Objectives: When open joint injury is suspected in a knee laceration, the saline load test has been recommended as a diagnostic modality, especially in small wounds, where inspection and palpation cannot confirm joint violation. The goals of this study are: 1) to correlate fluid volume needed for positive diagnosis with demographic factors, 2) to assess the sensitivity of using the commonly recommended volume of 50 mL, and 3) to identify the minimum fluid volume necessary to obtain 95% sensitivity.
Design: Prospective cohort.
Setting: University medical center.
Patients/participants: Thirty consecutive patients scheduled for elective outpatient knee arthroscopy were prospectively enrolled. Exclusion criteria include history of open traumatic injury, presence of active infection, or limited range of motion as evidence of arthrofibrosis.
Intervention: A standard lateral parapatellar portal was made with a no. 11 blade scalpel, and a 5.8 mm diameter cannula-trochar was inserted and withdrawn to create a standard arthrotomy size of 26.4 mm. Using an 18-gauge needle, saline was injected through a separate lateral suprapatellar site until outflow was noted.
Main outcome measurements: Upon fluid outflow, the volume of injected saline was recorded.
Results: The volume injected until outflow was similar between men and women (P = 0.87). No correlation was observed between the volume injected and age (P = 0.85), height (P = 0.18), weight (P = 0.46), and body mass index (P = 0.91). Injection of 50 mL successfully identified only 46% of known arthrotomies. A saline load of 194 mL was required to achieve 95% sensitivity.
Conclusions: For small lacerations around the knee, saline loads of less than 194 mL are of questionable sensitivity, and surgeons should not use the saline load test to rule out open knee injuries.