When the knee is flexed to about 45 degrees, what happens to the pain and the cyst?

When the knee is flexed to about 45 degrees, what happens to the pain and the cyst?

• A. Pain increases and the mass enlarges
• B. Pain remains the same and the mass unchanged
• C. Pain subsides but the mass persists
• D. Pain subsides and the mass decreases or disappears

Answer: (D)

A Baker's cyst forms from distension of the gastrocnemius–semimembranosus bursa that communicates with the knee joint. Its size and the associated pain track with the amount of intra-articular fluid and the position of the knee. When the knee is flexed to about 45 degrees, the posterior structures and the communication with the knee joint are less distended, allowing fluid to shift back into the joint and the cyst to collapse. This reduces the palpable mass behind the knee and often relieves pain, which is why this scenario describes both a decrease in the cyst and relief of symptoms. If the knee were extended or if joint effusion were heavy, the cyst would be more prominent and painful due to increased distension. So the finding that both pain and the mass subside with mid-range knee flexion fits the behavior of a Baker’s cyst associated with knee joint effusion.

A Baker's cyst forms from distension of the gastrocnemius–semimembranosus bursa that communicates with the knee joint. Its size and the associated pain track with the amount of intra-articular fluid and the position of the knee.

When the knee is flexed to about 45 degrees, the posterior structures and the communication with the knee joint are less distended, allowing fluid to shift back into the joint and the cyst to collapse. This reduces the palpable mass behind the knee and often relieves pain, which is why this scenario describes both a decrease in the cyst and relief of symptoms.

If the knee were extended or if joint effusion were heavy, the cyst would be more prominent and painful due to increased distension. So the finding that both pain and the mass subside with mid-range knee flexion fits the behavior of a Baker’s cyst associated with knee joint effusion.