Objective:To compare the efficacy of double thread elastic locking intramedullary nail (ELIN) and threaded elastic intramedullary nail (TEIN) in the treatment of mid-shaft clavicular fracture.Methods:From August 2017 to September 2020, 33 patients with mid-shaft clavicular fractures were treated with ELIN (double threaded nail group), including 14 males and 19 females, age 52.09±16.32 years old; Robinson classification: 20 cases of type 2A2, 6 cases of type 2B1, and 7 cases of type 2B2. Thirty-two patients were selected as the control group with TEIN fixation (single threaded nail group) during the same period, including 13 males and 19 females; age 43.25±15.03 years old; Robinson classification: 19 cases of type 2A2 and 5 cases of type 2B1, 8 cases of 2B2 type. The operation time, intraoperative incision length, fracture healing time, internal fixation removal time, Constant-Murley shoulder joint score, disabilities of the arm, shoulder, and hand (DASH) score, fracture reduction and postoperative complications were compared between the two groups.Results:The patients in both groups were followed up after operation, the double-threaded screw group was followed up for 16-48 weeks (average, 23.7 weeks), and the single threaded nail group was followed up for 15-51 weeks (average, 22.9 weeks). The operation time of the double threaded nail group and the single threaded nail group were 19.45±6.74 min and 19.59±4.98 min, and the length of the incision was 1.70±0.79 cm and 1.73±0.84 cm. The fracture healing time were 12.12±1.29 weeks and 13.88±1.84 weeks. The internal fixation removal time was 13.09±1.31 weeks and 15.69±1.94 weeks. The Constant-Murley shoulder score was 93.18±3.78 points and 90.09±4.03 points, and the DASH scores were 1.49± 0.49 points and 3.85±1.13 points; There was no significant difference in operation time and incision length between the two groups ( t=0.01, 0.19; P>0.05), while fracture healing ( t=3.70, P<0.001), internal fixation removal time ( t=6.34, P<0.001), Constant-Murley shoulder score ( t=3.19, P<0.001), DASH score ( t=10.95, P<0.001) differences were statistically significant. The length of the clavicle on the healthy side was 16.38±1.09 cm in the double threaded nail group, and the length of the clavicle on the affected side after internal fixation removal was 16.33±1.12 cm. There was no obvious shortening deformity on the affected side, and there was no significant difference in the length of the clavicle between the two sides ( t=1.57, P=0.127). The clavicle lengths of the healthy side and the affected side after internal fixation removal in the single threaded nail group were 16.55±1.12 cm and 15.12±1.18 cm, and the difference was statistically significant ( t=8.02, P<0.001). The postoperative shortening values of the double-threaded screw group and the single-threaded screw group were 9.47±2.12 mm and 17.41±2.42 mm, and the difference was statistically significant ( t=14.07, P<0.001). Postoperatively, 5 cases of bursitis and 2 cases of skin irritation occurred in the double threaded nail group; While 6 cases of bursitis, 3 cases of skin irritation, 4 cases of shortening malunion, and 1 case of broken nail occurred in the single threaded nail group (fracture delayed union after replacement of internal fixation); the other patients did not experience screw retraction, wound infection, delayed fracture union or nonunion, neurovascular injury, and achieved osseous union. Conclusion:Both elastic intramedullary nails are effective surgical methods for the treatment of middle clavicle fractures, and the operation time is short and minimally invasive. However, compared with the TEIN, the fracture healing time of the double-threaded ELIN is shorter, the internal fixation removal time is earlier, the shoulder joint and upper limb function is better, and the shortening deformity is less likely to occur.