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.
