Open surgery and minimally invasive repair of acute Achilles tendon rupture: stratified outcomes based on immobilization duration in a prospective cohort study

Abstract

Background

Acute Achilles tendon rupture (AATR) surgical repair debates center on the clinical efficacy of minimally invasive surgery (MIS) versus open surgery (OS), with immobilization duration poorly stratified. This prospective cohort study aimed to compare clinical outcomes of OS and MIS for AATR repair and evaluate the impact of immobilization duration (0, 2, or 4 weeks) on postoperative rehabilitation.

Methods

A total of 474 patients undergoing surgical repair for acute AATR were stratified into six groups based on surgical approach (OS: 265 cases; MIS: 209 cases) and immobilization duration (0, 2, or 4 weeks). The primary outcomes were postoperative complications, while secondary outcomes included recovery times for Achilles tendon function. Data regarding the operative times, incision lengths, the visual analog scale (VAS) score, the Achilles tendon Total Rupture Score (ATRS), and the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Scale score, and the relative Achilles tendon resting angle (ATRA) were also collected.

Results

MIS groups demonstrated significantly shorter operative times (34.1–34.4 vs. 45.1–46.1 min, P < 0.001) and reduced incision lengths (2.2–2.4 vs. 4.5–4.7 cm, P < 0.001) compared to OS. Postoperative VAS scores were markedly lower in MIS cohorts during the first 2 weeks (P < 0.001), with pain resolution comparable across all groups by 8 weeks. Despite the superior early functional recovery in PF (9.1–33.4 vs. 14.6–38.9 days, P < 0.001), Group D and E exhibited higher re-injury rates compared to OS (P < 0.05), in which Group D also demonstrated higher re-operation rates (5.6% vs. 0, P = 0.038). Prolonged immobilization (4 weeks) delayed functional recovery in both cohorts (P < 0.001). While transient differences in AOFAS Ankle-Hindfoot Scale and ATRS scores were observed at intermediate time points, all groups achieved near-maximal functional scores by 48 weeks, with no significant between-group differences (P > 0.05). Relative ATRA exhibited no significant intergroup differences at 48 weeks postoperatively (P > 0.05).

Conclusion

MIS for acute Achilles tendon rupture achieves faster early recovery but carries higher re-injury risks, mitigated by 4-week immobilization. OS benefits from shorter (2-week) immobilization. Both approaches yield equivalent long-term functions, emphasizing the need for tailored protocols and refined MIS techniques to optimize outcomes.

Trial registration

NCT04663542.

The Achilles tendon, formed by the distal extensions of the gastrocnemius and soleus muscles, attaches to the calcaneal tuberosity and is among the strongest tendons in the human body [1- 3]. In recent years, acute Achilles tendon rupture (AATR) has emerged as a prevalent sports injury, particularly affecting active individuals and middle-aged men, as awareness of physical fitness increases [4- 7]. AATR results in pain and restricted plantar flexion, and delayed treatment may lead to tendon retraction and degeneration, adversely affecting healing and functional recovery [8- 10]. Compared to nonsurgical approaches, early surgical intervention is generally recommended for young, high-demand patients, as it effectively restores tendon continuity and facilitates accelerated rehabilitation [4, 9, 11- 13]. Open surgery (OS) allows direct visualization for tendon repair but is associated with larger incisions [14- 16]. Advances in minimally invasive surgery (MIS), such as the Achillon system, have introduced alternative approaches that minimize surgical trauma while effectively repairing the tendon [14, 16, 17].

Postoperative immobilization duration represents a central debate in rehabilitation strategies [18-20]. Early mobilization is advocated to accelerate functional recovery, yet insufficient immobilization may increase re-injury risks [18, 20]. Optimizing postoperative protocols to balance functional recovery with tendon protection remains a clinical challenge.

This study evaluates the impact of surgical approach (OS vs. MIS) and immobilization duration (0, 2, or 4 weeks) on clinical outcomes, aiming to refine evidence-based treatment strategies for acute Achilles tendon rupture (AATR).

Method

The study was reviewed and approved by our institutional review board (Peking University Third Hospital Medical Science Research Ethics Committee; IRB00006761- M2020315) and registered at ClinicalTrials. gov (NCT04663542).

Design and population

This prospective cohort study consecutively enrolled 512 patients who underwent surgical repair for acute Achilles tendon rupture at our institution from September 2022 to February 2024. All patients recruited before April 2023 received OS. Beginning in April 2023, a protocol modification mandated that all enrolled patients initially undergo MIS; conversion to OS was performed intraoperatively if anatomical contraindications precluded safe MIS completion. Exclusion criteria included excessive interlayer separation (> 20 mm) between the gastrocnemius-derived outer layer and soleus-derived inner layer, inadequate tendon end approximation due to retraction or fragility, or technical failure to achieve secure fixation. Following exclusions of 20 patients lost to follow-up and 18 requiring intraoperative conversion to OS, 474 participants (92.6% retention rate) constituted the final analytical cohort. Written informed consent was obtained from all participants prior to study inclusion.

Participants were further categorized into six groups according to the surgical method (OS: 265 cases; MIS: 209 cases) and postoperative immobilization duration (0, 2, or 4 weeks): A (OS, 0 weeks, n = 88), B (OS, 2 weeks, n = 85), C (OS, 4 weeks, n = 92), D (MIS, 0 weeks, n = 71), E (MIS, 2 weeks, n = 72), and F (MIS, 4 weeks, n = 66). All participants adhered to a standardized rehabilitation protocol after the removal of external immobilization [2, 18, 21].

Preoperative diagnosis was confirmed via ultrasound, which assessed the rupture site, severity, and anatomical characteristics, including the gap distance of the rupture site (GDRS) and the distance from the rupture site to the tendon insertion (DRSTI). Inclusion criteria comprised: (1) age 18–60 years; (2) closed Achilles tendon injury; (3) acute complete rupture (≤ 7 days post-injury); (4) DRSTI > 3.0 cm. Exclusion criteria were: (1) partial rupture; (2) ATR at the tendon insertion point; (3) comorbidities that may affect functional test results (e.g., diabetes, neuropathy, autoimmune diseases); (4) loss to follow-up.

Surgical procedure

Patients were positioned prone and operated under spinal anesthesia with thigh-level tourniquet control. Bilateral Achilles tendon resting angle (ATRA) measurements (fibular long axis to fifth metatarsal headline) were recorded preoperatively [22].

For minimally invasive surgery (MIS; Groups D-F), a 2–3 cm longitudinal incision was created at the rupture site, followed by careful blunt dissection of the paratenon to expose both proximal and distal tendon stumps. Irregular tendon ends were sharply debrided to facilitate optimal apposition. The tendon stumps were then grasped with Allis clamps to apply axial traction, allowing assessment of tendon tension and achievable elongation while minimizing adhesion formation through gentle dissection between the proximal tendon and paratenon using vascular forceps. The proximal stump was secured with two Krackow locking-loop sutures using No. 2 non-absorbable polyester sutures (ETHIBOND, Johnson & Johnson, USA), with suture trajectories depicted by red lines in Fig. 1. The dual medial prongs of the Achillon^® instrument (Integra LifeSciences, USA) were carefully advanced through the potential space between the proximal tendon stump and paratenon. During insertion, the control nut was continuously rotated to facilitate gradual divergence of the medial prongs, ensuring optimal engagement with superior tendon fibers. Unlike conventional minimally invasive techniques that employ multiple percutaneous suture pairs with overlapping knots [14], our approach utilizes only a single suture pair to minimize potential nerve compression from multiple knot stacks. A guide needle loaded with absorbable No. 2 ETHIBOND suture (Johnson & Johnson, USA) was then passed sequentially through: (1) medial cutaneous tissue, (2) lateral prong of the Achillon device, (3) both medial prongs, (4) lateral cutaneous tissue, and (5) contralateral lateral prong. This trajectory guaranteed intratendinous suture placement while avoiding neurovascular structures. Following device withdrawal, the suture was externalized from the paratenon and tensioned to verify unrestricted gliding and adequate tendon purchase, creating a modified Kessler-type configuration (the red suture in Fig. 2). The distal tendon was addressed using identical instrumentation principles. Sutures were tensioned sequentially: Krackow sutures were tied first to establish primary stability, followed by the Achillon sutures to ensure anatomical alignment under intraoperative tension matching the contralateral ATRA. Dorsal and lateral reinforcement was achieved with four figure-of-eight sutures, with optional ventral sutures added if intraoperative stress testing demonstrated residual laxity. Finally, the paratenon was closed with 2 − 0 absorbable sutures (Monocryl™, Ethicon) and the skin with 4 − 0 absorbable sutures, followed by application of a below-knee brace in 30° plantar flexion. See Fig. 3 for details.

Fig. 1.

Krackow locking suture combined with modified Kessler suture

Fig. 2.

Achillon device withdrawal during minimally invasive Achilles tendon repair, demonstrating decompression suture (red line) traversing the surgical incision. Blue markers denote cutaneous penetration sites of the suture trajectory

Fig. 3.

Intraoperative Images of Minimally Invasive Achilles Tendon Repair: (a) Longitudinal incision exposure; (b) Tendon stump tension assessment; (c) Krackow locking suture configuration; (d) Decompression suture insertion via Achillon device; (e) Achillon device withdrawal; (f) Sequential suture tensioning; (g) Surgical incision closure

For open surgery (OS; Groups A-C), a traditional open repair was performed using the Krackow locking loop technique combined with a modified Kessler suture, as our previous study described [19]. The Krackow suture technique in the open surgery groups mirrored that used in the MIS groups, while the modified Kessler suture - like in the MIS approach - employed only a single suture pair (as illustrated in Fig. 1). See Fig. 4 for details.

Fig. 4.

Intraoperative Images of Open Achilles Tendon Repair: (a) Midline incision exposure of tendon stumps; (b) Debridement and fiber realignment of tendon ends; (c) Combined Krackow locking and modified Kessler sutures; (d) Sequential suture tensioning

All surgeries were conducted by the same team of surgeons following a standardized procedure.

Postoperative management

Groups A and D did not receive postoperative immobilization. Groups B and E received postoperative immobilization for two weeks, while Groups C and F underwent immobilization for four weeks. After the removal of the braces, all six groups began postoperative rehabilitation exercises according to the prescribed protocol (Table 1) [18]. During the early rehabilitation phase, the use of crutches was recommended to assist in training and to reduce the weight-bearing load on the affected limb.

Table 1.

Rehabilitation protocol

After surgery	Postoperative exercise and immobilization with the brace for the corresponding time.
Immediately after removing the brace	Ankle mobilization
0–2 weeks after removing the brace	Standing up for 1 h per day
2–4 weeks after removing the brace	Standing up for 2 h per day Deep squat
4–6 weeks after removing the brace	Double-legged heel raises Walking less than 1000 steps on flat ground
6–8 weeks after removing the brace	Single-legged heel raises Walking less than 2000 steps on flat ground
2 weeks after successfully performing single-leg heel raises	Jogging
4 weeks after successfully performing jogging	More vigorous training

Data collection

Operative duration and wound length were recorded after surgery. Patients were assessed postoperatively at 1, 2 weeks, and 4, 8, 12, 24, and 48 weeks. Follow-up evaluations were standardized and performed by a single surgeon to ensure consistency. Clinical outcomes included the visual analog scale (VAS) for pain, the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Scale [23], and the Achilles tendon Total Rupture Score (ATRS) [24], and the relative ATRA. VAS was utilized to assess pain intensity, employing a 10-cm linear scale ranging from “no pain” (0 cm, left endpoint) to “worst imaginable pain” (10 cm, right endpoint). Patients were instructed to mark their current pain level on the scale, with the corresponding value recorded as their VAS score. ATRS, a patient-reported outcome measure, consists of 10 items assessing symptom severity and physical activity limitations, with responses graded on an 11-point Likert scale (0–10 per item, total score range: 0-100), where higher scores indicate superior functional recovery. AOFAS Ankle-Hindfoot Scale, a clinician-administered tool, provides a comprehensive evaluation of ankle-hindfoot function with a maximum score of 100 points, categorized as excellent (90–100), good (75–89), fair (50–74), or poor (< 50). The relative ATRA is calculated by subtracting the non-injured side’s angle from the injured side’s angle, quantifying tendon length changes post-injury and during rehabilitation. A positive relative ATRA indicates the injured Achilles tendon has a larger resting angle than the non-injured side, suggesting shorter tendon length. Conversely, a negative value implies the injured tendon is longer, often due to elongation postoperation or insufficient healing.

Postoperative complications—including superficial infection, deep vein thrombosis (DVT), sural nerve palsy, Achilles tendon re-injury (confirmed by MRI following sudden falls), and re-operation (indicated for MRI-confirmed re-ruptures involving > 50% tendon width)—were meticulously documented. Functional recovery milestones were meticulously documented, including the time required to achieve the following outcomes: (1) restoration of plantarflexion (PF) to levels equivalent to the contralateral side; (2) resumption of light exercise (LE), defined as brisk walking and jogging; (3) return to work (RTW); and (4) recovery of one-leg heel-rise height (OHRH). The heel-rise height was measured as the vertical distance from the ground to the heel while the patient performed a heel rise with the knee fully extended (0° flexion) and without hyperextension. For standardized measurement, participants were instructed to slowly elevate the heel to maximal achievable height while maintaining full knee extension in the weight-bearing limb; rapid or compensatory movements were prohibited. Recovery time for OHRH was determined when the heel-rise height index (HRHI = [involved/uninvolved] × 100) reached 50% [25].

The primary outcome of the study was postoperative re-injury, while secondary outcomes included PF recovery times.

Statistical analyses

Statistical analyses were conducted using SPSS version 27.0 (IBM Corp., Armonk, NY, USA). The Kolmogorov-Smirnov test was applied to evaluate the normality of the data distribution. Continuous variables exhibiting a normal distribution were expressed as mean ± standard deviation (SD). For stratified comparisons between OS and MIS groups, independent samples t-tests were employed. Within-group comparisons for both OS and MIS were conducted using one-way analysis of variance (ANOVA), with post-hoc pairwise comparisons performed using the Bonferroni correction to adjust for multiple comparisons.

Categorical variables, including gender, affected side, and the presence of complications, were analyzed using the χ² test. For datasets with expected frequencies < 1 or sample sizes < 40, Fisher’s exact test was employed to ensure accuracy. A p-value of < 0.05 was considered indicative of statistical significance.

Results

Baseline characteristics

A total of 474 patients were stratified into six groups: OS with 0-, 2-, or 4-week immobilization (A: n = 88; B: n = 85; C: n = 92) and MIS with corresponding immobilization durations (D: n = 71; E: n = 72; F: n = 66). Baseline characteristics, including sex distribution, age, affected side, BMI, GDRS, and DRSTI, showed no significant intergroup differences (all P > 0.05). However, MIS groups exhibited significantly shorter operation times (all P < 0.001) and reduced incision lengths (all P < 0.001) compared to OS groups (Table 2).

Table 2.

Baseline characteristics

		OS		MIS		P value
			P value		P value
Gender (Male/Female)	0w	85/3	0.999	67/4	0.954	0.713
	2w	82/3		68/4		0.706
	4w	89/3		63/3		1.000
Age (years)	0w	45.5 ± 14.7	0.667	42.6 ± 15.5	0.671	0.228
	2w	44.3 ± 15.4		44.4 ± 14.7		0.973
	4w	46.2 ± 11.6		44.5 ± 12.3		0.395
Affected side (Right/Left)	0w	41/47	0.996	32/39	0.897	0.853
	2w	39/46		35/37		0.734
	4w	43/49		30/36		0.874
Body Mass Index	0w	26.4 ± 1.6	0.056	26.0 ± 1.7	0.569	0.086
	2w	25.9 ± 1.7		26.2 ± 1.5		0.234
	4w	26.5 ± 2.3		26.3 ± 2.0		0.463
Operation Time (min)	0w	46.1 ± 4.8	0.304	34.1 ± 4.6	0.913	< 0.001
	2w	45.1 ± 3.5		34.4 ± 4.0		< 0.001
	4w	45.4 ± 3.7		34.1 ± 3.1		< 0.001
GDRS (cm)	0w	1.7 ± 0.7	0.149	1.9 ± 0.6	0.820	0.054
	2w	1.9 ± 0.7		1.8 ± 0.6		0.689
	4w	1.9 ± 0.8		1.8 ± 0.9		0.735
DRSTI (cm)	0w	4.3 ± 0.7	0.415	4.5 ± 0.8	0.060	0.233
	2w	4.2 ± 0.7		4.2 ± 0.6		0.837
	4w	4.3 ± 0.6		4.3 ± 0.7		0.701
Incision length (cm)	0w	4.7 ± 0.8	0.347	2.3 ± 0.4	0.109	< 0.001
	2w	4.5 ± 1.1		2.4 ± 0.4		< 0.001
	4w	4.5 ± 1.0		2.2 ± 0.4		< 0.001

Data represent the mean ± SD;

GDRS, gap distance of the rupture site; DRSTI, distance from the rupture site to the Achilles tendon insertion

Pain scores

The VAS score for pain significantly decreased after surgery and reached 0 in all groups after 12 weeks. Preoperative pain scores were similar among the six groups (P > 0.05). Immediately postoperatively, VAS scores were significantly lower in MIS groups compared to OS groups (A vs. D = 4.1 ± 0.6 vs. 2.5 ± 0.6, B vs. E = 4.2 ± 0.6 vs. 2.4 ± 0.5, C vs. F = 4.1 ± 0.7 vs. 2.5 ± 0.8, P < 0.001), a trend that persisted at 1 week (A vs. D = 3.0 ± 0.8 vs. 1.2 ± 0.5, B vs. E = 1.8 ± 1.0 vs. 0.8 ± 0.5, C vs. F = 1.3 ± 0.8 vs. 0.7 ± 0.6, P < 0.001) and 2 weeks (A vs. D = 1.8 ± 0.7 vs. 0.8 ± 0.6, B vs. E = 0.9 ± 0.8 vs. 0.4 ± 0.5, C vs. F = 0.7 ± 0.6 vs. 0.3 ± 0.5, P < 0.001). Notably, the within-group analysis revealed higher VAS scores in Group A vs. Groups B and C (A vs. B vs. C = 3.0 ± 0.8 vs. 1.8 ± 1.0 vs. 1.3 ± 0.8 at 1 week; and 1.8 ± 0.7 vs. 0.9 ± 0.8 vs. 0.7 ± 0.6 at 2 weeks, both P < 0.001) and Group D vs. Groups E and F (D vs. E vs. F = 1.2 ± 0.5 vs. 0.8 ± 0.5 vs. 0.7 ± 0.6 at 1 week; and 0.8 ± 0.6 vs. 0.4 ± 0.5 vs. 0.3 ± 0.5 at 2 weeks, both P < 0.001) at 1 and 2 weeks. From week 4 onwards, there is no significant difference between OS and MIS groups (P > 0.05) (Fig. 5).

Fig. 5.

Visual Analogue Scale (VAS) for Pain: (a) Group A vs. Group D; (b) Group B vs. Group E; (c) Group C vs. Group F

Functional outcomes

AOFAS Ankle-Hindfoot Scale and ATRS showed improvement over time in all groups. For the AOFAS Ankle-Hindfoot Scale, significant differences were only observed at specific intervals: Group D had higher scores than its counterpart at 8 weeks (96.1 ± 2.7 vs. 94.7 ± 1.9, P < 0.001) and Group F at 24 weeks (99.4 ± 0.8 vs. 98.9 ± 0.8, P < 0.001). Within-group comparisons revealed that Groups A and D had higher AOFAS Ankle-Hindfoot Scale scores at 4 weeks postoperatively (both P < 0.001), whereas Groups B and E maintained higher scores at 8, 12, and 24 months (all P < 0.05). By 48 weeks, AOFAS Ankle-Hindfoot Scale scores for all groups approached 100 with no significant between-group differences (Fig. 6).

Fig. 6.

American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Scale

Similarly, for ATRS scores, notable differences were limited to certain periods: Group D scored higher at 4 weeks (49.0 ± 2.0 vs. 48.0 ± 1.9, P = 0.003) and Group E also showed higher scores at the same interval (46.2 ± 3.1 vs. 43.9 ± 2.7, P < 0.001). Within-group comparisons indicated that Groups A and D had higher ATRS scores at 4 weeks (both P < 0.001), while Groups B and E showed superiority at 8 and 12 weeks (all P < 0.001). No significant between-group differences in ATRS scores were noted at 24 and 48 weeks (Fig. 7).

Fig. 7.

Achilles tendon total rupture score (ATRS)

No significant differences in relative ATRA levels were observed among the six groups during the intraoperative period or at 48 weeks postoperatively (P > 0.05) (Table 3).

Table 3.

Relative ATRA

Time		OS		MIS		P value
			P value		P value
Intraoperative (degrees)	0w	7.2 ± 1.7	0.096	7.3 ± 2.1	0.398	0.794
	2w	7.4 ± 1.9		7.3 ± 1.6		0.666
	4w	6.8 ± 2.2		6.9 ± 1.3		0.747
48w (degrees)	0w	-5.2 ± 1.8	0.287	-5.1 ± 1.7	0.857	0.920
	2w	-4.8 ± 1.6		-5.0 ± 1.9		0.458
	4w	-5.0 ± 2.0		-5.1 ± 1.9		0.659

Data represent the mean ± SD;

ATRA, Achilles tendon resting angle

Recovery times

No significant differences in OHRH, LE, or RTW recovery times were found between corresponding MIS and OS groups (all P > 0.05). However, MIS groups achieved faster PF recovery (all P < 0.001). Prolonged immobilization (4w) in both OS and MIS subgroups delayed PF, OHRH, LE, and RTW recovery (all P < 0.001) (Table 4). Groups that received no post-operative immobilization (Groups A and D) demonstrated the best in PF recovery (both P < 0.001).

Table 4.

Recovery time

Time		OS		MIS		P value
			P value		P value
PF (days)	0w	14.6 ± 2.9	< 0.001	9.1 ± 2.6	< 0.001	< 0.001
	2w	26.9 ± 3.6 a		20.9 ± 3.7 a		< 0.001
	4w	38.9 ± 4.6 ab		33.4 ± 4.4 ab		< 0.001
LE (weeks)	0w	16.9 ± 1.3	< 0.001	17.1 ± 1.9	< 0.001	0.353
	2w	17.3 ± 2.0		17.0 ± 1.8		0.354
	4w	19.8 ± 1.7 ab		19.3 ± 2.4 ab		0.088
RTW (weeks)	0w	5.6 ± 1.2	< 0.001	5.6 ± 0.7	< 0.001	0.932
	2w	5.9 ± 1.2		5.8 ± 0.7		0.447
	4w	6.6 ± 0.9 ab		6.6 ± 0.7 ab		0.753
OHRH (weeks)	0w	12.4 ± 1.2	< 0.001	12.5 ± 1.8	< 0.001	0.467
	2w	11.9 ± 0.8 a		12.2 ± 1.2		0.065
	4w	14.9 ± 1.6 ab		14.8 ± 2.0 ab		0.726

Data represent the mean ± SD;

OHRH, one-leg heel-rise height; LE, light exercise; RTW, return to work; PF, plantarflexion;

^a significantly different from 0w groups (multiple pairwise within-group post hoc comparison tests);

^b significantly different from 2w groups (multiple pairwise within-group post hoc comparison tests)

Complications

There were no significant differences in superficial infection, deep vein thrombosis, or sural nerve palsy rates among all 6 groups (all P > 0.05). The re-injury rate was significantly higher in Groups D and E compared to Groups A and B (D: 14.1%vs A: 2.3%, P = 0.006; E: 12.5% vs. B: 1.2%, P = 0.006). In MIS groups, Group F demonstrated a lower re-injury rate compared to Groups D and E (F: 1.5%, P = 0.026), with no significant difference between Groups D and E. Postoperative reoperation rates for tendon rupture were higher in Group D than Group A (P = 0.038), with no significant differences among other groups (Table 5).

Table 5.

Complication

		OS		MIS		P value
		Cases (%)	P value	Cases (%)	P value
Superficial infection	0w	3(3,4%)	0.619	4(5.6%)	0.878	0.701
	2w	5(5.9%)		4(5.6%)		1.000
	4w	6(6.5%)		5(7.6%)		1.000
Deep vein thrombosis	0w	1(1.1%)	1.000	0(0)	0.765	1.000
	2w	0(0)		1(1.4%)		0.459
	4w	1(1.1%)		1(1.5%)		1.000
Sural nerve palsy	0w	2(2.3%)	0.873	0(0)	0.764	0.503
	2w	1(1.2%)		1(1.4%)		1.000
	4w	3(3.3)		1(1.5%)		0.641
Re-injury	0w	2(2.3%)	0.317	10(14.1%)	0.026	0.006
	2w	1(1.2%)		9(12.5%)		0.006
	4w	0(0)		1 (1.5%) ab		0.418
Re-operation	0w	0(0)	-	4(5.6%)	0.321	0.038
	2w	0(0)		1(1.4%)		0.459
	4w	0(0)		1(1.5%)		0.418

Data represent the mean ± SD;

^a significantly different from 0w groups (using the χ² test or Fisher’s exact test);

^b significantly different from 2w groups (using the χ² test or Fisher’s exact test)

Discussion

AATR predominantly occurs in physically active individuals, particularly during sports requiring explosive movements such as sprinting or jumping [2, 4, 18, 26, 27], where sudden acceleration or deceleration generates tensile forces exceeding 12.5 times body weight [28, 29]. Biomechanically, the midportion of the tendon, characterized by its hypovascularity and repetitive stress concentration, is the comparatively vulnerable site [1, 28, 30]. This region’s limited blood supply impairs self-repair capacity, predisposing it to cumulative microtrauma and eventual failure under high-load conditions [31]. Epidemiologically, AATR exhibits a striking male predominance (male-to-female ratio: 22.7:1 in our cohort), which aligns with global trends [4, 26, 32]. While this disparity may reflect higher male participation in high-risk sports, intrinsic biological factors such as sex-specific collagen composition, hormonal influences, and differences in tendon stiffness warrant further investigation [11, 33]. Notably, non-sport-related AATR cases, often associated with systemic risk factors (e.g., obesity, diabetes, corticosteroid use, or fluoroquinolone exposure), are increasingly reported, emphasizing the need to broaden research beyond athletic populations [24, 34, 35]. Current therapeutic strategies prioritize anatomical restoration and functional rehabilitation to mitigate complications like re-injury or prolonged immobilization-induced joint stiffness [18, 21, 36, 37]. However, debates persist regarding optimal surgical techniques and postoperative protocols [14-16, 38].

In this prospective cohort study, MIS cohorts exhibited significantly reduced incision lengths (P < 0.001) and operative times (P < 0.001) compared to OS, aligning with Grassi et al.’s meta-analysis of 358 patients (mean difference of surgical duration: -18.98 min; 95% CI: -11.14 to -26.82; P = 0.00001) [39]. The limited tissue dissection in MIS contributed to lower early postoperative VAS scores (P < 0.001 at first 2 weeks), which facilitated accelerated plantarflexion recovery (P < 0.001) by minimizing adhesion formation and preserving paratenon integrity [11, 38, 40]. Despite these early advantages, both approaches achieved comparable long-term functional restoration, with ATRS and AOFAS Ankle-Hindfoot Scale scores approaching 100 across all groups by 48 weeks (P > 0.05).

The Achillon instrument, a stainless-steel guide introduced by Assal et al. [41], facilitates MIS repair of AATR through a 2–3 cm longitudinal incision. Its dual-branch design with aligned apertures enables precise percutaneous suture deployment proximal and distal to the rupture site, preserving paratenon integrity and vascular supply while minimizing soft tissue trauma [41]. Conventional MIS protocols involved placing three sutures through distinct paired apertures in the device. However, Gatz et al.’s meta-analysis of 2,223 surgical cases (1,055 open vs. 1,168 MIS) [16] demonstrated a significantly higher risk of sural nerve injury in MIS cohorts compared to open repair (OS vs. MIS = 2.4% vs. 7.3%, OR: 0.45; 95% CI: 0.28–0.74; P = 0.001). This disparity may result from blind suturing and the use of multiple percutaneous sutures, which can inadvertently entrap or encircle nerve branches, thereby increasing the risk of direct nerve laceration or indirect irritation caused by perineural suture loops [5, 16]. To address the elevated risk of sural nerve injury [42], we modified the procedure by implementing a simplified suturing protocol: a single decompression suture is deployed through the paired guide apertures in each tendon stump. The percentage of sural nerve palsy in our research was 1.0% in the MIS group, which is much lower than in previous studies [15, 16, 39].

Meanwhile, many patients undergoing MIS in this study were young amateur athletes driven by rapid functional recovery goals. This eagerness, combined with a premature return to high-impact activities, such as single-leg hopping, predisposed them to accidental falls, resulting in higher rates of re-injury in Groups D and E (14.1% and 12.5%, respectively; P < 0.05) and re-operation rates in Group D (5.6% vs. 0 in Group A; P = 0.038). To mitigate this, our institution is prototyping a next-generation Achillon device featuring the deployment of multiple sutures through a single pair of guide apertures, thereby increasing suture density and enhancing biomechanical stability at the repair site.

The duration of postoperative immobilization significantly influenced recovery outcomes. Shorter immobilization periods (0 and 2 weeks) in both OS and MIS groups optimized functional recovery, particularly in PF recovery. Conversely, prolonged immobilization (4 weeks) delayed recovery metrics such as OHRH, LE, and RTW (all P < 0.001). Notably, the relative ATRA showed no statistically significant differences between surgical approaches (OS vs. MIS) or immobilization durations at 48 weeks (P > 0.05). This suggests that neither the repair technique nor immobilization protocol substantially influenced structural tendon lengthening, as ATRA indirectly reflects cumulative elongation through resting ankle positioning [43]. This finding is consistent with the prior study’s emphasis on standardized rehabilitation protocols, which advocate for early mobilization to enhance functional outcomes [14, 18, 21]. In the OS cohort, a 2-week immobilization protocol may represent the optimal strategy for early rehabilitation, as it was associated with relatively lower VAS pain scores, improved functional recovery, and no significant increase in complication rates, consistent with our prior study [18]. However, the higher re-injury and re-operation rates in MIS groups with shorter immobilization suggest a need for careful balance between early mobilization and tendon protection. The ATRA data further support this balance: despite equivalent long-term tendon length outcomes across groups, differential re-injury risks highlight the importance of protecting MIS repairs during early healing phases. These findings reinforce the rationale for 4-week immobilization protocols for MIS patients, particularly in high-demand populations.

This study has several limitations despite its clinical insights. First, preoperative activity levels and habitual loading patterns—critical confounders for rehabilitation—were not objectively quantified due to insufficient granularity in patient-reported exertion metrics, despite comparable occupational distributions. Second, the exclusion of 18 patients converted intraoperatively from MIS to OS introduced cohort heterogeneity, potentially limiting between-group comparability. Third, functional recovery milestones lacked objective biomechanical parameters (e.g., tendon lengthening or ROM) and relied on clinician-reported timelines rather than instrumented gait analysis or ultrasound-based quantification. Future studies should integrate imaging modalities to evaluate structural changes like tendon elongation alongside functional outcomes, complemented by large-scale RCTs with standardized protocols to validate findings. This work advances evidence for personalized AATR management by critically weighing the trade-offs between MIS and OS.

Conclusion

This study demonstrates that both minimally invasive surgery and open repair for acute Achilles tendon rupture yield excellent long-term functional outcomes. In this study MIS had a significantly higher re-injury and re-operation rate compared to open surgery. There were no significant differences in superficial infection rates, DVT or sural nerve palsy. MIS did offer better early pain resolution and faster plantar flexion recovery. Prolonged immobilization (4 weeks) for MIS groups may mitigate re-injury risks while balancing functional recovery. In contrast, a 2-week immobilization protocol may represent the optimal for OS groups. Future research should focus on refining MIS techniques, validating findings in larger cohorts, and exploring advanced rehabilitation strategies to enhance outcomes.

Author contributions

Yuan Cao and Xiuzhi Li contributed equally to this study. Yuan Cao and Xiuzhi Li: Data collection and analysis, article writing and revision; Yang Lv and Gao Si: Surgery, experimental design; Zengzhen Cui: Experimental design, research guidance, and supervision.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.