Effects of Higher Femoral Tunnels on Clinical Outcomes, MRI, and Second-Look Findings in Double-Bundle Anterior Cruciate Ligament Reconstruction with a Minimal 5-Year Follow-Up
Introduction
Anterior cruciate ligament reconstruction (ACLR) has become a widely adopted surgical procedure to restore knee stability and function following ACL injuries. Among the various techniques, anatomical ACLR has gained popularity due to its emphasis on restoring the native anatomy of the ACL. One critical aspect of anatomical ACLR is the placement of femoral tunnels, which significantly influences the biomechanical properties and clinical outcomes of the reconstructed ligament. Recent anatomical and biomechanical studies have highlighted the importance of positioning femoral tunnels to cover the central direct fibers of the ACL, which are located higher within the femoral footprint. However, the clinical outcomes of higher femoral tunnels (HFT) in double-bundle ACLR (DB-ACLR) remain unclear. This study aims to compare the clinical results, second-look arthroscopic findings, and magnetic resonance imaging (MRI) findings between HFT and lower femoral tunnels (LFT) in DB-ACLR with a minimum follow-up of 5 years.
Background
The femoral insertion of the ACL consists of direct and indirect fibers. The direct fibers are located closer to the resident ridge and are biomechanically more significant, bearing greater forces during stability testing and exhibiting more isometric behavior during knee flexion. In contrast, the indirect fibers contribute minimally to knee stability. Biomechanical studies suggest that femoral tunnels should be placed higher within the femoral footprint to replicate the biomechanical advantages of the direct fibers. This positioning is particularly relevant in DB-ACLR, where both the anteromedial (AM) and posterolateral (PL) bundles are reconstructed to restore native ACL kinematics. However, limited clinical studies have investigated the outcomes of HFT in DB-ACLR, necessitating further research to validate its effectiveness.
Methods
This retrospective study included 83 patients who underwent DB-ACLR between September 2014 and February 2016. Patients were divided into two groups based on the position of the femoral tunnels: HFT-ACLR (group 1, n = 37) and LFT-ACLR (group 2, n = 46). Inclusion criteria included unilateral ACL rupture with surgery performed within 6 months of injury, age between 18 and 45 years, and closed physes. Exclusion criteria included grade 3 or higher cartilage degeneration, subtotal or total meniscectomy, multiple ligament injuries, and previous knee surgery. Femoral tunnel positions were confirmed using 3D-computerized tomography (3D-CT) postoperatively.
Surgical Procedure
The hamstring autograft tendons were harvested from the affected limb, with the semitendinosus tendon used for the AM bundle and the gracilis tendon for the PL bundle. The femoral tunnels were created using the transportal technique, with the HFT group positioned higher within the direct insertion of the femoral ACL footprint. The tibial tunnel was drilled based on individualized tibial insertion landmarks. Grafts were fixed with Endobuttons at the femoral site and bio-absorbable interference screws at the tibial site. Postoperative rehabilitation followed a standardized protocol, emphasizing early range of motion and progressive weight-bearing.
Clinical Evaluations
Patients were evaluated preoperatively and at the final follow-up using the International Knee Documentation Committee (IKDC) score, Tegner activity score, and Lysholm score. Knee stability was assessed using the KT-2000 arthrometer, Lachman test, and pivot-shift test. Cartilage degeneration was evaluated using MRI according to the International Cartilage Repair Society (ICRS) grading system. Second-look arthroscopy was performed in a subset of patients to assess graft tension, continuity, and synovialization. Return-to-sports status was also recorded at the final follow-up.
Results
Patient demographic data showed no significant differences between the two groups in terms of age, gender, body mass index (BMI), period from injury, meniscus management, and follow-up duration. The HFT group demonstrated significantly better knee stability postoperatively, as measured by the KT-2000 arthrometer, Lachman test, and pivot-shift test. However, no significant differences were observed in the IKDC subjective score, Tegner activity score, and Lysholm score between the two groups. The HFT group had a higher return-to-sports rate (86.8%) compared to the LFT group (65.2%).
Second-look arthroscopy revealed significantly better outcomes for the PL bundle in the HFT group regarding graft tension, continuity, and synovialization. No significant differences were observed for the AM bundle. MRI findings showed cartilage worsening in both groups, but the difference was not statistically significant.
Discussion
The study’s findings support the hypothesis that HFT in DB-ACLR results in better knee stability and higher return-to-sports rates compared to LFT. The biomechanical advantages of positioning femoral tunnels higher within the direct insertion of the ACL likely contribute to these improved outcomes. The PL bundle, in particular, exhibited better graft integrity in the HFT group, which may be attributed to reduced tension and length changes during knee flexion. However, the lack of significant differences in clinical scores suggests that current scoring systems may not be sensitive enough to detect subtle improvements in knee function.
The study also highlights the importance of long-term follow-up to assess cartilage degeneration following ACLR. While both groups showed cartilage worsening, the difference was not statistically significant, indicating that HFT does not exacerbate cartilage damage. Further research with larger sample sizes and more sensitive imaging techniques, such as T2 mapping, is needed to confirm these findings.
Conclusion
In conclusion, HFT in DB-ACLR provides better knee stability and higher return-to-sports rates compared to LFT. The PL bundle in the HFT group demonstrated superior graft integrity on second-look arthroscopy, supporting the biomechanical advantages of higher femoral tunnel placement. Although no significant differences were observed in clinical scores, the improved stability and return-to-sports outcomes suggest that HFT is a viable option for ACLR. Long-term follow-up is necessary to further evaluate the impact of HFT on cartilage health and overall knee function.
doi.org/10.1097/CM9.0000000000002948
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