Objective To observe the effect of electroacupuncture（EA） on pain behavior

synovial inflammatory response and demyelination of saphenous nerve in the rats modeled with knee osteoarthritis（KOA） and explore the effect mechanism of EA for reliving allodynia. Methods Eighty-four male SD rats were randomly divided into a control group

a model group and an EA group

28 rats in each one. Intra-articular injection of sodium monoiodoacetate（MIA） was administered in right knee joint of each rat in the model group and the EA group to establish the KOA model. In the EA group

separately

on day 5

7 and 9 after modeling

EA was applied at "Zusanli"（ST 36） and "Yanglingquan"（GB 34） on the right side

with disperse-dense wave（2 Hz/15 Hz）

1 mA in current intensity

for 30 min in one intervention

once a day

and 3 interventions were required. On the 9th day after modeling

the weight-bearing rate was calculated for the affected limbs of the rats in each group

the synovial morphological changes were observed using HE and Masson staining

flow cytometry was adopted to detect the synovial immunocyte counts

and MSD multi-spot assay was used to detected the synovial inflammatory cytokine content. On the 14th day after modeling

the hind-paw mechanical withdrawal threshold was observed in each group and the ultrastructure of the saphenous nerve was observed under transmission electron microscopy. Results On the 9th day after modeling

compared with the control group

the weight-bearing rate of the affected limb was reduced（P

<

0.01）

the synovial hyperplasia

inflammatory cell infiltration and synovial fibrosis occurred in the affected limb; the counts of synovial CD11b

+

cells and M1 macrophages（CD11b

+

CD86

+

） were increased（P

<

0.01）

the contents of tumor necrosis factor-α（TNF-α）

interleukin（IL）-6

IL-1β

IL-10 and IL-13 in the synovial tissue were elevated（P

<

0.01

P

<

0.05） for the rats of the model group. Compared with the model group

the weight-bearing rate of the affected limb was increased（P

<

0.05）

the synovial hyperplasia

inflammatory cell infiltration and synovial fibrosis were mitigated

the counts of CD11b

+

cells and M1 macrophages（CD11b

+

CD86

+

） in the synovial tissue

and the contents of TNF-α and IL-6 were reduced（P

<

0.01

P

<

0.05） in the EA group. On the 14th day after modeling

the hind-paw mechanical withdrawal threshold was reduced in the model group when compared with the control group（P

<

0.01）

and it was increased in the EA group when compared with the model group（P

<

0.05）. Besides

in the model group

obviously

the myelin sheath structure was destroyed

the myelin layer was disintegrated and loosened

the axon was extruded or the layer thicken and cracked. Compared with the model group

the injury of saphenous nerve was alleviated remarkably in the EA group. Conclusion The intervention with EA may attenuate the synovial inflammatory response and the injury of saphenous nerve in the affected limb of the rat with KOA

so that the spontaneous pain during the synovial inflammatory response stage and allodynia at the later stage are relieved.