Chronic patellar tendon ruptures are a difficult clinical problem. Treatment options include repair and augmentation with hamstring tendons and other grafts. We describe a technique of extensor mechanism reconstruction using an allograft consisting of quadriceps tendon, a patellar bone block, patellar tendon, and a tibial bone block. This technique is a salvage procedure indicated only in the most severe cases of chronic rupture after failure of traditional treatment options. An appropriately size-matched allograft is prepared by shaping the anterior 10 mm of the patella into a graft resembling an hourglass. A similarly shaped trough 10 mm in depth is created in the patella of the patient, and a trough matching the tibial bone block is created in the recipient tibia. The graft is placed and secured with sutures in the quadriceps tendon, wires in the patella, and screws and staples in the tibia. Care must be taken to avoid iatrogenic patellar fracture and prominent hardware. Rehabilitation is slow, with gradual restoration of motion. Outcomes have been successful in 14 patients to date with a 4-year mean follow-up. Future work will include improvement of patellar fixation. This technically challenging procedure may restore extensor mechanism function in cases of chronic patellar tendon rupture that have failed other treatment modalities.