Custom-designed orthopedic implants evaluated using finite element analysis of patient-specific computed tomography data: femoral-component case study

<p>Abstract</p> <p>Background</p> <p>Conventional knee and hip implant systems have been in use for many years with good success. However, the custom design of implant components based on patient-specific anatomy has been attempted to overcome existing shortcomings of current designs. The longevity of cementless implant components is highly dependent on the initial fit between the bone surface and the implant. The bone-implant interface design has historically been limited by the surgical tools and cutting guides available; and the cost of fabricating custom-designed implant components has been prohibitive.</p> <p>Methods</p> <p>This paper describes an approach where the custom design is based on a Computed Tomography scan of the patient's joint. The proposed design will customize both the articulating surface and the bone-implant interface to address the most common problems found with conventional knee-implant components. Finite Element Analysis is used to evaluate and compare the proposed design of a custom femoral component with a conventional design.</p> <p>Results</p> <p>The proposed design shows a more even stress distribution on the bone-implant interface surface, which will reduce the uneven bone remodeling that can lead to premature loosening.</p> <p>Conclusion</p> <p>The proposed custom femoral component design has the following advantages compared with a conventional femoral component. (i) Since the articulating surface closely mimics the shape of the distal femur, there is no need for resurfacing of the patella or gait change. (ii) Owing to the resulting stress distribution, bone remodeling is even and the risk of premature loosening might be reduced. (iii) Because the bone-implant interface can accommodate anatomical abnormalities at the distal femur, the need for surgical interventions and fitting of filler components is reduced. (iv) Given that the bone-implant interface is customized, about 40% less bone must be removed. The primary disadvantages are the time and cost required for the design and the possible need for a surgical robot to perform the bone resection. Some of these disadvantages may be eliminated by the use of rapid prototyping technologies, especially the use of Electron Beam Melting technology for quick and economical fabrication of custom implant components.</p

Assessment of learning curves in complex surgical interventions: a consecutive case-series study

Background: Surgical interventions are complex, which complicates their rigorous assessment through randomised clinical trials. An important component of complexity relates to surgeon experience and the rate at which the required level of skill is achieved, known as the learning curve. There is considerable evidence that operator performance for surgical innovations will change with increasing experience. Such learning effects complicate evaluations; the start of the trial might be delayed, resulting in loss of surgeon equipoise or, if an assessment is undertaken before performance has stabilised, the true impact of the intervention may be distorted. Methods: Formal estimation of learning parameters is necessary to characterise the learning curve, model its evolution and adjust for its presence during assessment. Current methods are either descriptive or model the learning curve through three main features: the initial skill level, the learning rate and the final skill level achieved. We introduce a fourth characterising feature, the duration of the learning period, which provides an estimate of the point at which learning has stabilised. We propose a two-phase model to estimate formally all four learning curve features. Results: We demonstrate that the two-phase model can be used to estimate the end of the learning period by incorporating a parameter for estimating the duration of learning. This is achieved by breaking down the model into a phase describing the learning period and one describing cases after the final skill level is reached, with the break point representing the length of learning. We illustrate the method using cardiac surgery data. Conclusions: This modelling extension is useful as it provides a measure of the potential cost of learning an intervention and enables statisticians to accommodate cases undertaken during the learning phase and assess the intervention after the optimal skill level is reached. The limitations of the method and implications for the optimal timing of a definitive randomised controlled trial are also discussed

Celecoxib does not appear to affect prosthesis fixation in total knee replacement: A randomized study using radiostereometry in 50 patients

Background and purpose After joint replacement, a repair process starts at the interface between bone and cement. If this process is disturbed, the prosthesis may never become rigidly fixed to the bone, leading to migration—and with time, loosening. Cox-2 inhibitors are widely used as postoperative analgesics, and have adverse effects on bone healing. This could tamper prosthesis fixation. We investigated whether celecoxib, a selective Cox-2 inhibitor, increases prosthesis migration in total knee replacement (TKR)

The effects of exercise and weight loss in overweight patients with hip osteoarthritis: design of a prospective cohort study

BACKGROUND: Hip osteoarthritis (OA) is recognised as a substantial source of disability, with pain and loss of function as principal symptoms. An aging society and a growing number of overweight people, which is considered a risk factor for OA, contribute to the growing number of cases of hip OA. In knee OA patients, exercise as a single treatment is proven to be very effective towards counteracting pain and physical functionality, but the combination of weight loss and exercise is demonstrated to be even more effective. Exercise as a treatment for hip OA patients is also effective, however evidence is lacking for the combination of weight loss and exercise. Consequently, the aim of this study is to get a first impression of the potential effectiveness of exercise and weight loss in overweight patients suffering from hip OA. METHODS/DESIGN: This is a prospective cohort study. Patients aged 25 or older, overweight (BMI > 25) or obese (BMI > 30), with clinical and radiographic evidence of OA of the hip and able to attend exercise sessions will be included. The intervention is an 8-month exercise and weight-loss lifestyle program. Main goal is to increase aerobic capacity, lose weight and stimulate a low-calorie and active lifestyle. Primary outcome is self-reported physical functioning. Secondary outcomes include pain, stiffness, health-related quality of life and habitual activity level. Weight loss in kilograms and percentage of fat-free mass will also be measured. DISCUSSION: The results of this study will give a first impression of potential effectiveness of exercise and weight loss as a combination program for patients with OA of the hip. Once this program is proven to be effective it may lead to postponing the moment of total hip replacement. TRIAL REGISTRATION NUMBER: NTR1053

Contributions of matric and osmotic potentials to the unfrozen water content of frozen soils

Recent reports show that biogeochemical processes continue when the soil is frozen, but are limited by water availability. However, there is little knowledge about the interactive effects of soil and environmental variables on amounts of unfrozen water in frozen soils. The aims of this study were to determine the contributions of matric and osmotic potentials to the unfrozen water content of frozen soil. We determined the effects of matric and osmotic potential on unfrozen water contents of frozen mineral soil fractions (ranging from coarse sand to fine silt) at -7 degrees C, and estimated the contributions of these potentials to liquid water contents in samples from organic surface layers of boreal soils frozen at -4 degrees C. In the mineral soil fractions the unfrozen water contents appeared to be governed solely by the osmotic potential, but in the humus layers of the sampled boreal soils both the osmotic and matric potentials control unfrozen water content, with osmotic potential contributing 20 to 69% of the total water potential. We also determined pore size equivalents, where unfrozen water resides at -4 degrees C, and found a strong correlation between these equivalents and microbial CO2 production. The larger the pores in which the unfrozen water is found the larger the microbial activity that can be sustained. The osmotic potential may therefore be a key determinant of unfrozen water and carbon dynamics in frozen soil. (C) 2008 Elsevier B.V. All rights reserved