Design Process and Route to CE Marking

The design process for any medical device first begins with identifying what the device’s function will be and the safety requirements for the device. This is to ensure that the device is actually necessary and thus will be useful once made. In this case, the device to be developed is an orthopaedic screw that will be used in vivo and may remain inside the body after installation.

In order to ensure high standards of safety are maintained, there are a number of rules that are used to categorize devices by order of potential risk to the user into 4 different classes. The Classes are Low Risk (I), Medium-Low Risk (IIa), Medium-High Risk (IIb) and High Risk (III). The Medical Devices Directive (MDD) which came into effect on 1st January 1995, and is recognized all across Europe, developed this classification system based on the properties, function and intended purpose of a potential medical device.

There are 18 rules that assist project designers in classifying the designs they make. Part of Rule 8 which states that “All implantable devices and surgically invasive devices for long-term use to which no other rule applies: IIb” can be used to classify an orthopaedic screw as Class IIb (Medium-High Risk)

For all but Class I devices a QMS based on ISO9000 is required. These standards are set by international bodies such as ISO and IEC and are reviewed through rigorous process to keep them up to date. In knowing the classification of the device to be designed the safety requirements can be adjusted and considered all through the design process.

Design ProcedureThe design process of an implantable device like an orthopaedic screw involves a number of key stages summarized in the Figure 1 below, but expounded on afterwards.

Figure 1: Application of Design Controls to Waterfall Design Process (figure taken from FDA and Health Canada documentation).

In order to design a new device, the minimum requirements that the device has to achieve are defined. These requirements are set based on the functionality of the device, the user’s input and safety standards in order to minimize risk. For an implantable device, like the orthopaedic screw, there are basic requirements such as, it must be tolerated in the body with no short term or long term adverse effects, it must function without failure for the lifetime of its usage, it must be designed for accurate and reproducible insertion and it must be of acceptable cost. The device must also adhere to MDD and FDA approved standards in order to be marketable in Europe and America, respectively.

Design and developmental planning is the first step. In most cases it is useful to assemble a team of people with knowledge on the device type and designate a team leader to keep the team on track. In doing so, establishing a system of communication so that the team can share information as the development proceeds, is useful. Next, establish a basic plan with design activities listed and estimate deadlines for each design stage. Each stage will require review, verification, and validation and details of how these will be done should be stated. Assign team members or groups of team members’ responsibilities for different design activities. This is a basic overview of a plan but plans are documented, approved, reviewed and constantly updated as the design process continues.

Design input is the next stage and this is where the actual ideas for the new design a put forward. The collection of these ideas may occur during a brainstorming session will all or some of the team members. The team leader is helpful at this point to keep the ideas realistic and in line with the requirements.

At the end of the session a few ideas are decided on that are developed further into drawings, specifications, procedures, reports. Any form of these outputs can be used and they show the specific characteristics of the product, provide information on additional functions and reference the acceptance criteria. All outputted designs are reviewed prior to their release to ensure they meet the initial set requirements.

The design is then reviewed by the entire team, a specialist on the device, and an independent reviewer. This formal review is run through each stage of development to ensure the outputs meet the required inputs and to identify any issues with the design and deal with them.

Verification is to ensure planned outputs meet inputs and validation is to ensure that the design product meets the required specification for its intended use. Verification is done all throughout the design process, validation is done before product delivery, on initial production batches, and includes testing under actual/simulated conditions and includes a risk analysis.

After the design has been decided on and passed all the requirements, verifications, validations, and has been approved by the relevant regulatory bodies it may undergo production. Design transfer ensures that the design is correctly translated to the production specifications. A design history file is kept on the device as proof that it was developed according to the approved design plan.

Another crucial part of the design procedure it to perform a risk management to ensure the device poses minimal risk to the operator(surgeons) and the user(patients) . First a risk assessment is performed to identify potential hazards as a result of using the device, then a risk evaluation is performed which involves FMEA. Failure Modes and Effects Analysis ( FMEA) is a process that begins at the earliest stages of design and proceeds throughout the design procedure. Failure Modes identifies the possibilities of failure within the device during its lifetime and with regular use whereas Effects Analysis details the consequences of these potential failures. FMEA failures are prioritized based on how often they occur, how easily detectable they are, and how serious the failures are. FMEA documentation is continuously updated and documented.

The design process of an implantable device like an orthopaedic screw involves a number of key stages summarized in the Figure 1 below, but expounded on afterwards.

The desing process is a part of product development to see the device designed deciding on a time frame for the design to be complete, appointing a team of people with knowledge on that device and then defining the stages of the design.