Background Patellar tendon ruptures are the third most common injury to the extensor mechanism. They typically occur in skeletally mature adults younger than 40 years and are associated with trauma, steroid use, and chronic medical conditions, including lupus. These injuries can be defined as acute or chronic depending on time from injury. Chronic patellar tendon injuries are more difficult to manage given retraction, scarring, and atrophy of the surrounding tissues. Although primary repair is indicated for acute injuries, reconstructive surgery is typically required for chronic injuries in light of the above challenges. Purpose This video overview and case presentation demonstrates the technique of using Achilles allograft and semitendinosus autograft augmentation for chronic extensor mechanism reconstruction. Methods The examination, imaging, and treatment options for chronic extensor mechanism injuries are reviewed. We discuss possible treatment options, including graft choices for reconstruction of chronic patellar tendon injuries. We present the case of a 52-year-old woman with a chronic patellar tendon injury that had failed prior surgical repair. After a thorough discussion of risks, benefits, and prognosis, the patient elected to proceed with extensor mechanism reconstruction involving the use of Achilles allograft with semitendinosus autograft augmentation. Results Reconstruction of the patellar tendon with appropriate patellar height was obtained intraoperatively. The postoperative clinical outcome showed good motion and restoration of extensor mechanism. Conclusion Achilles allograft with semitendinosus autograft augmentation offers reliable reconstruction of the patellar tendon in the chronic and revision setting. Appropriate tensioning to restore patellar height is crucial to good functional outcome.