Context-dependent reduction in somatic condition of wild Atlantic salmon infested with sea lice

Funding: Marine Scotland Science (MSS).Wild Atlantic salmon Salmo salar stocks have globally declined over recent decades. On their migratory return to coastal waters, individuals typically are infested by ectoparasitic caligid sea lice (Lepeophtheirus salmonis Krøyer, Caligus elongatus Nordmann). Infestation in laboratory trials can exert non-lethal impacts on the host fish, including increased stress levels and reduced growth, physical condition and swimming performance. However, to date no evidence exists for non-lethal effects of sea lice on wild adult Atlantic salmon. Using observations for > 6000 return-migrant adult salmon captured from the coastline at Strathy Point (SP), North Scotland, in the estuary of the River North Esk (NE), East Scotland, and the lower reach of the River Tamar (TA), Southwest England, we show that the somatic condition (weight at length) of wild salmon is associated with mobile sea lice density. This putative sea lice-mediated reduction of condition varied with year and seasonal date of freshwater return, and increased with the proportion of adult female parasites on a given fish. Influence of host sex, sea-age and smolt age was negligible. The estimated impact differed between the 3 sampling sites likely due to underestimation of infestation levels at NE and TA — largely attributable to negative influences of reduced salinity on parasite retention prior to sampling. Caligid infestation in the present samples explained a small, but discernible, proportion of the variation in host condition. Reductions in somatic condition of Atlantic salmon are associated with disproportionate declines in accreted lipid reserves, which are critical to up-river migration and ultimately the provisioning of eggs.PostprintPostprintPeer reviewe

Context-dependent reduction in somatic condition of wild Atlantic salmon infested with sea lice

Wild Atlantic salmon Salmo salar stocks have globally declined over recent decades. On their migratory return to coastal waters, individuals typically are infested by ectoparasitic caligid sea lice (Lepeophtheirus salmonis Krøyer, Caligus elongatus Nordmann). Infestation in laboratory trials can exert non-lethal impacts on the host fish, including increased stress levels and reduced growth, physical condition and swimming performance. However, to date no evidence exists for non-lethal effects of sea lice on wild adult Atlantic salmon. Using observations for > 6000 return-migrant adult salmon captured from the coastline at Strathy Point (SP), North Scotland, in the estuary of the River North Esk (NE), East Scotland, and the lower reach of the River Tamar (TA), Southwest England, we show that the somatic condition (weight at length) of wild salmon is associated with mobile sea lice density. This putative sea lice-mediated reduction of condition varied with year and seasonal date of freshwater return, and increased with the proportion of adult female parasites on a given fish. Influence of host sex, sea-age and smolt age was negligible. The estimated impact differed between the 3 sampling sites likely due to underestimation of infestation levels at NE and TA — largely attributable to negative influences of reduced salinity on parasite retention prior to sampling. Caligid infestation in the present samples explained a small, but discernible, proportion of the variation in host condition. Reductions in somatic condition of Atlantic salmon are associated with disproportionate declines in accreted lipid reserves, which are critical to up-river migration and ultimately the provisioning of eggs

High reliability for semiautomated 3D measurements based on weightbearing CT scans

Background: A reliable assessment of the ankle using weightbearing radiography remains challenging. Semiautomated 3-dimensional (3D) measurements derived from weightbearing computed tomography (WBCT) scans may provide a more reliable approach. Methods: Thirty healthy individuals without any foot and ankle disorder were analyzed. We assessed 6 widely used ankle parameters (4 angles and 2 distances) using either semiautomated 3D (based on WBCT scans) or traditional 2-dimensional (2D; based on conventional radiographs) measurements. The reliability and discrepancy between both techniques were compared using intraclass correlation coefficients and the Bland-Altman method. Results: Five of 6 variables showed a lower reliability when derived from 2D measurements. The mean of 3 variables differed between the techniques: the 3D technique assessed that the talonavicular coverage angle was 18.9 degrees higher, the axial talocalcaneal angle was 5.5 degrees higher, and the talocalcaneal overlap was 3.7 mm lower when compared with 2D measurements. Conclusion: Semiautomated 3D measurements derived from WBCT scans provide more reliable information on ankle alignment compared with 2D measurements based on weightbearing radiographs. Future studies may show to what extent these parameters could contribute to current diagnostic algorithms and treatment concepts

Assessment of progressive collapsing foot deformity using semiautomated 3D measurements derived from weightbearing CT scans

Background: In progressive collapsing foot deformity (PCFD), hind- and midfoot deformities can be hard to characterize based on weightbearing plain radiography. Semiautomated 3-dimensional (3D) measurements derived from weightbearing computed tomography (WBCT) scans may provide a more accurate deformity assessment. In the present study, automated 3D measurements based on WBCT were used to compare hindfoot alignment of healthy individuals to patients with PCFD. Methods: The WBCT scans of 20 patients treated at our institution with either a flexible (N = 10) or rigid (N = 10) PCFD were compared with the WBCT scans of a control group of 30 healthy individuals. Using semiautomated image analysis software, from each set of 3D voxel images, we measured the talar tilt (TT), hindfoot moment arm (HMA), talocalcaneal angle (TCA; axial/lateral), talonavicular coverage (TNC), and talocalcaneal overlap (TCO). The presence of medial facet subluxation as well as sinus tarsi/subfibular impingement was additionally assessed. Results: With the exception of the TCA (axial/lateral), the analyzed measurements differed between healthy individuals and patients with PCFD. The TCA axial correlated with the TNC in patients with PCFD. An increased TCO combined with sinus tarsi impingement raised the probability of predicting a deformity as rigid. Conclusion: Using 3D measurements, in this relatively small cohort of patients, we identified relevant variables associated with a clinical presentation of flexible or rigid PCFD. An increased TCO combined with sinus tarsi impingement raised the probability of predicting a deformity as rigid. Such WBCT-based markers possibly can help the surgeon in decision-making regarding the appropriate surgical strategy (eg, osteotomies vs realignment arthrodesis). However, prospective studies are necessary to confirm the utility of the proposed parameters in the treatment of PCFD

Supramalleolar osteotomy for ankle varus deformity alters subtalar joint alignment

Background: Although correction of ankle and hindfoot deformity after supramalleolar osteotomy has been investigated extensively, the specific effect on the subtalar joint alignment remains elusive. This can be attributed to the limitations of 2-dimensional measurements, which impede an exact quantification of the 3-dimensional subtalar joint alignment. Therefore, we determined both the ankle, hindfoot, and subtalar joint alignment before and after supramalleolar osteotomy using autogenerated 3-dimensional measurements based on weightbearing CT imaging. Methods: Twenty-nine patients with a mean age of 50.4 +/- 10.6 years were retrospectively analyzed in a pre-post study design using weightbearing CT. Inclusion criteria were correction of ankle varus deformity by an opening wedge (n = 22) or dome osteotomy (n = 7). Exclusion criteria consisted of an additional inframalleolar arthrodesis or osteotomy. Corresponding 3-dimensional bone models were reconstructed to compute following autogenerated measurements of the ankle- and hindfoot alignment: tibial anterior surface (TAS), tibiotalar surface (TTS), talar tilt (TT) angle, hindfoot angle (HA). In addition, the talocalcaneal angle (TCA) in the axial (TCA(ax)), sagittal (TCA(sag)), and coronal (TCA(cor)) plane were measured to assess the subtalar joint alignment. Results: The preoperative radiographic parameters of the ankle joint alignment (TAS=88 +/- 4 degrees, TTS=82 +/- 7 degrees, TT=5.8 +/- 4.9 degrees) improved significantly relative to their postoperative equivalents (TAS = 93 +/- 5 degrees, TTS = 88 +/- 7 degrees, TT=4.2 +/- 4.5 degrees; P .05). Conclusion: This study quantified the 3-dimensional ankle, hindfoot, and subtalar joint alignment after a solitary supramalleolar osteotomy. We found alterations in the subtalar joint alignment, which occurred by 2 to 3 degrees in each anatomic plane. However, before recommendations can be given related to inframalleolar procedures in conjunction to supramalleolar osteotomies, further studies on the variation of subtalar joint alignment change are needed