ACL repair for athletes?

Abstract

Background

The current gold standard treatment for an anterior cruciate ligament (ACL) tear in an athlete is an arthroscopic ACL reconstruction with autografts. This restores the knee stability but is associated with unique complications like graft re-tear, kinesiophobia and graft donor site morbidity. ACL suture repair (ACLSR) is an attractive alternative method of surgical management of this injury.

Current science of ACLSR

The potential advantages of performing a repair are the preservation of native biology and proprioceptive function of ACL, elimination of a graft and preservation of bone stock. The purported benefits are better stability, reduction of kinesiophobia and faster rehabilitation. ACLSR is now performed only for proximal (femoral-sided) tears in the acute phase, when the tissue quality is good and using high-strength nonabsorbable sutures. There are several techniques for performing ACLSR but broadly speaking are either non-augmented, static augmented with suture tape, dynamic augmented or using bio-scaffolds.

Clinical outcome of ACLSR

There is a lot of literature on ACLSRs including case series, cohort studies and randomized controlled trials. The results from these studies are encouraging but mostly pertain to patient reported outcome measures, are in small numbers and in the short-term. The results are also inconsistent across different studies and not specifically performed for the athletic population. Moreover, most of these studies are from the innovator or designer surgeons and groups and have not been independently validated.

Conclusion

Currently, there is insufficient evidence to recommend ACLSR as a preferred method of managing even acute proximal tears in athletes. Improved rates of return to sports, lower retear rate and lesser kinesiophobia needs to be proven in athletes.

Highlights

• •ACL repair is gaining traction for treatment of acute proximal tears.
• •Athletes are likely to benefit from ACLSR as it has the potential of allowing early return to sports and low kinesiophobia.
• •Short-term results of ACL repair are encouraging but inconsistent.
• •Adequate high-quality data is not available at present to recommend any type of ACL repair for athletes.

1. Introduction

The Anterior Cruciate Ligament (ACL) tear is the most commonly treated ligament injury in the knee joint.¹ An ACL reconstruction (ACLR) is the preferred treatment for young and active individuals, especially those engaged in sports and willing to return to an active lifestyle.² This reconstruction is now far more commonly performed using autografts, with hamstrings tendons (HT) being the most popular, followed by bone-patella tendon-bone (BPTB) graft.³ Moreover, ACLR has progressed beyond a ‘one size fits all’ approach and is now individualized to improve outcomes.⁴ Outcomes become all the more relevant when the patient is a sportsperson, whether amateur or elite. It is in this context that ACL suture repair (ACLSR) has made a comeback of sorts but needs to be proven against the gold standard of ACLR.

ACLSR offers the unique advantage of preserving biology, anatomy and proprioceptive function on the native ligament.⁵ The ACL repairs which were done in the past fell out of favour due to the poor results. This was primarily because of an incomplete understanding of the tear patterns and healing potential of the ACL and poor indications or technique.¹ For an athlete, the most important aspects which can present a paradigm shift are reduction in re-tear rate, improvement in return to sports at the same level, avoiding graft site morbidity and reduction in kinesiophobia.⁶ This paper will review the current science and technology of ACL repairs and review the current literature to assess if ACLSR is a better option than ACLR for athletes.

2. Problems after ACLR for athletes

ACLR aims to maximize knee stability and functional capacity, permitting safe return to sport.⁷ The major drawbacks associated with ACLR for an athlete are graft retear, kinesiophobia and unpredictable rates of return to sports (RTS). These issues have been claimed to be reduced with an ACLSR.

Graft re-tear: The two principal graft choices for ACLR are autograft and allograft and the most commonly used autografts are BPTB or HT.⁸ Autografts have been shown to have lower failure risk than allografts, especially in younger more active patient population⁹ A recent meta-analysis comparing BPTB to HT autografts in over 47,000 patients showed slightly increased rate of hamstring graft re tear (2.84%) as compared to BPTB (2.8%).¹⁰ The use of quadriceps tendon (QT) graft has been increasing in the past 10 years and a study comparing QT to BPTB and hamstring tendon in 2856 patients showed similar rates of graft failure. However, QT had less donor site pain than BPTB and better Lysholm scores than HT.¹¹

Return to Sports: As athletes recommence their sports, they also face the risk of new ACL injury to the same knee or contralateral knee. Several studies have reported on RTS in athletes following ACLR. In Lefevre's series of 497 primary ACLRs, the rate of return to any sports activity was 90.9% and rate of return to usual sport was only 36.6%.¹² In a systemic review and meta-analysis by Ardern et al., 65% of patients returned to their preinjury level, and only 55% returned to competitive sports.¹³ However, in a systematic review of elite athletes, return to preinjury sports was as high at 83% after surgery.¹⁴ A long term evaluation (22–30 years) on RTS and participation in pivoting sports by Lindanger et al. found that ACLR does not necessarily enable a return to pre injury sports and by returning to pivoting sports, athletes are at a high risk of contralateral ACL injuries.¹⁵ ACL injury is a serious concern in a professional footballer's career. The risk of second ACL injury rate in professional male football players was 18% at a median follow-up of 4.3 years and 42% of players with an index non-contact isolated ACL injury suffered a second ACL injury.¹⁶

Kinesiophobia: It is defined as ‘the fear of movement as a result of a feeling of susceptibility to pain or reinjury’. It is a major psychological limiting factor in the return to pre-injury sport level after ACLR.¹⁷ A high rate of prevalence of 62% at 4–8 weeks post ACLR has been reported.¹⁸ Although the prevalence decreases during the postoperative rehabilitation, high level of kinesiophobia is still present in a large portion of ACLR patients. The combination of injury-to-surgery time, high preoperative pain level, male gender and low body mass index have been reported to predict high level of kinesiophobia (38.4%), three months after ACLR.¹⁹ Fear of movement is also associated with lesser hamstring strength, hop performance and patient reported function.²⁰ Preserving the native ACL's proprioceptive function and early rehab with ACLSR can potentially reduce this issue.

3. Current science of ACL repair

Patient Selection and Diagnosis: ACL repairs failed in their previous avatar due to several reasons, one of which was poor patient selection. This, combined with factors like performing the surgery by an arthrotomy and imperfect technique such as use of absorbable sutures, contributed to the fall of ACLSRs as techniques and technology of ACL reconstruction was evolving.²¹ The factors to consider for patient suitability for an ACLSR are timing of surgery, tear morphology and tissue quality. ACLSRs must be performed for acute tears only, since the gene expression of ligament healing factors diminishes as the interval increases.²² Specifically, the expression of COL1A1, COL5A1, COL12A1, and TNC genes were found to be significantly higher in the first 3 months after ACL injury.²²

Tear location is a critical factor when considering arthroscopic ACLSR and inability to recognize this nuance in historical studies led to its failure. The type 1 tears described by Sherman, which are peel-offs from the femoral footprint, are the ones which have been found to heal the best when repaired²³ (Fig. 1). van der List and DiFelice performed a systematic review of twenty-nine studies comprising 1457 patients who underwent open repair of the ACL using non-contemporary techniques. They found more favorable outcomes when repairs were performed for proximal tears compared to mid-substance ones.²⁴ This has much to do with the propensity of proximal ACL tears to heal due the biology at this site, in spite of the intra-articular milieu. Nguyen et al. have demonstrated by histology and immunostaining for α-smooth muscle actin and type 3 collagen that the intrinsic healing response of proximal ACL tears in similar to that of the medial collateral ligament (MCL).²⁵

Fig. 1.

Arthroscopic view of femoral avulsion of right ACL with good tissue quality and intact synovial sheath.

The tissue quality of the remnant ACL stump in proximal tears also has to be factored in when considering a repair.²⁶ A frayed or shredded stump will not be grasped well with sutures and this may lead to mechanical failure of the repair. From the biological perspective, Georgiev et al. have recently highlighted the importance of the tissue surrounding ligaments – the epiligament which contains substrates for cell, blood vessel and extracellular matrix formation.^27,28 This novel theory stresses on the structural and functional significance of the epiligament and its implications on ligament healing.^27,28 Although this knowledge is very new, it sheds new light on the importance of the sheath covering the torn ACL seen on arthroscopy.²⁹

Techniques: A successful repair of the ACL must have two elements necessary for healing-mechanical stability and biological augmentation. There are currently four different techniques which aim to achieve this goal by different methods but with the desired result of preserving the native ACL.³⁰

• 1Primary suture anchor repair: This technique was first described by DiFelice, wherein he used non-absorbable sutures and knotless suture anchors to secure the torn ACL to its femoral footprint. Two anchors were used, one each for the anteromedial and posterolateral bundles.³¹ A modification of this technique was described by Achtnich et al., who used a single knotless anchor in the femur and performed microfracture in the intercondylar notch area to enhance biology.³² These were non-augmented techniques but a suture tape can be used to augment the repair and fixed in the tibia using a second knotless anchor without drilling a tunnel³³ (Fig. 2).
• 2Internal Brace Ligament Augmentation (IBLA): This technique of ACLSR involves using an adjustable loop suspensory button to fix the sutures passed through the ACL stump in the femur. A suture tape in used as an internal brace to statically augment the repair and fixed on the tibial cortex after transtibial passage The adjustable loop femur button allows re-tensioning of the ACL in extension and microfractures in the notch is used to enhance biology³⁴ (Fig. 3).
• 3Dynamic Intraligamentary Stabilization (DIS): This technique of repair is performed using a spring-screw implant (Ligamys™, Mathys Ltd Bettlach, Switzerland) in the tibia, with the aim to provide a dynamic stable mechanical environment for the ACL to heal. A 1.8 mm polyethylene wire fixed to this implant is passed through the center of ACL tissue and fixed in the femur using a cortical button.^35,36 (Fig. 4).
• 4Bridge Enhanced ACL Repair (BEAR): This technique employs a bio-scaffold containing extracellular matrix proteins obtained from bovine tissue. Sutures are passed through the ACL stump and fixed on the lateral femoral cortex over a button. The scaffold is placed over the torn ACL through a small arthrotomy and secured with sutures.³⁷ The BEAR technique is different from other ACLSR techniques because it employs a scaffold and requires an arthrotomy.

Fig. 2.

ACL suture repair of the right knee using a knotless anchor along with static augmentation.

Fig. 3.

Internal Brace Ligament Augmentation technique of ACL repair. Figure adapted from Mahapatra et al.⁶ under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/).

Fig. 4.

Dynamic Intraligamentary Stabilization of the left knee using the Ligamys™ screw-sleeve implant. Figure adapted from Malahias et al.³⁰ under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/).

Hoogeslag recently performed a systematic review to compare the outcomes of a non-augmented, static segmented and dynamic augmented ACLSR.³⁸ They found that high quality evidence for ACLSR was lacking and high heterogeneity made it difficult to compare the results.³⁸ Moreover, the DIS and BEAR repairs have also been performed for middle-third ACL tears by their proponents, which is indeed controversial.^35,37 No repair technique has been specifically studied in athletes so far.

4. Clinical outcomes of ACL repair

The outcomes of some of the earliest studies of contemporary ACLSR performed by their innovators or designer surgeons are enumerated in Table 1. Systematic reviews of the outcomes of ACL repairs published in the last two years have a common finding-small number of participants and short duration of follow-up.42, 43, 44 Houck et al. found that the reported rates of re-rupture and reoperation were highly inconsistent, with a relatively high rate of repair failure.⁴³ As such, no difference has been found between ACLSR and ACLR in terms patient reported outcomes, sagittal or rotary laxity and re-rupture rates in a review which analysed five comparative studies.⁴⁴ In one review of 28 studies including both primary repair and DIS, the rates of re-rupture, revision ACL surgery and overall reoperation rates was much higher in the DIS group.⁴²

Table 1.

Overview of the earliest studies reporting outcomes and complications of contemporary ACL Repairs.

Authors	Technique	No. of patients	Failure rate of repair	Re-operation rate (any cause)	Mean Follow-up (months)	Overall survivorship
DiFelice et al.31	Suture anchor	11	1 (9%)	1 (9%) for instability	72	90.9%
Achtnich et al.32	Suture anchor	20	3 (15%)	4 (20%) 3 for instability, 1 for meniscus tear and cyclops lesion	28	81.8%
van der List et al.39	Suture anchor	52	1 (1.9%)	1 (1.9%) for instability	6	98.1%
Eggli et al.40	DIS	10	2 (20%)	6 (60%) 2 for instability, 4 for tibial implant removal	24	90.8%
Henle et al.35	DIS	278	8 (2.8%)	8 (2.8%) for instability	30	96%
Häberli et al.41	DIS	455	29 (6.4%)	39 (8.6%) for instability 29 had another traumatic event while 10 had no such history	28	91.4%

DIS- Dynamic Intraligamentary Stabilization.

Hooper et al. reported the outcomes of 38 patients who underwent combined IBLA type of ACL repair along with anterolateral ligament (ALL) internal brace augmentation. All these patients had a Segond fracture, grade 3 pivot instability or high level of sports participation pre-injury. Two patients (5.3%) sustained a re-rupture at mean 44.8 months follow-up.⁴⁵ When this same center reported the 5-year outcome of IBLA in 34 patients, the re-rupture rate was 17.6%. The failures were in patients who were statistically significantly younger and had a higher baseline Marx activity scale.⁴⁶ This information is important for the athletic population who are indeed younger and have higher activity levels.

In a randomized controlled trial on 48 patients undergoing either an all-inside ACLR or DIS, Hooglesag et al. found the repair to be non-inferior to reconstruction. There were two re-ruptures (8.7%) in the DIS group compared to four (19.0%) in the ACLR group. However, the incidence of repeat surgeries was higher in the patients who underwent a repair (20.8%) compared to reconstruction (14.3%)⁴⁷ Osti et al. have also reported a high rates of complications (57.9%) following DIS type of ACL repair. In their series of 57 patients, the rate of re-rupture was 17.5%, repeat arthroscopy was 22.8% and restricted motion was 53.8%. They did not recommend DIS for young and active patients due to a high incidence of complications and persistent laxity in almost half the cases.⁴⁸

5. Looking ahead

There is no doubt that ACLSR for athletes cannot be recommended over an ACLR at the present time. The biggest reason is a lack of high-quality evidence to prove its superiority in spite of several purported advantages. One such attempt is the LIBRƎ study which is a single-blind multi-center trial currently underway.⁴⁹ It aims to compare ACLR, DIS and IBLA for clinical efficacy and economic benefit in the treatment of acute ACL ruptures.⁴⁹ Another prospective multi-center randomized controlled trial is the REPAIR study. It will compare the results of IBLA and all-inside ACL reconstruction at minimum two years.⁵⁰ Another issue to be sorted especially with respect to contact athletes, is the management of high-grade anterolateral instability. A third aspect is clarity on rehabilitation protocols following ACLSR. A criterion-based rehabilitation protocol will need to be developed and validated to provide standard of care. Only when robust data is available, will ACLSR be more widely acceptable by surgeons and patients. Thus, the path ahead is to improve the evidence in support of ACLSR, especially for athletes.

6. Conclusion

ACL repair has made a comeback with the promise to be better-for the patient and surgeon. However, long-term data is lacking and there is insufficient evidence to recommend it as a preferred method of managing even acute proximal tears in athletes. Improved rates of return to sports, lower retear rate and lesser kinesiophobia needs to be proven in athletes, and not just improved patient reported outcome measures.

Funding

None.

Ethical approval

Not applicable.

Informed consent

Not applicable.

Author contribution

AS and ST planned the manuscript layout. AS, AP and PKM performed the literature search and wrote the manuscript. ST edited the manuscript. All authors have read the final draft and approve of it.

Declaration of competing interest

AS: None.

AP: None.

PKM: None.

ST: Dr. ST reports personal fees and paid presentations for Arthrex, Zimmer Biomet and Smith and Nephew; royalties from Jaypee Medical Publishers, New Delhi; and serves on the boards of ISAKOS, APKASS and Indian Arthroscopy Society. All disclosure are outside the submitted work.