Sudesh Sivarasu

STRUCTURAL RESPONSES OF A NOVEL HIGH FLEXION KNEE (SS316–UHMWPE) USED IN TOTAL KNEE ARTHROPLASTY USING FINITE ELEMENT ANALYSIS

The application of finite element modeling in medical applications has been evolving as the field of high importance especially in the development of medical. The generic artificial knee implants used in the total knee arthroplasty have the restriction in its range of motion with around 90 degrees. A new design allowing flexion extension range of over 120 degrees has been designed with a view to facilitate partial squatting and the same is used for the analysis purpose. The loading conditions of 10 times the body weight are considered. Finite element analyses of this design have been carried out based on standard biomaterial used in orthopaedic implants. In this paper we discuss the results of analyses of an artificial knee with stainless steel alloy. The results of the analyses were used in identifying areas of extreme stresses within the design and the spot prone for higher deformation. Based on these results slight modification on the designs was carried out. The results are also verified whether the body is within the linear deformation levels. As the results obtained were very satisfactory the models have been recommended for prototyping. It is verified from the results that the new models respond positive till a load of 300 kg and then they enter into the maximum yield stress levels. However, in reality, the loading on an artificial knee is less than 300 kg. So the results are inferred positive and the models were sent for prototyping.

Kinematic and kinetic gait deviations in males long after anterior cruciate ligament reconstruction

Background: Biomechanical deviations long (approx. 5 years) after anterior cruciate ligament reconstruction have not been quantified in males, despite their distinct risk profile as compared to females. These deviations can indicate altered joint loading during chronic, repetitive motions. Methods: Cross‐sectional study, comparing kinematic and kinetic variables between 15 male anterior cruciate ligament reconstructed patients and 15 healthy controls. During walking and running gait, measurements were taken of impact dynamics, knee and hip sagittal plane angles and moments, and knee varus angles and adduction moments. Findings: Comparing affected limbs to control limbs, significantly lower maximum (P = 0.001) and initial (P = 0.003) loading rates were found during running, but not in walking. Hip angles were lower for affected limbs of patients compared to the control group (P = 0.039) in walking, but not during running. Between‐limb comparisons showed important differences in symmetry of the affected patients. Maximum force during running was higher in the unaffected limb (P = 0.015), which was linked with a higher loading rate (P = 0.008). Knee flexion angle was reduced by 2° on average for the affected limb during running (P = 0.010), and both walking and running knee and hip moments showed differences. Knee varus angle showed a 1° difference during walking (P < 0.001), but not during running. Knee adduction moment was significantly lower (more valgus) during both walking and running. Interpretation: Male anterior cruciate ligament reconstructed patients demonstrate persistent, clinically important gait asymmetries and differences from healthy controls long after surgery in kinematics, kinetics, and impact biomechanics. HIGHLIGHTSAnterior cruciate ligament reconstructed females show persistent gait deviations.No previous research has investigated these during walking/running in male patients.Knee adduction moments and angles were lower in affected than unaffected limbs.Reduced knee flexion angles and moments were also found, but only during running.Deviations from controls were also found in impact during foot strike.

KINEMATIC ANALYSIS AND 3D FINITE ELEMENT ANALYSIS OF A MOBILE-BEARING ARTIFICIAL HIGH FLEXION KNEE

Total knee arthroplasty (TKA) has been the end-time surgical procedure for pain relief and movement restoration in cases of severe arthritis. The knee implant design plays a vital role in deciding the activity levels of a patient after total knee replacement (TKR). In about 90% of younger patients undergoing the knee replacement surgeries, the restriction is not from the subject but from the implant design. This paper discusses parameters affecting the activity levels after TKR. It also briefs the design aspects of a novel knee design that allows the normal high flexion activity even after TKR. The application of finite element modeling in medical applications has been evolving as the field of high importance especially in the development of medical devices. The TKA has been in existence for over six decades till now. The generic artificial knee implants used in the TKA have the restriction in its range of motion of about 90°. A new design allowing flexion extension range of over 120° was designed with a view to facilitate partial squatting and the same is used for the analysis purpose. The loading conditions of 10 times the body weight are considered. The finite element analyses of the designs were carried out based on standard biomaterial used in orthopedic implants. In this paper, we have discussed the results of analyses of an artificial knee with titanium (Ti) alloy. The results of the analyses were used in identifying areas of extreme stresses within the design and the spot prone for higher deformation. Based on these results, slight modification on the designs was carried out. The results are also verified whether the body is within the linear deformation levels. As the results obtained were very satisfactory, the models have been recommended for prototyping.

Design of mechanical interface to re-distribute excess pressure to prevent the formation of decubitus ulcers in bed ridden patients.

Pressure ulcers are the major problem in the stroke management and rehabilitation. Prevention of pressure ulcer is of keen interest and is achieved by frequently changing the position of patient on the mattress. However, the care needs to be intensive to address this issue; else it would lead to pressure ulcer or bed sores formation. Skin surface over the bony prominences provide comparatively more pressure than the other regions. Therefore they are called as pressure vulnerable regions. Skin over these regions is more susceptible for formation of ulcers. An engineering approach is needed to shift the accumulating pressure from the pressure vulnerable regions. Although pressure sensed in these region would be more than that of which sensed in other regions, shifting protocol has to be designed to channelize or to grade the pressure shift in order to avoid any injuries to the non pressure vulnerable region. This paper aims at devising one such protocol using MATLab and thereby designing the layout of mattress using Pro/Engineer: the number of partitions needed to cover the entire surface of the skin that is in contact with the mattress.

Anatomic variations in glenohumeral joint: an interpopulation study

Background This study focused on the unique aspect of investigating shoulder morphometric differences between 2 distinct populations. Methods We used 90 computed tomography images of cadaveric shoulders for this study; 45 scans belonged to the South African (SA) cohort (49.74 ± 15.4 years) and the rest were Swiss (CH; 53.8 ± 21 years). The articulating surfaces of the glenohumeral joint were extracted, and their morphometric features, such as head circular diameter, glenoid and humeral head radius of curvature, head height, and humeral height, were measured. Results The mean interpopulation difference in the circular diameter of the humerus was 2.0 mm (P = .017) and 1.86 mm (P > .05) in the anterior-posterior and superior-inferior directions, respectively. The difference in the radius of curvature between the populations was 1.17 mm (P = .037). The SA shoulders were found to be longer than the CH shoulders by 8.4 mm (P > .05). There was no significant difference in the glenoid radius of curvature. The SA shoulders had higher glenohumeral mismatch (P = .005) and lower conformity index (P = .001) in comparison to the CH shoulders. Conclusion This study presents anatomic differences between African and European glenohumeral articulating surfaces. The results suggest that the glenohumeral geometry is both gender and population specific, and future joint replacements may be designed to address these differences.

Open source modular ptosis crutch for the treatment of myasthenia gravis

ABSTRACT Introduction: Pharmacologic treatment of Myasthenia Gravis presents challenges due to poor tolerability in some patients. Conventional ptosis crutches have limitations such as interference with blinking which causes ocular surface drying, and frequent irritation of the eyes. To address this problem, a modular and adjustable ptosis crutch for elevating the upper eyelid in Myasthenia Gravis patients has been proposed as a non-surgical and low-cost solution. Areas covered: This paper reviews the literature on the challenges in the treatment of Myasthenia Gravis globally and focuses on a modular and adjustable ptosis crutch that has been developed by the Medical Device Laboratory at the University of Cape Town. Expert commentary: The new medical device has potential as a simple, effective and unobtrusive solution to elevate the drooping upper eyelid(s) above the visual axis without the need for medication and surgery. Access to the technology is provided through an open source platform which makes it available globally. Open access provides opportunities for further open innovation to address the current limitations of the device, ultimately for the benefit not only of people suffering from Myasthenia Gravis but also of those with ptosis from other aetiologies.

Finite element model-based evaluation of tissue stress variations to fabricate corrective orthosis in feet with neutral subtalar joint.

Background: The subtalar joint position during static stance is a crucial determinant of the peak plantar pressures and forms ideal reference point for any intervention in foot-related problems for leprosy-affected patients. Objectives: The study pursued the hypothesis through a three-dimensional model that stress will be minimal in the distal joints of the foot when the subtalar joint is in neutral static stance position. Study design: Finite element model. Methods: The computed tomography images of the feet for five patients suffering from Hansen’s disease having no muscle weakness and joint restriction were acquired. The gray intensities corresponding to the bones of the foot from the computed tomography images were three-dimensionally reconstructed. The three-dimensional model of the human foot, incorporating the realistic geometry, and the material properties of the hard tissues were then analyzed using a finite element solver for the stress distribution on bones of the foot. Results: The results demonstrate that the position of the calcaneum in the static stance position does contribute to the varying stress in the foot. Conclusion: The stresses in the bones of the foot are minimal while the subtalar is in neutral position; this position will be suitable for foot orthotic fabrication. Clinical relevance The clinicians, therapists, and podiatrists having less engineering skills can quickly assess the patient and get optimal results on the stress associated with the joints of the foot.

The Paediatric Metered Dosage Inhaler (pMDI) Sleeve Attachment

Asthma is a chronic disease that causes fixed airflow obstruction, swelling and inflammation of the lung airways. This results in shortness of breath, wheezing and coughing [1]. 3.9 million People in South Africa are estimated to suffer from the disease and 1.5% of this total die as a result, annually [2]. The disease is the 3rd most common cause of child hospitalisation in South Africa.In developing countries, the most common and affordable treatment option for asthma would be the standard metered dosage inhaler (MDI) [3, 4]. MDI’s provide a range of medications (including airway dilators and anti-inflammatories) contained within the aerosol canisters.A large number of paediatric and geriatric patients suffering from asthma are unable to produce the necessary force required to activate the standard MDI. The study investigated fingertip pinch (action carried out when activating an MDI) strengths to determine the activation force deficit for paediatric patients [5]. In addition, patients using a standard MDI are unable to track the number of dosages remaining in the aerosol canisters [5]. The study presents a solution to the above mentioned patient limitations. A sleeve attachment was developed to reduce the required activation force of a standard MDI and track patient medication adherence. Additional features included height adjustability for varied MDI sizes (55mm to 90mm in length) and paediatric patient aesthetic appeal.Copyright

Femoral neck anteversion measurement using linear slot scanning radiography.

Measurements between anatomical landmarks on radiographs are useful for diagnosis and treatment planning in the orthopedic field. Direct measurement on single radiographic images, however, does not truly reflect spatial relationships, as depth information is lost. We used stereo images from a slot scanning X-ray machine to estimate coordinates of three-dimensional (3D) bony landmarks for femoral neck anteversion (FNA) measurement. A set of 7 landmarks consisting of the centre of the femoral head; the centre of the base of the femoral neck; the medial and lateral condyles; the medial and lateral posterior condyles; and finally the centre of the knee; were found to be identifiable and suitable for radiographic measurement. The reconstructed 3D coordinates were then used to define the 3D geometry of the anatomical axes required to estimate FNA. Stereophotogrammetric measurements on a sample of 30 dry right adult femurs were compared to reference values obtained using the Kingsley Olmstead method applied to photographic images. A strong positive correlation (0.998) was found and the mean ± standard deviation of the stereophotogrammetric approach (13.08 ± 6.87)° was comparable to that of the Kingsley Olmstead method (13.14 ± 6.88)°. Intra- and inter-observer reliability were high, with the lower bound of the 95% confidence interval above 0.98 for the intra-class correlation coefficient. The results merit further validation against three dimensional imaging technology such as computed tomography, to confirm stereophotogrammetry as a suitable alternative for FNA measurement.

Palmar Pressure Thresholds in Grasp and Pinch Functions - Analysis on Patients with Peripheral Nerve Damage

The peripheral nerve damage causes significant impairments if not detected and treated early. The loss of protective sensation in the patients with peripheral neuropathy leads to high pressure areas thus leading to secondary impairments. Impairments further leads to inability in carrying out normal activities of daily living. The study aimed to develop a sensory glove with the tactile sensors embedded in fabrics and to predict the pressure threshold level caused by friction and further prevent the high pressure while caused by friction and further prevent the high pressure while carrying out specific hand functions. Customized software was developed and the variations in the superficial pressures of the hand were recorded using tactile sensors while the patients were being involved in their routine daily living activities. The distribution patterns of the pressure in pre defined areas of hand were traced while the patients hand function activities involved the grasp and pinch powers. The study were conducted on (n = 100) patients from different job profile, gender and from different geographical location. The glove embedded with the tactile sensors helped identify pressure variations while the patients were involved in specific hand function activities. The pattern of the result suggests that the pressure were maximal while in the middle of an activity and is minimal at the onset and the end of the activity. The buzzer set along the glove gave an instant auditory feedback to the patient on the activity which causes prolonged high pressures to the skin surface of the hand. The portable device can be used anywhere in the community and will help in prescribing appropriate orthosis and adaptive tools and appliances for the patients and help prevent ulcers while doing their activities.