Biomedical subjects

E Y Chao

Publications and source records attributed to E Y Chao.

At least 19 recordsLinked to original sources

PubMed1992

Fatigue strength of cantilevered metal frameworks for tissue-integrated prostheses.

The design of the metal alloy framework in cantilevered sections of fixed tissue-integrated prostheses, is critical. Several cross-sectional designs have been advocated, including the popular L-shaped beam, which permits the economical use of space for tooth placement. The fatigue strengths of 15 L-shaped cantilevered framework sections of the same metal alloy were tested. The castings were divided into three groups of five according to vertical wall heights of 4, 5, and 6 mm. Fatigue durability of each sample was determined by counting the number of cycles of vertical forces required to induce catastrophic failure. Statistical analysis revealed significant differences between all three groups in the cycles counted at failure (p less than 0.0019). Fatigue strengths improved significantly with increasing vertical wall height of the L-shaped cantilevered frameworks. In addition, beam flexure was shown to be indirectly proportional to fatigue strength. Theoretical beam deflection was calculated and shown to correlate with the actual beam deflection during the testing. Theoretical calculations in static bending specific for a cross-sectional design may aid in the predictability of fatigue strength.

Dental Alloys↗

PubMed1992

Changes in wrist and forearm configuration with grasp and isometric contraction of elbow flexors.

The purpose of this study was to determine the changes in wrist and forearm configuration with grasp and elbow flexor contraction by analysis of resting and grasping x-ray films of 15 normal adults and forearm scanograms of 10 other normal subjects. With grasp, a significant proximal migration of the radius (averaging 0.9 mm), a decrease in the carpal height ratio, and an increase in the lunate uncovering index were observed. With flexor contraction, there was a significant decrease in the forearm interosseous space.

Adult↗

PubMed1992

Force distribution across wrist joint: application of pressure-sensitive conductive rubber.

A new pressure-sensitive conductive rubber sensor was used for investigation of the pressure distribution through the radio-ulno-carpal joint. Twelve of these transducers were placed in the radio-ulno-carpal joint. Pressure was measured in seven different wrist positions under loads incrementally increasing from 0 to 12 kg. Half of the sensors showed less than 0.5 MPa, even at maximum load, while a high-pressure area was located palmary in each fossa. The peak pressure measured in the wrist neutral position was 2.4 MPa on the scaphoid fossa, 1.5 MPa on the lunate fossa, and 1.1 MPa on the triangular fibrocartilage with a 10 kg load. The peak pressure ratio between the scaphoid and the lunate was 1.7 in the neutral wrist position. This increased in radial deviation to 2.9 and decreased in ulnar deviation to 0.8. The force-transmission ratio was 50% through the scaphoid fossa, 35% through the lunate fossa, and 15% through the triangular fibrocartilage in the neutral position. The advantage of this sensor is that it is thin and flexible and provides reliable reproducible quasi-instantaneous measurements.

Biophysical Phenomena↗

PubMed1992

Plantar fasciotomy for intractable plantar fasciitis: clinical results and biomechanical evaluation.

Thirteen consecutive patients underwent plantar fasciotomy in 16 feet for intractable plantar fasciitis and had follow-up from 4.5 to 15 years. Plantar fasciotomy was successful (good or excellent results) for 71% of the 14 feet operated on and for which follow-up data were available. However, time to full recovery was prolonged, additional treatment was frequently required, and abnormalities of foot function persisted. Flattening of the longitudinal arch occurred. Dynamic force-plate studies showed differences in peak vertical, fore-aft, and lateral-medial forces between patients and matched controls. More rapid progression of weightbearing along the longitudinal axis of the foot during stance phase in patients indicated avoidance of heel loading.

Adolescent↗

PubMed1992

Salvage of failed first metatarsophalangeal joint implant arthroplasty by implant removal and synovectomy: clinical and biomechanical evaluation.

Implant removal and synovectomy were used to treat the failure of 14 first metatarsophalangeal joint implant arthroplasties. Revision surgery was performed at an average of 3.1 years after arthroplasty. Follow-up (average 4.9 years) was possible in 10 patients, and clinical results were excellent in seven patients, good in one patient, fair in one patient, and poor in one patient. No significant changes in alignment occurred, although a trend toward toe extension was noted. Dynamic force plate studies in these patients demonstrated less pressure under the first metatarsal head and greater loading under the lateral forefoot. The great toe had less contact time during gait in the involved feet than in the control feet.

Adult↗

PubMed1992

The radial forearm flap: a biomechanical study of donor-site morbidity utilizing sheep tibia.

The use of vascularized bone grafts to reconstruct extremity and mandibular defects is now commonplace in reconstructive surgery. Fibula, scapula, iliac crest, rib, and metatarsal as well as the radial forearm osseocutaneous flaps have all been utilized for this purpose. Troublesome spiral fractures of the distal radius are the most common fractures associated with the use of the distal radius as a vascularized bone-graft donor site. This study was proposed to investigate the effect of donor-site bone loss on the strength of the radius under torsional (rotational) loading. Previous clinical series and experimental studies have not examined this aspect of distal radius loading after harvesting the bone graft. Fifty pairs of sheep tibiae were utilized in the experiment. Five pairs were used in a pilot study and 45 pairs were used in the main experiment. Five pairs of human radii were used for the control in the pilot study. The pilot study attempted to make a comparison between the human radius and the sheep tibia for experimental purposes. For the biomechanical study of donor-site defects, four study groups were examined with random assignment and matched pairs. The control group (group 1) had no alteration to the bone. Each test condition included five matched pairs of sheep tibiae. Experiment 1 compared the difference in the depth of the osteotomy defect. In doing this, one-third of the total length of the bone was removed in each of the following specimens to include (1a) 30 percent of the cross-sectional area of the total bone, (1b) 37 percent of the cross-sectional area of the total bone, and (1c) 50 percent of the cross-sectional area of the total bone. In experiment 2, the osteotomy shape was varied. Instead of the ends of the cuts being squared, the ends were beveled or rounded. Experiment 3 compared different lengths of bone removed in the osteotomy defect and included the following: In experiment 3a the diameter of the sheep tibia was measured at the incisura fibularis. This dimension was one diameter of bone, and a one-diameter length of bone was removed. In experiment 3b, a two-diameter length of bone was removed. In experiment 3c, a three-diameter length of bone was removed. In experiment 3d, a four-diameter length of bone was removed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

A normal data base of posteroanterior roentgenographic measurements of the wrist.

In 120 adults, we measured the dominant wrist on posteroanterior roentgenograms in order to determine the normal dimensions and variations according to age and sex. Men and women were equally represented as were two age-groups (twenty-five to forty years and forty-one to sixty years). The roentgenograms were made, with standard exposure and development techniques, with the wrist and forearm in a neutral position and the x-ray tube aligned vertical to the radial styloid. The roentgenogram that was made with the wrist in the mid-coronal plane was digitized and was used to measure distances between specified landmarks. The mean ulnar variance was -0.9 millimeter (normal range, -4.2 to 2.3 millimeters). The average carpal height ratio was 53 per cent (normal range, 46 to 61 per cent). The mean radial inclination was 24 degrees (range, 19 to 29 degrees). The carpal-radial and carpal-ulnar ratios were smaller in women. The width of the distal radio-ulnar joint was reduced in the older subjects. There was a significant positive relationship (p < 0.0001) between the maximum force reached and the length of the third metacarpal. We believe that information concerning the normal roentgenographic measurements and relationship between the bones of the wrist can be used (1) to follow the progression of carpal instabilities, osteonecrosis, osteoarthrosis, or rheumatoid arthritis; (2) in clinical research; and (3) in the design of wrist implants.

Aged↗

PubMed1992

Roentgenographic and mechanical performance of centrifuged cement in a simulated total hip arthroplasty model.

Roentgenographic analysis showed that centrifugation significantly reduced the gross and regional porosity of the cement compared with hand-mixed controls in a simulated total hip arthroplasty model. Static failure test of the prosthetic system demonstrated that the centrifuged cement had significantly greater strength than the hand-mixed cement. Under low-cycle fatigue tests of the same composite models, there was a trend for the centrifuged cement to be stronger than the hand-mixed specimens, although statistically it was not significant. Thus, centrifugation can reduce porosity and significantly improve the static strength of cement in a simulated in vitro total hip replacement model. When cement is used, any possible improvement in the physical properties of bone cement should be considered.

Analysis of Variance↗

PubMed1992

Effect of titanium endoprostheses on bone mineral density measurements, using quantitative computed tomography.

Quantitative computed tomography has been used extensively to measure bone mineral density; particularly in the vertebral column and in the proximal portion of the femur in human beings with osteoporosis. Other potential applications of this technique include evaluation of bone adjacent to metallic endoprostheses and evaluation of fractures as they heal. Unfortunately, metal causes severe image degradation, principally seen as starburst streaking. One method used to decrease these artifacts is by imaging less-attenuating materials, such as titanium alloy. Titanium decreases image degradation sufficiently to allow accurate determination of the geometric properties of cadaveric bone. In our study, the effect of a titanium segmental endoprosthesis on bone mineral density measurement was determined by use of bone specimens from dogs and calibration standards. Titanium decreased the bone mineral density of calibration solutions from 6.8 (500 mg/cm3) to 17.7% (250 mg/cm3), and increased bone mineral density of cortical bone by 5.3%. Titanium did not affect the repeatability of these scans, indicating that the error caused by titanium was systematic and can be corrected. Our data were suggestive that quantitative computed tomography can be used to measure bone mineral density of cortical bone adjacent to titanium endoprostheses, with a predictable increase in density measurement.

Animals↗

PubMed1992

Composite fixation of salvage prostheses for the hip and knee.

A composite fixation method for a porous-coated modular segmental bone/joint prosthetic system was developed to improve fixation at revision surgery of the hip and knee after failure of the original implant with resulting massive bone loss. The porous coating is limited only to the segmental shoulder region of the prosthesis, while bone cement is used to provide initial implant stability. Autogenous bone grafts are applied over the porous-coated region to achieve extracortical bone bridging and ingrowth for long-term biologic fixation. Bench tests, theoretical analysis, and animal experiments were performed to validate this fixation concept. Clinical, roentgenographic, and functional results of revision patients using these prostheses and the underlying fixation principle are very encouraging. A number of limiting factors were identified and further improvements are being investigated to foster this concept as a viable salvage alternative.

Bone Regeneration↗

PubMed1992

[Natural history and biologic mechanism of the transition from grafted bone to extra-cortical bone bridge over porous-coated segmental prostheses].

The biologic mechanism of extra-cortical bone bridge formation over a porous-coating segmental prosthesis was studied. A 6 cm segment of the femoral diaphysis was bilaterally resected and replaced by a segmental prosthesis in 32 adult dogs. A morselized autogenous bone graft mixed with marrow cells was applied around the prosthesis and the adjacent cortex. The animals were sacrificed at 2, 4, 8 and 12 weeks postoperatively. Tissue samples from the extra-cortical bone formation zone were analyzed by fluorescent and light microscopy and transmission electron microscopy. Active intramembranous new bone formation occurred appositionally. Osteogenic foci were formed in the fibrous tissue by the determined osteogenic precursor cell contained in the marrow cells. Woven bone formation occurred within the matured callus through endochondral ossification. Extra-cortical bone bridges depended on bone/marrow grafts with good vascularity and mechanical stability as important ingredients. Extra-cortical bone bridges were reduced in volume and matured with time.

Animals↗

PubMed1992

Intersegmental elbow joint load during pushup.

Intersegmental loading pattern on the elbow joint during a push-up exercise was investigated. Electromagnetic motion sensors and a piezoelectric force plate were used to simultaneously record upper extremity motion and forces on nine healthy male subjects during push-ups in six different hand positions. Peak axial forces exerted on the elbow joint averaged 45 percent of the body weight. Peak torque to produce elbow flexion was 2305.9 N-cm, or 56 percent of maximal isometric extensor torque. The results of this analysis give insight to the biomechanics of a normal elbow and to its load carrying capacity.

Adult↗

PubMed1991

Bypassing femoral cortical defects with cemented intramedullary stems.

The objective of this investigation was to examine the effect of cemented intramedullary stem bypass on bone torsional property in the presence of femoral cortical defect. We intended to test two hypotheses; first, intramedullary fixation without bypass will accentuate the stress concentration effect and second, there will be an optimal length of stem bypass beyond the defect. Cemented intramedullary stems were used to bypass 50% diaphyseal diameter unicortical defects in paired, fresh-frozen canine femora. One member of each pair served as an unaltered control and all specimens were tested to failure in torsion. Both single-tailed paired t-test and analysis of variance were used for data analysis. Bones subjected to the cortical defect and no bypass were substantially weakened, exhibiting only 44 +/- 8% of control side maximum torque (p less than 0.001). Positioning of the intramedullary stem with its tip at the center of the defect provided a small degree of strength improvement, achieving 60 +/- 7% of control side maximum torque. One and two diaphyseal diameter bypass, however, significantly (p less than 0.01) improved bone torsional strength, resulting in 80 +/- 6% and 84 +/- 13% of control side maximum torque, respectively. Three diameter bypass achieved only 68 +/- 8% of control side maximum torque. This significant (p less than 0.05) decline in strength when compared to two diameter bypass appears to indicate that the length of stem bypass beyond the cortical defect does have an optimum, probably due to the geometric characteristics of the canine femora.

Animals↗

PubMed1991

Quantitative CT for the evaluation of bone healing.

Quantitative computed tomography (QCT) was used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks and imaged with QCT. Invasive techniques were used to determine (1) the torsional properties of the bone; (2) the local stiffness properties and calcium content within the bone; and (3) histologically determined new bone formation and porosity. QCT was strongly associated with the maximum torque (R2 = 0.44) and torsional stiffness (R2 = 0.69) of the healing bone. QCT had strong correlations with the local stiffness (R2 = 0.64), calcium content (R2 = 0.61), new bone (R2 = 0.84), and porosity (R2 = 0.84) of healing tissues.

Animals↗

PubMed1991

The determination of bone fracture properties by dual-energy X-ray absorptiometry and single-photon absorptiometry: a comparative study.

Dual-energy X-ray absorptiometry (DEXA) and single-photon absorptiometry (SPA) were used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks, and imaged with DEXA and SPA. Invasive techniques were used to determine (1) the torsional properties of the bone, (2) the local stiffness properties and calcium content within the bone, and (3) new bone formation and porosity by histology. There were no differences between SPA and DEXA in their associations with the torsional properties of bone. SPA and DEXA had strong correlations with the ultimate torque (R2 = 0.76, 0.51) and the torsional stiffness (R2 = 0.68, 0.53) of bone. SPA and DEXA of periosteal callus, endosteal callus, and cortical bone had similar associations with indentation stiffness, calcium content, new bone formation, and porosity. SPA of gap tissue had significantly stronger associations with these four parameters than DEXA (P less than 0.05). Correlation coefficients (R2) with these local material properties ranged as high as 0.82 for SPA with new bone formation in the gap tissue and 0.73 for DEXA with indentation stiffness of periosteal callus.

Absorptiometry, Photon↗

PubMed1991

The effect of defect size on the stress concentration and fracture characteristics for a tubular torsional model with a transverse hole.

The maximum stress location and crack resistance of a tubular torsional model with varying transverse circular defects were determined by the use of experimental and global-local finite element modeling techniques. The experimental results showed that the reduction in torsional strength was inversely proportional to defect size. In addition, the maximum stress location around the defect was closely related to the normalized defect diameter. By measuring the shifted angle associated with each defect ratio, a linear relationship, delta theta = -6.28 + 0.55*(d/D), was determined. Finite element results indicated that the stress concentration factor, Kg, for a single-cortex defect is similar to that of a double-cortex defect of identical dimension. Application of the strain energy density (SED) theory proposed by Sih and Oliveira Faria (Fracture Mechanics Methodology, Martinus Nijhoff, The Hague, 1984), indicated that the fracture toughness, KIC, for large defects was greater than that for small defects. This implies that tubular structures with large defects have a greater resistance to crack initiation and growth.

Animals↗

PubMed1991

Physiological prediction of muscle forces--I. Theoretical formulation.

A physiological model for predicting muscle forces is described. Rigid-body mechanics and musculoskeletal physiology are used to describe the dynamics of the segment model and muscle model. Unknown muscle and joint contact forces outnumber the equilibrium equations resulting in an indeterminate problem. Mathematical optimization is utilized to resolve the indeterminacy. The modeling procedure relies entirely on established physiological principles. Data describing the muscle anatomy and body structures are included. A model defining the force-length-velocity-activation relationship of a muscle is adopted. The force a muscle produces is assumed to be proportional to its maximum stress, physiological cross-sectional area, activation, and its functional configurations including the muscle architecture, muscle length, contracting velocity, and passive tension. These factors are incorporated into inequality equations which limit the force for each muscle. Minimal muscular activation is forwarded as the optimization criterion for muscle force determination.

Biomechanical Phenomena↗

PubMed1991

Physiological prediction of muscle forces--II. Application to isokinetic exercise.

The successful application of a physiological model of the musculoskeletal system capable of accounting for nonequilibrium dynamic loading and predicting individual muscle forces in the knee is presented. The model incorporates rigid-body mechanics and musculoskeletal physiology. Unknown muscle and joint contact forces outnumber the equilibrium equations resulting in an indeterminant problem. Mathematical optimization is utilized to resolve the indeterminacy. The model is used to estimate individual muscle forces during isokinetic exercise. Five subjects were tested at speeds of 60 degrees/s and 180 degrees/s. A newly proposed optimal criterion, minimizing muscular activation, results in muscle force predictions which have significantly higher correlations with myoelectric activity than other linear and nonlinear optimal criteria. The results demonstrate that properly constrained linear programming methods do not limit the number of active muscles and allow for uniform recruitment of the active muscles.

Adult↗