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Biomedical subjects

A D Milne

Publications and source records attributed to A D Milne.

8 recordsLinked to original sources
PubMed1997

Advanced cement technique improves fixation in elbow arthroplasty.

An in vitro study was conducted to assess the efficacy of advanced cementing techniques in the fixation of the humeral stem in elbow arthroplasty. Sixteen fresh frozen cadaveric distal humeri were prepared to accept an acrylic sham humeral stem. Conventional cementing technique using doughy cement manually inserted and packed was performed in 8 specimens. The advanced cementing technique, consisting of canal irrigation, brushing and drying with gauze, canal plugging, and low viscosity cement pressurization with a delivery system was performed in the other specimens. All humeri subsequently were sectioned into 10 mm thick sections, photographed, and digitized to quantify the perimeter and area of the stem, cement mantle, corticocancellous junction, and cement voids. The degree of cement filling, determined from the area fraction of cement to the total available area within the corticocancellous junction, was significantly greater in the advanced group compared with the conventional group. Mechanical assessment of the specimens consisted of a push out load to failure test of the cement mantle from bone. For all locations in the distal humerus, the failure load and failure stress in the advanced group was significantly greater than the conventional group. It is concluded that development of an effective cement restrictor and application of advanced cement techniques in vivo should improve the initial fixation of the humeral component and may decrease the incidence of aseptic loosening associated with elbow arthroplasty.

Biomechanical Phenomena↗
PubMed1996

Accuracy of an electromagnetic tracking device: a study of the optimal range and metal interference.

The positional and rotational accuracy of a direct-current magnetic tracking device commonly used in biomechanical investigations was evaluated. The effect of different metals was also studied to determine the possibility of interference induced by experimental test fixtures or orthopaedic implants within the working field. Positional and rotational data were evaluated for accuracy and resolution by comparing the device output to known motions as derived from a calibrated grid board or materials testing machine. The effect of different metals was evaluated by placing cylindrical metal samples at set locations throughout the working field and comparing the device readings before and after introducing each metal sample. Positional testing revealed an optimal operational range with the transmitter and receiver separation between 22.5 and 64.0 cm. Within this range the mean positional error was found to be 1.8 percent of the step size, and resolution was determined to be 0.25 mm. The mean rotational error over a 1-20 degree range was found to be 1.6% of the rotational increment with a rotational resolution of 0.1 degrees. Of the metal alloys tested only mild steel produced significant interference, which was maximum when the sample was placed adjacent to the receiver. At this location the mild steel induced a positional difference of 5.26 cm and an angular difference of 9.75 degrees. The device was found to be insensitive to commonly used orthopaedic alloys. In this study, the electromagnetic tracking device was found to have positional and rotational errors of less than 2 percent, when utilized within its optimal operating range. This accuracy combined with its insensitivity to orthopaedic alloys should make it suitable for a variety of musculoskeletal research investigations.

Alloys↗
PubMed1995

In-vitro strength of flexor-tendon repairs.

OBJECTIVE: To compare the standard Tajima technique for flexor-tendon repair of the hand with three new techniques with respect to strength and technical ease of the repair and bulk at the repair site. DESIGN: A randomized analysis of human cadaver flexor digitorum superficialis tendon repairs. SETTING: A musculoskeletal research laboratory at a university-affiliated health centre. MATERIAL: Thirty-nine fresh-frozen cadaveric flexor digitorum superficialis tendons from index, long and ring fingers harvested and divided transversely. The tendons were randomly allocated for repair by the current standard technique or one of three new techniques. INTERVENTIONS: The standard Tajima (modified Kessler) technique, and the Halsted, Savage or Silfverskiold technique. MAIN OUTCOME MEASURES: The time to perform each repair, the cross-sectional dimension and the load to failure of the tendon repairs. RESULTS: The Savage repair tolerated the highest loads, followed by the Halsted, Silfverskiold and Tajima repairs. The Silfverskiold technique was the least time-consuming to perform, followed by the Tajima, Halsted and Savage repairs. All of the techniques increased the cross-sectional dimensions of the tendon: the Silfverskiold repair by at least 50% and the Savage repair by over 100%. Although none of the techniques tested performed ideally, all three new techniques provided greater initial static strength than the standard Tajima method. CONCLUSION: Further in-vitro and in-vivo studies of these new techniques of flexor-tendon repair of the hand are necessary to optimize the treatment of these injuries.

Biomechanical Phenomena↗
PubMed1994

Compression forces generated by the Huene alignment guide alone.

To enhance the fixation of scaphoid fractures by providing precise alignment and compression at the fracture site, the Huene alignment guide has been used in conjunction with bone screws. In an effort to predict the compressive force generated by the Huene guide alone, these forces were measured with a calibrated, strain-gauge, instrumented device. Three orthopedic surgeons each tested the guide 10 times on one cadaver scaphoid bone specimen. The magnitude of the compressive forces generated ranged from 9.0 to 67.0 N (mean 36.0 +/- 15.0 N). Comparisons of the force measurements among the individuals revealed no significant differences. This wide range of measurements could be attributed to the variability of the ratchet mechanism on the device. Because the Huene alignment guide is used to generate transcaphoid compressive forces, these results demonstrate that it does not yield consistent compression.

Bone Screws↗
PubMed1992

Characterisation of a bis(5'-nucleosidyl) triphosphate pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia.

1. A P1,P3-bis(5'-nucleosidyl)triphosphate pyrophosphohydrolase (Np3 Nase) has been partially purified from Artemia embryos. 2. The Np3 Nase has a native Mr of 115,000 and preferentially hydrolyses substrates of the form Np3 N. Relative rates of hydrolysis are Ap3A (Vrel = 1.0), Gp3G (Vrel = 0.71), Ap4A (Vrel = 0.08), Ap5A (Vrel = 0.09), Gp4G (Vrel = 0.3) and Gp5G (Vrel = 0.33). An NMP is always one of the products. 3. The Km values for Ap3A and Gp3G are 15 and 10 microM respectively. 4. Mg2+, Mn2+ and Ca2+ ions all stimulate the activity, while Zn2+, Co2+ and Ni2+ ions are inhibitory. 5. The activity of the Np3 Nase remains constant during pre-emergence development of encysted embryos but decreases slightly after hatching.

Acid Anhydride Hydrolases↗
PubMed1989

Characterization of the bis(5'-nucleosidyl) tetraphosphate pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia.

The P1P4-bis(5'-nucleosidyl) tetraphosphate asymmetrical-pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia has been purified over 11,000-fold to homogeneity. Anion-exchange chromatography resolves two major species with very similar properties. The enzyme is a single polypeptide of Mr 17,600 and is maximally active at pH 8.4 and 2 mM-Mg2+. It is inhibited by Ca2+ (IC50 = 0.9 mM with 2 mM-Mg2+) but not by Zn2+ ions. It preferentially hydrolyses P1P4-bis(5'-nucleosidyl) tetraphosphates, e.g. P1P4-bis(5'-adenosyl) tetraphosphate (Ap4A) (kcat. = 12.7 s-1; Km = 33 microM) and P1P4-bis(5'-guanosyl) tetraphosphate (Gp4G) (kcat. = 6.2 s-1; Km = 5 microM). With adenosine 5'-P1-tetraphospho-P4-5"'-guanosine (Ap4G) as substrate, there is a 4.5-fold preference for AMP and GTP as products and biphasic reaction kinetics are observed giving Km values of 4.7 microM and 34 microM, and corresponding rate constants of 6.5 s-1 and 11.9 s-1. The net rate constant for Ap4G hydrolysis is 7.6 s-1. The enzyme will also hydrolyse nucleotides with more than four phosphate groups, e.g. Ap5G, Ap6A and Gp5G are hydrolysed at 25%, 18% and 10% of the rate of Ap4A respectively. An NTP is always one of the products. Ap2A and Gp2G are not hydrolysed, while Ap3A and Gp3G are very poor substrates. When the enzyme is partially purified from embryos and larvae at different stages of development by sedimentation through a sucrose density gradient, its activity increases 3-fold during the first 12 h of pre-emergence development. This is followed by a slow decline during subsequent larval development. The similarity of this enzyme to other asymmetrical-pyrophosphohydrolases suggests that it did not evolve specifically to degrade the large yolk platelet store of Gp4G which is found in Artemia embryos, but that it probably serves the same general function in bis(5'-nucleosidyl) oligophosphate metabolism as in other cells.

Acid Anhydride Hydrolases↗
PubMedDate not supplied

Plate fixation of comminuted olecranon fractures: an in vitro biomechanical study.

The stiffness, cyclic stability, and failure strength of posterior and lateral plating were compared in an in vitro model of a comminuted olecranon fracture. Loading was applied to the brachialis and triceps while displacements of the olecranon were measured with an electromagnetic tracking device in six degrees of freedom. No statistical difference was seen in the cyclic or static stability of either plating method. The triceps tendon suture attachment failed during destructive testing in each case between 300 and 500 N of applied loading. No gross failure of the bony fixation of the implant occurred before suture failure. These results suggest that both plating methods are likely to afford adequate stability to permit early protected postoperative range of motion.

Biomechanical Phenomena↗