Basic Anatomy

The Knee, the most famous joint in sports, is the junction of the upper leg bone (femur) and the lower leg bone (tibia). These two bones are held together by a series of tissues called ligaments.  The knee is much more than a meeting place.  It is both a hinge and a lever.

There are four large muscles on the front of the thigh called quadriceps.  These muscles power the extension of the leg.  The quadriceps connects to the quadriceps tendon, which attaches to the kneecap.  The kneecap is attached to the tibia by the kneecap tendon.  Thus, when the quadriceps contracts, the tibia lifts.

Like all joints in the body, the knee joint is a trade-off between mobility and stability.  For example, the shoulder is extremely mobile but quite unstable.  It is easy to dislocate.  The hip is not very mobile, but is very stable.  When compared to the hip and the shoulder for stability, the knee is somewhere in the middle.  The knee is one of the most mobile joints in the body.  You can bend your knee 150 degrees.  When sprinters run full out, maximum bending or flexion of the knee is reached (this is when the foot, after striding, almost touches the buttocks).

Almost all injuries to the knee restrict this normal range of motion.  When the knee is fully extended, it is like a stick - it is totally stable.  When it bends, it has play in it -from front to back and side to side.  It can even be slightly rotated.  You need this flexibility to change directions quickly.

The bones of the knee are held together by ligaments.  These are gristle like structures that join the femur and the tibia.  They make the knee sturdy and keep it from wobbling.

The knee has two major ligament systems.  One forms the sleeve-like connection between the two bones.  This is called the knee capsule.  Besides the five capsule ligaments, the knee has two additional ligaments that occupy the middle of the knee joint.   because they cross, they are called cross or cruciate ligaments.  The knee ligaments are what I term the static knee stabilizers. The muscles and tendons are the dynamic stabilizers of the knee.  They are dynamic because they can quickly spring into action.  The geometric shape of the femur and the tibia add to the knee stability.

The end of the femur has two knobs called condyles.  They are round and smooth.  They fit into the two shallow sockets in the top of the tibia.  Because of its design, there are at least five places where the knee can be injured: the ligaments, the cartridge, (called menisci), the muscles around the knee, the kneecap (a bone in front of the knee), and the tendons.

Knee Ligament Sprain

A sprained knee is a rip or tear of one, or a combination of, the seven knee ligaments.  It is probably the most common of all knee injuries I have seen in my practice.  I have seen knee sprains from football, skiing, tennis, and simple falls, to name a few.

any injury to the knee ligaments lead to some instability of the knee.  The degree of injury of the ligaments depends on the amount of the force applied to them.

Diagnosis and treatment:  When you sprain your knee, you will feel pain.   The degree depends on the severity of the rip or tear. The immediate treatment is rest, ice, compression and elevation.  I can gain the most valuable diagnostic information if I examine the injured person within the first 30 minutes following injury.  This is the grace period before swelling sets in.

A grade one sprain is relatively trivial and usually cost the athlete about 1 week of idleness.  A grade two sprain requires 2-3 weeks to heal.  A grade three sprain requires an operation without surgery, your knee will never work properly again .

Knee Cartilage Injury

The knee joint cartilage, called menisci, sit between the ends of the ends of the bones that make up the joint.  They act like knee shock absorber pads.  They are triangular in shape and are wedged between the bone ends.  Because of their shape, they increase the contact area between the two bones.  

The covering surface of the ends of the bone, the joint surface cartridge, is much like a tread on a tire.  This tread will wear down more quickly if there is a great deal of force applied to it per square inch.  Loss of any tread on the surface of the joint is called arthritis.

Knee cartilage have no blood supply of their own.  They are unique in the human body.  Because of this, a tear or rip cannot heal itself.  That is why so many athletes end up needing surgical treatment for torn knee cartridge.

Diagnosis and Treatment:  When the meniscus rips, you have the sensation that something is giving way in the knee.  Gradually over the next 6 hours, the knee fills with fluid.  With this fluid the knee becomes stiff and movement is difficult, if not impossible.  If the tear is large enough, the torn piece of cartridge slips into an abnormal position in the knee.  This will cause the joint to lock.

BURSITIS OF THE KNEE:  The knee has 14 bursa sacs that help the joints, tendons, bones and the skins function.  Think of the bursa sac as the body's ball bearings.  For example, if you did not have a knee bursa on your kneecap, you would split the skin over the cap whenever you fell down.  The most common way to injure a bursa sac is by repeated trauma to the bursa.