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Posterior cruciate ligament injury

Posterior cruciate ligament injury is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Posterior cruciate ligament injury rather than just read about it. In short: The function of the posterior cruciate ligament (PCL) is to prevent the femur from sliding off the anterior edge of the tibia and to prevent the tibia from displacing posterior to the femur. Common causes of PCL injuries are direct blows to the flexed knee, such as the knee hitting the dashboard in a car accident or falling hard on the knee, both instances displacing the tibia posterior to the femur.

Posterior cruciate ligament injury — main illustration
Posterior cruciate ligament injury — illustration

Key takeaways

  • Posterior cruciate ligament injury belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Posterior cruciate ligament injury to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Posterior cruciate ligament injury from memory before moving on to harder problems.

Reference excerpt

The function of the posterior cruciate ligament (PCL) is to prevent the femur from sliding off the anterior edge of the tibia and to prevent the tibia from displacing posterior to the femur. Common causes of PCL injuries are direct blows to the flexed knee, such as the knee hitting the dashboard in a car accident or falling hard on the knee, both instances displacing the tibia posterior to the femur. Surgery to repair the posterior cruciate ligament is controversial due to its placement and technical difficulty. The posterior drawer test is one of the tests used by doctors and physiotherapists to detect injury to the PCL. An additional test of posterior cruciate ligament injury is the posterior sag test, where, in contrast to the drawer test, no active force is applied. Rather, the person lies supine with the leg held by another person so that the hip is flexed to 90 degrees and the knee 90 degrees. The main parameter in this test is step-off, which is the shortest distance from the femur to a hypothetical line that tangents the surface of the tibia from the tibial tuberosity and upwards. Normally, the step-off is approximately 1 cm, but is decreased (Grade I) or even absent (Grade II) or inverse (Grade III) in injuries to the posterior cruciate ligament. Patients who are suspected to have a posterior cruciate ligament injury should always be evaluated for other knee injuries that often occur in combination with an PCL injuries. These include cartilage/meniscus injuries, bone bruises, ACL tears, fractures, posterolateral injuries and collateral ligament injuries.

Cause

Related anatomy

The PCL is located within the knee joint where it stabilizes the articulating bones, particularly the femur and the tibia, during movement. It originates from the lateral edge of the medial femoral condyle and the roof of the intercondyle notch then stretches, at a posterior and lateral angle, toward the posterior of the tibia just below its articular surface.

Related physiological features Although each PCL is a unified unit, they are described as separate anterolateral and posteromedial sections based on each section's attachment site and function. During knee joint movement, the PCL rotates such that the anterolateral section stretches in knee flexion but not in knee extension and the posteromedial bundle stretches in extension rather than flexion.

The types of mechanisms that lead to PCL injury In this position, the PCL functions to prevent movement of the tibia in the posterior direction and to prevent the tilting or shifting of the patella. However, the respective laxity of the two sections makes the PCL susceptible to injury during hyperflexion, hyperextension, and in a mechanism known as a dashboard injury. Because ligaments are viscoelastic (p. 50 ) they can handle higher amounts of stress only when the load is increased slowly (p. 30 ). When hyperflexion and hyperextension occur suddenly in combination with this viscoelastic behavior, the PCL deforms or tears. In the third and most common mechanism, the dashboard injury mechanism, the knee experiences impact in a posterior direction during knee flexion toward the space above the tibia. These mechanisms occur in excessive external tibial rotation and during falls that induce a combination of extension and adduction of the tibia, which is referred to as varus-extension stress, or that occur while the knee is flexed.

Prevention

Knee injury Knee injuries are very common among athletes as well as regular active people and can always be prevented. Ligament tears account for more than forty percent of knee injuries and the posterior cruciate ligament is considered one of the less common injuries. Although it is less common, there are still important measures that can be taken in order to prevent this type of knee injury. Maintaining proper exercise and sport technique is crucial for injury prevention, which include not exceeding the body or not going over the proper range of motion of the knee, properly warming up and cooling down

Quadriceps-to-Hamstring Strength Ratio Another important aspect of maintaining injury-free knees is having a sufficient hamstrings-to-quadriceps strength ratio because they help stabilize the knees. The ratio is a measure of the relative strength of the hamstrings compared to the quadriceps. This means having a 50% H/Q ratio equates to your hamstrings being half as strong as your quadriceps, while a 100% ratio means that your hamstrings and quadriceps are equally as strong. Generally the higher one's H/Q ratio, the better the hamstrings can help the ACL resist dangerous forces during sudden movements and in sports, while a low H/Q ratio is associated with a higher degree of knee injury. According to Sports Performance Bulletin, a 50% ratio is enough for "daily living activities", but the ratio needs to be higher near 80% for athletic activity, while for ACL injury prevention, the ratio should ideally be closer to a balanced 1.0 (100%). Exercises that primarily activates the quadriceps can increase "shearing-type" forces on the knee joint. This is why strong hamstrings are necessary to support the ACL by preventing the shin bone shifting forward as the knee straightens. When the H/Q ratio is low, meaning the hamstrings are relatively weak, certain exercises can help improve the ratio. These include Romanian deadlift, Nordic hamstring curls, Swiss ball hamstring curls, leg curls, leg lifts, prone knee flexion with resistance band, knee extensions, side stepping with an elastic band around the knees, and side and forward hop exercises. Some stretches to help prevent injury to the posterior cruciate ligament include stretching of the hamstring muscles by extending the legs, toes pointing up, leaning forward until the stretch is felt and holding for a few seconds.

… excerpt ends here. Continue reading the full article.

Illustrations

Posterior cruciate ligament injury illustration
Posterior cruciate ligament injury: In this medial view of the flexed knee, the lateral femoral condyle has been removed to reveal the structure of the PCL. Because the anterolateral bundle is stretched and the posteromedial bundle relaxed during flexion, excessive flexion in the form of hyperflexion causes tensile stress, shown in red, on the anterolateral bundle of the PCL that leads to PCL injury.
In this medial view of the flexed knee, the lateral femoral condyle has been removed to reveal the structure of the PCL. Because the anterolateral bundle is stretched and the posteromedial bundle relaxed during flexion, excessive flexion in the form of hyperflexion causes tensile stress, shown in red, on the anterolateral bundle of the PCL that leads to PCL injury.
Posterior cruciate ligament injury: In this medial view of the extended knee, the lateral femoral condyle has been removed to reveal the structure of the PCL. Because the posteromedial bundle is stretched and the anterolateral bundle relaxed during extension, excessive extension in the form of hyperextension causes tensile stress, shown in red, on the posteromedial bundle of the PCL that leads to PCL injury.
In this medial view of the extended knee, the lateral femoral condyle has been removed to reveal the structure of the PCL. Because the posteromedial bundle is stretched and the anterolateral bundle relaxed during extension, excessive extension in the form of hyperextension causes tensile stress, shown in red, on the posteromedial bundle of the PCL that leads to PCL injury.
Posterior cruciate ligament injury: Exercises that strengthen the knee joints and the hamstrings include prone knee flexion. Where the knee flexes all the way back to the rear end, hold for about 10 seconds, then slowly lower to original position and repeat.
Exercises that strengthen the knee joints and the hamstrings include prone knee flexion. Where the knee flexes all the way back to the rear end, hold for about 10 seconds, then slowly lower to original position and repeat.
Posterior cruciate ligament injury: This picture shows the rehabilitative exercise called a "lunge" used to treat and strengthen PCL injuries.
This picture shows the rehabilitative exercise called a "lunge" used to treat and strengthen PCL injuries.

Worked examples

Example 1 — a first encounter with Posterior cruciate ligament injury

Start with the simplest possible case. Write down what Posterior cruciate ligament injury claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Posterior cruciate ligament injury before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Posterior cruciate ligament injury ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Posterior cruciate ligament injury

In research
Posterior cruciate ligament injury appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Posterior cruciate ligament injury in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Posterior cruciate ligament injury is common in secondary-school and first-year university syllabi. It links to neighbouring topics Dislocations, sprains and strains, Knee injuries, Ligaments of the lower limb, so understanding it makes those chapters shorter.
In everyday life
Look for Posterior cruciate ligament injury outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Posterior cruciate ligament injury in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Posterior cruciate ligament injury means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Posterior cruciate ligament injury out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Posterior cruciate ligament injury in simple terms?

The function of the posterior cruciate ligament (PCL) is to prevent the femur from sliding off the anterior edge of the tibia and to prevent the tibia from displacing posterior to the femur. Common causes of PCL injuries are direct blows to the flexed knee, such as the knee hitting the dashboard in…

Why does Posterior cruciate ligament injury matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Posterior cruciate ligament injury?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Posterior cruciate ligament injury.

Tags

  • Dislocations, sprains and strains
  • Knee injuries
  • Ligaments of the lower limb

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