Direct Visualization of Existing Footprint and Outside-In Drilling of the Femoral Tunnel in Anterior Cruciate Ligament Reconstruction in the Knee

Abstract

Improper femoral tunnel placement in anterior cruciate ligament (ACL) reconstruction is a significant problem and may be a cause of ACL graft failure and abnormal kinematics, which may lead to late degenerative changes after reconstruction. Recently, there has been concern that the transtibial approach may contribute to nonanatomic placement of the femoral tunnel, resulting in abnormal knee kinematics. Tibial-independent techniques can provide more anatomic placement of the ACL graft, but these can be technically demanding. This technical note describes the senior author's technique to directly identify the femoral ACL remnant and use the center of the femoral ACL footprint and retrograde drilling to create an anatomic femoral socket for single-bundle reconstruction. This technique provides femoral tunnel placement based on identification of a patient-specific ACL footprint instead of averaged anatomic measurements from large groups. This technique has been shown to produce anatomic ACL graft position and orientation and restore more normal knee kinematics.

It is estimated that 200,000 anterior cruciate ligament (ACL) reconstructions are performed annually in the United States, with the vast majority performed using the transtibial technique in which the femoral tunnel is drilled through the tibial tunnel.¹ However, it has been shown that this technique may result in improper placement of the femoral tunnel, producing a nonanatomic graft that does not restore normal knee kinematics.^2-6

Alternatively, techniques in which the femoral tunnel is drilled independent of the tibial tunnel, for example, through the anteromedial portal or an accessory medial portal, have been shown in multiple studies to reproduce the native ACL location and orientation more accurately.^6-11 In a recent meta-analysis, the short-term clinical outcomes of a more anatomic graft placement were not significantly different compared with the transtibial approach.¹² However, individual studies have shown increased rates of repeat injury and graft failure in transtibial reconstruction cases.^13-15 These findings, as well as the known altered kinematics, have raised concerns about the long-term effects of the transtibial approach and its ability to prevent late degenerative changes. As a result, there has been a shift toward more anatomic tibial-independent techniques.

Multiple tibial-independent techniques have been described; however, some can be technically demanding and have a high learning curve.¹⁶ The purpose of this report is to present the senior author's (W.E.G.) technique to directly visualize the femoral ACL footprint and use “outside-in” retrograde drilling to create a patient-specific anatomic femoral tunnel for single-bundle reconstruction.

Technique

ACL injury is first confirmed by physical and magnetic resonance imaging examination. After routine patient preparation, the hamstring autograft is harvested. Muscle tissue is debrided, sutures are attached to both ends of the tendons, and the tendons are combined and doubled to produce a graft construct of at least 8.0 mm in diameter. If the construct is not 8.0 mm or greater, 1 or both hamstring tendons may be tripled or quadrupled or cadaveric allograft can be used for supplementation. The graft is then assembled with the TightRope RT Femoral Fixation device (Arthrex, Naples, FL) and placed into a moist gauze.

Standard anteromedial and superomedial arthroscopy portals are then created. An anterolateral portal is made at the lateral margin of the patellar tendon at the inferior tip of the patella. The femoral ACL remnant is identified on the lateral femoral condyle (Fig 1), and the bulk of the remnant stump and surrounding tissue is debrided with a shaver and radiofrequency wand, with care taken to leave enough of the footprint that it is easily recognizable (Fig 2). The remaining fibers are seen, but the anterior margin is not always clear. Kaseta et al.⁶ showed that the center of the ACL footprint lies in a line parallel to the femoral shaft, distal to the point of intersection of the proximal border of the cartilage and the reflection of the synovium (Fig 3). Starting at this point, the surgeon creates a swath along the femoral axis with the radiofrequency wand such that it passes through the center of the footprint (Video 1). The swath results in nearly equal remaining portions of the femoral ACL footprint above and below the ablated tissue (Fig 4). The center of the ACL footprint can then be readily identified in the proximal-distal and anteroposterior directions (Fig 5). We have found that, often, the ACL footprint cannot initially be identified, but once the swath has been created, it becomes more apparent and the center of the footprint is more easily appreciated (Video 1). Care should also be taken to create a single swath along a single line because unintentional ablation of the entire footprint will obscure targeting of the footprint center (Table 1).

Fig 1.

Arthroscopic view showing the remainder of the ruptured anterior cruciate ligament (ACL) stump on the lateral wall of the femur adjacent to the synovium overlying the posterior cruciate ligament (PCL) (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right).

Fig 2.

Arthroscopic view of the posterior border of the anterior cruciate ligament (ACL) footprint at the junction of the reflection of the synovium and the proximal border of the articular cartilage (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right). The center of the ACL lies straight distal to this point, and it acts as the starting point of the swath.

Fig 3.

Arthroscopic view of the lateral femoral condyle with identification of the anterior cruciate ligament remnant on the lateral intercondylar wall (oval) after debridement, distal to the point identified in Figure 2 in line with the axis of the femur (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right).

Fig 4.

Arthroscopic view of the swath through the center of the anterior cruciate ligament (ACL) footprint created by the radiofrequency probe, with equal parts of the footprint above and below (arrows) (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right). Only a swath is created because these remaining fibers aid in targeting the center of the ACL.

Fig 5.

Sagittal view of the intercondylar surface of the lateral femoral condyle. The black dashed lines represent the path of the swath, distal to the proximal border of the articular cartilage and parallel to the axis of the femur. The swath passes through the anterior cruciate ligament (ACL) footprint (yellow area) and the center of the footprint (red circle). Portions of the footprint remain above and below the swath. The white line represents the lateral intercondylar ridge, a reference for the anterior border of the footprint.

Table 1.

Pearls and Pitfalls

Pearls

After debridement of the ACL stump, start at the intersection of the reflection of the synovium and the proximal border of the articular cartilage and move distally, in line with the femoral shaft, to pass through the center of the ACL footprint.

Use the area of the footprint above and below the swath created with the radiofrequency wand to locate the ACL footprint center in the anteroposterior and proximal-distal axes.

The lateral intercondylar ridge can help define the distal boundary of the ACL footprint.

Incise the iliotibial band and elevate the vastus lateralis to directly place the femoral drill guide directly on the cortex and to allow direct visualization of the TightRope RT button.

Place the tibial drilling guide near the posterior margin of the tibial footprint to avoid impingement.

Pitfalls

Extreme lateral placement of the anterolateral portal will hinder the ability to create the swath and place the marking hook of the femoral guide.

Inadequate debridement of the ACL femoral stump will confound the boundaries of the footprint.

Be cognizant of the axis of the femur, and make the path of the swath distal to the intersection point of the synovial reflection and proximal articular cartilage (as described in Fig 5).

If the entire footprint is ablated, the anterior and posterior fibers cannot be used to target the center. Instead, a swath only through the middle of the footprint should be made.

ACL, anterior cruciate ligament.

The lateral intercondylar ridge (also referred to as the “resident's ridge”) can be a useful reference. Purnell et al.¹⁷ showed that this bony landmark, which runs from superior-anterior to inferior-posterior on the lateral wall of the intercondylar notch, is the anterior border of the femoral ACL footprint (Fig 5). The lateral intercondylar ridge can often be identified by direct arthroscopic visualization and as a tactile step-off with a probe (Fig 6). Shino et al.¹⁸ used quantitative imaging to show that the intercondylar ridge is 7 to 10 mm anterior to the posterior cartilage margin on the lateral femoral condyle and lies on an axis approximately 31° posterior to the axis of the femoral shaft. Because of its orientation, the lateral intercondylar ridge can be helpful in defining the distal boundary of the footprint when creating the swath.

Fig 6.

Arthroscopic view of the lateral intercondylar ridge (also called the resident's ridge), which can be used as a landmark to identify the anterior border of the anterior cruciate ligament (ACL) footprint (as described in Fig 5) (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right).

Once the ACL footprint center is identified, the center of the femoral marking hook (RetroConstruction System; Arthrex) is inserted through the anterolateral portal and placed over the center of the footprint (Fig 7). The arthroscope is positioned in the medial portal so that the footprint and the junction of the posterior articular cartilage and capsular reflection are best visualized. The tip of the drill guide is then placed on the outside of the joint on the lateral epicondyle at the thickest part of the iliotibial band. A small incision can be made in the skin over the lateral femoral condyle. Alternatively, a larger 5-cm incision can be carried down through the iliotibial band, followed by digitally elevating the vastus lateralis and sweeping it anteriorly, which allows for direct placement of the drill guide on the femoral cortex and direct visualization of graft fixation.

Fig 7.

Arthroscopic view of the femoral guide marking hook placed over the center of the anterior cruciate ligament (ACL) footprint (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right). This guide is inserted through the anterolateral portal.

A FlipCutter reamer (Arthrex), with a closed diameter of 3.5 mm and open diameter matching the measured graft size, is drilled in an outside-in fashion through the femoral tunnel guide from the lateral femoral cortex into the joint under direct visualization and with the arthroscopic camera (Fig 8). Once inside the joint, the FlipCutter is opened and a larger-diameter socket is reamed in a retrograde fashion to the desired length, typically 22 to 28 mm (Fig 9). The drill is then placed back into the joint, closed, and removed completely. This helps preserve the cortex of the lateral femoral condyle for femoral fixation. A passing suture is placed through the femoral tunnel.

Fig 8.

Arthroscopic view of the 3.5-mm FlipCutter reamer drilled through the anterior cruciate ligament footprint, opening to drill the femoral socket in a retrograde manner (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right).

Fig 9.

Arthroscopic view of the femoral socket drilled in retrograde fashion to the desired depth by the FlipCutter reamer (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right). A passing suture is then placed.

The tibial tunnel can then be drilled per surgeon preference. We start by identifying and debriding the center of the ACL footprint on the tibia. The footprint is preserved so that the graft tunnel can be entirely within the footprint. Specifically, we place the graft within the footprint near the posterior margin to avoid impingement (Fig 10). A tibial tunnel guide (Arthrex) is placed over the footprint, and the stylet is placed firmly against the tibia through the previously made incision for hamstring graft harvest. A guidewire is first drilled into the joint under direct visualization, followed by a reamer the size of the ACL graft. Any excess tissue around the tibial tunnel is debrided arthroscopically.

Fig 10.

Arthroscopic view of the tibial tunnel guide placed within the tibial anterior cruciate ligament footprint near the posterior margin to avoid impingement (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right). The stylet at the other end of the guide is placed on the tibia through the graft harvest incision (not shown).

The passing suture in the femoral tunnel is then pulled through the tibial tunnel through the joint to act as the graft-passing suture. The ACL construct is selected, and the length of the femoral socket or desired amount of graft in the socket is marked from the proximal end of the graft. The end of the passing suture out of the tibial tunnel is then wrapped around the TightRope RT button (Arthrex) and pulled through the tunnel to inside the joint. The button of the construct can be visualized arthroscopically entering the 3.5-mm femoral tunnel to ensure passage. In addition, if full exposure is obtained on the lateral femoral cortex, fixation of the TightRope RT button can be directly visualized while tension is applied to the tibial side of the graft. The graft can then be pulled up through the femoral socket until fixation is achieved, using the mark made on the graft as a guide (Fig 11).

Fig 11.

Arthroscopic view of the 4-stranded hamstring graft tensioned into the femoral socket by the TightRope RT construct until fixation is achieved (viewed through anteromedial portal, with lateral [L] on left and medial [M] on right). The graft is anatomically positioned at the posterior aspect of the lateral wall, there is no posterior cruciate ligament impingement, and there are no graft fibers at the apex of the intercondylar notch.

The leg is brought through a full range of motion to ensure that there is no impingement of the graft in extension. Tibial fixation of the graft is then obtained with a tibial staple on the anterior portion of the tibia and/or a soft-tissue interference screw in the tibial tunnel. Appropriate tension of the graft is assessed by bringing the leg into extension and confirming knee stability by performing the Lachman and flexion-rotation drawer tests. The wounds are then closed in appropriate fashion.

Discussion

Over the past 3 decades, the senior author has used multiple ACL reconstruction techniques that have evolved ultimately to the technique described in this report. This technique allows for direct visualization of the graft placement in the anatomic position, with no posterior cruciate ligament impingement and no graft fibers at the apex of the intercondylar notch. It has resulted in graft placement in a good position and orientation. The technique has been evaluated by sophisticated biomechanical techniques and has been shown to reproduce near-normal kinematics.^3,19 The disadvantage of this technique, as with all tibial-independent techniques, is that more steps are required, which may lead to a longer operating room time (Table 2).

Table 2.

Advantages and Disadvantages

Advantages

The FlipCutter reamer allows precise retrograde drilling of the femoral socket in line with the femoral tunnel through direct visualization.

Reliable patient-specific placement of the ACL graft femoral tunnel can be achieved, without reliance on averaged measurements.

Direct visualization of the graft placement in the anatomic position, posterior and distal on the lateral wall of the femur, is possible.

No posterior cruciate ligament impingement occurs.

There are no graft fibers at the apex of the intercondylar notch.

The technique reproduces near-normal kinematics.

Disadvantages

Additional steps and a longer operative time are required compared with transtibial drilling of the femoral tunnel.

ACL, anterior cruciate ligament.

Kaseta et al.⁶ found that the distance parallel to the femoral shaft from the proximal edge of the articular cartilage to the center of the ACL was 11.7 ± 1.2 mm. More recently, Piefer et al.²⁰ performed a meta-analysis of 11 studies and concluded that the center of the ACL footprint was 43% of the distance between the proximal and distal articular borders. These references are helpful to estimate the approximate location of the ACL center. However, an advantage of our technique is that by creating a swath directly through the ACL footprint, the center of the ACL can be reliably identified based on patient-specific anatomy without reliance on averaged measurements from large groups.

The use of retrograde drilling allows for dependable femoral tunnel placement and socket depth. Other techniques, such as the use of an anteromedial portal or a flexible reamer, use a tibial-independent femoral tunnel. It has been shown that when used effectively, these techniques can result in positioning similar to the outside-in technique described in this report.^7,8 However, these techniques use antegrade drilling and rely on tunnel placement through arthroscopic incisions and based on arthroscopic views, which may not result in anatomic placement of the femoral tunnel.^16,21 In conclusion, the described technique, performed by the senior author, provides reliable anatomic placement of the ACL graft through the use of direct identification of a patient-specific ACL footprint, an outside-in femoral tunnel, and retrograde socket drilling.

Supplementary Data

Video 1

Identification of the center of the anterior cruciate ligament (ACL) footprint through swath creation based on patient-specific anatomic landmarks and accurate outside-in drilling of the femoral tunnel. The retrograde drilling technique used to create the femoral socket, drilling of the tibial tunnel, and tightening of the ACL graft using the TightRope RT button are also shown.