Knee pain is a very common complaint that affects people of all ages. Knee pain affects as many as a third of all teenagers and young adults in the UK at some time. Due to knee pain, many people find they cannot perform usual activities of daily living such as getting out of bed, going up and down stairs or even driving the car. Going to work and even being able to perform a full day of work can be difficult, especially when the job involves prolonged standing, walking or sitting.
Anatomy of the Knee Joint
The knee joint is particularly vulnerable to damage and pain because it takes the full weight of your body and any extra force when you run or jump. The knee joint is the largest synovial (lined by synovial membrane) joint of the body and is made of three bones. On the top is the thigh bone (femur) below it the shin bone (tibia) and in the front is the knee cap (patella).
The part of the femur that forms the knee joint is expanded sideways and behind to form two oval structures called condlyes. Similarly the part of the tibia forming the knee is expanded and forms two condyles that articulate with the corresponding femur condyles.
The knee is divided into three compartments:
- The medial condyles form the medial compartment.
- The lateral condyles form the lateral compartment.
- Anterior compartment is between the patella and femur.
The bone ends are covered with cartilage (tough, smooth and resilient structure). Function of the cartilage is to provide a smooth surface, for the bones to move easily over one another. It also acts as a shock absorber. This joint also contains two semi-circular disc like structures, made of fibrous cartilage that are called menisci. They help to provide a congruent surface for the thigh bone to move on the shin bone.
Four main ligaments stabilize this joint. Medially (on the inner side) the medial collateral ligament. Laterally (on the outer side) the lateral collateral ligament. These ligaments stabilize the knee against angulation (tend to wedge open the joint) and translation (tend to slide the bones in opposite direction) forces. The other two ligaments are the anterior and posterior cruciate ligaments. The main function of the ligaments are to stabilize the joint against translation forces.
Muscles acting on this joint are extensors (straighten) and flexors (bend the joint). Extensors include the quadriceps muscle. Flexors include semitendenosus, semimembranosus and the biceps femoris (collectively called hamstring muscles).
Causes of Knee Pain
There are a huge number of causes of knee pain. In general, knee pain is either immediate (acute) or long-term (chronic). Acute knee pains can be caused by an acute injury or infection. Chronic knee pains are often from injuries or inflammation (such as arthritis) but can also be caused by infection.
The nerves that provide sensation to the knee come from the lower back and also provide hip, leg, and ankle sensation. Pain from a deeper injury (called referred pain) can be passed along the nerve to be felt on the surface. Knee pain, therefore, can arise from the knee itself or be referred from conditions of the hip, ankle, or lower back.
Symptoms of Knee Injury
Typical symptoms of a knee injury may include:
- Instability – you may feel like your knee is giving way or that it’s locking, or that you can’t stand on it
- A popping or snapping sensation at the time of the injury, or even hear a popping sound
Serious Symptoms with Knee Pain
If you are unsure of the cause of your symptoms, or if you do not know the specific treatment recommendations for your condition, you should seek attention. Treatment of knee pain must be directed at the specific cause of your problem. Some signs that you should be seen by a professional include:
- Inability to walk comfortably on the affected side
- Injury that causes deformity around the joint
- Knee pain that occurs at night or while resting
- Knee pain that persists beyond a few days
- Locking (inability to bend) the knee
- Swelling of the joint or the calf area
- Signs of an infection, including fever, redness, warmth
- Any other unusual symptoms