Focus on science

From the initial concept to the set of instruments

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By Stefan Saladin, Head of Knee Development, Mathys Ltd Bettlach

The growing success of endoprosthetic operations is based on more than just continuous improvements in implant design. It is first and foremost the user-friendly instruments – the orthopaedic surgeon’s «tools of the trade» – that make the surgical procedure easier and facilitate the use of new surgical techniques. 

Minimally invasive techniques only became mainstream thanks to specially adapted instruments, and only with smart instruments that offer intuitive handling can pre-operative planning can be translated into precise intra-operative procedures. The instruments’ precision and function, as well as their problem-free reprocessing, must be completely reliable over the course of many surgical procedures. 

Before a modern surgical instrument can be used during an endoprosthetic procedure on a patient, however, it must first undergo numerous developmental stages and checks. At Mathys, the process always begins with the question:

What does the user want?  

As a result, the technical concepts for the later instruments are optimised right from the outset in collaboration with clinicians and theatre personnel to ensure their compatibility and practically in the workplace. This initially takes place rapidly and interactively, using instruments generated on 3D printers and on artificial bone in a laboratory setting. Practical ergonomics and operating theatre processes shape the design around the technical requirements of functional elements. After a few prototype cycles, this is how a promising instrument design comes into being.

Over the course of the development of the instruments, aspects such as dimensional stability, optimisation of manufacturability and inherent product safety are refined. This latter aspect means anticipating potential risks associated with their use and constructively implementing risk reduction-measures such as design improvements.

Fig. 1 Ergonomics and 
optimisation of the 
functions of the design 
concept using artificial 



Prototype series put to the test

At this stage, the instruments are produced as a prototype series and then comprehensively tested. If all of the dimensional and geometric specifications are met, each individual function of the instrument is verified under simulated practical conditions. Fatigue and wear tests are carried out and the instruments are artificially soiled and their ability to be cleaned and sterilised is scrutinised. The biocompatibility of all materials and production processes used are confirmed. Packaging is selected that, in turn, is tested for functional integrity with the instruments using transport tests.  

Finally, practical user tests under simulated surgical conditions validate the design concepts. For this purpose, the instruments must be used by clinicians, operating theatre personnel and processing personnel who were not involved in the development process, based on the product information provided. If the instruments can be used intuitively and confidently in line with their intended purpose, and if no problems or safety-related incidents are observed, then their suitability for use is deemed to have been confirmed.

Fig. 2 Stability simulation for the dimensioning of a clamping lever


Fig. 3 Fatigue testing of a locking function on the instrument using a 3D-printed test specimen. Servo motors and software simulate instrument wear over the anticipated instrument lifecycle in the space of a few hours. The functionality must remain unimpaired even after many years of use and re-sterilisation.


Fig. 4 Radionuclide images of an instrument, (a) after artificial soiling with blood and bone dust, (b) after manual pre-cleaning and (c) after final cleaning by machine. The blood tagged with radionuclides emits locally detectable radiation which highlights even microscopically small areas of contamination in areas that cannot be seen with the naked eye. 


Fig. 5 Simulated surgery under realistic conditions, allowing preclinical confirmation of the instrument’s design and intra-operative workflows. The simulation includes a review of the user documentation, the preparation of the instruments by theatre staff, simulated surgery by the clinician and subsequent reprocessing of the instruments.


CE mark as a «birth certificate»  

The tests carried out are evaluated from both a technical and clinical perspective and the results documented. Together with other documentary evidence, they form the contents of the instruments’ technical documentation. This represents an important part of the development of any medical product. Specialists in the regulatory department then ultimately check that the products have been manufactured, checked and have documentation in full compliance with the applicable standards and regulations. If so, then the instruments are given their «birth certificate», the CE mark, and are ready for distribution, user training courses and the first surgical procedures in clinical centres – all for the patient’s benefit.


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