A safe technique for insertion of heel wires for hindfoot external fixation frames: an anatomical study.

Aims: Anatomical atlases document classical safe corridors for the placement of transosseous fine wires through the calcaneum during circular frame external fixation. During this process, the posterior tibial neurovascular bundle (PTNVB) is placed at risk, though this has not been previously quantified. We describe a cadaveric study to investigate a safe technique for posterolateral to anteromedial fine wire insertion through the body of the calcaneum. Materials and Methods: A total of 20 embalmed cadaveric lower limbs were divided into two groups. Wires were inserted using two possible insertion points and at varying angles. In Group A, wires were inserted one-third along a line between the point of the heel and the tip of the lateral malleolus while in Group B, wires were inserted halfway along this line. Standard dissection techniques identified the structures at risk and the distance of wires from neurovascular structures was measured. The results from 19 limbs were subject to analysis. Results: In Group A, no wires pierced the PTNVB. Wires were inserted a median 22.3 mm (range 4.7 to 39.6) from the PTNVB; two wires (4%) passed within 5 mm. In Group B, 24 (46%) wires passed within 5 mm of the PTNVB, with 11 wires piercing it. The median distance of wires from the PTNVB was 5.5 mm (range 0 to 30). A Mann-Whitney U test showed that this was significantly closer than in Group A (Hodges-Lehmann shift, 14.06 mm; 95% confidence interval (CI) 10.52 to 16.88; p < 0.0001). In Group B, with an increased angle of insertion there was greater risk to the PTNVB (rs = -0.80; p < 0.01). Conclusion: Insertion of wires using an entry point one-third along a line from the point of the heel to the tip of the lateral malleolus (Group A) appears to be the safer technique. An insertion angle of up to 30° to the coronal plane can be used without significant risk to the PTNVB. Insertion of wires halfway along a line from the point of the heel to the tip of the lateral malleolus (Group B) carried a significantly higher risk of injury to neurovascular structures and, if necessary, an angle of insertion parallel to the coronal plane should be used. Cite this article: Bone Joint J 2018;100-B:1054-9.

Fine mapping of a malting-quality QTL complex near the chromosome 4H S telomere in barley.

Malting quality has long been an active objective in barley (Hordeum vulgare L.) breeding programs.However, it is difficult for breeders to manipulate malting-quality traits because of inheritance complexity and difficulty in evaluation of these quantitative traits. Quantitative trait locus (QTL) mapping provides breeders a promising basis with which to manipulate quantitative trait genes. A malting-quality QTL complex, QTL2, was mapped previously to a 30-cM interval in the short-arm telomere region of barley chromosome 4H in a "Step-toe"/"Morex" doubled haploid population by the North American Barley Genome Project, using an interval mapping method with a relatively low-resolution genetic map. The QTL2 complex has moderate effects on several malting-quality traits, including malt extract percentage(ME), a-amylase activity (AA), diastatic power (DP), malt 13-glucan content (BG), and seed dormancy, which makes it a promising candidate gene source in malting barley-cultivar development. Fine mapping QTL2 is desirable for precisely studying barley malting-quality trait inheritance and for efficiently manipulating QTL2 in breeding. A reciprocal-substitution mapping method was employed to fine map QTL2. Molecular marker-assisted backcrossing was used to facilitate the generation of isolines. Fourteen different types of "Steptoe" isolines, including regenerated "Steptoe" and 13 different types of "Morex" isolines,including regenerated "Morex", were made within a 41.5-cM interval between MWG634 and BCD265B on chromosome 4H. Duplicates were identified for 12 "Steptoe" and 12 "Morex" isoline types. The isolines together with "Steptoe" and "Morex" were grown variously at three locations in 2 years for a total of five field environments.Four malting-quality traits were measured: ME, DP, AA,and BG. Few significant differences were found between duplicate isolines for these traits. A total of 15 putative QTLs were mapped; three for ME, four for DP, six for AA,and two for BG. Background genotype seemed to make a difference in expression/detection of QTLs. Of the 15 QTLs identified, ten were from the "Morex" and only five from the "Steptoe" background. By combining the results from different years, field environments, and genetic backgrounds and taking into account overlapping QTLsegments, six QTLs can be conservatively estimated: two each for ME and AA and one each for DP and BG with chromosome segments ranging from 0.7 cM to 27.9 cM. A segment of 15.8 cM from the telomere (MWG634-CDO669) includes all or a portion of all QTLs identified. Further study and marker-assisted breeding should focus on this 15.8-cM chromosome region.

Genetic control of dormancy in a Triumph/Morex cross in barley.

Seed dormancy in barley ( Hordeum vulgare L.) is one of the most important parameters affecting malting. Seed dormancy is quantitatively inherited and variously influenced by the environment. The objectives of the present study were to determine the genome location and effects of quantitative trait loci (QTLs) involved in the expression of seed dormancy in a barley cross between two varieties derived from different germplasm pools. Using a doubled-haploid population of 107 lines of the cross between the malting types Triumph (two-row, dormant) and Morex (six-row, non-dormant), seed dormancy phenotypic data sets from five environments and a 147-marker linkage map were developed in order to perform QTL analyses with simple interval mapping and simplified composite interval mapping procedures. Two different types of variables were considered for seed dormancy characterization: (1) level of dormancy induced during seed development, which was indirectly measured as germination percentage at 3 days and 7 days, GP3 and GP7 respectively; (2) rate of dormancy release in the course of a period after seed harvest (after-ripening). Different mechanisms of genetic control were detected for these two types of dormancy-related traits. A major and consistent dormancy QTL near the centromere on chromosome 7(5H) was associated with the establishment of dormancy during seed development and accounted for 52% and 33% of the variability for GP3 and GP7, respectively. Two other QTLs located in the vicinity of the vrs1 locus on chromosome 2(2H) and near the long arm telomere on chromosome 7(5H) explained 9% and 19% of variation, respectively, for the rate of dormancy release during after-ripening. Likewise, seed dormancy was assessed in an F(2) population derived from the cross between two dormant types of distinct germplasm groups, Triumph (European, two-row, malt) and Steptoe (North American, six-row, feed), which showed similar but not identical genetic control for dormancy. Interestingly, there is remarkable dormancy QTL conservation in both regions on chromosome 7(5H) identified in this study and among other barley mapping populations. These widely conserved QTLs show potential as targets for selection of a moderate level of seed dormancy in breeding programs.

Molecular dissection of a dormancy QTL region near the chromosome 7 (5H) L telomere in barley.

Moderate seed dormancy is desirable in barley (Hordeum vulgare L.). It is difficult for breeders to manipulate seed dormancy in practical breeding programs because of complex inheritance and large environmental effects. Quantitative trait locus (QTL) mapping opens a way for breeders to manipulate quantitative trait genes. A seed dormancy QTL, SD2, was mapped previously in an 8-cM interval near the chromosome 7 (5H) L telomere from a cross of 'Steptoe' (dormant)/'Morex' (non-dormant) by the North American Barley Genome Project using an interval mapping method and a relatively low-resolution genetic map. SD2 has a moderate dormancy effect, which makes it a promising candidate gene for moderate seed dormancy in barley cultivar development. The fine mapping of SD2 is required for efficient manipulation of SD2 in breeding and would facilitate the study of dormancy in barley. Ten different Morex isolines were generated, including regenerated Morex, of which nine lines had duplicates. The isolines together with Steptoe and Morex were grown in growth room and field environments for 2 years (2000 and 2001). In the growth room, relatively low growing temperatures (25 degrees C day/15 degrees C night) were employed to promote seed dormancy development. Seed germination percentage, determined at different post-harvest after-ripening periods, was used to measure seed dormancy. Fine mapping using the substitution mapping method based on differences among isolines resolved the SD2 QTL into an 0.8-cM interval between molecular markers MWG851D and MWG851B near the chromosome 7 (5H) L telomere. Relatively low temperatures (< or =25 degrees C) during seed development promoted the expression of the SD2 dormancy QTL. The chromosome region above the MWG851D-MWG851B interval might play a role in reducing barley seed dormancy during after-ripening.

Verification of barley seed dormancy loci via linked molecular markers.

Seed dormancy is a relatively complex trait in barley (Hordeum vulgare L.). Several dormancy loci were identified previously by quantitative trait locus analysis. Three reciprocal crosses were made in the present study between parents carrying specific dormancy alleles via linked molecular markers to verify individual dormancy locus effects and potential expression. Analyses of F2 progenies revealed that the dormancy allele at the locus flanked by the markers Ale and ABC302 on the long arm of chromosome 7 had a major effect on dormancy, and was at least partly epistatic to the dormancy locus in the ABC309-MWG851 interval near the telomere of the long arm of chromosome 7. In the absence of the dormancy allele in the Ale-ABC302 interval, the allele in the ABC309-MWG851 interval exerted moderate to large effects on dormancy. Cytoplasmic effects on dormancy were also observed. The germination percentages of progeny with relatively high levels of dormancy were more variable than those of non-dormant or less-dormant progeny, apparently due to environmental effects. Removal of the dormancy allele in the Ale-ABC302 interval, or introducing the dormancy allele in the ABC309-MWG851 interval, should suffice for adjusting dormancy levels in breeding programs to suit various production situations and end uses. The verification of dormancy loci via linked molecular markers allows manipulation of these loci in applied breeding programs.