Mathematical models of passive motion at the human ankle joint by equivalent spatial parallel mechanisms

The paper presents a theoretical model of the ankle joint, i.e. tibio-talar articulation, which shows how the articular surfaces and the ligaments, acting together as a mechanism, can control the passive kinematics of the joint. The authors had previously shown that, in virtually unloaded conditions, the ankle behaves as a single degree-of-freedom system, and that two ligament fibres remain nearly isometric throughout the flexion arc. Two different equivalent spatial parallel mechanisms together with corresponding kinematic models were formulated. These assumed isometricity of fibres within the calcaneal-fibular and tibio-calcaneal ligaments and rigidity of the articulating surfaces, taken as three sphere-plane contacts in one model, and as a single spherical pair in the other. Geometry parameters for the models were obtained from three specimens. Motion predictions compare quite well with the measured motion of the specimens. The differences are accounted for by the simplifications adopted to represent the complex anatomical structures, and might be reduced by future more realistic representations of the natural articular surfaces.     

Mechanically Supported Early Graft Failure After Heart Transplantation

BackgroundThe occurrence of early graft failure (EGF) after heart transplantation (Htx) often requires a mechanical circulatory support (MCS) therapy. The aims of our study were to identify risk factors of mechanically supported severe EGF and evaluate their impact on both early and late outcomes.MethodsBetween January 2000 and December 2019, 499 consecutive adult patients underwent Htx at our institution. Severe EGF was defined as the need for extracorporeal life support (ECLS) within 24 hours after surgery. All available recipient and donor variables were retrospectively analyzed.ResultsOverall, EGF occurred in 58 (11.6%) patients. Post-Htx peripheral or central ECLS was necessary in 32 (6.4%) cases. Independent predictors of severe EGF were, in the recipient group, preoperative transpulmonary gradient (TPG) >12 mm Hg (odds ratio [OR] 4.1, P = .013), preoperative inotropic score >10 (OR 7.3, P = .0001), and pre-Htx ECLS support (OR 5.2, P = .015), while in the donors, a Eurotransplant donor score ≥17 (OR 8.5, P = .005). The absence of EGF was related with a better survival at 1 year and 5 years (94% and 85%, respectively) compared with EGF requiring ECLS population (36% and 28% at 1 year and 5 years, respectively; P < .001). A five-year conditional survival rate did not differ significantly (85% no EGF vs 83% EGF requiring ECLS).ConclusionBoth donor and recipient factors may influence EGF occurrence. Post-Htx ECLS may impact negatively early; however, patients weaned from ECLS eventually benefit from such a rescue treatment with outcomes comparable with Htx patients who did not suffer EGF.     

Color-Doppler sonography in chronic venous insufficiency: what the radiologist should know

Chronic venous insufficiency (CVI) is a pathologic condition caused by valvular incompetence, with or without associated venous outflow obstruction, which may affect both the superficial and the deep venous system, causing venous hypertension and stasis. The most common form of CVI is primary varicose veins due to the insufficiency of the saphenous system. Color-Doppler sonography (CDS) is actually the main diagnostic technique of imaging for CVI. In this article, we describe the anatomy, the technique, and the information necessary to the radiologist to perform CDS in chronic venous insufficiency. The knowledge of the venous anatomy is the cornerstone for an adequate sonographic examination. The venous network in the lower extremities is divided into three systems: superficial, deep, and perforating veins. Deep veins are "comitantes" to the corresponding arteries and run under the muscular fascia. Superficial veins course into the subcutaneous fat, superficially to the deep muscular fascia; the main superficial veins are the greater and lesser saphenous and their tributaries. Connection between the saphenous veins are defined as communicating veins. Superficial and deep veins are connected by perforating veins, with flow directed, under normal circumstances, from the superficial to the deep system. The main perforating are the Hunter in the mid thigh, the Dodd in the lower thigh, the Boyd in the upper calf, and the Cockett's in the middle and lower calf. Sonographic examination must be performed in the upright and supine position. Compression sonography and color and PW Doppler are systematically employed to assess the absence of deep venous thrombosis. Femoro-popliteal veins are evaluated with color and PW Doppler for valvular insufficiency with reflux by performing Valsalva maneuver and calf compression. The sapheno-femoral and sapheno-popliteal junctions are examined to identify type of junction, continence, accessory saphenous, and incompetent collaterals. Perforating veins are usually identified at the medial aspect of the thigh and at the medial, lateral, and posterior aspects of the leg. Outward flow (lasting more than 500 ms) in the perforating veins should be considered a sign of their incompetence. Several surgical and interventional procedures are now available for the treatment of the CVI, as follows: vein ligation and stripping, stab avulsion, endoluminal occlusion of the saphenous trunks, subfascial endoscopic perforator surgery, and valvuloplasty.     

Overt ischemic colitis after endovascular repair of aortoiliac aneurysms

OBJECTIVE: Controversy exists as to the cause of ischemic colitis complicating endovascular aneurysm repair. Occlusion of the hypogastric arteries (HAs) during endovascular repair of aortoiliac aneurysms (AIAs) results in a significant incidence of buttock claudication, and has been suggested as a causative factor in the development of postprocedural colonic ischemia, in addition to factors such as systemic hypotension, embolization of atheromatous debris, and interruption of inferior mesenteric artery inflow. To analyze the relationship between perioperative HA occlusion and postoperative ischemic colitis, we reviewed our experience over 2 years with Food and Drug Administration-approved endovascular graft devices for treatment of AIAs. METHODS: Elective repair of AIAs with bifurcated endovascular grafts was performed in 233 patients over a 2-year period. These included 184 AneuRx grafts, 17 Ancure grafts, and 32 Excluder grafts. During the experience, 44 patients (18.9%) underwent unilateral perioperative HA occlusion (28 right, 16 left) during the course of endovascular AIA repair, and 1 patient (0.4%) underwent bilateral HA occlusion. RESULTS: In 4 patients (1.7%) signs and symptoms of ischemic colitis developed 2.0 +/- 1.4 days postoperatively. In all patients the diagnosis was confirmed at sigmoidoscopy, and initial treatment included bowel rest, hydration, and intravenous antibiotic agents. Three patients with bilateral patent HAs required colonic resection 14.7 +/- 9.7 days after the initial diagnosis, and 2 of these 3 patients died in the postoperative period. Pathologic findings confirmed the presence of atheroemboli in the colonic vasculature in all 3 patients who underwent colonic resection. The fourth patient had undergone multiple manipulations of the left HA in an unsuccessful attempt to preserve patency of this vessel during AIA repair. This patient recovered completely with nonoperative management. Perioperative unilateral HA occlusion was not associated with a significantly higher incidence of postoperative ischemic colitis. CONCLUSION: Perioperative HA occlusion during aortoiliac open or endovascular surgery may contribute to development of the rare but potentially lethal complication of ischemic colitis. However, our extensive experience suggests that embolization of atheromatous debris to the HA tissue beds during endovascular manipulations, rather than proximal HA occlusion, is the primary cause of clinically significant ischemic colitis after endovascular aneurysm repair.     

Gray platelet syndrome: Management of perioperative bleeding in redo cardiac surgery

Gray platelet syndrome (GPS) is a rare (<1/1 000 000) and inherited platelet function disorder characterized by macrothrombocytopenia, α-granule deficiency, and hemorrhages. Bleeding intensity does not correlate with platelet count nor with functional test results. We hereby describe the perioperative bleeding prevention and management of a patient with GPS requiring multiple redo cardiac surgeries.     

Heart Transplant and Hepato-Renal Dysfunction: The Model of End-Stage Liver Disease Excluding International Normalized Ratio as a Predictor of Postoperative Outcomes

IntroductionPreoperative liver and renal dysfunction remain surgical risk factors for both postoperative morbidity and mortality. The Model of End-Stage Liver Disease Excluding INR (international normalized ratio), or MELD-XI, score calculation may help as a predictor in patients with advanced heart failure. We analyzed the impact of progressive elevated MELD-XI values among recipients of heart transplant at our institution.MethodsThe data of a total of 425 consecutive adult patients who underwent heart transplantation, between January 2000 and August 2018, have been reviewed and divided into 3 cohorts according to preoperative MELD-XI calculations (MELD-XI < 11; MELD-XI 11-18; and MELD-XI > 18). Early and late outcomes have been analyzed.ResultsPatients with a MELD-XI score > 18 had a more critical clinical condition preoperatively and had a higher risk of early mortality (hazard ratio [HR] 1.45 [1.11-1.67], P < .001). They showed high risk for postoperative dialysis (HR 2.8 [1.5-5.3], P < .001), rethoracothomy for bleeding (HR 2.1 [1.2-4.1], P = .001), prolonged time of mechanical ventilation, time of intensive care unit stay (HR 2.2 [1.3-3.8], P = .005), and graft failure requiring mechanical circulatory support (HR 1.9 [1.1-3.3], P = .003). After risk adjustment per MELD-XI cohort, ischemic dilated cardiomyopathy, redo operation, and cold ischemic time > 240 minutes resulted in being the strongest predictors of early mortality (P < .001). The 5-year and 10-year survival for MELD-XI > 18 cohort was 63% and 47% vs 72% and 59% in the control group (MELD-XI < 18) (log-rank, P < .001).ConclusionsPatients with an elevated preoperative MELD-XI profile presented more comorbidities and significantly lower survival. This suggests the MELD-XI score may provide further insight into appropriate recipient and eventual donor selection. Renal insufficiency and congestive hepatopathy should be properly optimized before heart transplantation.     

Effects of AT1 Receptor Antagonism With Candesartan on Endothelial Function in Patients With Hypertension and Coronary Artery Disease

Endothelial dysfunction is a major determinant of atherosclerosis and a negative prognostic factor in patients with coronary artery disease and hypertension. Recovery of endothelial dysfunction has been associated with improved prognosis in these patients. The aim of the present study was to verify whether antagonism of angiotensin II AT1 receptors with an angiotensin receptor blocker, candesartan, improved endothelial function in patients with hypertension, stable coronary artery disease, and endothelial dysfunction. We studied 26 patients who were receiving β-blockers with optimal blood pressure control, in a randomized, double blind study. Patients were randomized to placebo (n=13) or to candesartan 16 mg/d (n=13) for 2 months. Endothelial function was assessed by ultrasound using hyperemic flow-mediated dilation of the brachial artery. Mean arterial blood pressure was unchanged in both groups (from 93.3±9.2 to 93.2±17.3 mm Hg in the candesartan group and from 101.3±14.2 to 102.3±13.9 mm Hg in the placebo group; both P =ns). Maximal blood flow was similar between placebo and candesartan groups at baseline and at the end of the study, whereas flow-mediated dilation significantly increased in the candesartan group (from 5.27%±1.69% to 7.15%±2.67%; P =0.01) but remained unchanged in the placebo group (from 4.49%±1.97% to 5.88%±2.30%; P =ns). AT1 receptor antagonism with candesartan, in addition to β-blocker therapy, improves endothelial function in high-risk hypertensive patients.