Pinn-ACL CrossPin System for Femoral Graft Fixation

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Chapter 35 Pinn-ACL CrossPin System for Femoral Graft Fixation

Arturo Almazan, Donald H. Johnson

Introduction

Graft fixation has been considered the weak link in the early postoperative period, especially with the soft tissue grafts. Initial fixation requires sufficient fixation strength during the rehabilitation period while the graft incorporates into the bone tunnels. Several techniques have been used for fixing hamstring grafts. Interference screw fixation for quadrupled hamstring grafts has failure strengths that may not be adequate for daily activities and a modern rehabilitation program ¹; suspension techniques are related to tunnel enlargement and the so-called “bungee effect.”²^–⁴ A recent study demonstrated that four-bundle hamstring grafts fixed with modern techniques produced higher stability rates than bone–patellar tendon–bone (BPTB) reconstructions.⁵

Transfixation pin fixation techniques were developed to improve femoral graft fixation; these techniques put a pin across the femur traversing the femoral tunnel. Within the transverse femoral tunnel, the pins either penetrate the graft, as with Rigidfix (Mitek, Ethicon, Westwood, MA); the two bundles of the hamstring graft fold around the pin to create a quadrupled graft, as with Bio-TransFix (Arthrex, Naples, FL), Cross-Screw (Stryker, Kalamazoo, MI) and Bone Mulch (Arthrotek, Warsaw, IN); or the two bundles are looped through a graft harness that a pin transverses to create a quadrupled graft (ConMed-Linvatec, Largo, FL). Femoral fixation of hamstring tendon grafts using transfixing pins is an accepted technique that yields excellent biomechanical properties with failure loads over 800N,^1,^6,⁷ which clearly surpasses the 500N accepted to adequately follow an aggressive rehabilitation protocol^8,⁹ and has demonstrated results in clinical trials comparable with other fixation methods.¹⁰^–¹³

The ConMed-Linvatec Pinn-ACL Cross-Pin System is designed to provide transverse femoral fixation in anterior cruciate ligament (ACL) reconstruction using a soft tissue graft. With existing systems, transverse femoral fixation was a blind procedure, but this surgical technique and the implant’s innovative design allow the surgeon to visualize the transverse tunnel and exact point of femoral fixation. With this system the graft is suspended in a harness and the pin transfixes the harness, not the graft. Laboratory testing has showed greater than 1700N pullout strength,¹⁴ which is superior to that of other available designs.^1,^6,⁷

Instruments and Implant Design

The Pinn-ACL CrossPin system for femoral graft fixation includes the implants and instrumentation to ensure accurate transverse fixation of the graft. The implant consists of two parts, the graft harness and the cross-pin implant (Fig. 35-1).

Fig. 35-1 CrossPin system: graft harness (purple) and cross-pin, both with their leading sutures.

The graft harness is composed of self-reinforced poly-L-lactic acid (PLLA), it has an eyelet in which the cross-pin locks, it also has a closed loop of high-strength Dyneema suture in which the graft sits and folds, and in its proximal aspect it has a lead suture for graft construct passing. The graft harness is available in 8- and 9-mm diameters. The cross-pin implant is also composed of self-reinforced PLLA, is available in three different lengths (40, 45, and 50 mm), and has a lead suture in its tip for implant passing. A disposable transverse cannula fits in the blue frame and slides over the drill bit to maintain the entrance of the transverse tunnel as opened and accessible. The U-Guide is an external aimer with two components—the main blue frame and the positioning rod, which fit in the tunnels—and is available in 8 and 9 mm. A specially designed drill bit with two different diameters is used to create the transverse tunnel. This drill bit is the same for every procedure regarding the cross-pin implant length. Being a transverse fixation system, the tip of the drill bit engages in the tip of the positioning rod to ensure the engagement of the implants (Fig. 35-2).

Fig. 35-2 Cross-pin drill bit as it engages the positioning rod.

Surgical Technique with Hamstring Tendons

Graft Harvesting and Preparation

The semitendinosus and gracilis tendons are harvested in the usual fashion. Each tendon must be at least 20 cm long because, when folded, a 10-cm-long final graft construction is desired. The free grafts are taken to the Grafix Prep Table for preparation. Both tendons are measured and cut to the desired length (20 to 22 cm), and then muscle is removed with an osteotome or a periosteal elevator. Once cut and cleaned, each end of the individual graft tendon is whipstitched approximately 35 to 40 mm from the end with a #2 nonabsorbable suture. If the surgeon plans to use the SE Graft Tensioner for tibial fixation, the graft’s bundles must be identified. This is easily accomplished by applying one knot to the semitendinosus sutures and two to the gracilis or by using a surgical marker pen.

Using the graft sizing block, the entire graft bundle diameter is measured. It is important to take measurements of the femoral and tibial ends (Fig. 35-3); these diameters will determine the proper sizes of the cross-pin graft harness and tunnel. The graft harness size (8 or 9 mm) should always be selected based on the diameter of the femoral end of the graft.

Fig. 35-3 Measure the diameter of the femoral and tibial ends.

Not infrequently, the entire graft size is not uniform; usually the tibial end increases 1 mm because of the morphology of the tendon and the placed sutures. If this is the case, the cross-pin graft harness must match the femoral graft diameter. For tunnel creation, two different drill bits will be used, with the smaller drill bit for the femoral tunnel and the larger for the tibial tunnel.

To load the graft strands into the graft harness (Fig. 35-4), place the graft harness onto the harness holder accessory and pass the graft strands individually through the continuous suture loop on the graft harness.

Fig. 35-4 Graft mounted in the harness.

Notchplasty and ACL Stump Removal

The ACL stump is removed with the shaver. The notchplasty is large enough to accommodate the graft; this is usually possible by just removing the soft tissues on the lateral wall of the notch with the shaver or a curette. Sometimes in chronic cases in which stenotic bone is found, notchplasty will include some bone resection.

Tibial and Femoral Tunnel Creation

The Pinn-ACL tibial guide, set at 55 degrees, is inserted into the knee through the medial working portal. The tip of the guide is placed in the posterior aspect of the tibial ACL stump following an imaginary line along the posterior border of the lateral meniscus anterior horn and centered in the midline of the joint. The guide pin should enter the tibia 5 cm below the medial joint line and 2 to 3 cm medial to the anterior tibial tuberosity in a position adjacent to the medial collateral ligament; this alignment will create a tibial tunnel that allows a more oblique femoral tunnel, usually around the 65-degree angle.^15,¹⁶ The guide pin is advanced into the tibia, and arthroscopic visualization is used to check the correct position of the guide pin in the joint. An AccuDrill reamer corresponding to the graft’s tibial size is used to create the tibial tunnel.

Select the correct Bullseye guide so to leave 1 to 2 mm of cortical back wall in the femoral tunnel. This selection is made according to the femoral end diameter of the folded graft. The Bullseye guide is inserted into the joint through the tibial tunnel. The knee is slightly extended, and the tip of the guide is directed toward the posterior femoral cortex, trying to aim to the 10-o’clock position for the right knee and 2-o’clock position for the left knee. Once the tip of the guide is hooked in the femoral back wall, the knee is bent to 90 degrees, and the graft-passing guide pin is inserted through the handle of the Bullseye guide and drilled until it exits the lateral portion of the femur and skin. Leaving the graft-passing guide pin in place, the femoral Bullseye guide is taken out, its tip is disengaged, and it is turned 90 degrees toward the posterior cruciate ligament (PCL). A C-Reamer or Badger drill of the appropriate size (8 or 9 mm) is used to create the femoral tunnel. The tunnel length of the femoral socket should be no less than 30 mm (35 mm is recommended). The femoral drilling must be visualized with the arthroscope to ensure the tunnel position and integrity of the posterior back wall.

U-Guide Position and Cortical Length Measurement

Based on the diameter of the femoral tunnel, select the appropriate positioning rod size (8 or 9 mm) and assemble it onto the U-Guide. Slide the black disposable transverse cannula, which is packaged with the graft harness, onto the U-Guide body.

With the U-Guide assembled, insert the positioning rod over the graft-passing guide pin, through the tibial tunnel, and completely into the femoral socket. The positioning rod has laser-etched marks to enable the surgeon to check its penetration. If the positioning rod is fully inserted in the femoral tunnel, the laser marks must match the tunnel length; otherwise it is not fully inserted or the tunnel depth was not accurate. Remove the graft-passing guide pin from the femoral tunnel.

After the U-Guide is fully inserted into the tunnels, rotate the U-Guide body until the black transverse cannula that is mounted on the U-Guide body is directed toward the lateral condyle. The transverse tunnel will be drilled from the lateral to the medial condyle.

Cross-Pin Implant Selection

With the U-Guide body in the correct orientation, insert the cross-pin drill bit into the drill guide aperture and identify the entrance point of the transverse tunnel. With the tip of the cross-pin drill bit touching the skin, use a scalpel to create a small, 3- to 5-mm incision to assist the passage of the drill bit through the soft tissue in order to make contact with lateral femoral cortex.

To identify the appropriate length of cross-pin to be used, utilize the U-Guide and cross-pin drill bit as a caliper to first determine the length of the cortical side of the transverse tunnel (i.e., the distance from the lateral cortex of the femur to the lateral wall of the femoral tunnel). To measure this distance, firmly press the cross-pin drill bit against the cortical surface, without drilling, and read the laser-etched depth markings where the drill bit enters the drill guide aperture (Fig. 35-5). This measurement is important in selecting the appropriate-sized cross-pin implant for cortical side fixation.

Fig. 35-5 The measurement on the transverse drill bit indicates the correct size of the cross-pin implant.

(Courtesy of ConMed-Linvatec.)

Each cross-pin has a cortical length designed to occupy the cortical side of the transverse tunnel, the available cortical lengths being 15, 20, and 25 mm. The proper length of the cross-pin is that in which the cortical length is less than or equal to the measured cortical tunnel length.

After the measurement is taken, drill the transverse tunnel until the drill bit stops against the U-Guide body. As you pull out the drill from the tunnel by hand, push the black transverse cannula into the transverse tunnel to prevent soft tissues from entering the transverse tunnel (Fig. 35-6). Note: The use of the transverse cannula is optional. The purpose of the cannula is to maintain the opening of the transverse tunnel in the event the transverse opening cannot be located.

Fig. 35-6 The transverse cannula remains in the transversal tunnel, facilitating instruments and device entrance.

(Courtesy of ConMed-Linvatec.)

Before removing the U-Guide, reinsert the graft-passing guide pin until it exits the lateral femur and skin, and then remove the U-Guide from the knee by sliding it over the guide pin as it exits the femoral and tibial tunnels.

Graft Passing

Draw the hamstring graft construct into the knee using the graft-passing guide pin. Pass the lead suture of the graft harness through the eyelet of the graft-passing guide pin and, while maintaining lateral-to-medial alignment of the axis of the eyelet in the graft harness, pass the graft construct into the tibial tunnel. It is very important to maintain the graft harness alignment; the eyelet on it must be parallel to the transverse femoral drill (Fig. 35-7).

Fig. 35-7 The harness lead suture is mounted in the graft-passing guide pin.

(Courtesy of ConMed-Linvatec.)

As the graft harness enters the joint space in the intracondylar notch, use an arthroscopic probe (if necessary) to maintain the eyelet orientation lateral to medial as it passes into the femoral tunnel (Fig. 35-8).

Fig. 35-8 Arthroscopic view of the graft harness as it enters the femoral tunnel.

Pull firmly on the graft construct until it is fully seated in the femoral socket.

Place a sheathed scope into the black transverse cannula to view the full insertion and alignment of the axis of the graft harness eyelet with the axis of the transverse tunnel (Fig. 35-9).

Fig. 35-9 Use of an arthroscope in the transverse tunnel to verify that the harness is centered in the tunnel.

(Courtesy of ConMed-Linvatec.)

Graft Fixation

With the graft fully seated in the femoral tunnel and the graft harness adequately oriented, pass the graft-passing guide pin through the black transverse cannula and the eyelet of the graft harness into the medial portion of the transverse tunnel by hand. When the graft-passing guide pin will advance no further, drill the graft-passing guide pin until it exits the medial femur and skin. To confirm proper placement of the graft-passing guide pin, pull tension on the graft construct to ensure the graft-passing guide pin intersects the graft harness construct. Pass the lead suture of the cross-pin implant through the eyelet of the graft-passing guide pin. Remove the graft-passing guide pin from the transverse tunnel by pulling by hand from the medial side until it fully exits the knee. The lead suture of the cross-pin implant should pass through the transverse tunnel and the graft harness and exit on the medial side of the knee.

A sheathed scope should be placed into the black transverse cannula to view the lead suture passing through the eyelet of the graft harness (Fig. 35-10).

Fig. 35-10 Use of an arthroscope in the transverse tunnel to verify that the implant’s lead suture passes through the harness eyelet.

(Courtesy of ConMed-Linvatec.)

Gently pull the cross-pin lead suture until it enters the black transverse cannula and the tunnel opening. Insert the cross-pin driver into the proximal end of the implant (Fig. 35-11, A), and tap the driver with a mallet, advancing the implant until it stops. After the cross-pin is fully seated, disengage the driver and ensure the cross-pin implant is flush with or slightly below the cortical surface (Fig. 35-11, B) by palpating the proximal end of the cross-pin at the insertion site.

Fig. 35-11 A, Tap the implant’s driver to insert the cross-pin into the transverse tunnel. B, Insert the implant until it is flush with the lateral cortex of the femur.

(Courtesy of ConMed-Linvatec.)

Apply tension to the graft construct by pulling the tibial sutures to check femoral fixation.

Finally, pull on one end of the lead suture attached to the cross-pin to remove the suture from the device. Additionally, pull on one end of the lead suture attached to the graft harness to remove its suture (Fig. 35-12).

Fig. 35-12 Final view of the femoral fixation. The cross-pin engages the graft harness.

(Courtesy of ConMed-Linvatec.)

Tibial Fixation

Tips and Tricks

The Pinn-ACL CrossPin system for femoral fixation, like other transfixation devices, has a steep learning curve, but the main advantage of this system is that it is the only one providing endoscopic visualization of the exact point of femoral fixation.

Several steps, which may be easily missed, facilitate the procedure as follows:

• The positioning rod is only 8 and 9 mm; for 7-mm grafts, use the 8-mm rod.

• When inserting the positioning rod in the femoral tunnel, it is useful to gently tap it to ensure it is fully inserted. The laser mark must match the previously drilled depth.

• Always remove the graft-passing guide pin from the femoral tunnel before transverse drilling; otherwise the transverse drill bit may not pass through the U-Guide or, if it does, a false way will be created.

• Do not forget to measure the length of the cross-pin implant before drilling the transverse tunnel, as this measurement will give you the proper size of the implant to use.

• The length measured in the transverse drill bit is the size of the cross-pin implant to use.

• When drilling the transverse tunnel, ensure the black transverse cannula is seated in the U-Guide, not in the skin incision. If it is in the incision when the power drill is activated, the black cannula will engage in the drill bit spinning or braking.

• The transverse drill bit always must be removed by hand, if the power drill is used; the black cannula will engage in the drill bit spinning or braking.

• Before removing the U-Guide, reinsert the graft-passing guide pin through the positioning rod.

• It is useful to introduce the shaver into the transverse tunnel entrance to remove the soft tissues that may interfere with scope visualization.

• Do not try to introduce the scope in the U-Guide if it is not removed first. The distance between the lateral border of the U-Guide and the transverse tunnel entrance is larger than the scope tip.

• The shaver can be used to remove soft tissues from the transverse tunnel; this maneuver may facilitate the introduction of the transverse cannula.

• The clue for success with this technique is that the graft harness eyelet must be parallel to the transverse tunnel. To accomplish this, the eyelet must be oriented so that it enters the tibial tunnel. It is extremely difficult to rotate it when it is within the bone tunnels, but it is easy to control rotation of the graft if the surgeon holds it in hand with the bundles separated in two pairs (Fig. 35-13). As the lead suture of the graft harness is pulled out and the graft prepares to enter the tibial tunnel, the surgeon can rotate the graft to match the eyelet–transverse tunnel orientation. Tension in the lead suture of the graft harness must be maintained while it enters the tunnels as the surgeon controls graft rotation by hand. Arthroscopic visualization is very helpful. If the surgeon observes that the graft harness is slightly rotated (less than 20 degrees), sometimes the harness can be rotated using the arthroscopic probe. If it is badly rotated (greater than 20 degrees), it is better to take the graft out and correct alignment.

• Once the graft harness enters the femoral tunnel, change the arthroscope to the transverse tunnel to visualize how it sits up in the tunnel. The surgeon must observe that the harness eyelet is centered in the transverse tunnel (Fig. 35-14); this will allow the cross-pin device to fit into the harness eyelet.

• If there is any doubt regarding whether the cross-pin was fully inserted until flush with the femoral cortex, the scope can be placed again through the skin incision to check the cross-pin position.