The role of the exhaustion test in lacertus syndrome

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. 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. 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. 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 0.05). 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. 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.