The “Fight Bite” Saline Joint Loading Test: Effectiveness in Detecting Simulated Traumatic Metacarpophalangeal Arthrotomies

Background: The saline load test is routinely used to recognize other joints’ traumatic arthrotomies; however, there are currently no studies evaluating the novelty of this test for metacarpophalangeal joints (MCPJs). This study aimed to investigate the effectiveness and sensitivity of saline load testing in identifying the traumatic arthrotomies of the MCPJs using human cadavers. Methods: This was a cadaveric study of 16 hands (79 MCPJs). Traumatic arthrotomies were created using 11-blade stab-incisions, followed by blunt probing into the joint on the radial or ulnar side of the flexed MCPJs. A 3-mL syringe was used to inject intra-articular methylene-blue-dyed saline from the contralateral side. The volume at saline extravasation was recorded. Test sensitivity and factors influencing extravasation volume were assessed. Results: The mean (range) volume injected to identify arthrotomy of all MCPJs was 0.18 mL (0.1-0.4 mL). The mean volume to identify MCPJ arthrotomy of the thumb, index, long, ring, and small fingers was 0.16 mL (0.1-0.3 mL), 0.19 mL (0.1-0.3 mL), 0.21 mL (0.1-0.4 mL), 0.17 mL (0.1-0.3 mL), and 0.16 mL (0.1-0.3 mL), respectively. Cadaver age, laterality, and joint range of motion were not significantly associated with the injected volume at extravasation( P > .05, each). Injection volumes of 0.3 and 0.32 mL were required to detect arthrotomies at 95% and 99% sensitivities across all MCPJs. None of the MCPJs required > 0.4 mL to detect arthrotomy. Conclusions: Saline joint loading volumes to detect traumatic arthrotomy were similar for all MCPJs. Injection volumes of 0.32 mL is suggested for 99% sensitivity. Our findings provide the first report, to our knowledge, on intra-articular injection volumes expected to detect an arthrotomy of MCPJ. This is critical for further validation using in vivo clinical studies.