Hemiarthroplasty implantation for proximal humerus fracture is challenging. In case of young demanding patients with functional rotator cuff, humeral head replacement is an option if open reduction internal fixation is not a viable solution. The criteria for success in terms of clinical outcomes and longevity are anatomic healing of the tuberosities and stem positioning (restoring correct height, version, and axis). The purpose of this article is to describe a technique including a new stem guide and a tuberosity anchor “lasso” system for the implantation of hemiarthroplasty in complex proximal humerus fractures. A standard delto-pectoral approach is performed. After humeral head removal and tuberosity mobilization and debridement, a stem-positioning system guarantees correct height and version of the humeral stem, established after anatomic reduction of the greater tuberosity. A centering device is added on the humeral stem to prevent any varus or valgus. Fixation of the tuberosities is achieved with 6 nonabsorbable sutures fixed on a polyester “lasso” anchoring system circling the humerus, respecting the direction of rotator cuff tendons and adding double circumferential tightening. After reduction of the implant, stability, and passive range of motion are assessed intraoperatively and fluoroscopic control of the prosthesis is performed. The patient is maintained in a sling in neutral rotation and passive motion is started after 4 weeks; active motion is allowed after 2 months. We believe this surgical technique could help limit complications and prevent revision of the humeral stem in case of further conversion to reverse shoulder arthroplasty.