Biomedical subjects
Publications and source records attributed to J M Prewitt.
Glenoid fossa prostheses, alone or in combination with metallic condyles, were placed in 192 joints (127 patients) for temporomandibular joint reconstruction. Anatomic requirements, material characteristics, indications, and surgical technique are presented.
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The problem of surveillance for metastasis in a cancer patient is modeled as an allocation problem. The hazard rate of metastasis appearing determines the efficient scheduling of follow-up exams. An optimal schedule of follow-up exams is shown to be dependent on the hazard rate, K, and D. K relates the cost of testing to the benefit of early detection. It diminishes as benefit increases or cost diminishes. D is the time by which a metastasis' detection by testing precedes its clinical presentation. Hence it is a direct measure of the effectiveness of testing. The optimal testing frequency = (hazard rate/2K)1/2. Testing may be stopped when the hazard rate drops below 2K/D2. Tests need never be routinely scheduled if the intervals between tests exceed D in length.
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The ingrowth of tissue into a coating of inert, highly porous, low-modulus composite of polytetrafluorethylene polymer and pyrolytic graphite on four-fluted intramedullary nails was used for stabilization of middiaphyseal femoral osteotomies and examined by microangiography. The observations were correlated with information obtained by histologic, microradiographic and tetracycline fluorescence technology. There was rapid healing of the osteotomy. The coating was invaded throughout by blood vessels and fibrous tissue. Invasion by bone was negligible. The composite thus appeared to retain its initial flexibility when implanted into the femoral intramedullary cavity. The force to distract both coated and uncoated nails was measured on intact femora. The unit retention strength increased to an average of 6.3 kg/cm2 up to 24 weeks, which is consistent with reported values. The composite would thus appear to have potential use as a coating for endoprostheses to produce enduring physiologic fixation.
Cruciate ligament stents have been developed to severe as internal splints which provide excellent temporary stability while allowing full range of motion of the knee during postreconstruction rehabilitation. Forty-three patients with disabling chronic knee instability were treated at one center using similar reconstruction techniques with either the anterior or posterior cruciate stent. When both cruciate ligaments were absent, only the posterior was used. All stents are intended only as temporary internal splints and all patients were advised that the structures were expected to break eventually. Followup of 15 patients with anterior cruciate stents revealed only 50% satisfactory overall results. Overall results were satisfactory in 80% of 20 patients with posterior cruciate stents. Longer implant survival is needed, and this must be accomplished by building more flexibility into the stent core and by improving surgical technique with more precise instrumentation.
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Proplast, a recently developed biologically acceptable synthetic polymer has been utilized in replacement of the cervical tracheas of five dogs. The results of this initial study are encouraging and, in the opinion of the authors, justify further experimentation with this refined prosthetic model.
A synthetic leader has been used in 18 cases of medial one-third patellar tendon substitution for the anterior cruciate ligament and in 10 cases of posterior cruciate substitution using the medial head of the gastrocnemius tendon. The device adds length and facilitates manipulation of the transplanted tissues. There have been no problems with biocompatibility and there have been no instances of staple loosening or disruption of the junction between the stabilizer and transplanted tissues. Early results with the anterior cruciate substitutions suggest thet anchoring the transfer in bony tunnels in both the tibia and femur does not allow sufficient flexibility to prevent stretching or disruption of the tendon transfer.