Search PubMed⌕ Search

Biomedical subjects

A F Tencer

Publications and source records attributed to A F Tencer.

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

Effect of controlled local release of sodium fluoride on bone formation: filling a defect in the proximal femoral cortex.

To assess the effect of sodium fluoride (NaF) in the healing of a defect in cortical bone, an experimental model was created by the drilling of 5.0 mm holes in the proximal ends of both femora of 12 adult male New Zealand White rabbits. An interlocking intramedullary implant constructed of poly(d,l-lactic acid) containing NaF was placed in the right femur and an identical implant without NaF (sham), in the left. The implant in the right femur was designed to release NaF in a controlled manner over the duration of the experiment. Ten weeks after implantation, the specimens were removed and were tested in torsion. The mechanical properties were not significantly different between the groups. The femora exposed to NaF had an 18.6% increase in intact cortex near the defect (p = 0.023), however, the deposition of mineralized bone within the defect was not significantly greater. In fact, healing appeared to be impaired by the presence of NaF. There was complete closure of the defect in all but one of the femora with a sham implant, but the tissue had not yet calcified. In contrast, only one femoral defect exposed to NaF had closed. Examination of the material filling the defects of the femora exposed to NaF showed that it was predominantly uncalcified osteogenic mesenchymal tissue.

Animals↗
PubMed1993

The use of resonant frequency measurements for the noninvasive assessment of mechanical stiffness of the healing tibia.

A study was performed to assess the usefulness of measuring the resonant frequency of vibration of the tibia as a determinant of its flexural rigidity in fracture healing. The measurement system consisted of an electronic tapper that struck the anteromedial distal surface of the tibia and an accelerometer, held against the proximal surface, that received the response. Custom software displayed the frequency spectrum from which the first mode bending frequency of the tibia could be pinpointed. We have found that resonant frequency was highly correlated to the log of tibial flexural rigidity, with an exponent of 0.582 (r2 = 0.815). In human volunteers, a series of four tests at monthly intervals showed a reproducibility of approximately 3% (95% confidence interval) with no significant variability between right and left legs. In 14 patients with healing tibial fractures, resonant frequency ratio (healing/injured leg) was correlated to time ratio (time of test/time healed) by a second-order polynomial fit (r2 = 0.58).

Adolescent↗
PubMed1993

Influences of some design parameters on the biomechanics of the unreamed tibial intramedullary nail.

Several questions relating to the biomechanics of the AO unreamed tibial nail were addressed in this study. These included the effects of the location of the nail bend on the reduction of a high proximal fracture, and the relation of proximal locking screw hole orientation and fracture component cortical contact to the mechanical stiffness of the construct. To measure fracture site malalignment with nail insertion, a motion transducer mounted on the distal tibial shaft was used to track the position of the proximal component during and after insertion of the nail. For studying the effect of screw hole orientation, the intramedullary (IM) nail was modified by drilling a second set of proximal screw holes with oblique instead of parallel alignment. The axial, torsional, and varus-valgus stiffnesses of the constructs with parallel or oblique screws and with or without fracture site contact were determined. In an experimental model with an osteotomy located proximal to the position of the bend in the nail when fully inserted, anterior displacement of the proximal fracture component (or posterior displacement of the distal component) of up to 1 cm was measured. Oblique proximal locking screws significantly decreased both varus/valgus angulation and medial/lateral translation under load, compared with the parallel screws. Constructs were 117% and 55% as rigid as the intact tibia in axial loading with and without cortical contact, and 6.5% and 3.1% as stiff in torsion.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1993

Biomechanics of indirect reduction of bone retropulsed into the spinal canal in vertebral fracture.

The biomechanics of indirect reduction of bone fragments retropulsed into the spinal canal in a burst fracture were investigated. In this model, tunnels were created in vertebrae L1 and C5 oriented anterior-to-posterior, allowing access to the posterior longitudinal ligament. A probe containing a load-sensing tip was passed through the tunnel. Both the location of the tip and the load acting on it by posterior deflection of the posterior longitudinal ligament were measured. In the lumbar spine, distraction was applied by spinal instrumentation that also permitted independent kyphotic-lordotic alignment of the vertebrae. In the cervical spine, axial traction was applied through direct loading. Several clinically relevant observations were made. It was not possible to produce an anteriorly directed force in the posterior longitudinal ligament at less than 35% canal occlusion, partly because the posterior longitudinal ligament stands away from the midbody of the vertebra. Distractive forces of up to 150 N were applied in the lumbar spine, which were nearly equal to the tensile breaking strength of the isolated posterior longitudinal ligament. Regardless of the relative sagittal plane angulation of the vertebrae, distraction was the governing factor in generating force in the posterior longitudinal ligament. Because positioning the vertebrae in lordosis before applying distraction significantly slackens the posterior longitudinal ligament, it is suggested that distraction be applied before angular positioning of the vertebrae is performed.

Biomechanical Phenomena↗
PubMed1993

Caudo-cephalad loading of pedicle screws: mechanisms of loosening and methods of augmentation.

The mechanism of failure and the effect of augmentation of single pedicle screws subjected to caudo-cephalad loads applied at the screw head were investigated. In each of 10 lumbar vertebrae, Steffee pedicle screws of appropriate diameter were placed in one pedicle. The cancellous bone of the contralateral pedicle was removed by curettage, a custom fabricated bushing was pressed by hand into the space, and a Steffee screw was inserted through the bushing and into the vertebral body. This arrangement was designed to transfer load directly from the pedicle screw to cortex, bypassing the cancellous bone of the pedicle. In a second experiment, a custom plate was mounted to the posterior surfaces of the articular facets allowing load transfer from the head of the screw directly to cortex. Caudo-cephalad loads were applied by a materials tester and toggle displacement (defined as the total caudo-cephalad movement of the screw under minimal load after loading through a complete cycle) was measured. Under peak loads of +199 N (caudal) and -224 N (cephalad), mean toggle at the screw head was 4.93 mm (standard deviation [SD] = 3.60 mm) for the screw alone and 4.96 mm (SD = 4.42 mm) for the screw augmented by the bushing. Screws without augmentation showed a characteristic pattern of loosening with the base of the pedicle acting as a fulcrum and a butterfly-shape void occurring in the vertebra and the pedicle where cancellous bone had been crushed. Problems with the bushing included poor fit, back-out, and split pedicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

A method for measuring tension in small ligaments: an application to the ligaments of the wrist carpus.

A new technique has been devised for measuring the in situ tension in small ligaments. It is based on measuring the tension in an axially loaded flexible cable with pinned endpoints by deflecting the cable laterally and measuring its lateral load and deformation. Studies were performed in which nylon line and bone ligament bone preparations were placed in a materials tester and loaded in axial tension. Axial load as measured by lateral load and deformation was found to agree with the known load to within 8 percent. The method was sensitive to error in determination of ligament length, nonperpendicularity of the laterally applied load to the long axis of the ligament, and when used in situ, impingement of the ligament on a third bone causing bending. A device, consisting of an LVDT mounted to a rigid frame with its core rod connected to a load cell, was developed. The position of the core rod was controlled by a manual screw drive, and a hook on the other end of the core rod was used to deflect the ligament laterally. This device was applied to the study of tensions in five ligaments of the palmar wrist carpus, in seven cadaver specimens. Results showed that the radioscaphocapitate (RSC) and radiolunate (RL) ligaments had significantly greater tensions than the lunotriquetral (LT), the triquetrocapitate (TC), and scaphocapitate (SC) ligaments. For the four positions of the hand tested, neutral, 14 deg radial and 14 deg ulnar deviation, and 28 deg of extension, ligament tensions were found to be unaffected by position.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

The effects of freeze-drying and rehydration on cancellous bone.

Processing technique significantly affects the strength and stiffness of bone for use as a structural alloimplant in reconstructive surgery. The effects of the rehydration of freeze-dried human cancellous bone were studied using 14-mm-diameter cancellous dowels taken from matched cadaveric sites. Three different methods of rehydration were evaluated and compared with unrehydrated freeze-dried and frozen grafts. All samples were biomechanically tested in anatomically matched pair groups to determine compressive strength and stiffness. The strength of each tested graft was expressed as a percentage of its matched pair control. Freeze-dried grafts rehydrated for 24 hours compared with frozen grafts showed no significant difference in mean compressive strength (92.6% +/- 13.3% of control). Analysis of in vacuo versus ex vacuo rehydration at one hour showed a 38% greater mean compressive strength and a 42% greater mean stiffness for the ex vacuo group. Unrehydrated grafts appeared to be both stronger and stiffer than their rehydrated counterparts. These results suggest that the rehydration of freeze-dried grafts may adversely affect graft strength and stiffness. Rehydration under a negative pressure may proceed more rapidly than the process at atmospheric pressures. These findings limit the acceptability of freeze-dried grafts as structural implants.

Adolescent↗
PubMed1992

Contact characteristics of the subtalar joint: load distribution between the anterior and posterior facets.

The pressure distribution properties of the normal talocalcaneal joint were studied in 13 fresh cadaver specimens using pressure-sensitive film. The film was inserted into the joint through a posterior approach for the posterior facet and an anteromedial approach for the anterior/middle facet. Specimens, comprising the distal half of the tibia and fibula and the intact ankle and foot, were positioned in neutral in the sagittal plane. In the coronal plane, specimens were positioned in neutral, inversion, or eversion, and the contact characteristics were determined in varying positions, with and without loading the fibula, under axial loads of 350 N, 700 N, 1,050 N, and 1,400 N. The transducers were video imaged for quantitative analysis of area and pressure. The contact/joint area ratio increased significantly with applied load in the posterior facet [e.g., in eversion from 0.336 (SD = 0.195) at 350 N to 0.631 (SD = 0.225) at 700 N], as did the proportion of the contact area greater than 6 MPa, indicating an increase in contact pressure. The contact/joint area ratio was significantly lower in inversion than in any other position of the foot; however, high-pressure zones were similar, indicating that higher pressures occur in inversion. In the anterior/middle facets both contact/joint area ratio and high pressure/contact area ratios increased significantly to 700 N, but not with further load increase. At 350 N the anterior/middle facet contact area was 31% that of the posterior facet, yet it carried 63.3% of the load of the posterior facet, so its mean contact pressure was 1.44 MPa compared with 0.93 MPa for the posterior facet.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Contact characteristics of the subtalar joint: the effect of talar neck misalignment.

In this study we determined the effects of misalignment of the talar neck on the contact characteristics of the subtalar joint. Each of seven fresh cadaver lower extremities was mounted in a loading jig and a vertical load was applied, 90% of which was directed through the tibia and 10% through the fibula. The foot was allowed to displace freely in the horizontal plane so that relative rotations, known to occur in the subtalar joint, would not be prevented. Pressure-sensitive film, inserted into the posterior and anterior/middle articulations, was used to quantify changes in contact characteristics. After testing in the normal condition, the talar neck was osteotomized and stabilized with internal and external skeletal fixation. Contact characteristics were then determined in each of the following stages: anatomic realignment, or with 2-mm displacement of the talar neck either dorsally, medially, laterally, or complex (dorsal and varus) with respect to the body of the talus. Measurements showed no significant changes in overall contact area or high pressure area in the posterior facet, although four of the seven specimens demonstrated increased localization of the contact area into two discrete regions. The combined anterior/middle facet, on the other hand, was significantly unloaded by all but medial displacement of the talar neck. An extraarticular load path and/or increased loading directly on the talonavicular joint was presumed to account for the loss of load transfer in the talocalcaneal joint.

Analysis of Variance↗
PubMed1992

Effect of controlled local release of sodium fluoride on trabecular bone.

Systemic sodium fluoride has been used in the treatment of osteoporosis. Recent studies have shown that it has a positive risk/benefit ratio for use in increasing spinal trabecular bone density. However, thinning of the cortices of the long bones with a resulting increase in fracture incidence has been observed. This study was designed to determine the response of bone to sodium fluoride released from a biodegradable polymer matrix, a technique which could potentially deliver it locally to a site of need in the skeleton which has a positive response to fluoride. In one group of mature New Zealand white rabbits, cylindrical poly(D,L-lactic acid) (PLA) implants, with or without impregnated sodium fluoride, were implanted into the contralateral femoral trochanters and tibial metaphyses. In a second group, similar implants were placed in adjacent vertebrae. Four weeks postimplantation, the femora, tibiae, and vertebrae were removed, sectioned, cleaned of all but mineralized tissue, and the surfaces of the sections stained. The stained surfaces were imaged and analyzed for morphometric properties of the trabeculae. Comparing contralateral vertebrae, those exposed to sodium fluoride had significantly thickened trabeculae, with decreased spacing between them and a greater bone fraction. A similar increase in trabecular width was found in the subchondral bone of the proximal tibiae exposed to local release fluoride. Femoral sections showed no difference, possibly due to the lack of extensive trabecular bone in the region chosen for study.

Animals↗
PubMed1992

Nerve tension and blood flow in a rat model of immediate and delayed repairs.

In vivo studies of rat sciatic nerves in models of immediate and delayed repairs demonstrated the viscoelastic properties of the nerve and the inverse correlation between nerve blood flow and tension. In both the proximal and distal segments of the divided nerve in models of immediate and delayed repairs, the nerve blood flow decreased approximately 50% with substantial recovery in 30 minutes after 8% elongation, whereas 15% elongation produced approximately an 80% reduction in blood flow with minimal recovery. However, the baseline blood flow of the nerves in the delayed-repair model was nearly two times higher than that of the acutely injured nerves. Maximal decrease in nerve tension and corresponding increase in blood flow occurred within the first 20 minutes after elongation. The suture pull-out with failure of the repairs occurred at more than 15% elongation for all nerves. The previously divided nerves had a sixfold greater decrease in length than the acutely divided nerves (p less than 0.02). For repairs of large nerves where vascular ingrowth is likely to be incomplete, elongation of more than 8% may cause ischemia that is detrimental to nerve regeneration. Mechanical failure of the repairs occurs after elongation of 16% to 17%. The combination of nerve ischemia and mechanical failure of suture repairs suggests that surgeons should be careful to limit the use of elongation in acute and delayed repairs.

Animals↗
PubMed1992

A comparison of scaphoid-trapezium-trapezoid fusion and four-bone tendon weave for scapholunate dissociation.

The contact characteristics of the radiocarpal joint (area, pressure, and ratios of scapholunate area, pressure and force transmitted) were determined with the use of pressure-sensitive film in seven normal wrists after ligament sectioning to create scapholunate instability, with reconstruction involving a scaphoid-trapezium-trapezoid fusion, and with reconstruction involving a four-bone tendon weave procedure. The results demonstrated that the scaphoid-trapezium-trapezoid fusion significantly altered the contact characteristics of the wrist, transferring load, pressure, and area to the radioscaphoid joint, thereby unloading the lunate. In contrast, the tendon weave reconstruction produced characteristics similar to those of the normal joint.

Arthrodesis↗
PubMed1992

Force applied during tracheal intubation.

This study quantitated the force applied during tracheal intubation to determine (a) whether the force differed among novice and experienced intubators, and (b) whether the force required differed when intubating patients' tracheas versus intubating the trachea of a commonly used training mannequin. We studied 27 tracheal intubations performed by 17 experienced (greater than 100 prior intubations) and 10 novice (less than 10 prior intubations) intubators. Each intubation was performed with a No. 3 Macintosh blade instrumented with strain gauges to determine force applied in the sagittal plane. The mean force applied was 24.6 +/- 2.9 N (mean +/- SEM) and the maximum force applied by each intubator was 47.6 +/- 3.8 N. There was no difference between groups in the mean force applied (28.8 +/- 6.1 N for the novice group vs 22.3 +/- 2.7 N for the experienced group, P = 0.27) nor in the maximum force applied (55.1 +/- 6.5 N for the novice group vs 43.2 +/- 4.7 N for the experienced group, P = 0.08). The only difference was in the impulse (force x duration), which was more for the novice group largely because of the longer average duration of intubation (40 +/- 12 s vs 19 +/- 4 s, P = 0.06). Among experienced intubators, we found that applied force correlated with patient weight and Mallampati class. Intubation of the Laerdal Airway Management Trainer required mean forces comparable to those required in patients (26.6 +/- 2.5 N vs 22.3 +/- 2.9 N), although the maximum force applied during the intubation effort was greater (58.3 +/- 4.7 N vs 43.2 +/- 4.7 N, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesiology↗
PubMed1991

Response of cortical bone to local controlled release of sodium fluoride: the effect of implant insertion site.

In a previous experiment, sodium fluoride in a biodegradable polymer matrix was introduced into the femoral canal of the rabbit and bone formation was compared with contralateral controls. We noted significant bone formation, but only in the distal third of the periosteal surface of the femur. This experiment was performed to distinguish fluoride-induced periosteal bone formation from that due to the reactive osteogenic changes associated with local injury caused by the process of implantation. A proximal approach on the right leg and a distal approach on the left were used for the insertion of the implants in rabbits. Femurs were removed after 30 days and tested for stiffness and load to failure. The cross-sectional area of mineralized bone was determined at proximal, midshaft, and distal locations. Fluorescent bone tissue growth labels were injected at weekly intervals to measure the rate of new periosteal bone formation. The results were compared with a control group that received sham implants. Results showed no difference between measured properties in right and left femurs in the control group or in those exposed to fluoride. A significant increase was found in the fluoride group in load to failure, along with cross-sectional area of mineralized bone, and periosteal growth rates compared with the control group, but no difference was seen in stiffness. No difference was detected between the response proximally and distally in the fluoride group regardless of the location of insertion. There were no detectable changes in serum fluoride level after implantation of the poly L-lactic acid/sodium fluoride matrix. These results show that fluoride exerts its osteogenic effects equally at proximal, midshaft, and distal regions of diaphyseal bone and is uninfluenced by the site of local injury due to insertion of the implant.

Animals↗
PubMed1991

Biomechanical comparison of methods of fixation of a midshaft osteotomy of the humerus.

Using paired humeri with a midshaft osteotomy, the biomechanical stiffness of four intramedullary internal fixation devices were compared with each other, a dynamic compression plate, and with the intact bone. In posterior and lateral bending and in torsion, flexible intramedullary pin fixed humeri (Enders and Hackethal) performed similarly and were less stiff than intact specimens were. Interlocking intermedullary nail constructs (Russell-Taylor and Seidel) also tested similarly to each other, and were stiffer than the flexible pins in all bending tests. Compared with the intact humerus, interlocking nails were stiffer in torsion, but in bending they more closely simulated the stiffness of the bone.

Biomechanical Phenomena↗
PubMed1991

Design and evaluation of a posterior laminar clamp spinal fixation system.

A new spinal instrumentation system for posterior applications was designed with the intent of minimizing intrusion of hardware into the neural canal during and postinsertion. Basic biomechanical measurements of posterior pullout strength led to the establishment of a clamp as an effective mechanism for gaining purchase on the vertebral lamina. These experiments defined the appropriate instrumentation size, as well as establishing that there was no loss of strength with the spinous process removed and the posterior laminar cortex compromised. There was no statistically significant difference between the maximum pullout strength achievable, using a band around the lamina as a control, and that produced by the implant system, in the thoracic spine. Comparative testing of a prototype system in flexion, extension, lateral bending, and torsion showed that the system, in general, had stiffness greater than segmental wiring and less than or equal to Cotrel-Dubousset fixation.

Biomechanical Phenomena↗
PubMed1989

The effect of local controlled release of sodium fluoride on the stimulation of bone growth.

This study was performed to test the feasibility of using a biodegradable delivery system for the local controlled release of sodium fluoride as a mechanism for the stimulation of local bone growth. Sodium fluoride grains were mixed with poly-DL-lactic acid (PLA), and the mixture was then dissolved in acetone. After driving off the solvent, sheets of this material were rolled into rods 3.2 mm in diameter and 28.6 mm long. These were inserted into the intramedullary canals of the right femora of adult New Zealand White rabbits. A sham implant, made the same way but containing no fluoride, was inserted into the contralateral left leg. The effects of three different concentrations of sodium fluoride, 0.125 g NaF/g PLA, 0.250 g NaF/g PLA, and 0.500 g NaF/g PLA, were determined after a 4-week implantation period. In a second set of experiments, the concentration was fixed at 0.500 g NaF/g PLA with implantation durations of 4, 8, and 16 weeks. Expressed in terms of property ratios (experimental/control), bending strengths of the femora were significantly raised in most groups with the notable exception of Group 3 (0.500 g NaF/g PLA, 4 weeks). Cross-sectional area ratios in the distal femora were increased in all groups compared to right/left values for a normal unoperated group (p less than 0.05), with the highest ratio being 1.50 (SD = 0.44) for Group 4 (0.500 g NaF/g PLA, 8 weeks). Only Group 4 animals showed significant (p less than 0.05) increases in midshaft area ratio and none had responses proximally. Growth rates, measured by sequential fluorochrome labeling of bone followed the area ratio data and were only significant for the distal femora.

Animals↗