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Biomedical subjects

H J Clarke

Publications and source records attributed to H J Clarke.

18 recordsLinked to original sources
PubMed1992

Computerized templating in uncemented total hip arthroplasty to assess component fit and fill.

The aim of the uncemented femoral component in total hip arthroplasty is to achieve a stable bone-prosthesis interface without the use of polymethyl methacrylate (PMMA). Maximal fill of the femoral canal by the prosthesis promotes initial stability and long-term optimal stress transfer to the bone. The percentage "fit and fill" of the proximal femur by three prostheses, the porous coated anatomic, anatomic medullary locking, and the Harris-Galante, was compared by use of a computerized templating model to assess preoperative radiographs of 20 patients. Results showed that overall percentage fit and fill was similar and satisfactory (greater than 60%) in 17 of 20 patients. If a satisfactory fill was not achieved with one prosthesis, another prosthesis did not significantly improve fill. Lack of bony contact in the proximomedial femur was the most common deficiency noted.

Computer-Aided Design↗
PubMed1992

Developmental regulation of chromatin composition during mouse embryogenesis: somatic histone H1 is first detectable at the 4-cell stage.

We have examined the distribution of histone H1 in oocytes and preimplantation embryos of the mouse, using a polyclonal antibody raised against the histone H1 subtypes present in somatic cells. Immunofluorescence and immunoblotting analyses failed to detect somatic histone H1 in germinal vesicle (GV)-stage oocytes. In contrast, somatic histone H1 was detectable by immunofluorescence in the nuclei of GV oocytes previously injected with histone H1 as well as the nuclei of ovarian granulosa cells, and by immunoblotting in 8-cell embryos. 1- and 2-cell embryos examined by immunofluorescence did not contain detectable somatic histone H1. At the early 4-cell stage (54-56 hours post-hCG), 5 of 52 embryos contained somatic histone H1 in one or more nuclei. By the late 4-cell stage (66-68 hours post-hCG), however, 58 of 62 embryos contained somatic histone H1. In 8-cell embryos, morulae and blastocysts, all nuclei contained somatic histone H1 in every case. When embryos were exposed to the transcriptional inhibitor, alpha-amanitin, beginning at the late 2-cell stage, they cleaved to the 4-cell stage but fewer than 10% developed histone H1 immunoreactivity. When treatment began at the early 4-cell stage, the embryos that remained at the 4-cell stage in the presence of the drug developed histone H1 immunoreactivity in half of the cases. Embryos that reached the 5- to 8-cell stage in the presence of the drug developed histone H1 immunoreactivity in every case.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Evaluation of acetabular stability in uncemented prostheses.

The stability of two commonly used uncemented acetabular prostheses fixed with either pegs or screws has been established by evaluating the torque strengths in ten cadaveric acetabulae. The initial stability of implants to simulated frictional loads was satisfactory compared to previous estimations of the frictional torques in polyethylene-on-metal and metal-on-metal articulations. Testing of the torque required to produce 2 degrees of rotation at the bone-implant interface showed that the peg fixation required significantly greater loads than did the screw fixation (P less than .03). Testing the prostheses to failure gave good results, although lower than previous cemented arthroplasty estimations. The margin of stability over the frictional torques that can be generated is such that it may affect the bony ingrowth into these prostheses. This may account for the common finding of fibrous ingrowth in these prostheses.

Acetabulum↗
PubMed1991

Tibio-talar stability in bimalleolar ankle fractures: a dynamic in vitro contact area study.

A dynamic weight-bearing model has been developed in a cadaveric ankle model to assess the contact areas of the talus in varying degrees of bimalleolar ankle fractures. A surgically created transverse fibula osteotomy with up to 6 mm of displacement did not cause a significant change in the contact area. Sectioning of the deltoid ligament, regardless of fibular displacement, created a 15% to 20% decrease in the contact area (P less than .001). This model represents a clinically relevant situation, as it examines motion of an unconstrained, axillary loaded ankle. Additional medial side disruption increases ankle instability by allowing anterior and lateral translation of the talus out of the mortise. Isolated lateral malleolar displacement does not appear to cause ankle instability.

Adult↗
PubMed1990

The effect of loading on tibiotalar alignment in cadaver ankles.

The tibiotalar movements which occur with axial loading, without applied moment forces were studied in cadaver ankles using a minimally constrained testing apparatus. Lateral translation of the talus measured up to 2 mm, which was associated with increased tibiotalar valgus angulation. Neither displacing the distal fibula laterally, nor sectioning the deltoid ligament, significantly influenced the talar shift. The tibiotalar motion which was observed after simple axial loading in a stable configuration (e.g., fibula and deltoid ligament intact) is of the same magnitude that is usually regarded as signifying an unstable ankle fracture. Consequently, this study suggests that the criteria for an unstable ankle fracture may need closer scrutiny.

Adult↗
PubMed1990

Surgical treatment for severe slipping of the upper femoral epiphysis.

We have used a modified technique of cervical osteotomy to treat a consecutive series of 23 patients with chronic slip of the upper femoral epiphysis. It has been successful in correcting both moderate and severe deformities with a low incidence of avascular necrosis, comparable to that seen after subtrochanteric osteotomies. We describe the operative details and discuss the features which make cervical osteotomy technically superior to intertrochanteric and subtrochanteric procedures.

Adolescent↗
PubMed1990

Clostridium difficile infection in orthopaedic patients.

In a review of the results of toxin assays, twenty-five orthopaedic patients who had a Clostridium difficile infection and associated diarrhea were identified. The infection was due to the use of antibiotics in all but one patient. Seventeen patients had received the antibiotics prophylactically. The two most commonly implicated antibiotics were cefazolin and clindamycin, because those drugs had been commonly used for prophylaxis at the study institutions. However, other antibiotics were implicated. There was a positive correlation between the delay in diagnosis and the severity of the illness. A white blood-cell count of more than 20 x 10(9) per liter indicated severe disease in our survey. The possibility of Clostridium difficile infection should be considered in patients who have signs and symptoms that mimic those of intestinal obstruction. Patients who have an unexplained fever or high white blood-cell count and in whom diarrhea develops in the postoperative period should be treated immediately with metronidazole, and a specimen of stool should be obtained for an assay for Clostridium difficile toxin. If the diagnosis of Clostridium difficile infection is confirmed by the presence of toxin in the stool and the patient has persistent, severe diarrhea, oral administration of vancomycin should be added to the regimen. The duration of antibiotic prophylaxis should be minimized to decrease the risk of Clostridium difficile colitis.

Adult↗
PubMed1990

Osteointegration of bone graft in porous-coated total hip arthroplasty.

Since 1983, 19 patients have had bone grafting of acetabular defects in association with a porous-coated acetabular prosthesis. The defects were defined by anatomic location to assess the rates of incorporation at different sites. The average time to incorporation was 12 months, judged by trabecular continuity. Superolateral grafts showed a greater degree of rarefaction than medial grafts. Nonprogressive migration of the graft was seen in only two cases before full incorporation of the graft. Developing lucency was seen up to 2 mm at the prosthesis-graft interface but not at the graft-ilium level. Roentgenograms suggested that integration of porous acetabular prostheses into bone may improve results of reconstructive surgery of the acetabulum.

Acetabulum↗
PubMed1989

Total replacement of the hip for avascular necrosis in sickle cell disease.

Total hip replacement was performed in 27 hips of patients who had sickle cell anaemia with avascular necrosis of the femoral head. The disease was bilateral in 11 patients. Considerable medical problems were encountered although most of the patients had exchange transfusion before surgery (86%), which prevented postoperative sickle cell crises in all but two cases. At the primary operation hard sclerotic bone was seen in nine femora with complete obliteration of the femoral canal. There were four femoral fractures, three following perforation of the shaft due to this hard bone. There was a very high morbidity due to loosening in both cemented and uncemented prostheses. With a rate of 59% over a cumulative 5.5 year period, revision was being performed at an average of only 43 months. Surgeons should be aware of these problems.

Adult↗
PubMed1988

The development potential of parthenogenetically derived cells in chimeric mouse embryos: implications for action of imprinted genes.

Parthenogenetic embryos of mice die shortly after implantation and characteristically contain poorly developed extraembryonic tissue. To investigate the basis of the abnormal development of parthenotes, we combined them with normal embryos to produce chimeras and examined the distribution of the parthenogenetically derived cells during preimplantation and early postimplantation development. The parthenogenetic embryos were derived from a transgenic mouse line bearing a large insert, which allowed these cells to be identified in histological sections using in situ hybridization. At the blastocyst stage, the parthenogenetic embryos contributed cells to the trophectoderm (TE) and inner cell mass (ICM) of chimeras. By 6.5 days, however, in almost every embryo, parthenogenetically derived cells were not detected in the extraembryonic trophoblast tissue descended from the TE. In contrast, parthenogenetically derived cells could contribute to all descendants of the ICM of 6.5-and 7.5-day chimeras, including the extraembryonic visceral and parietal endoderm. Quantitative analysis of the degree of chimerism in the embryonic ectoderm at 6.5-7.5 days indicated that parthenogenetically derived cells could contribute as extensively as normal cells. These results indicate that normal trophoblast development requires gene expression from the paternally inherited genome before 6.5 days of embryogenesis. Tissues of the ICM lineage, however, apparently can develop independently of the paternal genome at least to 7.5 days of embryogenesis. Comparison of these results with those of others suggests that the influence of imprinted genes is manifested at different times and in a variety of tissues during development.

Animals↗
PubMed1988

Suppression of chromosome condensation during meiotic maturation induces parthenogenetic development of mouse oocytes.

Mouse oocytes at metaphase I were treated with puromycin, which caused the chromosomes to become decondensed within an interphase nucleus. When the oocytes were allowed to resume protein synthesis, they returned to metaphase within 8-10 h and neither synthesized DNA nor cleaved, indicating that they had not been parthenogenetically activated by the puromycin treatment. However, when dibutyryl cyclic AMP was added to the medium after protein synthesis resumed, the oocytes remained in interphase. These oocytes maintained in interphase began DNA synthesis beginning 20 h after puromycin withdrawal, even though no activation stimulus had been given to them. After transfer to the oviducts of foster mothers, the oocytes could develop to the blastocyst stage. These results indicate that oocytes whose chromosomes were decondensed by puromycin treatment at metaphase I could begin parthenogenetic development in the absence of an activating stimulus, provided that they were prevented from returning to metaphase. In contrast, when the puromycin-treated oocytes were allowed to return to metaphase, they became developmentally arrested at the end of maturation. This suggests that the mechanism responsible for the developmental arrest of mature oocytes at metaphase II depends on cytoplasmic conditions that cause chromosome condensation to the metaphase state.

Animals↗
PubMed1987

Dose-dependent relationship between oocyte cytoplasmic volume and transformation of sperm nuclei to metaphase chromosomes.

We have studied the chromosome condensation activity of mouse oocytes that have been inseminated during meiotic maturation. These oocytes remain unactivated, and in those penetrated by up to three or four sperm, each sperm nucleus is transformed, without prior development of a pronucleus, into metaphase chromosomes. However, those penetrated by more than four sperm never transform any of the nuclei into metaphase chromosomes (Clarke, H. J., and Y. Masui, 1986, J. Cell Biol. 102:1039-1046). We report here that, when the cytoplasmic volume of oocytes was doubled or tripled by cell fusion, up to five or eight sperm nuclei, respectively, could be transformed into metaphase chromosomes. Conversely, when the cytoplasmic volume was reduced by bisection of oocytes after the germinal vesicle (GV) had broken down, no more than two sperm could be transformed into metaphase chromosomes. Thus, the capacity of the oocyte cytoplasm to transform sperm nuclei to metaphase chromosomes was proportional to its volume. The contribution of the nucleoplasm of the GV and the cytoplasm outside the GV to the chromosome condensation activity was investigated by bisecting oocytes that contained a GV and then inseminating the nucleate and anucleate fragments. The anucleate fragments never induced sperm chromosome formation, indicating that GV nucleoplasm is required for this activity. In the nucleate fragments, the capacity to induce sperm chromosome formation was reduced as compared with whole oocytes, in spite of the fact that the fragments contained the entire GV nucleoplasm. This implies that non-GV cytoplasmic material also was required for chromosome condensation activity. When inseminated oocytes were incubated in the presence of puromycin, the sperm nuclei were transformed into interphase-like nuclei, but no metaphase chromosomes developed. However, when protein synthesis resumed, the interphase nuclei were transformed to metaphase chromosomes. These results suggest that the transformation of sperm nuclei to metaphase chromosomes in the cytoplasm of mouse oocytes requires both the nucleoplasm of the GV and non-GV cytoplasmic substances, including proteins synthesized during maturation.

Animals↗
PubMed1985

Inhibition by dibutyryl cyclic AMP of the transition to metaphase of mouse oocyte nuclei and its reversal by cell fusion to metaphase oocytes.

Mouse oocytes at metaphase I of meiotic maturation were treated with puromycin, which caused the condensed chromosomes to become decondensed to form an interphase nucleus. The chromosomes returned to a metaphase state 6.3 hr after the oocytes were transferred to puromycin-free medium [H. J. Clarke and Y. Masui (1983) Dev. Biol. 97, 291-301]. In contrast, the chromosomes of the puromycin-treated oocytes remained decondensed within the nucleus if dibutyryl cyclic AMP (dbcAMP) was included in the puromycin-free medium. This implies that dbcAMP inhibited the development of conditions in the oocytes that were required for the transition to metaphase. The chromosomes of puromycin-treated oocytes that were incubated for 7.5 hr in dbcAMP-containing medium returned to metaphase just 1.9 hr after transfer to dbcAMP-free medium. Therefore, the protein synthesis-dependent process that is required for the transition to metaphase could occur in the presence of dbcAMP. Fusion to metaphase II oocytes, or to puromycin-treated oocytes that had returned to metaphase, rapidly induced transition of the nuclei of dbcAMP-inhibited oocytes to metaphase, despite the presence of the inhibitor. These results suggest that the transition of nuclei to metaphase can be induced by a cytoplasmic factor that is present in metaphase oocytes, and that dbcAMP inhibits the development of this factor.

Animals↗
PubMedDate not supplied

Nuclear and chromatin composition of mammalian gametes and early embryos.

Changes in nuclear structure and chromatin composition regulate gene activity in many cell types and could play a similar role during early mammalian embryogenesis. Oocytes of the mouse contain the three major lamin species present in somatic cells, although lamin A synthesized by oocytes has a higher molecular mass than the somatic species. Oocyte chromatin contains core histones similar to those of somatic cells, as well as elements that are immunologically related to protamines. In contrast, somatic-type histone H1 is not present. DNA topoisomerase II has not yet been identified in mammalian oocytes, but is abundant in frog oocytes. In contrast to oocytes, sperm do not contain a typical nuclear lamina. DNA topoisomerase II is detectable until late spermiogenesis. Although the DNA of sperm is associated mainly with protamines, some histone may be retained. There is also evidence that the arrangement of the DNA in the nucleus is nonrandom. These results demonstrate differences in nuclear and chromatin composition between oocytes and sperm. After fertilization, the nuclei of cleavage-stage blastomeres undergo programmed modifications. Lamin B is synthesized, whereas lamin A is not. In addition, a set of nuclear proteins is transiently synthesized in mice at the two-cell stage. Changes in embryonic chromatin composition also occur. The relative abundance of transcripts from different core histone genes differs between mouse oocytes and blastocysts. Furthermore, somatic histone H1 becomes detectable beginning at the mid-four-cell stage. As well, during early cleavage stages, expression of plasmid-borne genes becomes dependent on enhancers. Thus, developmentally regulated changes in nuclear and chromatin composition occur during early mammalian embryogenesis, and these may be important for the initiation and regulation of embryonic gene activity.

Animals↗
PubMedDate not supplied

A biomechanical analysis of solvent-dehydrated and freeze-dried human fascia lata allografts. A preliminary report.

UNLABELLED: This study compares the basic mechanical properties of two groups of commercially available fascia lata allografts processed by different means (solvent-dehydrated and sterilized via gamma radiation, and freeze-dried without secondary sterilization). The results reveal significantly (P less than 0.05) higher stiffness, higher maximum load to failure, and higher maximum load per unit width of graft with the solvent-dried as opposed to the freeze-dried fascia lata. Subsections of individual solvent-dried specimens were also more uniform in their mechanical properties than those of the freeze-dried allografts. CLINICAL RELEVANCE: Fascia lata is used as a graft material in a variety of orthopaedic procedures. Allograft fascia lata offers an increased cross-sectional area of material and eliminates the morbidity associated with the harvesting of autologous tissues. However, the structural uniformity of such large grafts has been questioned. Processing techniques used in the sterilization and storage of such grafts is varied and represents a potential source of variation in the mechanical properties of allograft specimens. The results of this study suggest that a commercially available solvent-dehydrated form of fascia lata provides a more suitable grafting material than freeze-dried specimens obtained from tissue banks.

Adult↗