Abstract
Purpose
The purpose of this study was to evaluate the reproducibility of the native anterior cruciate ligament (ACL) mid-substance cross sectional area in anatomic single-bundle ACL reconstruction.
Methods
Fifty-eight subjects who were performed anatomic single-bundle ACL reconstruction were included. Cross section size of the ACL graft was calculated from the graft diameter during surgery. Computed tomography (CT) of the knee was performed pre-operatively. Following Iriuchishima's report, native ACL size was estimated from the axial CT image of intercondylar notch area of femur at the most distal level of Blumensaat's line (In the report, native ACL size was equal to 14% of the intercondylar notch area of femur). The measured ACL graft cross-sectional size and estimated native ACL size were compared and correlation was evaluated.
Results
Measured ACL graft cross-sectional size was 49 ± 14 mm2. Measured intercondylar notch area of femur at the most distal level of Blumensaat's line was 372 ± 91.6 mm2, and estimated native ACL size was 53 ± 12.5 mm2. Measured ACL graft cross-section and estimated native ACL showed no significant size difference. Measured ACL graft cross-section and estimated native ACL had no significant size correlation.
Conclusion
Native ACL cross-sectional size was reproduced in anatomic single-bundle ACL reconstruction. However, as measured ACL graft and estimated native ACL showed no size correlation, it is possible that size of native ACL might not be reproduced. Such cases would be susceptible to the risk of graft impingement or knee instability.
Keywords: Anterior cruciate ligament, Anatomy, Mid-substance, ACL reconstruction
1. Introduction
In recent 20 years, Anterior cruciate ligament (ACL) has been reconstructed primarily as an anatomic procedure.1, 2, 3, 4 In comparison with isometric ACL reconstruction, it has been reported that better knee stability and function can be restored in anatomic ACL reconstruction.1,2,5 ACL reconstruction employs ACL graft transplantation, and ACL graft mid-substance morphology is the most critical element in the reproduction of native ACL anatomy.5, 6, 7 Reproducing native ACL mid-substance morphology is relatively difficult when performed during the surgery itself because the ACL does not exist in the injured knee. One method of determining native ACL size and morphology is through magnetic resonance imaging (MRI) of the contra-lateral ACL, if the ACL exists on the contra-lateral side6. However, MRI evaluation of the healthy knee is not common due to medical cost and the physical burden on the patient. Another method of determining native ACL size and morphology in ACL injured subjects is through the evaluation of knee bony morphology. Recently, Iriuchishima et al. reported significant correlation between size of ACL cross section and intercondylar notch area of femur at the level of most distal in Blumensaat's line.3 They also reported that native ACL cross-section size could be estimated from the measurement of the intercondylar notch area of femur at a proportion of 14%.
In many cases of ACL surgery with autograft, the ACL size which reconstructed in surgery is selected by graft size which can be harvested, and not by the native ACL size.7 Therefore, the clinical question remains as to whether the native ACL size is reproduced or not in such cases.
The aim of this study was to evaluate the reproducibility of the cross sectional area of native ACL mid-substance in anatomic single bundle (SB) ACL reconstruction with autograft by comparing the ACL graft size in surgery and the estimated native ACL size. It was hypothesized that the reconstructed ACL graft size would show difference between the estimated native ACL size. The clinical relevance of this study was that better understanding of the reproducibility of native ACL size in ACL surgery would allow surgeons to perform greatly accurate anatomic ACL reconstruction.
2. Materials and methods
2.1. Subjects
The ethics committee of institution approval had been obtained. Fifty-eight subjects (31 female and 27 male: average age 29 ± 12) who were performed anatomic SB ACL reconstruction were included. Inclusion criteria was initial ACL tear without bone injury. Exclusion criteria were, previous knee surgical history in both the ipsilateral and contralateral side, formation of bony spur, and grade 1 or more severe knee osteoarthritis in Kellgren-Lawrence classification.
2.2. ACL surgery
A single surgeon performed ACL surgery. Anatomic SB ACL reconstruction was performed using a hamstring autograft. At the beginning, harvest of a semitendinosus tendon (ST) was performed. When the harvested ST length was longer than 24 cm, a quadrable ACL graft was prepared using only the ST. When the harvested ST length was shorter than 24 cm, a gracilis tendon was harvested and the double folded semitendinosus (widest part) and gracilis tendons were used to produce an ACL graft with a length of approximately 10 cm. Graft ends were sutured using 2.0 ethibond. Graft diameter was measured with a metal sizing tube of the graft. The cross-sectional size of the ACL graft was calculated from the graft diameter during surgery as: 3.14×graft diameter 2/4 mm2.
2.3. Estimated native ACL cross-sectional size
Knee Computed tomography (CT) was taken pre-operatively (Toshiba Co,Ltd., Aquilion CX 64). Following Iriuchishima's report,3 native ACL size was estimated from the axial intercondylar notch area of femur at the most distal CT slice of Blumensaat's line. According to the Iriuchishima's method,3 native ACL size was equal to 14% of the intercondylar notch area of femur (Fig. 1). The measurement of Intercondylar notch area of femur was performed with a PACs system (measurement accuracy 0.1 mm and 0.01 mm2).
Fig. 1.
Estimation of the native ACL cross sectional size
Native ACL cross sectional size was estimated from the axial femoral intercondylar notch area at the most distal level of Blumensaat's line. Following Iriuchishima’ s method, native ACL cross sectional area was calculated as: 0.14 × axial femoral intercondylar notch area at the most distal level of Blumensaat's line.
2.4. Statistic calculation
The measured cross sectional size of ACL graft and estimated size of native ACL were compared using a Man-Whitney's U test.
Pearson's coefficient correlation test was performed for the evaluation of measured cross sectional size of ACL graft and estimated native ACL size correlation.
G*Power software was used for the calculation of sample size. And the calculated sample size was 34 (Test family: t-test, Type of power analysis: priori, Effectsize; 0.5α:0.05, power 0.8.).
3. Results
3.1. ACL graft cross-sectional size
SB ACL reconstruction was performed in 52 subjects with a quadrable ST, and in 6 subjects with a double fold ST and gracilis. The average ACL graft diameter was 7.9 ± 1.3 mm, and the calculated graft cross-sectional size was 49 ± 14 mm2.
3.2. Estimated native ACL size
The measured intercondylar notch area of femur in the most distal CT slice of Blumensaat's line was 372 ± 91.6 mm2, and the estimated native ACL size was 53 ± 12.5 mm2.
3.3. Statistic calculation
The measured ACL graft cross section and the estimated native ACL showed no significant size difference (p = 0.137) (Fig. 3). The measured ACL graft cross section and the estimated native ACL also showed no significant correlation (Pearson's coefficient correlation: 0.233, p = 0.104) (see Fig. 2).
Fig. 3.
Comparison of the ACL graft cross sectional size and the estimated native ACL cross sectional size.
No significant size difference was observed between the ACL graft cross sectional size and the estimated native ACL cross sectional size.
Fig. 2.
Correlation between the ACL graft cross sectional size and the estimated native ACL cross sectional size.
No significant correlation was observed between the ACL graft cross sectional size and the estimated native ACL cross sectional size.
4. Discussion
Considering that the measured ACL graft cross section and the estimated native ACL showed no significant size difference, the most important result of this study was that an accurate reproduction of native ACL cross-sectional size is possible in anatomic SB ACL reconstruction. However, since these two parameters showed no correlation, and despite the fact that ACL cross-sectional size was reproduced on average, it is possible that the reconstructed ACL size might be different from the native ACL size in some cases, and in such cases, accurate anatomical ACL reconstruction would not be achieved.
With the importance of ACL anatomy becoming more widely recognized, there have been many studies focusing on ACL anatomy.1,4, 5, 6, 7, 8, 9, 10 However, most of these studies concern femoral or tibial ACL footprint anatomy; mid-substance anatomy has not been well reported. In the previous anatomical reports focusing on the ACL mid-substance cross section,5,6,8 the size of the previously reported mid-substance cross section were 40–51.8 mm2. Similar cross sectional size in both the ACL graft and the estimated native ACL size were obtained in this study. In authors’ surgical methods, the ACL graft size was selected by the graft size which can be harvested, and native ACL mid-substance size was not taken into consideration .10 However, the resulting ACL graft size was almost the same as the estimated native ACL size. These results suggest that the reproduction of average size of ACL cross section can be archived even when ACL graft size was selected with harvested autograft size. On the other hands, no size correlation was observed between the measured ACL graft cross section and the estimated native ACL. It has been reported that no significant size correlation found between native ACL footprint and the commonly used harvested ACL autografts in a cadaveric study.10 In this study, the same trend was observed in in-vivo surgery. When native ACL cross-sectional size was not reproduced in the surgery, it can be inferred that femoral intercondylar notch-ACL graft size mismatch resulted. As previously reported, an ACL graft too large in size can be a cause of graft impingement.11, 12, 13 Graft-impingement brings about loss of knee extension, knee pain, and graft failure.11 On the other hand, an ACL graft too small in size can fail to stabilize the knee, and would likely be the cause of remaining knee instability.5,11 Although the size of ACL cross section was the same as the estimated native ACL size on average in this study, there exists the possibility that in some cases native ACL cross-sectional size might not be reproduced. In such cases, careful follow-up is needed to prevent the occurrence of future graft failure or re-injury of the ACL.
There was some limitations in this study, 1) Although native ACL cross-sectional size was estimated using a previously reported method, the ACL size could not be validated directly in this study. Direct validation using the contra-lateral knee MRI should be considered. 2) In this study, only Asian populations were included. In other ethnic groups the results might be different. 3) The included sample size was relatively small. In the authors’ surgical selection, ACL reconstruction was performed with double bundle as the first option, and therefore, the cases of anatomic SB ACL reconstruction were limited.
5. Conclusion
Native ACL cross-section size was reproduced on average in anatomic SB ACL surgery. However, as the measured ACL graft and the estimated native ACL showed no significant size correlation, size of native ACL might not be reproduced in some cases. Such cases would be susceptible to the risk of graft impingement or remaining knee instability, and careful follow up is needed in order to prevent ACL graft failure.
Authors’ disclosure
This study was approved by the ethics committee of institution.
No funding support, and no conflict of interest were existed on this study.
Ethical statement
Reproducibility of the native ACL mid-substance cross-sectional area in anatomical single bundle ACL reconstruction.
Takanori Iriuchishima, Bunsei Goto.
This study has been approved by the ethics committee of Kamimoku Spa Hospital. And the IRB number was KH04001.
Funding statement
Reproducibility of the native ACL mid-substance cross-sectional area in anatomical single bundle ACL reconstruction.
Takanori Iriuchishima, Bunsei Goto.
No conflict of interest and no funding support were existed on this study.
Guardian/patient's consent
Reproducibility of the native ACL mid-substance cross-sectional area in anatomical single bundle ACL reconstruction.
Takanori Iriuchishima, Bunsei Goto.
All subjects included in this study obtained informed consent before treatment.
Acknowledgement
None.
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