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About This Lesson Plan


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Lesson 9: Silvia's New Knees

Through this lesson, students will be familiarized with the risk factors, symptoms, diagnosis, and treatment of deep vein thrombosis (DVT).


  • Conduct background research on deep vein thrombosis (DVT), osteoarthritis, and joint replacement surgery
  • Become familiarized with risk factors for DVT
  • Understand the inherent risks of major surgery, such as DVT, pulmonary embolism (PE), and infection
  • Describe the procedures used to diagnose, monitor, and treat DVT
  • Discuss the issues to be considered by the patient and physician regarding joint replacement surgery



This case study is meant to familiarize students with the risk factors, symptoms, diagnosis, and treatment of deep vein thrombosis (DVT). It is geared toward students taking a high school biology course, and it is recommended that students have a general familiarity with the circulatory system, specifically blood flow and the major types of blood vessels and their functions. The case study reinforces the concepts of blood flow in arteries and veins, and the health risks of blood clots. These lessons use a case-based approach (mostly via dialogue) to deepen students' understanding of these concepts in the context of a real-life scenario. Students are given the patient's description of her symptoms and are asked to conduct additional background research as necessary to determine a possible diagnosis.

There are four parts to this case study, which should be distributed one part at a time. Each part of the case study should take approximately one 50-minute class period, though students may have to finish some questions as homework, depending on the library resources available during class. It is recommended that part 4 be spread over two days, to allow students enough time to conduct background research, answer all questions, and discuss the coagulation cascade. This case study can also be extended to allow students to discuss risks and benefits of having joint replacement surgery. Points of discussion may include putting oneself in the patient's position and trying to decide whether to have the surgery versus alternative treatments, such as taking anti-inflammatory medication or receiving cortisone injections. With a wrap-up day at the end of the case, the entire lesson should take four 50-minute class periods.

Extension activities for more advanced students, in an AP Biology class for example, may also include conducting more detailed research on the mechanism of the drug treatments (heparin and warfarin) for DVT. Discussion of the coagulation cascade in part 4 of the case study also provides an opportunity to review enzyme activity. As a closing activity, students can also work in groups to design an informational pamphlet for patients at risk for DVT.

Part 1 Questions

1. What is osteoarthritis?
Osteoarthritis, often called "wear and tear arthritis," is a disease characterized by degeneration of the cartilage and underlying bone at the joints. Symptoms include pain, swelling, and stiffness at the affected joint. This is the most common type of arthritis, and there is currently no cure, though treatments do exist. The disease progresses gradually over time, usually beginning after the age of 40. However, there are instances where a traumatic injury causes osteoarthritis to develop earlier in life.
2. What is joint replacement surgery? What are some risks associated with having this type of surgery?
Joint replacement surgery replaces the damaged cartilage and bone in the joint with an artificial joint (prosthesis).
3. Why did the patient need a double knee replacement? What are some alternative methods of treatment for osteoarthritis?
Osteoarthritis has no cure. However, the symptoms can be treated. Patients can take pain relievers such as acetaminophen or non-steroidal anti-inflammatory drugs (like ibuprofen) to relieve pain and inflammation. In some cases, narcotics may be prescribed, though this is not typical since these powerful drugs have side effects and are addictive. Non-drug treatments may include working with a physical therapist to design an exercise regimen to increase muscle strength and range of motion in the joint. An occupational therapist may be able to recommend ways to reduce strain on the affected joints by modifying everyday activities. Shoe inserts or braces may also be of help for some patients. In addition, cortisone injections can be given to reduce inflammation in the affected joint. If the affected joint is weight bearing, such as the knee or hip, weight loss would reduce the pressure on the joint.

Part 2 Questions

1. Why would the compression stockings aid in blood flow? Hint: Think about how blood flows in the veins (compared to how blood flows in an artery).
This is an opportunity for students to review the differences between the passive blood flow in  veins versus the muscle-driven blood flow in the arteries. Since the blood in the veins is not being pumped by the heart and flows passively, valves keep the blood flowing in the right direction. Muscle contractions are necessary to keep the blood moving--as the muscles "squeeze" the adjacent blood vessels, the blood is pushed through. The compression stockings create these muscle contractions for patients who lack mobility due to surgery or illness.
2. What symptoms did Silvia develop that concerned the nurse and Dr. Avery?
She had pain in her calf and developed a fever of 102 degrees.
3. Given the patient's medical history, what condition(s) could be causing these symptoms?
The fever and pain could be the result of an infection, though the localized pain in the calf is typical of a blood clot in the leg, a DVT. Students' answers may vary depending on what sources of information they find.
4. Why do you think the nurse asked if Silvia was having difficulty breathing?
The nurse likely suspects that Silvia has a DVT. Formation of a clot after surgery always carries with it the risk that the clot will embolize, or break off and travel to other parts of the body. If the clot become lodged in the lungs, a pulmonary embolism, the patient may have difficulty breathing.

Part 3 Questions

1. What is a DVT?
DVT stands for "Deep Vein Thrombosis." It is a blood clot that forms in a vein. The clot can block blood flow or, possibly, embolize (break off and travel elsewhere in the body).
2. What are some risk factors for deep vein thrombosis? What put Silvia at risk for getting a DVT?
Risk factors for DVT are described in part 3 of the case study and in the listed references, and include surgery (in this case joint replacement surgery in the leg, which is a high risk for DVT), damage to a blood vessel (which can occur during any surgery as well), obesity, clotting disorders, family history of blood clot formation, and stasis (immobility).
3. What is a pulmonary embolism? Why is this a potentially life threatening condition?
A pulmonary embolism results when a blood clot (most commonly a deep vein thrombosis in the leg) travels to and lodges within a patient's lung. This is a serious condition which can cause shortness of breath, lack of oxygen in the blood, possibly resulting in organ damage; and permanent damage to the affected lung. In extreme cases (one large clot or several clots), this condition can result in death.
4. What drug treatments are used for patients who develop a DVT or PE? How do these drugs work?
Typically patients are treated with a combination of anticoagulants (blood thinners), heparin followed by coumadin. Heparin prevents formation of blood clots and stops the growth of existing blood clots. Coumadin reduces the blood levels of the body's natural clotting factors, thereby reducing clot formation and decreasing the size of existing clots.

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