There is an individual tolerance to mechanical loading in compression induced deep tissue injury.

BACKGROUND: Deep tissue injury is a type of pressure ulcer which originates subcutaneously due to sustained mechanical loading. The relationship between mechanical compression and damage development has been extensively studied in 2D. However, recent studies have suggested that damage develops beyond the site of indentation. The objective of this study was to compare mechanical loading conditions to the associated damage in 3D. METHODS: An indentation test was performed on the tibialis anterior muscle of rats (n = 39). Changes in the form of oedema and structural damage were monitored with MRI in an extensive region. The internal deformations were evaluated using MRI based 3D finite element models. FINDINGS: Damage propagates away from the loaded region. The 3D analysis indicates that there is a subject specific tolerance to compression induced deep tissue injury. INTERPRETATION: Individual tolerance is an important factor when considering the mechanical loading conditions which induce damage.

MRI based 3D finite element modelling to investigate deep tissue injury.

Pressure ulcers occur due to sustained mechanical loading. Deep tissue injury is a severe type of pressure ulcer, which is believed to originate in subcutaneous tissues adjacent to bony prominences. In previous experimental-numerical studies the relationship between internal tissue state and damage development was investigated using a 2D analysis. However, recent studies suggest that a local analysis is not sufficient. In the present study we developed a method to create animal-specific 3D finite element models of an indentation test on the tibialis anterior muscle of rats based on MRI data. A detailed description on how the animal specific models are created is given. Furthermore, two indenter geometries are compared and the influence of errors in determining the indenter orientation on the resulting internal strain distribution in a defined volume of tissue was investigated. We conclude that with a spherically-shaped indenter errors in estimating the indenter orientation do not unduly influence the results of the simulation.

An advanced magnetic resonance imaging perspective on the etiology of deep tissue injury.

Early diagnosis of deep tissue injury remains problematic due to the complicated and multifactorial nature of damage induction and the many processes involved in damage development and recovery. In this paper, we present a comprehensive assessment of deep tissue injury development and remodeling in a rat model by multiparametric magnetic resonance imaging (MRI) and histopathology. The tibialis anterior muscle of rats was subjected to mechanical deformation for 2 h. Multiparametric in vivo MRI, consisting of T2, T2*, mean diffusivity (MD), and angiography measurements, was applied before, during, and directly after indentation as well as at several time points during a 14-day follow-up. MRI readouts were linked to histological analyses of the damaged tissue. The results showed dynamic change in various MRI parameters, reflecting the histopathological status of the tissue during damage induction and repair. Increased T2 corresponded with edema, muscle cell damage, and inflammation. T2* was related to tissue perfusion, hemorrhage, and inflammation. MD increase and decrease was reported on the tissue's microstructural integrity and reflected muscle degeneration and edema as well as fibrosis. Angiography provided information on blockage of blood flow during deformation. Our results indicate that the effects of a single damage-causing event of only 2 h of deformation were present up to 14 days. The initial tissue response to deformation, as observed by MRI, starts at the edge of the indentation. The quantitative MRI readouts provided distinct and complementary information on the extent, temporal evolution, and microstructural basis of deep tissue injury-related muscle damage. NEW & NOTEWORTHY We have applied a multiparametric MRI approach linked to histopathology to characterize damage development and remodeling in a rat model of deep tissue injury. Our approach provided several relevant insights in deep tissue injury. Response to damage, as observed by MRI, started at some distance from the deformation. Damage after a single indentation period persisted up to 14 days. The MRI parameters provided distinct and complementary information on the microstructural basis of the damage.

A MRI-Compatible Combined Mechanical Loading and MR Elastography Setup to Study Deformation-Induced Skeletal Muscle Damage in Rats.

Deformation of skeletal muscle in the proximity of bony structures may lead to deep tissue injury category of pressure ulcers. Changes in mechanical properties have been proposed as a risk factor in the development of deep tissue injury and may be useful as a diagnostic tool for early detection. MRE allows for the estimation of mechanical properties of soft tissue through analysis of shear wave data. The shear waves originate from vibrations induced by an external actuator placed on the tissue surface. In this study a combined Magnetic Resonance (MR) compatible indentation and MR Elastography (MRE) setup is presented to study mechanical properties associated with deep tissue injury in rats. The proposed setup allows for MRE investigations combined with damage-inducing large strain indentation of the Tibialis Anterior muscle in the rat hind leg inside a small animal MR scanner. An alginate cast allowed proper fixation of the animal leg with anatomical perfect fit, provided boundary condition information for FEA and provided good susceptibility matching. MR Elastography data could be recorded for the Tibialis Anterior muscle prior to, during, and after indentation. A decaying shear wave with an average amplitude of approximately 2 µm propagated in the whole muscle. MRE elastograms representing local tissue shear storage modulus Gd showed significant increased mean values due to damage-inducing indentation (from 4.2 ± 0.1 kPa before to 5.1 ± 0.6 kPa after, p<0.05). The proposed setup enables controlled deformation under MRI-guidance, monitoring of the wound development by MRI, and quantification of tissue mechanical properties by MRE. We expect that improved knowledge of changes in soft tissue mechanical properties due to deep tissue injury, will provide new insights in the etiology of deep tissue injuries, skeletal muscle damage and other related muscle pathologies.

Current techniques for management of transverse displaced olecranon fractures.

BACKGROUND: displaced transverse fractures of the olecranon are the most common fractures occurring in the elbow in adults that requires operative intervention. METHODS: a literature search was performed on PubMed, Web of Science, Science Direct/Scopus, Google Scholar and Google using the keywords 'olecranon', 'fracture', 'internal fixation' and 'tension band wiring', with no limit for time or restrictions to language. RESULTS: thirty-one clinical articles were selected: 20 retrospective studies, 9 prospective cohort studies, and 2 randomized control trials. The CMS ranged from 18 to 66 (mean 41.68): overall, the quality of the studies was poor, and no moderate or good quality studies were found. The mean follow-up was 46.7 months (range 1 to 350 months). Several complications occurred after surgery: prominent hardware, skin breakdown, wire migration and infections occurred frequently. Removal of the hardware was required in 472 patients, usually after complaints, but also removal was routinely undertaken. CONCLUSIONS: tension band wiring is still the most widely applied method to operatively manage olecranon fractures, with the transcortical method of using K-wires the most satisfactory. Plate fixation is a good alternative as complications are minimal. Other techniques using absorbable sutures are less investigated, but are promising, especially in children.

Biomechanical studies on transverse olecranon and patellar fractures: a systematic review with the development of a new scoring method.

INTRODUCTION: Several methods of transverse patellar and olecranon fixation have been described. This article compares biomechanical studies of various fixation methods using a newly developed scoring method. SOURCE OF DATA: The databases PubMed, Web of Science, Science Direct, Google Scholar and Google were searched for relevant studies. AREAS OF AGREEMENT: Fixation hardware failure remains a problem. Various materials and fixation techniques have been tested to provide an improved fixation of transverse olecranon and patellar fractures. AREAS OF CONTROVERSY: The difference in biomechanical testing setup between the studies makes it hard to compare different fixation techniques. GROWING POINTS: The newly developed grading method was proved to be unbiased and reliable; however, extra specifications need to be added at some criteria when adopting the scoring method. AREAS TIMELY FOR DEVELOPING RESEARCH: Non-metallic constructs may provide an improvement to the currently used metallic tension band wiring technique; however, clinical research is required.

Treatment of transverse patellar fractures: a comparison between metallic and non-metallic implants.

INTRODUCTION: Several methods of transverse patellar fixation have been described. This study compares the clinical outcome and the occurrence of complications of various fixation methods. SOURCES OF DATA: The databases PubMed, Web of Science, Science Direct, Google Scholar and Google were searched. AREAS OF AGREEMENT: A direct comparison between fixation techniques using mixed or non-metallic implants and metallic K-wire and tension band fixation shows no significant difference in clinical outcome between both groups. Additionally, studies reporting novel operation techniques show good clinical results. AREAS OF CONTROVERSY: Studies describing the treatment of patients using non-metallic or mixed implants are fewer compared with those using metallic fixation. GROWING POINTS: A large variety of clinical scoring systems were used for assessing the results of treatment, which makes direct comparison difficult. AREAS TIMELY FOR DEVELOPING RESEARCH: More data of fracture treatment using non-metallic or mixed implants is needed to achieve a more balanced comparison.