Buttock Tissue Research Articles

3D finite-element modeling of air-cell-based cushions and buttock tissues during prolonged sitting

IntroductionProlonged sitting can lead to serious health issues. Patients with spinal cord injuries may even develop pressure ulcers as stress accumulates on the ischial tuberosity. Air-cell-based (ACB) cushions have been shown to reduce tissue stress and help mitigate the effects of chronic sitting. Meanwhile, finite-element simulations have been implemented for different patient conditions. However, existing models are mostly two-dimensional with unrealistic simplifications. MethodsA realistic three-dimensional multi-physics model with fewer artificial assumptions is presented. A commercial ACB cushion and an emulational buttock consisting of an actual hip bone and soft tissue (muscle, fat, and skin layers) were considered. Computational Fluid Dynamics and Transient Structural Analysis using ANSYS were utilized to simulate the ACB cushion during expansion and buttock tissue during sitting. ResultsProfile of airflow and pressure distributions caused by the airflow within the ACB cushion were computed when the air was pumped into the cells. Expansion of the ACB cushion was simulated, and an optimal inner pressure range (100–500 Pa) was determined. The human buttock sitting on the cushion was then simulated and visualized. ConclusionsThe realistic three-dimensional model can accurately capture deformation and stress profiles pertinent to sitting on an ACB cushion. The model allows us to optimize the ACB cushions and operating conditions missing in previous studies. The model has also resolved several weaknesses in former models, such as the artificial air layers between air cells and unrealistically imposed internal pressure.

The Choice of Abdominal Flap Used in Breast Reconstruction Surgery

The incidence of breast cancer has been progressively increasing to the current level where 1 in 8 women now develop the disease. The National Breast Screening Programme has enabled us to diagnose many breast cancers at a much earlier stage. Coupled with an improved understanding of the oncoplastic approach to breast cancer surgery, genomics, hormone and targeted therapies as well as chemotherapy we now anticipate better outcomes.
 Despite the many advances in breast cancer there remains a significant cohort of women who are diagnosed with advanced forms of the disease that necessitates mastectomy i.e. the removal of all breast tissue. For many, reconstruction maybe immediately possible at the same time as mastectomy using either non-autologous (man-made) options such as breast implants and tissue expanders or autologous options using the latissimus-dorsi, abdominal or non-abdominal based flaps sited on thigh, buttock or lower flank tissue.
 Abdominal based reconstructions have evolved from crude operative procedures in which large parts of the lower anterior abdominal wall were harvested while remaining attached to the feeding vascular supply. This ‘flap’ of tissue is then rotated upon the pedicle of vessels into the new location in the breast. Pedicled Transverse Rectus Abdominus Myocutaneous (TRAM) flaps were often complicated by under-perfusion of the transferred flap resulting in fat necrosis. There were also issues with abdominal wall bulges and hernias as a result of the loss of the rectus abdominus muscle.
 With improvements in microsurgery the advent of free flap surgery was ushered in. Skin and fat were transplanted from the lower anterior abdominal wall using one of the rectus abdominus muscles and the perfusing artery and draining vein (donor-site). This free TRAM flap could be transplanted in the recipient-site after re-joining (re-anastomosing) the artery and vein using microsurgery. Aided by better anatomical knowledge, surgeons have been able to reduce the amount of rectus muscle sacrificed resulting in the muscle sparing-TRAM (MS-TRAM) and more latterly the deep inferior epigastric perforator (DIEP) flap which has no muscle included. The advantages of this muscle sparing approach are speedier recovery and reduced morbidity while maintaining operative cosmetic outcomes.

Buttock tissue response to loading in men with spinal cord injury.

Objective/BackgroundDespite the fact that most people with a spinal cord injury who use a wheelchair for mobility are considered at-risk for pressure ulcer (PrU) development, there still exists a spectrum of risk amongst this group. Efforts to differentiate risk level would benefit from clinical tools that can measure or predict the buttocks response to loading. Therefore, the goal of this study was to identify how tissue compliance and blood flow were impacted by clinically-measurable risk factors in young men with SCI.MethodsBlood flow at the ischial tuberosity was measured using laser Doppler flowmetry while the seated buttock was unloaded, and loaded at lower (40–60 mmHg) and high (>200 mmHg) loads. Tissue compliance of the buttock was measured using the Myotonometer while subject were lifted in a Guldmann Net.ResultsAcross 28 participants, blood flow was significantly reduced at high loads, while no consistent, significant changes were found at lower loads. At 40–60 mmHg, blood flow decreased in participants with a pressure ulcer history and lower BMI, but stayed the same or increased in most other participants. The buttock displaced an average of 9.3 mm (2.7 mm) at 4.2 N, which represented 82% (7%) of maximum displacement. BMI was related to the amount of buttock tissue displacement while smoking status explained some of the variation in the percent of max displacement.ConclusionWide variability in tissue compliance and blood flow responses across a relatively homogeneous population indicate that differences in biomechanical risk may provide an explanation for the spectrum of PrU risk among persons with SCI.

Diffuse-type giant cell tumor of tendon sheath occurring in the subcutaneous tissue of buttock

Diffuse-type giant cell tumor of tendon sheath occurring in the subcutaneous tissue of buttock

The Effects of a Dynamic Tuberal Support on Ischial Buttock Load and Pattern of Blood Supply

Sitting acquired pressure ulcers are places of tissue breakdown that mainly occur under the ischial tuberosities (ITs). Successive durations of pressure relief help the buttock tissue recover from sustained deformation and blood-flow stagnation. A computer-aided simulator chair was developed with two adjustable tuberal support elements (TSE) integrated in a force-sensing seating plane (FSP). This study investigated the redistribution of external buttock load in relation to the pattern (i.e., dynamics) of subtuberal blood supply in sitting with a dynamic tuberal support of 1/60 Hz (80 mm/min). Fifteen healthy male subjects were seated with their ITs on the TSE. The experiment involved periodic TSE adjustment in which buttock interface pressure was measured with the FSP and an external pressure mapping device (PMD). Light-guide tissue spectrophotometry was used for simultaneous noninvasive measurement of oxygenation and perfusion in the skin ( < 2 mm) and subcutaneous ( < 8 mm) tissue under the ITs. TSE adjustment seemed effective to regulate centre of buttock pressure and the forces under the ITs. Differences in measurement with the FSP and PMD have been found due to Hammocking at the seat interface and inaccurate peak pressure readings. Subtuberal blood supply was inversely related to the contact load under the ITs. A rapid inflow of blood in the initial stage of tuberal unloading, followed by a gradual outflow in the rest of the movement cycle indicates that the average blood supply increases when the adjustment frequency increases. Future studies must address the influence of a dynamic tuberal support on the ischial buttock load and pattern of blood supply in impaired individuals.

Effects of dynamic sitting interventions on tissue oxygenation in individuals with spinal cord disorders

An explorative cross-sectional study. The objective of this study was to investigate the possibility of imposing dynamic sitting behavior on individuals with spinal cord disorders by using the Dynasit chair and to investigate its effect on the (sub-)cutaneous tissue oxygenation. Rehabilitation Centre het Roessingh, Enschede, the Netherlands. Ten male subjects with a spinal cord disorder. The Dynasit chair, an experimental simulator chair, containing mechanical concepts for postural adjustments, regulation of tuberal load and pelvic rotation, was developed to allow individuals with a spinal cord disorder to sit in a dynamic way. An experiment was carried out in which a dynamic sitting pattern was imposed. The sitting pattern consisted of series of actuated changes in posture, tuberal load and pelvic orientation. Effects of these changes on (sub-)cutaneous buttock tissue oxygenation were investigated by transcutaneous measurement of tissue oxygenation. Nonparametric statistical analyses were carried out on nine subjects that completed the study. Results showed significant positive effects (P<0.05) of actuated changes in tuberal load on the cutaneous and subcutaneous tissue oxygenation. The Dynasit chair is effective in imposing dynamic sitting behavior in individuals with a spinal cord disorder and consequently might reduce the chance of tissue degradation.

Decoupled pelvis rotation in sitting: A passive motion technique that regulates buttock load associated with pressure ulcer development

Wheelchair-users who cannot reposition themselves often suffer from pressure ulcers which are places of tissue breakdown in the buttock region under the sacrum and ischial tuberosities. Periodic pressure relief is needed to recover the buttock tissue from continuous deformation and impairment of tissue perfusion. Because pelvis alignment directly affects body posture and buttock load, a passive motion technique was developed that adjusts pelvis orientation independent from the trunk and seat support. This study investigates the effects of the so-called decoupled pelvis rotation (DPR) on the loads at the buttock–seat interface and evaluates whether this technique is applicable to regulate buttock load in sitting. Eighteen healthy male subjects participated in this study. Experiments were performed with a computer-aided adjustable simulator chair, instrumented with a concept of DPR. Measurements involved quasi-static actuated pelvis movements in the sagittal and frontal plane. Pelvis orientation, buttock interface pressures, seat reaction forces and centre of pressure were simultaneously measured. As a result of the induced passive pelvis movements, the pelvis rotated 19±2° and 9±2° in the sagittal and frontal plane, respectively. Significant relations were found between pelvis rotation and most quantities of buttock load. Findings suggest that DPR is an effective technique to regulate buttock load in able-bodied individuals. For clinical application, this technique is still to be evaluated on individuals who cannot functionally reposition themselves. Impairments to the neuromuscular function influence postural response from chair adjustments which makes clinical investigation necessary.

Analysis of mechanical interaction between human gluteal soft tissue and body supports

Pressure sores are the most common complication associated with patient immobilization. They develop through sustained localized tissue strain and stress, primarily caused by body supports. Modifying support design can reduce the risk and extent of pressure sore development with computational simulations helping to provide insight into tissue stress-strain distribution. Appropriate material parameters for human soft tissue and support material, as well as precise anatomical modelling, are indispensable in this process. A finite element (FE) model of the human gluteal region based on magnetic resonance imaging (MRI) data has been developed. In vivo human gluteal skin/fat and muscle long-term material parameters as well as open-cell polyurethane foam support long-term material parameters have been characterised. The Ogden form for slightly compressible materials was employed to describe human gluteal soft tissue behaviour. Altering support geometries and support materials, effects on human gluteal soft tissue could be quantified. FE-analysis indicated maximal tissue stress at the muscle-bone interface, not at the skin. Shear strain maxima were found in the muscle layer near the fat-muscle interface. Maximum compressive stress magnitude at the sacral bone depended strongly on the behaviour of the pelvic diaphragm musculature. We hypothesize that the compliance of the muscles forming the pelvic diaphragm govern the relative motion of the buttock tissue to the adjacent bone structure under compression, thus influencing tissue stress magnitudes.

Autologous Gluteal Augmentation after Massive Weight Loss: Aesthetic Analysis and Role of the Superior Gluteal Artery Perforator Flap

Anatomical features that make the buttocks attractive include adequate volume, projection, and a defined infragluteal fold. The gluteal region in patients with massive weight loss after gastric bypass is characterized by excessive skin and exaggerated fat loss. Lower body lift procedures remove excess skin and lift sagging buttock tissue, but they typically result in further gluteal flattening. Procedures designed to augment the inferomedial aspect of the gluteal region restore projection and help define the infragluteal crease. The authors describe their technique of lower body lift with gluteal autologous augmentation using the superior gluteal artery perforator flap. Eighteen consecutive patients with massive weight loss after gastric bypass had lower body lifts with autoaugmentation performed by one surgeon. Superior gluteal artery perforator flaps were designed within the lower body lift markings, raised lateral to medial, and transferred to the inferomedial quadrant of the buttocks. Patients with a median age of 41 years (range, 24 to 56 years) had lower body lifts 2.8 years (range, 1.2 to 4.9 years) after gastric bypass after losing an average of 141 pounds (range, 92 to 272 pounds). Median body mass index decreased from 49 to 29 at the time of contouring. The autoaugmentation procedure added approximately 60 minutes to the overall buttock lift procedure time; there were no intraoperative complications. Postoperatively, patients were surveyed anonymously and reported noting substantial improvement in the volume and contour of the buttocks. Superior gluteal artery perforator flaps can be transferred reliably during lower body lifts to add volume and projection to the buttocks. Key anatomical landmarks for vascular anatomy and aesthetic design are emphasized.

The In-the-Crease Inferior Gluteal Artery Perforator Flap for Breast Reconstruction

Perforator free flaps harvested from the abdomen or buttock are excellent options for breast reconstruction. They enable the reconstructive surgeon to recreate a breast with skin and fat while leaving muscle at the donor site undisturbed. The gluteal artery perforator free flap using buttock tissue was first introduced by the authors' group in 1993. Of the 279 gluteal artery perforator flaps, the authors have performed for breast reconstruction, 220 have been based on the superior gluteal artery and 59 have been based on the inferior gluteal artery. The authors have found that for some women with excess tissue in the upper buttock and hip area, use of the gluteal artery perforator flap resulted in an improvement at the donor site, whereas for others the aesthetic unit of the buttock was clearly disrupted. Therefore, the authors have recently been placing the scar in the inferior buttock crease to improve donor-site aesthetics. The authors have now performed 31 in-the-crease inferior gluteal artery perforator free flaps for breast reconstruction and found that the results are very favorable. The removal of tissue from the inferior buttock results in a tightened, lifted appearance. The resultant scar is well concealed within the infrabuttock crease, and exposure or injury of the sciatic nerve has not occurred. Extended beveling at this site is also possible, with less risk of causing an unsightly depression. The final aesthetic result of the scar lying within the inferior buttock crease is very favorable. All patients report satisfaction with the donor site. Complications included one total flap loss, two reoperations for venous congestion, one hematoma, two cases with delayed wound healing at the recipient site, and one with delayed wound healing at the buttock. The in-the-crease inferior gluteal artery perforator flap from the buttock is now the authors' primary alternative to the deep inferior epigastric perforator flap from the abdomen for breast reconstruction.

Microvascular Breast Reconstruction Using Buttock Tissue: The Preferred Scar Location and Shape

Microvascular Breast Reconstruction Using Buttock Tissue: The Preferred Scar Location and Shape

Reliability of Bench Tests of Interface Pressure

Determination of an appropriate wheelchair cushion to optimize loading on buttock tissue is crucial to pressure ulcer prevention. Standardized test methods aim to simplify selection by helping clinicians and users identify a class or category of cushions that will meet the important medical need of adequate pressure distribution. The objective of this project was to determine the test-retest reliability of interface pressure measurements taken using bench tests as opposed to human subject tests. Ten wheelchair cushions were tested following the methods for interface pressure measurement as defined in a draft International Organization for Standardization document. Dispersion index, contact area, percent force in the ischial regions, peak pressure index, and seating pressure index–standard deviation are reliable measures. Average pressure is reliable but not very volatile between cushions. The data also indicate that peak pressure, seating pressure index–skew (SPI-sk), and the other five percent force regions are not reliable. Certain bench interface pressure variables were found to have adequate intralaboratory repeatability. Interlaboratory reliability must also be tested. If a bench interface pressure test is used to indicate cushion performance, its validity should also be studied. Research is underway to relate interface pressure variables to clinical measurements of wheelchair users. Once validity is shown, standardized test results can then be used by clinicians to simplify and improve the wheelchair cushion selection process.

Cellulite: Etiology and Purported Treatment

Much research must be undertaken before any of the treatments discussed can be validated as clinically effective. At present, it can be safely stated that there is no topical medication or manipulative process to which advanced cellulite visibly responds in a treatment period of less than 2 months.

A system for the analysis of seat support surfaces using surface shape control and simultaneous measurement of applied pressures.

A system for the design and analysis of seat support and buttock tissue interfaces has been developed. It has the ability to control the seating surface shape while measuring the pressure applied to the buttocks by the surface. Pressures are measured over an 11 x 12 rectangular array of support elements using silicon pressure sensors mounted in a swiveling head atop each support element. Control of surface shape is mediated by selective linear translation of the support elements along their respective vertical axes. Closed-loop control of the system allows for the dynamic formulation of a support surface on the basis of programmable criteria. The system is intended to function as a research tool to facilitate the study of the relationships between support surface shape and interface pressure, and support surface shape and soft tissue distortion. The purpose of this paper is to present the system instrumentation and the rationale behind its design and development. The paper also presents the results of several tests to evaluate the accuracy and performance of the system. This evaluation included a pilot study on 10 able-bodied subjects. The results of these system evaluations indicate that the system is capable of making repeatable and precise measurements of pressure and surface element position and can formulate support surface shapes that satisfy specified optimization criteria.

Deformation and Stress Analysis of Supported Buttock Contact

Non-linear finite element analysis has been used to investigate the contact problem between a buttock and a cushion of varying properties. The buttock tissue has been modelled on the macroscale by assuming it to be a hyperelastic (rubber-like) material with properties that correspond to the overall buttock response. Both rigid and flexible cushions have been considered. The contact between the cushion and the buttock has been modelled assuming both friction and friction-free conditions. The effect of these parameters on the buttock-cushion deformation and the tissue compressive and shear stress distributions have been presented. This study forms part of work towards the development of body segment simulators for use in investigations of seating and other support surfaces.