Proximal humerus fractures are common, accounting for about 40% of adult humerus fractures. Currently, the treatment of proximal humeral fractures is divided into conservative treatment and surgical treatment, which includes intramedullary nail fixation, open reduction and internal fixation (ORIF), minimally invasive plate osteosynthesis (MIPO), and reverse shoulder arthroplasty (RSA). Previous studies have shown that ORIF has a high incidence of complications, including varus malunion, osteonecrosis, screw perforation or cut-out, subacromial impingement syndrome, infection, etc. Compared with ORIF, MIPO has the advantages of less blood loss, shorter operation time, less postoperative pain, shorter fracture healing time, and improved muscle strength recovery. Previous studies have found that some imaging parameters may influence the outcome of ORIF. According to our literature search, no scholars have conducted detailed measurements of radiological parameters after MIPO. Therefore, in this study, we correlated baseline data and postoperative radiological parameters of patients undergoing MIPO with shoulder joint function to determine which factors influence surgical outcomes.

To investigate the relationship between radiological parameters and shoulder joint function after MIPO of proximal humeral fracture.

Fifty-one patients with proximal humeral fractures who received MIPO with the same senior physician in our hospital from January 1, 2016, to June 30, 2022, were selected, and radiological parameters of the X-ray radiographs of these patients were analyzed within three days after surgery. Humerus head diameter, humerus head height, vertical center, neck-shaft angle, angle of humeral head diameter and humeral axis, vertical height, head-tuberosity distance, and head-plate distance were included. Constant-Murley and rapid DASH scores were assessed at the 12th-month follow-up after surgery. The subjects were divided into two groups. They were divided into the excellent and good group and the average and poor group according to the Constant-Murley score, and divided into the good group and the poor group according to the rapid DASH score. Baseline data and radiological parameters were compared between the two groups. Regression analysis was used to evaluate the dependence of radiological parameters on shoulder joint function scores.

The patients' Constant-Murley score was (82.55±11.25) points. According to the results of the Constant-Murley score, 45 of the 51 patients had excellent or good results, and six patients had moderate or poor results. Patients with moderate or poor long-term follow-up results usually had larger humeral-shaft angle, humeral head diameter, and angle of humeral head diameter and humeral axis and smaller vertical height. The patients' DASH score was (12.06±8.55) points. According to the rapid DASH score results, 43 of 51 patients had good results, and eight patients had poor results. Patients with poor long-term follow-up results usually had longer injury to surgery interval, larger humeral neck-shaft angle and angle of humeral head diameter and humeral axis, and smaller humeral head height and vertical height.The reasonable range of some radiological parameters was obtained by regression analysis (humeral neck-shaft angle: 117.94-138.21°, angle of humeral head diameter and humeral axis: 28.72- 46.72° and vertical height: ≥36.61 mm) .

After MIPO of proximal humeral fractures, patients with larger humeral neck-shaft angle, larger angle of humeral head diameter and humeral axis, and smaller vertical height had poorer shoulder joint function. By regression analysis, we further determined the proper range of humeral neck-shaft angle, humeral head diameter, and angle of humeral head diameter and humeral axis, and the necessary vertical height, which can be used as references by orthopedic surgeons.