Hamstring Anterior Cruciate Ligament Reconstruction with INTRAFIX and BioINTRAFIX Tibial Fastener Systems

Introduction

Tibial side fixation of soft tissue grafts has been challenging because the line of pull on the graft in the tibia is parallel to the axis of the tunnel and because the bone in the tibia has a lower bone mineral density (BMD). Free tendon ends are more difficult to fix well than looped ends or a bone block. Finally, tendon grafts heal more slowly than bone–tendon–bone grafts, requiring that soft tissue fixation devices withstand more cyclical loading before biological fixation takes place.

The INTRAFIX and Bio-INTRAFIX systems were the first intratunnel, sheath, and screw anchors for tibial fixation of soft tissue grafts. These anchors employ an expansion screw and a four-channel sheath to separate and grip each tendon strand, thus ensuring that each strand is pressed into bone. Mechanically they were designed to improve upon the fixation strength of interference screws, which showed a relative lack of strength and stiffness in many tests in human and animal bone. In response, some surgeons would not use interference screws alone, and they recommended routine backup fixation. When compared with interference screws alone in human bone, INTRAFIX and Bio-INTRAFIX demonstrated a significantly higher failure load, greater stiffness, and lower slippage in cyclical tests. These results were confirmed by others in human and animal bone when manufacturer’s recommendations were followed. Other screw and sheath systems have similarly shown superior tensile properties.

From a biological standpoint, INTRAFIX compresses each tendon into bone in contrast to interference screws, which leave some tendons without direct bony contact. This arrangement theoretically improves osteointegration of the graft. Histology from an animal study employing the INTRAFIX demonstrated early developing, direct bone-to-tendon healing, typically seen with the use of interference screws on all sides of the device ( Figs. 80.1 and 80.2 ).

Fig. 80.1, Histology 12 weeks after reconstruction of the anterior cruciate ligament in a sheep using autogenous extensor tendons and tibial fixation with INTRAFIX, seen at the bottom right of the slide. Note Sharpey fiber formation (linear strands) and new bone ingrowth (dark blue) into tendon (light blue) .

Fig. 80.2, Appearance of the tibial tunnel using an arthroscope during revision surgery following removal of the INTRAFIX device. Note the apparent integration of tendons/sutures 360 degrees around the tunnel and imprint of the sheath’s ridges.

In addition to highly desirable mechanical and biological qualities, there are several other advantages to a screw and sheath design: First, the device is low profile and rarely requires later removal, a potential problem encountered with most extracortical devices that fix onto the tibial cortex. Second, tunnel widening is infrequently encountered. Third, the graft strands are protected from laceration and twisting during screw insertion, either of which can compromise the strength of the graft construct as a whole. Finally, it is possible to identify and separate the bundles to create a single tunnel, double-bundle construct when used with a similar device—the Femoral INTRAFIX system—on the femur.

Surgical Technique

Graft Preparation

The two autograft hamstring tendons are cut to a total length of 20–22 cm, and the opposite ends of the tendons are whipstitched for a distance of 4–5 cm using a #2 nonabsorbable suture. The doubled graft is then folded at its midsection over a passing suture, creating a four-strand 10–11-cm graft. The INTRAFIX and Bio-INTRAFIX can be used with five- and six-strand graft constructs but not with shorter grafts. This length of tendon graft allows for 25 mm of the doubled gracilis semitendinosus tendon (DGST) graft to be inserted into the femoral tunnel and typically results in a significant length of suture-reinforced tendon within the tibial tunnel and a short (1 cm) length of the tendons extending outside the tibial tunnel. Planning the length of the graft so that some sutured tendon lies within the tunnel is important because suture-reinforced tendon constructs fixed with interference screws have a 30%–40% increased pullout strength.

Use with Allografts

Doubled allograft semitendinosis, gracilis, or peroneus longus tendons are prepared in the same fashion described previously for the DGST autograft. However, if a large single soft tissue allograft such as a tibialis anterior tendon is used, we prefer to divide each end of the allograft in two for a distance of 5 cm and then whipstitch each strand so that a four-stranded construct comparable to a DGST is created at its distal end. If preferred, the graft can also be left in its two-stranded form, placing the limbs 180 degrees apart in the tibial tunnel as the sheath is inserted.

The graft construct is then placed on a tensioning board to remove creep from the graft-suture construct. This is particularly important if supplemental distal cortical fixation is deemed necessary, as described in the Troubleshooting section.

Tibial Tunnel

Because our preferred method for performing endoscopic anterior cruciate ligament (ACL) reconstruction is the three portal technique in which the femoral tunnel is drilled through an accessory anteromedial portal, the only constraint is that the start point of the tibial tunnel on the tibial crest allows the creation of a 35–45-mm tunnel. A tibial tunnel length of 35–40 mm is optimal because it will prevent the 30-mm INTRAFIX or Bio-INTRAFIX from protruding into the joint. If the surgeon chooses a transtibial approach, the tunnels are typically shorter than 30 mm and cannot be fixed with the current INTRAFIX and Bio-INTRAFIX. Positioning the tibial tunnel should be done in a manner that avoids graft impingement in the notch, which is associated with effusions, loss of extension, anterior knee pain, quadriceps weakness, and increased anterior laxity.

Tunnel Sizing

Whether using the plastic INTRAFIX or the Bio-INTRAFIX, the diameter of the tibial tunnel should equal the diameter of the suture-reinforced end of the graft ( Table 80.1 ). The tibial tunnel should be drilled with a fluted drill to prevent anterior drift of the tunnel as the dense proximal cortex at the ACL tibial attachment is breeched.

TABLE 80.1

Sizing Scheme for INTRAFIX and Bio-INTRAFIX (mm) ^∗

Graft	Tunnel	Trial	Sheath	Screw
7	7	Small (7–8)	Small	6–7
7.5	7.5	Small (7–8)	Small	6–7
8	8	Small (7–8)	Small	6–8
8.5	8.5	Small (7–8)	Small	6–8
9	9	Large (9)	Large	7–9
9.5	9.5	Large (9)	Large	7–9
10	10	Large (9)	Large	8–10
10.5	10.5	Large (9)	Large	8–10

INTRAFIX Sizing Guidelines (mm)
Graft	Tunnel	Screw ^∗∗
7	7	6–8
8	8	7–9
9	9	8–10
10	10	8–10

∗ The sizing guideline above is recommended for a four-stranded graft.

∗∗ Screw size is ultimately the decision of the surgeon.

After drilling the tibial tunnel, it is important to clear soft tissue from around the entry point of the tibial tunnel using an electrocautery pencil and a Cobb periosteal elevator. Direct visualization of this area helps ensure that the sheath and screw are neither over- nor underinserted into the tunnel, and it improves the ability to see and trim excess tendon and sheath at the end of the case so that there is no prominence that might later irritate the patient.

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