Design and manufacturing processes

Patients who are dependent on crutches for life need a secure footing even on uneven surfaces. The crutch tip, which connects the crutch to the ground, plays a crucial role in this. Conventional solutions are not suitable for everyone. A special jointed foot has been developed for one patient, which orthopedic technicians can manufacture themselves.

A 35-year-old patient with spastic tetraparesis is dependent on crutches for life (Fig. 1). He lives in a rural area where he is confronted with uneven, wet, and slippery terrain on a daily basis. Until now, the patient has been using commercially available crutch tips with four rubber feet designed for outdoor activities. In practice, however, this solution proved unsuitable:

• Insufficient contact surface: Due to spastic changes in gait mechanics, often only two of the four rubber feet are in contact with the floor. This uneven weight distribution significantly reduces stability.
• Material fatigue and breakage: The rubber feet are weakened by dynamic bending stresses. On average, they fail after six months. There have already been several cases of sudden breakage and dangerous falls.
• Health risks: Every fall carries the risk of fractures or traumatic brain injury. In addition, patients become increasingly fearful of the next accident, which leads to uncertainty when walking and limited mobility.
• Economic inefficiency: Although the end pieces only cost €30–38 in stores, the follow-up costs add up due to frequent replacements and adjustments. In addition, health insurance companies refuse to cover the regular replacements.

To solve these problems, Landshut University of Applied Sciences developed an end piece based on a commercially available ball joint (flange bearing) (Fig. 2). The flange bearing is screwed to a base plate. This allows different plates to be used in terms of color, material, geometry, elasticity, or profiling.

Although articulated feet for walking aids have been known from patents since at least the 1980s, they are not commercially available. In the new development, care was therefore taken to use as many off-the-shelf and standard parts as possible, supplemented by a few individual parts that can be manufactured using additive manufacturing (3D printing). This makes production by orthopedic technicians economically feasible. In addition, long-term supply security can be guaranteed.

New crutches with articulated ends were made for the patient (Fig. 3). Even when first used, there was a noticeable improvement in support. The articulated foot nestles evenly against the surface. Gait analysis confirmed what the patient immediately felt: greater stability, less uncertainty, and a secure step on any surface. The patient himself describes the treatment as a turning point in his life. After years of painful falls, he feels for the first time that he can really rely on his walking aids. The fear of the next accident has given way to a new sense of security that he feels with every step. Since the change, he has remained fall-free, and the articulated feet have shown no signs of wear and tear so far.

The articulated foot was developed in collaboration between Landshut University of Applied Sciences and the Ober medical supply store in Lindenberg:

• Prof. Dr.-Ing. Raimund Kreis teaches design and development as well as technical mechanics at Landshut University of Applied Sciences.
• Prof. Dr.-Ing. Norbert Babel heads the Additive Manufacturing Laboratory at Landshut University of Applied Sciences. He is the program director for the “Additive Manufacturing – Materials, Development, and Lightweight Construction” degree program. His areas of expertise are CAD, reverse engineering, additive manufacturing, and design.
• Peter Roidner is a laboratory engineer and lecturer in the Faculty of Mechanical Engineering and Construction at Landshut University of Applied Sciences.
• Dietmar H. Forster is a master orthopedic technician and master orthopedic shoemaker at the medical supply store Orthopädie OBER Schuh und Technik e. K. in Lindenberg im Allgäu.

Image credits: Dietmar H. Forster (Abb. 1 & Abb. 3), Hochschule Landshut (Abb. 2)

Contact: Prof. Dr N. Babel, Prof. Dr S. Remmele
Partner: Dr Helmut Ersch, Orthopaedics, Agatharied Hospital
Bachelor's thesis Edith Gramotke (2021)

Various methods are currently being researched in medical technology to preoperatively adapt implants to the anatomy either on virtual bone structures or by means of 3D-printed models.
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