Medial Portal Placement for ACL Femoral Tunnel Drilling With an Over-the-Top Guide: Concepts and Technique

Video Transcript

This video will highlight the concepts and technique associated with proper medial portal placement for anterior cruciate ligament (ACL) femoral tunnel drilling when using an over-the-top guide and rigid low-profile reamer. Disclosures are listed here, none relevant to this video.

Background

The rate of graft failure after ACL reconstruction ranges from 3% to 22% in the literature.^6,7 Femoral tunnel malposition is cited as the most common technical error related to graft failure. ³ Use of an over-the-top guide from the medial portal is an established technique for creating a femoral tunnel within the anatomic footprint of the native ACL. ² Therefore, proper placement of the medial portal is critical for success when using this technique. With that in mind, the purpose of our technique video is to discuss and highlight the concepts related to proper positioning of the medial portal. We will show how tunnel trajectory can be affected by portal placement and why hyperflexion of the knee is so important when using this technique. Finally, we will demonstrate our technique for ACL reconstruction using a single medial portal for both instrumentation and femoral tunnel drilling.

Indications

Here is a right knee cadaveric specimen, highlighting 3 possible options for medial portal placement: a more lateral portal that is close to the medial edge of the patellar tendon; a far medial portal, often described as an accessory portal for femoral tunnel drilling; and, finally, our preferred portal placement, which is typically 1.5 to 2 cm medial to the patellar tendon edge. Our technique for marking this portal involves flexion and extension of the knee to palpate the joint line. We like to feel for the interaction between the medial femoral condyle and tibial plateau and mark a spot on the joint line just lateral to this interaction.

As demonstrated here, it becomes clear how altering the location of the medial portal in the coronal plane will affect tunnel trajectory. This is a left knee saw bone specimen in 90° of flexion viewed superiorly. Placement of the medial portal close to the patellar tendon will result in a longer, more vertical femoral tunnel with an oval aperture. As the portal is moved medially, the tunnel will become shorter, be less vertical, and have a more circular aperture.

Therefore, establishing the medial portal under direct visualization is helpful to confirm appropriate positioning for femoral tunnel drilling. The spinal needle should be used as a guide to help predict the path of drilling. A portal placed too close to the medial edge of the patellar tendon will protect the medial femoral condyle from injury, but it will result in a more vertical tunnel that risks rotational instability. Conversely, a portal that is too far medial, as shown here, will allow for better tunnel trajectory with a less vertical tunnel better for rotational stability, but it will run the risk of iatrogenic damage to the medial femoral condyle. We find that with the previously demonstrated marking technique, our spinal needle is usually in a good position for safely avoiding damage to the medial femoral condyle during drilling while enabling a more perpendicular angle into the femoral footprint. The other key element is ensuring the portal is low, just above the medial meniscus. Compared to flexible reaming, a previous study by Moran et al ⁸ demonstrated that the apertures of the femoral tunnels do not differ between rigid reaming and flexible reaming, although flexible reaming leads to slightly longer tunnels that are more anteverted. Furthermore, flexible reaming does not rely on hyperflexion of the knee.

The purpose of a low medial portal and knee hyperflexion when drilling for the femoral tunnel with an over-the-top guide is demonstrated here on this left knee sawbone specimen. With the knee at 90° of flexion, we can see how the tunnel trajectory is limited in the sagittal plane by the tibia, which results in a tunnel with a smaller degree of anterior angulation that is at greater risk for posterior wall blowout. ¹ As the flexion angle of the knee increases, so does the anterior angulation of the tunnel, which helps protect from posterior wall blowout.

Technique Description

With those concepts in mind, we will now demonstrate our preferred technique for femoral tunnel drilling from the medial portal with an over-the-top guide and a rigid, low-profile reamer. The patient is a 21-year-old woman who sustained a right knee, noncontact injury while playing softball. Examination was consistent with an ACL rupture and medial meniscus tear. A magnetic resonance imaging scan was obtained confirming complete rupture of the ACL and a peripheral medial meniscus tear. The patient was therefore indicated for an ACL reconstruction with a bone–patella tendon–bone (BTB) autograft and a medial meniscus repair. Our setup includes the patient supine, with the operative side in a leg holder with the leg of the table dropped for the initial portions of the case. Markings for our standard portals are shown here on the patient’s right knee, which include our midline incision for the patellar BTB harvest in this case. As previously demonstrated, we mark our medial portal with flexion and extension of the knee, with the surgeon’s thumb on the medial joint line to feel for the interaction of the medial femoral condyle and tibial plateau.

After graft harvest, a standard anterolateral portal is made for viewing, and we enter the medial tibiofemoral compartment to visualize the establishment of our medial portal. We prefer to make this with the knee in slight flexion with a valgus moment to open up the compartment. A spinal needle is introduced through our previously marked portal. The trajectory of the spinal needle can be evaluated at this time. As shown here, this position will safely avoid the medial femoral condyle while allowing access to the femoral footprint of the ACL with the over-the-top guide. In addition, we confirm the low position of our portal just above the medial meniscus. This enables easy access for instrumentation of the medial and lateral compartments, as well as improvement in our femoral tunnel trajectory in the sagittal plane, as previously noted.

After completing a medial meniscus repair, the femoral footprint of the ACL is debrided, ensuring proper visualization of the back wall. The anatomic footprint of the native ACL is then identified using the lateral intercondylar ridge and bifurcate ridge as landmarks.^4,5 Here, the red arrow designates our preferred location of where we want the over-the-top guide to hook onto the back wall.

After preparation of the tibial tunnel, the leg of the table is raised with a new drape placed to maintain sterility, and the strap of the leg holder is undone to enable hyperflexion for femoral drilling. The over-the-top guide is then introduced and positioned with the knee in 90° of flexion. With our target location in mind, the guide is hooked onto the back wall, and the leg is slowly hyperflexed to 120°. As stated previously, this helps create a more anteriorly direct tunnel in the sagittal plane and also enables the guidewire to be less vertical and more perpendicular to the footprint. A guidewire is now introduced and advanced out the far cortex and skin. If the pin exits the skin anterior to the halfway mark of the thigh, that is usually a good indicator that the tunnel will be safe from posterior wall blowout. The guide is removed, and the position of the wire is confirmed. The low-profile reamer is introduced and drilled to a selected depth based on the graft length. The tunnel position is then confirmed to ensure an adequate back wall with a contained tunnel. The BTB graft is then passed, as seen here, and secured into place with interference screw fixation. Note that the knee is hyperflexed for placement of the screw to ensure there is no divergence of the screw with the femoral tunnel. Final tensioning on the tibial side is then performed with the knee in 20° of flexion with a slight posterior drawer. Final graft placement is shown here.

Results

Postoperatively, this patient is toe-touch weightbearing in a DonJoy X-Rom (DJO Global) postoperative brace locked in extension. The weightbearing restriction in this case is due to the concomitant medial meniscus repair. The brace is worn for 4 weeks, and the patient is on crutches for 3 weeks. Our standard protocol for isolated ACL reconstruction is weightbearing as tolerated in the same brace for 3 weeks, with the patient on crutches for 2 weeks. In both scenarios, therapy is initiated 5 to 7 days postoperatively with an early focus on range of motion and quad strength. The patient will progress through a standard ACL reconstruction rehab protocol over the next 7 to 9 months with the goal of returning to sport around 9 months.

Discussion/Conclusion

In summary, proper placement of the medial portal is critical when utilizing this technique for femoral tunnel drilling. When done correctly, it provides a consistent and reproducible tunnel position within the anatomic footprint of the native ACL. Remember that the placement of the medial portal can be considered a spectrum, with different risks and benefits based on its location. While we only demonstrated our preferred technique, the concepts illustrated can be applied to any method used for femoral tunnel drilling. Thank you.