Objective:To compare the efficacy of double Z-shaped suture and modified Kessler suture in the repair of acute closed Achilles tendon rupture.Methods:A retrospective cohort study was conducted to analyze the clinical data of 27 patients with acute closed Achilles tendon rupture admitted to the Second Affiliated Hospital of Xi′an Jiaotong University from July 2018 to July 2022, including 24 males and 3 females, aged 14-53 years [(35.7±8.2)years]. All the patients underwent primary open surgical repair of the Achilles tendon, among whom 16 patients were treated with the double Z-shaped suture technique (double Z-shaped suture group) and 11 with the modified Kessler suture technique (modified Kessler suture group). Visual analogue scale (VAS) scores preoperatively and at 2, 4, and 6 weeks postoperatively as well as at the last follow-up were compared between the two groups. American Orthopedic Foot & Ankle Society (AOFAS) ankle-hindfoot scores, Achilles tendon total rupture scores (ATRS), ankle range of motion (dorsiflexion and plantarflexion angles), and shear wave elastography (SWE) [with its results recorded as shear wave velocity (SWV)] were applied to evaluate the recovery of tendon function and quality. High-frequency ultrasonography was also used to evaluate the recovery of morphological structure of the Achilles tendon and soft tissue adhesion. Tolerance to early rehabilitation at 2 weeks postoperatively and the incidence of postoperative complications were compared between the two groups.Results:All the patients were followed up for 6-12 months [(9.6±1.3)months]. There was no statistically significant difference in preoperative VAS scores between the two groups ( P>0.05). At 2, 4, and 6 weeks postoperatively, the VAS scores in the double Z-shaped suture group were 4.6(4.0, 5.0)points, 1.6(1.0, 2.0)points, and 0.5(0.0, 1.0)points respectively, significantly lower than those in the modified Kessler suture group [6.9(6.0, 8.0)points, 2.5(2.0, 3.0)points, and 1.4(1.0, 2.0)points] ( P<0.05 or 0.01). At the last follow-up, the VAS decreased to 0.0(0.0, 0.0)points in both groups. VAS score in the double Z-shaped suture group significantly decreased at 2 weeks postoperatively compared to that preoperatively, with a consistent downward trend observed at all the postoperative time points ( P<0.05). In the modified Kessler suture group, there was no significant difference in VAS scores preoperatively and at 2 weeks postoperatively ( P>0.05), but a downward trend was noted at 4 and 6 weeks postoperatively and at the last follow-up ( P<0.05). There were no significant differences in AOFAS ankle-hindfoot scores, ATRS or SWV at 2, 4, and 6 weeks postoperatively and at the last follow-up ( P>0.05). At 2, 4, and 6 weeks postoperatively, dorsiflexion angles in the double Z-shaped suture group were (-18.2±3.9)°, (-13.7±2.8)°, and (-6.6±2.4)° respectively, significantly better than those in the modified Kessler suture group [(-24.1±2.7)°, (-18.3±3.0)°, and (-12.0±2.8)°] ( P<0.01). No significant difference in dorsiflexion angles was observed between the groups at the last follow-up ( P>0.05). No significant differences in plantarflexion angles were noted at 2 weeks postoperatively and at the last follow-up ( P>0.05). At 4 and 6 weeks postoperatively, plantarflexion angles in the double Z-shaped suture group were (37.5±3.8)° and (42.1±3.3)°respectively, significantly better than those in the modified Kessler suture group [(34.6±2.0)° and (38.0±1.4)°] ( P<0.05 or 0.01). Both groups showed increasing trends in AOFAS ankle-hindfoot scores, dorsiflexion and plantarflexion angles, and SWV at 4 and 6 weeks postoperatively, as well as at the last follow-up ( P<0.05 or 0.01). No significant differences were noted in ATRS at 2 and 4 weeks postoperatively in the double Z-shaped suture group ( P>0.05), but significant improvements were observed at 6 weeks postoperatively and at the last follow-up ( P<0.05 or 0.01). In the modified Kessler suture group, no significant changes in ATRS scores were observed at 2, 4 and 6 weeks postoperatively ( P>0.05), except a significant increase at the last follow-up ( P<0.05). High-frequency ultrasonography at 2, 4, and 6 weeks postoperatively as well as at the last follow-up indicated good morphological recovery of the Achilles tendon in both groups, while soft tissue adhesion was significantly less in the double Z-shaped suture group compared with that of the modified Kessler suture group. Thirteen patients (81.3%) in the double Z-shaped suture group and 3 patients (27.3%) in the modified Kessler suture group were observed to tolerate the early rehabilitation at 2 weeks postoperatively as scheduled in the rehabilitation plan ( P<0.05). There was no statistically significant difference in the incidence of postoperative complications between the groups ( P>0.05). Conclusion:Compared with the modified Kessler suture technique, the double Z-shaped suture technique can reduce postoperative pain at an early stage, enhance the restoration of ankle joint mobility, lower the risk of postoperative soft tissue adhesion, and improve tolerance to rehabilitation in the repair of acute closed Achilles tendon rupture.