Purpose: Prolonged untreated chronic anterior cruciate ligament (ACL) injury can lead to changes such as meniscal damage and osteoarthritis. The purpose of this paper was to investigate whether patients with chronic ACL injury combined with knee instability and osteoarthritis were suitable for ACL reconstruction and the outcome of treatment. METHODS: Twelve patients with chronic ACL injury combined with knee instability and osteoarthritis, aged 35 to 54 years (mean 46 years). No previous ACL injury had been diagnosed and treated accordingly. All patients had significant anterior knee instability with clinical manifestations of one or more knee instabilities, and the duration of symptoms ranged from 1 to 5 years. All used an autologous single bundle four-strand N-cord tendon to reconstruct the ACL with concomitant management of the corresponding lesions. The Lachman test and axial shift test were used to evaluate ligament stability, and the modified Lysholm score was used for the evaluation of patients’ subjective symptoms. RESULTS: Nine of the 12 patients combined with significant medial interventricular cartilage wear degeneration, and 10 combined with a composite tear of the posterior horn of the medial meniscus. There was no graft failure at 9 to 36 months of follow-up, and all patients showed significant improvement in knee instability symptoms and joint stability. The modified Lysholm score increased from 62.0 preoperatively to 89.5. CONCLUSION: ACL reconstruction in patients with chronic ACL injury in unstable knees combined with osteoarthritis can achieve satisfactory clinical results when performed under strict selection of indications.