Optimal entry position on the lateral femoral surface for outside-in drilling technique to restore the anatomical footprint of anterior cruciate ligament

Flat-Tunnel Technique With Independently Tensioned Bundles Better Restores Rotational Stability Than Round-Tunnel Technique in Anatomic Anterior Cruciate Ligament Reconstruction Using Hamstring Graft: A Cadaveric Biomechanical Study

PURPOSE

To investigate the kinematics differences between round-tunnel (ROT) and flat-tunnel (FLT) techniques in anterior cruciate ligament (ACL) reconstruction when using hamstring graft.

METHODS

Nine matched pairs of fresh-frozen cadaveric knees were evaluated for the kinematics of intact, ACL-sectioned, and either ROT or FLT reconstructed knees. The graft bundles for FLT technique were separately tensioned. A 6 degrees of freedom robotic system was used to assess knee laxity: (1) 134-N anterior tibial load at 0°, 15°, 30°, 60°, and 90°of knee flexion; (2) 10 Nm of valgus torque followed by 5 Nm of internal rotation torque simulates a pivot-shift test at 15° and 30°; (3) 5-Nm internal and external rotation torques at 0°, 15°, 30°, 60°, and 90°; (4) 10-Nm varus and valgus torques at 15° and 30°.

RESULTS

Significant differences were found for ROT versus FLT techniques in terms of the simulated pivot-shift test at 15° (2.5 mm vs 1.4 mm, respectively, difference from intact; P =.039) and the internal rotation test at 15° (2.5° vs 0.5°, respectively, difference from intact; P =.034) and 30° (2.0° vs 0.4°, respectively, difference from intact; P =.014). No significant differences were found between groups during 134-N anterior tibial load, external rotation and valgus/varus rotation. Neither technique was able to reproduce the intact state during an anterior tibial load and simulated pivot-shift test.

CONCLUSIONS

The FLT technique with independently tensioned bundles shows the same anterior control as the ROT technique but better restores rotational stability in terms of the simulated pivot-shift test and the internal rotation test in anatomic ACL reconstruction at time zero.

CLINICAL RELEVANCE

The FLT technique with independently tensioned bundles of ACL reconstruction appears to be a viable, more anatomic technique than the ROT technique in mimicking flat anatomy and rotational stability of native ACL.

The Ideal Cortical Button Location on the Lateral Femur for Anterior Cruciate Ligament Suspensory Fixation is 30 mm Proximal to the Lateral Epicondyle

Purpose

To determine the ideal location for anterior cruciate ligament (ACL) suspensory cortical button placement on the lateral femur with the highest failure load and to establish the relationship of tunnel diameter and cortical thickness on load to failure.

Methods

Computed tomography (CT) data were obtained from 45 cadaveric distal femurs. A Cartesian coordinate system was established along the lateral femur with the lateral epicondyle (LE) as a reference point. Locations 0, 20 and 30 mm from the LE along lines 0°, 25°, 50°, and 75° posterioproximal from the axial plane were created. Tunnels connecting from each location to the center of the ACL footprint were simulated. Cortical thickness and long axis diameter of the oval cortical holes were determined for each location. Based on the CT data, custom drill guides were created and used to drill 4.5 mm tunnels at each lateral femur location to the ACL footprint on the cadaver femurs. Cortical buttons were placed at each location and pulled using a servohydraulic testing system. The correlation of tunnel diameter and cortical thickness to button failure load were analyzed using a regression analysis.

Results

Significant differences were found for failure load (P<.0001) and cortical thickness between the locations tested (P<.0001). The location 30 mm proximal from the LE and 75⁰ from the axial plane had the highest failure load of 573 N. A regression analysis (R² = .15) indicated that the cortical thickness was significantly correlated with load to failure (P <.0001), whereas the long-axis diameter was not (P = .33).

Conclusion

The ideal cortical button location on the lateral femur for ACL suspensory fixation was located 30 mm proximal from the lateral epicondyle, based on this area’s high failure load. Oblique tunnel drilling of this proximal location may cause a larger long-axis diameter cortical hole, but the cortex is also thicker, which is more closely correlated with failure load.

Clinical Relevance

Different ACL suspensory cortical button locations on the lateral femur have different failure loads based on the cortical thickness of the bone supporting the button. It is important for surgeons to understand which drilling techniques place the button in a proximal and posterior location, especially if the bone quality of the patient is of concern.

Aperture elongation of the femoral tunnel on the lateral cortex in anatomical double-bundle anterior cruciate ligament reconstruction using the outside-in technique

In anatomical anterior cruciate ligament reconstruction surgery using the outside-in technique, the aperture of the femoral lateral cortex may become elliptical.Retrospective cross-sectional studyTo evaluate the extent of elliptical eccentricity in lateral apertures relative to aperture positioning and clinical failure rate in anatomical anterior cruciate ligament double-bundle reconstruction using outside-in technique.In 75 patients, the aperture elongation factor was defined as the ratio of the major axis of the elliptical aperture to the drill size. Using the lateral epicondyle as a reference point, the lateral femur was divided into sections by distance and angle, and the minimum area was evaluated to assess the relationship between the elongation factor and aperture position of the lateral cortex for each bundle. The incidence and associated clinical performance regarding cortical button migration were also investigated.Aperture elongation factors were 120.2 ± 13.3% and 120.0 ± 16.3% on the anteromedial (AM) and posterolateral (PL) sides, respectively. Femoral tunnel elongation was smallest when the entry point axis were both between 30 to 60° and distance was between 10 to 20 mm and 0 to 10 mm on the AM and PL sides, respectively. During the postoperative follow-up period, intra-tunnel migration was confirmed in 4 of 75 cases (5.3%). Fixation failure neither affected clinical scores nor knee laxity.Areas of minimum elongation for each bundle on both AM and PL sides were found anteroproximally to the lateral epicondyle and positioned near each other. Elongation did not directly affect the clinical outcome.Level of evidence grade: prognostic level III.

Comparison of graft bending angle during knee motion after outside-in, trans-portal and trans-tibial anterior cruciate ligament reconstruction

PURPOSE

To determine graft bending angle (GBA) during knee motion after anatomic anterior cruciate ligament (ACL) reconstruction and to clarify whether surgical techniques affect GBA. Our hypotheses were that the graft bending angle would be highest at knee extension and the difference of surgical techniques would affect the bending steepness.

METHODS

Eight healthy volunteers with a mean age of 29.3 ± 3.0 years were recruited and 3D MRI knee models were created at three flexion angles (0°, 90° and 130°). Surgical simulation of the tunnel drilling was performed with anatomic tunnel position using each outside-in (OI), trans-portal (TP) and trans-tibial (TT) techniques on the identical cases. The models were matched to other knee positions and the GBA in 3D was measured using computational software. Double-bundle ACL reconstruction was analysed first, and single-bundle reconstruction was also analysed to evaluate its effect to reduce GBA. A repeated-measures ANOVA was used to compare GBA difference at three flexion angles, by three techniques or of three bundles.

RESULTS

GBA changed substantially with knee motion, and it was highest at full extension (p < 0.001) in each surgical technique. OI technique exhibited highest GBA for anteromedial bundle (94.3° ± 5.2°) at extension, followed by TP (83.1° ± 6.5°) and TT (70.0° ± 5.2°) techniques (p < 0.01). GBA for posterolateral bundle at extension were also high in OI (84.6° ± 7.4°), TP (83.0° ± 6.3°) and TT (77.2° ± 7.0°) techniques (n.s.). Single-bundle grafts did not decrease GBA compared with double-bundle grafts. In OI technique, a more proximal location of the femoral exit reduced GBA of each bundle at extension and 90° flexion.

CONCLUSION

A significant GBA change with knee motion and considerably steep bending at full extension, especially with OI and TP techniques, were simulated. Although single-bundle technique did not reduce GBA as seen in double-bundle technique, proximal location of femoral exits by OI technique, with tunnels kept in anatomic position, was effective in decreasing GBA at knee extension and flexion. For clinical relevance, high stress on graft and bone interface has been suggested by steep GBA at full extension after anatomic ACL reconstruction.

LEVEL OF EVIDENCE

Therapeutic study (prospective comparative study), Level II.

Overestimation of femoral tunnel length during anterior cruciate ligament reconstruction using the retrograde outside-in drilling technique

PURPOSE

When the femoral tunnel socket is reamed in an oblique direction from the wall of inter-condylar notch in anterior cruciate ligament (ACL) reconstruction, the tunnel length can be shorter at the periphery than at the centre. Because surgeons can manipulate the direction of tunnel in the outside-in femoral tunnel drilling technique, this length mismatch would vary depending on the direction of the tunnel. The purpose of this study was to investigate this length mismatch when reamed in various directions.

METHODS

In total of thirteen points were defined as femoral drilling entry points on concentric lines with 0, 1, 2, and 3 cm radius from the lateral epicondyle of a three-dimensional bone model from 40 subjects. Femoral tunnel drilling was simulated on the models by connecting the centre of the ACL footprint with each defined point on the lateral femoral surface. The mismatch length was measured between the centre and the shortest peripheral side of the tunnel socket.

RESULTS

When the distance between the drilling entry point on the lateral femoral surface and the lateral epicondyle was increased to anterior proximal direction, there was a significant increase in the mismatch length. The mismatch length became more than 2 mm when the entry point was located more than 2 cm away from the lateral epicondyle.

CONCLUSIONS

When the drilling entry point is set far away from the lateral epicondyle, a significant increase was observed in tunnel length mismatch between the centre of the tunnel and its shortest peripheral side. Because the tunnel length is measured with a guide pin introduced at the centre of the tunnel before reaming in retrograde outside-in technique, this length mismatch could cause an overestimation of the tunnel length. Surgeons should recognise this mismatch when preparing the length of graft and socket to optimise the graft insertion length into the socket.

Asymmetry in Femoral Tunnel Socket Length During Anterior Cruciate Ligament Reconstruction With Transportal, Outside-In, and Modified Transtibial Techniques

PURPOSE

To investigate the mismatch between the length at the center and the length on the shortest and longest peripheral sides of the femoral tunnel socket, reamed with the transportal (TP), outside-in (OI), and modified transtibial (TT) techniques, in anterior cruciate ligament (ACL) reconstruction.

METHODS

Femoral tunnel drilling was simulated on 3-dimensional bone models from 40 subjects. The tunnel directions used with the TP, OI, and modified TT techniques were previously described. By use of the resulting angle, a femoral tunnel socket of 9 mm in diameter was drilled from the center of the femoral ACL insertion. The virtual femoral tunnel was extracted, and the length mismatch was measured between the center and the shortest and longest peripheral sides of the tunnel socket.

RESULTS

The mean socket length mismatch between the center and the shortest peripheral part of the femoral tunnel socket was 4.2 ± 0.9 mm with the TP technique, 5.2 ± 1.3 mm with the OI technique, and 3.2 ± 0.8 mm with the modified TT technique. The mean socket length mismatch between the center and the longest peripheral part of the femoral tunnel socket was 3.5 ± 0.9 mm with the TP technique, 4.8 ± 1.5 mm with the OI technique, and 3.3 ± 1.2 mm with the modified TT technique. The length mismatch was significantly higher when the tunnel socket was created by the OI technique (P < .01).

CONCLUSIONS

A length mismatch with the tunnel socket exists after reaming with either the TP, OI, or modified TT technique. In particular, there was a significant increase in length mismatch when the tunnel socket was created by the OI technique, and the length mismatch would easily become greater than 5 mm. The surgeon should recognize this mismatch when it is created and measure the femoral tunnel socket.

CLINICAL RELEVANCE

In anatomic ACL reconstruction, a mismatch between the length at the center and the length at periphery of the femoral tunnel socket occurs, and this is increased particularly when using the OI technique. The discrepancy in tunnel length between its center and its periphery could cause an overestimation of the tunnel length that could result in an error in length during graft preparation.