The femoral posterior fan-like extension of the ACL insertion increases the failure load

ACL anatomy: Is there still something to learn?

BACKGROUND

The different bony and soft tissue reference points and the micro and macroscopic structures of the knee continue to be the object of focused study and analysis. Upon reviewing the most recent literature, we saw the wide spectrum of studies that seek to define the different anatomical aspects of the anterior cruciate ligament (ACL).

PURPOSE

The purpose of this paper is to review the most recent publications on the ACL and its morphology in which its microscopic composition and macroscopic anatomy are addressed.

RESULTS

The ACL consists of typeI (90%) and typeIII (10%) collagen matrix. Its length ranges from 27 to 38mm and its width from 10 to 12mm. The ACL cross-section area measures an average of 44mm2, and its shape resembles that of an hourglass or a bow tie. ACL bundles have been defined as anteromedial, intermediate, and posterolateral. Femoral and tibial footprints were seen to present a high degree of variability in shape and size. Furthermore, the blood supply is given by the medial genicular artery and innervation by the tibial nerve branches. Additionally, the ACL functionally prevents anterior translation of the tibia and stabilizes against the internal rotation of the tibia and valgus angulation of the knee.

CONCLUSIONS

There is great variability in the anatomy of the ACL as well as its attachment sites. At the same time, the shape and size of its footprint has become a factor in determining individualized ACL reconstruction. The persistence of morphological variability in the aging of the ACL and important aspects of surgical planning and decision making with respect to anatomical risk factors suggest that further studies are called for.

ACL anatomy: Is there still something to learn?

BACKGROUND

The different bony and soft tissue reference points and the micro and macroscopic structures of the knee continue to be the object of focused study and analysis. Upon reviewing the most recent literature, we saw the wide spectrum of studies that seek to define the different anatomical aspects of the anterior cruciate ligament (ACL).

PURPOSE

The purpose of this paper is to review the most recent publications on the ACL and its morphology in which its microscopic composition and macroscopic anatomy are addressed.

RESULTS

The ACL consists of type I (90%) and type III (10%) collagen matrix. Its length ranges from 27 to 38mm and its width from 10 to 12mm. The ACL cross-section area measures an average of 44mm2, and its shape resembles that of an hourglass or a bow tie. ACL bundles have been defined as anteromedial, intermediate, and posterolateral. Femoral and tibial footprints were seen to present a high degree of variability in shape and size. Furthermore, the blood supply is given by the medial genicular artery and innervation by the tibial nerve branches. Additionally, the ACL functionally prevents anterior translation of the tibia and stabilizes against the internal rotation of the tibia and valgus angulation of the knee.

CONCLUSIONS

There is great variability in the anatomy of the ACL as well as its attachment sites. At the same time, the shape and size of its footprint has become a factor in determining individualized ACL reconstruction. The persistence of morphological variability in the aging of the ACL and important aspects of surgical planning and decision making with respect to anatomical risk factors suggest that further studies are called for.

Compositional, Structural, and Biomechanical Properties of Three Different Soft Tissue-Hard Tissue Insertions: A Comparative Review

Connective tissue attaches to bone across an insertion with spatial gradients in components, microstructure, and biomechanics. Due to regional stress concentrations between two mechanically dissimilar materials, the insertion is vulnerable to mechanical damage during joint movements and difficult to repair completely, which remains a significant clinical challenge. Despite interface stress concentrations, the native insertion physiologically functions as the effective load-transfer device between soft tissue and bone. This review summarizes tendon, ligament, and meniscus insertions cross-sectionally, which is novel in this field. Herein, the similarities and differences between the three kinds of insertions in terms of components, microstructure, and biomechanics are compared in great detail. This review begins with describing the basic components existing in the four zones (original soft tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone) of each kind of insertion, respectively. It then discusses the microstructure constructed from collagen, glycosaminoglycans (GAGs), minerals and others, which provides key support for the biomechanical properties and affects its physiological functions. Finally, the review continues by describing variations in mechanical properties at the millimeter, micrometer, and nanometer scale, which minimize stress concentrations and control stretch at the insertion. In summary, investigating the contrasts between the three has enlightening significance for future directions of repair strategies of insertion diseases and for bioinspired approaches to effective soft-hard interfaces and other tough and robust materials in medicine and engineering.

Remnant preserving ACL reconstruction with a functional remnant is related to improved laxity but not to improved clinical outcomes in comparison to a nonfunctional remnant

PURPOSE

The Anterior cruciate ligament (ACL) remnant has been pointed out as a ligamentization enhancer. Nonetheless, the remaining tissue can be functional if it still provides some stability or nonfunctional. This study intends to compare the clinical results and knee stability of functional vs. nonfunctional remnant preservation ACL reconstruction (ACLR).

METHODS

One hundred and seventy-five patients with ACL injuries were included and underwent remnant preservation ACLR. They were divided into two groups accordingly to remnant tissue functionality: functional (Group F) and nonfunctional (Group NF). Primary outcome was defined as patient reported outcomes measured with Lysholm, IKDC and Tegner continuous scales and improvements. Secondary outcomes comprised of Lachman test, anterior drawer test, pivot shift test, extension and flexion deficit, graft coverage by remnant preserved tissue and failure rate (persistent instability or new ACL lesion). Menisci lesions, cartilage lesions and time to surgery were also recorded for each group.

RESULTS

One hundred and forty-four patients were available at a mean of 30.2 ± 10.1 months: 69 Functional and 75 Nonfunctional. Lysholm, IKDC and Tegner functional outcomes demonstrated no difference between the groups, Functional compared to Nonfunctional: 88.4 ± 10.5 vs. 92.2 ± 4.9, n.s. and 83.2 ± 11.3 vs. 87 ± 5.3, n.s. and 6 (5-10) vs. 6 (5-9), n.s., respectively. Lysholm and IKDC functional outcomes improvements demonstrated differences between the groups: Functional compared to Nonfunctional (39.3 ± 9.4 vs. 42.3 ± 7.4, p = 0.014 and 37.7 ± 10 vs. 41.0 ± 6.6, p = 0.032); however, they were not clinically significant. Functional group showed more stability on physical examination pre- and post-operatively (p < 0.001, p < 0.001). There was no difference regarding extension deficit (n.s.); however, functional group had more flexion deficit (p = 0.02). Nonfunctional group had better graft coverage (p = 0.001). There was no difference regarding failure rate: 4% vs. 9%, (n.s.).

CONCLUSION

Both remnant preservation ACLR techniques were able to achieve satisfactory functional outcomes. A functional remnant was not related to improved functional outcomes in comparison to a nonfunctional remnant; however, it was related to less laxity pre and postoperatively and inferior graft coverage.

LEVEL OF EVIDENCE

II.

Tibial slope, remnant preservation, and graft size are the most important factors affecting graft healing after ACL reconstruction

PURPOSE

The aim of this study was to determine the anatomic, operative and biological factors that influenced graft healing after single-bundle anterior cruciate ligament (ACL) reconstruction.

METHODS

One hundred fourteen consecutive patients who underwent anatomic single-bundle ACL reconstruction with quadrupled hamstring tendon autografts between 2016 and 2019 were retrospectively analyzed. Ninety-four patients met the inclusion criteria with minimum follow-up of 12 months. Patients were evaluated with multiple clinical measurements, including International Knee Documentation Committee Subjective Knee Form (IKDC-SKF), Lyshom Scores, and Marx activity scale. To evaluate graft healing, the signal-to-noise quotient (SNQ) was measured at intra-articular graft and intra-tunnel integration were evaluated on magnetic resonance imaging (MRI) at one year after surgery. Potential factors affecting graft healing, including age, sex, body mass index, time from injury to surgery, posterior tibial slope, lateral femoral condyle ratio, notch width index, meniscal injury, remnant preservation, tunnel aperture locations, graft size, graft bending angle, graft/remaining notch volume ratio were evaluated for their association with graft SNQ value by stepwise regression analysis.

RESULTS

A total of 94 patients were evaluated with mean follow-up 28.5 ± 9 months. Univariate regression analysis showed that posterior tibial slope, notch width index, remnant preserving procedure, high femoral tunnel, anterior tibial tunnel, graft bending angle, and graft/remaining notch volume ratio significantly associated with graft SNQ values. Multivariate regression analysis showed that lateral tibial slope, remnant preservation, and graft/remaining notch volume ratio were independent factors correlated with graft SNQ values. Also, the graft SNQ values was weakly correlated with femoral tunnel integration and Marx activity scale at one year. There was no correlation between graft SNQ values and IKDC-SKF and Lysholm scores. There was no correlation between graft SNQ values and International Knee Documentation Committee and Lysholm scores.

CONCLUSIONS

Tibial slope, remnant preservation and graft/remaining notch volume ratio were significant independent associated factors of graft SNQ value at one year. The graft SNQ values were also weakly correlated with femoral tunnel integration and the Marx activity scale. These factors should be taken into account for ensuring the ideal graft healing and for the return to sport decision-making.

LEVEL OF EVIDENCE

Level IV.

A Modified Anatomic Transtibial Double-Bundle Anterior Cruciate Ligament Reconstruction Provides Reliable Bone Tunnel Positioning

Purpose

To evaluate the femoral and tibial tunnel positions via a modified anatomic transtibial double-bundle anterior cruciate ligament (ACL) reconstruction.

Methods

Patients who underwent double-bundle ACL reconstruction using the transtibial tunnel creation technique were identified. Double-bundle ACL reconstruction was performed for 94 knees using the transtibial tunnel creation technique. Tunnel aperture configurations and center positions of the anteromedial (AM) and posterolateral (PL) tunnels via postoperative 3-dimensional computed tomography were evaluated.

Results

There were 94 knees included. Regarding the intra-articular tunnel aperture configurations, the AM and PL tunnels overlapped at the femoral and tibial aperture in 66.0% and 94.7% cases, respectively. The mean femoral bone tunnel center was located at 23.0 ± 3.9% in the posterior-to-anterior ratio and 28.7 ± 6.0% in the proximal-to-distal ratio for the AM tunnels and at 32.8 ± 4.7% and 51.2 ± 5.2% for the PL tunnels, respectively. In the tibial tunnels, the mean AM tunnel center was located at 31.4 ± 3.6% in the anterior-to-posterior ratio and 44.3 ± 1.8% in the medial-to-lateral ratio and at 47.5 ± 3.8% and 44.3 ± 1.9% in the PL tunnel center, respectively. The femoral tunnels of outliers, both those created in nonanatomic positions as well as the posterior wall blowouts, were revealed in 7.4% cases. The nonanatomical bone tunnel group had significant heavier weight patients, lower tibial posterior slope, and were anterior in the AM and PL tunnel position. Posterior wall blowouts were related to posterior and proximal PL bone tunnel positions.

Conclusions

Modified transtibial double-bundle ACL reconstruction is a reliable tunnel creation technique with anatomic placement in 92.6% of the cases. The modification required that partially superimposing configuration of the 2 tibial tunnel apertures. The nonanatomic tunnels were related to patients of heavier weight and lower tibial posterior sloped knees, whereas the posterior wall blowouts were related to the posterior and proximal PL bone tunnel positions.

Level of Evidence

Level IV, therapeutic case series.

The morphology of the femoral footprint of the anterior cruciate ligament changes with aging from a large semicircular shape to a small flat ribbon-like shape

PURPOSE

Compare the differences in the morphology of the ACL femoral footprint between the cadavers of the young and elderly in consideration of the degenerative physiological process that occurs with aging.

METHODS

The femoral footprint of the ACL was dissected in 81 knees of known gender and age (45 male/36 female). They were divided into four groups by age and gender, establishing 50 years as the cut-off point to divide patients by age. Three observers analyzed the femoral footprint dissections, and the shapes were described and classified. The area and morphometric characteristics of the femoral insertion of the ACL were determined and these were compared between genders and age groups.

RESULTS

The femoral footprint of the ACL from the cadavers of males younger than 50 years of age presented a semicircular morphology in 90% of the cases. In males aged more than 50 years, a ribbon-like morphology was found in 96% of the cases. In women less than 50 years old, the semicircular morphology was observed in 93.7% of the cases. In women aged over 50 years old, the ribbon-like morphology was found in 95% of the cases. A significant difference was observed between the prevalence rates of the morphologies, area size and measurements of the younger and older groups (p < 0.001 for both genders).

CONCLUSIONS

The femoral insertion of the ACL presents variations in its morphology, area and morphometric characteristics over time. It goes from a large semicircular shape that almost contacts the posterior articular cartilage to a smaller, flattened ribbon-like shape that moves away from the edge of the articular cartilage. It is bounded anteriorly by the lateral intercondylar ridge. These findings should be considered to avoid employing reconstruction techniques in which femoral tunnels with oval or rectangular shapes are used in patients under 50 years of age because they do not correspond to the morphology of the femoral insertion of the ACL in this age group.

Failure load of the femoral insertion site of the anterior cruciate ligament in a porcine model: comparison of different portions and knee flexion angles

BACKGROUND

This study compared the failure load of the femoral insertion site of the anterior cruciate ligament between different portions and knee flexion angles.

METHODS

In total, 87 fresh-frozen, porcine knees were used in this study. Three knees were used for histological evaluation; the remaining 84 knees were randomly divided into 4 groups: anterior anteromedial bundle, posterior anteromedial bundle, anterior posterolateral bundle, and posterior posterolateral bundle groups (n=21 per group). The anterior cruciate ligament femoral insertion site was divided into these four areas and excised, leaving a 3-mm square attachment in the center of each bundle. Tibia-anterior cruciate ligament-femur complexes were placed in a material testing machine at 30°, 120°, and 150° of knee flexion (n=7), and the failure load for each portion was measured under anterior tibial loading (0.33 mm/s).

RESULTS

Histological study showed that the anterior cruciate ligament femoral insertion site consisted of direct and indirect insertions. Comparison of the failure load between the knee flexion angles revealed that all the failure loads decreased with knee flexion; significant decreases were observed in the failure load between 30 and 150° knee flexion in the posterior anteromedial bundle and posterior posterolateral bundle groups. Comparison of the failure load according to different portions revealed a significant difference between the anteromedial and posterolateral bundle groups at 150° of knee flexion, but no significant difference among the groups at 30° of flexion.

CONCLUSIONS

Although the failure load of the posterior portion decreased significantly in the knee flexion position, it (mainly consisting of indirect insertion) plays a significant role against anterior tibial load in the knee extension position; this appears to be related to the characteristics of the insertion site. Reflecting the complex structure and function of the ACL, this study showed that the failure load of the femoral insertion site varies with differences in positions and knee flexion angles.