Introduction

The number of surgeons using hamstring tendons for anterior cruciate ligament (ACL) reconstruction has continuously increased in the past years. As a result, various modifications associated with graft preparation and fixation have been introduced. However, despite these variations in technique, the goal of reconstructing a strong and viable graft with a dependable fixation system remains unaltered. The standard means by which mechanical fixation of hamstring grafts is achieved can either be through direct (interference screws) or indirect (Endobutton [Smith & Nephew, Andover, MA] or screw and washer) techniques. Direct fixation is achieved with an interference screw. With this technique, factors such as divergence, direction of screw placement, the geometry and material composition of the screw, and the graft and tunnel characteristics should be considered to increase the likelihood of a successful outcome.^1,2

Indirect fixation techniques, on the other hand, require a linkage material (tape or suture) that would connect the graft tissue to the fixation device. Factors to consider with this technique include: (1) the strength and stiffness of the linkage material to minimize both the potential for elongation of the graft-fixation device construct^3–5 and graft-tunnel motion^6–8 and (2) the distance of graft fixation from the joint line, which can also influence graft-tunnel motion, especially with early stress on the graft during aggressive rehabilitation. The farther the fixation site from the joint line, the greater the creep of the graft-fixation device construct.^2,5

The technique described here incorporates the use of the Fastlok device (Neoligaments, Leeds, United Kingdom), which is an indirect graft tibial fixation system for hamstring tendon grafts.

Scientific Rationale

A variety of options are available for hamstring tendon graft tibial fixation during ACL reconstruction. These include different types of washers (AO, Washerloc, and Spiked Washer), staples, suture/post, and bioabsorbable screws.^9–12 Ideally, the type of fixation chosen should provide the strength and stiffness necessary to withstand failure during cyclical loading, allow the strands to be equally tensioned and compressed into the tibial tunnel wall, and also have the provision for removal when the need arises for revision reconstruction.

The use of only the semitendinosus tendon for ACL reconstruction minimizes the possibility of having subsequent flexor weakness from the disruption of the hamstring muscle. With the quadrupled configuration of this graft construct, indirect fixation is usually required because of the total length of the graft achieved.^13,14 In the description of the technique that follows, the Fastlok device is combined with a tibial tunnel bone plug that provides additional tunnel compression, which facilitates tendon to bone healing and at the same time reduces the risk for tunnel widening by limiting the sagittal motion of the graft.¹⁵ The Fastlok, on the other hand, offers the ease of using a simple threading technique during application, which helps the graft to retain tension throughout the fixation procedure. In addition, it also minimizes slippage with the staple and buckle fixation, reducing the risk of suture and graft loosening while at the same time maintaining a low profile, which is very important considering the relatively thin soft tissues that cover the involved area of the medial aspect of the proximal tibia.

Surgical Technique

Following the administration of the appropriate anesthesia, the patient is positioned supine on the operating table. A thigh support is placed at the level of the tourniquet cuff while a foot bar is positioned at the end of the table to enable the knee to be fixed at 90 degrees of flexion during surgery while at the same time still allowing free range of motion. Standard prepping and draping of the operative field are performed. During the graft harvest, the tourniquet is kept inflated. Anatomical dissection is carried out to identify the semitendinosus tendon (ST) and separate its accessory limb to avoid premature amputation of the graft. The tendon’s proximal end is detached with the use of an open tendon stripper while its distal end is harvested with an attached tibial bone plug obtained with the aid of an osteotome. Ideally, a graft length of 28 to 30 cm is desired. In the meantime, diagnostic arthroscopy and any associated procedures (e.g., meniscectomy) are performed prior to the preparation of the bone tunnels.

The graft is then prepared at the back table, as described in Chapter 16, “Hamstring Anterior Cruciate Ligament Reconstruction with a Quadrupled or Tripled Semitendinosus Tendon Graft.”

Tunnel Preparations and Graft Fixation

On the tibia, the tunnel is drilled through the same incision used for tendon harvesting, the length of which depends on the total length of the graft construct, but 2 cm of the graft should remain inserted in the tibia. However, the tibial opening should not be too superior to maintain the desired low profile of the Fastlok device following fixation.

The desired entry point for the femoral tunnel is at the 10:30 position for the right knee. The appropriate tunnel depth and diameter are then drilled, and the intraarticular span between the tunnels is measured and recorded.

Based on these measurements, the graft is marked with a pen at the level coinciding with the opening of the femoral tunnel. Prior provisions have to be made to consider the length of the Endobutton (8 mm) attached at the end of the graft if it is to be effectively used as a reference point that indicates the graft is entirely seated in the tunnel with enough space for the Endobutton to be “flipped” into position.

Next, the graft is inserted in the tunnels with the standard technique. Proximal fixation is achieved by ensuring that the Endobutton is securely anchored against the posterolateral cortical surface of the femur. At the distal end of the construct, tension on the polyester tapes is maintained in preparation for the placement of the Fastlok fixation device.

The polyester tapes are initially passed through the buckle component, which is subsequently flipped. The two prongs of the staple are then threaded through the buckle (Fig. 41-1). Then, with the knee in 30 degrees of flexion, the surgical assistant holds the buckle with a forceps in a flipped position while holding the ends of the tape with the other hand. The Fastlok device is then pressed against the tibia. Once the Fastlok is in position, an impactor is used to drive the staple down in a perpendicular manner. During this step, it is important to maintain the graft’s tension. The protruding portion of the tape is trimmed, and the device is further impacted as needed to achieve a low profile for the device (Fig. 41-2, A–C). Finally, the bone plug obtained from reaming the tibial tunnel is impacted back into the tibia (Fig. 41-3, A, B). Arthroscopic assessment of the graft position during flexion and extension is carried out to make sure that no graft impingement exists.

Fig. 41-1 The ends of the polyester tape (C) are threaded through the buckle (A). The buckle is then flipped, followed by the insertion of the two prongs of the staple (B) attached at the end of the impactor (D).

Fig. 41-2 The staple is positioned perpendicular to the tibial surface with the aid of the impactor (A) while maintaining tension on the graft by pulling on the ends of the polyester tape. Actual appearance of the device prior to final impaction to demonstrate the relation of the tape relative to the device: anteroposterior view (B), lateral view (C).

Fig. 41-3 The bone plug obtained from the tibia during tibial tunnel preparation (A) is inserted back into the tibial tunnel after the Fastlok device is fixed (B).

Results

In a biomechanical study conducted to analyze the mechanical properties of linkage systems used in hamstring tendon ACL reconstruction,¹⁰ three constructs (5-mm braided polyester [Mersilene], double-loop; 3-mm woven polyester [Orthotape], double-loop; and 3-mm Orthotape, single-loop—all connected to the Fastlok fixation device in bovine bone sections) were compared using an Instron tensile test machine to document their pull tensile strength, residual tensile strength, and fatigue strength at a loading regimen of 540,000 cycles at 25-Hz frequency.

Findings indicate that the double-loop Mersilene-Fastlok construct was weaker than either the single-loop or double-loop Orthotape-Fastlok construct. The mean failure strength of double-loop Orthotape-Fastlok was 93% higher, and its mean stiffness was 40% greater at failure than the Mersilene-Fastlok. At a 150N load, Mersilene-Fastlok was stiffer, whereas at 300N, Orthotape-Fastlok was stiffer. At 600N, the Mersilene-Fastlok had already failed, whereas the Orthotape-Faslok maintained a stiffness of 128.91 N/m. The mode of failure in all constructs was tape breakage under the Fastlok device.

Protrusion heights of the constructs after cyclical loading demonstrated no significant increase in height, indicating absence of device pullout or slippage from the bone. The double-loop Orthotape-Fastlok construct had a mean protrusion height of 5.19 mm compared with 4.30 mm for the Mersilene-Fastlok construct.

Clinical results reviewed in 190 cases of hamstring ACL reconstruction using the Fastlok device for tibial fixation revealed 17 cases that required subsequent removal of the device. Thirteen cases were secondary to anterior knee pain (over the tibial fixation site) experienced during incidental contact, and four cases were secondary to wound infection (three superficial and one deep). Complaints of pain over the fixation site eventually subsided with removal of the device, and the infected cases were managed successfully with antibiotic administration, with only one case (deep streptococcal infection) requiring further treatment with arthroscopic débridement and lavage.

Troubleshooting

Achieving a stable and reproducible technique for tibial fixation is always a challenge for most surgeons. Although good results have been obtained with the use of conventional staples, certain aspects of both the device and the technique of achieving fixation can be improved. One of the main concerns when using staples for tibial fixation involves the occurrence of slippage. Because this is not immediately apparent at the time of surgery, the surgeon can only do so much in averting this problem. However, in cases in which proper tension is not achieved or the graft is found to be loose after the staple has been placed, the surgeon has no choice but to remove the staple and reapply it with proper tension. To minimize this problem, we recommend the use of a staple device in combination with a buckle (e.g., Fastlok). The addition of this simple component facilitates tensioning and locks the graft in position while the staple is driven down the tibia (see Figs. 41-1 and 41-2). The device can be easily fixed, assuming the surgeon maintains a perpendicular position while driving the Fastlok to the tibia. Concerns regarding the prominence of the device are addressed by allowing sufficient soft tissue coverage over the staple prior to skin closure. Moreover, once the graft has healed, removal of the staple remains an option.

Conclusions

Indirect fixation in quadrupled semitendinosus tendon ACL reconstruction with the use of a Fastlok device combined with a tibial bone plug enable the achievement of good clinical results with a reliable and secure tibial fixation. The profile compared with other staples and washers is lower; however, despite this advantage, we still had an 8% incidence of hardware removal, especially in thin female patients. Therefore we do not suggest the use of this device in this particular group of patients. In contrast, our findings suggest that Fastlok fixation is better suited for high-demand male athletes, with the better clinical results including the degree of knee stability achieved compared with the former group.