TriLink: Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction

Abstract

Cadaveric and clinical biomechanical studies show improved kinematic restoration using double-bundle anterior cruciate ligament (ACL) reconstruction techniques. These have been criticized in the past for being technically challenging. We present a novel 3-socket approach for anatomic “all-inside” double-bundle reconstruction using a single hamstring tendon fashioned to create a trifurcate graft: the TriLink technique. The semitendinosus alone is harvested, quadrupled, and attached to 3 suspensory fixation devices in a Y-shaped configuration, creating a 4-stranded tibial limb and 2 double-stranded femoral limbs. A medial viewing/lateral working arthroscopic approach is adopted using specifically designed instrumentation. Anatomic placement of the 2 femoral tunnels is performed by a validated direct measurement technique. A single mid-bundle position is used on the tibia. Both femoral and tibial sockets are created in a retrograde manner using outside-to-in drilling. This is a simplified operative technique for anatomic double-bundle ACL reconstruction that maximizes bone preservation. The TriLink construct replicates the 2 bundles of the ACL, conferring native functional anisometry and improving femoral footprint coverage while avoiding the complexities and pitfalls of double–tibial tunnel techniques. Preservation of the gracilis reduces the morbidity of hamstring harvest and allows greater flexibility in graft choice in cases requiring multiligament reconstruction.

The goal of anterior cruciate ligament (ACL) reconstruction is to stabilize the injured joint without restricting a normal physiological range of motion. Traditional reconstruction techniques are generally successful when measured in the short-term; however, poor long-term outcomes have been reported, with an increased incidence of early-onset degenerative arthrosis in the ACL-injured knee.^1,2 ACL reconstruction has not been shown to influence this irrespective of graft choice or technique used.^3,4 This has been attributed to various factors, including concomitant damage sustained during the original injury⁵; however, inadequate restoration of normal knee kinematics is possibly the most important cause.^6,7

Conventional techniques, such as transtibial drilling of the femoral tunnel, tend to put the graft in a nonanatomic, relatively vertical position, contributing to persistent rotational laxity postoperatively.⁸ Clinical kinematic evaluation corroborates this in the dynamic state.^7,9 This has led to a move toward “anatomic” reconstruction, focusing on locating the graft within the native ACL footprint, as championed by Fu and Karlsson.¹⁰ Lateral placement of the femoral tunnel toward a mid-bundle position has been shown to be biomechanically superior to traditional high and deep positions, such as those achieved with the “over-the-top” guide.¹¹ Despite this, even with mid-bundle positioning, some rotational laxity can still persist.^12,13 Consequently, there is continued interest in double-bundle reconstruction. Although long-term clinical outcomes are not yet available, robust biomechanical studies and emerging clinical evidence support the superiority of double-bundle reconstruction techniques.^14-20

Double-bundle ACL reconstruction presents a technical challenge to the surgeon. Numerous 4-tunnel techniques,^21-23 as well as variations using 3 tunnels,^24-26 have been described. These have all been criticized because of their associated increased operative complication rates and higher patient morbidity rates.^27,28 Specifically, problems with fracture of the lateral femoral condyle or tunnel communication have been cited.²⁹ In addition, graft choice and fixation remain widely debated. Grafts that have been used include semitendinosus and gracilis tendons, a split bone–patellar tendon–bone graft,²² a combination of gracilis and bone–patellar tendon–bone,²³ and tibialis anterior or tibialis posterior allograft.²¹ All have potential drawbacks, such as the small size of the gracilis graft, the morbidity of patellar tendon harvest, or the cost of allograft.

We present a novel approach for anatomic double-bundle ACL reconstruction using a single semitendinosus graft, which we term the TriLink technique. This is a simplified “all-inside” operative procedure with 2 anatomically placed femoral tunnels and a single mid-bundle tibial tunnel. The tendon is quadrupled and attached to 3 adjustable suspensory fixation devices in a Y-shaped trifurcate configuration, creating a 4-stranded tibial limb and 2 more slender double-stranded femoral limbs. The technique was developed and refined using cadaveric specimens, and the senior author has now started using this in the clinical setting. There have been no early operative complications.

Technique

The surgical approach is based on the TransLateral ACL reconstruction technique previously published by our group³⁰ (Video 1). A summary of the pertinent steps is presented in Table 1. A medial viewing/lateral working arthroscopic philosophy is adopted for femoral preparation, using instrumentation specifically designed by the senior author. These instruments are able to navigate around the lateral femoral condyle without impinging medially against the patellar tendon. They include an Opes radiofrequency (RF) probe (Arthrex, Naples, FL) for soft-tissue debridement, a modified curette (Arthrex), a curved marking/measuring device (Arthrex) (Fig 1), and an anatomic aiming arm for a retrograde drill (Arthrex). The senior author uses the FlipCutter (Arthrex) for this purpose. Recently, a calibrated version of the RF probe, the Caliblator (Arthrex), has also been introduced.

Table 1.

Summary of Technical Steps in TriLink ACL Reconstruction

Procedure Stage	Details
Patient setup	Supine, thigh tourniquet
	Knee at 90°, side support, footrest
Arthroscopic approach	Low AL portal, central AM portal
	Medial viewing/lateral working (TransLateral) approach for femoral work
Graft harvest and preparation	Single semitendinosus tendon harvest
	Tendon looped through 2 TightRopes and sutured end to end, then attached to third TightRope to form Y-shaped graft
Femoral preparation	Double bundle: 2 sockets at AM and PL positions
	Sockets created by outside-to-in drilling with FlipCutter device (typically 5.5 to 6 mm)
Tibial preparation	Single-bundle: socket created in mid-bundle position
	Use of FlipCutter (typically 8 to 8.5 mm)
Graft deployment	Two FiberSticks passed through FlipCutter guide holes into femoral sockets and single TigerStick into tibial socket as lead sutures
	Sutures collectively grasped through AM portal and attached to 3 limbs of TriLink graft
	Graft pulled into knee and limbs docked into sockets
Graft fixation and tensioning	Tibial limb drawn into socket to depth of 20 mm (pre-marked)
	AM bundle tensioned in extension, then PL bundle in extension
	AM bundle re-tensioned at 30° to 40° of flexion
	Knee cycled, followed by re-tensioning of all limbs

Fig 1.

TransLateral instrumentation. (A) Aiming jig for retrograde drill (FlipCutter). (B) Calibrated RF ablator (Caliblator). (C) Calibrated measuring/marking tool. (D) Use of femoral aimer and FlipCutter in a left knee.

Patient Positioning and Surgical Approach

The patient is positioned supine with the knee flexed to 90°. There is no requirement for knee hyperflexion throughout the procedure. A side support and footrest are used. A thigh tourniquet is used throughout. A modified lateral portal (Fig 2) is created, which is slightly lower and more medial than the traditional high anterolateral (AL) portal position. A 30° inclined arthroscope is inserted through the AL portal. The anteromedial (AM) portal is established under direct vision. Routine arthroscopic assessment of the knee is performed, and appropriate surgery is undertaken to address any chondral or meniscal pathology.

Fig 2.

Representation of modified positions of AL and AM portals used for TransLateral technique, as depicted in a draped left knee.

Graft Harvest and Preparation

The semitendinosus alone is harvested in the standard fashion using a curved incision over the pes anserinus. Two TightRope (Arthrex) tensionable suspensory fixation devices are placed along the tendon. The tendon ends are sutured with a nonabsorbable high–tensile strength suture to form a continuous loop (Fig 3A). The double-stranded graft is then effectively positioned with the knot centrally and the 2 loaded TightRopes at each end (Fig 3B). A third TightRope is passed, placed at the midpoint of the looped graft, and secured at 1 end of the preparation table. The other 2 TightRopes are secured at the other end of the table to form a Y-shaped trifurcate graft—the TriLink. Further nonabsorbable high–tensile strength sutures are used to fix the positions of the TightRopes (Fig 3C). The graft is tensioned and compressed. A more detailed description of graft preparation is available (unpublished data, S.K.Y., August 2013).

Fig 3.

Preparation of semitendinosus tendon as trifurcate TriLink graft. (A) Two TightRopes are loaded onto the semitendinosus, which is looped and secured. (B) A third TightRope is loaded at the mid position. (C) The tibial end is sutured, creating a 4-stranded limb and 2 double-stranded femoral limbs.

Femoral Socket Preparation

The medial wall of the lateral femoral condyle is prepared with the curved RF probe. Use of an RF device for soft-tissue debridement is preferable to shaving instruments because this allows better preservation of the bony anatomy of the ACL footprint.

Graft positioning in double-bundle reconstruction can be performed at the discretion of the surgeon. We advocate using a direct measurement technique for anatomic placement of the femoral sockets by locating the AM and posterolateral (PL) bundles based on the work by Ziegler et al.³¹ (Fig 4). This is performed with the curved measurement/marking tool and is now possible with a new calibrated RF device—the Caliblator (Arthrex). We aim to leave a 3-mm bone bridge between the sockets in the femoral notch. The direct measurement technique has previously been validated for single mid-bundle ACL reconstructions.³²

Fig 4.

Referencing of anatomic locations of AM and PL femoral bundles by direct measurement technique.

The FlipCutter aiming device (Arthrex) is inserted through the AL portal and positioned at the pre-marked anatomic femoral origin of the AM bundle. A drill sleeve is attached to the aiming arm and pushed down to abut against the femoral cortex through a small stab incision in the thigh. This permits the FlipCutter guide pin (with a diameter of 3.5 mm) to be inserted from outside to in, entering the joint under direct vision. After sizing of the TriLink, an appropriately sized FlipCutter is selected. We have found this to be 5.5 to 6 mm for the double-stranded femoral sockets. Once in the joint, the tip of the FlipCutter is flipped and retrograde drilling of the femoral socket is undertaken. Graduated laser markings on the guide pin can be read against the edge of the drill sleeve to produce a socket of appropriate depth. We routinely create a 25-mm femoral retro-socket. The procedure is repeated for the PL socket.

Tibial Socket Preparation

Tibial socket preparation is performed with arthroscopic viewing from the AL portal and instruments passed through the AM portal. A single tibial socket is produced in a similar retrograde manner using a FlipCutter mounted by the tibial aiming arm. This enters the knee in the mid-bundle position and is generally around 8 to 8.5 mm in diameter to accommodate the 4-stranded tibial limb of the TriLink construct. We routinely create a 30-mm retro-socket. The sum of the tibial and femoral sockets, along with the intra-articular distance, must be greater than the overall graft length to allow adequate graft tensioning.

Graft Deployment

Looped sutures are introduced into the joint by use of stiffened plastic sleeves through the three 3.5-mm guide pin tunnels. Our preference is to use a TigerStick (Arthrex) on the tibial side and 2 FiberSticks (Arthrex) on the femoral side. A Passport cannula (Arthrex) is inserted into the AM portal, through which these sutures are collectively grasped and withdrawn, ensuring no soft-tissue ensnarement (Fig 5). The sutures are individually attached to the 3 TightRopes of the TriLink and act as lead sutures to draw the graft into the knee. Each limb is docked into the femoral and tibial retro-sockets by pulling the TightRopes through the guide pin tunnels. Once the TightRope buttons are beyond the femoral and tibial cortices, they are flipped to allow subsequent tensioning.

Fig 5.

Passport cannula in the AM portal of a right knee used for retrieval of passing sutures during TriLink graft deployment.

Graft Fixation and Tensioning

A TightRope RT (reverse tension) (Arthrex) is used on the tibial side and for the AM femoral bundle. A standard TightRope is used on the PL bundle. The tibial limb is gently tensioned by use of the RT system to draw it into the tibial socket to a pre-marked depth of 20 mm. On the femoral side, the AM bundle is first tensioned in extension using the TightRope RT, followed by the PL bundle with the standard TightRope. The AM bundle is then re-tensioned at 30° to 40° of flexion. This is based on the typical physiological angles when these bundles become taut in the normal knee.³³ It is vital to ensure that the femoral sockets have sufficient depth to take up any slack in the graft. Insufficient tunnel depth will cause the graft to bottom out, leaving residual laxity, which is difficult to correct at this stage of the procedure. The knee is cycled, and any further tensioning can be performed before cutting the lead tensioning sutures of the TightRope buttons.

Postoperative Rehabilitation

The wounds and hamstring harvest tract are infiltrated with large-volume, dilute local anesthetic.³⁴ The wounds are closed with absorbable sutures and standard dressings applied. The postoperative regimen is unchanged from standard ACL surgery. Patients are allowed to bear weight immediately, but this is protected with crutches for the first 2 weeks. A full range of motion is encouraged, while avoiding hyperextension. Closed-chain activities are started at an early stage, and open-chain exercises are introduced at 3 months. Sport-specific training is allowed starting at 6 months, with the gradual introduction of cutting movements. Return to contact sports is delayed for a minimum of 9 to 12 months.

Discussion

The ACL was first described as a double-bundle structure in 1975.³⁵ This has been confirmed by anatomic studies of fetal specimens.³⁶ The AM and PL bundles are named according to their tibial insertions. On the femur, the AM bundle lies more superiorly and anteriorly, which corresponds to a high and deep location in the notch when viewed arthroscopically with the knee at 90°. The PL bundle lies lower and further toward the shallow articular margin, that is, in a more posterior and distal position anatomically.³⁷ The relative contribution of each bundle to knee stability has been debated, but this does vary throughout the arc of knee flexion. The PL bundle is taut in extension but slackens at higher flexion angles, with the AM bundle taking the majority of the load.^35,38 The biomechanical importance of the PL bundle in controlling rotational laxity has been emphasized.³⁹

Traditional single-bundle reconstruction techniques tend to put the graft in a nonanatomic high and deep femoral position, which may be outside of the native ACL footprint. Transtibial drilling is unable to achieve anatomic positioning of the femoral bundles of the ACL.⁴⁰ At best, this matches a PL position on the tibia to an AM position on the femur.⁴¹ Graft impingement against the posterior cruciate ligament or femoral notch may occur, predisposing to early failure.⁴¹ This nonanatomic position results in inadequate kinematic restoration and has been blamed for residual pivot glide postoperatively. It may also be responsible for progression toward early degenerative joint disease.^6,7

Anatomic single-bundle reconstruction has heralded a move toward placing the graft within the ACL footprint, typically using a mid-bundle position on both the tibia and femur. Drilling can be undertaken through an accessory AM portal or with our TransLateral technique.³⁰ ACL footprint anatomy has been defined,⁴² and identification of the mid-bundle position on the femur can be achieved with the direct measurement technique, which has been validated.³² Biomechanical testing has shown that single-bundle anatomic positioning confers advantages over traditional graft placement, but further improvements may be obtained by double-bundle reconstruction.^12,13

Such reconstructions have been criticized in the past for their operative complexity and potential for increased complications. Outside-to-in drilling reduces the risk of intraoperative cartilage damage during preparation of the femoral tunnels associated with the accessory AM portal technique.^43,44 Tunnel confluence can be a particular risk in the smaller knee and is a more significant problem on the tibial side.²⁹ The advantage of the TriLink technique is that it obviates the need for 2 tibial tunnels by having a single 4-stranded tibial limb. This is placed in the anatomic mid-bundle position.

The concept of double-bundle ligament reconstruction using 3, rather than 4, tunnels is not new. It is a well-established technique for posterior cruciate ligament reconstruction and represents the procedure of choice for many surgeons. It has also been described in ACL surgery, using either a single tibial tunnel matched to 2 femoral tunnels^25,26 or a single femoral tunnel with 2 tibial tunnels.²⁴ The kinematic stability of double-bundle/single-tibial 3-tunnel techniques versus 4-tunnel techniques has been confirmed in a cadaveric model.⁴⁵

The distance between the femoral and tibial attachment sites of the ACL changes as the knee flexes and extends, indicating that the positions are not isometric. There is growing evidence showing that the ACL exhibits favorable anisometry during knee range of motion. Raunest⁴⁶ reported that femoral malpositioning had a greater effect on disturbing isometry than changes with respect to the tibia, with the over-the-top position giving the most unsatisfactory result. A recent study using 3-dimensional computed tomography confirmed the anisometry of mid-bundle graft placement, with the greatest intra-articular distance being found in full extension and decreasing with knee flexion.⁴⁷ This suggests that single-bundle reconstructions can potentially allow the graft to slacken as the knee flexes.

Cadaveric studies by our group (unpublished data, J.O.S., July 2013) support this. We have found that variations at the tibial attachment site makes significantly less difference to overall anisometry than changes on the femoral side. Changing the femoral attachment site causes large alterations in the intra-articular distance between the tibial and femoral fixation points of the graft during knee range of movement. These findings have been confirmed using mathematical modeling (unpublished data, J.O.S., July 2013) and suggest that maximum stability may be gained using a graft with a single tibial attachment and multiple femoral attachments. Respecting the femoral attachments of the native ACL is thus evidently more important than tibial positioning. Using 2 bundles on the femoral side also improves footprint coverage, which has been shown to be beneficial when compared against single-bundle reconstructions.⁴⁸ This provides strong biomechanical justification for the use of a refined trifurcate graft, which allows the surgeon to maximize stability by re-creating the anatomic functional anisometry of the 2 bundles while minimizing operative complexity.

ACL anisometry underlines the importance of tensioning the AM and PL bundles independently at the appropriate knee flexion angle. The triple suspensory fixation system of the TriLink construct makes this possible, in contrast to previously published double-bundle/single-tibial techniques.²⁵ We tension the PL bundle in extension and the AM bundle in 30° to 40° of flexion to better replicate normal functional anatomy.

Other limitations of double-bundle/single-tibial techniques include the requirement for double-tendon hamstring harvest or the use of allograft. An additional advantage of the TriLink is that it uses a quadrupled semitendinosus graft. Single-tendon hamstring harvest allows the gracilis to be preserved as a secondary medial stabilizer in the ACL-injured knee. Furthermore, preservation of the gracilis has also been shown to reduce donor-site morbidity and limit loss in knee flexion strength.⁴⁹ In addition, it may be useful in cases requiring multiligament reconstruction. Quadrupling of the semitendinosus provides an excellent graft diameter in most cases. In our TransLateral series, our mean graft diameter is 8.6 mm. The femoral limbs are double stranded and typically measure 5.5 to 6 mm. This represents a significant advantage over the use of more traditional double–hamstring tendon techniques, in which 1 bundle is made up of a doubled semitendinosus graft and the other is a doubled gracilis graft. The doubled gracilis is frequently much smaller and is therefore at risk of failure.

One of the limitations of the described procedure is that it does remain more technically challenging than single-bundle techniques, but it is simpler than double-bundle approaches, while conferring similar advantages. Meticulous suture management during the procedure is key to avoid inadvertent soft-tissue ensnarement or entanglement of the graft during deployment. Table 2 summarizes the advantages and limitations of the technique.

Table 2.

Advantages and Limitations of TriLink ACL Reconstruction

	Description
Advantages
Double bundle on femur	Matching femoral anatomy
	Improved biomechanical stability
	Improved femoral footprint fill
Anatomic positioning of femoral bundles	No need for knee hyperflexion
	Matches functional ACL anisometry
Single tibial bundle	Avoids technical difficulties with 2 tibial tunnels
	No risk of tunnel confluence and/or fracture
Sockets created, not tunnels	Bone preservation
Single semitendinosus tendon used	Excellent size of graft—less risk of graft failure than traditionally “smaller” PL bundle
	Preservation of gracilis for multiligament cases or as secondary medial stabilizer
Cortical suspensory fixation using TightRopes	Robust and reliable fixation method
	Allows in situ adjustment of tension
Limitations
Technically challenging	More challenging than single-bundle reconstruction but easier than double-bundle techniques
Graft/suture entanglement	Meticulous suture management is required, which can be facilitated by use of Passport cannula through AM portal

TransLateral ACL reconstruction with the TriLink graft is a novel technique for anatomic double-bundle, all-inside surgery. This represents an opportunity to confer the biomechanical and kinematic benefits of double-bundle reconstruction using a simplified operative procedure, in addition to the advantages of single-tendon hamstring harvest. The TransLateral philosophy allows the surgeon to maintain an excellent view from the medial portal for anatomic placement of the femoral tunnels while working from the lateral side. Tunnel placement can be confirmed by direct measurement. The all-inside approach is bone preserving and achieves excellent cortical fixation on both the femur and tibia. A single tibial tunnel avoids the risk of tunnel confluence, which is a particular concern in smaller knees, but the construct still permits independent tensioning of the AM and PL bundles. These factors decrease operative complexity, reducing surgical time, and positively impact the cost and safety/efficacy profile of the procedure. Early clinical results have been encouraging.

Supplementary Data

Video 1

TriLink ACL reconstruction graft preparation and surgical technique performed in a right knee.