Comments on the Article ‘Radiological Evaluation of the Femoral Tunnel Positioning in Anterior Cruciate Ligament Reconstruction’

Dear Editor,

The debate on the ideal positioning of femoral tunnels is an important topic of research in recent times. In this regard, the article by Peres et al is very important, because it evaluates and compares the inclination angles and femoral tunnel lengths between two commonly used techniques of anterior cruciate ligament (ACL) reconstruction.¹ We found that they have made a very good comparison between the transtibial and the transportal techniques. They have used the coronal plane inclination angle and the femoral tunnel length as variables for comparison between the two techniques.

In this study, the authors have compared the femoral tunnel lengths in the coronal plane using a computed tomography (CT) based evaluation. This method of estimation of femoral length has serious flaws, as they are measuring the length in the coronal plane, while the tunnel is drilled at an angle starting posteriorly and ending anteriorly. This has been explained by providing examples from cases performed in our institute.

Fig. 1 shows two coronal images of the same patient, in whom the femoral tunnel has been drilled using transportal technique. The CT scan was performed 1 week after the surgery. The coronal cuts are taken at different depths from the anterior femoral articular surface. As can be clearly seen, there can be a significant difference in the measurement of femoral tunnel lengths at different positions from the anterior surface. The reason for this difference is that the tunnel is not drilled parallel to the coronal axis. Rather, it is drilled at an anteroposterior angle, with the entry point being more posterior than the exit point.

Fig. 1
Coronal computed tomography images of the same patient showing two different femoral tunnel lengths at two different positions.

We recommend that the femoral tunnel length can be best measured in axial plane CT scans using curved reformats, as shown in Fig. 2. Curved reformatting allows us to visualize the entire tunnel in its length and provides accurate length. A similar method of calculating the femoral tunnel length has been used by Sim et al in their article comparing two techniques of femoral tunnel preparation.²

Fig. 2
Axial curved reformatted computed tomography image visualizing the entire femoral tunnel and measuring the exact femoral tunnel length.

Excluding this error, we find that the article provides valuable information about the femoral tunnel placement in both techniques.

References

• ¹
  Peres LR, Teixeira MS, Scalizi Júnior C, Akl Filho W. Radiological evaluation of the femoral tunnel positioning in anterior cruciate ligament reconstruction. Rev Bras Ortop 2018;53(04):397-403
• ²
  Sim JA, Kim JM, Lee S, Song EK, Seon JK. No difference in graft healing or clinical outcome between trans-portal and outside-in techniques after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2018;26(08):2338-2344

Publication Dates

• Publication in this collection
  05 Apr 2021
• Date of issue
  Jan-Feb 2021

History

• Received
  12 Jan 2019
• Accepted
  19 Feb 2019