This article provides the overview about the articulation, type, capsule, synovium, ligaments and menisci of the knee joint.
Articulation of the Knee Joint:
- The knee joint is formed by the articulation of the condyles of the femur above and the condyles of the tibia and their menisci below.
- Anteriorly there is articulation between the patellar surface of the femur and the posterior surface of the patella.
Type of the Knee Joint:
- The knee joint is the synovial hinge joint between the femur and the tibia.
- It is synovial gliding joint between the femur and the patella.
Capsule of the Knee Joint:
- The capsule encloses the knee joint and is attached to the margins of the articular surface.
- The capsule is deficient anterosuperiorly from where the joint cavity communicates with the suprapatellar bursa (behind the quadriceps tendon).
- It is also deficient posteriorly where the joint cavity communicates with the semimembranosus bursa (under the medial head of gastrocnemius).
- Posteriorly the popliteus muscle tendon pierces the capsule.
- The synovial membrane lines the capsule and the associated bursae.
- The synovial membrane pouches anterosuperiorly extending beneath the quadriceps femoris tendon to form the suprapatellar bursa.
- Posteriorly the synovial membrane extends downwards on the tendon of popliteus muscle to form the popliteal bursa.
- The synovial membrane is reflected forward and around the front of the cruciate ligaments causing the cruciate ligaments to lie behind the synovial cavity.
- There is a fat pad in the joint deep to the ligamentum patellae called the infrapatellar fat pad.
- The synovial membrane covering this fat pad is projected into the joint and are called alar folds.
Ligaments of the Knee Joint:
The ligaments of the knee joint are divided into two categories:
- Extracapsular Ligaments:
Extracapsular ligaments are as follows:
Medial Collateral ligament:
- The medial collateral ligament is a flat band that is attached above to the medial condyle of femur and below to the medial surface of the shaft of tibia.
- The deep part of the ligament is attached to the medial meniscus.
- It is separated from the capsule by a bursa.
Lateral Collateral Ligament:
- The lateral collateral ligament is cordlike structure and it is attached above to the lateral condyle of the femur and below to the head of the fibula.
- It is separated from the lateral meniscus by the tendon of the popliteus muscle.
- The ligamentum patellae is a continuation of the quadriceps femoris muscle.
- It is attached above to the lower border of the patella and below to the tubercle of the tibia.
Oblique Popliteal Ligament:
- The oblique popliteal ligament is a tendinous expansion of the semimembranosus muscle.
- It strengthens the capsule posteriorly.
The other ligaments are the medial and lateral patellar retinacula.
Cruciate ligaments are the two strong intracapsular ligaments of the knee joint. They are called anterior and the posterior cruciate ligament according to their tibial attachments.
Anterior Cruciate Ligament (ACL):
- The anterior cruciate ligament arises from the anterior intercondylar area of the tibia.
- It passes upwards, backward and laterally to be inserted into the inner aspect of the lateral femoral condyle.
- The anterior cruciate ligament prevents hyperextension of the knee joint.
Posterior Cruciate Ligament (PCL):
- The posterior cruciate ligament arises from the posterior intercondylar area of the tibia.
- It passes upwards, forwards and medially to be inserted into the inner aspect of the medial femoral condyle.
- The posterior cruciate ligament prevents hyperflexion.
- The menisci are the two crescentic shaped fibrocartilage.
- The peripheral convex border of each menisci is thick and is attached to the capsule.
- The inner border is thin and concave and forms a free edge.
- The upper surfaces of the menisci are in contact with femoral condyles and the lower surfaces are in contact with tibia.
- The menisci are attached to the upper surface of the tibia by the anterior and the posterior horn.
- The menisci are triangular in cross-section.
- These menisci deepens the articular surface of the tibia.
- The medial meniscus is bigger, thinner and is less curved.
- The medial meniscus is attached to the medial collateral ligament, so is less mobile and is susceptible to injury.
- The posterior horn of the medial meniscus is thick measuring 14mm which thins out anteriorly, so the anterior horn measures 6mm.
- The lateral meniscus is smaller, curved and uniform in its thickness.
- It measures 10mm.
- The lateral meniscus is not well attached to the capsule and is grooved by the tendon of popliteus muscle posterolaterally which separates it from the capsule.
- The transverse ligament passes between the anterior horns of the menisci.
- The meniscofemoral ligament passes between the posterior horn of the lateral meniscus and the medial femoral condyle.
- This ligament has an anterior part that passes anterior to the posterior cruciate ligament called the meniscofemoral ligament of Humphrey.
- The posterior part of this ligament passes posterior to the posterior cruciate ligament and is called menicofemoral ligament of Wrisberg.