Lung Mechanics: A Review of Solid Mechanical Elasticity in Lung Parenchyma.

The lung is the main organ of the respiratory system. Its purpose is to facilitate gas exchange (breathing). Mechanically, breathing may be described as the cyclic application of stresses acting upon the lung surface. These forces are offset by prominent stress-bearing components of lung tissue. These components result from the mechanical elastic properties of lung parenchyma. Various studies have been dedicated to understanding the macroscopic behaviour of parenchyma. This has been achieved through pressure-volume analysis, numerical methods, the development of constitutive equations or strain-energy functions, finite element methods, image processing and elastography. Constitutive equations can describe the elastic behaviour exhibited by lung parenchyma through the relationship between the macroscopic stress and strain. The research conducted within lung mechanics around the elastic and resistive properties of the lung has allowed scientists to develop new methods and equipment for evaluating and treating pulmonary pathogens. This paper establishes a review of mathematical studies conducted within lung mechanics, centering on the development and implementation of solid mechanics to the understanding of the mechanical properties of the lung. Under the classical theory of elasticity, the lung is said to behave as an isotropic elastic continuum undergoing small deformations. However, the lung has also been known to display heterogeneous anisotropic behaviour associated with large deformations. Therefore, focus is placed on the assumptions and development of the various models, their mechanical influence on lung physiology, and the development of constitutive equations through the classical and non-classical theory of elasticity. Lastly, we also look at lung blast mechanics. No explicit emphasis is placed on lung pathology.

A meta-analysis assessing time for return to sport following hip resurfacing.

BACKGROUND: Hip resurfacing arthroplasty (HRA) is associated with excellent functional outcomes and return to pre-disease level of activity. The time for return to sport (RTS) following HRA remains unknown. The aim of this meta-analysis was to establish the time for RTS following HRA. METHODS: A search was performed on PUBMED, MEDLINE, EMBASE, and the Cochrane Library for trials on HRA and RTS, in the English language, published from the inception of the database to October 2020. In addition, a manual search was performed of relevant sports medicine and orthopaedic journals, and the bibliographies reviewed for eligible trials. All clinical trials reporting on time to RTS following HRA were included. Data relating to patient demographics, methodological quality, operation type, RTS, clinical outcomes, and complications were recorded by two independent reviewers. The PRISMA guidelines for reporting meta-analyses was used to undertake this study. RESULTS: The initial literature search identified 1559 studies and nine further studies were found. Of these, 11 studies with a total of 659 patients matched the inclusion criteria. Two studies involving a total of 94 patients demonstrated an overall pooled proportion of 91.8% (95% CI 71.8-100) of patients RTS by three months post-operatively. Four studies including a total of 265 patients determined a pooled proportion of 96.8% (95% CI 91.0-99.7) of patients able to RTS by the 6-month post-operative stage. Pooled proportion analysis from all 11 studies comprising 659 patients showed 90.9% (95% CI 82.2-96.9) of patients were able to RTS by final follow up of 3 years. CONCLUSION: Pooled proportion analysis showed an increasing number of patients were able to RTS after HRA over the first one year after surgery. There remains marked inter and intra-study variations in time for RTS but the pooled analysis shows that over 80% of patients were able to RTS at 6 to 12 months after HRA. The findings of this meta-analysis will enable more informed discussions between patients and healthcare professionals about time for RTS following HRA.

Tourniquet use in total knee arthroplasty and the risk of infection: a meta-analysis of randomised controlled trials.

PURPOSE: The intra-operative use of tourniquets during Total Knee Arthroplasty (TKA) is common practice. The advantages of tourniquet use include decreased operating time and the creation of a bloodless visualisation field. However, tourniquet use has recently been linked with increased post-operative pain, reduced range of motion, and slower functional recovery. Importantly, there is limited evidence of the effect of tourniquet use on infection risk. The purpose of this systematic review and meta-analysis is to fill this gap in the literature by synthesising data pertaining to the association between tourniquet use and infection risk in TKA. METHODS: A systematic literature search was performed on Pubmed, Embase, Cochrane and clinicaltrials.gov up to May 2021. Randomized control trials were included, comparing TKA outcomes with and without tourniquet use. The primary outcome was overall infection rate. Secondary outcomes included superficial and deep infection, skin necrosis, skin blistering, DVT rate, and transfusion rate. RESULTS: 14 RCTs with 1329 patients were included. The pooled incidence of infection in the tourniquet group (4.0%, 95% CI = 2.7-5.4) was significantly higher compared to the non-tourniquet group (2.0%, 95% CI = 1.1-3.1) with an OR of 1.9 (95% CI = 1.1-3.76, p = 0.03). The length of hospital stay, haemoglobin drop (0.33 95% CI =0.12-0.54), P = 0.002) and transfusion rates (OR of 2.7, 95%CI = 1.4-5.3, P = < 0.01) were higher in the tourniquet group than the non-tourniquet group. The difference in the length of inhospital stay was 0.24 days favouring the non-tourniquet group (95% CI = 0.10-0.38, P = < 0.01). The incidence of skin blistering (OR 2.6, 95% CI = 0.7-9.9, p = 0.17), skin necrosis (OR 3.0, 95% CI = 0.50-19.3, p = 0.25), and DVT rates (OR 1.5, 95% CI = 0.60-3.60, p = 0.36) did not differ between the two groups. CONCLUSION: Quantitative synthesis of the data suggested tourniquet use was associated with an increased overall risk of infection, intraoperative blood loss, need for blood transfusion and longer hospital stay. Findings of this meta-analysis do not support the routine use of tourniquet in TKA and arthroplasty surgeons should consider any potential additional risks associated with its use. LEVEL OF EVIDENCE: meta-analysis, Level II.

Time for return to sport following total knee arthroplasty: a meta-analysis.

INTRODUCTION: The frequency of total knee arthroplasty (TKA) is increasing, particularly in younger and more active patients. In these patients, there may be greater functional demands, with an expectation to return to sporting activities (RTS) following TKA. There is a paucity of data on the time to RTS following TKA and the aim of this meta-analysis is to determine the time to RTS following TKA. METHODS: Using the PRISMA guidelines, an electronic search of PUBMED, MEDLINE, EMBASE, and the Cochrane Library for trails was performed on TKA and RTS in English language, published since the inception of the database to 31st October 2020. Data evaluating the time to RTS and functional outcomes were recorded by two authors independently that were included in the analysis. Pooled analysis using random effect model on overall proportions at the different time intervals and at the end of the follow-up was carried out for all studies. RESULTS: In total, 1,611 studies were retrieved from literature search. Of these, nine studies met the inclusion criteria with 1,307 patients. Two studies with 148 patients demonstrated an overall pooled proportion of 18.7% (95% CI 8.2-32.3%) of patients RTS at 3 month post-TKA; Three studies reported RTS rate at 6 months 70.% (95% CI 48-88.4). Two studies with 123 patients demonstrated an overall pooled proportion of 84.0% (95% CI 77.1-89.9%) patients RTS at 12 months. 986 patients returned to sport from total of 1307, with an overall adjusted proportion return to sport of 87.9 (95% CI 80.5-93.8%) at the end of follow-up; mean 14 months (range 3-36 months). CONCLUSION: Patients undergoing TKA were found to successfully RTS, pooled proportion analysis showed an increasing rate of RTS with time, at a mean of 14 months following TKA, where 87.9% of patients had returned to sports. The findings of this study will enable more informed discussions and rehabilitation planning between patients and clinicians on RTS following TKA.

Day-case unicompartmental knee arthroplasty: a literature review and development of a novel hospital pathway.

INTRODUCTION: We have seen unparalleled changes in our healthcare systems globally as a result of the COVID-19 pandemic. As we strive to regenerate our full capacity elective services in order to contest the increasing demand for lower limb arthroplasty, this pandemic has allowed us a rare opportunity to revise and develop novel elective arthroplasty pathways intended to improve patient care and advance healthcare efficiency. We present an extensive evidence-based review of the approaches used to achieve day-case unicompartmental arthroplasty (UKA) as well as the development of a day-case UKA care pathway in a UK NHS institution based on the evidence provided in the literature. METHODS: An extensive search of the literature was performed for articles that reported on readmission or complication rates ≥30 days postoperatively following day-case UKA. FINDINGS: Fifteen manuscripts reporting the results of day-case UKA, defined as discharged on the same calendar day of surgery, were included in our review. Mean reported complication rates for day-case and inpatient UKA within the follow-up periods were 4.05% and 6.52%, respectively. Mean readmission rates were 2.71% and 4.36% for day-case and inpatient UKA, respectively. The mean rate of successful same-day discharge was 92.45%. CONCLUSION: We introduce our institutional Elective Day Surgery Arthroplasty Pathway (EDSAP) founded upon the evidence presented in the literature. Stringent patient selection complimented by a well-defined day-case arthroplasty pathway is fundamental for successful commencement of day-case UKA in the NHS.

Artificial intelligence and surgical innovation: lower limb arthroplasty.

The number of patients requiring hip and knee arthroplasty continues to rise each year. Patients are living longer and expecting to remain active into later life following joint replacement. Developments in computer-assisted surgery and robotic technology may optimise surgical outcomes and patient satisfaction following lower limb arthroplasty. The use of artificial intelligence in healthcare is rapidly growing and has gained momentum in lower limb arthroplasty. This article reviews the use of artificial intelligence and surgical innovation in lower limb arthroplasty, with a particular focus on robotic-assisted surgery in total knee arthroplasty.

Metacarpal Indices and Their Association with Fracture in South African Children and Adolescents.

This prospective study assessed whether metacarpal indices predict fracture risk in children and adolescents. Radiogrammetry was performed at the second metacarpal midshaft on annual hand-wrist radiographs of 359 South African (SA) children aged 10-17 years. Bone length, bone width, and medullary width were measured, and the following proxies for bone strength calculated: metacarpal index (MCI), bone mineral density (BMD), section modulus (SM), stress-strain index (SSI), and slenderness index (SLI). Height and weight were measured annually. Self-reported physical activity (PA) and fracture history were obtained at ages 15 years (for the preceding 12 months) and 17 years, respectively. At 17 years, 82 (23%) participants (black, 16%; white, 42%; p < 0.001) reported a previous fracture. None of the bone measures or indices were associated with fracture in black participants. In white females, after adjusting for PA, a 1 standard deviation (SD) greater SLI doubled the fracture risk [odds ratio (OR) 2.08; 95% confidence interval (CI) 1.08, 3.98]. In white males, a 1 SD greater BMD was associated with a 2.62-fold increase in fracture risk (OR 3.62; 95% CI 1.22, 10.75), whilst a 1 SD greater SM (OR 2.29; 95% CI 1.07, 4.89) and SSI (OR 2.23; 95% CI 1.11, 4.47) were associated with a more than twofold increase in fracture risk, after height, and PA adjustment. No single index consistently predicted fracture across the four groups possibly due to ethnic and sex differences in bone geometry, muscle mass, and skeletal loading. Metacarpal radiogrammetry did not reliably predict fracture in SA children.

A longitudinal comparison of appendicular bone growth and markers of strength through adolescence in a South African cohort using radiogrammetry and pQCT.

To compare growth patterns and strength of weight- and non-weight-bearing bones longitudinally. Irrespective of sex and ethnicity, metacarpal growth was similar to that of the non-weight-bearing radius but differed from that of the weight-bearing tibia. Weight- and non-weight-bearing bones have different growth and strength patterns. INTRODUCTION: Functional loading modulates bone size and strength. METHODS: To compare growth patterns and strength of weight- and non-weight-bearing bones longitudinally, we performed manual radiogrammetry of the second metacarpal on hand-wrist radiographs and measured peripheral quantitative computed tomography images of the radius (65%) and tibia (38% and 65%), annually on 372 black and 152 white South African participants (ages 12-20 years). We aligned participants by age from peak metacarpal length velocity. We assessed bone width (BW, mm); cortical thickness (CT, mm); medullary width (MW, mm); stress-strain index (SSI, mm3); and muscle cross-sectional area (MCSA, mm2). RESULTS: From 12 to 20 years, the associations between metacarpal measures (BW, CT and SSI) and MCSA at the radius (males R2 = 0.33-0.45; females R2 = 0.12-0.20) were stronger than the tibia (males R2 = 0.01-0.11; females R2 = 0.007-0.04). In all groups, radial BW, CT and MW accrual rates were similar to those of the metacarpal, except in white females who had lower radial CT (0.04 mm/year) and greater radial MW (0.06 mm/year) accrual. In all groups, except for CT in white males, tibial BW and CT accrual rates were greater than at the metacarpal. Tibial MW (0.29-0.35 mm/year) increased significantly relative to metacarpal MW (- 0.07 to 0.06 mm/year) in males only. In all groups, except white females, SSI increased in each bone. CONCLUSION: Irrespective of sex and ethnicity, metacarpal growth was similar to that of the non-weight-bearing radius but differed from that of the weight-bearing tibia. The local and systemic factors influencing site-specific differences require further investigation. Graphical abstract.

Veno-arterial extracorporeal membrane oxygenation in addition to primary PCI in patients presenting with ST-elevation myocardial infarction.

INTRODUCTION: Primary percutaneous coronary intervention (pPCI) in ST-elevation myocardial infarction (STEMI) can cause great haemodynamic instability. Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) can provide haemodynamic support in patients with STEMI but data on outcome and complications are scarce. METHODS: An in-hospital registry was conducted enrolling all patients receiving VA-ECMO. Patients were analysed for medical history, mortality, neurological outcome, complications and coronary artery disease. RESULTS: Between 2011 and 2016, 12 patients underwent pPCI for STEMI and received VA-ECMO for haemodynamic support. The majority of the patients were male (10/12) with a median age of 63 (47-75) years and 4 of the 12 patients had a history of coronary artery disease. A cardiac arrest was witnessed in 11 patients. The left coronary artery was compromised in 8 patients and 4 had right coronary artery disease. All patients were in Killip class IV. Survival to discharge was 67% (8/12), 1­year survival was 42% (5/12), 2 patients have not yet reached the 1­year survival point but are still alive and 1 patient died within a year after discharge. All-cause mortality was 42% (5/12) of which mortality on ECMO was 33% (4/12). Patient-related complications occurred in 6 of the 12 patients: 1 patient suffered major neurological impairment, 2 patients suffered haemorrhage at the cannula site, 2 patients had limb ischaemia and 1 patient had a haemorrhage elsewhere. There were no VA-ECMO hardware malfunctions. CONCLUSION: VA-ECMO in pPCI for STEMI has a high survival rate and neurological outcome is good, even when the patient is admitted with a cardiac arrest.

Biological aspects of periodontal tissue regeneration: cementogenesis and the induction of Sharpey's fibres.

The realm of periodontal tissue regeneration has a plethora of unanswered questions and challenges due to the complexity of restoring mineralised and fibrous connective tissues ultimately to be covered by epithelium in a very specific spatial organisation. Wound healing of the periodontium follows a highly ordered sequence of events that guides cellular morphology, differentiation, migration and proliferation and comprises a series of cellular, extracellular and molecular reciprocal interactions. The prerequisite for regeneration of any structure is the trio of a soluble molecular signal, a scaffold and responding stem cells. Striated muscle represents an abundant source of easily accessible tissue that contains several perivascular, pericytic and myoblastic cell niches capable of differentiating and inducing selected tissue phenotypes and morphogenesis. Morcellated autogenous rectus abdominis muscle combined with 75 microg of hTGF-beta3 in Matrigel matrix implanted into non-human primate class II and III furcation defects induced greater alveolar bone formation and cementogenesis when compared to furcation defects without the addition of morcellated autogenous bone. In situ hybr disation and immunohistochemistry during embryonic development and tooth morphogenesis have shown synchronous but spatially different bone morphogenetic proteins (BMPs) expression during tissue induction and morphogenesis. Preclin cal studies in the non-human primate Papio ursinus have shown a seemingly specific cementogenic function of osteogenic protein-1 (OP-1, also known as BMP-7) when treating Class II furcation defects of Papio ursinus. In context, hOP-1 is preferentially cementogenic when implanted into non-human primate class II and III furcation defects whilst hBMP-2 is highly osteogenic but not cementogenic when in contact with dentine extracellular matrix. Importantly, naturally-derived highly purified BMPs/OPs, recombinant hOP-1 and hTGF-beta3 when implanted into non-human primates Class II and III furcation defects induce cementogenesis with morphologically and functionally oriented periodontal ligament fibres coursing within a newly formed highly vascular periodontal ligament space with Sharpey's fibres generated within the newly secreted cementoid matrix. The grand challenge of molecular and therapeutic implications is the biological significance of apparent redundancy. The presence of several homologous but molecularly different isoforms all endowed with the striking capacity of inducing "bone formation by autoinduction" indicates that there is a structure/activity profile amongst soluble osteogenic molecular signals; this suggests a therapeutic significance in clinical contexts. The structure/activity profile finely tunes the vast pleiotropic activities of the soluble molecular signals in mineralised and non-mineralised tissues profoundly modulating epithelial/mesenchymal tissue interactions. Significant advances in regenerative tissue engineering may be expected if ongoing research is tailored to provide further mechanistic and morphological insights into the relevance of the apparent redundancy and the structure/activity profile of the recombinant human osteogenic proteins. The presence of the structure/activity profile together with the biological significance of apparent redundancy will necessitate re-shaping and re-engineering developing newly devised targeted therapeutics for periodontal tissue engineering.

Buttock cellulitis as a presentation of psoas abscess: a clinical reminder.

Cellulitis is a common condition that is frequently managed by the general physicians on an acute medical take. This case report describes buttock cellulitis as a presentation of an iliopsoas abscess and illustrates the importance of considering a deep abscess when there are atypical features, when the cellulitis is in an unusual location or when the patient fails to improve with standard anti-microbial therapy.

Geometry of porous hydroxyapatite implants influences osteogenesis in baboons (Papio ursinus).

Coral-derived porous hydroxyapatite disks of two geometric configurations were implanted in 16 calvarial defects, 25 mm in diameter, prepared in eight subadult male baboons (Papio ursinus). To determine whether the orientation of the exoskeletal microstructures (corallites) influences bone ingrowth and osteogenesis, hydroxyapatite disks were prepared by cutting the coral either longitudinally or transversally, to obtain two distinct implant geometries defined by the orientation of the corallites. In the same animals, 16 defects were left untreated to assess the regeneration potential of the subadult baboon calvaria. Disks of both geometric configurations were also implanted in heterotopic intramuscular sites to investigate their osteoinductive potential. Histomorphometric analysis on undecalcified and decalcified sections prepared from specimens harvested on day 90 after surgery showed that greater amounts of bone formed in porous hydroxyapatites cut in the longitudinal plane when compared with hydroxyapatites cut in the transversal plane (p < 0.01). Bone formed in hydroxyapatite specimens harvested from the intramuscular sites, but no difference in bone formation was found between the two geometric configurations. Untreated defects showed limited osteogenesis, comparable with a previous series of untreated defects identically prepared in adult baboon calvariae. This finding suggests that skeletally mature, adult primates may not be a requirement for evaluation of craniofacial bone substitutes. These results in a primate indicate that hydroxyapatite disks are able to induce bone differentiation when implanted in intramuscular sites, and that the geometric configuration of the porous hydroxyapatite influences bone ingrowth and osteogenesis in orthotopic calvarial sites. This should be taken into consideration when designing porous bone substitutes for craniofacial applications.

Hyperstimulation affects vascular permeability at implantation sites in the rat endometrium.

PURPOSE: It has previously been shown that deleterious changes occur in the epithelium and stroma of the endometrium of the rat following ovarian hyperstimulation by exogenous gonadotropins. The purpose of the present study was to investigate the formation of possible implantation sites following hyperstimulation. Female rats (n = 8) were injected in phase with their estrous cycle with follicle stimulating hormone (FSH), followed by human chorionic gonadotropin (hCG), and mated at proestrous. Control rats (n = 6) were uninjected and mated at proestrous. Animals were killed at 5.5 days of pregnancy. The pontamine blue technique was used to demonstrate the permeability of the uterine vessels. Implantation sites were demonstrated in the uterine horns of all control animals by segmental blue banding. RESULTS: Blue staining occurred only in a portion of one horn of one hyperstimulated animal. While fenestrations were found in the walls of capillaries of control animals, similar fenestrations were not observed in the vessels of hyperstimulated animals. CONCLUSION: As the walls of vessels in the hyperstimulated animals failed to become permeable, and as no implanting embryos were found in these animals, it is concluded that there was an inability of the endometrium to form implantation sites. These changes may impede attachment and implantation of the embryo.

Xenogeneic osteogenin, a bone morphogenetic protein, and demineralized bone matrices, including human, induce bone differentiation in athymic rats and baboons.

Subcutaneous implantation of xenogeneic demineralized bone matrix does not initiate endochondral bone differentiation. Dissociative extraction in 4 M guanidine-HCl or 6 M urea has shown that the apparent species-specificity of intact bone matrix resides in its insoluble immunogenic component, since there is homology in solubilized osteogenic proteins amongst mammals. To further investigate the species-specificity and cross-species reactivity of bone matrix components, baboon and human demineralized bone matrix (DBM) and bovine osteogenin, purified greater than 50,000-fold and with an apparent molecular mass of 28-42 kilodaltons, were implanted in the subcutaneous space of athymic and euthymic rats and into the rectus abdominis of 16 baboons (Papio ursinus). Baboon DBM was also implanted in athymic and euthymic mice. Alkaline phosphatase activity and histology of implants harvested at day 11 and 30 showed that baboon and human DBM induced endochondral bone differentiation both in athymic rats and baboons. Bovine osteogenin in conjunction with baboon insoluble collagenous matrix induced extensive bone differentiation in athymic rats and baboons. Baboon and human DBM did not induce bone differentiation in euthymic rats and, in athymic mice, baboon DBM failed to induce bone differentiation, determining instead the recruitment of multinucleated giant cells. The results indicate that in rodents bone differentiation induced by intact bone matrix is species specific and that T-cell functions are not a requirement for bone induction, although immunologically competent rats block bone differentiation from xenogeneic matrix. Bone differentiation induced by human DBM in baboons suggests that intact bone matrices may not be species-specific amongst primates.(ABSTRACT TRUNCATED AT 250 WORDS)