Subtalar joint arthrodesis is a commonly used surgical procedure for the management of rearfoot pathologic features. We present a technique guide for a posterior incisional approach to subtalar joint arthrodesis for correction of a calcaneal deformity secondary to calcaneal fracture malunion. This technique uses a monolateral external fixation device for controlled distraction and intercallary allograft placement. In contrast to a standard lateral approach, this incision provides better visualization of the joint space, and the use of a distractor enhances access to the joint surfaces for fusion preparation and maintains alignment while internal fixation is applied. A 44-year-old male underwent isolated subtalar joint arthrodesis to repair a malunion of a nonsurgically managed calcaneal fracture sustained 1 year before the surgical intervention. Controlled distraction was applied using a Hoffmann® Compact™ MRI external fixation device. This device maintained distraction and tibial–calcaneal alignment until placement of the allograft–bone marrow aspirate. The use of external fixation is a viable option for distraction arthrodesis in subtalar joint fusions. It facilitates frontal plane deformity correction. We have described the surgical technique and presented a case in which the posterior approach with distraction was successfully used in subtalar joint arthrodesis. At 12 weeks postoperatively, serial radiographs displayed incorporation of the graft, with distraction maintained at the subtalar joint arthrodesis site. At the 3-month follow-up visit, the patient had successfully transitioned to weightbearing in a CAM walker without any complications.