Disruption of the extensor mechanism is an infrequent but catastrophic complication after total knee arthroplasty. Treatment is technically challenging. For patellar tendon ruptures, multiple treatment options having been described with inconsistent results. Allograft tissue may provide the best means to adequately reconstruct the disrupted patellar tendon. Options for allograft reconstruction include an Achilles tendon bone block allograft or a whole extensor mechanism allograft. Important surgical principals include rigid fixation of the host allograft junction, coverage of the allograft tissue with as much autogenous tissue as possible to reduce the risk of infection, tensioning the graft in full extension, and not testing the completed repair is crucial. Current results with proper surgical technique show acceptable functional outcome for this devastating complication.