Introduction

Anatomic double-bundle anterior cruciate ligament (ACL) reconstruction has been advocated to replicate the anatomic structure of the ACL more closely than single-bundle ACL reconstruction and has proven to achieve better restoration of rotatory knee laxity. After anatomic double-bundle ACL reconstruction, two tunnels on each side of the femur and the tibia are occasionally communicated and tibial tunnel coalition more often happened than femoral one. Once tibial tunnel coalition occurs, the rotatory knee laxity would not be controlled as expected for double-bundle. In order to avoid tibial tunnel coalition, risk factors for tibial tunnel coalition should be recognized. Therefore, the purpose of this study was to identify risk factors for tibial tunnel coalition in anatomic double-bundle ACL reconstruction.

Methods

Subjects were 67 unilateral ACL injured patients (35 males, 32 females, average age 28 ± 12 years old) who had anatomic double-bundle ACL reconstruction. 3DCT of the affected knees were taken at two weeks postoperatively. The tibial tunnels were extracted by 3D image analysis using Mimics (Materialise inc., Leuven, Belgium), to determine whether tunnels were connected. A group of patients whose tibial tunnels were communicatedwas categorized as group C, and that without tunnel coalition was as group N. Basic demography (age, sex, height and weight), total tibial tunnel diameter, anteroposterior and mediolateral widths of the proximal tibia, and tibial tunnel position were compared between two groups as potential risk factors using t-test or chi-square test. In addition, multiple regression analysis was performed to determine strong factors for tibial tunnel coalition.

Results

34/67 cases (51%) had tibial tunnel coalition. There was no significant difference in demographic data between two groups. The total tunnel diameter of the tibia was significantly larger in group C (group C: 12.5±0.9mm, group N: 12.1±0.7mm; p=0.02). The anteromedial (AM) tunnel was located significantly more posteriorly in group C (group C: 34.4±7.8%, group N: 29.9±5.5%; p<0.01). In multiple regression analysis, the most significant factors associated with tibial tunnel coalition was the anteroposterior position of the AM and the posterolateral (PL) tunnels (AM tunnel: standard partial regression coefficient ß= -1.08, p<0.01, PL tunnel: ß= 1.10, p<0.01).

Discussion

Tibial tunnel coalition occurred in as much as 51% of our double-bundle cases, not surprisingly considering recent clinical reports of tunnel coalition after double-bundle ACL reconstruction. Posterior placement of the tibial tunnel in single-bundle reconstruction was reported to deteriorate clinical outcomes and rotatory knee laxity. In double-bundle reconstruction, posterior placement of the AM tunnels on the tibia could induce tibial tunnel coalition based on the current study, further resulting in impaired knee stability. Therefore, anterior placement of the AM tunnel may be advantageous for both anatomic reproduction and knee stability. Surgeons should create the AM tibial tunnel as far anteriorly as possible within the anatomical attachment while having a good separation from PL tunnel.

Conclusion

In double-bundle ACL reconstruction, tibial tunnel coalition was found in about half of the patients, and the malposition of tibial tunnels to the anteroposterior direction was identified as a risk factor for tibial tunnel coalition.