Medical device error

This article discusses principal concepts for the analysis, classification, and reporting of problems involving medical device technology. We define a medical device in regulatory terminology and define and discuss concepts and terminology used to distinguish the causes and sources of medical device problems. Database classification systems for medical device failure tracking are presented, as are sources of information on medical device failures. The importance of near-accident reporting is discussed to alert users that reported medical device errors are typically limited to those that have caused an injury or death. This can represent only a fraction of the true number of device problems. This article concludes with a summary of the most frequently reported medical device failures by technology type, clinical application, and clinical setting.     

Emergency Department Visits for Home Medical Device Failure during the 2003 North America Blackout

OBJECTIVES: During a widespread North American blackout in August 2003, the authors identified a cluster of patients presenting to their northern Manhattan emergency department (ED) with complaints related to medical device failure. The characteristics of this group with respect to presenting complaint, type of device failure, time spent in the ED, and disposition are described in an effort to better understand the resource needs of this population. METHODS: This was a retrospective chart review for all patients evaluated in an urban teaching ED during a 24-hour period spanning the duration of regional power failure. Charts for patients presenting with medical device failure as part of their triage complaint were abstracted. RESULTS: Twenty-three of 255 patients coming to the ED during the 24-hour period presented with medical device failure. Nineteen of the device failures were due to nonfunctioning oxygen conservers, three to ventilator failure, and two to airway suction device failure (one patient had two devices fail). Thirteen of these patients were admitted to the hospital and accounted for 22% of all admissions during the study interval. Discharged patients spent a mean of 15.1 hours (range: 3.8-24.4 hours) in the ED. CONCLUSIONS: Patients using electrical medical devices seek care in the ED when power failure occurs, and they require significant ED and hospital resources. Effective disaster planning should anticipate the needs of this population.     

Increasing bending strength of tibial locking screws: mechanical tests and finite element analyses

BACKGROUND: Healing of tibial fractures treated by locked nailing is threatened by locking screw failure. However, the effects of the design factors of the screws on their mechanical strength have rarely been studied. METHOD: Three-point bending tests and finite element analyses were used to investigate the bending strength of five types of commercially available tibial locking screws and two types of specially designed screws. Yielding strength and fatigue life measured in bending tests were correlated to total strain energy and maximal tensile stress computed in finite element analyses. Parametric analysis and design optimization were done according to the Taguchi method. Validation studies to assess the stress rising effect of the threads on the fatigue strength were conducted in two types of new screws made of either stainless steel or titanium alloy. FINDINGS: The yielding strength of the screws was closely related to their total strain energy, and the logarithm of the fatigue life was closely related to the maximal tensile stress with correlation coefficients of -0.95 and -0.90, respectively. Parametric studies indicated that fatigue strength of the screws was affected mainly by inner diameter (contribution, 63.8%) and root radius (27.8%). The yielding strength was determined primarily by inner diameter (88.5%). Titanium screws had a longer fatigue life than stainless steel screws, especially in screws with larger root radii. INTERPRETATION: A screw's strength is closely related to its design factors. Finite element models, which can reliably reflect the mechanical strength of screws can save time and effort during screw design. Larger root radius can effectively improve the fatigue strength, especially for titanium screws as compared with stainless steel screws.     

A short plate compression screw with diagonal bolts--a biomechanical evaluation performed experimentally and by numerical computation

INTRODUCTION: Decreasing the length of the side plate of the dynamic hip screw would theoretically allow a smaller surgical incision, a shorter surgical time, decreased operative blood loss and minimal periosteal stripping. A new design of a very short plate dynamic hip screw based on two diagonal screws has been developed. Our study compares the new design and the four-hole side plate in respect to mechanical properties and bio-mechanical outcomes utilizing the Finite Element Analysis method. METHODS: Four pairs of fresh frozen cadaveric femora were extracted from male corpses aged 25-43 years (mean 34.8). One femur of each pair was fixated by means of the new system and the other by means of the conventional design. Mechanical loading was applied to all four pairs. The decline which occurred during the periodical loadings and the breakage loads of fixated bones were measured. Mechanical performance and probability of failure was assessed by conducting a mathematical analysis using the finite element method. FINDINGS: The average deflection under excessive cyclic loading was 33% higher in the bones fixated with the very short plate-dynamic hip screw device than in those fixated with the conventional dynamic hip screw. The average load failure during the collapse-loading test was 3120N for the very short plate-dynamic hip screw as compared to 4160N for the regular device. Mechanical testing did not provide decisive results regarding failure. The mathematical analysis performed indicated that the maximal stress in the very short plate-dynamic hip screw reached values 3-4-fold higher than in the regular dynamic hip screw. INTERPRETATION: Although the new design offers a minimally invasive approach to subtrochanteric femur fracture fixation, it was found to have insufficient biomechanical performance resulting in high probability of mechanical failure. The authors believe that the finite element method may have the potential to serve as an additional clinical tool for performing surgical preplanning and assist in decision making.     

Bioengineering considerations in the prevention of medical device-related pressure ulcers

BackgroundIn recent years, it has become increasingly apparent that medical device-related pressure ulcers represent a significant burden to both patients and healthcare providers. Medical devices can cause damage in a variety of patients from neonates to community based adults. To date, devices have typically incorporated generic designs with stiff polymer materials, which impinge on vulnerable soft tissues. As a result, medical devices that interact with the skin and underlying soft tissues can cause significant deformations due to high interface pressures caused by strapping or body weight.MethodsThis review provides a detailed analysis of the latest bioengineering tools to assess device related skin and soft tissue damage and future perspectives on the prevention of these chronic wounds. This includes measurement at the device-skin interface, imaging deformed tissues, and the early detection of damage through biochemical and biophysical marker detection. In addition, we assess the potential of computational modelling to provide a means for device design optimisation and material selection.InterpretationFuture collaboration between academics, industrialists and clinicians should provide the basis to improve medical device design and prevent the formation of these potentially life altering wounds. Ensuring clinicians report devices that cause pressure ulcers to regulatory agencies will provide the opportunity to identify and improve devices, which are not fit for purpose.     

Design of a custom racing hand-cycle: Review and analysis

Purpose. This paper describes the design, manufacture and evaluation of a custom hand-cycle with a Delta-style frame and fork steering. The state of hand-cycle design and future design directions are also examined.

Method. The design of the custom hand-cycle was based on these criteria: Light weight, aerodynamics, climbing ability, ergonomic fit and the user's specific needs. We designed and built a custom hand-cycle for one expert user, therefore, the user's personal needs were key design drivers. The hand-cycle was evaluated by the user over three years of use.

Results. During three years of evaluation and over 8000 km of use there were two frame failures: (i) A crack propagated around one of the tubes connecting the mainframe tube to the headset tube; and (ii) a crack propagated around the circumference of the curved part of the main frame tube directly behind the seat. The first failure was repaired and after the second, the device was retired. The evaluation of this design serves as a basis for a new set of design criteria.

Conclusions. Large amounts of frame flexion can indicate eventual plastic deformation and failure. Future hand-cycle designs should see the use of more advanced materials, finite element analysis software, and continued incorporation of bicycle technology and design innovation.     

有限元分析Ilizarov技术对肘膝关节屈伸挛缩畸形矫正器作用的机制

背景：目前国内外鲜见采用有限元法分析Ilizarov技术在骨科疾病肢体延长及对关节挛缩外固定器的作用机制。目的：利用三维有限元分析Ilizarov技术对肘膝关节屈伸挛缩畸形矫正器的作用机制。方法：利用Ilizarov生物学理论设计出的符合人体生物力学特性和可以广泛应用于临床的关节挛缩矫正器。通过三维有限元分析应用Ilizarov技术在肘膝关节屈伸挛缩畸形矫正器设计中的力学有效性和科学性。结果与结论：建立了几何外型逼真、生物力学特性全面的肘膝关节三维有限元模型。通过三维有限元模型及力学分析计算出各组织包括骨与软组织的弹性模量和泊松比等力学指标,可通过施加关节挛缩矫正器的载荷分析其关节内、外的应力-应变分布及变化情况。Ilizarov技术可对肘膝关节挛缩畸形矫正器的设计与优化改良提供理论依据,利用有限元力学分析揭示了肘膝关节屈伸挛缩畸形病变组织结构的生物力学变化中的机制。     

数字化医学技术与脊柱外科的临床应用

背景：随着现代科学技术尤其是计算机技术和医学技术的迅猛发展,现代脊柱外科进入了一个崭新的时代,呈现出数字化、个性化、显微化、精确化和人工智能化的发展趋势。 目的：探讨数字化技术在脊柱外科中的应用研究进展。 方法：义乖检索词为“脊椎（spine）：腰椎（1umbar）;颈椎（cervical）;数字化（digitization）;脊柱外科（spinaIsurgery）;数‘弘骨科学（digitalorthopedics）;订限元模型（thefiniteelementmodel）：计算机辅助设计（computerassisteddesign,CAD）;微创技术（minimallyinvasivetechnology）;二维重建（threedimensionsreconstruction,3D）：CT：磁八振成像（MRI）：计锋机仿真（computeremulation）;内窥镜（endoscope）：椎间柱（intervertebraldisc）：绛戍内窥镜激光椎间鼎切除术（percutaneousendoscopiclaser-assisteddiscectomy,PELD）”,对有限元、计算机导航技术、微创技术以及医学影像在脊柱外科中的应用文献进行深入分忻,探讨数字化脊柱外科手术的特点,临床效果以及安全性。结果与结论：数字化医学在有限元模型、计算机导航技术、微创技术、医学影像等领域研究进展的基础上,建立独特的脊柱外科新方法,并将其广泛应用于临床骨科。有限元模型最大的优势在于町以反映集体内部的应力变化情况,有限元分析应用于医学生物力学后,取得了很_人的进步与发展。计算机导航技术的：【作原理是利用数字化影像信息通过媒介体输入计算机工作站,经运算处理后重建三维模型影像,通过相关软件,在此影像基础上进行术前计划并模拟进程,通过高解像度的显示屏从各个方位观察到当前的手术入路以及各种参数,完成微创手术。微创脊柱外科采用微小切口或穿刺通道,运用特殊的器械或装置在影像仪器监视下或导航技术的引导下进行于术。医学影像分析作为信息科学技术为基础的交叉学科研究,对脊柱外科的临床诊断和观察具有参考价值。数字化医学高效率、高精度、二维立体地了解疾病的分布、形态、结构,最大程度减少手术创伤,在脊柱外科应用中的前景广阔。     

Learning from adverse incidents involving medical devices

While an adverse event involving a medical device is often ascribed to either user error or device failure, the causes are typically multifactorial. A number of incidents involving medical devices are explored using this approach to investigate the various causes of the incident and the protective barriers that minimised or prevented adverse consequences. User factors, including mistakes, omissions and lack of training, conspired with background factors--device controls and device design, storage conditions, hidden device damage and physical layout of equipment when in use--to cause the adverse events. Protective barriers that prevented or minimised the consequences included staff vigilance, operating procedures and alarms.     

Recovery of pacemakers and defibrillators for analysis and device advance directives: electrophysiologists' perspectives

Background: Following high‐profile device failures, the Heart Rhythm Society emphasized the need for postmarketing surveillance by recommending that physicians return all explanted devices to the manufacturer for analysis. Methods: We conducted a national survey of electrophysiologists (EPs) regarding recovery for analysis of explanted pacemakers and implantable cardioverter defibrillators (devices), and attitudes toward device‐specific advance directives to facilitate return of devices. Online survey invitations were sent in four waves from December 2008 to June 2009 to 300 e‐mail addresses from the Heart Rhythm Society member database. Results: From 250 invitations, there were 95 responses (38%). Demographics included average age 50 years (range, 31–87); 95% male; 81% Caucasian. Only 23% reported returning all explanted devices to the manufacturers. Of all the respondents, 32% discarded >10 devices/year as medical waste, 42% stored devices in a box in the electrophysiology lab, and 10% donated at least 1 device/year to charity for reuse overseas. Sixty‐seven percent felt that it would not be helpful to have an advance directive specifying what the patient would want done with their device postmortem. Conclusions: Few EPs return all explanted devices or send interrogation reports to the manufacturers, though nearly all said it was easy to do so. A majority either dispose of explanted devices as medical waste or store them in laboratories or offices, and a small percentage donate for reuse in underserved nations or to veterinary hospitals. This study suggests a need for initiatives such as educational campaigns to increase the retrieval and return of devices, either for analysis or reuse. (PACE 2011; 659–665)     

A surgical simulation system of skin sutures using a three-dimensional finite element method

OBJECTIVE: To establish a surgical simulation system of skin sutures using a three-dimensional finite element method. DESIGN: Three-dimensional finite element models were developed from point data obtained with a rapid three-dimensional surface-measuring device and postoperative profiles were evaluated using these models. BACKGROUND: Since suturing a wound may result in undesirable skin extrusion, it is important to make the extrusion as inconspicuous as possible. We have investigated a means of determining appropriate suture methods to decrease the extrusion. METHODS: Affected body parts were measured non-invasively with a rapid three-dimensional surface-measuring device. Finite element models were prepared, and an appropriate method for reducing skin extrusion was evaluated by attempting various suturing methods. RESULTS: Two kinds of finite element models were prepared: a conventional spindle model and a modified S-shape model. The height of the extrusion of the modified S-shape model was decreased by 40% in comparison with that of the spindle model. These results agreed with clinical findings. CONCLUSIONS: Due to this surgical simulation system of skin sutures, with a rapid three-dimensional surface-measuring device and three-dimensional finite element analysis, it was possible to design an appropriate suturing method and to evaluate the postoperative skin profiles. The modified S-shape suture method would be a recommendable method. RELEVANCE: Using this surgical simulation system of skin sutures, a surgeon can evaluate an appropriate suturing method before operation. It is expected that this system will reduce a surgeon's labor.     

Role of the industry sponsor: protection of human subjects in early device-application studies

Industry sponsors face unique challenges when designing early studies of the application of medical devices studies for disease states in which standard treatments are ineffective. Although accountability for the protection of people who volunteer for these important research studies is shared by industry, investigators, regulators and institutional review boards, industry must play a principal role in balancing the goals of science, medicine, and regulatory approval. From an industry perspective, subject protection is predicated on an understanding of the disease state to be studied, predicting the potential effects of therapy with a particular device on disease, ethical study design, and compliant study conduct in accordance with recognized regulatory standards. Long-term planning and methodical approaches in the design of studies of early application of medical devices can mitigate conflicts of interest or improper research oversight that could result in harm or injury to study subjects.     

Fatigue failure in the cement mantle of an artificial hip joint

The cement mantle of an artificial hip joint was retrieved, largely intact, during a revision operation, and subjected to detailed failure analysis. The results reveal a number of features which are important to our understanding of the failure of bone cement in situ and its consequences for prosthesis loosening. Microscopic examination showed clear evidence of fatigue cracking in the mantle prior to removal. This took the form of worn areas in certain regions of the fracture surfaces, which elsewhere showed evidence of rapid, brittle fracture. The mantle contained two large defects which had been introduced during insertion; fatigue was shown to have originated both from these defects and from the proximal surface. Results from a finite element analysis were used, together with the techniques of fracture mechanics, in an attempt to explain the magnitude and direction of fatigue cracking. Fracture mechanics calculations, though subject to some uncertainty in this case, indicate that the local stress intensity in the region of the principal defect would have been sufficient to exceed the threshold for fatigue crack propagation in this material. This approach demonstrates the advantages of this 'defect-tolerance' analysis.     

Device and equipment evaluations

Device evaluation, which is an essential skill set for the respiratory therapist, ranges from comparing manufacturer's specifications to comprehensive device testing, either with patients or on the bench. Good device evaluations help guide decisions about device selection, procedure development, and risk and failure analysis. Poor evaluations cost time and money and fail to return value. Manufacturer's specifications alone are poor criteria for device selection, because of how and why those specifications are created and the potential gap between the manufacturer's test methods and the complexity of clinical situations. Proper clinical evaluation of devices with patients requires extensive preparation and resource expenditure, and clinical evaluations may not allow isolating key variables to determine specifics of device performance. In vitro testing, using models to simulate discrete components of device/patient interface, is less expensive and easier to conduct. This article discusses the process of experiment design and model development for device and equipment evaluations.     

Mechanical conditions in the internal stabilization of proximal tibial defects.

OBJECTIVES: The goal was to design a method which would permit an assessment of the suitability of a newly developed implant under physiological-like loading conditions. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to clinical utilization. DESIGN: In vitro mechanical stiffness testing and finite element analysis. METHODS: From in vitro testing of proximal tibiae with defects, the stiffness of an internal stabilization system was determined. Using a finite element model, the loading of both the implant and bone was analyzed including all muscle forces. The variation in implant loading and interfragmentary strain for different defect locations was also investigated. RESULTS: Conventional stiffness testing demonstrated the comparability of the experimental findings with the finite element predictions. Under physiological-like loading the implant experienced high bending and von Mises stresses if defects in the region of the shaft were stabilized. A short working length increased implant loading up to the yield strength of the material. CONCLUSIONS: The finite element analysis illustrated the appropriateness of this new device for proximal defects of the tibia, but the implant should be used with hesitation in fractures or defects extending into the diaphyseal region of the bone. RELEVANCE: This new analytical approach helped to identify clinical indications for the implant in which its mechanical attributes would prove advantageous.     

Fatigue resistance analysis of tibial baseplate in total knee prosthesis--an in vitro biomechanical study

BACKGROUND: Tibial baseplates were occasionally reported with clinical fatigue failures. This study postulated that tibial baseplate of a specific mobile bearing design with a uniform thickness across the baseplate offers more fatigue resistance than the fixed-bearing design. Tibial baseplates of a fixed bearing and a mobile bearing design were fatigue-tested in vitro to study their fatigue resistance. METHODS: Five samples of each design were tested under a sinusoidal loading between 90 N and 900 N at 30 Hz till failure or 10 million cycles. Experimental setup followed a standard published test method. Scanning electron microscope was used for inspecting the fracture surface of the failed baseplate. FINDINGS: Two baseplates of fixed bearing design failed before 10 million cycles. Fatigue crack advancement marks were visible on the fractured surface of the failed samples. The fractured cross-section showed that the failure started near the end of the fin, it was likely due to the stress concentration as stress singularity existed at a point of sudden geometrical change. Five mobile bearing baseplates passed the test. Design of the tibial baseplate without fin structure and with a uniform thickness across the whole baseplate could help reducing the incidence of fatigue failure. INTERPRETATION: The prosthesis survival rate was influenced by the long-term integrity of the metallic part of the prostheses such as the tibial baseplate. This study revealed that the tibial baseplate of a mobile bearing design with a uniform thickness provided better fatigue resistance than fixed bearing one. Standardized fatigue screening of the tibial baseplate was considered important in designing knee prostheses.     

Fatigue-life of two manual wheelchair cross-brace designs.

OBJECTIVE: To compare the durability of two designs of cross-braces for folding manual wheelchairs and to determine the nature of wheelchair cross-brace failures. DESIGN: Fatigue testing of two folding wheelchair cross-brace designs (one with a rectangular cross-section and the other with a circular cross-section). A total of 20 cross-brace pairs were tested. RESULTS: The cross-braces with a circular cross-section endured a mean +/- SD of 100,159 +/- 45,814 cycles before experiencing a fatigue failure, whereas the cross-braces with a rectangular cross-section endured an average of 261,254 +/- 160,741 cycles. A t test showed significant differences (p = .01) in fatigue-life between cross-braces with a circular cross-section versus cross-braces with a rectangular cross-section. All 20 cross-braces experienced similar fatigue failures that would develop at the bolt hole where the two cross-braces connect to form a hinge. CONCLUSION: The results suggest that the rectangular cross-brace design has a longer fatigue-life than the circular cross-brace design. People should regularly inspect the cross-brace for cracks. The area around the bolt forming the hinge should be inspected carefully. If a crack is observed, the cross-brace should be replaced immediately.     

Comparison of the diagnostic characteristics of two B-type natriuretic peptide point-of-care devices

Background

B-type natriuretic peptide (BNP) is used to diagnose heart failure (HF).

Objective

To compare the accuracy of two commercially available point-of-care (POC) devices for measuring B-type natriuretic peptide (BNP) in emergency department (ED) patients with suspected heart failure using the central laboratory testing results as the criterion standard.

Methods

Venous blood samples were collected from adults with suspected heart failure and split into three samples for BNP analysis: central laboratory (Siemens ADIVA Centaur; Siemens, Deerfield, IL), Triage BNP POC device (Biosite, San Diego, CA), and i-STAT BNP POC device (Abbott, East Windsor, NJ). The criterion standard for BNP levels was the central laboratory.

Results

Two hundred fifty patients were enrolled. Mean (SD) age was 70.7 (13.8) years; 200 (80%) were over age 55 years; 146 (58.4%) were male. A final hospital discharge diagnosis of heart failure was made in 108 (42%) patients. The i-STAT system yielded a result within a median of 9 min (interquartile range [IQR] 9–10 min). The Triage device yielded a result within a median of 19 min (IQR 15–22 min); p < 0.001. The device failure rate for the central laboratory (8 failures, 3.2%) was significantly higher than that of the i-STAT device (1 failure, 0.4%, p = 0.04), but not statistically different than the Triage device (3 failures, 1.2%). Neither the Triage nor the i-STAT were statistically different than the central laboratory result in terms of sensitivity; the i-STAT was less specific than the Triage result (p = 0.003). The area under the curve for the Triage device was 0.95 (95% confidence interval [CI] 0.91–0.98), whereas the area under the curve for the i-STAT device was 0.98 (95% CI 0.96–0.99; p < 0.01).

Conclusions

Both POC devices tested were accurate and rarely failed; however, the i-STAT was faster with single use.     

Critical assessment of new devices

Medical devices are one of the most highly regulated products in the world. Despite this, there is an unacceptable rate of medical error. Not solely due to the device, but also the user and/or system in which it is used. The current approach to testing of medical devices must be progressed so the concept of user beware is changed to user be aware. All health professionals should be well informed as to the various aspects of each new device. Also, testing in research facilities that are equipped with qualified personnel and the proper testing methods should be supported. The outcome of good research then can be translated into good practice. This implementation requires constant communication for quality improvements from and to professional committees, educational leaders, and experts in the field. Medical devices are thoroughly tested before they are marketed, but we, as clinicians and users, must continuously examine and improve the design of equipment, procedures, personnel, and the environment in which we work to optimize medical systems. Once the device is on the market, changes or modifications are costly. Finally, a factor for success in critical testing of new devices is not what is technically possible, but rather making a concrete contribution to improving medical problems.     

Unexpected ICD pulse generator failure due to electronic circuit damage caused by electrical overstress

Because it is a lifesaving device, the unexpected failure of an ICD can be catastrophic. We report ICD electronic circuit failure due to electrical overstress damage (EOS) to the high voltage hybird circuit and other electronic components in a series of ICD pulse generator models. Data were obtained from the Multicenter Registry of Pacemaker and ICD Pacemaker and Lead Failures, and from the manufactures' adverse event reports, that were in the FDA's Manufacturer and User Facility Device Experience (MAUDE) database. Of 16 nonbattery Guidant/CPI ICD pulse generator failures reported to the registry, 6 (38%) have been confirmed by the manufacturer to be EOS related, and Guidant/CPI has reported 273 such failures to the FDA as of 12/29/00. The signs of failure included loss of telemetry and inability to deliver therapy, and some patients have experienced serious adverse events. Hybrid circuit damage may have occurred during capacitor charging or reform, and the majority appears to have happened during normal ICD function. While the incidence of this problem is unknown, a management strategy should be adopted that includes routine follow-up every 3 months and device evaluation after a shock or exposure to external defibrillation or electrosurgical devices. This study suggests that additional data are needed to determine the incidence of this problem, and that our present methods for monitoring the performance of ICD's following market release are inadequate.