Subtalar fusion surgical procedure was performed to address the patient's subtalar joint pain and dysfunction.  The patient presented with chronic subtalar instability, hindfoot arthritis, pes planus deformity, and significant limitations in activities of daily living.  Conservative treatment options, including orthotics, physical therapy, and nonsteroidal anti-inflammatory drugs NSAIDs, failed to provide adequate relief.  Diagnostic imaging, including weight-bearing X-rays and potentially a CT scan or MRI, confirmed the diagnosis of subtalar joint degeneration and ruled out other conditions such as calcaneal fractures, tarsal coalition, or posterior tibial tendon dysfunction.  Preoperative evaluation included a thorough assessment of the patient's medical history, including any comorbidities such as diabetes or peripheral vascular disease, which could impact surgical outcome.  The surgical procedure involved arthrodesis of the subtalar joint, utilizing either internal fixation with screws or plates, or a combination of both, to achieve stability and pain relief.  Bone grafting may have been necessary to promote fusion.  Postoperatively, the patient's foot was immobilized in a cast or splint.  The patient will require ongoing monitoring for complications such as nonunion, infection, or nerve damage.  Postoperative care will include pain management, physical therapy, and gradual weight-bearing progression as tolerated.  Follow-up appointments will be scheduled to assess the fusion progress, evaluate range of motion, and address any postoperative complications.  ICD-10 code M96.70, Subtalar instability, and CPT codes 28725, Arthrodesis subtalar joint, extra-articular or combined extra-articular and intra-articular, and 27690-27692 if bone grafting was performed, are relevant to this surgical intervention. The prognosis for pain relief and improved functional outcomes following subtalar fusion is generally good.