Introduction

The Achilles tendon, being the thickest and most robust tendon in the human body, is also one of the most frequently injured tendons1. Acute Achilles tendon rupture (AATR) is defined as rupture occurring within 2 weeks. With the continuous improvement in the general population’s level of sports participation, the annual incidence of AATR has reached 37 per 100,000 individuals2,3. AATR often occurs without aura, and typical symptoms include localized swelling of the Achilles tendon, foot pain, and weakness in ankle movements4. Currently, MRI, high-frequency ultrasound and shear wave elastography (SWE) are the most ubiquitous imaging methods used to diagnose Achilles tendon rupture. Among these, SWE refers to the assessment of the hardness and elastic properties of the tissue by transmitting an elastic wave through the tissue and measuring the speed (i.e., the shear wave velocity, SWV) at which the wave travels5.

Appropriate post-injury treatment is crucial for patients following Achilles tendon rupture; failure to do so may result in motor deformities and associated motor dysfunctions such as difficulty lifting the heel, ultimately impacting the patient’s daily life, work, and overall quality of life4,6. Although there is no consensus on the optimal treatment for AATR, surgical intervention is often considered the definitive choice for the majority of patients with Achilles tendon rupture7.

Depending on the acuity of the injury and the size of the defect, the choice of surgical techniques for Achilles tendon rupture ranges from end-to-end suturing to complex reconstruction using augmentation8. According to most studies, an Achilles tendon rupture with a defect at the broken ends of up to 3 cm can be treated through in situ end-to-end anastomosis, while surgical treatment may involve bridging, reinforcement, and fixation using methods such as fascia reversal, tendon transposition, or transplantation for ruptures with a wider defect exceeding 3 cm or involving stop avulsion within a 2 cm range9,10,11,12. Previous research has extensively reported techniques such as double-row suture bridges for bridging the broken ends of the Achilles tendon fixed with oblique calcaneal anchors13,14,15,16,17. However, a number of studies have been reported on the expansion of such tilted fixed bone tunnel18,19. In addition, there have been no reported studies on transverse bone tunnels in the field of Achilles tendon reconstruction. Consequently, our team proposed a new approach to Achilles tendon reconstruction based on our clinical work experience. The retrospective study aimed to evaluate the clinical and functional outcomes of transversal calcaneal anchored reconstruction for acute Achilles tendon rupture using a free semitendinosus tendon autograft.

Materials and methods

This retrospective study was approved by the ethics committee of the Second Affiliated Hospital of Xi’an Jiaotong University (No. 2024-108). All the patients had surrendered informed consent preoperatively. This study complied with the Declaration of Helsinki and the patients of this study were treated following the AAOS guidelines for clinical practice20. The patients who underwent primary Achilles tendon reconstruction at our department from 2016 to 2021 were reviewed. Patients would be included if they met the following criteria: (1) age range of 16–65 years; (2) Achilles tendon rupture confirmed clinically and by MRI and high-frequency ultrasound; (3) patients with Achilles tendon defects > 3 cm; (4) primary Achilles tendon surgery; (5) no concomitant avulsion fracture; (6) unilateral Achilles tendon rupture; (7) no previous surgery on the affected ankle; (8) closed rupture of Achilles tendon due to fatigue injury, sports-related injury, and similar causes. The exclusion criteria included: (1) chronic Achilles tendon rupture (onset time > 2 weeks); (2) patients with Achilles tendon defects > 3 cm but without undergoing Achilles tendon reconstruction using transversal calcaneal anchored autogenous semitendinosus tendon graft; (3) patients with incomplete preoperative and postoperative imaging information; (4) individuals with a history of systemic, metabolic, or endocrine diseases; (5) prolonged use of corticosteroids, estrogens, quinolones, or cholesterol drugs. Overall, a total of 43 patients with Achilles tendon rupture met the inclusion criteria, while 26 cases were excluded based on the exclusion criteria, resulting in a final study cohort of 17 cases (Fig. 1). All surgical procedures were performed by an experienced orthopedic surgeon within our team.

Figure 1
figure 1

Flowchart of included patients.

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Surgical technique

Spinal anesthesia was administered to achieve satisfactory anesthesia. The patient was placed in the supine position. A pneumatic tourniquet was applied at the root of the operative thigh, and the area was routinely disinfected and covered with towels. After blood evacuation, the pneumatic tourniquet was inflated to 40 kPa.

Preparation of autogenous tendon graft. Here, the autogenous tendon we need to take is the ipsilateral semitendinosus tendon. The tibial tubercle of the operative lower limb was palpated, and a 3 cm longitudinal incision was made on the medial side. Blunt separation of the subcutaneous tissue and fascia was performed, exposing the gracilis muscle and semitendinosus muscle of the goosefoot structure. The proximal end was further dissected to remove the entire semitendinosus tendon which was approximately 25–28 cm long using a tendon extractor device (DELTA Medical, Beijing, China). The graft tendon was then sutured with baseball stitches, and the length of the grafted tendon was adjusted according to the size of the preoperatively planned defect. In addition, a suture line (DELTA Medical, Beijing, China) was inserted into both ends of the graft tendon as a guide wire. The graft tendon diameter was measured after the braiding process. Finally, the autologous tendon grafts were soaked in iodophor water for 15–20 min (Fig. 2a,b).

Figure 2
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Operation chart. (a) Body surface identification of autologous tendon removal site. (b) Autogenous tendon graft braiding. (c,d) Clean up the hematoma near the Achilles tendon and thoroughly expose the broken end of the Achilles tendon. (e) Fixation and suture of autogenous tendon graft and broken end of Achilles tendon. (f) Operation schematic diagram.

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After the tendon removal was completed, the patient’s position was adjusted to prone with the patient’s cooperation and the towel was re-sterilized. The patient’s chest and abdomen were elevated to keep the patient in a comfortable position during the procedure.

Open debridement of the ruptured Achilles tendon was performed. First, palpation was used to locate the depressed area of the Achilles tendon, which served as the reference for making a longitudinal median incision extending to the distal end of the Achilles tendon. The subcutaneous tissue was bluntly separated and the sural nerve was carefully protected. The ruptured ends of the Achilles tendon were identified and exposed. Hematomas surrounding the ruptured ends and nonfunctional fibers on both sides were thoroughly cleaned (Fig. 2c,d).

Preparation of calcaneal tunnel. The soft tissue surrounding the calcaneal tubercle was carefully separated to expose the calcaneal body on both sides. At the level of the tubercle, the calcaneal body was clamped and fixed with oval forceps, and the distal rings of the oval forceps were used for positioning. A Kirschner wire (DELTA Medical, Beijing, China) was transversally inserted into the calcaneal body at the level of the tubercle to prepare and locate the calcaneal tunnel. Following the guidance of the inserted Kirschner wire, a hollow drill (DELTA Medical, Beijing, China) corresponding to the graft tendon diameter was used to transversally prepare the calcaneal tunnel.

Bridging and reconstruction of broken end of Achilles tendon. Any remaining bone fragments around the calcaneal tunnel were cleared. The pre-prepared autologous tendon graft was passed through the calcaneal tunnel, guided by a guide wire, and woven inside the proximal Achilles tendon for 3–4 passes. The remaining autologous tendon grafts were then sutured and fixed on both sides of the proximal Achilles tendon using tendon sutures (DELTA Medical, Beijing, China). The autologous tendon graft and broken end of the Achilles tendon were secured and sutured using Double-Z anastomosis21. Encircling and strengthening sutures were performed at the broken end anastomosis as required. Finally, an interference screw (DELTA Medical, Beijing, China) was inserted from the medial of the calcaneal tunnel to provide additional fixation for the graft tendon. (Fig. 2e,f).

Postoperative nursing and rehabilitation

Prior to the operation, patients were instructed to bring their own ankle chuck braces or thick-soled calcaneal tendon boots. Functional rehabilitation training manuals were provided to patients immediately after the operation, along with appropriate guidance. Within the first 2 weeks post-operation, strict bed rest was advised with ankle plantarflexion at 30°, utilizing fixed braces. Patients were encouraged to move their toes to promote peripheral blood circulation and perform feasible muscle strengthening exercises such as straight leg elevation. A professional orthopedic surgeon within the research team regularly monitored the wound, changing dressings to maintain dryness and prevent infection. At the 2-weeks mark, stitches were removed, and the range of motion of the ankle brace was adjusted within the range of 15–30° plantarflexion (2–4 weeks post-operation). Patients were instructed to utilize double crutches to avoid weight-bearing and contact with the ground, while engaging in ankle joint flexion and extension exercises. At 4–6 weeks post-operation, the range of motion of the ankle brace was adjusted within 0–30° plantarflexion. Patients were instructed to walk with weight on double crutches while adjusting negative weight based on ankle joint motion, Achilles tendon function, and patient comfort. Gradual restoration of lower limb movement and weight-bearing was encouraged. At 6weeks post-operation, the braces were removed, and patients were guided to walk with double crutches, gradually transitioning to full weight-bearing on the operative limb. Within the 6–12 weeks post-operation period, normal gait was restored, and ankle functional exercise intensity was increased. Attempts were made to stretch the Achilles tendon and restore normal ankle circumference. Patients were advised to avoid strenuous exercise during this stage. Between 12 and 24 weeks post-operation, physical exercise levels were gradually restored based on individual patient conditions.

Postoperative follow-up

The patients underwent post-operative follow-up at the outpatient clinic. Follow-up visits took place at 2, 4, 6 and 8 weeks post-operation, and at 3, 6 and 12 months post-operation. One year later, a re-examination was conducted at the outpatient clinic, followed by subsequent follow-up visits every 6 months. During the follow-up period, the functional status of the Achilles tendon was objectively assessed by comparing the range of motion between the bilateral ankles and utilizing SWV. The patient assumed a supine position, and the tip of the lateral ankle, the fifth metatarsal axis, and the long axis of the fibula were marked on the lower extremity surface. The patient was instructed to perform ankle flexion and extension movements, and the range of motion was captured through mobile phone photography. The mobile app ImageMeter22 (version 3.8.7) was used to measure plantarflexion and dorsiflexion angles of the ankle: positioning the apex of the angle at the tip of the outer ankle, and the two arms of the angle being parallel to the fifth metatarsal axis and the fibula long axis, respectively. A professional ultrasound physician within the team utilized real-time shear wave elastography ultrasound diagnostic instrumentation (L6-9 linear array probe, frequency range 6–9 MHz) (Supersonic Imagine, France) for high-frequency ultrasound and SWE examination, and measured the corresponding SWV.

Subjective evaluation of Achilles tendon function after the operation was carried out using the VAS, AOFAS23 and ATRS24 at the preoperative and postoperative follow-up visits. At 6 and 12 months post-operation, ankle joint lateral position, CT scans, and MRI examinations were conducted to evaluate the recovery of the Achilles tendon’s anatomical structure and to assess signs of calcaneal tunnel dilatation. Thereafter, annual review of ankle joint lateral position, CT scans, and MRI examinations was recommended for patients, with no mandatory requirements.

Statistical hypotheses and analysis

The data of this study were analyzed by SPSS version 25.0 (IBM Inc. Chicago, Illinois). The most important outcome indicators in this study includes the AOFAS and ATRS. In addition, secondary outcome indicators includes VAS, ankle dorsiflexion and plantarflexion angles, and SWV. The above measures were expressed as the mean ± SD after normality testing using the Shapiro–Wilk method, and statistically analyzed by the paired sample t-test. The counting data is expressed in the number of cases or percentage (%). The test level of α was 0.05.

Ethics approval and consent to participate

The Ethics Committee of the Second Affiliated Hospital of Xi’an Jiaotong University approved the study protocol.

Results

Patient characteristics

Among the 17 patients, there were 12 males and 5 females, 10 with left Achilles tendon rupture and 7 with right Achilles tendon rupture. The mean ± SD age of the patients was 37.8 ± 6.2 years (range, 20–51 years), BMI scores ranged from 23.19 to 32.45 kg/m2 (average, 26.17 ± 3.43 kg/m2), and the mean duration from injury to operation was 3.41 ± 1.72 days (range, 2–5 days). The causes of injury included sports injury (15 cases), fall injury (1 case) and other causes (1 case). The average follow-up time was 26.3 ± 2.7 months (range, 12–38 months) (Table 1).

Table 1 Demographic data.
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Range of motion of ankle joint

The range of motion of both ankles, including the average angles of dorsal extension and plantarflexion, were performed in 17 patients. At the last follow-up, it showed a significant difference between the uninvolved ankles and involved ankles (P < 0.05).The deficit of dorsiflexion between the operative and nonoperative ankles was 6.88 ± 5.36° (range, 2.52–15.11°), and the deficit of plantarflexion between bilateral ankles was 9.15 ± 7.82° (range, 1.01–20.35°) (Table 2).

Table 2 Range of motion of ankle joint (last follow-up).
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Imaging evaluation

At postoperative follow-up, the imaging results of 17 patients showed that the continuity of the Achilles tendon was well restored after surgery, with clear borders with adjacent tissues, and the calcaneal tunnel did not show any obvious signs of enlargement.

X-ray and CT images of the ankle joint revealed regular edges of the calcaneal tunnel, without evident signs of bone destruction such as dissolution, loss, or collapse of adjacent bones, indicating no significant bone tunnel expansion. MRI images showed continuous and normal walking of the Achilles tendon with a uniform low signal observed on T2-weighted sequences. High-frequency ultrasound images demonstrated continuous progression of the Achilles tendon, gradually uniform internal echoes, clear boundaries with adjacent tissues, and absence of noticeable tissue adhesion or calcification. Shear wave elastography revealed a gradual increase in hardness of the operative-side Achilles tendon, recovering to the same level as the healthy side. However, compared to the preoperative state, the nonoperative Achilles tendon exhibited decreased tissue hardness. The SWV of the operated Achilles tendon increased from 27.59 ± 8.68 to 157.40 ± 11.01 kPa, while the SWV of the healthy Achilles tendon decreased from 184.19 ± 11.54 to 160.95 ± 15.71 kPa (P < 0.05) (Table 3, Fig. 3a–j).

Table 3 Shear wave velocity.
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Figure 3
figure 3

Typical case. A 42-years-old male suffered a sudden rupture of the left Achilles tendon while playing football. (a–c) Preoperative MRI and high frequency ultrasound examination showed that the left Achilles tendon was completely ruptured and the broken end was defective > 3 cm. (d–h) During the follow-up 2 years after operation, MRI, CT and X-ray examination of ankle joint showed that the continuity of Achilles tendon was complete, the edge of bone tunnel was regular, and there was no obvious tendency of bone tunnel expansion. (i,j) During the follow-up 2 years after operation, high-frequency ultrasound and shear wave elastography showed that the Achilles tendon recovered continuously, the boundary with the adjacent tissue was clear, there was no obvious calcification and adhesion, and the hardness of the Achilles tendon recovered. (k,l) The range of motion of the ankle is measured by the mobile app ImageMeter (version 3.8.7).

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Clinical outcomes and complications

Comparison between pre-operative and post-operative assessments revealed a significant reduction in pain and notable improvement in subjective Achilles tendon function among the patients. The Visual Analog Scale (VAS) score decreased from 5.35 ± 1.58 before the operation to 1.18 ± 0.53. Additionally, the AOFAS score and ATRS score increased from 53.94 ± 15.98 and 24.47 ± 7.36 before the operation to 83.41 ± 9.34 and 68.59 ± 5.44 after the operation, respectively (P < 0.05) (Table 4).

Table 4 Subjective function score.
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During the follow-up period, the postoperative complications were as follows: delayed wound healing occurred in 3 cases, sural nerve injury occurred in 1 case, and no re-rupture occurred in all patients.

Discussion

Surgical treatment of acute Achilles tendon rupture utilizing autologous tendon transposition and transplantation has been extensively reported. It is worth noting that, in order to increase the contact area between the tendon and bone and enhance the strength of the repaired Achilles tendon, most of these surgical treatments employ an inclined calcaneal tunnel for tendon fixation25,26,27. However, the latest research by Stake et al.28 demonstrates that there is no significant difference in pullout strength when various angles of calcaneal anchors are used for tendon fixation. This suggests that tendon fixation with a transversal calcaneal tunnel holds the same therapeutic potential as an inclined calcaneal tunnel for repairing acute Achilles tendon rupture. In this study, autogenous semitendinosus tendon grafts were utilized, fixed through a transversal calcaneal tunnel, and secured to the broken end of the Achilles tendon using Double-Z anastomosis for the repair and reconstruction of acute Achilles tendon rupture. Seventeen patients were included in this study, with an average follow-up time of 26.3 ± 2.7 months. All patients achieved favorable functional recovery of the Achilles tendon, with no incidences of secondary rupture observed.

In 2021, Osama et al.25 validated the effectiveness of the inclined Achilles tunnel fixation peroneal short tendon transposition technique for Achilles tendon reconstruction in a prospective study. After about 40 months of postoperative follow-up, the patients’ mean AOFAS and ATRS improved to 99.3 ± 1.2 and 95.9 ± 1.9, respectively. Three patients (7.1%) developed postoperative wound complications, including superficial skin necrosis in two cases. Interestingly, Niklas et al.29 proposed an endoscopically assisted longitudinal calcaneal screw fixation for Achilles tendon reconstruction. At 12-months postoperative follow-up, patients had a median ATRS of 76 (45–99). Postoperative complications occurred in 3 (13.6%) patients, including 2 minor wound complications and 1 sural nerve injury. In contrast, in the present study, the mean follow-up time of the 17 patients was 26.3 ± 2.7 months, and the mean AOFAS and ATRS of the patients improved from 52.81 ± 17.34 and 24.35 ± 7.26 preoperatively to 84.58 ± 10.44 and 68.47 ± 4.19, respectively. Postoperative complications occurred in 4 (23.5%) patients, including 3 patients experienced delayed healing of surgical wounds due to wound infection or their own poor nutritional status, and 1 patient experienced sural nerve injury. Postoperative recovery of Achilles tendon function was relatively slower in patients treated with Achilles tendon reconstruction using transversal calcaneal anchored autogenous semitendinosus tendon graft compared to comparable studies, but was still significantly improved from the preoperative period. In addition, the follow-up period of this study was relatively short, and further follow-up studies are needed to confirm the final level of the patients’ postoperative recovery of Achilles tendon function. As for the postoperative complication rate, Achilles tendon reconstruction using transversal calcaneal anchored autogenous semitendinosus tendon graft is still an open procedure and involves tendon grafting, which results in a greater extent of surgical trauma and a relatively high risk of surgical complications.

The selection of the end-to-end anastomosis technique is a crucial factor in open surgery for acute closed rupture of the Achilles tendon. Traditional techniques for end-to-end anastomosis include Krackow suture, Bunnell suture, Kessler, and modified Kessler suture. It has been established that there are significant biomechanical differences among these traditional techniques30,31,32. Furthermore, through clinical diagnosis, treatment, and prior research, we have observed that traditional end-to-end anastomosis techniques often result in more and larger sutures at the broken ends of the Achilles tendon. This can increase the risk of adhesion between the tendon and the adjacent soft tissue or necessitate the removal and repair of the Achilles tendon stump during the suturing process, thus exacerbating autologous Achilles tendon injury33,34. In this study, we employed the Double-Z anastomosis technique, which is a novel suture technique developed by our team based on the characteristics and advantages of various traditional end-to-end anastomosis techniques. Through previous studies on annular tendon grafts, our team verified the advantages of the Double-Z anastomosis technique through in vitro experiments, especially in terms of tensile stress resistance21. In this study, the graft tendon passed through both sides of the broken end of the Achilles tendon, forming the first “Double-Z-like” structure. A tendon suture was then used to fix and suture the autologous tendon graft and the broken end of the Achilles tendon, forming the second ‘Double-Z” structure. Consequently, two stable “Double-Z” structures were formed at the broken ends of the Achilles tendon, further enhancing the strength of Achilles tendon repair. This technique facilitates patients’ adaptation to more aggressive early accelerated rehabilitation treatment of the Achilles tendon and improves the prognosis of acute Achilles tendon rupture. All patients in this study achieved favorable functional outcomes in terms of Achilles tendon function post-operation.

Previous reports have documented the use of various tendons for Achilles tendon reinforcement repair or reconstruction, including the quadriceps tendon, semitendinosus tendon, gracilis tendon, and flexor pollicis longus tendon, among others. Among them, flexor pollicis longus tendon transplantation has been the preferred choice for most surgeons35. Maffulli et al.36 compared the surgical outcomes of ipsilateral semitendinosus tendon and flexor pollicis longus tendon transplantation for the treatment of Achilles tendon rupture, and their results demonstrated no significant difference between the two techniques. However, ipsilateral semitendinosus tendon transplantation can effectively avoid interphalangeal joint weakness and flexion loss associated with flexor pollicis longus tendon transplantation. For most patients, semitendinosus tendon regeneration occurs within 1 year post-operation, without causing severe lower limb strength decline or significant muscle atrophy37. Maffulli et al. also employed ipsilateral semitendinosus tendon transplantation as the primary choice for repair and reconstruction of acute Achilles tendon rupture in a follow-up study38. Based on the aforementioned findings, this study utilized ipsilateral semitendinosus tendon as an autologous tendon graft for repair and reconstruction of acute Achilles tendon rupture, resulting in successful structural and functional recovery of the ruptured Achilles tendon.

In assessing the clinical prognosis of patients objectively, we observed that the operative ankle exhibited a noticeable range of motion defect following the operation when compared to the healthy ankle. Yanbin Pi et al.’s study shares similar results to the findings of this study, employing statistical analysis to confirm a significant interaction between the Visual Analog Scale (VAS) score and ankle range of motion defect, indicating that postoperative pain is an important factor restricting the recovery of ankle range of motion after surgery39. Additionally, postoperative calcification and adhesion of the Achilles tendon can further restrict the postoperative range of motion recovery in the ankle joint. However, it is important to note that in this study, high-frequency ultrasound was utilized to dynamically examine postoperative recovery of the Achilles tendon, and no significant calcification or adhesion was observed. Thus, we believe that apart from postoperative pain, changes in the course of the Achilles tendon post-surgery also contribute to the recovery of ankle range of motion. After fixing the graft tendon through the transversal calcaneal tunnel and anastomosing it with the broken end of the Achilles tendon, the entire Achilles tendon exhibited an inverted “Y” shape. This change in the mechanical structure and shape of the Achilles tendon dispersed the forces exerted during contraction or relaxation, ultimately limiting the range of motion in the ankle.

Postoperatively, we employed dynamic elastic ultrasound to assess the quality of the Achilles tendon. The SWV values of the operated Achilles tendon gradually increased and predominantly recovered to levels comparable to those of the healthy Achilles tendon at the last follow-up. However, it is noteworthy that the nonoperative Achilles tendon exhibited a significant decrease in hardness after the operation, indicating a trend towards degeneration. This finding aligns with the study conducted by Qianru Li et al.40 in a publication from 2018. During the process of postoperative rehabilitation exercises, patients primarily rely on the healthy lower limb to bear weight, with the healthy Achilles tendon shouldering most, if not all, of the body weight. This places a substantial burden and challenge on the healthy Achilles tendon. Consequently, the nonoperative Achilles tendon demonstrates a tendency towards strain and degeneration post-operation. This serves as a reminder that, during the rehabilitation process following Achilles tendon rupture, attention should not only be given to the postoperative functional recovery of the operated Achilles tendon but also to the protection of the healthy Achilles tendon. The decline in Achilles tendon quality caused by excessive strain significantly increases the risk of rupture in the nonoperative Achilles tendon.

In the field of Achilles tendon rupture repair and reconstruction, we have not encountered any research reports on bone tunnel enlargement. However, related studies in the field of anterior cruciate ligament reconstruction serve as a reminder that bone tunnel enlargement is an adverse event postoperatively that cannot be overlooked41,42. In this study, we utilized X-ray, CT scans, and other imaging techniques to examine the calcaneus, finding regular interfaces and no apparent signs of bone destruction or tunnel dilatation in adjacent bones. Comparing the transversal bone tunnel approach with the oblique bone tunnel approach, the former alters the direction of force transmission during tendon movement. Whether it is anterior cruciate ligament reconstruction or acute Achilles tendon rupture, the use of oblique bone tunnels achieves the purpose of mimicking natural anatomy and preserving the native course and shape of the tendon. However, during postoperative rehabilitation, the graft tendon undergoes forward stretching along the oblique bone tunnel, leading to friction with the tunnel’s edges, which can cause varying levels of wear at the tendon interface. This not only hampers postoperative tendon healing but also increases the risk of bone tunnel expansion due to excessive graft tendon movement within the tunnel (referred to as the “windshield-wiper effect” and “bungee effect”)43. The transversal tunnel utilized in this study not only modifies the course of the Achilles tendon to some extent but also alters the direction of force transmission during tendon movement. The friction between the graft tendon and the bone tunnel during movement is transformed into compressive pressure exerted on the tendon interfaces. This means that instead of rubbing against the bone tunnel in the sagittal plane, the graft tendon fills the bone tunnel in the coronal plane, promoting an increase in tendon interface strength, facilitating postoperative tendon healing, enhancing tendon stability, and reducing bone tunnel enlargement.

This study still has some limitations. Some of the patients in this study had poor compliance with postoperative functional rehabilitation and slow recovery of Achilles tendon function after surgery. Ikuta et al.44 reported similar adverse events, with individual patients experiencing re-ruptures of the Achilles tendon postoperatively due to poor postoperative compliance. In further studies, while we continue to expand the sample size, we need to focus on patient and family counseling to improve patients’ adherence to postoperative functional rehabilitation. In addition, in terms of the assessment of operative efficacy, compared with the studies by Osama et al.25 and Niklas et al.29 this study focused on the assessment of Achilles tendon imaging and subjective functional scores, but lacked in the evaluation of objective indicators, such as the patient’s operative time, length of the surgical incision, length of hospitalization, postoperative lengthening of the Achilles tendon, and measurements related to the dilatation of the bony tunnels. In a follow-up study we will include such clinical metrics in a comparative study to further assess the clinical value of Achilles tendon reconstruction using transversal calcaneal anchored autogenous semitendinosus tendon graft.

In conclusion, transversal calcaneal anchored reconstruction of acute Achilles tendon rupture using a free semitendinosus tendon autograft demonstrates favorable clinical outcomes. The structure and function of the ruptured Achilles tendon recover effectively, with a low incidence of postoperative complications. Furthermore, the transversal calcaneal tunnel provides stability and reliability, showing no evident indications of bone tunnel expansion. Therefore, transversal calcaneal anchored Achilles tendon reconstruction with a free semitendinosus tendon autograft proves to be an effective treatment option for acute Achilles tendon rupture.