It is a very unstable joint due to its anatomy and the shape of the articular surfaces.
The Knee is the joint between the femur and the tibia. The patella is a bone located in the anterior part of the knee that serves as a lever to enhance the extensor mechanism. The fibula is also around it, it is not part of the knee joint itself, but it is important because some structures are inserted there that stabilize the lateral face.
The knee is vulnerable to bone, ligamentous and meniscal trauma.. It is a very unstable joint due to its anatomy and the shape of the articular surfaces; since a convex femoral surface joins with a semi-flat one, the tibia. The patella protects the knee on the anterior surface.
Who gives the stability of the Knee?
Knee stability It is given by muscular and ligamentous balance.
The most important ligaments are:
- Anterior cruciate ligament (ACL): this ligament prevents the Knee from moving forward. It originates from the anterior and central part of the tibial plateau towards the posterior part of the lateral femoral condyle within the intercondylar notch of the knee.
- Posterior cruciate ligament (PCL): This ligament prevents the knee from going backwards. It originates in the central and posterior part of the Knee on the tibial plateau forward to the anterior medial condyle in the intercondylar notch. If you see the graph they look like an X, that’s why they are called crossed
- Medial or internal collateral ligament (MCL): this ligament prevents the Knee from going inward. It originates from the medial epicondyle of the femur on the inner side and inserts into the inner or medial region of the tibia.
- Lateral or external collateral ligament (LCL): this ligament prevents the Knee from going outward. It originates from the lateral epicondyle of the femur and inserts into the head of the fibula.
The most frequently injured ligaments of these are the ACL and MCL. Unfortunately, the ACL does not have the ability to heal and that means it is almost always surgical. The MCL does have the ability to heal and therefore in rare cases when it generates residual or great instability it must be operated on. The PCL ruptures infrequently and has the ability to heal and is therefore rarely operated on. The LCL has no recovery capacity and when it ruptures and generates instability, surgery must be performed, but fortunately these injuries are less frequent than those of the MCL.
What are the muscles that pass around the Knee?
The most important muscles around the Knee are:
- Quadriceps femoris that go in the anterior (front) part and have four parts: rectus femoris, vastus medialis, vastus lateralis and vastus intermedius. They are responsible for the extension of the Knee. They originate from the pelvis forward towards the thigh and insert into the kneecap where the four muscles come together in a joint tendon called the Quadriceps tendon.
- Hamstrings that go on the back (back) of the thigh and there are three: semitendinosus, semimembranosus, biceps femoris. They are responsible for bending the knee backwards. They also originate in the pelvis and insert into the tibia and fibula near the knee.
- Adductors that go on the inner (medial) part of the thigh. There are four: adductor brevis, adductor longus, adductor magnus and gracilis. They make the thigh move inward
- Iliotibial band and fascia lata that run on the outer (lateral) part of the thigh. This is responsible for bringing the thigh outwards. It originates in the hip on the lateral side (greater trochanter of the femur) and inserts into a tendon on the tibia anteriorly and laterally. (Gerdy tuber)
- Medial and lateral gastrocnemius (gastrocnemius) that run at the back of the knee on the femur and leg and insert into the calcaneus bone at the back of the heel via a joint tendon called the Achilles tendon.
- The goose foot is the insertion of three muscles on the anterointernal part of the knee. The semitendinosus, gracilis and sartorius. This insertion site is frequently the site of knee pain due to lack of flexibility of these muscles.
The extensor mechanism, as its name indicates, achieves the extension of the knee, that is, the knee is straight. It is made up of the following structures:
• The Quadriceps muscle
• The Quadriceps tendon
• The kneecap (patella)
• The patellar (patellar) tendon
• The anterior tibial tubercle
What are Menisci?
The Menisci are fibroelastic structures located between the femur and tibia, C-shaped whose main function is to cushion loads. They are made up of the anterior horn, body and posterior horn. They have very poor vascularization and that is the reason why they do not have good healing capacity and when they rupture they must be operated on.
They are frequently injured in rotational trauma or forced flexion. and they often accompany ligament injuries such as the medial collateral ligament and the anterior cruciate ligament. There are two Menisci:
- C-shaped internal meniscus
- O-shaped external meniscus
There is an anatomical variant of the menisci which is the discoid meniscus. This meniscus is in the shape of an arepa and is more frequently the lateral meniscus. It is a congenital deformity that, due to its shape, predisposes it to rupture, even with minor trauma.
What is the patellofemoral joint?
The patellofemoral joint is between the kneecap and the femur at the front of the knee. It is very important because it is a frequent site of pain and injuries. Among others, the most frequent cause of consultation for things related to the Knee is pain in front of the Knee or patellofemoral pain, which has many causes and we will discuss them in another article. Patella dislocations are also common, mainly in young people, although there are also poor alignments of the patella that do not cause dislocation but pain.
What is articular cartilage?
articular cartilage It is a structure formed by hyaline cartilage that covers the bones in the joints, whose functions are to cushion the load of the joint contact surfaces. and generate little friction to allow the sliding of these bone surfaces with the least possible friction. Its live appearance is white since it has no vascularization. Which is why it also has no regeneration or healing properties. It also has no innervation, therefore it does not produce pain. The pain in these injuries occurs from the subchondral bone (under the cartilage). All of these injuries and their treatment will be covered in another article.