knee joint

The Knee Joint**

The knee joint is a remarkable and complex joint within the human body, playing a pivotal role as the primary weight-bearing joint. Over time, it is susceptible to degenerative changes, often leading to a condition known as osteoarthritis. This intricate joint merits a thorough examination for better comprehension.

**Joint Classification**

The knee joint is classified as a synovial joint of the modified hinge variety. Although it primarily functions as a hinge joint, it also exhibits a certain degree of rotational movement during flexion and extension, making it distinct from a typical hinge joint. The knee joint, in fact, is a compound joint composed of three distinct articulations.

**Components of the Knee Joint**

1. **Condylar Joints of Femur and Tibia**

- The knee joint comprises right and left condylar joints located between the condyles of the femur and tibia.

- The articulation of these condylar joints allows for flexion and extension of the knee.

2. **Saddle Joint between Femur and Patella**

- Another crucial component of the knee joint is the saddle joint between the femur and the patella.

- This joint enables the patella to glide over the trochlear surface of the femur during knee movements.

**Articular Surfaces**

The knee joint features several essential articular surfaces:

1. **Medial and Lateral Condyles of the Femur**

- The articular surfaces of the medial and lateral condyles of the femur occupy the anterior, inferior, and posterior aspects of these condyles, respectively.

- These surfaces are convex both anteroposteriorly and mediolaterally.

- The medial condylar surface is longer anteroposteriorly but narrower mediolaterally compared to the lateral condyle.

- Anteriorly, they are continuous through the trochlear surface, while posteriorly, they are separated by an intercondylar notch.

2. **Trochlear Surface of the Femur**

- The trochlear surface, located on the anterior aspect of the lower end of the femur, articulates with the posterior surface of the patella.

- This surface is pulley-shaped, characterized by medial and lateral sloping surfaces that meet in a median vertical groove. The lateral sloping surface is longer than the medial one

3. **Articular Surface of the Patella**

- This surface is located on the posterior aspect of the patella and articulates with the trochlear surface of the femur.

- The articular surface of the patella has a larger lateral area and a smaller medial area.

- Near the medial margin of the patella, a narrow semilunar strip comes into contact with a similar strip on the medial condyle of the femur during full flexion.

4. **Medial and Lateral Condyles of the Tibia**

- The knee joint's articular surfaces on the upper surfaces of the medial and lateral condyles of the tibia are separated by a rough intercondylar area.

- The articular surface on the medial tibial condyle is oval and larger, with an anteroposterior diameter greater than the transverse diameter.

- Conversely, the articular surface on the lateral tibial condyle is circular.

- These surfaces are slightly concave at their central regions and flat at the periphery, where they are covered by corresponding menisci.

**Stability of the Knee Joint**

Structurally, the knee joint poses challenges to stability due to the incongruence of its articular surfaces. The tibial condyles are relatively small and shallow compared to the large convex femoral condyles. Furthermore, the femoropatellar articulation lacks complete stability due to the shallow articular surfaces and an outward angulation between the long axes of the femur and tibia.

**Factors Maintaining Knee Joint Stability**

The knee joint's stability is ensured by several key factors:

1. **Strength and Actions of Surrounding Muscles and Tendons**

- The surrounding muscles and tendons, such as the quadriceps and hamstrings, play a crucial role in stabilizing and controlling knee movements.

2. **Medial and Lateral Collateral Ligaments**

- These ligaments are essential for maintaining side-to-side stability in the knee joint.

3. **Cruciate Ligaments**

- The anterior and posterior cruciate ligaments are vital for maintaining anteroposterior stability within the knee joint.

4. **Iliotibial Tract**

- The iliotibial tract contributes to the stabilization of a partially flexed knee.

**Ligaments of the Knee Joint**

The knee joint features a complex network of ligaments that provide stability and support. These include:

1. **Capsular Ligament**

- The capsular ligament surrounds the knee joint and is thin and fibrous. It is deficient anteriorly, where it is replaced by structures such as the patella, quadriceps femoris, medial and lateral patellar retinacula, and the ligamentum patellae.

- **Femoral Attachment**: The capsular ligament attaches to the femur approximately 1/2 to 1 cm beyond the articular margins. It has three distinctive features:

- Anteriorly, it is deficient in the middle, allowing the passage of the suprapatellar bursa.

- Posteriorly, it is attached to the intercondylar line.

- Laterally, it encloses the origin of the popliteus muscle.

- **Tibial Attachment**: The ligament attaches to the tibia approximately 1/2 to 1 cm beyond the articular margins. It presents three special features:

- Anteriorly, it descends along the condylar margins to the tibial tuberosity, where it is deficient for the attachment of the ligamentum patellae.

- Posteriorly, it forms a gap behind the lateral condyle for the passage of the popliteus muscle's tendon.

2. **Ligamentum Patellae**

- This ligament is involved in the stabilization of the patella and attaches to the tibial tuberosity. It plays a significant role in knee extension.

3. **Tibial and Fibular Collateral Ligaments**

- These ligaments provide side-to-side stability for the knee joint and connect the femur to the tibia and fibula, respectively.

4. **Anterior and Posterior Cruciate Ligaments**

- The anterior and posterior cruciate ligaments are integral for anteroposterior stability. They crisscross within the joint and help prevent excessive movement.

5. **Medial and Lateral Menisci**

- These structures are not ligaments but serve as vital components of the knee joint. They act as shock absorbers and enhance joint stability.

**Additional Ligaments of the Knee Joint**

In addition to the primary ligaments, there are several secondary ligaments associated with the knee joint:

1. **Oblique Popliteal Ligament**

2. **Arcuate Popliteal Ligament**

3. **Transverse Ligament**

4. **Coronary Ligaments**

**Synovial Membrane**

The synovial membrane lines the inner aspect of the fibrous capsule, covering the portions of the bones enclosed within it. However, it stops at the periphery of the articular cartilages, specifically the medial and lateral menisci.

- Above the patella, it extends as the suprapatellar bursa.

- Below the patella, it covers the deep surface of the infrapatellar pad of fat, separating it from the ligamentum patellae.

- A median triangular fold of the synovial membrane, called the infrapatellar fold, extends upward and backward from the fat pad to the intercondylar fossa of the femur.

- The lateral margins of the infrapatellar synovial fold are free and form the alar folds, which contain fibrofatty tissue.

- Posteriorly, the synovial membrane extends as a cul-de-sac in the intercondylar region to envelope the sides of both cruciate ligaments and the anterior cruciate ligament.

**Ligamentum Patellae (Patellar Ligament)**

The ligamentum patellae is actually the tendon of insertion for the quadriceps femoris muscle, extending from the apex of the patella to the upper part of the tibial tuberosity. It plays a critical role in knee function.

- **Length and Width**: This ligament is approximately 7.5 cm long and 2.5 cm wide.

- **Attachment Points**:

- Above, it is attached to the margins and the rough posterior surface of the patella.

- Below, it attaches to the smooth upper part of the tibial tuberosity.

- **Related Structures**:

- It is closely related to the subcutaneous and deep infrapatellar bursae.

- It also interacts with the infrapatellar pad of fat, which separates it from the ligamentum patellae.

**Tibial (Medial) Collateral Ligament**

The tibial collateral ligament is a robust, lengthy (approximately 10 cm), and flat fibrous structure, composed of superficial and deep parts. These components play a pivotal role in stabilizing the medial aspect of the knee joint.

- **Attachment Points**:

- Both parts of the ligament are attached above to the medial epicondyle of the femur, just below the adductor tubercle.

- The superficial part extends below to the upper part of the medial border and the posterior part of the medial surface of the tibia.

- **Covering and Relationships**:

- The superficial part covers the inferior medial genicular nerve and vessels, along with the anterior part of the semimembranosus tendon.

- The tendons of sartorius, gracilis, and semitendinosus superficially cross its lower part.

- The deep part of the ligament blends with the fibrous capsule and connects with the peripheral margin of the medial meniscus.

- It is attached below to the medial condyle of the tibia, just above the groove for the tendon of the semimembranosus.

**Fibular (Lateral) Collateral Ligament**

This ligament is relatively short, measuring about 5 cm in length, and has a cord-like appearance. It serves as a critical stabilizer for the lateral aspect of the knee joint.

- **Attachment Points**:

- Above, it attaches to the lateral epicondyle of the femur, just above the popliteal groove.

- Below, it is embraced by the tendon of the biceps femoris and attaches to the head of the fibula, situated in front of its apex.

- **Relationships**:

- The deep surface of the fibular collateral ligament is not adherent to the fibrous capsule.

- It is separated from the capsule and the lateral meniscus by the tendon of the popliteus muscle.

- Its lower part is separated from the capsule by the inferior lateral genicular nerve and vessels.

**Cruciate Ligaments**

The cruciate ligaments are two strong, fibrous bands located inside the knee joint that serve as direct connections between the femur and tibia. They are vital for maintaining the anteroposterior stability of the knee joint. The cruciate ligaments are named anterior and posterior based on their attachment sites to the tibia. Importantly, they are intracapsular but extrasynovial, meaning they are within the joint but outside the synovial membrane.

- **Crossed Configuration**: These ligaments cross each other in an X-shaped pattern, earning them the name "cruciate."

**Anterior Cruciate Ligament (ACL)**

The anterior cruciate ligament is attached to the anterior part of the intercondylar area of the tibia. It runs upward, backward, and laterally, attaching to the posterior part of the medial surface of the lateral condyle of the femur. The ACL becomes taut during knee extension, preventing the posterior dislocation of the femur on the tibia and the anterior dislocation of the tibia on the femur.

**Posterior Cruciate Ligament (PCL)**

The posterior cruciate ligament is attached to the posterior part of the intercondylar area of the tibia. It runs upward, forward, and medially, attaching to the anterior part of the lateral surface of the medial condyle of the femur. The PCL becomes taut during knee flexion, preventing the anterior dislocation of the femur on the tibia and the posterior dislocation of the tibia on the femur.

**Medial and Lateral Menisci (Semilunar Cartilages)**

Medial and lateral menisci are two crescent-shaped intra-articular discs made of fibrocartilage, serving crucial roles in the knee joint's structure and function.

- **Structure**: These discs have a thick peripheral border and a thin inner border, deepening the articular surfaces of the tibial condyles. They partially divide the joint cavity into two compartments: the upper (meniscofemoral) and lower (meniscotibial). Flexion and extension of the knee occur in the upper compartment, while rotation takes place in the lower compartment.

Each meniscus is characterized by:

- Two ends, namely anterior and posterior, which attach to the tibia.

- Two borders: the thick outer border, which is fixed to the fibrous capsule, and the thin inner border, which is free.

- Two thin surfaces: the upper surface, which is concave for the femur, and the lower surface, which is flat for the peripheral 2/3rd of the tibial condyles.

**Medial Meniscus**

The medial meniscus is nearly semilunar in shape, wider behind than in front, and exhibits anterior and posterior ends or horns. These horns attach to the intercondylar area of the tibia, and the medial meniscus adheres to the deep part of the tibial collateral ligament. Firm attachment to the tibial plateau is achieved through coronary ligaments.

**Lateral Meniscus**

The lateral meniscus is nearly circular in shape and maintains a uniform width. Similar to the medial meniscus, it presents anterior and posterior horns attached to the intercondylar area of the tibia. The posterior horn of the lateral meniscus is connected to the medial condyle of the femur through the anterior and posterior meniscofemoral ligaments. Specifically:

- The anterior meniscofemoral ligament (ligament of Humphrey) passes in front of the posterior cruciate ligament.

- The posterior meniscofemoral ligament (ligament of Wrisberg) passes behind the posterior cruciate ligament.

The lateral meniscus also attaches to the medial part of the popliteus tendon, providing control over the mobility of its posterior horn through the action of the popliteus muscle and the two meniscofemoral ligaments.

**Functions of the Menisci**

The menisci perform several vital functions within the knee joint:

1. **Enhanced Congruence**: The menisci increase the concavities of the tibial condyles, improving congruence with the femoral condyles. This enhanced fit contributes to joint stability.

2. **Lubrication**: They act as swabs to lubricate the joint cavity, reducing friction during knee movement.

3. **Shock Absorption**: The menisci function as shock absorbers, protecting the articular cartilage from damage during weight transmission and sudden movements.

4. **Adaptation**: They adapt to the varying curvatures of different parts of the femoral condyles, optimizing the contact area between the articulating surfaces of the femur and tibia, ensuring proper load distribution and joint function..

**Differences Between the Medial and Lateral Menisci**

The medial and lateral menisci in the knee joint have distinct characteristics and are prone to different types of injuries.

**Medial Meniscus:**

1. **Shape**: C-shaped or semilunar in shape.

2. **Attachment**: Attached to the medial collateral ligament.

3. **Prone to Injury**: More prone to injury due to its firm fixation to the tibial collateral ligament and greater excursion during rotatory movements.

4. **Injury Protection**: Less protected by surrounding structures.

**Lateral Meniscus:**

1. **Shape**: "O"-shaped or circular in shape.

2. **Attachment**: Attached to the tendon of the popliteus muscle.

3. **Prone to Injury**: Less prone to injury compared to the medial meniscus.

4. **Injury Protection**: Protected by the popliteus muscle, as its medial fibers pull the posterior horn of the meniscus backward, preventing it from being crushed between the articular surfaces.

**Meniscal Tears:**

Meniscal tears can occur due to various factors, with twisting strains in a slightly flexed knee, such as those experienced while kicking a football, being a common cause. These tears can take various forms, including:

- **Separation from the Capsule**: The meniscus may become separated from the capsule.

- **Longitudinal Tear**: The meniscus may tear longitudinally.

- **Transverse Tear**: A transverse tear across the meniscus may occur, known as a "bucket-handle tear."

**Medial Meniscus Injury**: The medial meniscus is more susceptible to injury because of its strong attachment to the tibial collateral ligament and its greater mobility during rotatory movements. It is less protected by surrounding structures.

**Lateral Meniscus Injury**: The lateral meniscus is relatively less prone to injury, partially due to the protection provided by the popliteus muscle. The medial fibers of the popliteus muscle pull the posterior horn of the meniscus backward, preventing it from being crushed between the articulating surfaces.

**Diagnostic Clues for Injuries**:

Pain during certain movements can provide clues about the type of meniscal injury:

- **Medial Rotation of Tibia**: Pain on the medial rotation of the tibia on the femur often indicates injury to the medial meniscus.

- **Lateral Rotation of Tibia**: Pain on the lateral rotation of the tibia on the femur suggests injury to the lateral meniscus.

**Oblique Popliteal Ligament**

The oblique popliteal ligament is an important structure in the knee joint and has several key characteristics:

- **Origin**: It originates as an expansion from the tendon of the semimembranosus muscle.

- **Course**: This ligament runs in an upward and lateral direction, superficial to the knee joint capsule.

- **Attachment**: It is attached to the intercondylar line of the femur.

- **Reinforcement**: The ligament blends with and strengthens the posterior aspect of the knee joint capsule.

- **Relationships**: The oblique popliteal ligament is closely related to the popliteal artery and is pierced by several structures, including the middle genicular nerve, middle genicular vessels, and the posterior division of the obturator nerve.

**Arcuate Popliteal Ligament**

The arcuate popliteal ligament is a Y-shaped fibrous band with specific attachments and relationships:

- **Stem Attachment**: The stem of the band is attached to the styloid process of the fibula.

- **Large Posterior Limb**: The larger posterior limb of the Y-shaped band arches over the tendon of the popliteus muscle and is attached to the posterior border of the intercondylar area of the tibia.

- **Small Anterior Limb**: While the larger posterior limb is well-defined, the smaller anterior limb is often deficient. When present, it passes deep to the fibular collateral ligament and attaches to the lateral condyle of the femur.

**Transverse Ligament**

The transverse ligament extends horizontally and serves to connect the anterior ends of the medial and lateral menisci. It is not uniformly present and is found in only about 40% of individuals. Its function is to help stabilize the menisci within the joint.

**Coronary Ligaments**

Coronary ligaments are portions of the fibrous capsule of the knee joint that provide attachment to the peripheral margins of the medial and lateral menisci on the tibia. These ligaments contribute to the stability and secure positioning of the menisci within the joint, facilitating their proper function as shock absorbers and joint congruence enhancers.

These ligaments and fibrous bands in the knee joint play significant roles in maintaining joint stability, supporting the menisci, and protecting the surrounding structures. Understanding their anatomy is crucial for diagnosing and treating various knee-related conditions and injuries.

**Bursae Around the Knee**

Around the knee joint, there are approximately 12 bursae, which are fluid-filled sacs that help reduce friction and facilitate smooth movement of tendons and ligaments. These bursae are categorized into four groups: anterior, lateral, medial, and posterior.

**Anterior Bursae**

1. **Subcutaneous Prepatellar Bursa (Bursa of Housemaid's Knee)**: Located deep to the skin, it is found in front of the lower half of the patella and the upper half of the ligamentum patellae and tibial tuberosity.

2. **Subcutaneous Infrapatellar Bursa**: Positioned between the skin and the smooth lower part of the tibial tuberosity.

3. **Deep Infrapatellar Bursa**: This bursa lies between the ligamentum patellae and the tibial tuberosity.

4. **Suprapatellar Bursa**: Situated between the anterior surface of the lower part of the femur and the deep surface of the quadriceps femoris.

**Lateral Bursae**

1. The bursa located between the fibular collateral ligament and the tendon of the biceps femoris.

2. The bursa positioned between the fibular collateral ligament and the tendon of the popliteus.

3. The bursa found between the tendon of the popliteus and the lateral condyle of the femur. This bursa, in reality, is a synovial tube around the tendon of the popliteus and communicates with the joint cavity.

**Medial Bursae**

1. The bursa that separates the tendons of the sartorius, gracilis, and semitendinosus from each other and from the tibial collateral ligament, often referred to as the "bursa anserine."

2. The bursa positioned between the tendon of semimembranosus and the medial collateral ligament.

3. The bursa located between the tendon of semimembranosus and the medial condyle of the tibia. This bursa may have communication with the knee joint.

**Posterior Bursae**

1. The bursa between the lateral head of the gastrocnemius muscle and the capsule of the knee joint.

2. The bursa between the medial head of the gastrocnemius muscle and the capsule of the knee joint, known as "Brodie's bursa."

**Clinical Correlations**

- **Housemaid's Knee (Prepatellar Bursitis)**: Inflammation of the prepatellar bursa due to friction against the patella, often occurring in housemaids who kneel frequently. This condition can cause significant swelling and may lead to the bursa dropping below its original position.

- **Clergyman's Knee (Subcutaneous Infrapatellar Bursitis)**: Inflammation of the subcutaneous infrapatellar bursa caused by friction against the tibial tuberosity due to kneeling. It is seen in professions such as Christian priests/clergymen, roofers, and floor tilers.

- **Baker's Cyst**: A chronic inflammation of the bursa deep to the semimembranosus can result in a cystic swelling in the medial part of the popliteal fossa, known as Baker's cyst.

**Relations of the Knee Joint**

The knee joint has various anatomical relations in different directions:

**Anteriorly:**

1. **Tendon of the Quadriceps Femoris**: The powerful quadriceps muscle group, including the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris, collectively forms the tendon of the quadriceps femoris. This tendon surrounds and stabilizes the patella.

2. **Patella**: The patella, a sesamoid bone embedded within the quadriceps tendon, moves during knee flexion and extension.

3. **Ligamentum Patellae**: Also known as the patellar ligament, it connects the patella to the tibial tuberosity.

4. **Patellar Plexus of Nerves**: A network of nerves around the patella, including sensory nerves.

**Anteromedially:**

1. **Medial Patellar Retinaculum**: A thickening of the medial portion of the extensor retinaculum that helps stabilize the patella medially.

**Anterolaterally:**

1. **Lateral Patellar Retinaculum**: A thickening of the lateral portion of the extensor retinaculum that helps stabilize the patella laterally.

2. **Iliotibial Tract**: The iliotibial tract, or IT band, is a thick band of fascia that runs down the lateral side of the thigh and attaches to the lateral condyle of the tibia. It helps stabilize the lateral aspect of the knee.

**Posteriorly:**

1. **Popliteal Vessels**: These are the blood vessels located in the popliteal fossa, which is the diamond-shaped space at the back of the knee.

2. **Tibial Nerve**: A branch of the sciatic nerve, it provides sensory and motor innervation to the posterior thigh and leg.

3. **Oblique Popliteal Ligament**: This ligament extends from the tendon of the semimembranosus muscle and reinforces the posterior aspect of the knee joint.

**Posterolaterally:**

- In the upper part, the tendon of the biceps femoris muscle and the common peroneal nerve.

- In the lower part, the lateral head of the gastrocnemius muscle and the plantaris muscle.

**Posteromedially:**

- In the upper part, it is related to the sartorius, gracilis, semimembranosus, and semitendinosus muscles.

- In the lower part, it is associated with the medial head of the gastrocnemius muscle and the popliteus muscle.

**Blood Supply of the Knee Joint**

The knee joint is well-vascularized and receives its blood supply through an arterial anastomosis. This anastomosis is formed by various arteries, including genicular branches of the popliteal artery, the descending genicular branch of the femoral artery, the descending branch of the lateral circumflex femoral artery, two recurrent branches of the anterior tibial artery, and the circumflex fibular branch of the posterior tibial artery.

**Nerve Supply of the Knee Joint**

The knee joint is richly innervated by several nerves, including:

- The femoral nerve, which provides branches to the vastus muscles, especially the vastus medialis.

- The tibial and common peroneal nerves, which supply genicular branches.

- The obturator nerve through its posterior division.

**Movements of the Knee Joint**

The knee joint allows for several movements, including:

1. **Flexion**: Decreasing the angle between the posterior thigh and leg.

2. **Extension**: Increasing the angle between the posterior thigh and leg, returning to the anatomical position.

3. **Medial Rotation**: Rotation toward the midline of the body.

4. **Lateral Rotation**: Rotation away from the midline of the body.

**Locking and Unlocking of the Knee Joint**

The knee joint has a unique mechanism known as "locking and unlocking" to ensure stability during weight-bearing activities. This mechanism is defined by two essential phases:

**Locking of the Knee:**

- Locking of the knee occurs during the terminal phase of knee extension, especially when the foot is on the ground.

- It is characterized by the medial rotation of the femur on the tibia.

- When the knee is locked, it becomes absolutely rigid, and all the ligaments of the joint are taut.

- This mechanism is often referred to as the "screw home mechanism."

- Locking of the knee is essential for bearing weight during an erect posture.

**Unlocking of the Knee:**

- Unlocking of the knee takes place during the initial phase of knee flexion, particularly when the foot is on the ground.

- It is facilitated by the popliteus muscle.

- When the knee is unlocked, it can be further flexed, allowing for movements such as walking or running.

- The popliteus muscle plays a crucial role in initiating the unlocking of the knee.

- This alternation between locking and unlocking of the knee is essential for smooth locomotion during activities like walking or running.

**Differences Between Locking and Unlocking of the Knee:**

- **Locking** involves medial rotation of the femur on the tibia during the terminal phase of extension, while **unlocking** consists of lateral rotation of the femur on the tibia during the initial phase of flexion.

- Locking is primarily brought about by the quadriceps femoris muscles, while unlocking is facilitated by the popliteus muscle.

- When the knee is locked, it becomes rigid, and all ligaments are taut. In contrast, when the knee is unlocked, all ligaments are relaxed.

- Locking is essential for weight-bearing and stability, while unlocking allows for further flexion of the knee during movement.

The range of motion (ROM) for knee flexion is approximately 130 degrees, while the ROM for knee extension ranges from 0 to 50 degrees. The ROM for flexion is greater when the hip joint is fixed, and the ROM for extension is greater when the hip is extended but limited when the hip is flexed. These movements are critical for various activities and functions of the lower limb.

**Common Knee Joint Conditions and Clinical Considerations:**

1. **Osteoarthritis:** Osteoarthritis is a common condition affecting the knee joint due to degenerative wear and tear of the articular cartilages. It often leads to painful and limited joint movements. Radiographic examination typically reveals the presence of osteophytes, which are peripheral lipping of the articular ends.

2. **Injuries to Cruciate Ligaments:** Injuries to the cruciate ligaments are not uncommon, with the anterior cruciate ligament being more frequently damaged than the posterior ligament. The anterior cruciate ligament is typically injured in cases of anterior dislocation of the tibia, while the posterior cruciate ligament is affected in posterior tibial dislocations. Ligament tears can result in abnormal anteroposterior joint mobility. Clinical signs of these injuries include:

- **Anterior Drawer Sign:** Excessive forward movement of the tibia on the femur when the anterior cruciate ligament is torn.

- **Posterior Drawer Sign:** Excessive backward movement of the tibia when the posterior cruciate ligament is torn.

3. **Aspiration of the Knee Joint:** Collections of fluid within the knee joint are common and can lead to swelling above and around the patella. Patellar tap is a diagnostic technique used to detect a floating patella. Aspiration of the fluid can be performed on either side of the ligamentum patellae, but the lateral approach is often preferred. Three bony landmarks, including the tibial tuberosity, lateral epicondyle of the femur, and apex of the patella, are used to guide needle insertion during the procedure. This triangular area is also suitable for administering drug injections to treat knee pathologies.

4. **Arthroscopy of the Knee Joint:** Arthroscopy is an endoscopic procedure that allows for the visualization of the interior of the knee joint with minimal disruption of surrounding tissues. It is commonly used for diagnostic purposes and can also be employed for ligament repair or replacement.

5. **Knee Replacement:** In cases of severe knee joint damage, especially due to advanced osteoarthritis, knee replacement surgery may be necessary. This procedure involves the removal of damaged joint components and the insertion of an artificial joint. The artificial joint typically consists of a plastic tibial component and a metal femoral component, which are securely attached to the tibial and femoral bone ends.

6. **Unhappy Triad of the Knee Joint:** The "Unhappy Triad" is a term used to describe a combination of injuries involving the (a) tibial collateral ligament, (b) medial meniscus, and (c) anterior cruciate ligament in the knee joint. This combination of injuries can lead to significant joint instability and requires thorough evaluation and appropriate treatment.