[SUMMARY] The aim of this prospective cohort study was to document the preliminary results of the direct medial approach, a novel surgical technique for primary total knee arthroplasty. From September 2015 to May 2018, 100 patients were consecutively registered. The inclusion criteria were a primary total knee arthroplasty via the direct medial approach performed by the first author（consultant group）or by residents supervised by the first author（residents group）. The follow-up period was three months. The essence of the surgical technique was a medial oblique skin incision of 14 cm from the medial aspect of the tibial tuberosity along the mid-point of the muscle belly of the vastus medialis. The deep synovial layer was preserved in a V-shaped flap, which was useful to reconstruct the medial capsule. Ten percent of the patients had severe adverse events, but all complications completely resolved conservatively and no revision surgeries were required. The complication rates were similar for the consultant and the residents. Surgical time was significantly shorter for the consultant than the residents（92±13［mean±standard deviation］minutes versus 104±15 minutes, p＝0.001）. Postoperative range of motion was significantly larger in patients operated on by the consultant than by the residents（124±13 degrees versus 120±11 degrees, p＝0.026）. Less postoperative pain, larger preoperative range of motion, and surgery performed by the consultant were predictive factors for better postoperative range of motion. This preliminary study demonstrated that the direct medial approach would be safe and effective for primary total knee arthroplasty.

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