Effectiveness of the saline load test in diagnosis of simulated traumatic ankle arthrotomies

Limited studies have been conducted to determine the minimum amount and sensitivity of the saline load test of the ankle. Prior studies, only performed in arthroscopic models, have suggested a wide range of volumes necessary to confirm arthrotomy. The purpose of this study was to investigate the amount of fluid required and the sensitivity of the saline load test to identify an intra-articular arthrotomy of the ankle. Using cadavers without prior ankle trauma or surgeries we aim to assess volume needed to detect ankle arthrotomies at varying arthrotomy locations. We hypothesized that the volume needed would vary based on site of arthrotomy.

Twenty thawed, fresh-frozen below knee cadavers were divided into four groups based on arthrotomy location. An ankle arthrotomy was made using a 4 mm trochar at the four standard ankle portal sites; anteromedial, anterolateral, posteromedial, and posterolateral. To confirm intra-articular location, a arthroscope was inserted for direct visualization of the ankle joint. An 18-gauge needle was then inserted into the ankle joint, and saline mixed with methylene blue was injected. During the injection, the known arthrotomy site was viewed for extravasation. Amount of saline required to diagnose arthrotomy was recorded. All injections were confirmed as intra-articular by demonstrating methylene blue staining of the anterior joint.

The saline volume required to achieve extravasation ranged from 3 mL to 11 mL. The mean saline volume required to achieve extravasation was 5.3 mL. A total of 8 mL was required to achieve 90% sensitivity, 10 mL for 95% sensitivity and 11 mL for 99% sensitivity. For the anterolateral, anteromedial, posteromedial, and posterolateral arthrotomy sites the mean saline volume needed to detect a traumatic arthrotomy was 5.2 mL, 6.2 mL, 5 mL, and 4.8 mL respectively. There was no statistically significant difference in volume needed to detect arthrotomies across all four locations (p = 0.69).

In this cadaveric model, an injection of 10 mL identified 95% of arthrotomies approximately 4 mm in size. No difference in volume needed to detect extravasation was found across all four arthrotomy locations. Prior studies performed in arthroscopic models with patients undergoing ankle arthroscopy may overestimate volume needed to detect arthrotomies.

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