Surgical Adjustment of the Guide Pin to Perform a Correct Tibial Tunnel in Anatomical Anterior Cruciate Ligament Single-Bundle Reconstruction

Surgical Adjustment of the Guide Pin to Perform a Correct Tibial Tunnel in Anatomical Anterior Cruciate Ligament Single-Bundle Reconstruction

Bharath S. Kumar, M.D., Renato Andrade, B.Sc., Ana Leal, M.Sc., André Sarmento, M.D., Hélder Pereira, M.D., Nuno Sevivas, M.D., João Espregueira-Mendes, M.D., Ph.D

Abstract

Anatomical positioning of the graft in anterior cruciate ligament reconstruction is important to restore normal knee kinematics and prevent early joint degeneration. Inadequate position of a first attempt to place the guide pin within the center of the tibial footprint may occur. Therefore, its adjustment is important to achieve the anatomical positioning of the graft within the tibial footprint. When the guide pin exits eccentrically in an inadequate position, it is possible to correct it to the center of the footprint. A small tunnel with a 4.5-mm reamer is made and the guide pin is shifted to the center of the footprint. The center of the tunnel can be corrected until 50% and in all direction in relation to the initial drilled tunnel, without additional associated morbidity. Once the correct position of the center is achieved, the guide pin is fixed in the femoral notch roof to guarantee the accurate correction of the axis, without toggling of the guide pin inside the tunnel and metal dusting. The final tunnel is then drilled with the same size of the graft. With this technique it is possible to adjust an eccentrically misplaced guide pin to the center of the footprint without additional morbidity.

Arthroscopic anterior cruciate ligament (ACL) reconstruction has become the standard care for the ACL-deficient knee. Several techniques have been described to be capable of reconstructing the ACL to improve the knee stability, restore joint kinematics, normal anatomy and function, and prevent early joint degeneration in the ACL-deficient knee.1 Although no consensus on the best technique, including indication, tunnel placement, graft selection, and fixation method, has been reached so far,1, 2, 3 the “anatomic reconstruction” philosophy and remnant preserving techniques have been very popular, which may allow a more accurate ligament repair and further augment the graft biology.3

Presently, ACL reconstruction techniques have advanced to the extent that the native anatomy of the ACL is capable of being closely replicated. Therefore, both tibial and femoral tunnels should be placed in the native ACL footprint, independently of the technique used, to restore the normal anatomy of the ACL.4, 5 Hence, the accurate positioning of the tunnel plays a crucial role in the success of the ACL reconstruction.

There have been concerns regarding the transtibial tunneling technique due to the limitations imposed by the tibial tunnel positioning.6, 7, 8 In this sense, the transtibial tunnel technique leads to a vertical graft placement and subsequently residual rotational laxity, as a result of an anteriorly and superiorly femoral tunnel position in relation to the native ACL femoral footprint.7 Hence, there has been a pursuit for more anatomic ACL reconstruction, with the tunnels placed at the center of the native ACL footprints. In this sense, the anteromedial tunneling technique may play a role once it allows the anatomic tunnel placement and greater coronal obliquity of the femoral tunnel with access to the anteromedial and posterolateral footprints.9, 10 Moreover, this tunneling technique reduces the residual sagittal and rotation laxity; reduces the graft-bending stress at the opening of the femoral; allows the parallel placement of the interference screw, an all-inside technique and augmentation procedures for remnant fibers; and provides greater short-term range of motion and faster return to competition.9, 11, 12 In addition, incorrect pin placement may require additional corrective intraoperative steps, often inefficient and difficult to perform.13

Because the misplacement of the guide pin may occur, its correction to the center of the footprint plays an important role in the anatomical ACL reconstruction. In a previously described surgical technique to adjust the guide pin within the ACL tibial footprint in single-bundle ACL reconstruction,14 the guide pin is held by a clamp, which may result in toggling of the guide pin within the tunnel, thereby leading to metal dusting while reaming.

This technical report describes a surgical technique for single-bundle ACL reconstruction that can accurately adjust the guide pin eccentrically placed in the tibial footprint by serial reaming, starting with a 4.5-mm reamer.

Surgical Technique

Anatomical single-bundle ACL reconstruction starts by examining the knee under general anesthesia to evaluate the degree of instability, with the patient in a standard supine position. Meniscal and articular cartilage lesions are evaluated to assess the need for additional surgical procedures. After, the ACL deficiency is arthroscopically confirmed and the footprint length is identified and accordingly measured (Fig 1). The graft of choice, bone–patellar tendon–bone graft or hamstring, is harvested and prepared according the required size and diameter. With the knee positioned in full flexion, the femoral tunnel is drilled from a standard or accessory anteromedial portal.
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Fig 1

Identification and measurement of the tibial anterior cruciate ligament footprint—arthroscopic view (A) and phantom representation (B). The dimension marker shows the length of the footprint.

 

The tibial tunnel is made using a tibial drill guide aimer (Acufex Director Drill Guide, Smith & Nephew, Andover, MA), inserted at 55° from the standard anteromedial portal. After, a 2.4-mm guide pin is drilled from the anteromedial aspect of proximal tibia, passing through the tibial footprint (Video 1). The accuracy of its position is then confirmed through the anterolateral viewing portal. If the pin has exited exactly in the middle of the tibial footprint, the tibial tunnel is made with a reamer with the same size as the graft.

On the other hand, if there is an eccentric exit of the drill pin in the tibial footprint (Fig 2), the tibial tunnel is drilled with a 4.5-mm reamer to make a smaller tunnel (Fig 3). Afterward, the guide pin is adjusted within the tunnel so that it lies in the center of the tibial footprint (Fig 4). This adjustment can be made in the four poles (north, south, east, and west) in relation to the center of the first drilled tunnel (Fig 5). In this sense, different reamer sizes can be used to approximate to the adequate required length (Table 1). Next, the guide pin is fixed to the femur notch roof (Fig 6). This can be achieved by drilling it further into the notch roof. After the guide pin is locked, the axis can be accurately corrected in all directions from the initial tunnel.

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Fig 2

Inaccurate eccentric exit of the guide pin—arthroscopic view (A) and phantom representation (B). The arrows indicate the eccentric exit direction of the guide pin.

 

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Fig 3

A small tunnel is made with a 4.5-mm reamer—arthroscopic view (A) and phantom representation (B). The smaller dotted circle indicates the new 4.5-mm tunnel in relation to the footprint size (larger circle).

 

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Fig 4

Adjustment of the guide pin to the correct position of the center of the tibial footprint—arthroscopic view (A) and phantom representation (B).

 

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Fig 5

Correction of the guide pin within the north, south, west, and east poles.

 

Table 1Reamer Sizes Used and Approximate Adjusted Length
Reamer Used for First TunnelPossible Length CorrectedFinal Tunnel
4.5-mm reamer 2.25 mm to N/S/W/E 9 mm
5-mm reamer 2.5 mm to N/S/W/E 10 mm
5.5-mm reamer 2.75 mm to N/S/W/E 11 mm
6-mm reamer 3 mm to N/S/W/E 12 mm

N/S/W/E, north, south, west, and east poles in relation to the guide pin.

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Fig 6

Fixation of the guide pin to the femoral roof top—arthroscopic view (A) and phantom representation (B). The arrows indicate the fixation of the guide pin.

 

In case the guide pin is still not in the center of the tibial footprint, the tunnel can be reamed with the next available smallest reamer (6 mm) and the guide pin is brought to the center of the footprint. Lastly, the final tibial tunnel is made with a reamer the same size as the graft, with the guide pin in the center of the footprint (Fig 7).

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Fig 7

Overdrill to achieve the final tunnel in the anatomic position—arthroscopic view (A) and phantom representation (B). The circle indicates the final tunnel with the same size as the tibial footprint.

 

To fix the graft, different methods of fixation can be used on both sides of the graft. In particular, an interference screw as a fixation method was used for this technique.

Through this technique it is possible to gradually and accurately shift the eccentrically misplaced guide pin to the center of the tibial footprint, without the need for redrilling (Fig 8). The pearls and pitfalls of this technique are described in Table 2.

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Fig 8

Representation of adjusting the eccentrically placed guide pin in the anterior cruciate ligament tibial footprint. Incorrect position of the guide pin (A), small tunnel made with a 4.5-mm reamer (B), adjustment of the guide pin to the center of the footprint (C), and overdrill to achieve the final tunnel in the anatomic position (D).

 

Table 2Pearls and Pitfalls of the Guide Pin Adjustment
PearlsPitfalls
Anatomical reconstruction of the ACL can restore the normal kinematics by placing the graft in footprints. A significant misplacement of the pin may require a classic intraoperative corrective step.
The guide pin fixation on the roof of the notch guarantees the correct axis to drill the tibial tunnel.  
Correction of the final tunnel center is possible until 2.25 mm (within the full 360° directions), without additional morbidity.  
If the guide pin is misplaced at the first attempt, it can be corrected up to 50% (2.25 mm repositioning, using a reamer of 4.5 mm).  
The guide pin should be, at least, 2 mm inside the ACL tibial footprint limits, with a length of 9-11 mm, to adjust to the center.  

ACL, anterior cruciate ligament.

Discussion

 

One of the keys to success in ACL reconstruction is to anatomically place the graft within the anatomical ACL footprints.

In recent years, the focus on the ACL reconstruction has turned to the isometric graft placement, with the center of the tibial tunnel placed 7 mm anteriorly to the posterior cruciate ligament, as also aligned with the posterior border of the anterior horn of the lateral meniscus. In the past few years, the focus has shifted toward the anatomic reconstruction with greater emphasis on tunnel position in the center of the native ACL footprint, once it further restores sagittal and rotational stability of the ACL-deficient knee.3, 5, 9 Hence, surgeons who perform anatomical reconstruction must accurately identify where the centrum of the tibial footprint is, so they can enhance their surgical outcomes. In this sense, Hwang et al.5 performed a systematic review to characterize the anatomic centrum of the ACL tibial footprint, from which they concluded that the anatomic centrum of the ACL tibial footprint is 15 mm anterior to the posterior cruciate ligament and two-fifths the medial to lateral width of the interspinous distance. Nevertheless, using the remnant of the ACL allows a better anatomic placement.

Beginning with a 4.5-mm reamer and a serial reaming with the smallest available reamer up to 3 to 4 mm, the adjustment of the guide pin can be performed within a footprint diameter of 9 to 11 mm. For instance, using a 4.5-mm reamer it is possible to correct a misplacement of the center of the final tunnel in all directions until 2.25 mm (50%) on the first placement of the guide pin (Table 1). It is possible to start with the smaller reamers and gradually increase its size. This can be performed until the required size to adjust the center of the tunnel to the center of the tibial footprint is achieved. Thus, this technique is able to correct the guide pin misplacement without any additional morbidity associated by increasing the size of the reamers, once the final tunnel encompasses the initial drilled tunnel. However, to avoid potential-associated morbidity, this adjustment is limited to half of the diameter of the first drill tunnel.

The advantage of locking the guide pin to the femur notch roof is that it avoids toggling of the guide pin within the tunnel while reaming and metal dusting, which may occur when it is held with a straight clam (Table 3). In addition, once the guide pin is fixed into the femoral roof, it is possible to accurately correct the axis to correctly drill the final tibial tunnel (Table 2).

Table 3Advantages, Risks, and Limitations of the Guide Pin Adjustment
AdvantagesRisks and Limitations
This technique is able to eccentrically place the tibial guide pin into the center of the tibial footprint without the need for additional redrilling.

By locking the guide pin into the femoral notch roof, toggling of the guide pin within the tibial tunnel and metal dusting can be prevented.

This technique is able to correct 50% of a misplacement of the guide pin at the first attempt positioning.
The guide pin correction is limited to 50% of the diameter of the first drilled tunnel.

Difficult to apply in double-bundle ACL reconstruction.

If you do not use a drill with half or less of the diameter of the final tunnel to do the first drill, the procedure may turn out to be eccentric.

ACL, anterior cruciate ligament.

Although the technique has limitations, it is agreed on that the pin should be, or at least close to, 2 mm inside the ACL tibial footprint limits and 9 to 11 mm in length with the goal of adjustment toward the center.

Using the above presented technique, the anatomical placement of the graft is accomplished, restoring the normal kinematics and providing increased knee stability, without the need for additional redrilling.

Acknowledgment

 

The authors would like to sincerely acknowledge Dr. Alberto Monteiro and Dr. Rui Rocha for their support in this study, particularly their substantial contributions to the conception and design of this work.