A Comparative Study of Haptic Stiffness Identification by Veterinarians and Students

Palpation is an important clinical skill in both veterinary and medical health professions. The present study compares the ability of practicing veterinarians and veterinary students to identify the stiffness of virtual surfaces through palpation. An absolute identification paradigm was used where a force-feedback haptic device rendered virtual surfaces with five levels of stiffness within a "clinically relevant" range (0.2-0.5 N/mm). The mean information transfer was 0.97 bits (almost two perfectly identifiable stiffness levels) for 12 veterinarians and 0.58 bits (one correctly identified level) for 14 veterinary students. Although the difference between the two groups was significant (p <; 0.001), neither group was able to reliably identify more than two levels of stiffness, indicating that the success of veterinarians in clinical practice probably relies on additional properties such as size, shape, and texture. Analyses of force versus time and displacement versus time recordings suggest that the superior performance of the veterinarians may be partially attributable to motor strategy. Specifically, veterinarians used a greater mean maximum force (2.0 N) compared to students (1.6 N) (p <; 0.05). However, further studies are required to investigate motor strategy in more detail. The implications of our findings for veterinary education and quantitative skill assessment are discussed.

Investigation of human mammary stem and progenitor subpopulations from BRCA1 mutation carriers and noncarriers

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Background: We have previously isolated discrete populations of mouse mammary epithelial cells (MECs) and defined a population that expresses ‘basal’ markers and is highly enriched for mammary stem cells. This subset was ‘triple negative’ for ER, PR and ErbB2 expression and is reminiscent of the basal subtype of breast cancer, suggesting that the mammary stem cell may be the ‘cell of origin’ for this poor prognosis group. Since tumors arising in BRCA1 mutation carriers often exhibit a ‘basal’ phenotype, we hypothesized that the mammary stem cell pool is aberrant in these women. Our objective was to define the human MEC hierarchy and evaluate the functional characteristics of MECs from BRCA1± and normal breast tissue. Methods: Single cell suspensions prepared from fresh human BRCA1± and normal breast tissue were sorted by flow cytometry. Hematopoietic (CD45+, CD235a+) and endothelial (CD31+) cells were removed, and the remaining viable ‘lineage minus’ (Lin-) MECs fractionated based on cell surface markers. These subpopulations were evaluated by immunostaining, RNA profiling, in vitro culture in Matrigel and in vivo xenotransplantation into ‘humanised’ mammary fat pads of immunocompromised mice. Results: Lin- cells fractionated with α6-integrin (CD49f) and epithelial cell adhesion molecule (EpCAM) revealed three discrete MEC subpopulations. A stem/progenitor population that preferentially yields breast outgrowths in vivo has been identified. These subpopulations gave rise in vitro to colonies that were either large and heterogenous or small and homogenous. Only the latter differentiated into milk-producing cells when exposed to lactogenic stimuli. Immunostaining confirmed their origins from myoepithelial and luminal progenitor cells respectively. Intriguingly, BRCA1± MECs exhibited perturbed in vitro growth properties when compared to normal controls. Conclusions: Our studies provide evidence for a human MEC hierarchy, a model to interrogate the perturbation noted in pre-neoplastic tissue derived from BRCA1 mutation carriers and the identification of the cell of transformation in BRCA1 associated breast cancer. These findings may have implications on developing prevention strategies for hereditary breast cancer.

No significant financial relationships to disclose.

Femoral head viability after Birmingham resurfacing hip arthroplasty: assessment with use of [18F] fluoride positron emission tomography

BACKGROUND

Total hip resurfacing has become increasingly popular over the last decade. There remains concern about the effect of the surgical approach on femoral head viability and the role of resurfacing in the management of established osteonecrosis. In view of these concerns, we examined femoral head viability following resurfacing through a modified anterolateral approach.

METHODS

The viability of the femoral heads of ten patients who had undergone successful unilateral Birmingham hip resurfacing was assessed with use of positron emission tomography in conjunction with the injection of fluorine at a mean of twenty months after surgery. For each patient, in both the hip that had undergone resurfacing and the contralateral nonresurfaced hip, activity was measured in four regions of interest: the lateral aspect of the femoral head, the medial aspect of the femoral head, the lateral aspect of the femoral neck, and the proximal aspect of the femur. The uptake of fluorine in each area was converted to standard uptake volumes.

RESULTS

No areas of osteonecrosis were seen in the femoral head of any patient. There were no significant differences in the standard uptake volumes as measured in the four regions of the nonresurfaced hips, whereas the median values were higher in all four regions of the resurfaced hips. The difference between the values in the resurfaced hips compared with those in the nonresurfaced hips was only significant (p < 0.05) in the lateral aspect of the femoral head.

CONCLUSIONS

This study establishes positron emission tomography in conjunction with injection of fluorine as a possible modality for the assessment of femoral head viability after hip resurfacing. Viability following successful Birmingham hip resurfacing performed through a modified anterolateral approach has also been demonstrated. The increase in bone activity that was seen in the resurfaced hips in our study group may be related to bone remodeling or reperfusion of small areas of osteonecrosis. This technique offers the potential to study femoral head perfusion and viability following all types of resurfacing.

LEVEL OF EVIDENCE

Diagnostic Level IV. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

Regulation of DNA synthesis and capacity for initiation in DNA temperature mutants of Escherichia coli. III. Synthesis of the dnaA protein and of DNA-binding proteins

The synthesis and action of the dnaA product with respect to DNA initiation and the synthesis of DNA-binding proteins in Escherichia coli was examined. Results indicate that when dnaA product is irreversibly denatured and must be synthesized before initiation can occur, its synthesis and action appear to be complete approximately 30 min before initiation takes place. However, in mutants whose dnaA product is temperature reversible the action of the dnaA product appears to occur near the time of initiation. Examination of the DNA-binding proteins from the mutants suggests that a 53 kd protein, possibly the dnaA product, may be synthesized at the time of initiation under normal conditions at permissive temperature. The presence of active dnaA product appears to trigger the synthesis of a 60-65 kd protein which may be responsible for preventing another immediate initiation event.

Regulation of DNA synthesis and capacity for initiation in DNA temperature sensitive mutants of Escherichia coli. II. Requirements for acquisition and expression of initiation capacity

This paper deals with the conditions that are necessary for the acquisition and expression of initiation potential in dnaA temperature sensitive mutants after they have been held for periods of time at nonpermissive temperature and then returned to permissive temperature in the presence of chloramphenicol. The following conditions were found to be essential: (1) 40-60 min at nonpermissive temperature during which time protein synthesis must occur; this period must be followed by (2) return to permissive temperature under which conditions active dnaA product is present, and (3) protein synthesis must be blocked during the first 10-20 min immediately after return to permissive temperature (when initiation takes place). In order for expression of the initiation potential (4) the chloramphenicol must be removed to allow the progression of the replication forks which had been initiated to occur and (5) the recA+ phenotype appears to be required for acquisition or expression (or both) of the initiation potential.

Regulation of DNA synthesis and capacity for initiation in DNA temperature sensitive mutants of Escherichia coli I. Reinitiation and chain elongation

The capacity for initiation and subsequent chain elongation was examined in several DNA temperature sensitive mutants of Escherichia coli after the mutants had been held at nonpermissive temperature for approximately 1.5 generation equivalents and then returned to permissive temperature in the presence of chloramphenicol. The results obtained indicate that 4-5 sets of replication forks can be initiated after return to permissive temperature in the presence of chloramphenicol but the forks apparently become stalled and fail to complete chromosomal replication in the presence of chloramphenicol. In temperature reversible dnaA mutants, once the chloramphenicol is removed the forks appear to be able to resume replication at the nonpermissive temperature. The relationship between premature initiation and premature chain termination is discussed.

Effect of blocking protein synthesis at nonpermissive temperatures on temperature-sensitive deoxyribonucleic acid mutants of Escherichia coli

When protein synthesis was blocked in temperature-sensitive deoxyribonucleic acid synthesis mutants of Escherichia coli at nonpermissive temperatures, it reduced the amount of apparent subsequent chain elongation to approximately half that observed in the mutants either at nonpermissive temperatures alone or when protein synthesis was blocked at the permissive temperature. Blocking protein synthesis at the nonpermissive temperatures for periods of 40 min caused the loss of ability to reinitiate deoxyribonucleic acid synthesis at the permissive temperature.