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Study Overview
Title: Identification of Knee Effusions With Ultrasound: A Comparison of Three Methods
Design: Prospective cohort study
Setting: Outpatient orthopaedic clinic
Participants: 52 adults (104 knees), including 57 painful knees
Objective
Determine whether two simple dynamic techniques improve ultrasound detection of suprapatellar knee effusions compared with static scanning.
Ultrasound Methods Compared
Static scanning: Patient relaxed; standard long- and short-axis views.
Parapatellar pressure (Method 1): Examiner compresses medial and lateral parapatellar recesses during scanning.
Quadriceps contraction (Method 2): Patient actively contracts quadriceps during scanning.
Outcome Measure
Presence of fluid in the suprapatellar recess (graded using a standardized ultrasound effusion scale).
Key Results
Effusions detected:
Static scanning: 45
Parapatellar pressure: 58
Quadriceps contraction: 77
Comparative performance:
Quadriceps contraction was superior to parapatellar pressure for detecting:
All effusions (PR 1.33; P < 0.001)
Painful knees (PR 1.24; P = 0.036)
Painless knees (PR 1.50; P = 0.006)
Both dynamic methods outperformed static scanning.
Additional detection beyond static scanning:
Parapatellar pressure: +16.9% of knees
Quadriceps contraction: +54.2% of knees
Reliability (Inter-rater Agreement)
Static scanning: ? = 0.771
Parapatellar pressure: ? = 0.686
Quadriceps contraction: ? = 0.846
All methods showed high reliability, with quadriceps contraction highest.
Conclusions
Both parapatellar pressure and patient-initiated quadriceps contraction significantly improve ultrasound detection of suprapatellar knee effusions.
Quadriceps contraction is the most effective method, especially for small or occult (grade 1) effusions.