In-vivo three-dimensional MR imaging of the intact anterior cruciate ligament shows a variable insertion pattern of the femoral and tibial footprints.

PURPOSE: Failure to reconstruct the natural footprints of the ruptured anterior cruciate ligament (ACL) may lead to premature graft-failure. Therefore, precise analyses of insertion site anatomy and inter-individual variations of the morphology of the ACL are highly important to facilitate optimal individualized graft placement. Therefore, the purpose of this study was to analyze the inter-individual variation of the morphology of the femoral and tibial ACL footprints. METHODS: Thirty subjects with an intact ACL were included in this study for MR imaging of their knee joint. A three-dimensional (3D) dual-echo steady-state sequence with near 0.8 mm isotropic resolution was acquired on a 3 T system with a 15-channel knee-coil. The ACL was subsequently manually segmented using dedicated medical imaging software (VitreaAdvanced®, Vital Images). The lengths and widths of the footprints were measured after reconstructing an axial oblique (tibial footprint) or coronal oblique (femoral footprint) section at the bone-ligament junction and descriptive analysis was conducted to describe morphology orientation of the footprint. RESULTS: The femoral footprint measured on average 14 mm ± 2 mm (range 8-19 mm) in length and 5 mm ± 1 mm (range 3-8 mm) in width. The mean value of the tibial footprint measured 10 mm ± 2 mm (range 5-14 mm) in length and 7 mm ± 2 mm (range 5-13 mm) in width. Descriptive analysis showed a stretched, ribbon-like appearance of the femoral footprint, while the tibial footprint revealed larger variability, stretching from anterolateral to posteromedial around the anterior horn of the lateral meniscus. CONCLUSION: 3D imaging of the ACL footprints reveals a distinct difference in insertion site morphology and fiber bundle orientation between the femoral and tibial footprint. This questions the concept of strict anatomical separation of the ACL into an anteromedial and posterolateral bundle.

Graft remodeling and ligamentization after cruciate ligament reconstruction.

After reconstruction of the cruciate ligaments, replacement grafts have to undergo several phases of healing in the intra-articular graft region and at the site of graft-to-bone incorporation. The changes in the biological and mechanical properties of the healing graft in its intra-articular region are described as the ligamentization process. Significant knowledge has been added in the understanding of the several processes during the course of graft healing and is summarized in this article. The understanding of the spatial and time-dependent changes as well as the differences between the different models of graft healing are of significant importance to develop strategies of improved treatment options in cruciate ligament surgery, so that full restoration of function and mechanical strength of the intact cruciate ligaments will be achieved.

The extracellular remodeling of free-soft-tissue autografts and allografts for reconstruction of the anterior cruciate ligament: a comparison study in a sheep model.

Our study was aimed to advance the currently limited knowledge about differences in the biological remodeling of free soft-tissue tendon allografts and autografts for ACL reconstruction. Allogenic and autologous ACL reconstructions were performed in a sheep model using the flexor digitalis superficialis tendon. After 6, 12 and 52 weeks the animals were sacrificed. We analyzed the collagen crimp formation and its relationship to expression of contractile myofibroblasts in both graft types. Additionally, structural properties and ap-laxity were compared during biomechanical testing. At 6 weeks only descriptive differences were found between autografts and allografts with a more organized crimp pattern and myofibroblast distribution in autografts. Significant differences in myofibroblast density and crimp formation were found after 12 weeks. At these early stages, the progress of remodeling in autografts was more advanced toward the central areas than in allografts. At 1 year, grafts in both study groups returned to an ACL-similar structure. Structural properties and ap-laxity did not vary significantly between auto- and allografts at early healing stages. However, at 52 weeks, failure loads, stiffness and ap-drawer test showed superior values for autograft ACL reconstruction. Extracellular remodeling of allografts develops slower than in autografts. Therefore, rehabilitation procedures will have to be adapted according to graft and patient selection. Postoperative treatment regimens from autograft primary ACL reconstruction should not be directly transferred to allograft ACL reconstructions.

Biomechanical comparison of human bone-patellar tendon-bone grafts after sterilization with peracetic acid ethanol.

Recent reports of disease transmission following ACL reconstruction with fresh-frozen non-sterilized allografts have highlighted the need for new sterilization techniques that do not impair the mechanical properties as it was shown for most of the current sterilization techniques. In this in-vitro biomechanical study, it was investigated if peracetic acid ethanol sterilization (PES) has any adverse effects on the mechanical properties of human bone-patellar tendon-bone grafts (BPTB). Paired human BPTB grafts either underwent PES or were used as fresh-frozen non-sterilized grafts. Viscoelastic properties (strain, creep) were analyzed during cyclic submaximal loading and mechanical properties were investigated during load-to-failure (LTF) testing. It was found that there were no differences in viscoelastic and mechanical properties between both groups. The findings of this study provide baseline data for future in vitro and in vivo analyses of this promising new sterilization technique for soft-tissue allografts.

Structure and function of the healing medial collateral ligament in a goat model.

In this study knee joint function with a healing medial collateral ligament (MCL) at six weeks was examined with a robotic/universal force-moment sensor testing system during the application of two loading conditions: (1) 5 Nm valgus moment and (2) 67 N anterior load. Additionally the structural properties of the femur-MCL-tibia complex and the mechanical properties of the MCL substance were determined by uniaxial tensile tests. The histological appearance of the healing MCL was also observed. At 30 degrees and 60 degrees of knee flexion, valgus rotation of the healing knee was significantly increased compared to the sham. The in situ force in the healing MCL was significantly lower (34+/-17 N vs 54+/-12 N) at the same flexion angles (50+/-10 N vs 62+/-7 N). The anterior translation of the knee had returned to normal values at 30 degrees and 60 degrees of knee flexion. However, no differences could be found between the corresponding in situ forces in the healing MCL at all flexion angles examined during application of an anterior load. The stiffness of the healing group (52.5+/-19.4 N/mm) was significantly lower than the sham group (80.3+/-26.4 N/mm) (p<0.04). The modulus of the healing group was also significantly decreased (p<0.05). The findings suggest that the tensile properties of the healing goat MCL and valgus knee rotation have not returned to normal at six weeks after an isolated MCL rupture, however, anterior translation appeared to return to sham levels.

[Current aspects of anchoring hamstring tendon transplants in cruciate ligament surgery]. / Aktuelle Aspekte in der Verankerung von Hamstringsehnen-Transplantaten in der Kreuzbandchirurgie.

The use of hamstring tendon grafts in cruciate ligament surgery has recently raised strong interest. Hamstring tendons are superior to the mid third patellar tendon graft by virtue of lower harvest site morbidity combined with high tensile strength. Osseous graft incorporation relies on a proper tendon-to-bone healing, which relies on specific biomechanical and biological boundary conditions. Several different fixation devices have recently been introduced, with special emphasis on high initial fixation strength and moving the level of fixation closer to the joint line, the so-called aperture fixation. The goal of the present review is to focus on the advantages and disadvantages of different fixation principles for hamstring tendon grafts in order to give a comprehensive insight into current developments, such as interference fit fixation, cross-pin fixation, and the concept of hybrid fixation.

Mechanical behavior of two hamstring graft constructs for reconstruction of the anterior cruciate ligament.

We compared the mechanical behavior of two common hamstring graft constructs that are frequently used for reconstruction of the anterior cruciate ligament-Graft A: quadrupled semitendinosus tendon fixed with titanium button/polyester tape and suture/screw post, and Graft B: a double semitendinosus and double gracilis tendon fixed with a cross pin and two screws over washers. The experimental protocol used to evaluate each graft construct included stress relaxation (with and without preconditioning), cyclic loading, and a tensile load-to-failure test. The amount of stress relaxation without preconditioning was 60.6% for Graft A and 53.8% for Graft B. With preconditioning, it significantly decreased (p < 0.05) to 48.7 and 42.3%, respectively. Elongation of the graft construct in response to 100 cycles of loading (20-150 N) was 1.8 and 0.6% of the original length for Grafts A and B, respectively. However, after a series of five cyclic loading tests, the residual permanent elongation for each construct was 3.8 +/- 1.2 and 0.3 +/- 0.2 mm, a significant difference (p < 0.05) between the two graft constructs. Further analysis found more than 90% of the permanent elongation in the proximal and distal regions of Graft A, which consisted of polyester tape tied to a titanium button (proximal) and sutures tied around a screw post (distal). The tensile load-to-failure tests also revealed significant differences (p < 0.05) between the two graft constructs. Linear stiffness was 32 +/- 1 and 119 +/- 19 Nmm and ultimate load was 415 +/- 36 and 658 +/- 128 N for Grafts A and B, respectively. For Graft A, the polyester tape consistently failed; for Graft B, slippage or tearing from the washers was the mode of failure. We conclude that a quadruple-hamstring graft fixed over a cross pin proximally and with metal washers distally (Graft B) has less permanent elongation in response to cyclic loading and has structural properties superior to those of a graft construct that includes suture and tape material (Graft A). The large permanent elongation following repetitive loading of a graft construct with tape and suture material during the early postoperative period is of concern.