The synovial cyst of knee cruciate ligament (SCKCL) that cause severe knee pain is a pseudo-cyst, resulted from previous intra-ligament inflammation or minor hemorrhage as per a recent paper published in International Orthopaedics. SCKCL is the condition that occurs frequently but when occurs, cause a lot of pain. The etiology of SCKCL is not known and due to which it is hard to diagnose and control the condition.

Therefore, Jun Xiao and colleagues explain the SCKCL etiology on the basis of cyto- and histopathological examination via this recent study. The patients who went through arthroscopy were selected for the analysis. Out of these patients, five patients showed issues of the previous knee injury. The staining of cyst fluid smear and cyst wall tissue sections was done via papnicolaou stain and hematoxylin + eosin stain, respectively. Prussian blue staining is used to stain both the cyst fluid smear and wall section. The possible association of various cells such as epithelial cells (CK), monocytes (CD68), mesothelial cells (MC), vascular endothelial cells(CD31) and hematogenous stem cells (CD117) with SCKCL development was evaluated via immunohistochemical staining.

Hemosiderin particles were diagnosed in the fluid and cyst wall through prussian stain, which demonstrated that patients were suffered from hemorrhage previously. However, fluid showed no evidence of the erythrocyte. Both fluid and cyst wall was found to have abundant plasmocytes and lymphocytes.  The proliferated capillaries were found with CD31, and cyst lining was known to have abundant  CD68(+) monocytes. Four samples found to have very few MC (+) and eight specimens were presented with CD117-positive hematogenous stem cells. As per these findings, SCKCL is not a mature cyst.