This study hypothesizes that the tunnel positioning and drilling direction in two single-bundle reconstruction techniques (Anatomical Single-Bundle Reconstruction, ASBR, and Central Axial Single-Bundle Reconstruction, CASBR) influence the biomechanical environment of the graft, thereby affecting graft remodeling and maturation, ultimately impacting postoperative outcomes. Studies have shown that the graft bending angle (GBA) is a critical factor affecting graft ligamentization. ASBR, with a higher GBA, may result in poorer graft maturation, while CASBR, with a lower GBA, may provide a more favorable biomechanical environment. Additionally, graft volume has been identified as an important factor influencing postoperative graft maturation. Therefore, this study also examines the double-bundle reconstruction (DBR) technique, which has a GBA similar to CASBR.
The Impact of Three Techniques on Graft Maturation Anatomical Single-Bundle Reconstruction (ASBR)
ASBR involves drilling a single tunnel at both the femoral and tibial ends, with the tunnel positioned at the center of the dense fiber area of the ACL footprint. The femoral tunnel is positioned at 90° knee flexion and drilled at 120°, while the tibial tunnel is positioned at 70° knee flexion. Due to the higher GBA in ASBR, the graft may experience greater bending stress during motion, leading to impaired graft maturation, limited ligamentization, and increased stress concentration around the tunnel, potentially causing tunnel widening.
Central Axial Single-Bundle Reconstruction (CASBR)
CASBR also involves drilling a single tunnel at both ends, but the tunnel is positioned in the posterior region of the dense fiber area of the ACL footprint, mimicking the central axis of the native ACL. The femoral tunnel is positioned at 90° knee flexion and drilled at 120°, while the tibial tunnel is positioned at 70° knee flexion. Compared to ASBR, CASBR's lower GBA results in more uniform graft stress distribution, promoting better graft maturation and reducing the risk of stress concentration and tunnel widening.
Double-Bundle Reconstruction (DBR)
DBR involves drilling two tunnels at both the femoral and tibial ends, targeting the dense fiber areas of the anterior medial bundle (AMB) and posterior lateral bundle (PLB) of the ACL footprint. The positioning of the PLB tunnel is similar to CASBR, while the AMB tunnel is located in the anterior region of the footprint. DBR provides a more anatomically accurate distribution of forces, leading to a more even biomechanical environment. However, the increased number of tunnels may complicate stress distribution.
Impact on Postoperative Outcomes ASBR, with its higher GBA, may lead to poor graft maturation and increased tunnel widening. CASBR, with a lower GBA, offers a more favorable biomechanical environment for graft maturation. While DBR ensures a more uniform force distribution, the additional tunnels may introduce complexities in stress distribution, potentially affecting postoperative recovery and return to sports (RTS).
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Parallel
Procedure: Anatomical Single-Bundle ACL Reconstruction
Procedure/SurgeryPatients undergo anatomical single-bundle ACL reconstruction with femoral and tibial tunnel drilling.
Procedure: Central Axial Single-Bundle ACL Reconstruction
Procedure/SurgeryPatients undergo central axial single-bundle ACL reconstruction with optimized tunnel positioning.
Procedure: Double-Bundle ACL Reconstruction
Procedure/SurgeryPatients undergo double-bundle ACL reconstruction targeting AMB and PLB footprints.
tunnel widening
Tunnel widening is measured as the percentage change in cross-sectional area of the graft tunnel. Using CT and MRI, we measure the cross-sectional area perpendicular to the graft tunnel two days after surgery (baseline) and again during follow-up. The tunnel enlargement rate is calculated as: Tunnel Enlargement Rate = (Follow-up Tunnel Area - Postoperative Day 2 Tunnel Area) / Postoperative Day 2 Tunnel Area × 100% The measurement unit is percentage (%), with higher percentages indicating greater tunnel widening.
Return to sport
The Return to Sport (RTS) Safety Assessment evaluates functional recovery following ACL reconstruction through comprehensive testing of muscle strength and functional performance. Testing includes: Isokinetic quadriceps strength tests at 60°/s using an electromechanical dynamometer (Biodex System III dynamometer, Biodex Medical Systems) Four types of single-legged hop tests Each participant receives a demonstration and two practice sessions prior to the formal tests, which occur 20 minutes post-exercise. All tests are performed on both the injured and uninjured legs. The measurement unit is the Leg Symmetry Index (LSI), calculated as a percentage (%) by comparing the performance of the injured leg to the uninjured leg. The final score is recorded as the mean LSI% across both the hop and isokinetic tests. An LSI of 100% indicates perfect symmetry between legs, with higher percentages representing better functional recovery.
IKDC 2000
The IKDC 2000 Subjective Knee Evaluation is a patient-reported outcome measure that assesses symptoms, sports activities, and function. The preoperative score is measured as baseline data for comparability, and the follow-up score after more than two years postoperatively is used to compare clinical outcomes among the three surgical techniques. The measurement unit is a standardized score ranging from 0 to 100, where 0 represents the lowest level of function and highest level of symptoms, and 100 represents the highest level of function and lowest level of symptoms.
Lyholm score
The Lysholm Knee Scoring Scale evaluates knee function in activities of daily living. The preoperative score is measured as baseline data for comparability, and the follow-up score after more than two years postoperatively is used to compare clinical outcomes among the three surgical techniques. The measurement unit is a numerical score ranging from 0 to 100, where 0 represents severe knee problems and 100 represents normal knee function.
Tegner
The Tegner Activity Scale assesses activity level specifically related to knee function. The preoperative score is measured as baseline data for comparability, and the follow-up score after more than two years postoperatively is used to compare functional recovery among the three surgical techniques. The measurement unit is a numerical score ranging from 0 to 10, where 0 represents disability due to knee problems and 10 represents participation in competitive sports at a national or international elite level.
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