Development of a continuous passive motion device for post surgical rehabilitation of the knee.

Cseki, Liviu Bogdan ; Drstvensek, Igor ; Balc, Nicolae 等

1. MEDICAL INSIGHT

The knee is essentially made up of four bones. The femur, which is the largest bone in your thigh, is attached by ligaments and a capsule to your tibia. Just below and next to the tibia is the fibula, which runs parallel to the tibia. The patella (the knee cap) slides up and down in a groove in the femur (the femoral groove) as the knee bends and straightens (Vaida et al, 2006).

The articular cartilage in the knee is called the menisci and it is located between the weight bearing joint surfaces of the femur and the tibia. The knee has two menisci, one located at the exterior side--lateral meniscus and one in the interior called medial meniscus. The menisci act as cushions and absorb the shocks that occur between the femur and the tibia.

The ligaments are very important in the knee because they stabilize the joint. There knee has four important ligaments: medial collateral ligament, lateral collateral ligament, anterior cruciate ligament and posterior cruciate ligament.

Knee problems can be the result of disease or injury. One of the most frequent injuries affects the ligaments and the meniscus and it can be corrected through reconstructive surgery. Diseases have degenerative causes that can even lead to the need for total knee reconstruction.

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2. REST VS. MOTION

One of the problems of orthopedics is that the effects of surgery on the soft tissue are more unfavorable to patient progress and recovery than the issue resolved by the procedure itself (Lenssen et al., 2003).

Rest and motion have varied as treatment of choice following surgery or injury for many centuries and the proper treatment is still in debate nowadays. Among the negative effects of immobilization there can be mentioned orthostatic hypotension, pneumonia and soft tissue contractures. Other unfavorable effects are edema, stiffness and pain at the affected site.

Studies proved that rest is actually more hazardous to proper healing than early motion (Prundeanu et al., 2004). At the beginning of the 20th century, researchers in the field of orthopedics started a trend toward manipulation and mobilization. This idea has been the subject of many controversies, but finally triumphed and has become a commonly practiced therapeutic technique following trauma.

Early motion can be achieved by physical therapy or with a continuous passive motion device. The benefits of early motion include decreased edema, decreased pain and shorter hospital stay.

3. CUSTOMER NEEDS

When developing a new product or service, exploratory market and customer research should be an essential and continuous component of the process. It provides the foundation and platform for effective idea generation and creativity management. This describes customer, or customer needs, wants, gripes, complaints, and problems that each have about the performance of a certain activity, function, process, life event, or product. This research prior to idea generation provides the basis for setting up problem-solving mindset towards idea generation.

The market for the continuous passive motion device was narrowed down to hospitals and rehabilitation centers. The main users of such a device are the patients and the hospital staff that handles the device. Discussions with hospital staff and patients have revealed a lot of useful information like the problems with our competitors' products and their view of the ideal product. This information was collected, sorted and prioritized using specialized software.

The needs of the customer with their importance served as a key component for a quality planning of the developing of the product. The House of quality was used for doing this and the result was the importance of each module of the product. This importance served as an indicator in the developing of the product, showing which part of the product needs the most attention and the higher price. This analysis was performed using the specialized quality control software Qualica QFD.

4. CONCEPT

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One of the biggest disadvantages of the competitors is the price of the device. In order to reduce the cost of the device the preferred option was a construction as simple as possible without affecting the performances of the device. The main focus was to eliminate as many parts as possible and design a safe, simple device that would have all the features necessary for a successful rehabilitation of the knee articulation.

Brainwriting (Blebea et al., 2007) was used to generate a number of ideas which were analyzed at a later date. Using the data previously obtained in the brainwriting session we calculated the mechanisms that are part of the CPM device and built the virtual prototype based on the needs of the customers.

Calculi showed that the device needs only a 5W direct current motor and a belt transmission in order to overcome the resistance of the patient's leg. To control the motor there is the need for a regulator and also a current transformation unit from alternative current to direct current.

A very important feature of the CPM device is the speed of the exercise. This, along with the range of motion is designated by the physician based on clinical parameters. Discussions with several orthopedists revealed that the device should be capable of achieving a speed as low as 30 degrees / minute and as high as 150 degrees / minute. Anything lower than this would not have the desired effect and above this would cause pain to the patient and possibly harm the articulation.

5. DESCRIPTION OF THE DEVICE

In order to reduce weight as much as possible the metal structure of the device is fabricated from 6061 Aluminum, an alloy used for chassis and other similar structures. This type of aluminum offers very good rigidity and durability without adding to the weight of the device. The other components of the device can be fabricated through injection molding from plastic (Balc et al., 2006).

The device is composed of 2 nickelled aluminum guiding cylinders that have role of guiding the footplate on a horizontal path. On the guiding cylinders slides the component that holds the weight of the leg and serves as a nut for the screw that ensures movement. This component is made up of three parts: the upper part, which is part of the joint corresponding to the ankle, the bottom part that holds the bearings in place and the part that holds the actual nut.

The foot of the patient rests onto the footrest. This part is connected to the lateral tubes of the device through an L-shaped part. This part has the role to hold the foot of the patient in place. It can be adjusted to fit all foot sizes with the help of an M5 screw that fixes in place the top sliding part to the lower part that can be adjusted to make the patient feel as comfortable as possible.

The CPM device is controlled by a remote control that translates the needs of the patient into electrical signals that are sent to the motor and controls the device.

A very important feature of the device is its ability of creating a gradual movement of the leg. In the rehabilitation of any member it is crucial that the articulation is not forced at all.

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Gradual movement is the only type of movement recommended. Because of this, our device bends the knee gradually. The muscles are stimulated using electrodes. Three types of electrodes were designed each of a different size to fit the desire of any user. This feature is very useful in eliminating the numbness of the muscles that occurs after the surgical intervention. The best type of movement in the rehabilitation is active movement, but that can not be achieved until the patient has control over his or hers muscles.

6. CONCLUSION

This project has started from an idea on how to help people who have suffered surgical interventions at the knee joint rehabilitate faster and safer. The premises of this study were to develop a device that could help patients in their rehabilitation after having had surgery performed on the knee articulation. A solution was needed for reducing costs without affecting the performance of the device and to reduce the weight in order to improve handling the device.

Using specialized software, the needs of the potential customers were analyzed and used as guides in the development of the virtual prototype which was used in the fabrication of the physical prototype. The final product is lighter than other continuous passive motion devices and because of its simple construction is cheaper.

Further research will focus on the gradual movement and the muscle stimulating feature. This implies creating the software and creating the link between the hardware and the software.

The result of this study is a product that is cheaper and better than the competition has to offer. With proper management this continuous passive motion device could become part of any hospital and bring significant benefits to all involved.

7. REFERENCES

Balc, N., Gyenge, C., Berce, P. (2006). Proiectare pentru fabricatia competitiva: teorie, aplicatii si studii de caz, U.T. Pres, 973-7893-31-1, Cluj-Napoca

Blebea, I, Dobocan, C. (2007). Proiectarea produselor--de la teorie la practica, U.T. Pres, 978-973-662-292-2, Cluj-Napoca

Lenssen, A. F., Koke, A. J. A., Bie de R. A., Geesink R. G. T. (2003). Continuous passive motion in rehabilitation following total knee arthroplasty; short and long term effects on range of motion. Physical Therapy reviews, 2003:113-121, doi: 10.1179/108331903225003028

Prundeanu H., Brad S., Dressler O., Prundeanu A., Epure V. (2004) . Notiuni de biomecanica, Artpress, 973-653-12-4, Timisoara

Vaida, M., Bolintineanu, S. Niculescu, M. (2006). Anatomie Humaine Compendium, Eurostampa, 973-687-251-3, Tirnispara