gms | German Medical Science

Objectives: Meniscal extrusion in MRI is normally described as pathologic finding and associated with a loss of function of the affected meniscus. We hypothesize that in healthy knees there is also physiological meniscal extrusion as a functional adjustment on various load bearing condition. Therefore meniscal extrusion is described as the difference in extrusion between standing and lying position in ultrasound as a new diagnostic tool to evaluate the function of a meniscus.

Methods: We analysed voluntary test persons with non-symptomatic knee and without any operation to the knee in the past and age >18 years. Knee malalignment and ligament instability were excluded by clinical examination. All test persons underwent standardized ultrasound examination of the meniscus in a lying position and in 20° of Flexion under weight bearing in a standing position. Afterwards measurements of lying ultrasound were compared with the current gold standard (MRI), to assess the extrusion of the meniscus. Patients were subsequent excluded if the MRI shows osteoarthritis or meniscus lesions.

Results and conclusions: 75 patients were enrolled to this study. The mean US MME was 1.1 mm ± 0.5 mm in supine position and 1.9 mm ± 0.9 mm under full weight bearing. The mean Delta-US extrusion was 0.8 mm ± 0,6 mm. With rising age, a significant increased MME in US and MRI could be demonstrated (p < 0.001). Furthermore, elevated BMI was significant correlated to increased US MME under full weight bearing (p = 0.002) and to Delta-US extrusion (p = 0.003). Based on the results of this study, medial meniscus extrusion is an age-depending phenomenon in healthy knees. Ultrasound examination of the MME might be favorable compared to MRI due to the ability of dynamic evaluation. As a consequence, the current cut-off value of 3 mm for meniscus pathologies should be reconsidered.