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Biomedical subjects

J B Finlay

Publications and source records attributed to J B Finlay.

At least 37 records · Page 2Linked to original sources
PubMed1988

In-vivo comparison of four absorbable sutures: Vicryl, Dexon Plus, Maxon and PDS.

Absorbable sutures are initially equal or superior to nonabsorbable sutures in terms of tensile strength but are absorbed at variable rates by the action of hydrolysis. This study demonstrated that the in-vivo half-life tensile strength of the braided absorbable sutures polyglycolic acid (Dexon Plus) and polyglactin 910 (Vicryl) is 2 weeks, whereas those of the monofilament absorbable sutures polyglyconate (Maxon) and polydioxanone (PDS) are 3 and 6 weeks respectively. The addition of a single hitch or six knots reduced the in-vitro tensile strength by 30% to 35%. Polyglyconate (Maxon) suture demonstrated the best in-vitro knot security.

Animals↗
PubMed1988

External skeletal fixation: choosing a system based on biomechanical stability.

Due to the increased popularity of external fixators for treating long-bone fractures, many devices are being introduced to the market. The choice of a particular fixation device depends on the anticipated loading conditions or the demands the fixator might encounter during the healing process. This study compares the biomechanical stability (rigidity, yield-load, failure-load) and load to produce 1 mm of fracture-gap displacement of various half-frames of five systems tested in axial compression, torsion, and both anterior-posterior and medial-lateral bending; the slippage tolerances of various interfaces of the universal joints or clamps were also analyzed. The frames were mounted on acrylic rods, with a midshaft transverse saw-cut, displaced by 10 mm, and set to standardized dimensions and tightened at set torques. In terms of stability, the Brooker and Hoffman systems are, in general, less stable than the RxFx, AO, and Orthofix fixators. The single half-frames of all systems, except the Orthofix, were particularly weak, and the double and stacked half-frames of each system were more stable.

Biomechanical Phenomena↗
PubMed1987

Kinematic I and Oxford knee arthroplasty. A 5-8-year follow-up study.

Sixty-seven consecutive Oxford Meniscal total knee arthroplasties (TKAs) were compared prospectively with 66 Kinematic I TKAs. At follow-up examination an average of 5.5 (range, 5-8) years later, 20 (30%) of the Oxford Meniscal TKAs had been revised (nine due to aseptic loosenings, seven to aseptic loosening and patellofemoral syndrome, two to patellofemoral syndrome, one to meniscal bearing dislocation, and one to sepsis) and in 16% one or more of the remaining tibial components was radiographically at risk. Three (5%) Kinematic I TKAs had been reoperated upon (one for anterior dislocation, one for a loose patellar component, and one for sepsis) and no component was considered radiographically at risk. The remaining cases demonstrated good and excellent knee ratings (Oxford, 82 +/- 11; Kinematic I, 88 +/- 6; P less than .01; Hospital for Special Surgery). This study suggests that the results of Kinematic I TKA are superior to those of Oxford Meniscal TKA; that patellofemoral resurfacing is advisable; and that Kinematic I TKA yields 5-year data comparable to those of total hip arthroplasty.

Activities of Daily Living↗
PubMed1987

Cancellous bone support for patellar resurfacing.

The purpose of this study was to determine the compressive resistance of the cancellous bone in nine fresh specimens of human patellae. Standardized radiographic assessment and subsequent osteotomies were performed on each specimen. Grid patterns based on patellar anatomy enabled topographic compression on a material test system (MTS) Model 835 Bionix Universal Testing Machine (MTS Corporation, Minneapolis, MN) using a 4-mm diameter indentor. It was demonstrated that sacrifice of the patellar subchondral bone removes with it the strong cancellous bone support and topographic strength patterns of the cancellous bone on the surface of a patellar osteotomy does not have a consistent pattern in relation to the intracondylar eminence. Consequently, placement of fixation pegs is not critical with respect to strength of bony support.

Adult↗
PubMed1987

Stability of ten configurations of the Hoffmann external-fixation frame.

The rigidity, load to yield, and load to failure of ten configurations of the Hoffmann external fixator were investigated using a model of wooden pylons with a simulated fracture that consisted of either a reduced transverse cut or a ten-millimeter gap. The axial compressive, torsional, anterior-posterior bending, and medial-lateral bending characteristics of four forms of the single half-frame (half-pinned), four double half-frame, and two full-frame (transfixion-pinned) configurations were examined. Of the single half-frame configurations, a system with a second stacked connecting-rod proved to be superior; however, the system yielded at a mean axial compressive load of only 199 newtons and failed totally at 355 newtons. The delta frame (two rods connecting or triangulating two half-frames set at an angle of 45 degrees to one another) was as rigid as the quadrilateral full frame in axial compression; however, it exhibited low loads to yield and to failure, with means around 200 and 350 newtons, respectively. The use of only two pins in each pin-cluster did not significantly affect the performance of the delta frame. The two full-frame systems performed poorly in torsion and particularly poorly in anterior-posterior bending. The loads that caused a one-millimeter movement within the fracture gap in axial compression were notably low: for the stacked half-frames the load did not exceed a mean value of 174 newtons; for the double half-frame, 190 newtons; and for the quadrilateral frame, 412 newtons. We concluded that no frame had a good over-all performance with regard to rigidity.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1987

A biomechanical study of wire fixation.

A biomechanical study of wire fixation was performed using 18-gauge stainless steel wire on an Instron universal testing machine. Six groups of wires were tested--an intact piece of wire (control), a wire bent to a right angle five times, a simple knot, a square knot, a loop knot and a twist knot. The tensile load-to-failure value for each wire was recorded. The intact wire broke at a mean load of 67 kg. The wires with the bend, the simple knot and the square knot all broke at similar loads. Those wires with a knot broke at the knot. The loop and the twist knots pulled apart at much lower loads. These results indicate that bending the wire does not weaken it substantially, but kinking may initiate the site of breakage. The square knot is the strongest knot; the loop and twist knots are not recommended if the wire is to be under tension.

Animals↗
PubMed1986

Pelvic stresses in vitro--I. Malsizing of endoprostheses.

Seven embalmed human cadaveric hemi-pelves have been stripped of all soft tissues except the articular cartilage and instrumented with 25 strain-gauge rosettes on both the medial and lateral surfaces. Loads up to 2.5 kN were applied, without simulated muscle forces, to mimic the line-of-action of the resultant joint-force in a single-legged stance. In this parametric study, endoprostheses were studied at the 'correct' size and in sizes of 1 and 2 mm above and below the correct size. The correct size of endoprosthesis produced similar periacetabular stress data to those obtained with the normal femoral head; however, significant changes in stress on the medial and lateral aspects of the ilium suggested the correctly-sized spherical endoprosthesis had a different moment arm than its anatomical counterpart. Endoprostheses of 1 mm greater than the correct size caused major increases in the magnitude of both periacetabular and medial-wall stresses, while prostheses of +2 mm created dramatic and significant increases in magnitudes of these stresses. Endoprostheses smaller than the correct size caused only small but significant changes in the pattern of stresses up to -2 mm malsizing and, in particular, were associated with the disappearance of all periacetabular tensile stresses; however, stress data on the medial and lateral aspects of the ilium were more closely matched to the 'normal' for this -2 mm of undersizing.

Hip Prosthesis↗
PubMed1986

Pelvic stresses in vitro--II. A study of the efficacy of metal-backed acetabular prostheses.

Six embalmed human cadaveric hemi-pelves with their associated proximal femurs have been tested in vitro using 25 strain-gauge rosettes on each hemi-pelvis. Loads were applied up to 2.5 kN and principal stresses were computed from the principal strain data. Acetabular prostheses, cemented in place upon a cartilage-devoid but intact subchondral bone-plate, showed little change in stress-patterns when compared with the normal data, regardless of whether or not the component employed metal-backing. The use of 30 anchoring holes of 6.4 mm diameter, in the intact subchondral bone-plate, had little effect upon the stress-patterns, regardless of whether metal-backing was employed upon the prosthesis. When the subchondral bone-plate was removed, there were notable changes in the stress-pattern in the periacetabular region and on the medial wall of pelvis. The metal-backed prosthesis did not produce such notable changes as its plastic counterpart, when the subchondral bone-plate was removed. The use of a plastic prosthesis cemented in a Protrusio ring, in an acetabulum devoid of subchondral bone, produced notable changes in the stress-patterns in the whole periacetabular region and on the medial wall.

Acetabulum↗
PubMed1986

The influence of tibial component intramedullary stems and implant-cortex contact on the strain distribution of the proximal tibia following total knee arthroplasty. An in vitro study.

High implant-bone stress levels, particularly on rather weak cancellous bone, have been implicated as the predominant cause of aseptic tibial component loosening, the most frequent cause of total knee arthroplasty (TKA) failure. This strain gauge study on six fresh cadaver specimens has revealed that loss of tibial component-cortex contact resulted in a 33%-60% decrease in principal strain values in the proximal tibia. The implication of this finding is that in the absence of implant-cortex contact, the cancellous bone of the proximal tibia must assume the increased load, with the risk of implant loosening and/or sinkage. This study has also demonstrated that the use of tibial components with intramedullary stems was accompanied by marked stress shielding of the proximal tibial cortex over the length of the given stem. This observation refutes the claim that such intramedullary stems are non-weight-bearing and points out the potential risks of cortical atrophy and tibial fracture at the tip of the stem when such implants are used. Although caution must be exercised in extrapolating in vitro laboratory data to clinical practice, this study favors the use of TKA tibial components that rest on the cortical bone and have either no stems or only short intramedullary stems.

Adult↗
PubMed1985

Indentation stiffness of the cancellous bone in the distal human tibia.

Total ankle arthroplasties tend to fail mainly on the tibial side. Fifteen fresh amputation specimens were used for assessment of the stiffness of the cancellous bone in the distal tibia. Because all current ankle replacements sacrifice the subchondral bone plate, the change in stiffness of cancellous bone was studied in transverse sections taken proximal to the subchondral plate of the ankle. The articular cartilage was removed from the tibial plafond, and serial 1-cm sections were taken, radiographed, and tested in compression on an Instron 1125 Universal Testing machine with the use of a 4-mm-diameter indentor. In the distal tibia, it was found that subchondral bone has an elastic modulus on the order of 300-450 MPa; removal of the subchondral bone plate reveals bone with a compressive resistance that is 30%-50% lower than with the bone plate intact; there is virtually no resistance to compression in the trabecular bone at a distance of more than 3 cm proximal to the subchondral bone plate; and stiffness characteristics in the distal tibia parallel the radiographic appearance of the trabeculae. The strongest cancellous bone in the region of the distal tibia is that near the subchondral bone plate. This material should be preserved, if possible, in the surgery for total ankle implants.

Biomechanical Phenomena↗
PubMed1984

In vitro strain distribution in the proximal tibia. Effect of varus-valgus loading in the normal and osteoarthritic knee.

Six human cadaver legs were tested with strain-gauge rosettes to determine the effects of varus/valgus loading on the distribution of strain on the cortical bone of the proximal tibia at loads of up to 250 kg. Changes in the femorotibial angle of 1.5 degrees and 3.1 degrees, to create varus/valgus deformities, produced significant unloading of the opposite aspect of the normal leg. A varus deformity of 3.1 degrees in the medial compartment osteoarthritic model virtually unloaded the lateral compartment and, because of the bending effect, placed the whole of the lateral aspect of the leg into axial tension. Under these conditions, the axial strains in almost the whole of the medial aspect of the tibia were doubled, from an initial value of 250 microstrain (compressive) to a value of approximately 500 microstrain (compressive). While a change in load-action, to simulate a 3.1 degrees valgus deformity in the medial compartment osteoarthritic model, did not completely unload the medial plateau of the tibia, it was suggested that such unloading could be achieved with slightly greater valgus loading. Successful clinical results, employing valgus osteotomies in patients with medial compartment osteoarthritis, are obtained by unloading the medial compartment while markedly increasing compressive loads on the whole of the lateral aspect of the leg.

Adolescent↗
PubMed1984

The effect of medial meniscectomy on strain distribution in the proximal part of the tibia.

The tibiae of five fresh adult human cadaver legs (amputated proximal to the knee) were instrumented with twenty-five strain-gauge rosettes and were tested in axial compression, simulating single-limb stance, at loads of as much as 2450 newtons. We compared the status of the normal knee, with menisci intact, with the status of the same knee after partial or total medial meniscectomy. The resultant changes in strain on the cortical bone of the tibia indicated that medial meniscectomy caused reduced compressive strains on the whole of the lateral aspect of the tibia, while on the medial aspect compressive strains were increased at all levels beyond seventy millimeters distal to the joint-line; however, within fifty millimeters of the joint-line on the medial aspect, there was a significant reduction of compressive strains.

Adolescent↗
PubMed1982

A technique for the in vitro measurement of principal strains in the human tibia.

An experimental technique employing strain-gauge rosettes is described for the in vitro study of principal strains in the tibia as they are affected by various modes of loading on the knee joint. The experimental procedure, based around a Hewlett-Packard 9830A desk-top computer and an HP 3495A 80-channel scanner, is described in detail. The linearity of strain versus load up to 150 kg is shown in the "normally" loaded knee-joint. In these studies, the angle between the principal compressive strain and the vertical axis of the left tibia is reported to vary between 2.2 degrees and -60.2 degrees (Mean -16.5 degrees +/- 16.2 degrees), depending upon the position on the bone. Due to the gross variation of strain at a given point with respect to the angle of measurement, it is essential that strain-gauge rosettes be used to obtain meaningful data in any study of the strain distribution in the tibia.

Adult↗
PubMed1981

A study of Dupuytren's tissue with the scanning electron microscope.

This study was designed to determine if structural changes in the palmar fascia in Dupuytren's disease, as viewed by the scanning electron microscope, might provide some information about the pathogenesis of this disease. The palmar fascia from seven uninvolved hands and from 21 patients with Dupuytren's disease was examined. There were distinct differences between normal and diseased collagen. The diseased tissue showed collagen that was more tightly bound and had a shorter wave pattern. In the Dupuytren's tissue the waves were frequently in a helix, but this was never seen in the normal tissue. The most striking differences were noted in the nodule, presumably because it appears first, followed by the cord proximal to the nodule (pretendinous cord). Similar but less obvious changes were noted in the cord distal to the nodule (central cord) presumably because it is last to form. These observations suggest a mechanism of contraction. The short wave length and helix formation of the collagen indicate shortening. If the concept of the myofibroblast as a contractile cell is accepted, the contraction of these cells in stepwise fashion could produce the changes in the structure of the collagen that have been observed and result in joint contracture.

Collagen↗