Chapter 40 Anatomical Retroscrew Anterior Cruciate Ligament Fixation

Single- and Double-Bundle Anterior Cruciate Ligament Reconstruction with Retroscrew Biointerference in a Single Femoral Socket

The concept of anatomic graft positioning for anterior cruciate ligament reconstruction (ACL) has been previously described by many authors.^1–6 In the past, anatomical graft tunnels were believed to obtain an optimal ACL reconstruction; the position of the graft within bone tunnels had to avoid the intercondylar roof and wall impingement. Studies have documented the landmarks for the placement of endoscopic tunnels in anatomical reconstructions through a full knee range of motion that will avoid impingement.^7,8

Recently, issues regarding graft fixation position have become important. Experimental and clinical trials have shown that anatomical graft fixation and position at or near the origin and insertion of the native ACL in contrast to nonanatomical fixation position will (1) minimize graft tension, (2) minimize graft length change, (3) produce a more stable reconstruction through full knee range of motion, and (4) avoid anteroposterior, sagittal, windshield wiper–type graft motion.^1,2,4,7–10 Five-year follow-up studies comparing anatomical and nonanatomical fixation for ACL reconstruction have shown absence of tunnel expansion up to 5 years with an anatomically fixed graft at the intraarticular tibial tunnel orifice (Fig. 40-1)^5,6,8,11,12

Fig. 40-1 A, An all-inside anterior cruciate ligament (ACL) reconstruction with a quadriceps tendon autograft fixed anatomically at the intraarticular tibial and femoral socket orifices. Retrograde and antegrade headed titanium interference screws (Arthrex) were used in the tibial and femoral sockets, respectively. B, A lateral radiograph of the same case illustrating anatomical interference screw positioning.

The Retroscrew (Arthrex, Naples, FL) (Fig. 40-2) is inserted into the tibial tunnel in an inside-out position so that the head of the screw achieves aperture fixation at the intraarticular tunnel orifice. Standard interference screw fixation is used on the femoral side. The Retroscrew is beneficial during tensioning because unlike an antegrade screw, the Retroscrew will pull the graft tighter into the tunnel, especially during tensioning.

Fig. 40-2 The femoral and tibia Retroscrews are shown. The screws are tethered by a #2 Fiberwire suture.

Morgan et al⁴ first described an “all-inside” technique for ACL reconstruction that addressed the issues of anatomical fixation. However, the procedure was not popular because of its technically demanding nature^3,5,6,13 (Fig. 40-3).

Fig. 40-3 A, A 2.5-year follow-up magnetic resonance image (MRI) of an all-inside quadriceps tendon autograft anterior cruciate ligament (ACL) reconstruction using bioabsorbable interference screws. Graft and screw resorption up to the intercondylar floor where biological graft incorporation appears similar to a native ACL without tunnel widening. B, Radiograph 6 years after a quadriceps tendon autograft ACL reconstruction illustrates the absence of tunnel expansion on either the femoral or tibial side of the joint.

Graft choices for this technique include quadriceps tendon autograft, quadrupled hamstring autograft, Achilles allograft, hamstring allograft, and tibialis tendon allograft.

Once a graft has been selected, prepared, and sized, the appropriate tunnels are placed: 7 mm anterior to the posterior cruciate ligament (PCL) between the tibial spines for the tibia and at the 2-o’clock position for a left knee or 10-o’clock position for a right knee on the lateral intercondylar wall.

Operative Technique: Single Femoral Socket, Single-Bundle Graft

Once the appropriate anatomical bone tunnels have been placed, the graft is passed in a routine fashion. Femoral fixation may be achieved using an interference screw equal to the diameter of the tunnel placed through the anteromedial portal with the knee in hyperflexion. Alternatively, femoral fixation may be accomplished with a specially designed, cannulated Retroscrew driver (Arthrex) passed through the tibial tunnel to achieve parallel interference screw fixation. This is performed using a preloaded Fiberstick Suture (Arthrex) withdrawn from the tip of the screw driver and out the anteromedial portal (see Fig. 40-3).

The #2 suture is then passed through the cannulation of the Retroscrew, and a 3-mm Mulberry knot is tied to prevent the screw from disengaging the driver. Intraarticular passage of the femoral Retroscrew from the anteromedial portal is facilitated with the aid of a flexible slotted cannula (shoehorn cannula, Arthrex) at the same time as the suture exiting the handle portion of the screwdriver is pulled (Fig. 40-4). The shoehorn cannula avoids hang-up of the screw in the fat pad. This is used to secure and lead a femoral Retroscrew (7 to 10 mm × 20 mm) onto the driver tip. Once the screw has been securely placed onto the end of the driver, the suture may be removed. With the leg in approximately 90 degrees of flexion, the screw is advanced into the femoral socket to secure the femoral side of the graft.

Fig. 40-4 Tibial Retroscrew insertion via anteromedial portal assisted by flexible slotted cannula (shoehorn cannula).

Tibial fixation can next be performed by placing a tibial Retroscrew equal to the tunnel diameter. As previously described, the tibial Retroscrew (8 to 10 mm × 20 mm) is placed onto the driver tip over a #2 Fiberwire suture from the medial portal. It is important that the screwdriver tip be anterior to the graft and free of all soft tissue. Obscuring the tip will prevent seating of the screw on the driver. Once inside the joint, the screw is “flipped” onto the driver by pulling the suture exiting the driver handle at the same time as the driver tip is lowered into the aperture (Fig. 40-5). The screw is then secured to the driver by wrapping the exiting suture around the grommets on the driver handle.

Fig. 40-5 Placement of tibia Retroscrew into the aperture of the tibial tunnel.

The graft is then tensioned as the screw is advanced counterclockwise until its head is flush with the intraarticular aperture of the tibial tunnel. With the arthroscope turned toward the tibial surface, the knee may be extended to near full extension as the screw is advanced into the top of the tibial tunnel. If additional tibial fixation is desired, a second interference screw may be placed from outside in, antegrade and posterior to the graft. This will result in an interlocking screw–graft fixation construct.

Operative Technique: Single Femoral Socket, Double-Bundle Graft

The simplicity of this technique is what makes it appealing. Only minor modifications are made to the previously described single-bundle procedure. Our preferred graft source for the double-bundle technique is a two-limbed tibialis tendon allograft. During preparation, it is recommended that it be prepared in the manner described by Charlick and Caborn.¹⁴ Specifically, this may be carried out by suturing (#2 Fiberwire) 20 mm to either side of the midline of the folded soft tissue graft (Fig. 40-6). If a hamstring graft is chosen, the semitendinosus and gracilis tendons should first be sutured together under tension to create a two-limbed, folded graft. Further suturing is performed distally after accommodating 30 to 35 mm for the intraarticular portion of the graft. This additional whipstitch aids in controlling the anteromedial bundle (AMB) and posterolateral bundle (PLB) as they are oriented into the femoral and tibial tunnels. Caborn stitching has been shown to increase pullout to failure by approximately 30% when using interference screw fixation for soft tissue grafts.¹⁴

Fig. 40-6 Demonstration of the two-bundle soft tissue anterior cruciate ligament (ACL) graft with suture preparation to accommodate femoral and tibia interference screws. Note the suture pattern performed to enhance thread contact of the interference screw. This preparation also assists in orienting the bundles on the femoral and tibial attachment sites.

After standard femoral and tibial socket preparation, to create the double-bundle socket on the femur, a notching device is used to create two slots on the femoral socket intraarticular orifice, for the AMB and PLB of the ACL graft, respectively. The slots can be further delineated using a motorized bur or shaver or a curved curette (Fig. 40-7). With the knee flexed 90 degrees, the AMB slot is made at the 10- or 2-o’clock position and the PLB slot is made at the 4- or 8-o’clock position within the circumference of the tunnel orifice. Each slot is typically 6 to 7 mm in width.

Fig. 40-7 Single socket, double-bundle femoral socket preparation featuring specific notches created for the anteromedial and posterolateral bundles.

The graft is then passed in routine fashion using a Beath pin. While the graft is held into the tunnel by an assistant, the limbs of the graft are rotated into their respective notches. The AMB is retraced by a probe from the anteromedial portal. Femoral fixation is then carried out with a concentrically placed femoral Retroscrew placed central between the bundles and secured into position by the driver, which is passed through the tibial tunnel as described previously (Fig. 40-8). As the screw is advanced in the tunnel, the graft strands will seek the two-bundle origin of the ACL in their respective slots (Fig. 40-9).

Fig. 40-8 Concentric placement of femoral Retroscrew separating the graft into the anteromedial and posterolateral bundle positions.

Fig. 40-9 Final inspection of the single-tunnel, double-bundle, soft tissue anterior cruciate ligament (ACL) reconstruction.

The graft strands are then anatomically positioned directly anterior and posterior to one another within the tibial tunnel (AMB, anterior; PLB, posterior). Tibial fixation is carried out using a tibial Retroscrew, as previously described, medial to the strands with the knee flexed approximately 70 degrees. Both bundles are equally tensioned at 70 degrees of flexion prior to tibial Retroscrew fixation. Secondary backup fixation can be applied with a bicortical post and washer or a second interference screw secured to the distal tibial cortex.