Primary tumors of the calcaneus present a reconstructive challenge. Their relatively low incidence leads to limited evidence, clinical experience, and ongoing discussion regarding the optimal surgical strategy. In this report, we present a case of a 19-year-old male diagnosed with an aggressive osteoblastoma who underwent subtotal calcanectomy. A custom 3D-printed titanium endoprosthesis was designed for limb-salvage reconstruction. Trabecular porous structure and screws were used to achieve subtalar and calcaneo-cuboid fusion and to compensate for the deficient ligamentous apparatus following resection. An innovative system for reattachment of the calcaneal tuberosity with spared of the Achilles tendon was also utilized. At 3 months, the implant was completely incorporated, allowing full weight bearing. At the 18-month follow-up, the implant showed no signs of loosening, the patient had no signs of recurrence, had excellent function, and successfully returned to all his pretreatment activities, underscoring the effectiveness of this reconstructive approach in the management of calcaneal tumors.