Introduction



The DEsign of a device used to hold a leg in order to analyze knee movement

BME 273

Kelly Braun

Tera George

April 27, 1999

ABSTRACT

The management of any disorder of the knee must begin with an understanding of the basic properties and functions of the joint. It is critical to know the physiologic processes and the biomechanics of the knee in order to appropriately evaluate and treat any problem. The ligamentous structure of the knee guides the motion of the knee through six independent degrees of freedom, three translational and three rotational. The injury analyzed was that of an injured anterior cruciate ligament (ACL), the most common of knee joint injuries in athletes. This goal was accomplished by first designing and building some sort of device which would hold onto the femur of the leg and allow unconstrained movement of the knee joint from flexion to extension. During the engineering process, dog legs were gathered to use in the device. A specification important to this design was the need for adjustability. The desired goal was to be able to place different size legs in the device since the dog’s legs used were between 12-16 inches. To begin the design process, a literary search was performed and information was gathered on the knee joint. After the sketches were perfected and discussed, the parts were ordered and delivered, thus beginning the building process. During the building process, problems arose with the design and materials and immediately the re-engineering began. The final result was the device. The device was tested by potting a dog’s leg and placing it in the device. The device accurately held onto the leg and allowed unrestrained movement of the knee. In terms of the safety of the device, this proved a trivial matter. Further testing of the device is going to be performed by Dr. Dawson using the Optotrak Motion Sensing System. Dr. Dawson will be able to go on and learn about the movement of injured knees in hopes of applying it to human knee joints. Hopefully, this device will enhance the knowledge of the knee joint.

Introduction

Literary Review

The management of any disorder of the knee must begin with an understanding of the basic properties and functions of the joint.1 This basic knowledge includes physiologic responses of the tissues as well as their chemical and mechanical interaction.1 It is critical to know the physiologic processes and the biomechanics of the knee in order to appropriately evaluate and treat any problem.1 Because the knee is the link between the hip and the ankle, it must therefore provide sufficient motion with adequate stability in order to transmit the load through the lower extremity.1 This function places an enormous mechanical burden on the joint.1 When the muscles and ligaments do not function normally, the result is excessive load on the articular cartilage.1 For these reasons, the attempt to replicate knee function by arthroplastic replacement has led to a concerted effort to better understand the role each ligament and muscle plays in the movement of the knee.2

[pic]

The knee joint is a complex articulation whose biomechanics are incompletely understood.2 The knee joint is composed of four bones, (the femur, tibia, fibula, and the patella), a number of ligaments and tendons, and the meniscus, which encloses the knee joint itself. The collateral ligaments run along the sides of the knee and limit sideways motion. The anterior cruciate ligament, or ACL, connects the tibia to the femur at the center of the knee. Its function is to limit rotation and forward motion of the tibia. The posterior cruciate ligament, or PCL (located just behind the ACL) limits backward motion of the tibia.3 The anatomic configuration of the tibia and the femur provide for little inherent stability, thus the ligaments and the menisci not only provide for stability but also guide normal joint motion.1 The ligamentous structure of the knee guides the motion of the knee through six potential motions.1 The ligaments provide the linkage that controls this motion and its potential degrees of freedom.1 Most authors have assumed that the linkage between the cruciate ligaments (posterior and anterior) is the most importance of these guides to motion of the knee.1 Thus, the ligaments provide the knee with the stability needed to walk, run and perform normal human gait functions. An injury to one of these cruciate ligaments could pose serious problems to someone’s mobile activities.

Far from being a simple hinge joint, the knee exhibits as many as six independent degrees of freedom, three translational and three rotational.2 Axial rotation of the tibia in relation to the femur is an important component of normal knee motion. As the knee proceeds from flexion to extension the tibia externally rotates, a concept known as the “screw-home” mechanism.2 More recently, the bony anatomy has been cited as causing this external tibial rotation as the knee extends.2 The axis about which this rotation occurs as well as the influence of the cruciate ligaments on rotation was evaluated by Shaw and Murray.4 They were able to demonstrate that the surgical removal of the anterior cruciate ligament (ACL) was associated with anterior “skid” of the tibia on the femur during the screw-home mechanism, which remained intact.4 Resection of the posterior cruciate ligament alone caused little change.4 Another group , Lipke et al, reported that significant increases in internal rotation were found only after sectioning the ACL.5

Gliding or sliding motion is accompanied by some degree of rolling between the femoral and tibial surfaces.6 This motion is controlled by both the anatomy of the joint surface and the constraints imposed by the cruciate ligaments, both the ACL and the PCL.2 The rolling motion accounts for some degree of normal posterior translation of the femur on the tibia with knee flexion.2

Injury of the ACL is a common knee injury in humans, especially in athletes. Usually damage occurs when the fibers are torn due to a sudden change in direction involving twisting or pivoting movements or when a deceleration force crosses the knee.7 It can also be injured by external rotation with fixed foot or hyperextension. There does not need to be contact with another athlete or object to cause the ACL to tear.7 Another possibility is that an individual is unable to prepare for the landing phase of foot strike, resulting in an unprepared muscle response. Ligament failure is an instantaneous response process. Failure occurs within two hundredths of a second.7

There exist various testing methods which can be used to determine whether the ACL in a patient is injured. A commonly performed testing method is the Anterior Drawer Test. This is performed by the examiner grasping the patient’s tibia and pulling forward while noting the degree of anterior tibial displacement.8 A variant of the Anterior Drawer Test is the Lachman’s Test, in which the examination is carried out with the knee in 15 degrees of flexion. For a right knee, the examiner's right hand grips the inner aspect of the calf and the left hand grasps the outer aspect of the distal thigh.9 This test attempts to quantify the displacement in millimeters, comparing this displacement to the normal side.9 The end point of the displacement should be graded as hard or soft. The end point is said to be hard when the ACL abruptly halts the forward motion of the tibia on the femur and is said to be soft when there is no ACL and restraints are more elastic secondary stabilizers.9 A third test performed to analyze the ACL is the Chunk Test. This test begins with the knee in flexion while a valgus stress and internal rotation force are applied. The thumb pushes the tibia forward, and the clunk of reduction is felt as the knee approaches full extension.10 Subluxation of the lateral femorotibial articulation becomes maximum at about 30 degrees of flexion, then as the knee extends further, spontaneous relocation occurs which usually takes the form of a sudden jerk.10 As for imaging methods, Magnetic Resonance Imaging (MRI) may be used to detect ACL injury, but it is not necessary and often overused. The history and a physical exam of the patient are most important for determining knee joint injuries.

The rehabilitation of knee injuries involving the ACL is controversial.11 The orthopedic surgeon faces a dilemma in optimizing the treatment of ACL injuries. The wide variety of treatment regimens available for both acute and chronic ACL disruptions suggest that not one single method is uniformly regarded as superior.11 There have been very few studies providing long-term evidence that the ligament has been successfully repaired or reconstructed.11 The rehabilitation of the ACL has remained an enigma.11 Usually the joint is immobilized for six weeks for more. However, early unprotected motion could cause excess strain leading to permanent deformation of repaired or replaced ligaments.11 Thus, a better method of repair and rehabilitation is needed to more effectively heal the injured ACL than what is done today.

Goals

Our project held several goals that we attempted to achieve. The overall specific goal for our project was to analyze the motion of a knee joint from flexion to extension using a device we designed and an Optotrak Motion Sensing System. We wanted to compare the movement of an injured knee joint to the movement of a non-injured knee joint. The injury we chose was that of an injured anterior cruciate ligament (ACL), the most common of knee joint injuries in athletes. We accomplished this goal by first designing and building some sort of device which would hold onto the femur of the leg and allow unconstrained movement of the knee joint from flexion to extension. By executing the engineering skills required to design and build something, we accomplished the goal required by this course. The knee joints we chose to study came from dogs. A dog’s knee is very similar to a human’s knee in terms of anatomy and physiology. We were able to harvest actual knees from dogs that did not need them anymore (they were killed for other medical purposes and we got extra use out of them). The item that we required to reach our overall goal was the Optotrak 3-Dimensional Motion Analysis System, which would give us data about the movement of a knee with which we could then analyze, comparing data between injured and non-injured knees. The knowledge we hoped to learn from dog’s knees would be applied to human knees to help find better ways of treating replaced or reconstructed ACL’s. Thus, our humanitarian goal included working to help the benefit of others. By working on this project, we accomplished personal goals such as using the design process and having a final product that we were proud of, as well as attempting to accomplish the overall goal for the benefit of those athletes who may injure their knees.

Methodology

To begin our design process, we first performed a literary search and gathered information on the knee joint. Our research included articles and books on both the human knee and the dog knee. We compared their similarities and took notice of their differences. We also looked for articles containing previous knee testing methods, as well as tests performed by a physician on a patient to determine it there existed a ligament injury in the knee joint. Several of the articles we found described testing methods used on animals.

Our concentration was mainly directed towards recent articles and also those dealing with the anterior cruciate ligament (ACL). Because we found such a great number of articles on knee testing methods, we decided to limit our search. A few of the articles contained diagrams of previous testing devices that aided us in our own design of a testing device. By using these articles and designs we began our design process.

Designing our device was the most time consuming of the process. The sketch we drew during our first week of designing was a preliminary design, and was only about half the size of a normal sheet of paper. After discussing it with our advisor, we modified our design and increased the size of our sketch to its actual size. When our second design was completed, once again we spoke to our advisor and decided to alter a few details. We drew our third sketch in a three dimensional perspective. After we perfected and discussed our third sketch (shown in figure 1 on the last page) with our advisor, we felt positive about our design and decided we were ready to build.

While ordering the parts, we took into consideration the type of materials needed for strength and stability, the amount needed for our measurements, and the price. The base of our device was measured to be 12 inches by 12 inches, and its height was measured to be 18 inches. We decided on steel for the legs of the base and nylon for the platform on the top of our device. We did not need a lot of strength in our materials since we were only planning on using a weight of about 5-10 pounds to force the leg from flexion to extension. After finding the exact materials for our device, we ordered them from McMaster-Carr through the BME office.

Following the delivery of our parts, we began construction of our device. This involved cutting our perforated steel, the angles, flats, and Nylon to their appropriate sizes in the machinist shop and also degreasing them. We also had to drill holes for our pipe clamps and pulley through the nylon platform so they could be screwed on. Since everything was perforated, we used nuts and bolts to hold the legs together and to hold the angles and flats to the legs. The steel angles made shelves on which we laid the nylon sheet. The nylon sheet was then attached with the bolts. During the building process, we found some problems with our design and materials.

Almost immediately our re-engineering began. One of our first problems was that the pulley would not allow the cable to hang down straight, but rather it came off the pulley at an angle and rubbed against the nylon platform about an inch behind the pulley itself. We solved this problem by enlarging the back hole on the pulley, which was originally meant for a screw. We then hung the cable down this hole. The pulley was held on by only one screw in the front of it, and the second hole in the back of the pulley allowed the cable to hang down straight. Another problem was that our pipe claps did not fit the pipe that had been ordered. After searching a hardware store unsuccessfully for a bigger pipe clamp, we found some flexible metal that was strong enough to hold down the pipe, yet still adjustable (if another size pipe was ever used). Other small problems that we occurred were easily fixed, such as finding the right size screw. All in all the design was successful.

We tested our device by potting a dog’s leg and placing it in the device. The dog’s leg was potted by cutting off the femur head, filling a piece of three inch pipe with Bond-o, and then placing the bone in the pipe. After about twenty minutes, the Bond-o hardened. We then placed the leg in the device and forced movement to see the motion of the knee by lifting the tibia up manually. Once the dog’s leg was on the device, we were able to figure out how long the cable would have to be to connect the quadriceps muscle to the weights. To connect the weights to the cable, we put a loop in the cable and held it with a small metal tube that we crushed to hold the loop in the cable. We then hung a hook from the loop and fashioned it so that we could string washers on it to act as the weights. We made a loop on the other end of the cable in the same way and then hooked the quadriceps muscle to the cable. In this manner, we were able to see how many washers it took to force the leg from flexion to extension.

Due to time constraints, we were unable to use the Optotrak 3-D Motion Sensing System in conjunction with our device. However, our advisor will continue to use our device with the Optotrak and examine the differences in the movement of the healthy and the injured knee.

RESULTS

The main result of our project consisted of our finished device. We were able to design, build, and use the device which we created. In order to achieve this goal, there were many steps that led us there. These steps enabled the correct design and construction of the device.

The first result was a better understanding of the knee anatomy, physiology, and movement. We learned how the individual components of the knee were related to their movement. Another factor we encountered was the six degrees of motion of the knee, which led us to discover the complicated movement of the knee joint. This was influential in our design because our device had to incorporate these different movements into its construction and its testing. Since we were concentrating on the ACL, it was necessary to be able to detect rotation.

A literary search proved fruitful because of the ideas we gathered from previous experiments. Though some were testing other aspects of the knee, such as stress and strain of the muscles prevalent in the movement of the knee joint, general information was used to spark ideas about our design. These articles also showed the proper technique for designing and testing a device.

While we were performing these reviews, we also gathered dog legs. With one set, we examined the movement and the ligaments that make up the knee joint. Then we injured a knee by cutting the ACL. After investigating the movement changes, we used the information to help design a device that would allow the unconstrained movement of the knee joint and also hold the femur rigidly.

The design process not only resulted in the device, but also a better understanding of the engineering process. There were certain specifications that we had to take into consideration. We wanted our device to clamp onto the quadriceps muscle so that the weights hung from the pulley could simulate the quadriceps muscle. The device also needed to allow the six degrees of motion of the knee with enough room to place pins on the leg so the Optotrak 3-D Motion Sensing System could sense the pins. Sturdiness was also a key issue since we wanted to make sure the device did not fall over or shake and interfere with the testing. Another influence was the need for adjustability. We wanted to be able to place different size legs in the device since the dog’s legs we used were between 12-16 inches. The perforations on the steel tubing and flats allowed our platform to be lowered or raised if necessary, which ridded us of this problem. The pipe clamps were adjustable in the case that another width of pipe was ever used. These features allow our device to change as different situations come up.

We were able to sketch our idea, and then see what would or would not work.

This resulted in re-designing. This is an important function in the process, that as students we had overlooked. However, by re-designing we were able to eliminate some of the problems that would have come up later. After re-designing twice, we still found that problems arise when building anything.

In choosing our materials, we knew our device did not need to support a great deal of weight, but needed to be stable. We chose perforated steel for the legs so that our device would have an adjustable height. The steel also provided the legs with stableness and the device with a solid structure. The angles and flat pieces were also steel, which added to the stability of our device. The nuts and bolts we used to hold our device together are easily loosened using the proper tools to raise or lower the platform, depending on the length of the leg being analyzed. We chose a nylon sheet as the platform because of the ease of drilling holes for the clamps and pulleys and the easy clean up of the surface. Instead of pipe clamp, we used a strip of perforated metal which allowed for adjustment in the case of a pipe diameter change. This metal strip provided a secure hold on the pipe even when the leg was being pulled or manipulated. We picked a cable that was resilient enough to hold our weight and flexible enough to fit in the pulley. For the goniometer, we used an alligator clip to hold the protractor. (We glued the protractor to a piece of cardboard so that it would be easier to read.) We wanted the goniometer to be easily movable so that the angle could be measured accurately from the center of the knee. By choosing the correct materials, our device was sturdy enough to hold and allow movement of the leg.

Our actual device was built by Kelly, Tera, and Dr. Dawson. Our device had the base dimensions of 1 foot square and 1 ½ feet high. This allowed ample room for length of the leg and the movement of the knee. Through the help of Dr. Dawson, we learned many different things about construction. We learned the correct techniques on how to use tools, such as the drill press, and how to measure correctly and accurately. Due to problems with equipment, we also learned how to improvise and find an object that met our needs. We learned to make something useful out of something that appeared useless. This for instance happened when our pipe clamps did not fit our pipe. After a trip to the hardware store, we found a malleable metal that we could use to hold down the pipe. This metal proved fully adjustable to any size of pipe, which was better than the original idea. By learning to improvise, we saw the importance of the critical thinking. Another issue we gained insight about from Dr. Dawson was the physical look of our device. He showed us how a more finished and polished product greatly increases its value. For instance, the filing of steel edges, not only made the device safer, but also more professional.

The final result was our device. It is shown in the conclusion. We were able to place a dog’s leg in the device and see the movement of the knee. Further testing of the device is going to be performed by Dr. Dawson using the Optotrak Motion Sensing System.

In terms of the safety of our device, this proved a trivial matter. The user of the device is the only person about whom the safety issues had to be addressed, of these there were few. The main safety issue we saw right away when building the device was the rough edges of the steel flats, tubing and angles. We took care of this problem by coarsely filing all the edges until they were no longer sharp enough to cut through human skin. When the user uses our device, the main action he/she will be performing is the tightening down of nuts and bolts in order to securely hold down the femur. In doing this, his/her arms may brush against the steel edges, yet we paid enough attention to this detail to prevent injury in this manner.

CONCLUSION

[pic]

Our conclusion was the completion of our device. Our testing device accurately held onto the leg and allowed unrestrained movement of the knee. It will be further used with the Optotrak Motion Sensing System to test for injury of the knee. We hope that it will have an impact on the testing and treatment of human knees.

Recommendations

Our advisor, Dr. John Dawson works in orthopedics in Medical Center North. He plans to continue using the device we built in conjunction with the Optotrak Motion Sensing System to gather data about the rotational movement of the injured knee joint to further his research in that area. Because we did not get a chance to try it out with the Optotrak, Dr. Dawson may come across changes that need to be made in order for it to be compatible with the Optotrak. Dr. Dawson will be able to go on and learn about the movement of injured knees in hopes of applying it to human knee joints. Our device hopefully, will enhance the knowledge of the knee joint.

The main ethical issue we came across while working on our project was the use of animals. In order to use and test our device, it required the legs of a dog. The legs had to be cut off of the dog and then skinned, thus the dog was killed. In our case, the death of each dog that we used was not due to our need of his legs. He was killed for some other medical purpose and then we were allowed to take his legs because neither the dog nor the doctor studying him needed them anymore. So in a sense, we got extra use out of the dog in his death. While this may be a positive aspect of the whole thing, the fact that dogs need to die to use our device may still remain an ethical issue for some people.

We recommend that our device be used in the testing of knees. We believe that there is a great deal of information about the knee that is yet unknown. By observing movement in the knee injuries, hopefully, more information will be available for the treatment of ligament injuries of the human knee.

REFERENCES

1. Larson R, Grana W: The Knee Form, Function, Pathology, and Treatment. W.B. Saunders Company. Pp. 52-71. 1993.

2. Scott, WN: The Knee Volume 1. Mosby-Year Book, Inc. St. Louis Missouri. Pp. 75-94. 1994.

3.

4. Shaw JA, Murray DG: The longitudinal axis of the knee and the role of the cruciate ligaments in controlling transverse rotation. J Bone Joint Surg [Am] 56:1603-1609, 1974.

5. Lipke JM et al: The role of incompetence of the anterior cruciate and lateral ligaments in anterolateral and anteromedial instability, J Bone Joint Surg [Am] 63:954-960, 1981.

6. Kapendji IA: The physiology of the joints. New York, 1970, Churchill Livingstone, pp. 114-123.

6.

8.

9.

10.

11. Arms SW, Pope MH et al: The biomechanics of anterior cruciate ligament rehabilitation and reconstruction. Amer Jour Sports Med. 12(1):8-18, 1984.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download