Sergio A. Puigcercer Palau1; José María Baydal Bertomeu1; Paola Piqueras Fiszman1; Carolina Soriano García1; Jordi Uriel Moltó1; Joan Requena Miró1; Daniel Iordanov López1; Ignacio Bermejo Bosch1y2; Leopoldo Fernández Barrachina3; Pedro Fernández Barrachina3; Gabriel Gallego3; Laura Martínez Gómez1
(1) Instituto de Biomecánica (IBV) Universitat Politècnica de València (Edificio 9C) Camino de Vera s/n (46022) Valencia (Spain)
(2) IBV’s Healhcare Technology Group. CIBER in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN)
(3) EMO - Especialidades Medico Ortopedicas
The orthopedics sector is increasingly demanding and competitive. Patients suffering from osteoarthritis need solutions that improve their personal autonomy and mitigate the effects of the disease without losing autonomy and life quality. EMO and IBV have designed and developed a new generation of knee orthoses that adapt to the anthropometry and biomechanics of the users, considering the context of use, usability and the needs and preferences of both users and professionals. In order to achieve such an advanced solution, a multidisciplinary team and various laboratory studies were necessary to define the user-centered design and the development process.
Knee osteoarthritis is a chronic and degenerative pathology that is considered as one of the main causes of disability in the world. Its onset is associated with the progressive deterioration of the articular cartilage, tissue responsible for the proper cushioning and functioning of the joints. When it starts to disappear, the bone ends begin to rub against each other, and they are consequently damaged, deformed and even become fractured. Knee osteoarthritis causes intense pain when moving and stiffens the affected joint; therefore, the patient's mobility is clearly reduced.
In Spain, knee osteoarthritis affects 10.2% of the adult population (especially those over 55 years); around 6.4 million people.
To the problems associated with knee osteoarthritis already mentioned, the typical limitations of the elderly must be added: limitation of movement capacity, endurance and muscle tone, more variable anthropometric characteristics, greater tendency to suffer skin problems due to continuous high pressures, and lack of skills when interacting with products.
Knee osteoarthritis is a degenerative pathology whose process cannot be reversed. Therefore, the treatments are preventive, palliative, surgical or to slow down the progression of the illness. Such treatments include orthotic solutions, which are used as mechanical support for the joint to fix and correct the possible misalignment of the load axis of the lower limb so as to move the pressure towards the bone area that is less damaged, thus avoiding the more deteriorated area. In this way, pain is reduced, and the degenerative advance slows down, delaying or avoiding more drastic treatments such as surgery.
Currently, there are many knee orthoses on the market. Most of them include mono or polycentric joints, which do not adapt well to the natural knee flexion movement. The difference between the displacement curve of the orthosis and that of the knee during the flexion movement causes relative displacements between the joint and the fixations of the orthosis, which usually involves discomfort, skin chafing and even overloads on the knee itself.
The solution to these problems must be sought in gait biomechanics. The trajectory of the instant center of rotation during the knee flexion movement requires a multi-center joint, which can be adjusted to the natural pattern of knee movement.
Especialidades Médico Ortopédicas (EMO) and Instituto de Biomecánica (IBV) have collaborated in a research and development project to create a new concept of orthosis for knee osteoarthritis that, based on the participation of users and professionals in the design, combine biomechanical and anthropometric knowledge, as well as emotional and usability aspects.
Co-creation with users and professionals: conceptual design
The co-creation methodologies take into account the sensitivity of all the actors involved in the value chain (prescriber, manufacturer, distributor and user). It is the most effective way to identify the pains of the existing solutions and to detect non-apparent improvement opportunities.
The first phase of the co-creation process of this new knee orthosis was to identify emotional and functional requirements of both professionals and end users.
For this, a group dynamic included 9 experts from different fields related to knee osteoarthritis: traumatologists, rehabilitators, physiotherapists and orthopedists, as well as representatives of the EMO manufacturing company, all of whom were essential for the development of the new orthosis (Figure 1). The collaboration of these participants was possible thanks to the IBV extensive network of contacts in the medical and health sector.
Figure 1.- Medical professionals during group dynamics.
The methodology used has allowed us to gather useful information about the most common problems associated with osteoarthritis and the use of knee orthoses. Likewise, the experience and knowledge of the experts made it possible to gather information about the needs that the existing orthoses meet or not, as well as recommendations to improve their performance. The most relevant aspects highlighted during these group dynamics include problems related to dimensional adjustment and lack of adaptation to the natural movement of the knee.
The second phase of this co-creation process involved generating a series of emotional, functional and usability requirements for the product. All the actors in the sector and the IBV design team also participated in this phase.
From these requirements, a list of design specifications was generated, both for the knee joint and the rest of the components (frame, support and padding materials).
Figure 2.- Digitization of the markers during knee flexion when going down a step. Green line: leg markers. Yellow and red lines: orthosis markers, medial and lateral, respectively.
Next, users who were used to wearing knee orthoses assessed 3 existing products on the market. A kinematic gait analysis using photogrammetry techniques based on high-speed cameras (Figure 2) and an analysis of comfort and usability using our own methodologies (Figure 3) were performed. These assessments allowed us to objectively contrast the perceptions of the different participants.
Figure 3.- Activities performed during the usability and comfort test.
Finally, the IBV design team, together with users and professionals, generated two conceptual designs that solved the pains identified and adjusted to the requirements listed (Figure 4).
Figure 4.- Conceptual designs of the orthosis to be developed.
Orthotic joint compatible with the natural movement of the knee
The first challenge of the design was to ensure that the orthosis accurately adjusted to the natural movement of the knee when flexing. To this end, the information available on joint kinematics, particularly about the Instant Center of Rotation (ICR) of the knee (Figure 5), was considered. To replicate this movement, a multi-center mechanism was selected, and the optimal configuration for both the lateral and medial side of the knee was determined.
Figure 5.- Natural movement of the physiological knee (Walker P.S., et al.), which shows the instant axis of rotation (IAR) and the instant centers of rotation (ICR) on the medial and lateral side of the knee.
Then, this configuration was transferred to a CAD geometric design of the different components of the joint (Figure 6). This process was repeated through an iterative process of calculation, design, manufacturing of rapid prototypes, and user checking, until a balance among the error of the trajectory of the joint ICR with respect to that of the knee, the manufacturing cost, usability, comfort and aesthetics is reached.
Figure 6.- CAD design of the joint mechanism in the lateral side of the knee.
The end result is a mechanism that optimally adjusts to the natural movement of the knee, substantially improving the functioning of the current mechanisms (usually mono or polycentric) of the orthoses on the market (Figure 7).
Figure 7.- Error of the new joint developed (lateral side) with respect to the instant center of rotation of the physiological knee. Comparison with the error of other joints currently available on the market (both monocentric and polycentric).
Adaptation of the design to the anthropometry of the target population
The target population of this product are elderly men and women. The anthropometric characteristics of these people are very different from the rest of the population. If an articulated orthosis does not correctly adjust, the joint will not work properly, which will cause pain and problems regarding the effectiveness of the product.
To ensure that the orthosis frames adapt to the highest possible percentage of the target population, anthropometric information on the variability of the lower thigh and the upper calf areas of the target population was analyzed. This information was extracted from the IBV anthropometric database, using more than 700 3D scans of men and women over 55 years.
Based on the anthropometric information and considering the type of materials and the adjustment system used, a sizing proposal was made based on 4 sizes, which covered 93% of the target population (Figure 8).
Figure 8.- Sizing proposal for the knee orthosis based on 4 sizes covering 93% of the target population.
Finally, a morphotype or 3D leg mannequin was generated for each size (Figure 9) in order to design the shapes, dimensions and geometry of the different components of the knee orthosis and thus achieve an optimal fit for most users.
Figure 9.- Leg morphotype to use as a design pattern for the L size orthosis.
Product manufacturing and validation
Once the orthosis detail design was finished, EMO manufactured functional prototypes to validate the new product.
The objective of the validation was to verify whether this new generation of orthoses for osteoarthritis improved the comfort, usability and functionality of the current orthoses.
To do this, patients with knee osteoarthritis used the prototypes during a month in their daily life activities. After the trial period, they answered questionnaires about comfort and usability and had clinical tests done by specialized health professionals based on functionality and pain scales (Figure 10).
On the basis of the results obtained in the validation, it can be concluded that the product developed meets the requirements identified in terms of autonomy, comfort, usability and clinical usefulness.
The orthoprosthetic sector is highly demanding and competitive. In order to develop innovative products, it is necessary to consider the requirements and expectations of all the actors involved in the process: prescribers, professionals, users, insurance companies, etc. The methodologies that guarantee co-creation are essential in the innovation process of medical devices.
The factors that have the greatest impact on the purchase intent and the acceptance of orthopedic products are usability and comfort, clinical efficacy, anthropometric adaptation and biomechanical adaptation.
Currently, the effects that the different design proposals have on the patient must be assessed to ensure that the innovations improve the existing solutions.
The integration of all this knowledge and contrasts has allowed EMO to offer a new product with high added value and advanced features to compete in the market of orthopedic products with high quality and functionality.
We thank the users and professionals of UMIVALE, Hospital Clínico, Hospital Universitario de la Ribera, Hospital Casa de la Salud, Atenea clinics, ICM clinic and COS orthopedics, who have participated in the project.
We also thank IVACE and the ERDF funds for supporting the project within the IVACE grant program for R&D projects of SMEs (project code IMIDTA/2018/95).