Cartilage covers each end of the long bones of the thigh and the shin. Arthritis sets in when this cartilage wears down to the bone. Arthritis can be present in just one part of the knee, or throughout the entire joint. It may also coexist with a torn cartilage (meniscus), thus creating a completely different condition.

Chondromalacia is a very confusing term that means different things to different people. Patients would be well-advised to ignore the term, although it is still commonly used by insurance companies and certain health professionals. It can mean any of the following:

• Pain in the front of the knee
• Pain coming from the kneecap
• Cartilage abnormalities under the kneecap
• Articular (joint) cartilage abnormalities anywhere in the knee
• Articular cartilage abnormalities anywhere in the body

Though often a source of great misdiagnosis, kneecap pain can be divided into three broad categories:

• Conditions that do not pertain to the patella proper: In these cases, the kneecap has nothing to do with the pain. Such conditions include:

• Conditions in which identifiable lesions within the patella cause the pain: In these instances, the doctor can see something within the kneecap. These conditions are unusual, and can include:

• Conditions caused by non-focal disorders of the patella: In these cases, the problem lies with the kneecap and the surrounding tissues, while there is no obvious problem within the kneecap itself. These can include:

A Note on Patella (kneecap) Malalignment:
A tilted kneecap is a potential source of pain. However, tilting of the patella has only recently come to be appreciated as a source of pain, and thus remains under-diagnosed. Conversely, malalignment of the kneecap is not an automatic cause of pain. The doctor must decide when malalignment is a significant factor in any given patient. Though kneecap pain can usually be treated non-operatively, surgery for this condition is one of our specialties.

Diagnostic Tests
Doctors can obtain vast amounts of information from x-rays, provided that the appropriate views are gathered and the quality of the pictures is reasonable. The necessary views include a true lateral (side) and a Merchant view, which is a special view of the kneecap taken with the knee bent no more than 30 degrees.

The Merchant view technique. (reprinted with permission from Grelsamer RP, Weinstein C: Patellar Instability. Chapter 59 in The Adult Knee. Callaghan JJ, Rosenberg AG, Rubash HE, Simonian PT, Wickewicz TA, Ed. Lippincott, Williams & Wilkins, 2003)

Occasionally, a doctor may order an MRI. Such a test is generally unnecessary, however, as it can often be misleading in knee pain cases.

A ligament is a sophisticated, biological rope that connects two bones. Some joints are quite solid (and referred to as “stable”), with ligaments that are somewhat expendable.

The knee and shoulder are at the other extreme. The knee is akin to two large knobs resting on a flat surface, a structure that would be completely unstable without ligaments. There are four ligaments of the knee:

• Medial Collateral Ligament (MCL): This is the most commonly injured knee ligament. The MCL is typically injured when the lower leg rotates outwards while the upper leg remains straight, as when catching the tip of a ski, or when the knee is struck from the side as in a tackle.
  
  The MCL can be injured with one of three degrees of severity:

• Anterior Cruciate Ligament (ACL): A commonly injured ligament, the ACL lies deep inside the knee, as opposed to the more close to the skin MCL. It courses obliquely from the outer part of the thighbone at the back of the knee down to the table-like portion of the upper shinbone (the tibial plateau). The ACL prevents the knee from bending backwards (over-extending) and from shifting or becoming unhinged during certain twisting motions.
  
  
  

  ACL ligament (red arrow)

  
  The ACL can be likened to a cable made of many strands. These strands are visible to the naked eye and can be seen to twist subtly around each other. There is some elasticity to these fibers, and therefore some give when the knee is pushed too far. Some people are loose-jointed; by definition, their ligaments tend to have more stretch. These people are less likely to tear their ACL; however, in the event of such an injury, other ligaments are less able to pick up the slack.
  
  An ACL tear generally requires significant medical attention, as the knee has to be forcibly twisted (or hyperextended). Sports like skiing, soccer, and football typically produce this injury. An athlete who tears an ACL usually feels a pop and/or notices rapid swelling of the knee. If fluid is drained from the knee, it is usually bloody. Upon further examination, the shinbone (tibia) can be pulled forward. This is called the "drawer" maneuver, and may also be called the Lachman. The doctor may also try a pivot test, wherein the tibia snaps in and out of place as the knee is carefully manipulated.
  
  Non-contact ACL tears also exist, in which an individual tears his or her ACL without any obvious injury. The cause of such tears is usually undetermined, and remain a major source of investigation.
  
  
  

  Normal ACL on MRI

  
  
  

  Torn ACL on MRI (no ACL visible [red arrow])

  
  Are ACL injuries preventable?
  Though proper training helps decrease the odds of suffering an ACL injury, the risk never fully disappears; high level athletes especially tear this ligament with alarming frequency. Even if a brace did exist to protect from this injury, it would probably be too cumbersome and expensive for routine prescription.
  
  Why are women more at risk?
  Studies have shown that women are three to ten times more likely to suffer an ACL tear than men. There are a number of theories about this gender disparity, including joint laxity, estrogen levels, menstrual cycle-related hormonal variations, muscle reaction times, and body position. Strength, however, does not seem to be an issue. Prevention programs have been developed and are part of our ACL program here at Mount Sinai.
  
  Does an ACL tear always require surgery?
  A perfect ACL is not always necessary, and a tear does not automatically develop into arthritis. Therefore, the decision to surgically reconstruct the ACL depends on a patient’s age, activity, and symptoms.
  
  What options do children suffering from ACL tears have?
  A child with a torn ACL cannot be allowed to participate in twisting activities. However, surgery for a torn ACL involves making holes in the bones about the knee in the area of the major growth plates. Therefore, ACL surgery might affect the growth of the bones. This is particularly true in children who are not fully grown, and is of lesser importance to those whose growth is nearly complete. Ideally, the surgeon should wait until the child’s growth is almost complete to perform surgery. However, this means holding the child back from certain sports, which is not always a popular option. A Mount Sinai surgeon is available to discuss each child’s surgical options.
  
  Can the new, surgically reconstructed ACL rupture too?
  A great paradox of sports medicine is that we operate on knees so athletes can go back to the sport that caused the rupture of the ACL in the first place. Since the new ACL is a relatively crude version of the original, it also can tear.

• Posterior Cruciate Ligament (PCL)/Lateral Collateral Ligament (LCL)
  The Posterior Cruciate Ligament lies in the center of the knee where it crosses behind its anterior counterpart, the Anterior Cruciate Ligament (ACL). It shares some functions with the ACL to the extent that it helps provide smooth, controlled knee motion. It does so, however, in a manner opposite the ACL, as it proceeds in a different direction. The PCL prevents the thighbone from sliding forward when one goes down steps, and, as with the ACL, prevents abnormal twisting.

• Isolated PCL
  The Isolated PCL tears when the tibia is forcibly pushed backwards.
  These tears are quite rare, and the surgical need to address this problem is controversial. Many patients with an isolated PCL tear do not even realize that they have a torn ligament.

• The Lateral Collateral Ligament (LCL)
  The LCL, also known as the fibular collateral ligament, is the equivalent of the MCL, as it lies relatively close to the skin along the outer aspect of the knee. Similar to the MCL, it takes its origin on the femur; instead of inserting on the upper tibia, as does the MCL, it inserts on top of the fibula, the skinny bone on the outer aspect of the leg.
  
  Whereas the MCL is the most commonly injured ligament, the LCL is arguably the least commonly injured ligament. This is fortunate, because when the LCL is torn, the PCL is commonly torn as well. This combination nearly always mandates surgery. It will not heal on its own, and left untreated will lead to a very unstable knee.

In the context of knee pain, the term “cartilage” may refer either to the smooth rounded areas at the ends of the long bones of the thigh and shin, or to the rubbery, shock-absorbing pad that lies within the knee joint (known as the meniscus). The gradual erosion of the cartilage of the long bones is referred to as arthritis.

Though commonly over-diagnosed, meniscal tears can be a source of knee pain, and may be treated with minimally invasive arthroscopic surgery.