Biomedical subjects
Publications and source records attributed to M B Mayor.
A brief discussion of the importance of the collaboration of engineers and surgeons in solving the many problems that continue to vex patients with orthopaedic and related diseases.
Allergy to metal implants is under study at the Dartmouth-Hitchcock Medical Center using in vitro examination of white blood cell migration. Retrospective data from 121 patients confirm that allergic responses do occur. Prospective data are being gathered to investigate the incidence, prevalence and relation to morbidity.
The mechanism of obstruction of closed-wound drainage tubing was investigated by means of coagulation tests performed on wound drainage fluid and by examination of the contents of the tubes after their removal. Although clotting is commonly thought to be responsible for the obstruction, the wound drainage fluid was found to be essentially incoagulable and little fibrin was evident within the tubes. By contrast, bits of tissue were frequently found within the tubes, and these frequently virtually occluded the lumen. This observation, that tissue fragments are responsible for tube obstruction, permits a rational approach to the solution of this problem. For example, meticulous wound flushing and irrigation, or perhaps tubing of different design, might lead to a reduced incidence of tube failure.
Surgically produced fractures of rabbit tibiae were internally stabilized with intramedullary rods of stainless steel (316LVM), titanium (6A1,4V), polyacetal (Delrin), and polyamide (Nylon 101). Periodic radiographs were taken until sacrifice at 16 weeks after fracture. Structural properties of the tibiae were determined in torsion with the rods in situ, and then the tissue was prepared for histology or microradiography. The results demonstrated that fracture remodeling was adversely affected by the metal rods. New bone was seen to have formed over the ends of the metal rods, and cortical bone resorption was observed in the fracture region, suggestive of transfer of mechanical stress to the rods, resulting in stress shielding of the diaphysis. Negligible osseous response to the polymeric rods was observed; fracture callus remodeling was extensive. The torsional test results demonstrated that fractures with polymeric rods were significantly stronger and tougher than those with metallic rods. With the exception of titanium, the strength of healed fractures was inversely related to the elastic moduli of the implant materials.
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A 0.5 MHz pulse-transmission ultrasonic device is described and results obtained with an animal model presented. Two waveform components have been identified which correlate with the healing process. The "bone wave" is indicative of endosteal callus formation and the strength of cortical union. The "callus wave" is indicative of early periosteal callus formation. Recordings are presented to demonstrate the nature of the in vivo recordings, and the changes seen during the early stages of healing. In vitro recordings are presented to demonstrate that the signals are indicative of the properties of the bone and fracture, and are not soft tissue artifacts.
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