17:43:59 – Flexible Reamers for Anterior Cruciate Ligament Reconstruction

Introduction

An anterior cruciate ligament (ACL) reconstruction will best restore physiologic stability to the knee when both the femoral and tibial attachment sites of the new ligament are within the anatomic footprints of the native ACL. This is described as an “anatomic” ACL reconstruction. There is still controversy regarding where the graft should be placed within the femoral and tibial footprints, but there is consensus that the tunnels for the graft should be within the footprints. A challenge exists particularly on the femoral side to first identify the location for an anatomic tunnel and to second technically utilize a drilling method to create the tunnel.

The first commonly used drilling technique was to drill through a lateral incision starting on the lateral cortex of the femoral condyle. This method, known as outside-in drilling, provides the opportunity to place a tunnel within the femoral footprint. However, a lateral incision will add time and morbidity to a procedure, and a drill guide is required, thus adding a technical challenge. New outside-in drilling technologies have been introduced, but their use continues to be a technical challenge, particularly because of uncertainty regarding where the pin will enter the notch.

The limitations of outside-in drilling led to the use of transtibial drilling, whereby the femoral tunnel was drilled through the tibial tunnel. This method has been popular, but the technique has a tendency to place nonanatomic femoral tunnels. Either the tibial tunnel or the femoral tunnel will necessarily be compromised if anatomic tunnels are sought with this method.

As an alternative, the method of drilling through the anteromedial portal with traditional rigid instruments has been explored. This enables a precise anatomic guide pin placement based on well-visualized anatomic landmarks. However, the method requires a challenging hyperflexion of the knee of at least 125 degrees throughout guide pin placement and reaming. The position of hyperflexion distorts the arthroscopic view of intra-articular anatomy, and it is difficult to maintain hyperflexion throughout guidewire placement and reaming. If hyperflexion is not used, the femoral tunnel will be short, and there may be a violation of the posterior femoral cortex.

In order to attain the goal of anatomic femoral tunnel placement and to avoid the technical challenges and limitations of outside-in drilling, transtibial drilling, and anteromedial drilling with rigid instruments, flexible instruments have evolved over the years. This flexible technology allows anatomic femoral tunnel placements without hyperflexion and even knee motion during reaming.

Technique

Patient Positioning

The use of a flexible reaming system permits the knee to be placed in virtually any degree of flexion that provides a view of the intercondylar notch. The knee does not need to be held rigidly for guide pin placement and reaming. Therefore the lower extremity can be positioned either with a conventional leg holder and the foot of the bed flexed, or with the foot of the bed extended and a lateral post buttressing the thigh and a foot post holding the knee in approximately 90 degrees flexion ( Fig. 49.1 ). This latter position allows a consistent view of the intercondylar notch and consistent identification of landmarks for anatomic tunnel placement.

The photograph shows patient on operating table with knee flexed 90 degrees, stabilized by padded posts to allow secure positioning and clear access for femoral tunnel placement in ACL surgery. The photograph shows patient lies on an operating table with the leg positioned in 90 degrees of knee flexion, stabilized by padded cylindrical posts placed on either side of the thigh and lower leg. The setup secures the knee for surgical access, aiding visualization and identification of intra-articular anatomy during femoral tunnel placement in anterior cruciate ligament reconstruction. — Fig. 49.1

Locating the Femoral Footprint

A standard lateral arthroscopic viewing portal is used. The medial working portal is placed slightly above the medial meniscus and only moderately moved in the medial direction to avoid injury to the medial condyle during reaming. The flexible reaming system obviates the need to place the medial working portal far medial. Meniscal and chondral injuries are addressed prior to locating the femoral tunnel site.

Viewing the notch from the lateral portal to assess the ACL insertional anatomy is a challenge. The lateral portal view allows a good evaluation of height within the notch but little perspective on depth within the notch. The medial portal provides an excellent view of the anatomy ( Fig. 49.2 ), but the medial portal is a working portal and generally only used for viewing when verifying an anatomic location. Thus the site for a femoral tunnel placement is identified when viewing from a lateral portal, which has limited perspective. Multiple strategies have evolved to address this challenge. Generally these have relied upon either identifying the ACL remnants, identifying the intercondylar ridge, or using a clockface analogy. The author has found identification of ACL remnants and the intercondylar ridge to be inconsistent, and the use of a clockface analogy has been inexact.

The arthroscopic view shows femoral notch with probe, faint lateral intercondylar ridge, and ACL remnants, aiding height and depth assessment for tunnel placement. The arthroscopic view from the medial portal shows the interior of the femoral notch, with a surgical probe pointing toward bony surfaces. The lateral intercondylar ridge and remnants of the anterior cruciate ligament are faintly visible, though difficult to distinguish. The perspective provides visual assessment of notch height and depth, aiding orientation for accurate femoral tunnel placement during reconstruction surgery. — Fig. 49.2

The alternative is to use measurements from known anatomy on the lateral wall. Using this method, the center of the ACL can be located when the knee is placed in 90 degrees flexion with measurements made from the low point of the lateral wall. From the low point, measuring up the lateral wall 8.5 mm and then moving 2 mm deep will locate a point well within the ACL footprint and within 4 mm of the ACL center in over 90% of knees ( Fig. 49.3 ). Alternatively a 7-mm offset aimer can be introduced from the medial portal and elevated 8.5 mm, and this will locate a point within the ACL footprint with equal accuracy ( Fig. 49.4 ).

The photograph shows the ACL footprint, yellow line for measurement path, and blue dots marking ACL, anteromedial, and posterolateral bundle centers. The photograph shows the femoral footprint outlined with purple ink markings. The low point of the lateral wall is identified, and a yellow L-shaped line shows a measurement path-8.5 mm upward along the lateral wall and 2.0 mm deeper to locate the anterior cruciate ligament center. Blue ink dots mark the centers of the ACL, anteromedial bundle, and posterolateral bundle, providing anatomical reference points for tunnel placement in reconstruction procedures. — Fig. 49.3

The arthroscopic view shows aimer through medial portal, 7 mm offset and 8.5 mm high from posterior condyle, with black dot marking ACL center for femoral tunnel placement. The arthroscopic view shows a surgical aimer introduced through the medial portal of a knee, positioned with its flange posterior to the condyle. The aimer is aligned to a point 8.5 mm above and 7 mm offset from the posterior condylar surface with the knee flexed at 90 degrees. A black dot marks the precise center of the anterior cruciate ligament, providing a visual landmark for accurate femoral tunnel placement during reconstruction. — Fig. 49.4

Tunnel Creation

A minimal notchplasty (2 mm) of the lateral wall will facilitate visualization, and a débridement of soft tissue from the lateral wall will also help locate the ACL center. After identifying the point for the femoral tunnel, an awl is used through the medial portal to create a pilot hole for reaming ( Fig. 49.5 ). It is helpful to verify the position of the pilot hole by visualization through the medial portal. The pilot hole should be approximately 8.5 mm (range 8.0–9.5 mm) up the lateral wall and slightly deep to the midpoint between the front and back of the notch ( Fig. 49.6 ).