Femoral Graft Bending Angle and Graft Maturity are Affected by Knee Flexion Angle during Femoral Tunnel Creation using Transtibial Technique in ACL Reconstruction
Author(s):
Tomihara T. (Japan)
,
Tomihara T. (Japan)
Affiliations:
Taniuchi M.
,
Taniuchi M.
Affiliations:
Takigami J.
,
Takigami J.
Affiliations:
Shimada N.
Shimada N.
Affiliations:
ESSKA Academy. Tomihara T. 05/09/18; 209486; P06-256
Tomohiro Tomihara
Tomohiro Tomihara
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Abstract
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Objectives: In anterior cruciate ligament (ACL) reconstruction, steep femoral graft bending angle (GBA) between femoral tunnel axis and graft at the femoral tunnel aperture would increase local strain to the graft and affect graft healing status. Previous studies indicated that deep flexion angle during femoral tunnel creation in transtibial technique would result in steep GBA. Conversely, shallow knee flexion would make femoral tunnel posterior wall blow-out. The purpose of this study is to determine the adequate knee flexion angle for femoral tunnel creation in transtibial technique to reduce GBA in anatomical ACL reconstruction. Additionally, graft healing status was assessed by graft signal intensity on post-operative MRI.

Methods: Forty-eight patients who underwent ACL reconstruction using bone patellar-tendon bone autograft in transtibial technique, CT scan at one week, and MRI at six months postoperatively were included in this study. Knee flexion angle was measured by intra-operative lateral radiograph. A femoral guidewire insertion into aimed femoral position at the medial wall of the femoral lateral condyle was started at about 75 degrees of knee flexion. When the tip of the guidewire was blown out into femoral posterior wall, the guidewire was inserted again after increasing knee flexion angle. Femoral and tibial tunnel position was measured using quadrant methods on 3-D CT images. In addition, GBA was measured on reconstructed 2-D CT images.
Intra-articular graft signal intensity in three regions (proximal, middle, and distal regions) of interest was measured on coronal oblique T2-weighted images using 3.0-T MRI scanner. The signal/noise quotient (SNQ) was calculated based on the signal intensity of the PCL. Patients were divided into two groups depending on knee flexion angle at femoral tunnel creation.

Results: Femoral tunnel could be created at less than 80 degrees of knee flexion in 32 patients (21 men and 11 women) (group A) and at 80 degrees or more in 16 patients (7 men and 9 women) (group B). Average knee flexion angle was 77.2 degrees (74.2-79.7) in group A and 83.6 degrees (80.0-88.1) in group B, respectively. There was no significant difference in the femoral and tibial tunnel position between group A and B. A mean GBA was 50.9 degrees in group A and 54.2 degrees in group B, respectively (p<0.05). A mean SNQ value at the proximal region (2.02 vs 2.49) in group B was higher than that in group A, while a mean SNQ value at the middle (1.23 vs 1.20) and distal (0.97 vs 0.91) regions in group A was similar to that in group B.

Conclusions: Anatomical femoral tunnel could be created at less than 80 degrees of knee flexion in two third of patients. This shallow flexion angle led to gentler GBA and lesser intra-articular graft signal intensity at the proximal region compared to 80 degrees or more of knee flexion. Therefore, femoral tunnel creation in transtibial technique should be started at between 75 and 80 degrees of knee flexion.

Keywords:
Anterior cruciate ligament, Graft bending angle, Graft maturity, Transtibial technique
Objectives: In anterior cruciate ligament (ACL) reconstruction, steep femoral graft bending angle (GBA) between femoral tunnel axis and graft at the femoral tunnel aperture would increase local strain to the graft and affect graft healing status. Previous studies indicated that deep flexion angle during femoral tunnel creation in transtibial technique would result in steep GBA. Conversely, shallow knee flexion would make femoral tunnel posterior wall blow-out. The purpose of this study is to determine the adequate knee flexion angle for femoral tunnel creation in transtibial technique to reduce GBA in anatomical ACL reconstruction. Additionally, graft healing status was assessed by graft signal intensity on post-operative MRI.

Methods: Forty-eight patients who underwent ACL reconstruction using bone patellar-tendon bone autograft in transtibial technique, CT scan at one week, and MRI at six months postoperatively were included in this study. Knee flexion angle was measured by intra-operative lateral radiograph. A femoral guidewire insertion into aimed femoral position at the medial wall of the femoral lateral condyle was started at about 75 degrees of knee flexion. When the tip of the guidewire was blown out into femoral posterior wall, the guidewire was inserted again after increasing knee flexion angle. Femoral and tibial tunnel position was measured using quadrant methods on 3-D CT images. In addition, GBA was measured on reconstructed 2-D CT images.
Intra-articular graft signal intensity in three regions (proximal, middle, and distal regions) of interest was measured on coronal oblique T2-weighted images using 3.0-T MRI scanner. The signal/noise quotient (SNQ) was calculated based on the signal intensity of the PCL. Patients were divided into two groups depending on knee flexion angle at femoral tunnel creation.

Results: Femoral tunnel could be created at less than 80 degrees of knee flexion in 32 patients (21 men and 11 women) (group A) and at 80 degrees or more in 16 patients (7 men and 9 women) (group B). Average knee flexion angle was 77.2 degrees (74.2-79.7) in group A and 83.6 degrees (80.0-88.1) in group B, respectively. There was no significant difference in the femoral and tibial tunnel position between group A and B. A mean GBA was 50.9 degrees in group A and 54.2 degrees in group B, respectively (p<0.05). A mean SNQ value at the proximal region (2.02 vs 2.49) in group B was higher than that in group A, while a mean SNQ value at the middle (1.23 vs 1.20) and distal (0.97 vs 0.91) regions in group A was similar to that in group B.

Conclusions: Anatomical femoral tunnel could be created at less than 80 degrees of knee flexion in two third of patients. This shallow flexion angle led to gentler GBA and lesser intra-articular graft signal intensity at the proximal region compared to 80 degrees or more of knee flexion. Therefore, femoral tunnel creation in transtibial technique should be started at between 75 and 80 degrees of knee flexion.

Keywords:
Anterior cruciate ligament, Graft bending angle, Graft maturity, Transtibial technique
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