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Risk management of Nitinol gripping plate
Jul 21, 2018

Nickel-titanium alloy is a kind of shape memory alloy. Its expansion ratio is over 20%, fatigue life is up to 1×107, damping characteristic is 10 times higher than that of ordinary spring, and its corrosion resistance is better than the best medical stainless steel. Therefore, it can meet the application needs of various engineering and medicine, and is a very excellent functional material. In addition to its unique shape memory function, memory alloys are also resistant to wear, corrosion, high damping and superelasticity. It also meets the requirements of chemical and biological aspects, namely good biocompatibility. Nitinol forms a stable passivation film with the organism. Therefore, nickel-titanium alloy has been developed into many medical device products. Most of the medical device products that have been developed and put into market application are more than two or three types of medical devices, some of which are implanted in the human body, and are placed in the body for comparison. Long, so risk management of Nitinol products is particularly important. Risk management of its products will be carried out in accordance with the requirements of medical device risk management standards and procedures.


1. Determination of the intended use and safety characteristics of Nitinol gripping bone plates

Intended use: It is mainly used for internal fixation of fractures in patients with bone injuries, helping patients with early healing and functional exercise. Nickel-titanium alloy gripping plate is a new type of internal fixation device for tubular bone fractures of extremities. It uses the shape memory effect of Nitinol to realize the circumferential circumferential embracing and fixing mode of the limbs. The advantage is that the operation is convenient. Simple; fixed holding is firm and reliable, in line with AO and BO fixation theory; the material has good biocompatibility and is an ideal internal fixation implant material. The product is provided to the user in a non-sterile state. The hospital doctor organizes the disinfection before the operation, and expands the arms around the ice under the salt water to make it larger than the outer diameter of the bone, so as to be easily inserted into the fracture, after adjustment and resetting, Heating with warm salt water causes the embracing arm to return to hold. This product is a one-time use, which can effectively avoid cross-infection between patients.

Second, the judgment of visible or potential harm

After preliminary analysis, the relevant potential hazards are judged as follows: (1) Damage to the patient: bacteria, causing pyrogen reaction or infection, and serious death. Improper selection of the model results in unreliable fixation and secondary fractures. After being loaded into the human body, it is repeatedly adjusted to cause the function of the product to be lost. The microcrack defects in the finished product cause crack propagation after the patient is loaded, causing failure. The doctor did not follow the steps and forced the deformation, resulting in incomplete shape recovery and failure. The patient did not follow the doctor's postoperative training, premature weight bearing, causing fatigue and fracture of the device, causing bone deformity to heal. Due to the thin wall of the material of the device or the insufficient strength of the material, the patient's end function is restored, causing fatigue deformation of the device, causing bone malformation or false healing. The device's functional temperature setting is inaccurate, causing premature shape recovery or slow shape recovery, causing surgical delays. (2) Damage to the user: The tines are too sharp to scratch the patient's tissue or the operator's hand. Insufficient equipment for taking out the equipment, causing cumbersome secondary removal. The device has no memory function and cannot be used normally. The memory function of the device has been vandalized and cannot be used normally. Hazards associated with use, resulting in incorrect use.

Third, the risk assessment

The degree of damage to the bone plate can be defined as four levels.

Judgment of the potential cause of each damage: During normal operation of the doctor, the tool and the instrument should be in constant contact to facilitate adjustment and reset. The metal surface may be scratched and does not affect normal use. The instrument is a hoop arm structure, and a claw is added to the hoop arm, and the claw portion is conveniently set for entering the bone surface. There is a claw tip at the time of production and processing, and how much affects the individual length, but does not affect the use. Improper selection of specifications results in unstable instability or shedding, resulting in incomplete healing and malformation. This problem can be solved by using the instructions and training instructions. Such problems are unavoidable in metallic materials, but the incidence is extremely low. There is no statistical data available, and ultrasonic secondary testing can be used to reduce the risk to acceptable levels.

The probability classification criterion can be determined according to qualitative (semi-qualitative) and divided into the following six levels.

Fourth, take risk control measures

The measures that must be taken to reduce the risk are: the qualification verification of the material supplier. Raw material factory certificate and warranty. Inspection report and third party verification report. The surface marking of the board. Double-sided inspection of each in-stock sheet with a coverage of 100%. Repeat the inspection of the panel in question, and identify the defective area with a red pen and record it. In the production process, control and labeling are carried out according to the operation instructions for traceability. In the brightening process, use a 5 times magnifying glass to check one by one, to prevent defective products from flowing into the subsequent process. In the product packaging or instructions for use, the use of the product, step by step, and use warning instructions. The sales staff should repeat the explanation and essential guidance before the operation, and ask the experienced doctor to be the main surgeon; for the inexperienced physician, it is best to arrange the on-site teaching and demonstration of the company's guidance physician. Before the operation, the X-ray film should be measured with a steel ruler, and the error should be taken into account. Select the bone plate with the smaller size than the bone for the first use. At the same time, prepare a bone plate with the same bone size for spare, and disinfect the two pieces at the same time. After the surgical incision is made, the damaged bone is measured with a caliper. If the size measured by the X-ray film is the same, the smaller one is used; if the measured is larger than the X-ray, the larger one is selected. Place the two bone plates in the prepared ice brine at a temperature of <5 °C. According to the measured results, the small bone plate was selected and used in the ice salt to spread it to the prescribed size (greater than the outer edge of the damaged bone). And the amount of deformation cannot be greater than 8%. The operating doctor uses a clamp to grasp the bone plate and quickly move it to the affected bone for placement and positioning. After the adjustment and resetting is completed, the bone plate is heat-applied with a hot temperature of about 40 ° C or gauze. The plate is affected by temperature, resulting in memory recovery, and the bones that hold the fracture. If it is found that the partially damaged bone is not in the clamping arm of the bone plate or the overall fixation is not perfect, the bone plate can be cooled again, and then the arms are opened with pliers to adjust an angle. During the placement process, the doctor should avoid barbaric operation and forced deformation during operation.

Through each of the above links and details, the risk level can be controlled and reduced. Compared with other similar operations, the risk is smaller. From the acceptable side, the advantages and benefits are far higher than the risk. It is acceptable. .

V. Risk Management Report

From the overall analysis of potential risks, it can be prevented in the process of product processing. No new risks are generated after taking measures. Therefore, the above risks are acceptable to patients, and clinical use is safe and reliable, and users can use them with confidence.