From the Guidelines
Swelling in the back of the knee, also known as the popliteal fossa, is most commonly caused by a symptomatic popliteal (Baker’s) cyst, which is characterized by swelling, tenderness, and is not intermittent. This condition is often associated with exercise and can also be present at rest, with no specific relief from position changes 1. Other possible causes of swelling in this area include hip arthritis, foot/ankle arthritis, nerve root compression, spinal stenosis, venous claudication, and chronic compartment syndrome. However, these conditions typically present with additional symptoms such as pain, weakness, or limited mobility, and can be distinguished from a Baker’s cyst through a thorough clinical history assessment and physical examination.
Some key characteristics of a Baker’s cyst include:
- Swelling and tenderness behind the knee
- Presence of symptoms with exercise and at rest
- No relief from position changes
- No intermittent symptoms
It is essential to note that a thorough vascular examination, including palpation of lower extremity pulses and evaluation for signs of peripheral artery disease (PAD), should be performed to rule out other potential causes of leg symptoms 1. Additionally, imaging studies such as ultrasound or MRI may be necessary to confirm the diagnosis and guide treatment. Treatment for a Baker’s cyst typically involves rest, anti-inflammatory medications, and physical therapy, although more severe cases may require surgical intervention.
From the Research
Causes of Swelling in the Popliteal Fossa
The popliteal fossa, also known as the back of the knee, can experience swelling due to various reasons. Some of the possible causes include:
- Baker's cyst: a fluid-filled swelling that causes a bulge and a feeling of tightness behind the knee 2, 3, 4, 5, 6
- Knee osteoarthritis: a type of arthritis that causes cartilage loss and bone friction, leading to pain and swelling in the knee joint 2, 4, 5
- Meniscus tears: a tear in the cartilage of the knee joint, which can cause pain and swelling in the popliteal fossa 6
- Chronic knee effusions: a condition where fluid accumulates in the knee joint, leading to swelling and pain 6
Risk Factors
Certain factors can increase the risk of developing swelling in the popliteal fossa, including:
- Age: older adults are more likely to develop knee osteoarthritis and Baker's cysts 2, 4, 5
- Trauma: a blow to the knee or a sudden twisting motion can cause a meniscus tear or knee osteoarthritis 6
- Overuse: repetitive stress on the knee joint can lead to chronic knee effusions and Baker's cysts 6
Diagnosis and Treatment
Diagnosing the cause of swelling in the popliteal fossa typically involves a physical examination, medical history, and imaging tests such as ultrasound or MRI. Treatment options may include:
- Ultrasound-guided aspiration and corticosteroid injection: a procedure where a needle is inserted into the Baker's cyst to drain the fluid and inject corticosteroids to reduce inflammation 2, 3, 4, 5
- Arthroscopy: a surgical procedure where a small camera is inserted into the knee joint to diagnose and treat intra-articular pathology 6
- Conservative management: rest, ice, compression, and elevation (RICE) to reduce pain and swelling, as well as physical therapy to improve knee function 6