Background Decreased computed tomography (CT) attenuation of muscle is independently associated with muscle weakness. The CT attenuation of the abdominal wall muscles may correlate with that of the psoas in patients without ventral hernias. This means that the CT attenuation of the psoas may be related to the occurrence of incisional hernias (IH). CT-determined sarcopenia was deemed inefficient in predicting the development of IH, while limited attention has been paid to the association between muscle fatty infiltration and incidences of IH. In this study, we aim to investigate whether the psoas’ CT measurement parameters, including the average CT attenuation, fatty infiltration rate and psoas muscle index, are associated with IH. Methods In this study, adult patients who had undergone an appendicectomy in the past and had then, for any reason, been hospitalised in our hospital from January 2018 to December 2019 were enrolled. The patients were classified into an IH group and a non-IH group. Their psoas’ CT attenuation, fatty infiltration rate (FIR) and psoas muscle index (PMI) were measured or calculated. Sarcopenia was defined according to their PMI. Differences between the two groups’ indices were then compared. A logistic regression model was applied to assess the effects of psoas’ CT measurement parameters on the occurrence of IH. Results One hundred twenty patients were included in this study. The psoas’ CT attenuation (p = 0.031) and PMI (p = 0.042) in the IH group were significantly lower than those in the non-IH group, and FIR in the IH group was significantly higher than in the non-IH group (p < 0.001). The patients’ psoas’ CT attenuation, FIR, PMI, age, gender and whether they had a history of smoking, were all significant factors in the univariate logistic regression analysis. After adjusting for confounding factors, a multivariate logistic regression analysis demonstrated that the psoas’ CT attenuation was an independent protective factor (p = 0.042), and FIR was an independent risk factor (p = 0.018), while neither PMI (p = 0.118) nor sarcopenia (p = 0.663) showed a significant effect on the incidence of IH. Conclusions When an appendectomy has been performed, a decreased CT attenuation and increased FIR of the psoas can be considered risk factors for IH.

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