We employed a new surgical method for the treatment of spontaneous osteonecrosis of the medial femoral condyle of the knee joint. Twelve spontaneous osteonecrosis patients of Koshino's classification stage 2 or 3 underwent core decompression curettage with an artificial bone graft [hydroxyapatite ceramic with an interconnected porous structure (IP-CHA)]. The mean age at surgery was 69.6 years and the mean follow-up term was 24.6 months. All patients reported a decrease in knee pain, immediately after surgery. The Japanese Orthopaedic Association (JOA) scores of all the patients also improved post-surgery; X-ray and MR imaging indicated no worsening of the osteoarthritis, and smooth surfaces at the grafted areas of the artificial bone. No severe complications appeared in the patients. Our procedure was, therefore, less invasive and achieved results comparable to those involving traditional, more invasive methods. We recommend our novel procedure as a treatment for spontaneous osteonecrosis of the femoral condyle.