Finite element analysis of mechanical behavior of human dysplastic hip joints: a systematic review.

Developmental dysplasia of the hip (DDH) is a common condition predisposing to osteoarthritis (OA). Especially since DDH is best identified and treated in infancy before bones ossify, there is surprisingly a near-complete absence of literature examining mechanical behavior of infant dysplastic hips. We sought to identify current practice in finite element modeling (FEM) of DDH, to inform future modeling of infant dysplastic hips. We performed multi-database systematic review using PRISMA criteria. Abstracts (n = 126) fulfilling inclusion criteria were screened for methodological quality, and results were analyzed and summarized for eligible articles (n = 12). The majority of the studies modeled human adult dysplastic hips. Two studies focused on etiology of DDH through simulating mechanobiological growth of prenatal hips; we found no FEM-based studies in infants or children. Finite element models used either patient-specific geometry or idealized average geometry. Diversities in choice of material properties, boundary conditions, and loading scenarios were found in the finite-element models. FEM of adult dysplastic hips demonstrated generally smaller cartilage contact area in dysplastic hips than in normal joints. Contact pressure (CP) may be higher or lower in dysplastic hips depending on joint geometry and mechanical contribution of labrum (Lb). FEM of mechanobiological growth of prenatal hip joints revealed evidence for effects of the joint mechanical environment on formation of coxa valga, asymmetrically shallow acetabulum and malformed femoral head associated with DDH. Future modeling informed by the results of this review may yield valuable insights into optimal treatment of DDH, and into how and why OA develops early in DDH.

Micro-scale finite element modeling of ultrasound propagation in aluminum trabecular bone-mimicking phantoms: A comparison between numerical simulation and experimental results.

The present study investigated the accuracy of micro-scale finite element modeling for simulating broadband ultrasound propagation in water-saturated trabecular bone-mimicking phantoms. To this end, five commercially manufactured aluminum foam samples as trabecular bone-mimicking phantoms were utilized for ultrasonic immersion through-transmission experiments. Based on micro-computed tomography images of the same physical samples, three-dimensional high-resolution computational samples were generated to be implemented in the micro-scale finite element models. The finite element models employed the standard Galerkin finite element method (FEM) in time domain to simulate the ultrasonic experiments. The numerical simulations did not include energy dissipative mechanisms of ultrasonic attenuation; however, they expectedly simulated reflection, refraction, scattering, and wave mode conversion. The accuracy of the finite element simulations were evaluated by comparing the simulated ultrasonic attenuation and velocity with the experimental data. The maximum and the average relative errors between the experimental and simulated attenuation coefficients in the frequency range of 0.6-1.4 MHz were 17% and 6% respectively. Moreover, the simulations closely predicted the time-of-flight based velocities and the phase velocities of ultrasound with maximum relative errors of 20 m/s and 11 m/s respectively. The results of this study strongly suggest that micro-scale finite element modeling can effectively simulate broadband ultrasound propagation in water-saturated trabecular bone-mimicking structures.

Symmetry analysis of talus bone: A Geometric morphometric approach.

OBJECTIVE: The main object of this study was to use a geometric morphometric approach to quantify the left-right symmetry of talus bones. METHODS: Analysis was carried out using CT scan images of 11 pairs of intact tali. Two important geometric parameters, volume and surface area, were quantified for left and right talus bones. The geometric shape variations between the right and left talus bones were also measured using deviation analysis. Furthermore, location of asymmetry in the geometric shapes were identified. RESULTS: Numerical results showed that talus bones are bilaterally symmetrical in nature, and the difference between the surface area of the left and right talus bones was less than 7.5%. Similarly, the difference in the volume of both bones was less than 7.5%. Results of the three-dimensional (3D) deviation analyses demonstrated the mean deviation between left and right talus bones were in the range of -0.74 mm to 0.62 mm. It was observed that in eight of 11 subjects, the deviation in symmetry occurred in regions that are clinically less important during talus surgery. CONCLUSIONS: We conclude that left and right talus bones of intact human ankle joints show a strong degree of symmetry. The results of this study may have significance with respect to talus surgery, and in investigating traumatic talus injury where the geometric shape of the contralateral talus can be used as control. Cite this article: Bone Joint Res 2014;3:139-45.

The finite element method for micro-scale modeling of ultrasound propagation in cancellous bone.

Quantitative ultrasound for bone assessment is based on the correlations between ultrasonic parameters and the properties (mechanical and physical) of cancellous bone. To elucidate the correlations, understanding the physics of ultrasound in cancellous bone is demanded. Micro-scale modeling of ultrasound propagation in cancellous bone using the finite-difference time-domain (FDTD) method has been so far utilized as one of the approaches in this regard. However, the FDTD method accompanies two disadvantages: staircase sampling of cancellous bone by finite difference grids leads to generation of wave artifacts at the solid-fluid interface inside the bone; additionally, this method cannot explicitly satisfy the needed perfect-slip conditions at the interface. To overcome these disadvantages, the finite element method (FEM) is proposed in this study. Three-dimensional finite element models of six water-saturated cancellous bone samples with different bone volume were created. The values of speed of sound (SOS) and broadband ultrasound attenuation (BUA) were calculated through the finite element simulations of ultrasound propagation in each sample. Comparing the results with other experimental and simulation studies demonstrated the capabilities of the FEM for micro-scale modeling of ultrasound in water-saturated cancellous bone.

Cardiopulmonary bypass in surgery for complex-combined vascular malformation of the lower limb: case report.

A 16-year-old boy was referred with features of Parkes Weber syndrome (PWS) involving the right lower limb. He had presented at birth with cutaneous vascular malformations (VM) in the right thigh and at the age of 7 years developed congestive cardiac failure, which was controlled with drugs. He received alpha interferon and steroids during this period without any benefit. He defaulted follow-up and at 12 years of age presented with further enlargement of the VM in the right thigh and leg with skin and soft tissue thickening. At this stage, embolization and subsequent excision of the VM were tried, but the surgery was abandoned because of massive hemorrhage. Over the next 4 years, the boy became totally bedridden because of massive increase in the size of the limb, repeated hemorrhages, and secondary infection of the VM. Right hip disarticulation was considered the best option to improve his quality of life. To prevent uncontrollable hemorrhage during surgery, the disarticulation was done under cardiopulmonary bypass with low circulatory flow. Postoperatively, the patient required intensive care nursing for a week. He is presently ambulatory with crutches. Cardiopulmonary bypass with low flow has been used for treating posttraumatic arteriovenous malformations. However, its use in surgery for PWS has not been reported earlier.

Coarctation of aorta repair at the National Heart Institute (1983-1994).

This retrospective study illustrates our approach to this problem over the years, from performing subclavian flap aortoplasty initially to the more accepted procedure now, which is resection and end-to-end anastomosis. Coarctation of aorta in our population is seen in a varying age groups and are also associated with other cardiac anomalies including both acyanotic and cyanotic congenital cardiac defects. Therefore a wide variety of surgical procedures were performed including resection of the coarcted segment and end-to-end anastomosis, subclavian flap aortoplasty, patch aortoplasty and synthetic tube graft interposition. Subclavian flap aortoplasty is not widely practised anymore in favour of resection with end-to-end anastomosis. Fifty four point four percent of patients had isolated coarctation, 10.5% had associated valvular defects, 28.1% had other simple congenital defects and 7.0% had associated complex cyanotic congenital defects. Perioperative mortality was 5.26% and is correlated with the younger age of patients at time of surgery and severity of cardiac failure at time of presentation. We did not see any difference in mortality for patients with complex congenital disease or between the different surgical procedures. However, we did find that in the early period when resection with end-to-end anastomosis was performed, there was a significantly higher incidence of morbidities.

Outpatient treatment of spontaneous pneumothorax using an improved pocket sized Heimlich valve.

We report two patients, who have used Pneumostat to replace the conventional underwater seal drainage system for recurrent pneumothorax. Both patients had required repeated chest tube insertion for recurrent pneumothorax and needed a longer hospital stay. Both patients were able to be discharged with the Pneumostat device and were reviewed in outpatient clinic. Both patients had optimal clinical improvement and chest X-ray showed no residual pneumothorax.

The ethnic characteristics and prevalence of diabetes mellitus, hypertension and hyperlipidaemia in patients who underwent coronary artery bypass grafting in Hospital Universiti Kebangsaan Malaysia.

A retrospective study was done on 302 patients who had undergone coronary artery bypass grafting (CABG) in Hospital Universiti Kebangsaan Malaysia--46.0% were Chinese, 40.1% were Malays and 11.6% were Indians. Overall and irrespective of race and sex, the prevalence of diabetes mellitus, hypertension and hyperlipidaemia was 45.7%, 78.8% and 89.1% respectively indicating that hyperlipidaemia was the most prevalent risk factor amongst this cohort. The Indians had the highest prevalence of the three risk factors. The Chinese and the Malays most frequently presented with the combination of hypertension and hyperlipidaemia.

Primary repair with in-situ interposition graft for infrarenal mycotic aortic pseudoaneurysm.

This is a case report of a pseudoaneurysm due to Salmonella aortitis in a 52 year old man. The condition is rare and represents one of the few cases reported in Malaysia. The diagnosis was made preoperatively by ultrasonography and computed tomography. This was confirmed at surgery where there was a 3 cm defect at the posterior wall of the aorta at L2/3 level. The aneurysmal sac extended to the retrocrural space at the 12th vertebra level cranially on the right side to the lower border of the 3rd lumbar vertebra caudally. It had a smooth fibrous wall and contained a mixture of organised haematoma and pus. At operation the aneurysm was excised, the affected region was carefully debrided and the aorta grafted with an in-situ in-lay graft. Antibiotic therapy was instituted until clinical response was evident, leukocytosis was reduced and blood culture was negative. However 4 months after surgery, the patient returned in irreversible shock and succumbed to disseminated intravascular coagulation secondary to massive upper gastrointestinal haemorrhage from an aortoduodenal fistula.