corresponding intervals of motion are significantly greater than zero, regardless of forearm orientation. The included angles of the proximal carpal row bones are significantly greater than those of the distal carpal row bones during third metacarpal radial-ulnar deviation. The carpal bone rotation magnitudes are significantly attenuated relative to the prescribed rotation magnitudes of the third metacarpal, with the exception of the trapezoid during third metacarpal extension. The rotational attenuation is greatest in the proximal carpal row bones and is most pronounced during third metacarpal flexion-extension motion and ulnar deviation. Evidence from this investigation favors a carpal row concept of wrist motion, as opposed to a carpal column model.

Carpal Bones↗
PubMed1981

The center of pressure path in treated clubfeet.

The center of pressure paths of foot-floor contact were examined in detail in normal subjects and a group of 44 patients with treated clubfeet. The foot-floor contact areas were wide and the center of pressure paths more variable in clubfeet patients. The center of pressure paths did not always distinguish between normal and abnormal subjects nor between abnormal subjects with varying functional ratings. Foot prints are not sensitive enough to be a diagnostic aid and are of only limited application to the problem of evaluation of treatment of clubfoot deformity.

Adult↗
PubMed1981

An analysis of soft tissue loading in the foot--a preliminary report.

The foot's response to load during weightbearing is investigated using finite element stress analysis of a two-dimensional model. The analysis predicts the stress states within the plantar aspect tissue during a variety of shoe conditions. Shoe soles with a range of elastic properties are modeled in an attempt to find a shoe sole that minimizes peak stresses within the foot's soft tissue. This presently simplified and idealized model of the foot and shoe during mid-stance demonstrates significant dependency of stress development within the tissue on shoe elastic properties. These results would seem to justify further more detailed and realistic modeling of shoeing mechanics, and systematic efforts to correlate physical measurements and clinical experience with the trends indicated by finite element analyses.

Body Weight↗
PubMed1980

An analysis of femoral component stem design in total hip arthroplasty.

UNLABELLED: A comparative study of the various aspects of the design of the femoral components of total hip replacements was done using three-dimensional finite-element stress analysis. The aspects of deisgn that were considered included: length, cross-sectional size, and material properties of the stem; presence or absence of a medial collar; and material properties of the cement. We found that increasing the length of the stem generally increased the stress present in the stem while decreasing the stress present in the cement. Increasing the cross-sectional size of the stem decreased the stress in both the stem and the cement. Decreasing the modulus of elasticity of the stem material decreased the stress in the stem but increased the stress in the cement. Increasing the modulus of elasticity of the cement decreased the stress in the stem and increased the stress in the cement. Contact of the collar of a femoral prosthesis with the calcar femorale increased the longitudinal component of stress within the region of the calcar femorale. CLINICAL RELEVANCE: The mechanical longevity of a total joint reconstruction is related to the stress distribution throughout the prosthesis, cement, and bone. The stress distribution is related to a number of factors, including the design of the prosthetic components (for example, stem size, stem length, stem modulus of elasticity, and cement modulus of elasticity). Reducing the stresses in prosthetic components to minimize the risk of failure can be accomplished only through systematic analysis of all components of the reconstruction.

Bone Cements↗
PubMed1979

Reconstruction of the hip. A mathematical approach to determine optimum geometric relationships.

The normal mechanical function of the hip is substantially altered by a variety of disorders. The surgical treatment of such conditions, particularly total hip replacement, offers the opportunity not only to replace the articular surfaces of the joint, but also to improve long-term mechanical function by reducing the loads on the joint. A mathematical model of the hip was developed to evaluate the effects of such surgically achievable mechanical alterations as acetabular placement, femoral shaft-prosthetic neck angle, neck length of the femoral prosthesis, and transfer of the greater trochanter. The loads on the hip were lowered significantly by placing the center of the acetabulum as far medially, inferiorly, and anteriorly as was anatomically feasible. Minimum joint contact forces occurred when the femoral shaft-prosthetic neck angles were small, while the minimum moments about the prosthesis stem-neck junction were found when the angles were 130 to 140 degrees. A neck length of the femoral prosthesis of thirty-five millimeters resulted in moments that were lower than those for a neck length of forty-five millimeters. Lateral transfer of the greater trochanter reduced hip-joint forces and moments but distal transfer had little mechanical effect.

Acetabulum↗
PubMed1976

The strength and failure characteristics of rat medial collateral ligaments.

Traumatic loading of the knee joint in man occurs at strain rates ranging from 0.5-1,500 m/m/sec. Experiments on the medial collateral ligament of rats demonstrate that the mode of failure is a function of the strain rate. Avulsions occurred more often at low rates; ligament tearing occurred more often at high rates.

Animals↗
PubMedDate not supplied

The effect of femoral stem cross-sectional geometry on cement stresses in total hip reconstruction.

A three-dimensional numerical stress analysis of a prosthesis-cement-proximal femur system was performed to reveal functional differences of total hip femoral component stems with varying cross-sectional shapes. The analysis was performed on stem cross-section shapes similar to many of the variations presently available in femoral components. The results indicate that the predicted levels of stress in the cement are often close to critical (i.e., failure) levels. The magnitude and mode (i.e., compression versus tension) of loading in the cement are significantly affected by the stem cross-sectional shape. Particular attention is paid to the stress in the cement within the proximal portion of the structure. High compression stresses in the cement are shown to result from prostheses with narrow medial surfaces and small area moments of inertia. High cement tensile stresses result from prostheses with small area moments of inertia. A large region of cement compression results from prosthesis cross-sections with relatively large anterior-posterior dimensions about their lateral aspect. Desirable stress distributions result from prostheses with broad medial surfaces and even broader lateral surfaces.

Biomechanical Phenomena↗
PubMedDate not supplied

The effect of cane use on hip contact force.

Canes may be used to reduce hip pain by reducing the joint contact force. Previous estimates suggest that this force could be reduced to 17-26% of normal. We have calculated 3-dimensional hip contact forces during gait in 4 groups: normals, preoperative hip patients walking without a cane, preoperative hip patients walking with a cane, and patients postoperative total hip reconstruction. Preoperative patients walking with a cane exhibited hip contact forces of about 60% normal force (from age-matched and velocity-matched normals). Preoperative patients walking without a cane and postoperative patients had hip contact forces which were not significantly different from age-matched and velocity-matched normals. Considering that patients probably rarely place more than 20% of their body weight on a cane, it is likely the hip contact force will rarely be reduced below 60% of body weight with use of a cane.

Aged↗