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Biomedical subjects

A Sarmiento

Publications and source records attributed to A Sarmiento.

At least 73 records · Page 4Linked to original sources
PubMed1993

Control of motion of tibial fractures with use of a functional brace or an external fixator. A study of cadavera with use of a magnetic motion sensor.

A computer-linked magnetic motion transducer was used to monitor and record the six components of motion of the bone fragments in eight cadaveric tibiae in which a simulated, oblique fracture of the middle of the shaft had been stabilized with a functional brace. The limbs were mounted in a servo-hydraulic testing frame, and a cyclic load of 150 newtons was applied along the axis of the tibia. Motion sensors, attached to each side of the fracture, measured and displayed the values of the three translations (axial, anterior-posterior, and medial-lateral), the axial rotation, and the two angulations (anterior-posterior and varus-valgus) as they occurred. Although only an axial load was applied, the off-axis motions were comparable in magnitude with the motion along the axis. The elastic (recoverable) translations of the fragments ranged from 0.5 to 1.9 millimeters, about four to ten times larger than the corresponding motions that were recorded in an earlier study of such fractures that had been stabilized with two types of external fixators. The recoverable rotation and angulations of the fragments of the limbs in the functional brace ranged from 0.7 to 1.2 degrees, about ten times those recorded when the external fixators were used.

Braces↗
PubMed1993

Healing and remodeling of articular incongruities in a rabbit fracture model.

Healing of 0.5 or 1.0-millimeter step-off defects associated with displaced intra-articular fractures of the medial femoral condyle was examined in fifty-four adult New Zealand White rabbits. The rabbits were treated with either immobilization for three weeks, intermittent active motion, or continuous passive motion for seven days. At twelve weeks, the healing and remodeling of the step-off defects were examined with use of contact-pressure maps on pressure-sensitive film, light microscopy (with hematoxylin and eosin or safranin-O staining), and scanning electron microscopy. Macroscopically, the sharp profile that had been present initially with both sizes of step-off defect had rounded off; however, there was less residual incongruity with the 0.5-millimeter step-offs than with the 1.0-millimeter step-offs. Among step-off defects of the same size, the method of treatment had no discernible effect on the macroscopic appearance of the surface of the joint. With fresh step-offs (the control group), the contact pressure of the cartilage on the elevated side was approximately three times greater than that at a distance from the step-off. On the depressed side, an unloaded zone extended approximately three times the height of the step-off, with an average width of 3.4 millimeters for the 1.0-millimeter step-offs and 1.6 millimeters for the 0.5-millimeter step-offs. After healing and remodeling, the unloaded zone still averaged 2.5 millimeters in width for the 1.0-millimeter step-offs but had decreased to only 0.35 millimeter in width for the 0.5-millimeter step-offs. For seven of the nine 0.5-millimeter step-offs, the contact pressure in the previously unloaded zone ranged from 0.5 to 1.5 megapascals, with a mean of 0.8 megapascal (40 per cent of the normal mean contact pressure at this location). Under light microscopy, the cartilage on the elevated side of the healed step-offs had decreased in thickness, was displaced toward the defect and tapered toward the depressed side, and ended in a hypocellular tissue flap. In contrast, the cartilage on the depressed side had thickened as a result of hyperplasia of the chondrocytes and hypertrophy of the cartilage and had failed to establish continuity between the sides of the defect. There was a marked increase in the subchondral vascular bed and re-establishment of the subchondral plate. With the exception of the aforementioned hypocellular tissue flap, safranin O stained the cartilage on both levels of the step-off uniformly, which indicated the absence of glycosaminoglycan depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The interosseous membrane of the forearm: structure and its role in Galeazzi fractures.

A cadaveric study was performed to anatomically describe and mechanically document the interosseous membrane of the forearm using gross, histologic, scanning electron microscopic, and mechanical testing. The membrane was found to be a complex structure composed of nerves and vessels but mainly of collagen fibers that thicken to form bands coursing from radius to ulna. Strain-gauge studies demonstrated that the load transfer occurs from the radius to the ulna via the membrane and changes with supination or pronation. With specimens under a specific test load, sectioning of the membrane allowed the fractured radius to shorten by 6.25 mm and sectioning of the triangular fibrocartilage complex resulted in shortening of 7.7 mm. Total shortening after osteotomy and sectioning of the complex structure and membrane ranged from 15 to 40 mm. In Galeazzi fractures, the interosseous membrane acts as a constraint to radial shortening. Anatomic reduction with internal fixation is indicated for this fracture-dislocation.

Aged↗
PubMed1992

Angular deformities and forearm function.

Angular deformities were created in cadaver forearms at proximal, middle, and distal third levels of the radius and ulna separately, and at middle and distal third levels of both bones, to determine the corresponding limitations of pronation and supination. The ranges of pronation and supination were recorded using a rotational motion measurement apparatus instrumented with a 360 degrees goniometer. These experimental results were compared to data obtained from clinical and radiographic examination of 105 patients with similar residual deformities following treatment of fractures by nonsurgical means, to evaluate the accuracy of the experimental model and to determine if loss of rotational motion could be predicted based on radiographic findings. With cadaver forearms, on the average, angulation of 10 degrees of the radius or ulna in coronal or sagittal planes limited pronation and supination by less than 24 degrees, whereas angulation of 10 degrees of both the radius and the ulna limited pronation and supination by less than 18%. Comparison of experimental results with clinical findings showed that, despite the errors involved in measuring forearm deformities in patients using biplanar radiographs, the experimental results predicted the clinical loss of pronation and supination to within 17% for the fractures of the radius, and within 8% accuracy for the fractures of the ulna.

Cadaver↗
PubMed1992

Interface corrosion of a modular head total hip prosthesis.

Wear and corrosion products released from metallic prosthetic joints can stimulate adverse reactions in the surrounding tissues that may eventually require revision of the prostheses. The authors report here a case of a modular total hip prosthesis removed after 35 months that showed evidence of corrosion and fretting at the Morse taper interface between the titanium alloy femoral stem and the cobalt-chromium ball.

Aged↗
PubMed1992

Graft perforations favor osteoinduction. Studies of rabbit cortical grafts sterilized with ethylene oxide.

The healing of freeze-dried, ethylene oxide sterilized, segmental, allogenic cortical bone grafts was investigated in 15 rabbits using a 2-cm ulnar diaphyseal defect. Five different groups of bone grafts were evaluated: 1) unperforated undemineralized, 2) perforated undemineralized, 3) unperforated demineralized, 4) perforated demineralized, and 5) perforated demineralized grafts enclosed by silicone rubber (Silastic) sheets. There were 3 animals in each group. At 18 days, the study was terminated, and the implants were examined using radiographs and qualitative histologic preparations. We observed that healing of perforated demineralized bone was superior to unperforated demineralized bone, that undemineralized bone was partially sequestered in reactive lacunae, and that perforations in demineralized bone became centers of osteoinduction. Demineralized bone sterilized with ethylene oxide by this method vigorously formed new bone.

Animals↗
PubMed1991

Comparison of the stability of press-fit hip prosthesis femoral stems using a synthetic model femur.

The motion of three different press-fit hip prosthesis femoral components was compared with that of a cemented stem and an Austin Moore noncemented hemiarthroplasty. Synthetic composite femurs were used as an experimental model to reduce the variations in shape and quality typical among cadaver femurs. Motion was measured under axial and rotational loading approximating a walking load. On the initial application of load, axial subsidence was as much as several millimeters for the noncemented stems. Considerable tightening occurred during the 5,000 walking cycles, such that the motion of the noncemented stems in some directions eventually was as small as that of the cemented stem, on the order of tens of microns.

Biomechanical Phenomena↗
PubMed1991

Total hip replacement after failed hemiarthroplasty or mould arthroplasty. Comparison of results with those of primary replacements.

We compared the radiographic results of secondary total hip replacements, 99 following failed uncemented hemiarthroplasties and 21 following failed mould arthroplasties, with those of 825 primary cemented total hip replacements. The probability of occurrence of a number of radiological changes over time was calculated using survival analysis. The mean follow-up was 7.6 years (range one month to 20 years). The performance of the secondary total hip replacements varied with the preceding implant and was different for acetabular and femoral components. The incidence of radiological loosening was higher for femoral components implanted after failed hemiarthroplasties and for acetabular components after failed mould arthroplasties. However, the incidence of continuous radiolucent lines was lower for the acetabular components of converted hemiarthroplasties than for the primary replacements.

Arthroplasty↗
PubMed1991

The effect of simulated fracture-angulations of the tibia on cartilage pressures in the knee joint.

The effects of angular deformities of the tibia on the contact areas and pressures on cartilage in the knee were measured with use of pressure-sensitive film. Six cadaver knees were mounted in a test-frame, such that the offset and tilt of the knee relative to the load-axis simulated that due to angular deformities of the tibia of 5, 10, 15, or 20 degrees of varus or valgus at the levels of the proximal, middle, and distal thirds. Angulation had little effect on the contact area. The change in pressure was least for fractures of the distal third and greatest for fractures of the proximal third. For example, a 20-degree angulation of the distal third increased the maximum contact pressure by an average of 26 per cent in the compartment toward the load-axis and reduced it by 32 per cent in the opposite compartment. With an angulation of 20 degrees at the level of the proximal third of the tibia, the increase in pressure averaged 106 per cent and the decrease averaged 89 per cent. The changes in pressure with fractures at the middle third were between these extremes.

Biomechanical Phenomena↗
PubMed1991

[Three-dimensional measurement of fracture gap motion. Biomechanical study of experimental tibial fractures with anterior clasp fixator and ring fixator].

A computer-linked magnetic motion tracker was used to monitor the six components of elastic fracture motions in cadaver tibia with simulated mid-shaft oblique fractures or segmental defects. The limbs were mounted in a servo-hydraulic load frame and stabilized with an Ilizarov frame or an AO-Unifix external fixator. A cyclic load of 150 or 300 N was applied along the long axis of the tibia. Under 150 N load, elastic displacements ranged up to 1.7 mm and elastic rotations ranged up to 0.6 degrees. Under 300 N load, elastic displacements went up to 3.6 mm and elastic rotations ranged up to 1.5 degrees. Comparison of the two fixators showed that the Ilizarov permitted up to 1.75 times more axial pistoning and up to 4 times more A-P displacement. The AO-Unifix permitted up to 4 times more varus-valgus and up to 7 times more A-P angulation. The technique developed for measuring the three-dimensional motion of fractures may have wide applications in further biomechanical and fracture healing studies.

Biomechanical Phenomena↗
PubMed1991

A comparison of the healing properties of rabbit Achilles tendon injuries at different levels.

Rabbit Achilles tendons were transsected at the muscle-tendon junction (Group 1), midtendon (Group 2), or at the calcaneus insertion (Group 3). Treatment consisted of immobilization in a long leg cast without surgical repair. The contralateral leg served as a control. Tensile testing was performed at four weeks. Groups 1 and 2 failed most often in the proximal muscle rather than at the healing site. In contrast, Group 3 failed more often at the healing site than in the muscle and was statistically superior to Groups 1 and 2 with respect to strength and stiffness. Statistically, control specimens showed failure at the musculotendinous junction at greater loads and were stiff compared to the experimental groups.

Achilles Tendon↗
PubMed1990

Functional bracing for comminuted extra-articular fractures of the distal third of the humerus.

From 1982 to 1987 we treated 85 extra-articular comminuted distal third humeral fractures in adults with prefabricated plastic braces. Of these, 15% were open fractures and 18% had initial peripheral nerve injury. On average, the sleeve was applied 12 days after injury and used for 10 weeks. There was 96% union, with no infections. All nerve injuries resolved or were improving at the latest examination. At union there was varus deformity averaging 9 degrees in 81% of patients, but loss of range of movement was minimal and functional results were good.

Adolescent↗
PubMed1990

Cup containment and orientation in cemented total hip arthroplasties.

We reviewed the radiographs of 864 Charnley and STH (Zimmer) cemented total hip arthroplasties with a mean follow-up of seven years (maximum 16 years). Survivorship analysis was used to assess the correlation between radiographic performance and the bony containment or the coronal orientation of the acetabular cup. The cup orientation and containment were interrelated; all vertically oriented cups were completely contained, whereas 25% of more horizontal cups were only partially contained. Completely contained cups had significantly lower incidences of complete cement-bone radiolucency (p = 0.02) and of wear (p = 0.09). Vertically oriented cups had a lower incidence of continuous radiolucency than neutrally oriented cups, but this was not statistically significant (p = 0.25). Our results confirm the importance of complete bony containment, and also indicate that it is better to accept vertical orientation and obtain full bony coverage than to have a more horizontal orientation with partial containment.

Alloys↗
PubMed1990

Total hip arthroplasty with cement. A long-term radiographic analysis in patients who are older than fifty and younger than fifty years.

The long-term performance of a total of 712 Charnley and STH prostheses was evaluated as a function of the patient's age (older than fifty years or younger than fifty years) and of the underlying disease (osteoarthrosis, rheumatoid arthritis, or avascular necrosis). In patients who were older than fifty years, there were lower incidences of continuous cement-bone radiolucency about the acetabular component (p = 0.04), wear of the polyethylene acetabular cup (p = 0.03), and resorption of the calcar (p = 0.03). However, larger percentages of younger patients had rheumatoid arthritis or avascular necrosis. In the cohort of patients who had osteoarthrosis, the performance of the prosthesis did not differ significantly between older and younger patients; therefore we attributed the differences that were observed to the disease--that is, to rheumatoid arthritis or avascular necrosis.

Age Factors↗
PubMed1990

In vivo wear of titanium-alloy hip prostheses.

We examined samples of tissue and components that had been removed during twenty revisions of total hip arthroplasties in which a titanium-alloy femoral component had been used. Minute amounts of metallic debris were detected in the tissues from two patients. The amounts of polyethylene and methylmethacrylate debris and the histological reactions in the tissues corresponded closely with those reported in earlier studies of total hip prostheses made of stainless steel or cobalt-chromium alloy.

Acrylates↗