Objective This study aimed to observe the impact of sinomenine hydrochloride on the proliferation of fibroblasts and the mRNA expression of related genes in knee joint adhesion and contracture in rabbits. Additionally, we sought to explore its potential mechanisms in combating knee joint adhesion and contracture.Methods Fibroblasts were cultured in vitro, and experimental groups with varying concentrations of sinomenine hydrochloride were established alongside a control group. Cell proliferation was assessed using the CCK-8 assay. Changes in the mRNA expression of fibroblast-related genes following sinomenine hydrochloride treatment were evaluated using RT-qPCR. The impact of the drug on serum levels of inflammatory cytokines was determined using the ELISA method, and the expression of related proteins was assessed using Western blot.Results Sinomenine hydrochloride was found to inhibit fibroblast viability, with viability decreasing as the concentration of sinomenine hydrochloride increased. The effects of sinomenine hydrochloride in all experimental groups were highly significant (P<0.05). At the mRNA expression level, compared to the control group, sinomenine hydrochloride led to a significant downregulation of inflammatory cytokines in all groups (P<0.05). Additionally, the expression levels of apoptosis-related proteins significantly increased, while Bcl-2 mRNA expression decreased (P<0.05). The mRNA expression levels of the PI3K/mTOR/AKT3 signaling pathway also decreased (P<0.05). At the protein expression level, in comparison to the control group, the levels of inflammatory cytokines IL-6, IL-8, IL-1β, and TGF-β were significantly downregulated in the middle and high-dose sinomenine hydrochloride groups (P<0.05). The expression levels of cleaved-PARP, cleaved caspase-3/7, and Bax increased and were positively correlated with the dose, while the expression levels of the anti-apoptotic protein Bcl-2 and the PI3K/AKT3/mTOR signaling pathway were negatively correlated with the dose. Sinomenine hydrochloride exhibited a significant inhibitory effect on the viability of rabbit knee joint fibroblasts, which may be associated with the downregulation of inflammatory cytokines IL-6, IL-8, and IL-1β, promotion of apoptosis-related proteins cleaved-PARP, cleaved caspase-3/7, and Bax, suppression of Bcl-2 expression, and inhibition of gene expression in the downstream PI3K/AKT3/mTOR signaling pathway.Conclusion Sinomenine hydrochloride can inhibit the inflammatory response of fibroblasts in adhesive knee joints and accelerate fibroblast apoptosis. This mechanism may offer a novel approach to improving and treating knee joint adhesion.