Purpose

The purpose of this study was to determine whether intra-operative identification of osseous ridge anatomy (lateral intercondylar “residents” ridge and lateral bifurcate ridge) could be used to reliably define and reconstruct individuals' native femoral ACL attachments in both single-bundle (SB) and double-bundle (DB) cases.

Background: Studies have shown that normal tibio-femoral rotational kinematics is not regained following single-bundle ACL reconstruction and that 14–30% of patients may have a residual “pivot glide”. It has been suggested that 2-bundle reconstruction could better control this laxity, but this not been demonstrated conclusively in-vivo. This study tested the hypothesis that 2-bundle ACL reconstruction improves the control of the Pivot Shift.

Methods: We measured the mean maximum tibial translation and coupled rotation occurring during the pivot shift (using a previously validated surgical navigation based methodology) in 35 consecutive patients undergoing hamstrings ACL reconstruction. 17 patients had a standard single-bundle reconstruction and 18 patients a 4-tunnel, 2-bundle reconstruction. 10 pivot shift tests were performed pre- and post operatively by a single operator and the differences compared.

Results: The two groups were equally age and sex matched. There was no difference in pre-operative pivot shift measurements. 2-bundle reconstruction decreased the tibial rotation occurring with the pivot shift test more than single-bundle reconstruction (Table 1). There was no detectable difference in the control of tibial translation.

Conclusions: This study quantifies, in-vivo, the differences between single and 2-bundle ACL reconstruction in controlling pivot shift. It suggests that anatomic, 2-bundle ACL reconstructions could reduce pivot instability more effectively than a single-bundle. Whether the 10% additional control of the rotational component of the pivot improves functional stability or is necessary every patient and, in the longer term, limits the development of gonarthrosis secondary to abnormal motions, remains to be seen

Cadaveric experiments using knee testing machines have suggested that anatomical ACL reconstruction, replacing both antero-medial (AM) and postero-lateral (PL) bundles, restores knee rotation kinematics more effectively than does a single-bundle. The aim of this study was to measure intra-operatively the control of the translation and coupled rotations that occur with standard clinical laxity tests (anterior drawer, Lachman and pivot shift).

The knee kinematics of 10 patients were measured using a surgical navigation system and described in terms of tibial axial rotation and antero-posterior translation. In the ACL deficient knee, the average maximum tibial rotation during the pivot shift test was 29.0° and the mean maximum translation 17.0 mm. Reconstruction of the AM bundle (which behaves in a biomechanically similar way to a single-bundle reconstruction) reduced the rotational component to 16.4° (p< 0.0001) and translation to 6 mm (p = 0.0002). Addition of the PL bundle further reduced rotation to 12.6° (p = 0.0007) but had no significant effect on translation. Addition of the PL bundle also significantly reduced coupled tibial internal rotation during the Lachman and Anterior draw tests.

The pivot shift test simulates the instability suffered by patients with ACL deficiency and this study suggests that its rotational component is better restrained by anatomical, 2 bundle ACL reconstruction.

Introduction: By characterising ACL strain behaviour in intact and posteromedial deficient knees under a variety of external loading conditions the aim of this work was to demonstrate whether posteromedial corner insufficiency could increase strain in an ACL reconstruction graft.

Materials and Methods: 15 fresh cadaveric knees were mounted on a materials testing machine. A miniature extensometer was implanted onto the anteromedial bundle (AMB) of the ACL. The knees were loaded in: Anterior draw (150N), varus/valgus rotation (5Nm) and internal/external rotation (5Nm) at 0°, 15°, 30°, 60° & 90° flexion. The posteromedial corner structures – posteromedial capsule, superficial MCL and deep MCL – were cut sequentially and the effect AMB strain measured.

Results: Strain data for analysis was available for 11 intact knees: Tibial internal rotation produced increased strain in the AMB at all angles of knee flexion (p< 0.05). Tibial external rotation reduced ACL strain at 0° to 30° (p< 0.05) and 60° to 90° knee flexion (p> 0.05).

Anterior loading of the tibia increased AMB strain. With the tibia free to rotate, strain was highest at 90 degrees knee flexion (5.3%) and lowest at 0 degrees (1.6%). Fixed internal and external tibial rotation reduced AMB strain produced by a 150 N anterior drawer force at all knee flexion angles.

Strain data for analysis was available for 6 Posteromedial Corner deficient knees:

With the tibia free to rotate or when locked in internal rotation, cutting the posteromedial structures had no effect on AMB strain with a 150 N anterior drawer force applied to the tibia. However, with the tibia locked in external rotation, cutting the posteromedial structures increased AMB strain at 60 and 90 degrees flexion. This difference however did not reach statistical significance.

Conclusions: The findings that division of the posteromedial structures may cause increased AMB strain and that there is significant load sharing by the peripheral ligamentous structures, suggests that valgus and rotational stresses to the knee in a patient with posteromedial corner insufficiency could lead to increased strain in the ACL graft, that would otherwise have been restrained by the posteromedial corner complex. It would also therefore seem to be appropriate to recommend the use of a collateral ligament brace in the post-operative period when combining a repair of the posteromedial structures and the ACL, to again prevent excessive graft strains.

Objective: To provide a functional, anatomical description of the posteromedial structures, allowing future biomechanical studies to evaluate how they act to restrain tibio-femoral joint motion and contribute to joint stability.

Methods: Twenty fresh cadaveric knee joints were dissected. The appearance of the medial ligament complex was recorded using still and video digital photography as the specimens were flexed, extended, internally and externally rotated.

Results: We divided the medial structures into thirds, from anterior to posterior, and into three layers from superficial to deep: Layer 1: Fascia. Layer 2: Superficial MCL. Layer 3: Deep MCL and capsule. In the Posteromedial Corner (posterior third) it is not possible to separate Layers 2 and 3. The posteromedial corner (PMC) envelops the posterior medial femoral condyle. A discrete posterior oblique ligament (POL) is not identifiable. The PMC appears to be a functional unit with a role in passively restraining tibio-femoral valgus and internal rotation with the knee extended. The semimembranosus, through its tendon sheath attachments, may act as a dynamic stabiliser.

Conclusion: The MCL appears to have three functional units:Superficial MCL, Deep MCL and PMC. We believe that this description allows a logical approach to understanding the biomechanics and surgical reconstruction of the posteromedial structures. We plan to use this anatomical study as the basis for further work to evaluate the how these functional units act.