Objectives Ruptured popliteal artery aneurysm is a rare entity, which can cause severe nerve neuropathy. Open surgical repair is the preferred treatment for ruptured popliteal artery aneurysm but may aggravate nerve injuries or lead to postoperative aneurysm enlargement. The current surgical techniques for ruptured popliteal artery aneurysm have some deficiencies. Methods We present the case of a 78-year-old woman with sudden swelling of left knee joint and left foot drop, which was caused by the ruptured popliteal artery aneurysm and its compression. A modified open surgical repair was applied in our case, and glucocorticoid therapy was given perioperatively. Results The motor function of left lower limb had rapidly recovered after operation, and six-month follow-up showed patency of prosthetic vessel and significant shrinkage of aneurysm sac. Conclusions Our modified open surgical repair can relieve the compression and prevent possible “type II endoleak” without dissecting in popliteal fossa. Acute common peroneal nerve neuropathy and foot drop are reversible with immediate removal of compression and glucocorticoid therapy for patients with ruptured popliteal artery aneurysm.