- The knee joint is the largest joint in the body.
- The knee is a synovial
- hinge type joint.
- The entire weight-bearing load is transferred
through the knee joints.
When describing the knee, four bones and
their articulations should be discussed:
the femur, the tibia, the fibula, and the
- Each articulation surface is covered with hyaline cartilage.
- The primary articulation of the knee is between the
condyles of the femur and tibia.
- This articulation is separated by the medial and lateral
menisci, which serve to deepen the articular surfaces
and aid in lubrication and cushioning of the joint.
Although not a part of the knee joint, the articulation
of the tibia and fibula is significant due to its
importance in weight bearing.
- The patellofemoral joint is a synovial gliding type joint.
- The patella is a sesamoid bone contained in the tendon of the
quadriceps muscle. The articulation consists of the
underside of the patella and the patellar grove of
the femur. The gliding of the patella in the femoral
grove allows for increased efficiency of the
MUSCLES OF THE KNEE
- Many muscles acting on the thigh have their insertions around
- Although not participating in gross knee movements these
muscles are significant in the dynamic stabilization of the knee
- Only the muscles specifically participating in knee flexion, extension,
internal, and external rotation are discussed here.
- The anterior muscles of the knee act primarily as knee extensors.
- The quadriceps femoris muscle is the principle muscle involved in
This muscle can be divided into four distinct parts:
1. the rectus femoris
2. vastus medialis
3. vastus lateralis
4. vastus intermedius.
- All four parts of this muscle come together to insert on the
proximal edge of the patella, which then transfers their action,
by way of the patellar tendon, to the tibia.
The principle muscles involved in knee flexion
hamstring muscle group. This group is comprised of:
1. the biceps femoris
3. semimembranosus muscles.
- Their insertion occurs on the proximal tibia and head
of the fibula.
- The biceps femoris muscle has an additional action of
externally rotating the tibia.
- While the semitendinosus and semimembranosus muscles also
have an additional role of internally rotating the tibia.
- Other muscles participating in knee flexion and internal
rotation are the sartorius, and gracilis muscles.
- The popliteus muscle also serves to internally rotate the
knee in a non-weight bearing position.
- Additional muscles involved in isolated knee flexion include
the gastrocnemius and plantaris muscles.
- Blood is supplied to the knee via the popliteal artery.
- The popliteal artery originates from the external iliac artery, which
gives rise to the femoral artery in the proximal thigh.
- The femoral artery passes posterior to the knee and becomes
the popliteal artery.
- The knee joint and surrounding musculature is innervated by a
number of nerves of the lower limb. Originating from the
lumbosacral plexus the femoral and obturator nerves innervate
the front and anteromedial sides of the thigh.
- The sciatic nerve, which rises from the sacral plexus supplies
the posterior thigh and divides above the knee to form the
common peroneal and tibial nerves.
- Various bursae are located about the knee joint for purposes of
decreasing friction over tendons and bones.
- The suprapatellar bursa is located between the deep surface of
the quadriceps muscle and the distal part of the femur.
- This bursa is in communication with the joint capsule of the knee.
- The prepatellar bursa is located between the superficial surface
of the patella and the skin.
- An infrapatellar bursa is located between the patellar ligament
and the skin.
- The deep infrapatellar bursa is situated between the proximal
tibia and the patellar ligament.
- Other bursae decrease friction at the attachment sites of the
gastrocnemius, gracilis, sartorius, semitendinosus, and
JOINT AND LIGAMENTS
- Static stabilization of the knee is provided by the ligamentous
structures and to a lesser extent the joint capsule surrounding
the knee articulations.
- The principle stabilizing ligaments of the knee are discussed here.
- The anterior portion of the knee joint is stabilized partly by the
medial and lateral patellar retinacula, which are extensions of the
quadriceps femoris muscle
- The patellar tendon gives added support to the anterior portion
of the knee.
- The oblique popliteal ligament and the arcuate popliteal ligament
stabilize the posterior aspect of the knee.
- The oblique popliteal runs from the intercondylar fossa of the
femur to the head of the tibia. While the arcuate popliteal rises
from the lateral condyle of the femur to attach to the styloid
process of the head of the tibia.
- The tibial (medial) collateral and the fibular (lateral) collateral
ligaments serve to stabilize the medial and lateral aspects of the
knee joint respectively.
- These ligaments also serve to restrain rotation of the knee
- The tibial collateral ligament is a broad, flat ligament that runs from
the medial condyle of the femur to the medial condyle of the tibia.
- A deep portion of this ligament blends posteriorly with the joint
capsule of the knee, which is also attached to the medial meniscus.
- The fibular collateral ligament is more rounded and cordlike and
extends from the lateral epicondyle of the femur to the lateral
aspect of the head of the fibula.
- These ligaments are especially important stabilizers of rotational
and lateral movement when the knee is in the extended position
- Two important intra-articular ligaments that provide static support
to the knee are the anterior (ACL) and posterior (PCL) cruciate
- Although the ligaments are intra-articular they are not contained
within the joint capsule of the knee.
- The ACL extends from the anterior area between the condyles
of the tibia in a posterior and lateral direction to a posterior area
on the medial surface of the lateral condyle of the femur
- The ACL functions to prevent anterior displacement of the tibia
on the femur.
- The PCL runs from a posterior depression between the condyles
of the tibia in an anterior and medial direction to the lateral side
of the medial femoral condyle
- The PCL functions to prevent posterior translation of the tibia on
- Additionally both the ACL and PCL serve to reduce rotation of
the femur on the tibia. The ligaments are tense in all positions,
but increase their tension in the extremes of flexion and
- The principle motions of the knee joint are flexion and extension;
however, it does allow for some degree of rotation
- The arc of motion of the knee defined by Hoppenfeld (1976) is
typically about 0° extension to 135° of flexion.
- The amount of internal and external rotation about the knee is
approximately 5° to 10° in each direction
- It is in extension that the rotational component of the knee joint
- The knee is unable to reach full extension without a small amount
of external rotation of the tibia on the femur.
- This need for external rotation is due to the fact that the medial
femoral condyle is approximately 1/2-inch longer than the lateral
- The external rotation of the tibia allows the knee to achieve full
- This mechanism is known as the "screw home" mechanism and it
allows the knee to be held in full extension without undue fatigue
of the surrounding musculature