The surgical treatment of bone sarcoma involves wide surgical resection and endoprosthetic replacement. Surgical resection for proximal tibia bone sarcoma includes the patellar tendon. The secondary extension lag is a common complication and, although many have been described, the options for reconstruction of the patellar tendon are suboptimal. We propose adding a biological reinforcement, the hamstring tendons, to our extensor mechanism reconstruction technique (polyprolene mesh and gastrocnemius flap). We describe the surgical technique and, using an illustrative case, compare the outcome of this technique with the outcome following reconstruction without reinforcement. Level of evidence: Level III.