Biomedical subjects

J Medige

Publications and source records attributed to J Medige.

16 recordsLinked to original sources

PubMed2000

Functional assessment in the rat by ground reaction forces.

Although the rat sciatic nerve model is used extensively in the investigation of repair techniques, and a variety of evaluation methods utilized to assess the results, a means to measure directly and accurately the return of function in these animals is absent. Histologic, histomorphometric, and electrophysiologic methods can be reliable indicators of nerve regeneration but do not correlate to functional recovery. The purposes of this study were to develop apparatus to continuously measure ground reaction forces (GRF) and use GRF parameters in the assessment of gait parameters in normal rats preoperatively and following peripheral nerve severance and repair. Three neurorrhaphy methods: direct sciatic nerve repair, direct tibial nerve repair and double sciatic nerve repair simulating autograft, as well as a non-repaired tibial nerve transection were evaluated. The testing apparatus was designed to measure the spontaneous and voluntary effort of the rat with objective data. Three orthogonal components - vertical, craniocaudal (braking and propulsion), and mediolateral - of the ground reaction force were measured. Preoperative data showed that vertical forces were comparable among the four limbs but propulsion and braking forces displayed significant differences. At 12 weeks, functional recovery was most evident in the direct tibial nerve repair group and absent in the non-repaired tibial defect group. Direct sciatic nerve repairs and sciatic nerve grafts resulted in lesser degrees of improvement. Results indicated that the propulsive force is the optimal GRF parameter for evaluating recovery of useful function.

Analysis of Variance↗

PubMed1999

Effect of bone quality on the forces generated by compression screws.

Internal fixation of the fractured scaphoid bone is used to promote union between bone fragments and to decrease wrist immobilization. Headless screws are commonly used because they minimize interference with articular surfaces and reduce tissue irritation and immobilization. In the present experiment, compressive force was measured as a function of bone quality for two headless screw types, the Herbert and the Acutrak. Forty-seven cylindrical samples of cancellous bone were prepared from fresh, previously frozen human cadaveric distal femora. The compressive forces generated as the screws were advanced into the specimens were measured and correlated to the specimens' bone mineral density (BMD) and density. Over the range tested, the average compressive force for the Acutrack screw was approximately 42% higher than that of the Herbert. Statistical significance, however, could not established because of the low statistical power of the test due to the inherent spread in the data. For the Acutrak screw, force was best fit to BMD and to density by second-order polynomials. Regression analysis indicated that similar correlations did not exist between force and BMD or between force and density for the Herbert screw. The correlation shown by the Acutrak screw indicates that it may be a more predictable as well as more effective system and therefore there may be some advantage in selecting this system. Furthermore, results suggest that the Acutrak screw generates greater forces with increasing bone density and could be more effective for a younger population.

Biomechanical Phenomena↗

PubMed1999

The lateral hypothalamic syndrome in the weanling rat: bone geometry and biomechanics.

Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the lateral hypothalamic area (LHAL). One group of sham-operated controls was fed ad lib (CON-ADLIB), another was pair fed to the LHAL group (CON-PF). The experiment was terminated 1 month after surgery. At that time, LHAL rats were 49% and CON-PF rats were 41% lighter than CON-ADLIB. Carcass protein in LHAL rats was significantly reduced in LHAL: versus CON-ADLIB. Linear growth was significantly reduced by 18% in LHAL versus CON-ADLIB, as well as LHAL: versus CON-PF by 6%. Mean caloric intake was significantly reduced by 48% in LHAL versus CON-ADLIB, as was caloric efficiency (body weight gained per calories eaten) by 36%, as well as, in CON-PF versus CON-ADLIB by 20%. LHAL rats showed a significantly shorter (10%), narrower (15%) and thinner (25 %) cortex at midshaft of the femur. Resistance to torsional loads was reduced by 25% in both LHAL and CON-PF, but this did not reach statistical significance, in comparison to CON-ADLIB. There was no statistical significance among the groups in stiffness and maximal angular displacement. We conclude that the reduced bone geometrical and biomechanical properties in both LHAL rats and CON-PF versus CON-ADLIB are similar because both former groups of rats were greatly subcaloric. Thus, the changes here observed are not due to a specific neuroendocrine/autonomic lesion effect but may be attributable to the reduced food intake, i.e., nutritional factors.

Animals↗

PubMed1997

Ultrasound velocity and broadband attenuation as predictors of load-bearing capacities of human calcanei.

The main purpose of this study was to determine whether calcaneal ultrasound parameters, measured in the mediolateral direction, reflect load-bearing capacities of human calcanei. Broadband ultrasound attenuation (BUA) and ultrasound velocity (UV) were measured in 20 cadaveric calcanei with a mean age of 74.1 (SD 8.8). Normalized BUA (nBUA) was determined by dividing BUA by the calcaneal thickness obtained using a pulse-echo technique. The bone mineral density (BMD) of each calcaneus was measured by quantitative computed tomography. The calcanei were embedded in PMMA to simulate the midstance physiologic orientation during compressive testing in the load-bearing direction. The failure load, stiffness, and energy absorption were determined for each calcaneus. It was shown that BMD was well correlated with all ultrasound parameters (P < 0.0001). BMD, BUA, nBUA, and UV were all significantly associated with calcaneal failure load, stiffness, and energy absorption capacity (P < 0.05). nBUA was found to be the strongest predictor of all compressive properties. BUA and BMD demonstrated similar predictability of stiffness and energy absorption capacity, however, BUA showed a more significant relationship to the failure load of the calcaneus than did BMD. UV was found to be inferior to BMD, as well as BUA or nBUA, in assessing failure load, stiffness, and energy absorption capacity. It was also shown that nBUA was superior to BUA in the assessment of load-bearing capacity, but not in the prediction of BMD. Multivariate regression analysis showed that the combination of BUA or nBUA with UV did not improve the predictability of failure load, stiffness, and energy absorption capacity over that of BUA or nBUA alone (P > 0.5).

Absorptiometry, Photon↗

PubMed1997

The ability of quantitative ultrasound to predict the mechanical properties of trabecular bone under different strain rates.

The ability of quantitative ultrasound to predict the mechanical properties of trabecular bone under different strain rates was investigated. Ultrasound velocity (UV) and broadband attenuation (BUA) were measured for 60 specimens of human trabecular bone. Samples were divided into two equal groups and loaded in compression at the strain rates of 0.0004 and 0.08 s-1. The ultimate strength, elastic modulus, and energy absorption capacity were determined for each specimen. Specimens tested at 0.08 s-1 had a mean value of strength 63% higher than the specimens tested at 0.0004 s-1. The elastic modulus and energy absorption capacity were 82% and 42% higher, respectively, for the higher strain rate. UV and BUA were significantly associated with most mechanical properties at both strain rates. All mechanical properties were also correlated strongly with a linear combination of UV and BUA for both the low and high loading rates. The use of ultrasound parameters may provide good clinical means for assessing the resistance of trabecular bone to both low and high energy trauma.

Aged↗

PubMed1997

Shear properties of human brain tissue.

The objective of this study was to determine a relationship between shear stress and strain for human brain tissue by performing transient, single-pulse, high-rate, shear displacement tests. A constant velocity, parallel plate shear test device was designed and fabricated. This equipment generated constant rate shear strains in cylindrical tissue samples mounted between the shear plates. The transverse reaction force at the upper end of the sample was measured during the event with a sensitive quartz piezoelectric force transducer, thus obtaining the force associated with the displacement versus time ramp. Shear tests were performed on 125 tissue samples taken from twelve fresh cadaver brain specimens. The average true shear stress and finite strain were calculated. A nonlinear, viscoelastic, standard solid model was fit to the constant rate test data and the material constants were determined.

Aged↗

PubMed1996

Biomechanical comparison of the dewar and interspinous cervical spine fixation techniques.

STUDY DESIGN: This study evaluates and compares the stiffness of two cervical spine fixation techniques. OBJECTIVES: This biomechanical study was carried out to compare the interspinous and Dewar cervical spine fixation techniques. SUMMARY OF BACKGROUND DATA: Interspinous wiring is a commonly used method of fixation in the cervical spine. The Dewar technique is less commonly known and practiced, and clinical experience has suggested that it may be a more stable technique. METHODS: Cervical spine specimens stabilized with the interspinous and "Dewar" techniques were biomechanically tested in flexion and in torsion. Stiffness and energy absorption under moderate loads were compared. The Dewar technique uses contoured double corticocancellous iliac grafts as internal grafts/splints fixed to the spine with threaded pins and wire. The interspinous technique is a single interspinous wire loop. Eleven fresh human cervical spines were harvested from cadavers. The spines were destabilized at C4-C5 by sectioning all tissue except the anterior longitudinal ligament. Each fixation technique was applied alternatively and tested on each spine. RESULTS: In torsion testing (n = 5), the Dewar fusion was 61% stiffer than the interspinous technique (P < 0.02). Dewar: 11.3 N/mm (s.d. 4.9 N/mm) and interspinous: 8.4 N/mm (SD 3.3 N/mm). In flexion testing (n = 6), the Dewar technique was 35% stiffer than the interspinous technique (P < 0.10). Dewar: 655.4 Nmm/degree (SD 293 Nmm/degree) and interspinous: 406.8 Nmm/degree (SD 113.0 Nmm/degree). Energy absorption with the interspinous technique was greater in flexion (P < 0.10) and in torsion (P < 0.005), indicating more deformation with the interspinous technique. There was no statistically significant difference between the means of specimens tested first and those tested second independently of the fixation technique. CONCLUSIONS: These tests indicate that the Dewar cervical spine fixation is stiffer than the single interspinous wire in both flexion and particularly torsion. This project is the only biomechanical study of the Dewar technique that we are aware of, and the results support the clinical findings regarding the effectiveness of this technique.

Biomechanical Phenomena↗

PubMed1996

Ultrasound velocity and broadband attenuation over a wide range of bone mineral density.

Ultrasound velocity (UV) and broadband ultrasound attenuation (BUA) were studied in human and bovine bone with a wide range of bone mineral density (BMD). The BMD of 98 fresh specimens was measured by quantitative computed tomography: 42 cancellous specimens from women in the age group of 64 +/- 4 years; 51 bovine cancellous and 5 bovine cortical. BMD values ranged from 90 to 400 mg/cm3 for the human cancellous bone, 310 to 870 mg/cm3 for the bovine cancellous bone, and 1750 to 1780 mg/cm3 for the bovine cortical bone. BMD showed a strong linear correlation with apparent density over the entire range of density (r = 0.979). UV of human and bovine cancellous bone was 1480-2650 m/s and 2880-3100 m/s for bovine cortical bone. BUA values were 1-61 dB/MHz/cm for the cancellous specimens and 5-12 dB/MHz/cm for cortical specimens. UV was found to be linear with BMD for all specimens; however, BUA was linear with BMD only for the specimens from elderly women. A quadratic relationship between BUA and BMD was found when the bovine samples were included.

Animals↗

PubMed1996

The effect of ultrasonically determined anisotropy on longitudinal fracture of cortical bone.

This study examines the effects of density and microstructural anisotropy on longitudinal crack propagation in compact bone. Bovine cortical bone samples were demineralized by acid, producing specimens with a wide range of bone density. Ultrasound velocity was measured in the radial and longitudinal directions of each specimen using a pulse transmission technique. A proposed microstructural anisotropy parameter based on these ultrasound velocities was introduced and evaluated. The critical stress intensity factors K(IC) of these specimens were determined by mechanical fracture toughness tests. A linear regression study demonstrated that assessment of fracture toughness was precisely achieved by the combined effect of density and microstructural anisotropy of compact bone (r2 = 0.951, p < 0.0001).

Animals↗

PubMed1995

Effect of restorative materials on cuspal flexure.

The purposes of this study were (1) to establish a methodology for determining surface strains in two locations of the same tooth under intact, prepared, and restored conditions and (2) to compare the effects on stiffness of different restorative materials in a tooth subjected to cuspal loading. Two linear strain gauges were mounted on each of 30 extracted maxillary premolar teeth. Teeth were mounted in poly(methyl methacrylate) resin and randomly assigned to one of three study groups according to the restorative material and application technique to be used. Statistical analysis indicated a statistically significant interaction between restorative material and tooth condition at both proximal and buccal sites and a statistically significant difference in stiffness between teeth restored with Tenure/Marathon V and those restored with either amalgam or Scotchbond 2/P-50 at the proximal site. Results suggest that the methods employed provide a useful, nondestructive means of testing the same tooth under various conditions.

Analysis of Variance↗

PubMed1993

Assessment of oral implant mobility.

Most of the implant literature suggests that successful dental implants are immobile and any detected mobility indicates implant failure. This study evaluated the ability of the Periotest instrument to measure implant mobility in a controlled in vitro model with a sample of 56 in vivo implants. In the in vitro portion of the study, implant model mobility was determined by an axial testing machine (0 to 5 N at 0.2 mm/minute) and the Periotest instrument. The comparison showed a high level of correlation (Pearson's r 0.984). The load that the Periotest placed on the implants during mobility measurements was approximately 5 N, depending on the compliance of the test object. The in vivo portion evaluated the range of mobility of 56 clinically successful endosseous implants. The range of mobility as determined by the Periotest instrument was -6 to +2. This range corresponds to an in vitro model displacement (5 N load) of 0.038 mm to 0.113 mm with a mean of 0.066 mm +/- 0.018 mm (SD). These data demonstrate that clinically successful implants are not immobile, but have a range of mobility.

Analysis of Variance↗

PubMed1992

Ideal scaphoid angle for intercarpal arthrodesis.

This experimental study was conducted to determine the best scaphoid position, measured as the radioscaphoid (RS) angle for optimum wrist motion after scapho-trapezio-trapezoid (STT) and scaphocapitate (SC) fusion and to assess the implications of radial styloidectomy on motion after STT fusion. STT and SC fusions were simulated in six fresh cadaver hands with the scaphoid in horizontal, neutral, and vertical positions with respect to the long axis of the radius seen on lateral x-rays. RS angle and wrist motion were measured on x-ray films before and after each simulated arthrodesis. Radial deviation and wrist extension increased as the RS angle increased (i.e., increased as the scaphoid became more nearly vertical). Ulnar deviation and flexion decreased as the scaphoid became more nearly horizontal. We found no statistically significant differences in RS angle between SST and SC fusions with respect to ulnar deviation, flexion, or extension. However, radial deviation was more sensitive to RS angle after STT fusion than after SC fusion, but the differences were not statistically significant. The ideal radioscaphoid angle (range) for maximal wrist motion when STT fusion is performed is 41 to 60 degrees; when SC fusion is performed, it is 30 to 57 degrees. Motion is not improved by radial styloidectomy after simulated STT fusion.

Arthrodesis↗

PubMed1987

Electromyographic changes of leg muscles with heel lift: therapeutic implications.

The effects of heel lifts on activity in gastrocnemius and tibialis anterior muscles were analyzed by signal averaged EMG. The goal was to formulate a more rational approach to prescribing heel lifts for conditions such as tendoachilles bursitis and postoperative management of heel cord rupture. Thirteen men walked on a level floor and a treadmill with heel heights of zero, 1.9, 3.8, and 5.7 cm. Results showed that as heel height increased there was a significant decrease (p = 0.03) in gastrocnemius EMG activity and an increase (p = 0.04) in tibialis anterior EMG activity during level floor walking. Treadmill walking produced less remarkable decreases in gastrocnemius activity and increases in tibialis anterior activity, indicating differences between treadmill and level walking. We conclude that heel lifts of 1.9 to 5.7 cm for men decrease gastrocnemius muscle activity, thereby reducing tension in the Achilles tendon during normal level walking. Therefore, therapeutic use of heel lift is justified for men with tendoachilles bursitis, tenosynovitis of Achilles tendons, and postoperative management of ruptured Achilles tendons.

Achilles Tendon↗

PubMed1986

Reactive synovitis after silicone arthroplasty.

A number of patients with silicone rubber implants performed by us and other surgeons initially had excellent results; however, they returned with swelling and discomfort. We studied 18 patients ranging in age from 16 years to 57 years who presented 8 to 78 months (average, 31.7 months) after silicone arthroplasty (four scaphoid, six lunate, one scapholunate, four finger, two wrist, one trapezium, and one ulnar head for metacarpal hemiarthroplasty). Erosive osteolysis was seen on x-ray films, with progressive destruction evident in patients followed serially. None of the patients' conditions responded to conservative care. The severity of the proliferative, inflammatory synovitis and the foreign material in the multinucleated giant cells correlated with the interval since arthroplasty. Implant surface analysis by scanning electron microscope and x-ray spectrometer showed that silicone microparticles were the result of implant degeneration and erosion. All joint cultures were negative. Silicone particulate synovitis and destruction were arrested by the removal of the implant, a synovectomy, and curettage of the lytic lesions at salvage (resection arthroplasty or arthrodesis). Patients who have had silicone arthroplasties should be followed indefinitely, at regular intervals, by x-ray films and clinical examination.

Adolescent↗

PubMed1986

Silicone rubber replacement of the severely fractured radial head.

Ten patients, at an average of 3.4 years after Swanson silicone rubber radial head replacement following acute trauma, were evaluated for pain, motion, and grip strength. Three had excellent results, one had a fair result, and two had poor results. Three patients had arthritis at the distal radioulnar joint. The arthritis was correlated with a positive ulnar variance in the uninjured wrist. Degenerative arthritis at the elbow was present in 56% (five out of nine). Ulnar variance was increased significantly in the wrists on the injured side, compared with the opposite wrist and to a control group. A 20-kg grip stress radiograph analysis showed the silicone rubber prostheses to deform and wrist subluxation to occur. A biomechanical study of six human cadaver upper extremities indicated that the flexible implants transferred minimal forces across the radiocapitellar joint. A radial head replacement with a modulus of elasticity similar to bone showed a more physiologic loading at the elbow. Both the clinical and biomechanical studies indicated that the silicone rubber prostheses is unable to transmit physiologic forces from the proximal radius to the capitellum. A less flexible radial head prosthesis should provide more normal physiologic stresses and may lead to improved clinical results.

Biomechanical Phenomena↗

PubMed1982

Remodeling of large, persistent bone defects.

Large, standard, persistent, metaphyseal defects were surgically produced in adult dogs' distal femora to simulate clinical defects. Dogs were killed at intervals after surgery ranging from zero to 48 weeks. Biomechanical testing revealed that initially, the torsional strength was reduced to 44% of normal. A gradual return of torsional strength to 90% of normal occurred by 48 weeks. Roentgenographic and histologic studies of the animals and specimens correlated remodeled bone formation with increasing strength. In a small group of animals, suspected microfractures occurred early, induced bone regeneration, and resulted in accelerated recovery of strength.

Animals↗