Correlation between Morphological Features of the Anterior Cruciate Ligament: A Quantitative Study Using a Porcine Model

Background: Inadequate restoration of the rotational knee stability is often reported after ACL reconstruction, mainly due to insufficient restoration of the morphology of the ACL. This study aimed to explore the quantitative correlation between morphological features of the ACL, thus to provide useful information for improving anatomical reconstruction techniques and designing artificial ligaments. Methods: Porcine model was used in this study mainly because the morphology and function of porcine ACLs have been reported to be similar to those of the human ACL. 19 porcine knees (1 year, male) were fixed at full extension using 10% formalin and were dissected to expose the ACL. ACL lengths were measured using a caliper. Mid-substances of the ACL were cut and scanned using X-ray microscopy, and the cross-sectional area (CSA) was measured at the isthmus. Margins of direct and indirect bone insertion sites were distinguished and marked. Measurements were performed on digital photographs to obtain the areas of bone insertions. Statistical analysis using nonlinear regression was used to identify potential correlations among the measurements. Results: The results showed large individual differences on all of the measurements (e.g. the CSA at ACL isthmus ranged from 44.7 to 87.2 mm2, when the area of its femoral and tibial insertion sites ranged from 188.1 and 233.6 mm2 to 258.4 and 412.0 mm2, respectively). The CSA at the isthmus was significantly correlated with the total area of the bone insertion sites and the area of tibial insertion. The area of the tibial insertion was significantly correlated with the area of its direct insertion site. In contrast, the area of the femoral insertion was significantly correlated with the area of its indirect insertion site. The area of the indirect tibial insertion showed a weak correlation with the length of ACL, whereas the length of the ACL was not able to predict or be predicted by any other parameters.Conclusions: The CSA at the ACL isthmus might be more suitable for assessing the morphology of the ACL. However, ACL length has little correlation with the CSA of the isthmus or bone insertion sites, thus should be evaluated independently before surgery.

IS THE “U-SIGN” RADIOLOGIC FEATURE OF A POSTERIOR CRUCIATE LIGAMENT TIBIAL AVULSION FRACTURE?

ABSTRACT Objective: By analyzing our cases of posterior cruciate ligament (PCL) tibial avulsion fracture, we noted that a U-shaped image was present in the anteroposterior plain radiographs view of the affected knee, even in cases where the profile view of the knee had been inconclusive as to tibial PCL avulsion fracture, a “hidden” fracture. Therefore, we aimed to investigate whether there was an anatomical correlation between this radiological U sign and the tibial insertion of the PCL and to ascertain the intra- and inter-rater reliability of this sign in clinical practice. Methods: The data of the widths and heights area of the PCL tibial insertion area, and the U sign area were measured and compared to the largest width of the tibia. Two moreover, the reliability and reproducibility of this imaging were analyzed. Results: The areas height of the U-sign area and the anatomical insertion area of the posterior cruciate ligament showed no difference, and both were topographically located in the two central quarters of the proximal end of the tibia. The radiographic assessment showed excellent Kappa agreement rates between interobserver and intraobserver, with high reliability and reproducibility. Conclusion: The U sign is a radiographic feature of PCL tibial avulsion fracture seen on the radiograph AP view, there is a high association between the ratios of the U-sign area height in the X-ray and the anatomical height of the PCL tibial insertion site MRI with the largest width of the proximal tibia. The radiographic U sign showed excellent rates of interobserver and intraobserver agreement with Kappa values higher than 0.8. Level of Evidence IV; Dignostic Studies - Investigating a Diagnostic Test.

Multiplanar reformation improves identification of the anterolateral ligament with MRI of the knee

The anterolateral ligament (ALL) is subject of the current debate concerning rotational stability in case of anterior cruciate ligament (ACL) injuries. Today, reliable anatomical and biomechanical evidence for its existence and course is available. Some radiologic studies claim to be able to identify the ALL on standard coronal plane MRI sections. In the experience of the authors, however, ALL identification on standard MRI sequences frequently fails and is prone to errors. The reason for this mainly lies in the fact, that the entire ALL often cannot be identified on a single MRI image. This study aimed to establish an MRI evaluation protocol improving the visualization of the ALL, using multiplanar reformation (MPR) with the goal to be able to evaluate the ALL on one MRI image. A total of 47 knee MRIs performed due to atraumatic knee pain between 2018 and 2019 without any pathology were analyzed. Identification of the ALL was performed twice by an orthopedic surgeon and a radiologist on standard coronal plane and after MPR. For the latter axial and coronal alignment was obtained with the femoral condyles as a reference. Then the coronal plane was adjusted to the course of the ALL with the lateral epicondyle as proximal reference. Visualization of the ALL was rated as “complete” (continuous ligamentous structure with a tibial and femoral insertion visible on one coronal image), “partial” (only parts of the ALL like the tibial insertion were visible) and “not visible”. The distances of its tibial insertion to the bony joint line, Gerdy’s tubercle and the tip of the fibular head were measured. On standard coronal images the ALL was fully visible in 17/47, partially visible in 27/47, and not visible in 3/47 cases. With MPR the ALL was fully visible in 44/47 and not visible in 3/47 cases. The median distance of its tibial insertion to the bony joint line, Gerdy’s tubercle and the tip of the fibular head were 9, 21 and 25 mm, respectively. The inter- (ICC: 0.612; 0.645; 0.757) and intraobserver (ICC: 0.632; 0.823; 0.857) reliability was good to excellent. Complete visualization of the ALL on a single MRI image is critical for its identification and evaluation. Applying multiplanar reformation achieved reliable full-length visualization of the ALL in 94% of cases. The described MPR technique can be applied easily and fast in clinical routine. It is a reliable tool to improve the assessment of the ALL.

Treatment of Anterior Cruciate Ligament Tibial Insertion Avulsion Fractures with a Single Tunnel using a Double-strand Suture Anchor Under Arthroscopy

Purpose Anterior cruciate ligament (ACL) tibial insertion avulsion fractures cause instability of the knee joint, and minimally invasive techniques are the first choice for treating this type of intra-articular injury. The aim of this study was to investigate the clinical effect of a single tunnel with a double-strand suture anchor in the treatment of ACL tibial insertion avulsion fractures. Methods A retrospective analysis was performed on the data for 29 patients, comprising 15 males and 14 females, with Meyers-McKeever type II or III ACL tibial insertion avulsion fractures treated with a single tunnel using a double-strand suture anchor under arthroscopy from January 2014 to June 2018. All 29 patients in this group were followed up for 12 months. The Lachman test was used to evaluate knee joint stability, the Lysholm score was used to evaluate knee joint function, and postoperative X-rays were used to evaluate healing after fracture reduction. Results All 29 patients completed the follow-up. During the 12-month follow-up period, postoperative X-rays showed that all ACL tibial insertion avulsion fractures healed well and the pre-fracture function was restored. All incisions performed in patients healed well, and no surgical complications, such as infection or fracture nonunion, occurred. The anterior drawer test (ADT) and Lachman test were negative for the patients, and the knee function recovered well. The preoperative Lysholm score was 51.14 ± 2.34, and the preoperative International Knee Documentation Committee (IKDC) subjective score was 51.24 ± 3.16; the Lysholm score at the last follow-up was 92.52 ± 1.35, and the IKDC subjective score at the last follow-up was 92.93 ± 2.59 (P < 0.05). Conclusion Within the limitations of this study, a single tunnel with a double-strand suture anchor under arthroscopy for the treatment of ACL tibial insertion avulsion fracture was a simple procedure. The procedure caused minimal trauma, achieved good reduction, had firm fixation, ensured quick recovery, caused few complications, ensured good functional recovery, and provided satisfactory clinical results.Level of evidence: IV

The Anterior Oblique Ligament description in the knee anteromedial compartment

Purpose: To describe a ligamentous structure in the anteromedial region of the knee identified in a series of anatomical dissections of cadaveric specimens.Methods: Sixteen cadaveric knees were dissected to study the medial compartment. Exclusion criteria were signs of trauma, previous surgery, signs of osteoarthritis and poor preservation state. The main structures of this region were identified during medial dissection. After releasing the superficial medial collateral ligament (sMCL) of the tibia, the Anterior Oblique Ligament (AOL), was isolated. The morphology of the structure and its relationship with known anatomical parameters were determined. For the statistical analysis, the means and standard deviations were calculated for continuous variables. A 95% confidence intervals was defined as significant. Student's t-tests were used for continuous variables.Results: After dissection a distinct ligamentous structure (AOL) was found in the medial region of the knee. This structure was found in 100% of the cases, was located extracapsularly and originated in the anterior aspect of the medial epicondyle, running obliquely toward the tibia. When crossing the joint, the ligament presented a fan-shaped opening, exhibiting a larger area at the tibial insertion. The AOL had a mean thickness of 6.83±1.34 mm at its femoral origin and 13.06±1.91 at its tibial insertion. It had a significantly (p = 0.0009) longer mean length with the knee at 90° of flexion (33.82±9.50 mm) than with the knee in total extension (26.56±9.48 mm), indicating that the ligament is tensioned in flexion.Conclusion: A structure was identified in the anteromedial compartment of the knee with a ligamentous appearance originating in the medial femoral epicondyle and with tibial insertion anterior to the sMCL. Clinical relevance: This study demonstrates the anatomy of a new medial structure of the knee. As a result, there will be a better understanding of the stability of the knee.