From the Guidelines
For tightness and tenderness behind both knees (worse on the right), I recommend starting with a thorough physical examination followed by ultrasound imaging as the first-line diagnostic approach. This approach is supported by the Society of Radiologists in Ultrasound consensus conference, which suggests that ultrasound is a suitable initial imaging modality for evaluating symptoms of deep venous thrombosis, such as tightness and tenderness behind the knees 1. Ultrasound can effectively visualize soft tissue structures like the popliteal fossa, including Baker's cysts, tendon abnormalities, or vascular issues that commonly cause posterior knee symptoms.
If ultrasound findings are inconclusive or suggest deeper pathology, MRI would be the next appropriate step as it provides detailed images of all knee structures including ligaments, menisci, cartilage, and can detect subtle inflammation or fluid collections 1. The American College of Radiology suggests that MRI without IV contrast is more sensitive than radiography for evaluating chronic knee pain and can accurately depict the extent of an effusion, presence of synovitis, and presence or rupture of a popliteal cyst.
Some key considerations in the differential diagnosis for bilateral posterior knee tightness include:
- Baker's cysts
- Hamstring tendinopathy
- Popliteal artery entrapment syndrome
- Referred pain from lumbar spine issues The asymmetric presentation (worse on the right) potentially indicates different stages of the same condition or separate pathologies. X-rays have limited value for posterior knee pain but may be considered to rule out bony abnormalities if there's any history of trauma or if arthritis is suspected. Blood tests including inflammatory markers (ESR, CRP) may be helpful if inflammatory conditions like rheumatoid arthritis are suspected.
From the Research
Diagnostic Tests for Tightness Behind the Knees
The symptoms described, such as tightness behind both knees with tenderness that's worse on the right side, could be indicative of several conditions, including Baker's cyst or deep vein thrombosis (DVT). To diagnose these conditions, several tests and imaging studies can be utilized:
- Ultrasound of the femoral vein and popliteal fossa to exclude obvious thrombus or ruptured Baker's cyst 2
- Phlebography to exclude calf vein thrombosis if ultrasound is negative 2
- Contrast arthrography to look for rupture of the cyst if phlebography is negative but a Baker's cyst is present or deviation/compression of the popliteal vein is detected 2
- Venous duplex scanning to diagnose Baker's cysts and distinguish them from DVT 3
- Magnetic Resonance Imaging (MRI) to investigate the leg and demonstrate a Baker's cyst, especially if other tests are inconclusive 4, 5
Imaging Studies
Imaging studies play a crucial role in diagnosing the cause of tightness behind the knees.
- MRI can be particularly useful in visualizing the anatomy of the knee and detecting Baker's cysts, as well as evaluating for DVT 4, 5, 6
- Ultrasound-guided aspiration of the cyst can provide immediate and sustained relief if a Baker's cyst is diagnosed 4
Considerations
It's essential to consider the possibility of a Baker's cyst when symptoms mimic those of DVT, as management differs between the two conditions 2. A thorough examination of the popliteal fossa should be performed during venous duplex examinations to detect Baker's cysts 3.