Summary

Two types of cystic wall were confirmed arthroscopically, white wall and transparent fatty wall in 26 cases of popliteal cyst. Continuity between joint cavity and cyst could affect the nature of cystic wall.

Abstract

Introduction

Popliteal cyst is common disease in clinical practice. But, details of the cyst such as continuity between cyst and joint, nature of the cystic wall had not been known, yet.

Material And Method

We treated 26 cases by arthroscopic procedures. All cases failed conservative treatment over 6 months. We used anterior portals and posteromedial portal for treatment. We did not use transcutaneous portal. We injected 1 ml of Indigo carmine into popliteal cyst under ultrasound guidance to investigate the continuity of cyst and joint cavity. We removed small part of posterior capsule and curetted the wall of the cyst under arthroscopic vision. We paid attention on the relationship between cyst-joint continuity and nature of cystic wall.

RESULT
Eight of 26 cases (69%) had cartilage degeneration at medial tibiofemoral joint. Injuries or degeneration of medial meniscus were found in 73% of the cases. Among 26 cases, 15 cases had leakage of the dye into knee joint from the cyst, and other 11 cases had no leakage. Two types of cystic wall were confirmed, white wall and transparent fatty wall. Cysts which had continuity to joint had white wall in 14, and fatty wall in 1. On the other hand, cysts which had no continuity to joint had white wall in 5, and fatty wall in 6. Significant difference was confirmed by chi-square analysis (p=0.03). In all cases, improvement of the symptom was confirmed, and diminishment or decrease of the cyst was observed by MRI.

Discussion

Arthroscopic procedure was useful for treatment of symptomatic popliteal cyst. Indigo carmine injection into the cyst prior to the surgery was helpful to investigate the continuity between cyst and joint cavity, and also identity the location of the continuity. We speculated that the continuity to joint cavity could affect the pressure of the cyst, and nature of the cyst had been changed by the pressure. When the cyst had continuity to joint cavity, the pressure of the cyst should be high, and the cyst had white wall to resist the high pressure. On the other hand, when the cyst lost continuity to joint cavity, the pressure of the cyst became low, and the cyst had transparent fatty wall.