The role of the exhaustion test in lacertus syndrome.

Background: Lacertus syndrome involves dynamic median nerve compression by the lacertus fibrosus, leading to sensory symptoms and loss of strength. Prevalence in the general population is unclear.

Objective: This study aimed to determine the prevalence of lacertus syndrome in the Belgian population and to evaluate the effectiveness of the exhaustion test combined with the scratch collapse test.

Methods: In a cross-sectional study from May 2023 to February 2024, 362 healthy individuals, aged 18 to 86 years underwent clinical examinations, including the scratch-collapse test and exhaustion test, to assess signs of lacertus syndrome.

Results: 11.3% of participants (95% CI: 8.2-15.1%) reported discomfort on lacertus fibrosus palpation. The scratch-collapse test at the lacertus fibrosus was positive in 7.2% of cases (95% CI: 4.8-10.4%), increasing to 25.7% (95% CI: 21.3-30.5%, p < 0.001) following the exhaustion test. There were no significant differences in gender, occupation, or hand dominance (all p > 0.05). Hagert's clinical triad and positive scratch-collapse test over the lacertus fibrosus were found in 2.21% (95% CI: 1.0-4.2%) of this general population after the exhaustion test.

Conclusion: The prevalence of lacertus syndrome was 2.21% after the exhaustion test, and 0.83% before. The exhaustion test led to significant conversion of negative to positive scratch-collapse test from 7.2% to 25.7%. The exhaustion test enhanced the scratch-collapse test's diagnostic accuracy, revealing a spectrum of lacertus syndrome symptoms, from unnoticed mild cases to severe manifestations, and confirmed the importance of Hagert's clinical triad in diagnosing lacertus syndrome.