Background: Imaging-based logistic models are widely used for non-invasive risk stratification; however, their structural robustness and transportability across heterogeneous biological contexts remain insufficiently examined. Purpose: This study aimed to develop a simulation-based stress-testing framework to evaluate the structural robustness and transportability of a radiology-adapted logistic risk model across distinct cutaneous lesion phenotypes under both aligned and structurally perturbed conditions. Methods: A simulation-based methodological framework was implemented using three synthetic cohorts representing nodular, subcutaneous, and vascular lesion phenotypes (n = 2000 per cohort). Model performance was evaluated under naïve transfer, recalibration, and revision conditions. To address potential structural alignment bias, additional simulation scenarios incorporating coefficient perturbations, nonlinear transformations, and interaction effects were used to generate outcome processes partially independent from the original model structure. Model performance was assessed using discrimination (ROC-AUC, PR-AUC), calibration metrics, decision curve analysis, and Monte Carlo-based stability assessments. Results: Under naïve transfer, discrimination remained stable across phenotypes (ROC-AUC ≈ 0.78–0.84). Calibration shifts were observed but were effectively corrected through recalibration. Under structurally perturbed outcome generation, discrimination showed only modest reduction, while overall performance patterns remained consistent. Structural variables demonstrated high transferability, whereas vascular features exhibited phenotype-dependent variability. Decision curve analysis indicated consistent clinical utility across relevant thresholds. Conclusions: The radiology-adapted logistic model demonstrated structural robustness across heterogeneous phenotype conditions, with performance variations driven primarily by calibration differences rather than structural failure. Importantly, robustness was preserved under conditions of structural perturbation, supporting the model’s stability beyond idealized alignment assumptions. These findings suggest that simulation-based stress-testing frameworks provide a rigorous methodological approach for evaluating model transportability prior to large-scale clinical validation.

Introduction: Increasing the thickness of the capsule around the tissue expander, as in breast reconstruction complicates the expansion process and increases the time to achieve the required flap size. The aim of this study was to investigate the effect of changes in inflation intervals and amounts on the capsule thickness around the tissue expander. Methods: Fifteen adult rats were divided into 3 groups, and 25 cc elliptical tissue expanders were placed on the back of each, and inflated with 5 cc saline. Expanders were inflated daily in Group 1, every 3 days in Group 2, and every 10 days in Group 3. Inflation was stopped, then expanders were removed and skin flaps were harvested after the results of the expansion were measured. Biopsies containing skin and capsule tissue were evaluated by histomorphometry and immunohistochemistry. Results: Skin flaps were measured as 81 cm ² in Group 1 and 89.3 cm ² in both Groups 2 and 3. When capsule thickness and number of vessels were examined; the thickest capsule was found in Group 2 while Group 3 had the densest vascularization. On histopathological examination of the biopsies, no significant difference was found between groups, except for the histiocyte density, which was the lowest in Group 1 and the highest in Group 3. Conclusions: This experiment showed that inflating tissue expander in small amounts at frequent intervals decreased the thickness of the capsule but it resulted in smaller skin flaps. Thus, it may be beneficial to adopt this protocol in some patients, for example in patients who are predicted to have increased capsule thickness due to the effect of radiotherapy and/or chemotherapy, or who are prone to fibrosis. Additionally, in patients whose flap size is important, it may be reasonable to inflate the tissue expander at less frequent intervals and in relatively large volumes for preventing flap loss and avoiding an increase in capsule thickness.

Background: Pigmented superficial skin lesions pose a persistent diagnostic challenge due to overlapping clinical and dermoscopic appearances between benign and malignant entities. While histopathology remains the gold standard, there is growing interest in non-invasive imaging models that can preoperatively stratify malignancy risk. This methodological pilot study was designed to explore the feasibility and initial diagnostic performance of a novel radiology-adapted logistic regression approach. To develop and preliminarily evaluate a new logistic model integrating both structural (lesion size, depth) and vascular (Doppler patterns) ultrasonographic features for non-invasive risk stratification of pigmented superficial skin lesions. Material and Methods: In this prospective single-center pilot investigation, 44 patients underwent standardized high-frequency grayscale and Doppler ultrasound prior to excisional biopsy. Lesion size, depth, and vascularity patterns were systematically recorded. Three logistic regression models were constructed: (1) based on lesion size and depth, (2) based on vascularity patterns alone, and (3) combining all parameters. Model performance was assessed via ROC curve analysis. Intra-observer reliability was determined by repeated measurements on a random subset. Results: The lesion size and depth model yielded an AUC of 0.79, underscoring the role of structural features. The vascularity-only model showed an AUC of 0.76. The combined model demonstrated superior discriminative ability, with an AUC of approximately 0.85. Intra-observer analysis confirmed excellent repeatability (κ > 0.80; ICC > 0.85). Conclusions: This pilot study introduces a novel logistic framework that combines grayscale and Doppler ultrasound parameters to enhance non-invasive malignancy risk assessment in pigmented superficial skin lesions. These encouraging initial results warrant larger multicenter studies to validate and refine this promising approach.

Perforator flaps have been successfully applied in the treatment of decubitus ulcer.[1] [2] [3] Large flaps extending to the lumbar or posterior thigh area are needed in the large sacral defects. In this situation, the distal area of the flap may stay outside the angiosome region of the pedicle and cause circulation problems. The flaps, described in detail here, are planned within the boundaries of the gluteal region, in accordance with the principles of the angiosome. Due to the use of local tissues covering the defect area, the flaps are moved shorter distances with excellent blood supply, and the donor area is closed primarily. We call this technique “the walking crab,” because its final scar resembles a walking crab. Operative planning: An imaginary rectangle (ACDF) was planned with the borders of the four corners of the defect. An imaginary line (x), drawn from the midline, divides the defect into two, right and left. A separate reconstruction plan is made for both regions. Draw diagonals to cross the x line at a 45-degree angle (a-a' and b-b'). The axis of the a' and b lines determine the long axis of the flap. The length of the flap (F-F' and D-D') is approximately 2 to 3 cm longer than the length of the a' and b lines inside the defect (BF and BD). Its width (r1 and r2) depends on the length of the a and b' lines within the defect (EA and EC), which are planned equally. The medial flap border starts 3 to 4 cm lateral to the midline and ends elliptically to the midline of the lateral of the defect. Surgical details are shown in [Fig. 1]. We have utilized this technique in eight patients. The average postoperative follow-up duration was 16.1 months, and no recurrence was observed ([Fig. 2]). This procedure provides tension-free closure with local flaps in a single session for large sacral defects. None. Article published online: 24 June 2022 © 2022. Association of Plastic Surgeons of India. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Medical and Scientific Publishers Pvt. Ltd. A-12, 2nd Floor, Sector 2, Noida-201301 UP, India