3D visualization of the human anterior cruciate ligament combining micro-CT and histological analysis.

PURPOSE: The study aimed to obtain a comprehensive 3D visualization of knee specimens, including the cruciate ligaments and corresponding femoral and tibial bone insertions using a non-destructive micro-CT method. METHODS: Knee specimens were fixed in anatomical positions and chemically dehydrated before being scanned using micro-CT with a voxel size of 17.5 µm. RGBA (red, green, blue, alpha) transfer functions were applied to virtually colorize each structure. Following micro-CT scanning, the samples were rehydrated, decalcified, and trimmed based on micro-CT 3D reconstructions as references. Histological evaluations were performed on the trimmed samples. Histological and micro-CT images were registered to morphologically and densitometrically assess the 4-layer insertion of the ACL into the bone. RESULTS: The output of the micro-CT images of the knee in extension and flexion allowed a clear differentiation of the morphologies of both soft and hard tissues, such as the ACL, femoral and tibial bones, and cartilage, and the subsequent creation of 3D composite models useful for accurately tracing the entire morphology of the ligament, including its fiber and bundle components, the trajectory between the femur and tibia, and the size, extension, and morphology of its insertions into the bones. CONCLUSION: The implementation of the non-destructive micro-CT method allowed complete visualization of all the different components of the knee specimens. This allowed correlative imaging by micro-CT and histology, accurate planning of histological sections, and virtual anatomical and microstructural analysis. The micro-CT approach provided an unprecedented 3D level of detail, offering a viable means to study ACL anatomy.

Smaller intercondylar notch size and smaller ACL volume increase posterior cruciate ligament rupture risk.

PURPOSE: Little is known about risk factors for sustaining a posterior cruciate ligament (PCL) rupture. Identifying risk factors is the first step in preventing a PCL rupture from occurring. The morphology of the knee in patients who ruptured their PCL may differ from that of control patients. The hypothesis was that the intercondylar notch dimensions, 3-D volumes of the intercondylar notch and, the 3-D volumes of both the ACL and the PCL were correlated to the presence of a PCL rupture. METHODS: The magnetic resonance imaging (MRI) scans of 30 patients with a proven PCL rupture were compared to 30 matched control patients with proven intact ACL and PCL. Control patients were selected from patients with knee trauma during sports but without cruciate ligament injury. Patients have been matched for age, height, weight, BMI, and sex. The volumes of the intercondylar notch and both the ACL and PCL were measured on 3D reconstructions. Second, the bicondylar width, the notch width, and the notch width index were measured of all subjects. The relationship between our measurements and the presence of a PCL rupture was analysed. RESULTS: The results show a significant difference in the volumes of the intercondylar notch and the ACL between patients with a ruptured PCL and control patients. Patients with a PCL rupture have smaller intercondylar notch volumes and smaller ACL volumes. There were no significant differences in the bicondylar width, notch width, and notch width index. In the control patients, a significant correlation between the volume of the PCL and the volume of the ACL was found (0.673, p < 0.001). CONCLUSION: Patients with a PCL rupture have smaller intercondylar volumes and smaller ACL volumes when compared to control patients. Second, patients with smaller ACL volumes have smaller PCL volumes. This study shows, for the first time, that there are significant size and volume differences in the shape of the knee between patients with a PCL rupture and control patients. LEVEL OF EVIDENCE: IV.

The ligamentum mucosum: A new classification.

The ligamentum mucosum (LM) is a ligamentous structure within the synovial layer of the knee joint capsule. For a long time LM was perceived as the vestigial remnant from the embryological development of the knee. However, last years have shown increased interest in this structure due to its potentially significant clinical role. Fifty-one, 12 females (mean age 83.1 ± 3.4 years) and 39 males (mean age 84.2 ± 6.8 years) fixed in 10% formalin were examined. Upon dissection, the following morphological features of the LM were assessed: the types of LM, morphometric measurement and histological analysis of each type. The LM was present in 66.7% of all examined specimens. Three different types were recognized: Type I (55.9%)-single band with attachment to the intercondylar notch, Type IIa-bifurcated ligament with attachment to the anterior cruciate ligament, Type IIb-bifurcated ligament with both attachments to the intercondylar notch, Type III-double ligament with two independent bands and attachments to the intercondylar notch and to the knee joint capsule. The LM is variable and probably evolutionary changes are the reason. In our study we propose the new clinically useful classification supported by its anatomical and histological characteristics. Type IIa seems to be the most important from the clinical point of view, as it may be responsible for clinical issues and should be paid attention while diagnosing patients suffering from anterior cruciate ligament torn or anterior knee pain.

A comparative study of the epiligament of the medial collateral and anterior cruciate ligaments in the human knee: Immunohistochemical analysis of CD 34, α-smooth muscle actin and vascular endothelial growth factor in relation to epiligament theory.

BACKGROUND: This study evaluated and compared the expression of VEGF, CD34, and α-SMA in the anterior cruciate ligaments and medial collateral ligaments in healthy human knees in order to enrich the epiligament theory regarding ligament healing after injury. METHODS: Samples from the mid-substance of the anterior cruciate ligament and the medial collateral ligament of 12 fresh knee joints were used. Monoclonal antibodies against CD34, α-SMA, and VEGF were used for immunohistochemical analysis. Photomicrographs were analyzed using the ImageJ software. RESULTS: The epiligament of the anterior cruciate ligament showed slightly higher expression of CD34, α-SMA, and VEGF than the epiligament of the medial collateral ligament. Overall, among the tested markers, α-SMA expression was most pronounced in anterior cruciate ligament epiligament images and CD34 dominated in medial collateral ligament epiligament images. The intensity of DAB staining for CD34, α-SMA, and VEGF was higher in vascular areas of the epiligament than in epiligament connective tissue. CONCLUSIONS: The results illustrate that CD34, α-SMA, and VEGF are expressed in the human epiligament. The differences between the epiligament of the investigated ligaments and the fact that CD34, α-SMA, and VEGF, which are known to have a definite role in ligament healing, are predominantly expressed in the main vascular part of the ligament-epiligament complex enlarge the existing epiligament theory. Future investigations regarding better ligament healing should not overlook the epiligament tissue.

An anatomical study of the meniscal roots of the knee: landmarks for its surgical reconstruction and implications for knee surgeons.

PURPOSE: The aim of this anatomical study was to describe the anatomy of the meniscal roots and their relationships with respect to the main adjacent structures in order to improve their surgical reconstruction. METHODS: Fourteen knees were included. The mean age of the donors was 92 years (range 89-96). We studied the general characteristics of the anterior and posterior roots of the medial meniscus and lateral meniscus by measuring their widths at their base and area. We investigated the relations between anterior and posterior roots of the medial and lateral menisci with respect to the anterior and posterior cruciate ligaments (ACL and PCL). RESULTS: The mean width of the anterior root of the lateral meniscus was 10.5 ± 1.4 mm. The mean width of the anterior root of the medial meniscus was 10 ± 1.5 mm. The mean width of the posterior root of lateral meniscus was 11.4 ± 1.4 mm. The mean width of the posterior root of medial meniscus was 10.5 ± 1.0 mm. The mean distance between the anterior cruciate ligament and the anterior root of lateral meniscus was 9.8 ± 2.9 mm, for the medial meniscus it was 15.9 ± 3.4 mm. The mean distance between the posterior cruciate ligament and the posterior root of the lateral meniscus was 11.5 ± 2.7 mm, for the medial meniscus, it was 11 ± 2.6 mm. CONCLUSION: The anterior and posterior meniscal roots have precise landmarks, and this article contributes to define the location of the meniscal roots with respect to their adjacent anatomical structures: ACL, PCL and intercondylar tubercle. Having precise measures of the distances between the meniscus roots and these structures allows knee surgeons to perform ACL reconstruction, meniscal root repair and meniscal allograft transplantation.

First detection of primary cilia in injured human anterior cruciate ligament: A pilot study with pathophysiological reflections.

The anterior cruciate ligament (ACL) plays a significant role in knee stability, protects the joint under multiple loading conditions and shows complex biomechanics. Beside mechanical stability, the ACL seems to play a crucial role in proprioception, and it is well known, that ACL injuries can cause functional deficits due to decreased proprioception. However, the mechanism of proprioception is not completely understood yet. In this context, primary cilia (PC), which play a significant role in the signaling between the intra- and extracellular space, could be of interest. However, until today, primary cilia are not yet described in human ACL. In total, seven human ACL's underwent transmission electron microscopical examination. Three cadaveric ACL's and four freshly injured ACL's were examined. Single cells of each ACL were examined regarding the presence of axonemes or basal bodies, which represent components of a PC. In total, 276 cells of the cadaveric ACL's and 180 cells of the injured ACL's were examined. Basal bodies could be detected in three of the four specimens of the injured ACL's as well as in one of the three cadaveric ACL's, resulting in a mean positivity of 2.54% in the cadaveric group and 2.78% in the injured group. In case of PC-presence, only one PC per cell could be detected. No statistically significant difference regarding the frequency could be detected between both groups. In this pilot-study, we present for the first time an ultrastructural study of human ACLs with respect to the occurrence of PC and any structural and morphological features of these complex and dynamic cell organelles. PCs are present in almost all non-hematopoietic tissues of the human body. However, there are different reports on the number, incidence, orientation, and morphology of these cell organelles in the respective tissues. Compared to other tissues and ligaments of other species, we found a significantly lower rate of PC positive cells. This observation might represent a tissue-specific characteristic of ACL tissue. However, our observations need to be explored in more detail in further studies.

Preoperative and Postoperative Magnetic Resonance Imaging of the Cruciate Ligaments.

The anterior cruciate ligament and posterior cruciate ligament are key stabilizers of the knee. Magnetic resonance (MR) imaging excels at depiction of injury in both the native and reconstructed cruciate ligaments as well as associated injuries. This article reviews the anatomy, injury patterns, and relevant surgical techniques crucial to making accurate interpretation of MR imaging of the cruciate ligaments.

Correlation between ACL size and dimensions of bony structures in the knee joint.

It is difficult to measure the dimensions of the anterior cruciate ligament (ACL) in vivo, which makes choosing an individualized graft size for ACL reconstruction particularly troublesome. The morphology and function of porcine ACL have been reported to be similar to the native human ACL. This study aimed to identify bony morphological parameters on X-ray images that were significantly correlated with features of the native ACL. Anteroposterior X-ray images of 19 porcine knees were obtained. The width, height and area of the femoral notch, the widths of the femoral and tibial condyles and the width and area of the interspinal fossa of the tibia were measured. ACL length was measured using a caliper. The ACL was then resected and the outline of the bone insertion sites were marked and photographed for measuring the areas of the insertion sites. The excised ACL substance was scanned using X-ray microscopy and reconstructed to measure the medial-lateral (ML) and anterior-posterior (AP) widths, the long and short axes and cross-sectional area of the ACL isthmus. Linear regression analyses showed that the area of the interspinal fossa of the tibia was significantly correlated with the long axis and ML width of the ACL, and with the AP / ML width (p value = 0.038, 0.032 and 0.016 respectively). The width of the femoral condyle was significantly correlated with the area of the tibial insertion and the length and ML width of the ACL (p value = 0.013, 0.000 and 0.038 respectively). The area of the interspinal fossa of the tibia / notch width index (NWI) was significantly correlated with the long axis / short axis of the ACL (p value = 0.016). The width of the interspinal fossa of tibia / NWI was significantly correlated with the short axis of the ACL isthmus (p value = 0.009). However, the dimensions of the femoral intercondylar notch and the width of the interspinal fossa of the tibia were not significantly correlated with any of the ACL parameters. In conclusion, the dimension of the interspinal fossa of the tibia and the width of the femoral condyle measured from X-ray images might be used to estimate the shape and size of the ACL, which might be helpful for choosing a suitable graft size for ACL reconstruction. DATA STATEMENT: All data relevant to the study are included in the article.

High variability in anterior cruciate ligament femoral footprint: Implications for anatomical anterior cruciate ligament reconstruction.

BACKGROUND: The study aimed to (1) investigate the variability of the femoral ACL center in ACL-ruptured patients, (2) identify whether the currently available over-the-top femoral ACL guides could allow for anatomical reconstruction of the native ACL footprint. MATERIAL AND METHODS: Magnetic resonance images of 95 knees with an ACL rupture were used to create three-dimensional models of the femur. The femoral ACL footprint area was outlined on each model, and the location of the femoral ACL center was reported using an anatomical coordinate system. The distance of the femoral ACL center from the over-the-top position was measured. RESULTS: The femoral ACL center demonstrated a high intersubject variability ranging from 1.8 mm (9%) to 12.3 mm (60%) posterior and from 7.7 mm (37%) distal to 4.8 mm (23%) proximal using the posterior condyle circle reference. The average distance of the femoral ACL center from the over-the-top position was 1.9 ± 1.5 mm posterior and 13.8 ± 2.7 mm distal, respectively. The contemporary over-the-top femoral ACL aimers could restore the femoral ACL center in only 6.5% of the patients. CONCLUSIONS: The femoral ACL center demonstrated a high variation on its location, which resulted in a high intersubject variability from the over-the-top position. The contemporary over-the-top femoral tunnel guides do not provide sufficient offset to allow for an anatomical ACL reconstruction. Anteromedial-portal specific femoral ACL guides with a femoral offset ranging from 10 to 18 mm in the proximal/distal direction are required to restore the native ACL footprint.

Development of a three-dimensional computer model of the canine pelvic limb including cruciate ligaments to simulate movement.

Gait analysis as subjective visual assessment forms the foundation of the veterinarian's lameness examination. Pelvic limb lameness is frequently seen in dogs and the stifle joint with its cruciate ligaments, is a main cause of lameness due to cruciate ligament deficiency. In this study, we developed an open-source three-dimensional musculoskeletal pelvic limb model of a 30 kg Labrador Retriever including cruciate ligaments, simulating the gait cycle of the walking movement with the open-source programs NMSBuilder (Institutio Ortopedico Rizzoli, Bologna, Italy) and OpenSim (National Center for Simulation in Rehabilitation Research (NCSRR), Stanford, CA, USA). The computer model generated muscle activations based on motion data. The computed activations were similar to experimental electromyogram data. Highest joint torque was in extension/flexion in the stifle joint at 54 Nm at 14% of the gait cycle with cruciate ligaments. Highest stifle joint reaction force was 408 N at 16% of the gait cycle and was reduced after adding cruciate ligaments. Especially the cranial cruciate ligament loads up to 102 N (34% body weight). Cranial cruciate ligament forces increase with stifle extension and decrease with stifle flexion. On the contrary, the caudal cruciate ligament loads up to 27 N (9% body weight) during the swing phase with a flexed stifle joint. The model was validated with electromyogram data. The model's predictions are plausible because joint torques and forces match the applied ground reaction forces in curve progression and in timing. This model forms a basis for further investigations into stifle surgery after cruciate ligament deficiency.

Anthropometric study as a predictor of anterior cruciate ligament sizes in Asian Indonesian population.

OBJECTIVES: To evaluate whether anthropometric data can predict anterior cruciate ligament (ACL) sizes on magneti resonance imaging (MRI) in Asian population. BACKGROUND: Reconstruction of ACL has been performed over a decade ago. Recently, more individualized ACL reconstruction is performed taking account of each patient's ACL characteristics. However, there has been limited study regarding ACL sizes in Asian Indonesian population. This study aimed to evaluate the role of anthropometric data in ACL sizes using MRI in Asian Indonesian population. STUDY DESIGN: Retrospective Study. METHOD: A series of 531 knees from 420 patients with knee pain and intact ACL confirmed by MRI study. Length, width and inclination angle of ACL were measured using a T2-weighted sagittal MRI 3.0 Tesla Magnetom Skyra. Height, weight, body mass index (BMI) and age were recorded. Multiple regression analysis was used to determine relationship between the anthropometric data and size of ACL measurements. RESULT: ACL length and width were significantly different between male and female, consecutively. Mean ACL length was 35.36 ± 3.63 mm, male was significantly longer (36.59 ± 3.24 mm) compared to female (32.77 ± 2.99 mm), p < 0.0001. Mean ACL width was 10.23 ± 1.84 mm, male was significantly wider (10.85 ± 1.59 mm) compared to female (8.93 ± 1.64 mm), p < 0.0001. The mean ACL inclination angle was 47.75° ± 3.07° (range 40.17°-57.12°). The strongest correlation for ACL length was height and weight (r = 0.437; r = 0.341 consecutively, p < 0.0001). Females had stronger correlation compared to males for ACL length (R2 = 0.489 vs R2 = 0.418). ACL width showed weak correlation with anthropometric data. The following regression analysis equation was obtained for ACL length: ACL length = 60.697 - 0.11*age + 0.461*weight (kg) - 16.522*height (meter) - 1.093*BMI (R2 = 0.539; p < 0.0001). CONCLUSION: Anthropometric data can be utilized as a predictor of ACL length in Asian Indonesian population. The ACL length in Asian Indonesian population is shorter than that in Western population study.

A comparative immunohistochemical and quantitative study of the epiligament of the medial collateral and anterior cruciate ligament in rat knee / Estudio inmunohistoquímico y cuantitativo del epiligamento del ligamento colateral medial y cruzado anterior en rodilla de rata

SUMMARY: The aim of the present study was to evaluate the importance of the epiligament for the difference in the healing potential of the knee anterior cruciate and medial collateral ligament. To do so, we compared the structure of the anterior cruciate and the medial collateral ligament and evaluated the differences in the expression of collagen types I, III and V in a rat knee. We have also conducted a comparative quantitative analysis of the number of cells per mm2 in the two ligaments. Tissue samples were obtained from the anterior cruciate and medial collateral ligament of 10 knee joints taken from five 8-month-old Wistar rats. We used standard hematoxylin and eosin staining, in addition to immunohistochemical staining with monoclonal antibodies against collagen types I, III and V. A semi-quantitative analysis of the expression was made through ImageJ, while Student's T-test was used for the statistical analysis. Our results showed higher expression of all collagen types in the epiligament, compared to the ligament proper and difference in the expression between the medial collateral and the anterior cruciate ligament in favor of the first. We also reported a statistically significant difference in the number of cells per mm2 between the two ligaments and their epiligaments. Our findings show a higher number of cells and a stronger expression of certain collagen types in the epiligament of the medial collateral compared to the anterior cruciate ligament, which may be related to the difference in their healing potential.

RESUMEN: El objetivo del presente estudio fue evaluar la importancia del epiligamento para la diferencia en el potencial de curación del ligamento cruzado anterior y colateral medial de la rodilla. Comparamos la estructura del ligamento cruzado anterior y el ligamento colateral medial y evaluamos las diferencias en la expresión de los tipos de colágeno I, III y V en una rodilla de rata. También se realizó un análisis cuantitativo comparativo del número de células por mm2 en los dos ligamentos. Se obtuvieron muestras de tejido del ligamento cruzado anterior y colateral medial de 10 articulaciones de rodilla tomadas de cinco ratas Wistar de 8 meses de edad. Utilizamos tinción estándar con hematoxilina y eosina, además de tinción inmunohistoquímica con anticuerpos monoclonales contra colágeno tipo I, III y V. Se realizó un análisis semicuantitativo de la expresión mediante ImageJ, mientras que para el análisis estadístico se utilizó la prueba T de Student. Nuestros resultados mostraron una mayor expresión de todos los tipos de colágeno en el epiligamento, en comparación con el ligamento y una diferencia en la expresión entre el ligamento colateral medial y el ligamento cruzado anterior. También informamos una diferencia estadísticamente significativa en el número de células por mm2 entre los dos ligamentos y sus epiligamentos. Nuestros hallazgos muestran un mayor número de células y una expresión mayor de ciertos tipos de colágeno en el epiligamento colateral medial en comparación con el ligamento cruzado anterior, lo que puede estar relacionado con la diferencia en su potencial de curación.

Age-related changes in ACL morphology during skeletal growth and maturation are different between females and males.

Despite a well-established role of anterior cruciate ligament (ACL) anatomy on its biomechanics, little is known on how ACL anatomy develops and changes during skeletal growth. We hypothesized that ACL size and orientation will change by age during skeletal growth and maturation with different trends in males vs females. Magnetic resonance images of 269 unique knees (3-18 years old; 51% female) were used to measure ACL length, cross-sectional area, length-to-cross-sectional area ratio, and elevation angles. In both males and females, ACLs became longer, thicker, and more vertical in sagittal and coronal planes by increasing age (R2 > 0.2; P < .001 for all associations). ACL cross-sectional area-to-length ratio increased by age only in males (R2 = 0.06; P = .003). Despite similar ACL sizes between males and females at early age, adolescent males had significantly longer and thicker ACLs compared to the age-matched females (P < .05). There were no sex differences in ACL elevation angles (P > .2) except for larger coronal elevation in 7 to 10 years old females compared to age-matched males (P = .012). Observed changes in ACL cross-sectional area-to-length ratio indicate that age- and sex-dependent changes in ACL size are not homogenous. The trends seen in normalized ACL size measurements suggest that unlike ACL cross-sectional area, ACL length is primarily controlled by body size. Smaller ACLs and lower cross-sectional growth rates observed in females may be contributing factors to the higher risk of ACL injuries in females. Further investigations are required to identify the intrinsic and extrinsic factors responsible for these discrepancies.

Developmental changes in ACLs and semitendinosus tendons dimensions according to age in children.

PURPOSE: Managing anterior cruciate ligament (ACL) injuries in skeletally immature patients remains difficult. The main aim of this study was to retrospectively compile normative data on the cross-sectional area (CSA) of the semitendinosus tendon (ST) and the diameter of the ACL in children and young adults. METHODS: Knee magnetic resonance imaging (MRI) examinations were performed for a 2-year period in 132 patients (83 female and 49 male patients). The mean age was 14.9 years (8-18 years). Measurements of the ST CSA were performed on axial views in greyscale by two independent researchers. The ACL diameter was measured as well. RESULTS: The results show the CSA of the ST was related to age, and its growth was not linear. The highest growth rate of the CSA of the ST occurred at age 12-13 at the level of the femoral growth plate and at the level of the tibial plateau. The growth of the ACL diameter was linear until 18 years of age. CONCLUSIONS: ST growth (measured in CSA increments) is almost complete at the age of 13, even though the growth is not linear. ACL growth measured in diameter increments proceeds linearly from 8 to 18 years of age. MRI is a clinically useful tool for assessing hamstring tendon grafts preoperatively. LEVEL OF EVIDENCE: Level III, diagnostic studies.

Knee Ligament Anatomy and Biomechanics.

An understanding of knee ligament anatomy and biomechanics is foundational for physicians treating knee injuries, especially the more rare and morbid multiligamentous knee injuries. This chapter examines the roles that the cruciate and collateral anatomy and morphology play in their kinematics. Additionally, the biomechanics of the ACL, PCL, MCL, and LCL are discussed as they have surgical and reconstructive implications.

[Postoperative knee : Tips and pitfalls for the interpretation of ACL surgery]. / Postoperatives Knie : Tipps und Fallstricke für die Befundung der VKB-Plastik.

The anterior cruciate ligament (ACL) is the most important restraint against anterior tibial subluxation and provides stability in flexion, extension and internal rotation as well as varus and valgus stress. Certain sports activities, such as soccer, rugby, skiing, and dancing increase the risk of ACL injuries. The decision for surgical treatment is primarily clinically based under consideration of multiple factors, such as age, body habitus, gender and specific physical activities. There are numerous different techniques for ACL reconstruction each with advantages and disadvantages. The radiologist and the clinician should be familiar with the different appearances of ACL grafts on postoperative imaging depending on the time interval between arthroscopy and imaging. This article reviews the anatomy of the ACL and the most common ACL reconstruction techniques and discusses the normal postoperative findings and complications of ACL reconstruction based on different imaging techniques.

Reconsidering Reciprocal Length Patterns of the Anteromedial and Posterolateral Bundles of the Anterior Cruciate Ligament During In Vivo Gait.

BACKGROUND: Some cadaveric studies have indicated that the anterior cruciate ligament (ACL) consists of anteromedial and posterolateral bundles that display reciprocal function with regard to knee flexion. However, several in vivo imaging studies have suggested that these bundles elongate in parallel with regard to flexion. Furthermore, the most appropriate description of the functional anatomy of the ACL is still debated, with the ACL being described as consisting of 2 or 3 bundles or as a continuum of fibers. HYPOTHESIS: As long as their origination and termination locations are defined within the ACL attachment site footprints, ACL bundles elongate in parallel with knee extension during gait. STUDY DESIGN: Descriptive laboratory study. METHODS: High-speed biplanar radiographs of the right knee joint were obtained during gait in 6 healthy male participants (mean ± SD: body mass index, 25.5 ± 1.2 kg/m2; age, 29.2 ± 3.8 years) with no history of lower extremity injury or surgery. Three-dimensional models of the right femur, tibia, and ACL attachment sites were created from magnetic resonance images. The bone models were registered to the biplanar radiographs, thereby reproducing the in vivo positions of the knee joint. For each knee position, the distances between the centroids of the ACL attachment sites were used to represent ACL length. The lengths of 1000 virtual bundles were measured for each participant by randomly sampling locations on the attachment site surfaces and measuring the distances between each pair of locations. Spearman rho rank correlations were performed between the virtual bundle lengths and ACL length. RESULTS: The virtual bundle lengths were highly correlated with the length of the ACL, defined as the distance between the centroids of the attachment sites (rho = 0.91 ± 0.1, across participants; P < 5 × 10-5). The lengths of the bundles that originated and terminated in the anterior and medial aspects of the ACL were positively correlated (rho = 0.81 ± 0.1; P < 5 × 10-5) with the lengths of the bundles that originated and terminated in the posterior and lateral aspects of the ACL. CONCLUSION: As long as their origination and termination points are specified within the footprint of the attachment sites, ACL bundles elongate in parallel as the knee is extended. CLINICAL RELEVANCE: These data elucidate ACL functional anatomy and may help guide ACL reconstruction techniques.

The location of the femoral ACL footprint center is different depending on the Blumensaat's line morphology.

PURPOSE: The purpose of this study was to evaluate the difference in the center point of the femoral ACL footprint according to the morphological variations of the Blumensaat's line. METHODS: Fifty-nine non-paired human cadaver knees were used. The ACL was cut in the middle, and the femoral bone was cut at the most proximal point of the femoral notch. Digital images were evaluated using the Image J software. The periphery of the femoral ACL footprint was outlined and the center point was measured automatically. Following Iriuchishima's classification, the morphology of the Blumensaat's line was classified into straight and hill types (small and large hill types). The center of the femoral ACL footprint and hilltop placement were evaluated using the quadrant method. A quadrant grid was placed uniformly, irregardless of hill existence, and not including the articular cartilage. A correlation analysis was performed between the center point of the femoral ACL footprint and hilltop placement. RESULTS: The straight type consisted of 19 knees, and the hill type 40 knees (small hill type 13 knees and large hill type 27 knees). The center of the femoral ACL footprint (shallow-deep/high-low) in the straight and hill type knees was 33.7/47.6%, and 37.2/50.3%, respectively. In the hill type, the ACL footprint center was significantly more shallow when compared to the straight type. Significant correlation was observed between the center point of the femoral ACL footprint and hilltop placement of the Blumensaat's line. CONCLUSION: The center point of the femoral ACL footprint was significantly more shallow in the hill type knees when compared to the straight type. For clinical relevance, considering that the location of the femoral ACL footprint center is different depending on the Blumensaat's line morphology, to perform accurate ACL reconstruction, femoral ACL tunnel placement should be made based on Blumensaat's line morphological variations.

ACL Growth With Age in Pediatric Patients: An MRI Study.

BACKGROUND: There is limited knowledge of morphologic changes of the anterior cruciate ligament (ACL) during childhood. The purpose of the study is to describe normal ACL growth in pediatric patients. METHODS: We performed retrospective review of patients under 19 years of age with at least 2 serial magnetic resonance imaging (MRI) examinations of the same knee without ACL tear. The parameters measured included length of the ACL, width of the ACL in sagittal and coronal planes, physeal status, ACL-tibial inclination angle, Notch Width Index, ACL tibial attachment width and midpoint, and anterior to posterior length and height of the tibial epiphysis. Pearson correlation coefficients were calculated to determine the strength of correlation of each parameter relative to age. Growth curves were calculated for individual parameters, producing a predictive model for growth of the ACL over time. RESULTS: One hundred forty-seven patients (365 MRIs) were included. The average age at initial MRI was 12.2 years (range: 1.2 to 18.4 y). The Pearson correlation coefficient for each parameter was statistically significant relative to age. Younger patients had more oblique, anteriorly attached ACLs. Three distinct phases of growth were observed: patients age 1.5 to 5.75 years average 2.25 mm of growth per year; patients aged 6 to 11.5 average 1.46 mm of growth per year; growth slows at age 11.75, stopping by 18.5 years. The growth model for ACL sagittal width increased 0.45 mm/y from age 1.5 to 14.5 after which it plateaus, whereas coronal width increased 0.22 mm/y from age 1.5 to 18.75. CONCLUSIONS: In the pediatric patient, the ACL grows in length and width in a predictable manner until age 18. This model aids clinicians in predicting normal ACL parameters for anatomic reconstruction procedures in the skeletally immature patient. LEVEL OF EVIDENCE: Level IV.

Correlation between notch width index assessed via magnetic resonance imaging and risk of anterior cruciate ligament injury: an updated meta-analysis.

PURPOSE: To analyze the correlation between notch width index (NWI) and/or femoral intercondylar notch width (NW) assessed by magnetic resonance imaging (MRI) and risk of anterior cruciate ligament (ACL) injury. METHODS: We searched the PubMed, Embase, China National Knowledge Infrastructure and Wanfang databases for literature reporting a correlation between ACL injury and NWI and/or NW. Subgroup analyses were stratified by ethnicity, sex and control source. The weighted mean difference (WMD) and 95% confidence intervals (95% CIs) were calculated for the ACL injury cases and controls using random- or fixed-effects models. Begg's test and sensitivity analyses were applied to assess publication bias and stability of the results, respectively. RESULTS: Twenty-eight eligible studies were finally enrolled. The NW was significantly narrowerin the ACL injury cases than in the control cases (pooled WMD, - 1.88 [95% CI, - 2.43 to - 1.32]). The results were similar when stratified by ethnicity and sex. Similarly, the NWI was lower in ACL injury cases than in the controls. Asian populations presented similar results when stratified by ethnicity, among the self-control group when stratified by control source, and among men when stratified by sex. No publication bias was identified; however, the sensitivity analysis suggested unstable results in the NWI subgroup analysis. CONCLUSIONS: The current meta-analysis evidenced that the NW assessed via MRI was significantly smaller in ACL injury cases than in the controls. The NWI was lower in ACL injury cases among men. Prevention strategies for ACL injury could be applied for people with intercondylar notch stenosis.