Biomedical subjects

M H Jofe

Publications and source records attributed to M H Jofe.

3 recordsLinked to original sources

PubMed1991

Compressive behavior of human bone-cement composites.

Current surgical practice in the implantation of cemented total joint arthroplasties generally creates a zone of variable thickness in which polymethylmethacrylate (PMMA) is intermixed with trabecular bone. The authors' objectives in these experiments were to characterize the compressive mechanical properties of this bone-cement composite material. They found that the mechanical properties of bone-cement composite specimens, fabricated under in vitro conditions that would promote nearly complete cement filling, are closer to the properties of trabecular bone than to those of cement. For both low-viscosity cement (LVC) and PMMA specimens, with the cement introduced by either hand-packing or pressurized injection at periods of 2 and 7 minutes, the compressive strengths ranged from 29 MPa to 50 MPa and the compressive moduli from 539 MPa to 1,210 MPa. Cement volume fractions achieved using different filling methods ranged from 76% to 87%. In contrast to previous studies of bone-cement composites using high-density bovine bone, neither mechanical properties nor filling parameters correlated significantly with bone porosity measured prior to filling. The authors expect that the mechanical properties of bone-cement regions created at surgery under less than these ideal in vitro filling conditions will only approach their values as an upper limit. Thus, bone-cement composites created in situ at surgery will also exhibit mechanical properties well below previously assumed values.

Aged↗

PubMed1988

Reconstruction for defects of the proximal part of the femur using allograft arthroplasty.

One of the most difficult problems in orthopaedic oncology is reconstruction after resection of a tumor of the proximal end of the femur. In order to achieve a wide margin about a primary or secondary malignant neoplasm of bone, it is often necessary to resect not only the hip joint and fifteen or more centimeters of the proximal part of the femur, but also the surrounding envelope of soft tissue. In some patients, little is left but the sciatic and femoral nerves and vessels. Since 1971, we have done reconstructions in forty-four patients, using an allograft and an implant or else an osteoarticular graft alone to replace the proximal end of the femur. Twenty-eight of these reconstructions were performed in patients who had had a malignant tumor and were followed for two to fifteen years postoperatively. Fifteen of the patients had only an osteoarticular graft, and thirteen had an allograft and a prosthesis (nine Austin Moore, two bipolar, and two long-stem total hip replacements). The average length of the femoral segment was 18.4 centimeters; the longest one measured thirty-one centimeters. Using an evaluation system of functional end-results that includes failures as a result of recurrence of the tumor, we recorded approximately 70 per cent excellent and good results for both groups. When the two failures that were due to recurrence of the tumor were omitted from the statistics (in order to evaluate the allograft procedure more fully), the successful results increased to about 80 per cent. In general, the patients who had an osteoarticular reconstruction fared less well than did those who had an allograft and a prosthesis, but the series were not quite comparable. The major complications were metastases in nine patients (five of whom died), infection in five, and fracture of the allograft in six. Restoration of the reconstruction was possible for most of the patients who had a problem that was not related to the tumor, and only one patient required an amputation for recurrent tumor. Despite the many difficulties, we think that an allograft, with or without a prosthetic implant, should be given primary consideration as a means of reconstruction of the limb when resection of a tumor necessitates resection of a long segment of the proximal end of the femur.

Adult↗

PubMed1983

Monitoring fracture site properties with external fixation.

An in-vitro system has been devised to monitor the properties of an idealized fracture site immobilized with a Hoffman-Vidal external fixator. A dial gage was used to measure the relative pin displacements under controlled axial loading. The displacement measurements were then used in conjunction with a finite element model to predict the modulus of an idealized fracture site. Five fracture sites made of neoprene disks of different mechanical properties were monitored in order to simulate the increasing modulus of a healing fracture. Good agreement was observed between directly measured mechanical properties of the neoprene and those inferred from the combined finite element and pin displacement tests.

Aluminum↗