A retrospective analysis of the clinical and imaging data of proximal humeral osteosarcoma cases was performed to summarize the results of limb-preserving treatment and the relationship between local recurrence and the extent of resection and imaging evaluation. Thirty-eight patients with osteosarcoma of the proximal humerus were treated with neoadjuvant chemotherapy and limb preservation therapy with a mean follow-up of 43.2 months. The reconstruction methods included custom-made proximal humeral prosthesis replacement in 31 cases, artificial prosthesis allograft composite in 4 cases, bone cement temporary prosthesis in 1 case, and autologous bone graft in 2 cases. The imaging data of the intra-articular resection cases were analyzed to determine whether the scapular glenoid and deltoid muscle might have been invaded. Local recurrence occurred in 5 patients (13.2%). The recurrence rate was 20% (1 /5) for extra-articular resection and 12.1% (4 /33) for intra-articular resection. Of the patients who underwent intra-articular resection, seven patients had imaging evaluation showing invasion of the scapular glenoid and deltoid muscle, four of which had local recurrence. The overall 5-year survival rate was 56.4%, and the tumor-free survival rate was 40.5%. Complications included two autograft bone fractures, one upper extremity arterial embolism combined with radial nerve injury, and shoulder instability in four patients with intra-articular resection prosthesis reconstruction, with an overall complication rate of 18.4% ( 7/38). Active shoulder abduction failed to exceed 30° in extra-articular resection patients compared to 45° in intra-articular resection patients. Intra-articular resection of proximal humeral osteosarcoma cases without scapular glenoid or deltoid invasion on imaging resulted in better oncologic and functional outcomes. The proximal humeral prosthesis reconstruction had a low complication rate and better maintenance of upper extremity and hand function. Intraoperative specimens of osteosarcoma of the right upper humerus showed extensive resection of the tumor at 3 years postoperative follow-up, and radiographs showed a well-positioned prosthesis at 3 years postoperative follow-up, with good function of the affected shoulder joint as on the healthy side.