To investigate the application effect of 3D printing technology combined with PMMA (polymethylmethacrylate) bone cement intramedullary support assisted locking plate in the treatment of proximal humeral Neer Ⅱ, Ⅲ and Ⅳ osteoporotic fractures.

From September 2017 to may 2020, 33 cases of proximal humeral neer Ⅱ, Ⅲand Ⅳ osteoporotic fractures were retrospectively analyzed. There were 5 males and 28 females, with an average age of (68.4±2.5) years. According to neer classification, there were 3 cases of two-part fracture, 21 cases of three part fracture and 9 cases of four part fracture. The CT scanning data of three-dimensional reconstruction of bilateral humerus were collected before operation, and the simulated reduction and mirror image comparison were carried out through mimics research 20.0 software to obtain the bone defect range after fracture reduction, and then the intramedullary support prosthesis mold was designed. The mold of intramedullary support prosthesis was printed by 3D printing technology, and the mold was used to make PMMA bone cement intramedullary support prosthesis during operation. The prosthesis was implanted into the medullary cavity of the proximal humerus to support the fracture block of the humeral head, and the locking plate was used to reduce and fix the fracture. Immediately after the operation, the proximal humerus positive and lateral X-ray was performed to evaluate the quality of fracture reduction. After the operation, regular reexamination was performed to observe the fracture healing and complications, and the changes of the proximal humeral neck shaft angle and the height of the humeral head were measured and recorded; One year after operation, it passed the constant Murley shoulder function score and VAS pain score. In neer's four part fracture, there was significant difference between the healthy side of the neck shaft angle (146.44±3.74) ° and the preoperative neck shaft angle (96.22±14.09) ° (P<0.05), but there was no significant difference between the healthy side of the neck shaft angle and the postoperative neck shaft angle (141.11±3.96) ° one year later.

All 33 patients were followed up for (13.2±1.5) months. In neer's two-part fracture, there was a statistically significant difference in the cervical trunk angle of the healthy side, before operation and one year after operation (F=39.038, P<0.05). In the two-part comparison, it was found that there was a statistically significant difference between the cervical trunk angle of the healthy side (145.33±1.52) ° and the preoperative cervical trunk angle (102.00±11.13) ° (P<0.05), and there was no statistically significant difference between the cervical trunk angle of the healthy side (145.67±2.52) ° and the postoperative cervical trunk angle of one year. In neer's three part fractures, there was a statistically significant difference in the angle of the neck trunk on the healthy side, before operation and one year after operation (F=13.957, P<0.05). It was found that there was a statistically significant difference in the angle of the neck trunk on the healthy side (145.86±3.18) °, compared with the angle of the neck trunk before operation (173.90±35.33) ° (P<0.05), and there was no statistically significant difference in the angle of the neck trunk one year after operation (143.81±4.19) °. In neer's four part fractures, there was a statistically significant difference in the cervical trunk angle between the healthy side, before operation and one year after operation (F=89.297, P<0.05). There was a statistically significant difference in the cervical trunk angle between the healthy side (146.44±3.74) ° and the preoperative cervical trunk angle (96.22±14.09) ° (P<0.05), and there was no statistically significant difference between the healthy side and the postoperative cervical trunk angle one year after operation (141.11±3.96) °. In neer's second, third and fourth part fractures, there was no significant difference between the height of humeral head during operation and that one year after operation. In neer two-part fracture, the average height difference of humeral head is (0.70±0.18) mm, in neer three part fracture, the average height difference of humeral head is (1.12±0.24) mm, and in neer four part fracture, the average height difference of humeral head is (1.92±0.21)mm. There was no significant difference in the height of humeral head between intraoperative and 1 year after operation. One year after operation, three-dimensional reconstruction CT showed that all patients had achieved fracture healing. In the constant Murley shoulder function score, patients with two-part fractures scored (78.42±4.31), patients with three-part fractures scored (74.34±3.82), patients with four part fractures scored (69.31±3.43), patients with two-part fractures scored (1.53±0.81), patients with three part fractures scored (2.12±0.63), and patients with four part fractures scored (3.14±1.22).

Using 3D printing combined with PMMA bone cement intramedullary support technology to assist locking plate in the treatment of elderly proximal humeral neer Ⅱ, Ⅲ and Ⅳ osteoporotic fractures can enhance the stability of fracture fixation, effectively maintain the postoperative neck shaft angle and humeral head height, and obtain better clinical results.