Joint laxity in canine hip dysplasia assessed using the hip flexed not distracted ventrodorsal view

OBJECTIVES

The ventrodorsal hip extended standard view is conventionally used for radiographic screening of canine hip dysplasia. However, because the ventrodorsal hip extended standard view minimises hip joint laxity, several alternative views have been proposed. Our aim was to evaluate a new ventrodorsal hip flexed and not distracted view to assess joint laxity, by comparing it with the ventrodorsal hip extended standard and ventrodorsal hip flexed and distracted views.

MATERIALS AND METHODS

Between April 2013 and March 2017, all dogs referred to the University of Naples "Federico II" for the diagnosis of canine hip dysplasia were studied using the ventrodorsal hip extended standard, ventrodorsal hip flexed and not distracted and ventrodorsal hip flexed and distracted views. The Norberg angle and the laxity index were measured for each view.

RESULTS

Overall, 102 dogs, 67 males and 35 females, mean age 15 months, were included. The mean (±standard deviation) Norberg angles were 99.77° (±10.42°), 89.29° (±14.32°) and 91.80° (±13.50°) for the ventrodorsal hip extended standard, ventrodorsal hip flexed and not distracted and ventrodorsal hip flexed and distracted views, respectively. The mean (± standard deviation) laxity indices were 0.19 (± 0.14), 0.39 (± 0.25) and 0.36 (± 0.21), respectively. The ventrodorsal hip flexed and distracted and ventrodorsal hip flexed and not distracted views had lower Norberg angle and higher laxity index values compared with the ventrodorsal hip extended standard view. The ventrodorsal hip flexed and distracted and ventrodorsal hip extended standard views are in strong agreement for the measurement of both Norberg angle and laxity index, as confirmed by Bland-Altman analysis and the intraclass correlation coefficient.

CLINICAL SIGNIFICANCE

The ventrodorsal hip flexed and distracted and ventrodorsal hip flexed and not distracted views obtained with the hip in a neutral position reveal joint laxity better than the ventrodorsal hip extended standard view. Unlike the ventrodorsal hip flexed and distracted view, the ventrodorsal hip flexed and not distracted view does not require human operators or special devices for positioning the dog. The wide age range of the dogs enrolled might have influenced the laxity index measurements, since capsular fibrosis in older dogs reduces laxity.

Structure, function, and chromosome mapping of the growth-suppressing human homologue of the murine gas1 gene

We describe the isolation, growth-suppressing activity, and chromosomal localization of the human homologue of the murine growth-arrest-specific gene gas1. Overexpression of h-gas1 is able to block cell proliferation in the A549 lung carcinoma and the T24 bladder carcinoma cell lines. No effect was observed when h-gas1 was introduced into the osteosarcoma cell line SAOS-2 and into the adenovirus-type-5 transformed cell line 293. This finding is related to our previous evidence that simian virus 40-transformed NIH 3T3 cells are also refractory to murine gas1 overexpression, suggesting that the retinoblastoma and/or p53 gene products have an active role in mediating the growth-suppressing effect of gas1. We also show that h-gas1 is on chromosome 9q21.3-22.1, in a region considered to be a fragile site. Altogether, the results raise the possibility that h-gas1 may be a target for genetic alterations leading to its inactivation in tumor cells.

Requirements for excision and amplification of integrated viral DNA molecules in polyoma virus-transformed cells

The integration of polyoma virus DNA into the genome of transformed rat cells generally takes place in a tandem head-to-tail arrangement. A functional viral large tumor antigen (T-Ag) renders this structure unstable, as manifested by free DNA production and excision or amplification of the integrated viral DNA. All of these phenomena involve the mobilization of precise genomic "units," suggesting that they result from intramolecular homologous recombination events occurring in the repeated viral DNA sequences within the integrated structures. We studied polyoma ts-a-transformed rat cell lines, which produced large T-Ag but contained less than a single copy of integrated viral DNA. In all of these lines, reversion to a normal phenotype (indicative of excision) was extremely low and independent of the presence of a functional large T-Ag. The revertants were either phenotypic or had undergone variable rearrangements of the integrated sequences that seemed to involve flanking host DNA. In two of these cell lines (ts-a 4A and ts-a 3B), we could not detect any evidence of amplification even after 2 months of propagation under conditions permissive for large T-Ag. An amplification event was detected in a small subpopulation of the ts-a R5-1 line after 2 months of growth at 33 degrees C. This involved a DNA fragment of 5.1 kilobases, consisting of the left portion of the viral insertion and about 2.5 kilobases of adjacent host DNA sequences. None of these lines spontaneously produced free viral DNA, but after fusion with 3T3 mouse fibroblasts, R5-1 and 4A produced a low level of heterogeneous free DNA molecules, which contained both viral and flanking host DNA. In contrast, the ts-a 9 cell line, whose viral insertion consists of a partial tandem of approximately 1.2 viral genomes, underwent a high rate of excision or amplification when propagated at temperatures permissive for large T-Ag function. These results indicate that the high rate of excision and amplification of integrated viral genomes observed in polyoma-transformed rat cells requires the presence of regions of homology (i.e., repeats) in the integrated viral sequences. Therefore, these events occur via homologous intramolecular recombination, which is promoted directly or indirectly by the large viral T-Ag.

Loss of integrated viral DNA sequences in polyomatransformed cells is associated with an active viral A function

Rat cells transformed by polyoma virus contain, in addition to integrated viral DNA, a small number of nonintegrated viral DNA molecules. The free viral DNA originates from the integrated form through a spontaneous induction of viral DNA replication in a minority of the cell population. Its presence is under the control of the viral A locus. To determine whether the induction of free viral DNA replication was accompanied by a loss of integrated viral DNA molecules in a phenomenon similar to the "curing" of lysogenic bacteria, we selected for revertants arising in the transformed rat populations and determined whether these cells had lost integrated viral genomes. We further investigated whether the viral A function was necessary for "curing" by determining the frequency of cured cells in populations of rat cells transformed by the ts-a mutant of polyoma virus following propagation at the permissive or nonpermissive temperature. A large proportion of the revertants isolated were negative or weakly positive when assayed by immunofluorescence for polyoma T antigen and were unable to produce infectious virus upon fusion with permissive mouse cells. The T antigen-negative, virus rescue-negative clones can be retransformed by superinfection and appear to have lost a considerable proportion of integrated viral DNA sequences. Restriction enzyme analysis of the integrated viral DNA sequences shows that the parental transformed lines contain tandem repeats of integrated viral molecules, and that this tandem arrangement is generally lost in the cured derivatives. While cells transformed by wild-type virus undergo "curing" with about the same frequency at 33 degrees or 39 degrees C, cells transformed by the ts-a mutant contain a much higher frequency of cured cells after propagation at 33 degrees than at 39 degrees C. Our results indicate that in polyoma-transformed rat cells, loss of integrated viral DNA can occur at a rather high rate, producing (at least in some cases) cells which have reverted partially or completely to a normal phenotype. Loss of integrated viral DNA is never total and appears to involve an excision event. The polyoma A function (large T antigen) is necessary for such excision to occur. In the absence of a functional A gene product, the association of the viral DNA with the host DNA appears to be very stable.