What Is Your Preferred Fixation Method for Soft-Tissue Grafts on Both Tibial and Femoral Sides?
Because the 4-strand hamstring tendon graft is known to have a load to failure of over 4000 Newtons (N) and a strength that approximates that of a similarly sized patellar tendon graft,1 the quadrupled hamstring tendon graft is an attractive choice for anterior cruciate ligament (ACL) reconstruction. Use of the hamstring autograft ACL reconstruction does not disturb the extensor mechanism of the knee, thus avoiding the potential morbidity associated with harvesting the patellar tendon. Proponents of bone-patellar tendon-bone autografts often state that they prefer the security of initial bone-to-bone fixation that is provided with the interference screw fixation typically used with these grafts. As such, the initial fixation strength of a hamstring ACL reconstruction has long been considered the weak link of this technique. Optimizing initial graft fixation in ACL reconstruction has been a focus for both surgeons and industry over the past 25 years. Consequently, the fixation strengths for devices used to secure soft-tissue ACL grafts have improved considerably. Currently, the authors recommend the use of a cross-pin fixation device for 4-strand hamstring tendon ACL grafts on the femoral side using the Bio-TransFix implant (Arthrex, Naples, FL), and the Intrafix device (Depuy-Mitek, Westwood, MA) for graft fixation on the tibial side (Figure 19-1).
Figure 19-1. (A) Bio-TransFix femoral cross-pin soft-tissue graft-fixation device. (B) Intrafix sleeve-screw for fixation of soft-tissue grafts on the tibial side.
There are 2 fixation types for ACL grafts in bone tunnels: aperture fixation and suspensory fixation. Aperture fixation describes graft fixation at the opening of the bone tunnel, typically with an interference screw. Suspensory fixation describes graft fixation that is remote from the intra-articular space (ie, at the femoral or tibial cortices). Suspensory fixation approaches include graft fixation using a screw (post) and washer, graft fixation using sutures suspended from a femoral fixation device such at the EndoButton (Smith & Nephew, Andover, MA), or graft fixation using a cross-pin type device (so-called cortico-cancellous fixation). The primary goal of initial fixation in ACL reconstruction is to resist graft slippage until tendon-to-bone healing occurs; ACL grafts should be stable enough to withstand the physiologic loads applied to the knee during activities of daily living (ADLs). Moreover, graft fixation should also allow for the application of accelerated rehabilitation protocols. Ultimately, successful tendon to bone healing should occur without tunnel widening. The native ACL resists an estimated load of up to 454 N during activities of daily living.2 The initial fixation of a soft-tissue graft should be able to resist this magnitude of load to be successful.
For soft-tissue ACL grafts, both cortico-cancellous cross-pin fixation and cortical suspensory (eg, EndoButton) fixation have demonstrated superior graft stability and strength compared to aperture fixation (interference screws) on the femoral side in laboratory studies. In a study by Ahmad et al, the load-to-failure and graft slippage profile of the Bio-TransFix device was superior to that of the EndoButton CL, and an interference screw in porcine femora.3 In this study, the Bio-TransFix cross-pin device (tendons pass over the pin within the femoral tunnel) was also superior to a cross-pin fixation device that pierced the tendon graft (Rigidfix, Mitek, Westwood, MA). Kousa et al compared the initial fixation strength of 6 femoral fixation devices for soft-tissue grafts in porcine femora.4 These authors found that the Bone Mulch Screw (Arthrotek, Warsaw, IN), which is also a cross-pin fixation device, had a load to failure of 1112 N and had the lowest graft displacement (2.2 mm) when compared to the EndoButton CL (1086 N) and 3 interference screws (all less than 800 N load to failure).
The literature suggests that cross-pin fixation that does not pierce the ACL graft (eg, Bone Mulch Screw, TransFix, Bio-TransFix) are sufficiently strong enough to withstand knee forces associated with ADLs after ACL reconstruction. Both the cross-pin and suspensory techniques were consistently stronger when used with a soft-tissue graft compared to interference screw fixation on the femoral side. Some authors describe increased graft motion within the bony tunnels (bungee cord or windshield wiper effect) that is associated with the use of the EndoButton fixation device. The remote cortical fixation associated with the use of the EndoButton may correlate to the tunnel widening phenomena that is often observed after hamstring ACL reconstruction.5 We prefer the Bio-TransFix device because it requires the drilling of a relatively short femoral tunnel compared to using the EndoButton. Use of the BioTransFix facilitates the application of strong early fixation that lies approximately 20 to 25 mm from the femoral tunnel opening.
After drilling the femoral tunnel to approximately 35 to 40 mm, a jig that includes an intra-articular hook and a lateral drill guide is seated in the tibial and femoral tunnels. A guide pin is drilled from lateral to medial in through both femoral cortices. The guide pin is pulled medially and replaced by a guide wire. This guide wire is pulled inferiorly out through the tibial tunnel. The ACL graft is loaded through the wire loop that has emerged from the tibial tunnel and pulled into the femoral tunnel by simultaneously pulling both ends of the wire. The Bio-TransFix device is then implanted into the distal femur (lateral to medial) over the wire and through the axilla of the ACL graft. The head of the implant should sit flush with the lateral femoral cortex (Figure 19-2).
Figure 19-2. The authors’ current method of femoral (cross-pin) and tibial (screw-sleeve) fixation for anterior cruciate ligament reconstruction with a hamstring tendon autograft. (Reprinted with permission from Williams RJ III, Hyman J, Petrigliano F, Rozental T, Wickiewicz TL. Anterior cruciate ligament reconstruction with a four-strand hamstring tendon autograft. Surgical technique. J Bone Joint Surg Am. 2005;87[suppl 1, pt 1]:51-66.)
Because the tibial bone quality (density) is variable and often inferior to that of the femur, tibial fixation is considered more problematic compared to femoral fixation in hamstring ACL reconstruction.6 Kousa et al compared 6 different tibial fixation devices in porcine tibiae, and found that the Intrafix device had the highest stiffness (223 N) and highest load to failure (1332 N).6 This device utilizes a sleeve-screw configuration that allows for the tensioning of the individual graft limbs and maximizes apposition of the graft tendon ends to bone within the tunnel. The WasherLoc (Arthrotek, Warsaw, IN; 975 N) was also superior to a group of interference screws and a post/washer device in this study. Because the WasherLoc requires the removal of a large quantity of anteromedial tibial bone to seat the implant, we prefer the Intrafix to this device.
After fixing the graft on the femoral side, the graft is cycled to remove creep. With the knee slightly flexed (20 degrees), tension is put upon each of the four strands of the quadrupled tendon graft. A sheath trial (tap) is advanced into the tibial tunnel centrally between the limbs of each graft strand. The tap is removed and the Intrafix sheath is then impacted into the tibial tunnel until flush with the cortex. The IntraFix screw (typically size 8 to 10 mm) is advanced into the sleeve. Advancement of the screw causes expansion of the sleeve and compression of each tendon strand separately against the wall of the tibial tunnel (see Figure 19-2).
Clearly there are several different choices for graft fixation on both the femoral and tibial sides that can yield successful results following ACL reconstruction using a hamstring or soft-tissue graft. Biomechanical studies suggest that interference screw fixation alone for fixation of a hamstring graft is inferior to cross-pin fixation on the femoral side and second-generation fixation devices (Intrafix and WasherLoc) on the tibial side. Because these newer soft-tissue graft-fixation devices often require more steps for insertion compared to those steps needed to use the typical interference screw, we recommend performing these techniques in a cadaver or saw-bones model prior to using these implants in the operating room.
1. Simonian PT, Williams RJ, Deng XH, Wickiewicz TL, Warren RF. Hamstring and patellar tendon graft response to cyclical loading. Am J Knee Surg. 1998;11(2):101-105.
2. Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am. 1984;66(3):344-352.
3. Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med. 2004;32(3):635-640.
4. Kousa P, Jarvinen TL, Vihavainen M, Kannus P, Jarvinen M. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part I: femoral site. Am J Sports Med. 2003; 31(2):174-181.
5. Williams RJ III, Hyman J, Petrigliano F, Rozental T, Wickiewicz TL. Anterior cruciate ligament reconstruction with a four-strand hamstring tendon autograft. J Bone Joint Surg Am. 2004;86-A(2):225-232.
6. Kousa P, Jarvinen TL, Vihavainen M, Kannus P, Jarvinen M. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part II: tibial site. Am J Sports Med. 2003; 31(2):182-188.