Chapter 33 EZLoc Femoral Fixation of a Soft Tissue Graft

Abstract

The EZLoc (Arthrotek, Warsaw, IN) is a cortical femoral fixation device for a soft tissue anterior cruciate ligament (ACL) reconstruction that combines superior fixation properties (high resistance to slippage, infinite stiffness, and 1427N strength) with a simple surgical technique. The EZLoc consists of a deployable lever arm connected to an axle in a slotted body through which the ACL graft is looped. The EZLoc comes sterilely package with a sharp-tip passing pin that is secured in the slotted body with a suture tied under tension. The passing pin is passed through the tunnels, the gold lever arm is positioned lateral, and the soft tissue graft is looped through the slot in the EZLoc. The graft is pulled into the femoral tunnel. When the lever arm clears the femoral tunnel, the suture is cut, the passing pin is removed, the suture is tensioned, and the lever arm is deployed, which fixes the EZLoc on cortical bone. The EZLoc can be used with both the one- and two-tunnel ACL reconstruction techniques, and it is available in three diameters and three lengths. The EZLoc femoral fixation resists slippage and is stiffer and stronger than other femoral fixation techniques currently in use with a soft tissue ACL graft. The EZLoc is an ideal fixation for the skeletally immature knee.

Introduction

Fixation of the looped end of a soft tissue ACL graft to the femur poses different challenges than fixation of the free ends to the tibia. Metal cross-pin devices such as the Bone Mulch Screw and Transfix have set the standard for femoral fixation because of their superior slippage resistance, stiffness, and strength.¹^–⁴ Although these metal cross-pin devices work extremely well, their surgical techniques consists of multiple challenging steps and a lateral incision through the iliotibial band, which can damage the lateral collateral ligament.⁵ Prominent seating of the head of the cross-pin causes iliotibial band pain,⁶ and countersinking below the cortex complicates and may prevent hardware removal at the time of revision surgery (Fig. 33-1).

Fig. 33-1 Radiographs of a two-stage revision in which the cross-pin was buried beneath the cortical bone on the femur and could not be removed at the time of hardware removal and bone grafting of the originally misplaced femoral and tibial tunnels (denser bone). At the second stage, the tibial tunnel was placed at an angle of 60 to 65 degrees in the coronal plane, which moved the femoral tunnel farther down the sidewall, which prevented posterior cruciate ligament impingement, and more posterior in the sagittal plane, which prevented roof impingement. The EZLoc sits low in profile but is still easy to find at the time of revision surgery because the lever arm rest on cortical bone.

The design of the EZLoc femoral fixation device (Arthrotek) replicates the superior fixation of the metal cross-pins while simplifying the surgical procedure. The use of the EZLoc does not require a lateral incision, and the lever arm seats on cortical bone so that it is neither prominent nor countersunk, which facilitates revision surgery. Both the high-volume and occasional ACL surgeon should find the EZLoc to be simpler, quicker, and easier to use than other femoral fixation techniques including the cross-pins. Brace-free, aggressive rehabilitation is safe because the EZLoc provides superior slippage resistance, stiffness, and strength.

Design, Diameter, Length, Packaging, and Mechanism of the EZLoc

The EZLoc is a cortical fixation device that consists of a deployable lever arm connected to an axle in a slotted body through which the ACL graft is looped. The lever arm grips cortical bone on the anterolateral side of the femur, which provides superior slippage resistance, high stiffness, and strong cortical fixation. The lever arm provides rigid fixation that is better than that of a cross-pin because the lever arm seats on cortical bone on the anterolateral femur, which is 50 times stronger than cancellous bone ⁷ (Fig. 33-2).

Fig. 33-2 The EZLoc is a cortical femoral fixation device consisting of a gold-colored lever arm (a) connected to a slotted body (b) by an axle (c). The lever arm provides slippage-resistant, stiff, and strong fixation similar to a cross-pin because it seats on cortical bone (circle). The lever arm prevents proximal and distal micromotion, and the body prevents anteroposterior and medial lateral micromotion. The slot in the body accepts both one- and two-strand soft tissue anterior cruciate ligament grafts.

The EZLoc is available in three diameters (5/6, 7/8, 9/10) and three lengths (short, standard, long). The diameter of the EZLoc is selected to match the diameter of the femoral and tibial tunnels. The 7/8 EZLoc is used with a 7- and 8-mm diameter tunnel, and the 9/10 EZLoc is used with a 9- and 10-mm diameter tunnel. The 5/6 EZLoc is used in the posterolateral tunnel with the two-tunnel technique, and the 7/8 EZLoc is used in the anteromedial tunnel.

The EZLoc comes in different lengths, which control the length of the graft in the femoral tunnel and ensure that enough graft extends beyond the tibial tunnel for secure fixation. The most commonly used EZLoc length is the standard version. The standard version is used in a femoral tunnel from 35 to 50 mm in length, which provides 22 to 37 mm of soft tissue graft in the tunnel, promoting rapid, stiff, and strong tendon tunnel healing.⁸^–¹⁰ The long version is used in a femoral tunnel that is longer than 50 mm, and the length of the soft tissue graft in the femoral tunnel is computed by subtracting 22 mm from the length of the lateral wall of the femoral tunnel. The short version is used in a femoral tunnel that is shorter than 35 mm, and the length of the graft in the tunnel is computed by subtracting 7 mm from the length of the lateral wall of the femoral tunnel.

For ease of use, each EZLoc comes preassembled on a 16-inch-long, sharp-tip passing pin that is secured by a suture tied under tension and is sterile (Figs. 33-3 and 33-4). The suture has two functions: to keep the passing pin in the body of the EZLoc during passing of the graft and to deploy the lever arm once the lever arm clears the femoral tunnel. The suture passes through a hole in the lever arm and through two holes at the sharp end of the passing pin. The suture is tied under tension, which keeps the dull end of the passing pin inside the EZLoc and keeps the lever arm undeployed. The lever arm is positioned laterally, tension is applied to the pin, and the EZLoc and soft tissue graft are pulled across the knee. Once the ACL graft is pulled into the femoral tunnel, the suture is cut, the passing pin is removed, the suture is tensioned, and the lever arm deploys.

Fig. 33-3 The EZLoc comes in a sterile package with a passing pin and suture. The dull end of a 16-inch-long, sharp-tip passing pin is secured in the proximal end of the slotted body by a suture tied under tension. The passing pin is used to orient the lever arm laterally and to pull the anterior cruciate ligament (ACL) graft into place. In the special situation when the EZLoc is used in the posterolateral femoral tunnel in a two-tunnel ACL reconstruction technique and the posterolateral femoral tunnel is not in the same axis as the tibial tunnel, the passing pin is removed from the EZLoc and the suture is used to pull the graft.

Fig. 33-4 Radiograph showing two EZLocs fixing the graft in the femur in the two-tunnel technique. A 5/6 short EZLoc fixes a single loop of gracilis tendon in the posterolateral femoral tunnel. A 7/8 standard EZLoc fixes a single loop of semitendinosus tendon in the more vertical anteromedial femoral tunnel.

Fixation Properties of the EZLoc

A successful ACL reconstruction with a soft tissue graft depends on the use of a femoral fixation device that has superior fixation properties and enhances biological healing of the tendon to the tunnel wall. The fixation properties of the femoral fixation device should provide high strength and high stiffness, be resistant to slippage, and allow circumferential healing of the tendon to the tunnel wall.^4,^9,¹¹^–¹³ Because a soft tissue graft takes longer to heal to the tunnel than a bone plug, the femoral fixation of a soft tissue graft should be more slippage resistant, stiffer, and stronger than the femoral fixation of a bone plug graft.¹⁴

The use of the EZLoc to fix a soft tissue graft in the femur is a sound choice because its fixation properties are second to none and the device allows circumferential healing. The strength of the EZLoc is 1427N, which is stronger than the closed-loop Endobutton (1086N) and the cross-pins (Bone Mulch Screw, 1112N; Transfix, 1303N; RigidFix, 868N).^2,¹⁵ The stiffness of the lever arm of the EZLoc on cortical bone is infinitely high compared with the stiffness of the more elastic soft tissue graft. A benefit of using a high-stiffness femoral fixation device such as the EZLoc is that the tension applied to the graft to restore anterior laxity is lowered^4,^12,^13,¹⁶ and the risk of developing anterior laxity during early motion is lessened.¹¹ The slippage resistance of the EZLoc under cyclical loading has not been measured; however, the slippage with a metal lever arm on cortical bone should be at least as small as a cross-pin because the mechanism of looping the graft over a metal post is identical in both types of fixation methods.¹⁷ The EZLoc promotes healing of the tendon to the tunnel wall better than an interference screw because the soft tissue graft fixed with the EZLoc heals circumferentially to the tunnel wall.⁹