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Archive for the ‘Knee Anatomy’ Category

Bursa

Bursa

A bursa is the fluid-filled sac that provides a cushion between the bones, tendons, and muscles surrounding a joint.  This helps the knee move freely and protects the bones and cartilage.  The knee bursa is filled with synovial fluid.  Bursa is latin for “purse” because the fluid-filled sac looks a lot like a small purse.

Receiving an injection of synovial fluid is a treatment option for knee osteoarthritis.



Knee Cartilage

Knee Cartilage

Cartilage is a slippery cushion-like tissue between your bones. It serves as a smooth, resilient cushion that allows your knee joint to move freely.

There are two types of joint cartilage in your knees: fibrous and hyaline.

1.  Fibrous cartilage comprises the menisci, two pads of cartilage that disperse friction in between the lower leg and thigh. Acting like shock absorbers, it has tensile strength and can resist pressure.

2.  Hyaline cartilage covers the bony surfaces that joints move along. Flexible and strong, its smooth surface is slippery. This allows the knee joint to move easily. Hyaline cartilage will wear over the years, and has a limited capacity for self-restoration.

Osteoarthritis occurs when the cartilage in your knee erodes.



Calf Muscles

Calf Muscles

Triceps Surae: The calf muscles are located beneath the knee on the back of your leg.  They are responsible for lifting your foot so you can walk, run, and stand.    There are two muscles that connect to the foot by means of the Achilles tendon:

  1. Gastrocnemius – Branches off into two heads that connect above the knee to the bottom of the femur.
  2. Soleus – Lies beneath a portion of the gastrocnemius and attaches to the top of the tibia.

A torn calf muscle can change the way your knee moves.  This can lead to osteoarthritis.  If you already have OA, then keeping your calves stretched and strong can make your knees feel better.



Quadriceps_Osteoarthritis

Quadriceps

The quadriceps is a large group of muscles located on the front of the thigh.  They are responsible for extending the leg and they’re strongest muscles in the body.

The quadriceps is divided into four sections.  All four parts attach to the knee cap through the patella tendon.

Rectus Femoris – Located in the middle of the thigh, this section of the quadriceps covers most of the other three sections of muscle (listed below).  Along with knee extension, this muscle also helps flex the hip.  It is attached to the ilium, or the top of the hip.

Vastus Lateralis – Located under the rectus femoris, this section of the quadriceps is attached to the femur and lies on the outside (lateral side) of the thigh.

Vastus Medialis – Located under the rectus femoris, this section of the quadriceps is attached to the femur and lies on the inside (medial side) of the thigh.

Vastus Intermedius – Located under the rectus femoris, this section of the quadriceps is attached to the femur and lies between the vastus medialis and vastus lateralis.

Since all four sections of the quadriceps attach themselves to the knee cap, these muscles play an important role in how the knee slides and glides.  Injury of weakness can lead to or affect osteoarthritis of the knee.



Hamstrings

Hamstrings

Hamstrings refer to the muscles located on the back of your thigh.  These four muscles are responsible for flexing the knee, and three of the four help extend the hip.  The hamstrings are comprised of the:

Semitendinosus: is located on the back of the thigh, on the inside of the body (medial aspect).  This muscles helps straighten the hip and bend the knee.  It also assists rotating the knee inward (medially).

Semimembranosus – is located on the back of the thigh, on the very inside of the leg.  This muscle helps straighten the hip and bend the knee.

Biceps Femoris – is located on the back of the thigh, and has two parts:

  1. Long Head – attaches from the hip to the fibula and tibia.  It is responsible for extending the hip and bending the knee.  It also helps rotate the leg.
  2. Short Head – attaches from the femur to the fibula and tibia.  It is responsible for bending the knee and rotating the leg.

Keeping the hamstrings flexible is important if you have osteoarthritis.  Tight hamstrings will affect how your knee bends and straightens.



Knee Tendons

Knee Tendons

Tendons usually connect bones to muscles.  Tendons, also called sinew, are tough bands of connective tissue made from collagen.  The Patellar tendon is about 10cm in length and is flat and strong.  It connects the Quadriceps muscle to the tibia, and passes along either side of the patella.  It is divided into two distinct sections:

Patella Tendon: Connects to the front of the tibia at a place called the tibial tubercle, to the bottom of the patella.  Since this connective tissue is attached to two different bones, it is actually a ligament.
Quadriceps Tendon:  Connects the quadriceps femoris (thigh muscle) to the top of the patella.  Tears of the patellar tendon are more common in middle-aged people.  Falls, jumping and chronic diseases that disrupt blood supply can all weaken the patellar tendon.  Injuries do not always result in complete tears, many times some of the fibers become frayed, like a worn or damaged rope.
The patellar tendon is responsible for how your knee bends and straightens.  If it is injured, long-term wear-and-tear can affect how your knee slides and glides.  This can damage the cartilage in your knee, resulting in osteoarthritis.


Ligaments of the Knee

Ligaments of the Knee

A ligament is a band of fibrous tissue that connects bones to other bones.  There are four ligaments holding your knee together:

Anterior Cruciate Ligament (ACL):  This band of fibrous tissue connects the tibia to the femur.  It is responsible for keeping the femur from sliding too far backwards (posterior).

Posterior Cruciate Ligament (PCL):   This ligament also connects the tibia to the femur.  It is responsible for keeping the femur from sliding too far forwards (anterior).

Medial Collateral Ligament (MCL): This ligament connects the tibia to the femur on the inside (medial side)  of your knee.  It is responsible for keeping your knee from rotating too far outward (abduction).

Lateral Collateral Ligament (LCL):  This ligament connects the tibia to the femur on the outside (lateral side) of your knee.  It is responsible for keeping your knee from rotating too far inward (adduction).

If anyone of these ligaments becomes injured it can affect how your knee moves.  Over time the resulting tracking problems could lead to osteoarthritis.  The knee is a complicated joint.  Even the slightest change in how it slides and glides can cause problems.



Knee Joint

Knee Joint

A joint in the human body is where two or more bones come together.  The knee joint is where the thigh and lower leg meet, and it is the largest joint in the Human body.  It is a very complicated pivotal hinge joint that allows your leg to bend and straighten while at the same time turn slightly inward and outward.  When you walk your knee at times supports the entire weight of your body.  That is why it so susceptible to osteoarthritis, or wear-and-tear arthritis.

The knee is also a synovial joint.  A synovial joint is the most common and moveable joint in the Human body.  A capsule protects the synovial joint that is filled with a lubricating fluid.  This synovial fluid helps protect the surfaces of the knee that move against one another.  We will look at synovial capsules and fluids in a later blog post.



Knee Bones

Knee Bones

To understand how osteoarthritis affects your knee you need to understand how your knee works.  This series of blog posts will introduce you to the anatomy of your knee.  Let’s begin with the basic building blocks – the bones.  There are four bones we need to discuss:

Femur: Also known as the thigh bone is the longest bone in the human body.  The top of the femur forms the hip joint while the bottom of the femur forms the knee.

Patella: Also known as the knee cap.  It kind of looks like a triangle with its tip facing down towards your feet.  It is the largest sesamoid bone in your body.  A sesamoid bone is a bone embedded inside a tendon.  The patella’s primary role is to help you straighten your leg.

Tibia: Also known as the shin bone is the second largest bone in the human body.  It is the longest and strongest of the two bones that comprise the bottom of your knee and the top of your ankle.  It is the strongest weight-beaing bone in most people.

Fibula: Also known as the calf bone is the smaller on the two bones that comprise the bottom of your knee and the top of your ankle.  It’s located alongside the tibia towards the outside of your body.