MMP9 and major depressive disorder: The modification of extracellular disk matrix has a significant negative statistic a and clinical impact on the improvement of post–surgery psychical state; this process being associated in epidemiology with a high recurrence of pre–surgery depression and a poorer pre–surgery quality of life (average EQ–5D pre–operatory in MMP–9 positive is 0,4969 versus 0,5623 in MMP–9 negative subjects.