Traumatic arthrotomies may predispose patients to subsequent septic arthritis and therefore are regarded as serious injuries requiring emergent treatment. The saline arthrogram is a commonly used test to determine if a patient has a traumatic arthrotomy. We determined the sensitivity of the saline arthrogram to identify known intraarticular wounds in 78 patients (80 knees) undergoing elective arthroscopic procedures. There were 66 infrapatellar and 14 suprapatellar incisions. The average length of the incision was 7.5 mm. Intraarticular position was confirmed with a blunt probe. A saline arthrogram then was performed using 60 mL normal saline. The known arthrotomy (operative wound) was observed during the injection for evidence of saline leakage (positive static test). If no leakage was observed, the knee was brought through a range of motion with continued observation for leakage from the arthrotomy (positive dynamic test). Twenty-two of 80 knees had a positive test without passive range of motion of the knee (static sensitivity, 36%). Eight additional knees had a positive test with subsequent passive motion (dynamic sensitivity, 43%). Our data suggest a saline arthrogram has low sensitivity for detecting known small traumatic arthrotomy wounds of the knee. METHODS Level I, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.