Comparable Mid- to Long-term Outcomes of Semitendinosus and Semitendinosus/Gracilis Grafts in ACL Reconstruction: Median 8-Year (Range,5-10 Years) Results From a Randomized Controlled Study

Abstract

Background:

The hamstring tendon autograft used for anterior cruciate ligament reconstruction commonly entails both the semitendinosus and gracilis (ST/G) tendons for sufficient graft thickness, but they may impair function. To mitigate this, a tendon-sparing ST-only graft has been explored. However, less is known of the mid- to long-term outcomes comparing these configurations.

Purpose/Hypothesis:

The purpose was to investigate differences between the quadrupled ST tendon graft and the doubled ST/G graft configuration. The primary hypothesis was that there would be no difference in the International Knee Documentation Committee 2000 Subjective Knee Form (IKDC-SF) outcomes between groups. The secondary hypothesis was that there would be no differences in knee flexion strength, KT-1000 arthrometer side-to-side measurements, or need for secondary surgery (including revision) between the 2 techniques.

Study Design:

Randomized controlled trial; Level of evidence, 1.

Methods:

At baseline, 98 patients were randomized to receive either the quadrupled ST tendon graft or the doubled ST/G graft configuration. Preoperatively and after 2 and median 8 years (range, 5-10 years) postoperatively, the investigators collected results for the IKDC-SF, Knee injury and Osteoarthritis Outcome Score, Tegner Activity Scale, a sports and activity participation questionnaire, knee laxity (KT-1000 arthrometer) side-to-side measurements, Lachman test, and flexion rotation drawer test. Need for secondary knee surgery was evaluated 5 to 10 years postoperatively.

Results:

Seventy-seven patients completed median 8-year follow-up (range, 5-10 years): 38 patients in the ST group and 39 patients in the ST/G group. No statistically significant differences were observed between the ST and ST/G groups in IKDC-SF scores (81.7 vs 82.1; P = .93), knee stability, or revision rates. Both groups demonstrated statistically significant improvements in self-reported function (P < .001) until final follow-up. The overall anterior cruciate ligament revision rate was 10.4%, and no increased risk of graft failure or excessive residual laxity was associated with the ST-only graft.

Conclusion:

No statistically significant differences were found between the ST group and the ST/G group in terms self-reported function, knee laxity, or need for secondary surgery at median 8 years (range, 5-10 years) after surgery. The ST-only graft configuration did not increase the risk of graft failure or excessive residual laxity compared with the ST/G graft configuration.

Keywords

anterior ligament reconstruction orthopaedic surgery hamstring tendon autograft semitendinosus semitendinosus/gracilis

The most commonly used graft for anterior cruciate ligament (ACL) reconstruction (ACLR) is the hamstring tendon autograft, which often involves harvesting both the semitendinosus and gracilis (ST/G) tendons.^6,37,41 The purpose of using both tendons is to achieve sufficient graft thickness, as studies have suggested that the ACL graft should be at least 8 mm in diameter to reduce the risk of graft failures.^24,39 Disadvantages related to this graft technique include pain from tendon harvesting and reduced hamstring strength, which potentially affect functional recovery.^12,16,33

Surgical techniques have focused on achieving sufficient graft thickness by quadrupling the semitendinosus (ST) tendon and therefore sparing the gracilis tendon. This is facilitated by the use of adjustable-loop flipping buttons and retrograde graft socket reaming.^21,22 Studies have reported inconclusive evidence to support this technique over other graft configurations with regard to clinical and functional outcomes.^{9,17,20,23,31,38} However, concern persists about higher graft failure rates and excessive residual knee laxity when using the single hamstring ST graft configuration with adjustable-loop fixation.^4,28

Most studies investigating the effect of different graft configurations on outcomes are limited to short-term follow-up. Because failures continue to occur beyond the first 2 years after surgery,^19,30 further long-term follow-up evaluation is important. The current study aimed to compare clinical outcomes 5 to 10 years after ACLR using either the quadrupled ST or the ST/G tendon configuration. The main hypothesis was that there would be no difference in the International Knee Documentation Committee 2000 Subjective Knee Form (IKDC-SF) outcomes between groups. Secondary hypotheses included no difference in knee flexion strength, KT-1000 arthrometer (MEDmetric Corp) side-to-side (STS) measurements, or need for secondary surgery (including ACL revision surgery) between the 2 techniques.

Methods

The current study is a mid- to long-term follow-up of a randomized controlled trial (RCT) conducted at Haraldsplass Deaconess Hospital between April 2014 and December 2019. Two-year outcomes from the current RCT have been published previously.²⁸ In total, 98 patients were enrolled for ACLR (47% women) at baseline. Patients were randomly assigned to receive either the quadrupled ST-only graft (n = 49) or the doubled ST/G tendon graft configuration (n = 49). One patient receiving the quadrupled ST graft was converted to bone–patellar tendon–bone graft because the ST tendon that was too short for quadrupling; this patient was consequently excluded from analyses. For patients receiving the ST/G configuration, full tibial tunnel reaming was performed, and a fixed-loop suspensory device with tibial screw fixation for a more rigid construct was used. For patients receiving the ST-only graft configuration, shorter bone sockets with retrograde reaming were made that used adjustable-loop suspensory fixation, minimizing bone removal and preserving native anatomic features. The surgical procedures were described in detail in a previous publication.²⁸ Of the included patients, 98% were operated on by a single primary surgeon (T.H.), who completed cadaveric training and piloted the new technique before inclusion to minimize any effect of learning curve. The final follow-up evaluation was done at median 8 years (range, 5-10 years) after the primary surgery and included 38 patients in the ST-only graft group and 39 patients in the ST/G graft group (Figure 1).

Patients were eligible for inclusion if they were scheduled for ACLR with hamstring tendon autograft. Additional criteria for inclusion were age ≥16 years, no previous injury to the current or contralateral knee (ACL), and skeletal maturity. Criteria for exclusion included concomitant ligament and/or major cartilage injuries in need of surgery. The need for meniscus surgery did not lead to exclusion. Other reasons for exclusion included medical disorders disrupting rehabilitation, substance abuse, or having deviant anatomic characteristics (valgus/varus alignment >5° of normal and no other gross anomalies). Before enrollment in the study, patients gave their written consent to participate. The study was approved by the regional committee for medical and health research and ethics (ID No. 2013/198).

Follow-up Evaluation

After attending scheduled follow-ups at 9 and 24 months, patients were invited for a midterm follow-up evaluation at minimum 5 years after surgery. Pre- and postoperative assessments were done by independent examiners who were not involved in surgery or rehabilitation. Results of functional tests (isokinetic hamstring and quadriceps strength and 4 hop tests) performed preoperatively and 9 and 24 months after surgery were previously reported.²⁸

Patient-reported outcome measures (PROMs) included the IKDC-SF, Knee injury and Osteoarthritis Outcome Score (KOOS), and Tegner Activity Score (TAS). The IKDC-SF assesses patients’ symptoms, function, and sports and activity. The score ranges from 0 to 100, where a higher score is associated with better knee function¹⁴; a Patient Acceptable Symptom State (PASS) threshold is 76.2 in ACLR patients 10 years after surgery.⁴² The KOOS evaluates 5 domains of knee-related functioning: symptoms, pain, activities of daily living, sport and recreation, and quality of life. A KOOS score of 100 indicates having no knee issues.³⁶ The TAS is a quantification of sport and recreational levels of activity and participation, where a score of 0 indicates being on sick leave or disability pension because of knee problems and a score of 10 indicates performing pivoting sports (soccer, football, rugby) at international or national elite levels.⁷

At final follow-up, patients also completed a sports and activity participation questionnaire investigating their development in sports activity over the study period (Table 1).¹¹ Patients not attending the clinical examination at the long-term follow-up filled out PROM instruments and were asked about reinjury (yes/no) by letters distributed through mail correspondence; they were asked to specify which injury occurred and whether the injury had been verified by an orthopaedic surgeon and/or magnetic resonance imaging.

Table 1

Sports and Activity Before and After Anterior Cruciate Ligament Reconstruction ^a

Questions	Response Options
1. What was your primary sport/activity before your ACL injury?	Soccer, handball, alpine skiing, hiking
2. At what level did you perform this sport/activity before your ACL injury?	Elite, medium/highly competitive, low competitive, recreational
3. At what level are you currently performing this sport/activity?	Elite, medium/highly competitive, low competitive, recreational, no longer engaged in this sport/activity, not tried this sport/activity yet
4. How does your knee function when performing this sport/activity?	As before my ACL injury with no discomfort/limitation
	With an insignificant amount of discomfort/limitation
	With a significant amount of discomfort/limitation
	Tried, but gave up because of my ACL injury
	Not tried, because I am afraid of suffering new injuries
	Not tried, other reasons

ACL, anterior cruciate ligament.

The clinical examinations performed preoperatively, at 24 months, and at the current follow-up included assessment of anterior tibial translation measured by the KT-1000 arthrometer (quantified as the STS difference, in millimeters, between the injured vs healthy knees with maximal manual pull¹⁰). Anterolateral rotational instability was evaluated by use of the flexion rotation drawer test (pivot-shift test), categorized as 0 (negative), 1+ (glide), 2+ (clunk), or 3+ (gross) in comparison to the uninjured side.^29,43 The Lachman test was performed to evaluate degree of tibial displacement compared with the uninjured knee, graded as 0 (normal), 1+ (close to normal), or 2+ and 3+ (abnormal).¹³ At final follow-up, clinical examination was performed by the lead author (I.F.M.). It was also noted whether the patients had reinjured their knee since the initial ACLR or had undergone revision surgery or other knee surgery at any time until final follow-up. Patients who had undergone ACLR revisions are accounted for but excluded from further comparison in primary and secondary outcome.

Statistical Analyses

All data were analyzed and processed using IBM SPSS Statistics Version 26 software (IBM Corp). The sample size was determined using the IKDC-SF score (primary outcome). A 9-point difference was considered clinically significant. To achieve 80% power level and an alpha level of .05, we calculated that 88 patients were needed. This calculation was based on a standard deviation of 15, meaning that individual scores in a similar population varied by approximately 15 points from the mean.¹⁵ Accounting for a 10% dropout rate, 98 patients were enrolled at baseline.

A P value of <.05 was predefined to indicate statistical significance. Categorical variables are presented as frequencies and percentages, whereas continuous variables are presented as means and standard deviations. The normality of the score distribution was assessed using the Shapiro-Wilk test. Independent-samples t tests were used to compare the means of continuous variables, and Fisher exact tests were conducted to compare categorical variables. A mixed-effect model was used to compare changes between groups over time.

Results

Of the 98 patients included at baseline (Figure 1), 77 patients (78.6%) were accounted for at median 8-year follow-up (range, 5-10 years). Of these patients, 57 were available for clinical examination whereas 20 patients completed the PROMs remotely, via either mail or telephone. A total of 17 patients could not be reached, and 3 patients declined participation. In all, 8 patients were excluded from analyses due to ACL revision. The mean age at follow-up was 41 ± 9.8 years, with 39 men (51%) and 38 women. No differences were seen between groups at baseline or final follow-up (Table 2).

Table 2

Baseline Demographic Data and Perioperative Findings for Patients Completing Final Follow-up (n = 77) ^a

	ST-Only Group(n = 38)	ST/G Group(n = 39)
Age, y	42.5 ± 11.1	41.9 ± 9.6
Sex
Female	17 (44.7)	22 (56.4)
Male	21 (55.3)	17 (43.6)
Operated knee
Left	15 (39.5)	18 (46.2)
Right	23 (60.5)	21 (53.8)
Body mass index ^b	26	25

Categorical variables are expressed as n (%); continuous variables are expressed as mean ± SD. ST, semitendinosus; ST/G, semitendinosus and gracilis.

Data were obtained from 15 patients in the ST group and 16 in the ST/G group.

Repeat Surgery

At median 8-year follow-up (range, 5-10 years), 8 patients had undergone ACL revision surgery; 3 of these patients required revision due to new trauma to the knee at median 7 years (range, 7-3 years) after initial ACLR, 4 patients required revision due to residual laxity without known knee trauma at median 3 years (range, 2-4 years), and 1 patient was revised immediately after a postoperative computed tomography scan showed that adjustable loop fixation was stuck in the bone tunnel. A total of 54 repeat knee-related procedures (Table 3) were registered throughout the follow-up period, 26 in the ST-only group and 28 in the ST/G group. A statistically significant difference was noted in cyclops removal between the groups, with 6 patients in the ST/G group and none in the ST-only group (P = .014). In those who had repeat arthroscopy, 12 grafts were described as insufficient. These were evenly distributed between the 2 groups.

Table 3

Repeat Surgery Between Groups at Median 8-Year (Range, 5-10 Years) Follow-up (n = 54) ^a

Type of Surgery	ST-Only Group	ST/G Group	P ^b
ACL revision surgery	5	3	.48
New trauma to the operated knee	2	1
Residual laxity without known knee trauma	2	2
Surgical complication where adjustable loop button got stuck in bone tunnel	1	0
Median years from primary ACLR to ACL revision surgery (range)	3 (0-7)	3 (2-4)
Medial meniscal resection	7	4	.37
Medial meniscal suture	1	0	.32
Lateral meniscal resection	3	1	.32
Lateral meniscal suture	1	0	.32
Diagnostic arthroscopy	1	5	.1
Cyclops removal	0	6	.014
Other procedure	8	8	≥.999
Total	26	28	.79

Values are expressed as number of patients unless otherwise noted. Boldface indicates statistical significance. ACL, anterior cruciate ligament; ACLR, anterior cruciate ligament reconstruction; ST, semitendinosus; ST/G, semitendinosus and gracilis.

Chi square test.

Self-Reported Function at Median 8 Years (Range, 5-10 Years) After Surgery

At baseline, the mean IKDC-SF score was 55.1 ± 12.6, and an overall improvement was seen at the median 8-year (range, 5-10 years) follow-up, where a mean score of 81.9 ± 13.1 was reported (P < .001). At the final follow-up, the ST group (n = 34; 4 patients missing data) reported a mean IKDC-SF score of 81.7 ± 12.1, and the ST/G group (n = 34; 5 patients missing data) reported a mean score of 82.1 ± 14.2 (P = .93). Overall, 47 patients (69%) of the patients had reached PASS criteria for IKDC-SF score: 23 patients in the ST group (67.6%) and 24 patients in the ST/G group (70.6%).

All patients demonstrated statistically significant improvements across all KOOS subscales from baseline to 8-year follow-up (range, 5-10 years) (P < .001). However, no statistically significant changes were observed between the 2-year and the median 8-year (range, 5-10 years) follow-up (Figure 2). Additionally, no statistically significant differences were found between groups in any subscales at final follow-up (Figure 3).

Preinjury, the median TAS score was 7 (range, 1-9), and at final follow-up it was 4 (range, 1-9) in both groups (P = .59). In total, 87% of patients reported a lower TAS score compared with their preinjury scores at median 8-year follow-up (range, 5-10 years).

Responses to the sports and activity participation questionnaire indicated that 55% of the patients continued to engage in their primary sport or activity at their preinjury level. Among the 29 patients reporting a decrease in participation level, 96.5% had previously been involved in pivoting sports, such as soccer, handball, alpine skiing, and basketball (Table 4).

Table 4

Sports and Activity Before and After Anterior Cruciate Ligament Reconstruction (n = 66) ^a

	n (%)
Four main sports/activities before ACL injury
Soccer	20 (29.4)
Hiking	12 (17.6)
Trail running	5 (7.4)
Alpine skiing	5 (7.4)
Preinjury level of sport/activity
Elite	00 (0)
Medium/highly competitive	7 (10.3)
Low competitive	18 (26.5)
Recreational	41 (60.3)
Current level of sport/activity
Elite	00 (0)
Medium/highly competitive	00 (0)
Low competitive	4 (5.9)
Recreational	36 (52.9)
No longer engaged in this sport/activity	23 (33.8)
Not tried this sport/activity yet	3 (4.4)
How would you describe your knee function when performing your sport/activity?
As before my ACL injury with any discomfort/limitation	15 (22.1)
With an insignificant amount of discomfort/limitation	22 (32.4)
With a significant amount of discomfort/limitation	3 (4.4)
Tried, but gave up because of my ACL injury	10 (14.7)
Not tried, because I am afraid of having a new knee injury	7 (10.3)
Not tried, other reasons	9 (13.2)

ACL, anterior cruciate ligament.

Clinical Examination at Median 8 Years (Range, 5-10 Years) Postoperatively

The mean KT-1000 arthrometer STS difference was reduced significantly from preoperatively (6.7 ± 2 mm) to the median 8-year (range, 5-10 years) follow-up (3 ± 1.6 mm). No statistically significant difference was seen in anterior tibial translation between the ST group (2.85 ± 1.4 mm) and the ST/G group (3.11 ± 1.9 mm) at final follow-up (P = .58). No statistically significant differences were found between groups in knee stability measured with the Lachman and pivot-shift tests (Table 5).

Table 5

Anterolateral Rotational Laxity and Anterior Tibial Translation in the ST and ST/G Groups at Median 8 Years (Range, 5-10 Years) After Surgery (n = 50) ^a

KT-1000 STS Difference ^b	<3 mm	3-5 mm	6-10 mm	>10 mm
ST only (n = 27)	9	17	1	0
ST/G (n = 23)	7	13	3	0
P					.47
Pivot-Shift Grade	0	+1	+2	+3
ST only (n = 27)	6	19	2	0
ST/G (n = 23)	4	16	3	0
P					.82
Lachman Grade	0	+1	+2	+3
ST only (n = 27)	3	18	6	0
ST/G (n = 23)	2	17	4	0
P					.91

Data are expressed as numbers of patients. ST, semitendinosus; ST/G, semitendinosus and gracilis; STS, side to side.

According to the International Knee Documentation Committee classification: normal, <3 mm; nearly normal, 3-5 mm; abnormal, 5-10 mm; severely abnormal, >10 mm.¹³

Discussion

This study did not find any statistically significant differences between the quadrupled ST tendon graft configuration and the doubled ST/G tendon graft configuration at median 8-year follow-up in primary outcome (IKDC-SF score), secondary outcomes (KT-1000 arthrometer STS difference, Lachman test, pivot-shift test, self-reported knee function [KOOS, TAS, sports and activity participation questionnaire]), revision rates, or need for any other knee-related surgery other than cyclops removal. Both techniques resulted in statistically significant improvements in self-reported function and knee stability at median 8 years (range, 5-10 years) after ACLR.

The overall findings of the current study align with those of a similar RCT conducted by Kuliński et al¹⁷ with a median follow-up of 5.6 years (range, 4.3-6.3 years). Both studies indicate that both graft configurations yielded comparable outcomes in mid- to long-term follow-up after ACLR. Notably, Kuliński et al observed an increase in anterior tibial translation in female patients receiving an ST-only graft yet overall found no anterior tibial translation differences between groups, consistent with other short-term studies.^4,28 In the 2-year results of the current RCT, we reported a nonsignificant trend toward increased excessive residual laxity in patients receiving the ST-only graft²⁸ and questioned whether this was related to the adjustable loop-fixation system used in the ST-only technique. This system has been reported to potentially cause excessive residual laxity and graft elongation over time.^4,27 Malesa et al²⁵ also addressed this concern, finding the ST-only graft configuration to be less stable than the ST/G graft at various follow-up points. However, our median 8-year (range, 5-10 year) data show no increased risk for residual laxity or higher revision risk for patients receiving the ST-only graft configuration compared with the traditional ST/G hamstring configuration. This suggests that the initial concerns regarding ST grafts and the adjustable loop-fixation may not transpire into mid- to long-term follow-up.

In the present study, the overall ACL revision rate was 10.4% (n = 8), which is consistent with previous reports indicating revision rates between 3% and 15% up to 8 years after ACLR.^18,34,45 Although hamstring tendon autografts have historically been considered reliable, they have demonstrated higher revision rates compared with other graft types.^18,19,37,44 Particularly in the Norwegian setting, data from the National Knee Ligament Registry have reported a lower revision rate with the use of bone–patellar tendon–bone grafts.³² Kuliński et al¹⁷ described a notably higher failure rate in the ST group (42%) compared with the ST/G group (9%), corresponding with findings from other short-term studies.^4,8 The distribution of revision surgeries between the ST (n = 5) and ST/G (n = 3) groups in the current study suggests that both grafts offer similar mid- to long-term stability, with no increased risk of graft failure when using the ST graft with adjustable-loop cortical fixation. However, given the multifactorial nature of risk factors associated with ACL graft failure,^45,46 the reasons behind the current revision rate may not be fully uncovered by the present study.

We found a statistically significant difference in cyclops removal—6 patients in the ST/G group compared with none in the ST-only group (P = .014). A retrospective cohort study comparing ST and ST/G grafts also reported a higher incidence of cyclops removal in patients receiving ST/G grafts, although the difference was not statistically significant.² This similarity in study findings may be related to differences in tunnel drilling techniques. In our study, patients receiving ST/G grafts underwent full tibial tunnel reaming and a fixed-loop suspensory device with tibial screw fixation to secure the graft, whereas the ST-only group received retrograde reaming and adjustable-loop suspensory fixation. Notably, the cohort study used a uniform all-inside technique with tightrope fixation for all patients, regardless of graft type.² These variations in drilling techniques may influence cyclops lesion development. However, given the small sample size in our study, this finding should be interpreted with caution.

A decline in sports participation and activity level after ACLR is common and is influenced by multiple factors.^1,3,35,40 In the current study, 37% of patients reported some degree of discomfort or limitation related to sports/activity participation, and 25% had discontinued their sports/activity because of issues related to their knee at final follow-up. In addition, the median TAS score had dropped from 7 before injury to 4 at median 8 years (range, 5-10) after surgery. Despite the reported issues with sports and activity participation and the decline in activity levels, other patient-reported outcomes reflected satisfactory knee function in mid- to long term. The mean IKDC-SF score at final follow-up was 81.9, surpassing the PASS threshold of 76.2 for 10 years after ACLR.⁴² This aligns with findings from a network meta-analysis comparing different graft preparation techniques that suggested a quadrupled ST graft configuration could be a viable option for patients with lower sport expectations.²⁵ This suggests that having knee-related issues in sports/activity participation does not affect patients’ overall self-reported knee function and that a lower sports and activity level reflects a natural decrease in activity due to age and changing life priorities, rather than dissatisfaction with general knee function.

Improved hamstring strength when sparing the gracilis tendon was one of the suggested advantages of the quadrupled ST graft configuration in early stages of rehabilitation.^21,22 However, as the previous publication from this study showed, there were no differences between the graft options at 9- or 24-month measurements,²⁸ in accordance with other studies comparing flexion strength between different hamstring techniques.^5,26 A systematic review recently concluded that the benefit of sparing the gracilis diminishes 6 months after ACLR,²⁶ and further examination of isokinetic knee flexion strength was therefore not investigated at final follow-up because the benefit of tendon sparing would assumably reduce further over time.

This study is one of few RCTs comparing mid- to long-term outcomes between the ST and ST/G graft configurations and therefore provides valuable insight into ACLR using these graft options. However, several limitations must also be acknowledged. Due to migration, loss of interest, or lack of response from patients, the study did not reach predefined power for its primary outcome (IKDC-SF). Therefore, a limited sample size may reduce the generalizability of the results. A follow-up rate of 78.6% is acceptable but should be taken into consideration when interpreting the results. Although there is potential for bias due to attrition, we have no evidence to suggest that the characteristics or outcomes of the 21% missing patients are significantly different from those included in the study results.

Conclusion

Both the ST-only graft with adjustable-loop cortical fixation and the ST/G graft with closed-loop fixation provided comparable mid- to long-term outcomes regarding self-reported function, clinical stability, and overall good patient satisfaction at a median 8 years (range, 5-10 years) after ACLR. The ST graft did not increase the risk of graft failure or excessive residual laxity when compared with the ST/G technique. The current study therefore concludes that both graft configurations yield reliable results for ACLR.

Footnotes

Acknowledgements

The authors thank all the patients who participated in this study for their valuable time and contribution. The authors also extend their gratitude to the clinical and research personnel whose efforts made the completion of this RCT possible.

Submitted November 18, 2024; accepted April 7, 2025.

One or more of the authors has declared the following potential conflict of interest or source of funding: E.I. and T.H. received travel support and laboratory access from Arthrex during piloting of the study. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

ORCID iD

Ingunn Fleten Mo

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