BACKGROUND:
The saline solution load test helps to determine if a wound extends into the knee joint. Little is known about the volume of injected intra-articular saline solution that is needed to effectively rule in or rule out a traumatic arthrotomy of the knee. The purpose of the present study was to determine the appropriate volume and needle location for the diagnosis of a traumatic knee arthrotomy and to assess the effect of associated variables, including knee circumference, body mass index, and sex.

METHODS:
Fifty-six consecutive patients scheduled for knee arthroscopy were enrolled. A standard inferolateral arthroscopic portal was made with a single stab incision with use of a number-11 blade. Injection sites were randomized to either a superomedial or inferomedial location. The injection of normal saline solution at a rate of 5 mL/sec through an 18-gauge needle was continued while the knee was moved through a range of motion until fluid extravasated from the iatrogenic laceration. The volume of injected fluid was recorded.

RESULTS:
The study group included thirty-one female patients and twenty-five male patients with a combined average age of fifty years and an average body mass index of 30.9. In order to effectively diagnose 50% of the arthrotomies, 75 mL of injected fluid was needed; the volumes that were needed in order to effectively diagnose 75%, 90%, 95%, and 99% of the arthrotomies were 110, 145, 155, and 175 mL, respectively. The mean volumes of injected fluid needed for a positive result at the inferomedial and superomedial needle locations were 64.0 and 95.2 mL, respectively; this difference was significant (p = 0.01). There was no correlation between necessary injection volume and sex, body mass index, or knee circumference.

CONCLUSIONS:
In order to detect 95% of 1-cm inferolateral arthrotomies of the knee with use of the saline solution load test, 155 mL must be injected. An inferomedial injection location requires significantly less fluid than a superomedial injection location does for the diagnosis of inferolateral arthrotomies of the knee.



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