OrthoDx: Painful Stiff Knee

Slideshow

  • Figure 1. Sagittal MRI view of right knee.

  • Figure 2. Axial MRI view of knee.

A 65-year-old man presents with right knee pain and fullness behind the knee that has been present for the past 3 months. He has a known history of osteoarthritis in the knee and has had at least a few intra-articular steroid injections, with the most recent injection given 2 months ago. The knee has progressively become stiff and, over the last few weeks, he is having trouble bending the knee. He also describes pain with full extension and is starting to develop lower extremity edema in the right leg over the last week. Sagittal and axial magnetic resonance imaging (MRI) show a large popliteal cyst behind the knee (Figures 1 and 2).

A popliteal synovial cyst, or a Baker cyst, is a fluid-filled cyst that forms behind the knee capsule as a result of an intra-articular disorder. The most common cause of a Baker cyst is knee osteoarthritis, followed by a meniscus...

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A popliteal synovial cyst, or a Baker cyst, is a fluid-filled cyst that forms behind the knee capsule as a result of an intra-articular disorder. The most common cause of a Baker cyst is knee osteoarthritis, followed by a meniscus tear. Intra-articular conditions such as osteoarthritis cause inflammation and fluid to build up in the knee. The fluid escapes out of the knee and encapsulates behind the knee. A one-way valve is created from the knee to the cyst as knee fluid can make the cyst bigger but the fluid usually doesn’t return to the knee.1

Baker cysts are often asymptomatic but can grow large enough to create fullness behind the knee and knee stiffness. The cysts are usually unilocular but can be multilocular as well. In rare cases, large Baker cysts can cause thrombophlebitis, compartment syndrome, compressive neuropathies, and lower extremity edema due to venous obstruction.1,2

Treatment starts with identifying the underlying condition. Intra-articular steroid injection is the most common first step for treatment. This has been shown to decrease the size of the cyst. If the cyst becomes large then an ultrasound-guided aspiration may be performed. However, patients should be counseled that this may be a short-term fix as the reoccurrence rate is high. The amount of fluid volume drained is proportional to the amount of pain relief achieved after aspiration.2

Bottom line, large symptomatic Baker cysts are one of the few types of cysts that are reasonable to drain.1,2

Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopaedics for Physician Assistants.

References

1. Frush TJ, Noyes FR. Baker’s cyst: diagnostic and surgical considerations. Sports Health. 2015;7(4):359-365. doi:10.1177/1941738113520130

2. Köroğlu M, Çallıoğlu M, Eriş HN, et al. Ultrasound guided percutaneous treatment and follow-up of Baker’s cyst in knee osteoarthritis. Eur J Radiol. 2012;81(11):3466-3711. doi:10.1016/j.ejrad.2012.05.015

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