Knee Joint Flashcards
What kind of joint is the knee?
The knee joint is a bicondylar type synovial joint, which mainly allows for flexion and extension (and a small degree of medial and lateral rotation). It is formed by articulations between the patella, femur and tibia. The shape of the knee joint means that it is relatively weak, and so it relies on muscles and ligaments to ensure stability.
What are the articulating surfaces of the knee joint?
Tibiofemoral – The medial and lateral condyles of the femur articulating with the tibia.
Patellofemoral – The anterior and distal part of the femur articulating with the patella.
The tibiofemoral joint is the weightbearing joint of the knee.
The patellofemoral joint allows the tendon of the quadriceps femoris (the main extensor of the knee) to be inserted directly over the knee, increasing the efficiency of the muscle. Both joint surfaces are lined with hyaline cartilage, and enclosed within a single joint cavity.
The patella is formed inside the tendon of the quadriceps femoris; its presence minimises wear and tear on the tendon.
What are the menisci?
The medial and lateral menisci are fibrocartilage structures in the knee that serve two functions:
To deepen the articular surface of the tibia, thus increasing stability of the joint.
To act as shock absorbers.
They are C shaped, and attached at both ends to the intercondylar area of the the tibia.
In addition to the intercondylar attachment, the medial meniscus is fixed to the tibial collateral ligament and the joint capsule. Any damage to the tibial collateral ligament results in tearing of the medial meniscus.
The lateral meniscus is smaller and does not have any extra attachments, rendering it fairly mobile.
Describe the bursae of the knee
Suprapatella bursa – This is an extension of the synovial cavity of the knee, located between the quadriceps femoris and the femur.
Prepatella bursa – Found between the apex of the patella and the skin.
Infrapatella bursa – Split into deep and superficial. The deep bursa lies between the tibia and the patella liagment. The superficia lies between the patella ligament and the skin.
Semimembranosus bursa – Located posteriorly in the knee joint, between the semimembranosus muscle and the medial head of the gastrocnemius.
Describe the ligaments of the knee
- Patellar ligament – A continuation of the quadriceps femoris tendon distal to the patella. It attaches to the tibial tuberosity.
- Collateral ligaments – These are two strap-like ligaments. They act to stablise the hinge motion of the knee, preventing any medial or lateral movement:
Tibial (medial) collateral ligament – A wide and flat ligament, found on the medial side of the joint. Proximally, it attaches to the medial epicondyle of the femur, distally it attaches to the medial surface of the tibia.
Fibular (lateral) collateral ligament – Thinner and rounder than the tibial collateral, this attaches proximally to the lateral epicondyle of the femur, distally it attaches to a depression on the lateral surface of the fibular head.
- Cruciate Ligaments – These two ligament connect the femur and the tibia. In doing so, they cross each other, hence the term ‘cruciate’ (latin for like a cross):
Anterior cruciate ligament – attaches at the anterior intercondylar region of the tibia and ascends posteriorly to attach to the femur, in the intercondylar fossa. It prevents anterior dislocation of the tibia onto the femur.
Posterior cruciate ligament – attaches at the posterior intercondylar region of the tibia, and ascends anteriorly to attach to the femur in the intercondylar fossa. It prevents posterior dislocation of the tibia onto the femur.
What movements occur at the knee?
Extension: Produced by the quadriceps femoris, which inserts into the tibial tuberosity.
Flexion: Produced by the hamstrings, gracilis, sartorius and popliteus.
Lateral rotation: Produced by the biceps femoris.
Medial rotation: Produced by five muscles; semimembranosus, semitendinosus, gracilis, sartorius and popliteus.
NB: Lateral and medial rotation can only occur when the knee is flexed (if the knee is not flexed, the medial/lateral rotation occurs at the hip joint).
Describe the patella
The patella (knee-cap) is located at the front of the knee joint, within the patellofemoral groove of the femur. It attaches superiorly to the quadriceps tendon and inferiorly to the patellar ligament.
It is classified as a sesamoid type bone due to its position within the quadriceps tendon, and is the largest sesamoid bone in the body.
Describe the bony landmarks of the patella
The patella has a triangular shape, with anterior and posterior surfaces. The apex of the patella is situated inferiorly, and is connected to the tibial tuberosity by the patella ligament. The base forms the superior aspect of the bone, and provides the attachment area for the quadriceps tendon.
The posterior surface of the patella articulates with the femur, and is marked by two facets:
Medial facet – articulates with the medial condyle of the femur.
Lateral facet – articulates with the lateral condyle of the femur.
What are the functions of the patella?
The patella has two main functions:
Leg extension – Enhances the leverage that the quadriceps tendon can exert on the femur, increasing the efficiency of the muscle.
Protection – Protects the anterior aspect of the knee joint from physical trauma.
