Anatomy of the knee (Bones Muscles Arteries Veins Nerves)

The Anatomy of the knee, knee Bones, knee Muscles knee Arteries knee Veins and Nerves looking into the anatomy of the knee. full list of the names of bones , muscles ,veins ,arteries and veins found in the knee.

Fig. 1 Bonny structure of the knee joint. Drake et al: Grays Anatomy for Students
Fig. 1 Bonny structure of the knee joint. Drake et al: Grays Anatomy for Students | Source

Bone and Ligaments

Bone and Ligaments

Bones of the knee (Fig.1):

Femur: the longest and the heaviest bone in the body. Important anatomical features: femoral head (articulates with the pelvis at the acetabulum; greater and lesser trochanters (muscle attachment sites); linea aspera (muscle attachment site); medial and lateral epicondyles (participate in the knee joint).

Tibia: the large medial bone of the low leg. The hip joint transfers weight to the femur, and the knee joint passes the weight from the femur to the tibia. Important anatomical features: medial and lateral tibial condyles (articulate with the medial and lateral condyles of the femur); tibial tuberosity (attachment for the patellar ligament); intercondylar eminence (attachment sites for the cruciate ligaments); medial malleolus (important in the ankle joint).

Fibula: a thin bone with relatively small diameter which parallels the lateral border of the tibia. The head of the fibula articulates with the tibia. The fibula does not play a vital role in the knee joint. It does not articulate with the femur and thus does not bear much the weight of the lower leg. The fibula has an important role in the ankle joint where it forms part of the joint.

Patella: the largest sesamoid (forms within the tendon) bone which sits anteriorly at the knee. It gives mechanical advantage to the knee joint so there is minimum tear of the ACL.

Knee joint is the largest and most complex joint of the body. It is a hinge joint, a special type of mobile trochoginglymus, where flexion of the joint combines rolling and gliding movements.

There are three articulations:

1. Lateral femoral and tibial condyles with corresponding meniscus which is weightbearing.

2. Medial femoral and tibial condyles with corresponding meniscus.

3. Patella and femur which allows the pull of the quadriceps femoris muscle to be directed anteriorly over the knee to the tibia without tendon wear.

The articular surfaces of the joint are not similar: the articular surfaces of the proximal tibia are relatively flat whereas the femoral condyles are rounded (Fig.2). Therefore the menisci (fibrocartilage discs which are attached to the intercondylar eminence of the tibia) are essential for the joint stability as they form some sort of cushions between the tibia and femur. 

Fig.2 Articulating surfaces of the tibia. Drake et al: Grays Anatomy for Students
Fig.2 Articulating surfaces of the tibia. Drake et al: Grays Anatomy for Students | Source

The joint is relatively weak mechanically, thus stability depends on surrounded muscles and ligaments.

Name Location and functions of knee legaments

Name
Location
Function
Medial (tibial) collateral ligament (MCL)
Attaches by much of its deep surface to the underlying fibrous membrane. It is anchored superiorly to the medial femoral epicondyle just inferior to the adductor tubercle and descends anteriorly to attach to the medial margin and medial surface of the tibia above and behind the attachment of sartorius, gracilis, and semitendinosus tendons
Stabilises the hinge-like motion of the knee and prevents knee abduction
Lateral (fibular) collateral ligament (LCL)
Attaches superiorly to the lateral femoral epicondyle just above the groove for the popliteus tendon. Inferiorly, it is attached to a depression on the lateral surface of the fibular head. It is separated from the fibrous membrane by a bursa
Stabilises the hinge-like motion of the knee and knee adduction. It is stronger than MCL
Anterior cruciate ligament (ACL)
Attaches to a facet on the anterior part of the intercondylar area of the tibia and ascends posteriorly to attach to a facet at the back of the lateral wall of the intercondylar fossa of the femur
Interconnect the femur and tibia, stops tibia moving forward on femur, prevents hyperextension and excessive internal rotation. ACL crosses lateral to the PCL as they pass through the intercondylar region
Articular capsule and the bursa
Articular capsule presents only at the sides and posterior aspects of the knee, where it covers the bulk of the femoral and tibial condyles. It is stabilised and straighten by the joint ligaments and the muscle tendons. Bursa are extensions of the knee synovial cavity and are filled with synovial fluid
The capsule consists of an external fibrous layer (fibrous capsule) and an internal synovial membrane, which is continuous with the synovial lining of the bursa. They act as cushions against friction and rubbing of the tendons and bones around the knee joint
Table 1. Ligaments of the knee

Muscles and Movements

Muscles and Movements of the knee

Muscles are important contributors the knee joint stability, as the joint itself is mechanically weak. There are a number of muscles are found in the knee region. Their names, function and innervation listed below in the Fig. 3 and Table 2.  

Fig. 3. Posterior (left) and Anterior (right) view of the knee muscles
Fig. 3. Posterior (left) and Anterior (right) view of the knee muscles
Movement and range of movement
Name
Action
Knee flexors 135°-150°
1. Hamstrings ( semitendinosus, semimembranosus, biceps femoris) 2. Popliteus
Flexes and rotes leg medially, locks and unlocks the knee from beginnings of flexion
Knee extensors 0°-10°
Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedialis)
extends leg, (but flexes thigh by action of rectus femoris)
Knee rotation
Popliteus
Weakly flexes knee, unlocks knee by rotating femur 5° laterally on fixed tibia
Table 2. Muscles of the knee. Their function and innervation.

Neurovascular supply of the lower limb

Arteries

The main arteries supplying the knee region are femoral, popliteal, anterior tibial and posterior tibial arteries. Although the popliteal artery is deep in the popliteal fossa, the popliteal pulse can still be felt but the knee has to be bent and the person still has to press deep into the fossa.

Veins of the knee

Veins

There are deep and superficial veins. The names of the deep veins are the same as the names of the artery they accompany. There are two important superficial veins: the great and lesser saphenous veins. The great saphenous is often used in coronary bypass operations as it has thicker walls than most veins and therefore it can substitute for an artery. Removal of this vein does not cause a problem as there are still the deep veins to return the blood to the heart.

The venous return is often against gravity thus there are special mechanisms that assist in the venous return. These are negative pressure in the thorax; venous valves; calf muscle pressure.

Nerves

Nerves,The two plexi that contribute to the nervous innervation of the lower limb are the lumbar plexus and sacral plexus.

The lumbar plexus (L1-5) gives rise to the femoral and obturator nerves that innervate the hip flexors and adductors and the knee extensors.

The sacral plexus (L4-S4) forms the sciatic nerve which will divides into the common peroneal and tibial nerves at the popliteal fossa. 

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