ACL Size, but Not Signal Intensity, Is Influenced by Sex, Body Size, and Knee Anatomy

Background: Little is known about sex-based differences in anterior cruciate ligament (ACL) tissue quality in vivo or the association of ACL size (ie, volume) and tissue quality (ie, normalized signal intensity on magnetic resonance imaging [MRI]) with knee anatomy. Hypothesis: We hypothesized that (1) women have smaller ACLs and greater ACL normalized signal intensity compared with men, and (2) ACL size and normalized signal intensity are associated with age, activity levels, body mass index (BMI), bicondylar width, intercondylar notch width, and posterior slope of the lateral tibial plateau. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Knee MRI scans of 108 unique ACL-intact knees (19.7 ± 5.5 years, 62 women) were used to quantify the ACL signal intensity (normalized to cortical bone), ligament volume, mean cross-sectional area, and length. Independent t tests were used to compare the MRI-based ACL parameters between sexes. Univariate and multivariate linear regression analyses were used to investigate the associations between normalized signal intensity and size with age, activity levels, BMI, bicondylar width, notch width, and posterior slope of the lateral tibial plateau. Results: Compared with men, women had significantly smaller mean ACL volume (men vs women: 2028 ± 472 vs 1591 ± 405 mm3), cross-sectional area (49.4 ± 9.6 vs 41.5 ± 8.6 mm2), and length (40.8 ± 2.8 vs 38.1 ± 3.1 mm) ( P < .001 for all), even after adjusting for BMI and bicondylar width. There was no difference in MRI signal intensity between men and women (1.15 ± 0.24 vs 1.12 ± 0.24, respectively; P = .555). BMI, bicondylar width, and intercondylar notch width were independently associated with a larger ACL ( R 2 > 0.16, P < .001). Younger age and steeper lateral tibial slope were independently associated with shorter ACL length ( R 2 > 0.03, P < .04). The combination of BMI and bicondylar width was predictive of ACL volume and mean cross-sectional area ( R 2 < 0.3). The combination of BMI, bicondylar width, and lateral tibial slope was predictive of ACL length ( R 2 = 0.39). Neither quantified patient characteristics nor anatomic variables were associated with signal intensity. Conclusion: Men had larger ACLs compared with women even after adjusting for BMI and knee size (bicondylar width). No sex difference was observed in signal intensity, suggesting no difference in tissue quality. The association of the intercondylar notch width and lateral tibial slope with ACL size suggests that the influence of these anatomic features on ACL injury risk may be partially explained by their effect on ACL size. Registration: NCT02292004 and NCT02664545 ( ClinicalTrials.gov identifier).

Diagnostic of Injury Risk in the Anterior Cruciate Ligament Based On Shape Context Description of the Intercondylar Notch Curvature

An estimated number of 300,000 new anterior cruciate ligament (ACL) injuries occur each year in the United States. Although several magnetic resonance (MR) imaging-based ACL diagnostics methods have already been proposed in the literature, most of them are based on machine learning or deep learning strategies, which are computationally expensive. In this paper, we propose a diagnostics framework for the risk of injury in the anterior cruciate ligament (ACL) based on the application of the inner-distance shape context (IDSC) to describe the curvature of the intercondylar notch from MR images. First, the contours of the intercondylar notch curvature from 91 MR images of the distal end of the femur (70 healthy and 21 with confirmed ACL injury) were extracted manually using standard image processing tools. Next, the IDSC was applied to calculate the similarity factor between the extracted contours and reference standard curvatures. Finally, probability density functions of the similarity factor data were obtained through parametric statistical inference, and the accuracy of the ACL injury risk diagnostics framework was assessed using receiver operating characteristic analysis (ROC). The overall results for the area under the curve (AUC) showed that method reached a maximum accuracy of about 66%. Furthermore, the sensitivity and specificity results showed that an optimum discrimination threshold value for the similarity factor can be pursued that minimizes the incidence of false positives and false positives simultaneously.

Analysis of intercondylar notch size and shape in patients with cyclops syndrome after anterior cruciate ligament reconstruction

Background Cyclops lesion is the second most common cause of extension loss after anterior cruciate ligament reconstruction. This study focused on the correlation between the anatomy of the intercondylar notch and the incidence of cyclops lesion. To determine whether the size and shape of the intercondylar notch are related to cyclops lesion formation following anterior cruciate ligament reconstruction according to magnetic resonance imaging (MRI) findings. Methods One hundred twenty-five (125) patients were retrospectively evaluated. The notch width index (NWI) and notch shape index (NSI) were measured based on coronal and axial MRI sections in patients diagnosed with cyclops syndrome (n = 25), diagnosed with complete anterior cruciate ligament (ACL) tears (n = 50), and without cyclops lesions or ACL ruptures (n = 50). Results Imaging analysis results showed that the cyclops and ACL groups had lower mean NWI and NSI values than the control group. Significant between-group differences were found in NSI (p = 0.0140) based on coronal cross-sections and in NWI (p = 0.0026) and NSI (p < 0.0001) based on axial sections. Conclusions The geometry of the intercondylar notch was found to be associated with the risk of cyclops lesion formation and ACL rupture.

Stenotic intercondylar notch is not a risk factor for posterior cruciate ligament rupture: a morphological analyses using magnetic resonance imaging

Purpose The present study aimed to examine the factors related to the morphological characteristics of the femoral condyle in posterior cruciate ligament rupture in female and male populations. Methods One hundred and three patients (41 females, 62 males) with posterior cruciate ligament rupture from 2010 to 2020 were included in this retrospective case–control study. The sex and age of the posterior cruciate ligament rupture group were matched to those of the control group (41 females, 62 males; age range 16–69 years). Magnetic resonance imaging was used to measure the intercondylar notch width, femoral condylar width, and intercondylar notch angle in both the axial and coronal images. The ‘α’ angle was also measured using magnetic resonance imaging. The notch width index is the ratio of the intercondylar notch width to the femoral condylar width. Three types of intercondylar notch shapes (types A, U, and W) were evaluated in the axial magnetic resonance imaging images. Results The difference in the mean coronal notch width index between the study groups was statistically significant in the female population. The difference in the mean coronal femoral condylar width between the study groups was statistically significant in the male population. Conclusions A larger coronal notch width index was the greatest risk factor for posterior cruciate ligament rupture in the female population. In the male population, decreased coronal condylar width was the greatest risk factor for posterior cruciate ligament rupture. The results did not indicate that patients with a PCL rupture have a stenotic intercondylar notch. Posterior cruciate ligament injury prevention strategies could be applied to females with a larger coronal notch width index and males with a decreased condylar width. Levels of evidence Level III.

Association of Geometric Characteristics of Knee Anatomy (Alpha Angle and Intercondylar Notch Type) With Noncontact ACL Injury

Background: The femoral intercondylar notch type and the alpha angle (the angle between the femoral notch roof and the long axis of the femur) are easily measured in clinical settings; however, their associations with anterior cruciate ligament (ACL) injury remain unclear. Hypothesis/Purpose: The purpose was to determine if the alpha angle and the femoral notch type are associated with noncontact ACL injury univariately and in combination with previously identified knee geometric risk factors. We hypothesized that the alpha angle and the femoral notch type are associated with noncontact ACL injury and that the association differs between men and women. Study Design: Case control study; Level of evidence, 3. Methods: The alpha angle and the femoral notch type were measured via 3T magnetic resonance imaging (MRI) acquired from 61 women and 25 men with a first-time noncontact ACL injury. Each injured patient was matched with a control participant based on age, sex, and participation on the same sports team. A conditional logistic regression was used to assess univariate associations with ACL injury as well as multivariate associations using MRI-based risk factors of knee geometry identified in previous analyses: femoral intercondylar notch width at the anterior outlet, femoral intercondylar notch anteromedial ridge thickness, volume of the ACL, tibial plateau lateral compartment subchondral bone slope, lateral compartment middle articular cartilage slope, lateral compartment meniscus-cartilage height, lateral compartment meniscus-bone angle, and medial tibial spine volume. Results: For female athletes, the alpha angle (odds ratio, [OR], 1.82 per 1-degree increase; P = .001), the tibial lateral compartment articular cartilage slope (OR, 1.25 per 1-degree increase in the posterior-inferior directed slope; P = .022), and the femoral notch anteromedial ridge thickness (OR, 3.36 per 1-mm increase; P = .027) were independently associated with ACL disruption. For men, no other variables entered the models after the alpha angle was inputted as the first step (OR, 2.19 per 1-degree increase; P = .010). Conclusion: For women, ACL injury was most strongly associated with increased alpha angle, increased tibial plateau slope, and increased femoral notch ridge thickness. For men, increased alpha angle was the most significant factor associated with ACL injury. The mechanism of injury might be associated with a combination of impingement of the ACL against the bone and increased ligament loading.

Applicability of Semi-Quantitative Evaluation of the Intercondylar Notch

The intercondylar notch (IN) can differ in morphology and size, influencing the contained ligaments. For a better understanding of the influence of the IN’s anatomy on knee pathologies, a classification of different shapes was proposed. However, a detailed evaluation of the reliability of these classifications is lacking thus far. In coronal knee MRIs of 330 patients, the IN width was measured and three shapes were calculated to generate objective control results. Notch shapes were classified by two blinded investigators, first without and then with visual assistance to guide the shape classification. The distribution of the three different shapes was as follows: A-shape: n = 43, 13.0%; inverse U-shape: n = 100, 30.3%; Ω-shape: n = 183, 56.7%. The semi-quantitative evaluation distribution was as follows: A-shape: n = 44, 13.3%; inverse U-shape: n = 37, 11.2%; Ω-shape: n = 249, 75%; there was fair (κ = 0.35) agreement compared to that of the control results. The assisted semi-quantitative evaluation distribution was as follows: A-shape: n = 44, 13.3%; inverse U-shape: 103, 31.2%; Ω-shape: n = 183, 55.3%; there was very good (κ = 0.92) agreement compared to that of the control results. In the shape evaluation of the IN, rigid guidelines and visual assistance must be used to ensure reliability. The utilization of visual assistance led to higher inter- and intra-rater agreements in the semi-quantitatively evaluation of the IN shape when compared to those in the classification without visual assistance.