Quantitative Analysis of the Patellar Tap Test for Knee Joint Effusion

ABSTRACT

PURPOSE: The purpose of this study was to detect the amount of the saline which was injected into a knee joint and made the patella ballottable. MATERIALS AND METHODS: From January 2002 to June 2003, into 37 knees, saline was instilled through a needle inserted at 2 cm distant form superolateral aspect of the patella. The patellar ballottement was examined after every 1 cc injection of the saline. We checked the amount of the injected saline when the ballottement of the patella was developed and when ballottement was disappeared by milking fluid distally from suprapatellar pouch.my. RESULTS: The patella tap test was positive when the amount of instilled saline was between 14 cc and 45cc, and the pattern of distribution was biphasic. A patella tap disappeared if more than 39~110 cc of fluid was injected, which showed triphasic pattern of the distribution. CONCLUSION: The amount of knee effusion between 14~110 cc got the patella ballottable. And the pattern of distribution was variable. Therefore we need more numbers of data to analyze the differences.