From the Guidelines
The diagnostic approach for posterior left knee swelling should prioritize MRI with and without IV contrast, as it provides the most comprehensive assessment of internal knee structures and is highly sensitive in detecting inflammation and associated conditions 1. When evaluating posterior knee swelling, it is essential to consider a range of potential causes, including soft tissue infections, Baker's cyst, meniscal tears, and ligament injuries.
- A thorough physical examination should be performed, including tests such as the bulge sign, patellar tap test, and ballottement to detect joint effusion.
- The Thessaly test and McMurray test can help identify meniscal tears, while the posterior drawer test and sag test assess posterior cruciate ligament integrity.
- Imaging studies should begin with plain radiographs to rule out bony abnormalities.
- Ultrasound is a useful adjunct for identifying Baker's cysts and other soft tissue pathologies, but its limitations, such as underestimating disease extent and limited visualization of deeper structures, should be considered 1.
- MRI, particularly with and without IV contrast, is the preferred imaging modality due to its high sensitivity in detecting inflammation, fasciitis, myositis, and areas of necrosis, as well as its ability to delineate the anatomic extent of soft-tissue infections 1.
- The use of CT scans with IV contrast may be considered in certain cases, but its lower rating and variable relative radiation level make it a less preferred option compared to MRI 1.
From the Research
Diagnostic Tests for Posterior Left Knee Swelling
The diagnostic tests for posterior left knee swelling include:
- Ultrasound scan to assess for a clinically suspected Baker's cyst 2
- Physical examination, including passive and active range-of-motion testing, palpation of the joint line spaces, and a variety of maneuvers to evaluate knee stability 3, 4
- Valgus and varus testing to assess the collateral ligaments 3
- Lachman and pivot shift tests to evaluate the anterior cruciate ligament 3
- Posterior drawer and tibial sag tests to evaluate the posterior cruciate ligament 3, 4
- Bounce test, McMurray's test, and Apley's grind test to aid in the diagnosis of meniscal injury 3
- Standard x-ray's and stress views to assess for ligament injuries 4
- Magnetic resonance imaging (MRI) as the gold standard imaging study for detecting ligament injuries 4, 5
- Reverse KT-1000 testing to assess for posterior cruciate ligament laxity 5
- Sonographic evaluation to confirm MRI findings of posterior cruciate ligament laxity and buckling 5
Imaging Studies
Imaging studies play a crucial role in the diagnosis of posterior left knee swelling, including:
- Ultrasound scan to assess for Baker's cyst 2
- MRI to detect ligament injuries 4, 5
- Standard x-ray's and stress views to assess for ligament injuries 4
- Sonographic evaluation to confirm MRI findings of posterior cruciate ligament laxity and buckling 5
Physical Examination
Physical examination is essential in the diagnosis of posterior left knee swelling, including:
- Passive and active range-of-motion testing 3, 4
- Palpation of the joint line spaces 3
- Valgus and varus testing to assess the collateral ligaments 3
- Lachman and pivot shift tests to evaluate the anterior cruciate ligament 3
- Posterior drawer and tibial sag tests to evaluate the posterior cruciate ligament 3, 4