From Jonathan Cluett, M.D.,
Your Guide to Orthopedics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

Understanding what is causing your knee pain must be understood in the context of the pain. How old are you? Was there a traumatic event? Where is the pain located? Did the symptoms develop immediately or over time?

Once these questions are answered, you can begin to investigate the symptoms. Putting the symptoms together with the history often leads to a diagnosis.

Common Knee Symptoms

Popping
Popping and snapping within the knee is quite common, and often not a symptom of any particular problem. When the pops or snaps are painless, there is usually no problem--the bigger concern is when these sounds are associated with pain. A pop is often heard or felt when a ligament, such as the ACL, is torn.

Crunching/Grinding
A sense of grinding or crunching is most often associated with bone grinding against bone once the cartilage is worn away. This is commonly found in arthritis. Patients who are young (under 50 years old) seldom have arthritis that will cause these severe symptoms, unless there has been a severe injury to the knee in the past.

Locking
Locking is a symptom that occurs when a patient cannot bend or straighten their knee. The locking can either be due to something actually blocking motion of the knee (this can occur when a piece of cartilage wedges within the joint) or when pain prevents the patient from moving the knee. These two causes must be differentiated, as something physically caught in the joint should be evaluated in a timely manner. Often injecting the knee with numbing medication can help determine the cause of locking.

Giving-Way/Instability
The stability of the knee is provided by the ligaments that connect the shin bone (tibia) to the thigh bone (femur). When the ligaments are stretched or torn, the knee may feel as though it is giving way beneath the patient. A sensation that the knee may give out from beneath you is a common symptom of ligament injury.

Swelling
Swelling of the knee is common with several different knee problems. When there is swelling immediately after an injury (within an hour), the most common causes are an injury to the anterior cruciate ligament or a fracture of the top of the shin bone. When swelling develops gradually over hours to days, the injury is more likely a tear of the meniscus or a ligament sprain. Swelling that occurs without the presence of a known injury can be due to arthritis (common), gout (less common), or a joint infection (uncommon).

Location of Pain
The location of the pain can be an important part of tracking down the symptoms.

• Front of the knee: Pain over the front of the knee is most commonly related to the knee cap. Kneecap pain can be caused by several different problems.

• Inside of the knee: Pain on the inside, or medial aspect, of the knee is commonly caused by medial meniscus tears, medial collateral ligament injuries, and arthritis of the joint.

• Outside of the knee: Pain on the outside of the knee, or lateral aspect of the knee joint, is commonly caused by lateral meniscus tears, lateral collateral ligament injuries, IT band tendonitis, and arthritis of the joint.

• Pain in the back of the knee: Pain in the back of the knee can be due to the formation of a cyst, called a Baker's Cyst, in the back of the knee joint. Also common is for kneecap pain to be felt in the back of the knee.

Timing of Pain
Some common situations cause pain typical of certain conditions.

• While going down stairs: Pain while walking down steps is very commonly associated with kneecap problems, such as chondromalacia.

• Morning pain: Pain after first waking in the morning that resolves with gentle activity is typical of early arthritis. Often patients loosen the knee over the course of the day.