Dr. Delee Talks about the Anatomy of the Knee
Anatomy
To better understand conditions of the knee let's look at the anatomy
of the knee joint and how the parts of the knee work together to
maintain normal function.
The medial side of the knee is the side closest to the other knee. The
lateral side of the knee is the side away from the other knee.
Structures on the medial side usually have medial as part of their
name, such as the medial meniscus.
Important Structures
The important parts of the knee include bones, ligaments, tendons and cartilage. The bones forming the knee joint include: the Femur, the large bone in the thigh, the Tibia, the large bone in the lower leg, the Fibula is the small bone in the lower leg and the patella or kneecap. Two ligaments are found on either side of the knee joint - the Medial Collateral Ligament and the Lateral Collateral Ligament. (See Fig. 2)
Inside the knee joint, two ligaments pass between the femur and the tibia. The Posterior Cruciate Ligament and the Anterior Cruciate Ligament.
The posterior cruciate ligament prevents the lower leg bone (tibia)
from going posteriorly on the upper leg bone (femur). The anterior
cruciate ligament prevents the lower leg bone (tibia) from going
anteriorly on the upper leg bone (femur) (see figure 3).
Two structures called Menisci reside between
the femur and the tibia. These structures are sometimes referred to as
the "cartilages" of the knee. (See Fig. 4)
Articular Cartilage, on the other hand, is a white
shiny material with a rubbery consistency that covers the end of the
femur, the top of the tibia, and the back of the patella. The function
of articular cartilage is to absorb shock and provide an extremely
smooth bearing surface to facilitate motion.
Finally, the Extensor Mechanism sits in front of the knee joint.(Figure 5) The Patella is the fourth bone of the knee joint. The Patellar Tendon connects the patella to the tibia. This tendon covers the patella and continues up the thigh as the Quadriceps Tendon.
Important Functions
Ligaments
The ligaments of the knee joint are primarily stabilizers of the
joint. Most joints in the body have a stable bony configuration. For
instance, the hip joint is a ball which sits inside a deep socket. The
ankle joint has a shape similar to a mortise and tenon. The knee has
very little bony stability, and behaves more like a round ball on a
flat surface. Because there is no inherent bony stability, the
ligaments of the knee are very important for stability.
The Medial Collateral and Lateral Collateral Ligaments prevent the knee
from moving too far in the side-to-side direction
The Anterior
Cruciate ligament and the Posterior Cruciate ligaments control the
front to back motion of the knee joint. The Anterior Cruciate ligament
keeps the tibia from sliding too far forward in relation to the femur.
The Posterior Cruciate ligaments keep the tibia from sliding to far
back in relation to the femur. Working together, the two cruciate
ligaments control the back and forth motion of the knee. The ligaments,
all taken together, are the most important structures controlling
stability of the knee.
Menisci
The menisci of the knee are important for two reasons:
- They work like a gasket, to spread the force of weight-bearing over a larger area.
- They help the ligaments with stability of the knee.
The menisci actually wrap around the end of the thigh bone to fill the
space between the round femur and the flat tibia. The menisci act like
gaskets helping to distribute the weight from the femur to the tibia.
Without the meniscus, any weight on the femur will be concentrated to
one point on the tibia. With the menisci the weight is spread out
across tibial surface. Weight distribution by the meniscus is important
because it protects the articular cartilage from excessive forces.
Without the meniscus, the concentration of force into a small area on
the articular cartilage can damage the surface, leading to degeneration
over time.
How does the meniscus help the ligaments with stability of the knee?
The meniscus enhances stability by acting like a chock under a tire,
and keeps the round femur from rolling on the flat tibia. In essence,
the meniscus converts the tibia surface into a shallow socket. A socket
configuration is more stable and more efficient at transmitting the
weight bearing forces. Hence, the meniscus enhances the stability of
the knee and protects the articular cartilage from excessive
concentration of force.
Articular Cartilage
Articular Cartilage covers the ends of the bones that makes up the
joint. This material is about ¼ of a inch thick in most large joints.
Articular cartilage is a tough, very slick material that allows the
surfaces to slide against one another without damage to either surface.
Damage to or loss of articular cartilage is commonly referred to as
arthritis.
Quadriceps Mechanism
The Quadriceps Mechanism is the motor that drives the knee
joint, and allows us to walk. The Quadriceps Mechanism is composed of
the patellar tendon, the patella, and the quadriceps muscle/tendon on
the front of the thigh. The patella fits into a groove called the
Patellofemoral Groove on the front of the femur. The way in which the
patella fits into this groove, and slides as the knee bends, can affect
the overall function of the knee. The patella functions like a fulcrum,
and increases the force exerted by the quadriceps muscle as the knee
straightens. When the Quadriceps Muscle contract, the knee straightens.
When it relaxes, the knee bends. While this is not a complete anatomy
of the knee, it represents a brief discussion of the most common
problematic portions of the knee.
|
|
home |
location |
privacy policy
