Pain Felt Deep Within the Knee

By Ben Benjamin, PhD

Question: What condition is a person likely to have if he or she hears a "crackling" sound while performing a deep-knee bend, and experiences pain (that can be brought on by damp, rainy weather) deep inside the knee?

Answer: Chondromalacia, also called patello femoral arthritis.

The crackling sound felt and heard within the knee is known as crepitus.

When the sound of crepitus starts, it may feel strange but may not be painful because cartilage may still be rubbing against cartilage; however, when the articular cartilage thins and breaks away, bone begins to grind against bone. This is when the knee begins to swell and become painful. Changes in barometric pressure often cause the pain and discomfort to increase.

Chondromalacia generally affects both knees, but can occur in only one if the condition began as the result of an accident or injury. More commonly, patellofemoral arthritis develops slowly over many years. Certain activities can accelerate its onset. For example, the impact of running hastens the onset of full-blown chondromalacia in the knee. While running, the knee must absorb 700 to 1,000 pounds of impact with each step; when we run a mile, we take between 1,500 and 2,000 steps.

If the knee is out of alignment, due to excessive pronation of the foot, or if the person is not adequately warmed up before running, the knee can suffer.