Knee Pain: The Common Causes

Knee pain is a very common musculoskeletal complaint and the causes can range widely, from arthritis ( cartilage degeneration ) to ligament and tendons to meniscus ( soft cartilage ).  Causes may be traumatic ( such as a fall or twisting injury ) to atraumatic ( slow and chornic to acute in onset ).  The key to determining the best course of treatment is to have a detailed examination with appropriate history review and a detailed physical examination.  Often times, x-ray images are needed to aid in the diagnosis process.  Usually most conditions are able to be treated non-operatively, however some require surgery to correct the cause.

The knee is a complex joint with three bones ( femur, tibia, and patella ) and numerous ligaments and tendons as well as cartilage ( articular cushioning and meniscii ).  Injury and damage to any of these structures may result in knee pain.

Common causes of knee pain include:

Knee Arthritis-

The two most common ones are osteoarthritis ( "wear and tear") and rheumatoid arthritis (inflammatory).  Both forms result in loss of articular cartilage ( essentially the cushioning on the end of the bones ).  This loss of cartilage can create pain, swelling, and stiffness and often times may create a buckling sensation. 

Knee Ligament Injuries-

The four main ligaments of the knee include two collateral ligaments (medial and lateral) and two cruciate ligaments (anterior and posterior).

The collateral ligaments are on the side of the knee and connect the femur to the tibia or fibula.  Medial collateral ligament injuries usually are the result of trauma with a fall with a twist or a direct blow to the outside part of the knee.   Lateral collateral ligament injuries are uncommon in isolation and usually occur with ACL tears and knee dislocations.

The cruciate ligaments (anterior cruciate and posterior cruciate) are deep within the center of the knee.   Anterior cruciate liagment ( ACL ) injuries are one of the most common knee ligament injuries and usually occur with sports twisting injuries.  The knee often swells and may intially feel stiff then loose.

Posterior cruciate ligament ( PCL ) injuries are less common and usually occur with a direct hit to the front of the knee.  Pain, swelling and a sensation of buckling is common.

Meniscal Tears- 

The meniscii are two cartilage cushions that lie between the articular cartilage on the medial and lateral aspects of the knee.  Tears are a common injury and usually occur with a twisting or deep bending motion although the onset may not be readily apparent to the person.  Symptoms include pain and occassional swelling, particularly with twisting.  

Patellar Tendonitis and Tear

Patellar tendonitis is most common in people who engage in sports or running / jumping activivities.  Often, people with this condition describe a constant dull pain that becomes sharp with activity.  Patellar tendons may rarely tear which usually causes pain and difficulty with ambulation.  

Patellofemoral Pain Syndrome-

Patellofemoral pain syndrome is one of the most common causes for knee pain.  Patients may complain of pain ranging from dull and aching to sharp and severe and activities such as jumping, stairs, running, and squatting may exacerbate the pain.

Baker's Cyst-

A Bakers cyst ( also called a popliteal cyst ) is a benign swelling in the back of the knee joint, that is often associated with knee arthritis or meniscal tears but may occur without either.  Knee stiffness can occur if the cyst becomes large and a visible bulge in the back of the knee may be palpable.

Prepatellar Bursitis

Swelling of the prepatellar bursa (a fluid-filled sac) is located right over the kneecap.  This usually presents with a mildly aching knee pain with visible swelling at the front of the knee.  

Iliotibial Band Syndrome

The iliotibial band is a thick collection of fibers that runs on the lateral aspect of the knee and thigh.  This condition is most common in runner's and cyclists that may be a dul;, aching pain that can worsen to severe pain with activity.

Careful medical evalaution with a detailed history as well as physical exam and imaging ( often x-rays and occassionally MRI ) allow physicians to determine the cause of the knee pain and symptoms and hence guide treatment.