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Xiao-bing Pu, M.D., Department of Orthopaedics, West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
To observe the morphology of the transverse geniculate ligament of the knee (TGL) by magnetic resonance imaging (MRI) and to analyze the cause of the pseudotear sign of the anterior horn of the meniscus caused by the TGL.
Methods
Patients who underwent MRI examination of the knee joint in the orthopaedics department of our hospital from July 2016 to August 2019 were identified. The occurrence rate, length, width, thickness, cross-sectional shape, pattern, appearance, and position relative to the anterior horn of the lateral and medial meniscus and anatomical variations were observed by multiplane and multisequence MRI. The frequency and cause of the pseudotear sign also were observed.
Results
The data of 101 patients were analyzed. Among them, 60 were male, and 41 were female. The average age was 42.01 (18-75) years. The occurrence rate of the TGL was 67.3% (68/101), the average length was 38.75 ± 3.56 mm, the median coronal diameter was 1.79 ± 0.60 mm, the median sagittal diameter was 1.88 ± 0.35 mm, and the cross-sectional morphology was mostly oval and round. There were 5 types of TGL connection to the anterior horn of the medial meniscus: type 1, located at the front edge; type 2, located at the upper front edge; type 3, located at the upper edge; type 4, located at the back upper edge; and type 5, was located at the back edge of the anterior horn of the medial meniscus. There was only one type of TGL insertion into the anterior horn of the lateral meniscus, located at the anterior superior edge of the anterior horn of the lateral meniscus. There were 4 cases of the pseudotear sign in the anterior horn of the meniscus, 3 in the lateral meniscus and 1 in the medial meniscus. The pseudotear sign of the anterior horn of the meniscus caused by the TGL was observed at a rate of 5.88% (4/68).
Conclusions
In MRI examination of the knee, the anterior horn of the meniscus sometimes shows a pseudotear sign. According to the shape and route of the TGL on MRI and the direction and position of the pseudotear sign of the anterior horn of the meniscus, true and false tears of the anterior horn of the meniscus can be identified.
Level of Evidence
Level III, diagnostic study (retrospective, noncomparative, observational case series without a consistently applied reference “gold” standard).
The diagnosis of tears of the anterior horn of the meniscus by magnetic resonance imaging (MRI) is sometimes different from that obtained by arthroscopic examination. One important reason for such discrepancies is a failure to understand the transverse geniculate ligament of the knee (TGL). The knee joint is the largest and most complex joint of the human body.
Quantifying quadriceps muscle strength in patients with ACL Injury, focal cartilage lesions, and degenerative meniscus tears: Differences and clinical implications.
MRI can be applied for multidirectional, multiparametric imaging with arbitrary cross-sections and high resolution regarding soft-tissue density. It is the best noninvasive method for diagnosing meniscal injury.
The authors found that a tear of the meniscus anterior horn was diagnosed by MRI before arthroscopic surgery in some patients, but no real tear was found during arthroscopy surgery. The common cause may be the pseudotear sign. The formation of the pseudotear sign in the anterior horn of the meniscus is often related to the course of the TGL. Although the TGL has gradually gained attention, there is still a lack of comprehensive and quantitative studies on this ligament. In this study, the MRI data of the knee joints patients were examined qualitatively and quantitatively, the occurrence rate of the TGL was determined, and morphologic characteristics of the TGL, such as length, width, thickness, cross-sectional shape, pattern, characteristics of TGL insertion into the lateral and medial meniscus, and anatomical variations, were observed to improve the understanding of the TGL and find an effective method to distinguish the TGL from true tears of the anterior horn of the meniscus. The purposes of this study were to observe the morphology of the TGL by MRI and to analyze the cause of the pseudotear sign of the anterior horn of the meniscus caused by the TGL. It is helpful for sports physicians to enhance their understanding of the morphology of the TGL. It was hypothesized that the pseudotear sign of the TGL would be prevalent.
Methods
Materials
Data from 101 randomly selected adult patients who underwent MRI examination in the orthopaedics department of our hospital from July 2016 to August 2019 due to knee joint degeneration, traffic accident injury, and sports injury were analyzed retrospectively. The patients included 60 males and 41 females, with an average age of 42.01 ± 14.57 (18-75) years; there were 43 left and 58 right knees (Table 1).
Table 1The Distribution of Sex and Side in 101 Cases
The inclusion criteria were as follows: age ≥18 years; complete MRI data; complete arthroscopy; and exclusion of true tears of the anterior horn of the meniscus. The exclusion criteria were as follows: arthroscopy and/or MRI examination showing severe knee trauma (fracture of the tibial plateau, rupture of the anterior and posterior cruciate ligament); severe degeneration (radiological Kellgren–Lawrence grade ≥3); or obvious motion artifacts.
Methods
MRI Scanning Methods and Sequence Parameters
A Siemens Verio 3.0-T superconductive MRI machine made in Germany was used for scanning with a wrapped surface coil. With the patient in the supine position, the knee joint was straightened, the lower edge of the patella was positioned in the center of the coil, and the knee joint was fixed with a plastic fixator. Routine coronal, sagittal, and axial scans were performed. The MRI scanning sequences, planes, and parameters are shown in Table 2.
Table 2MRI Scanning Sequences, Planes, and Parameters
Sequence
Planes
TR, ms
TE, ms
TS, mm
Gap, mm
FOV, mm
Matrix
PD-TSE-FS
SAG
1500
15
4
0.4
150
216 × 512
T1WI-TSE
SAG
400
9
3
0.4
150
384 × 256
T2WI-TSE
COR
4000
61.6
3
1
150
352 × 288
PD-TSE-FS
COR
3600
29
3
1
150
448 × 320
T2WI-TSE-FS
TRA
4000
80
1
1
150
352 × 288
COR, coronal; FOV, field of view; PD-TSE-FS, proton density-weighted fat suppression fast spin echo sequence; SAG, sagittal; T1WI-TSE, T1-weighted fast spin echo sequence; T2WI-TSE, T2-weighted fast spin echo sequence; T2WI-TSE-FS, T2-weighted fat suppression sequence; TE, echo time; TR, repetition time; TRA, transverse; TS, saturation time.
MRIs were observed via a single-blind method by a skeletal muscle radiologist and a chief orthopaedic physician. The occurrence rate of the TGL was determined, and morphologic characteristics of the TGL, such as length, width, thickness, cross-sectional shape, pattern, characteristics of TGL insertion into the anterior horn of the lateral and medial meniscus, and anatomical variations, as well as the pseudotear sign of the anterior horn of the meniscus caused by the TGL, were observed. If the result was a quantitative index, it was measured twice, and the average was used for statistical analysis; if the conclusion for a qualitative index was inconsistent, it was determined after discussion.
Definition of Measurement Standards and Determination of Anatomical Landmarks
The width defined in this study refers to the anteroposterior diameter of the midpoint of the ligament observed on the sagittal plane. To unify the observational plane, a standardized plane that could display both the anterior and posterior cruciate ligaments clearly at the same was selected for measurement. The thickness defined in this study refers to the diameter of ligaments on the coronary plane, using a standardized plane above the intercondylar eminence, which clearly showed the observed ligament selected for measurement.
Statistical Analysis
SPSS 18.0 statistical software (SPSS Institute, Chicago, IL) was used for data processing. The Shapiro–Wilk test was used to test the normality of the distribution of quantitative data. Measurement data with a normal distribution are expressed as the mean ± standard deviation. Count data are expressed as percentages. The χ2 test was used to compare the rate and frequency, and P < .05 was considered statistically significant (2-tailed).
Results
Occurrence Rate of the TGL
Of the 101 knee joints in this study, the TGL was observed in 68 knees, for an incidence rate of 67.3%. Among them, the TGL was observed in the left knee in 29 cases (67.4%) and the right knee in 39 cases (67.2%). There was no significant difference in the incidence of the TGL between the left and right knees (P = .985). The TGL was observed by different MRI sequences and scanning directions (Fig 1 A-D )
Fig 1Observation of the TGL by different MRI sequences and scanning directions (arrow). (A) T1WI-TSE-SAG, right knee. (B) PD-TSE-FS-COR, right knee. (C) T2WI-TSE-COR, right knee. (D) T2WI-TSE-FS-TRA, right knee. (MRI, magnetic resonance imaging; PD-TSE-FS-COR, proton density-weighted fat suppression fast spin echo sequence, coronal view; T1WI-TSE-SAG, T1-weighted fast spin echo sequence, sagittal view; T2WI-TSE-COR, T2-weighted fat suppression sequence, coronal view; T2WI-TSE-FS-TRA, T2-weighted fat suppression fast spin echo sequence, transverse view; TGL, transverse geniculate ligament.)
On sagittal MRI, the TGL was located in front of the tibiofemoral joint and behind the infrapatellar fat pad. The average length of the TGL was 38.75 ± 3.56 mm. The thickness was 1.79 ± 0.60 mm. There were 2 patterns regarding the TGL route, with one being more common; for this pattern, the relationship with the tibial plateau was loose, i.e., the TGL passed through the middle of the fat pad under the patella. There were 57 cases of this type, accounting for 83.8% (57/68). The other pattern was relatively rare; for this pattern, the relationship with the tibial plateau was close, i.e., the TGL creeped on the articular surface of the tibial plateau. There were 11 cases of this type, accounting for 16.2% (11/68), as shown in Figure 2, A-D. The cross-sectional shape of the TGL was observed on the sagittal plane; the shape was oval in 45.6% of cases (31/68), round in 33.8% (23/68), irregular (including similar triangle, semilunar, etc.) in 14.7% (10/68), flat in 2.9% (2/68), and short rod-like in 2.9% (2/68), as shown in Figure 3, A-G. The TGL appeared as a single bundle in 91.2% of cases (62/68), 2 bundles in 5.9% (4/68), and 3 or more bundles in 2.9% (2/68), as shown in Figure 4, A-F. The TGL insertion into the lateral meniscus was located at the front and upper edge of the anterior horn in all cases (100%, 68/68), with a cross-section shaped like a round cable, as shown in Figure 5A . There were 5 types of TGL connection to the anterior horn of the medial meniscus: those located at the front edge (5.88%, 4/68), the upper front edge (22.05%, 15/68), the upper edge (32.35%, 22/68), the back upper edge (20.58%, 14/68), and the back edge (17.64%, 12/68). Those located at the back upper edge were mostly oblate, as shown in Figure 5, B-F.
Fig 2Observation of the TGL pattern on sagittal MRI and simulation diagram. (A) PD-TSE-FS-SAG, left knee. Loose relationship between the TGL and tibial plateau (arrow). (B) T1-TSE-SAG, left knee. Close relationship between the TGL and tibial plateau (arrowhead). (C) Simulation diagram of the loose relationship between the TGL and tibial plateau (pass through infrapatellar fat pad). (D) Simulation diagram of the close relationship between the TGL and tibial plateau (creeped on the articular surface). (ACL, anterior cruciate ligament; IFP, infrapatellar fat pad; LM, lateral meniscus; MM, medial meniscus; MRI, magnetic resonance imaging; PD-TSE-FS-SAG, proton density-weighted fat suppression fast spin echo sequence, sagittal view; T1-TSE-SAG, T1-weighted fast spin echo sequence, sagittal view; TGL, transverse geniculate ligament; TP, tibial plateau.)
Fig 3Observation of the middle section of the TGL on sagittal MRI and simulation diagram. (A) PD-TSE-FS-SAG, right knee. Oval shape. (B) PD-TSE-FS-SAG, left knee. Round shape. (C) PD-TSE-FS-SAG, right knee. Similar triangle shape. (D) PD-TSE-FS-SAG, right knee. Semilunar shape. (E) T1-TSE-SAG, right knee. Flat shape. (F) PD-TSE-FS-SAG, left knee. Short rod-like shape. (G) Simulation diagram of the middle section of the TGL. (MRI, magnetic resonance imaging; PD-TSE-FS-SAG, proton density-weighted fat suppression fast spin echo sequence, sagittal view; T1-TSE-SAG, T1-weighted fast spin echo sequence, sagittal view; TGL, transverse geniculate ligament.)
Fig 4Observation of the TGL bundle on axial, sagittal, and coronal MRI and simulation diagram. (A) T2-TSE-FS-TRA, right knee. One bundle. (B) PD-TSE-FS-SAG, right knee. Two bundles. (C) T2-TSE-FS-TRA, right knee. Two bundles (B and C) are images from the same patient. (D) PD-TSE-FS-COR, left knee. Two bundles. (E) T1-TSE-SAG, right knee. Three bundles. (F) Simulation diagram of the TGL bundle. (LM, lateral meniscus; MM, medial meniscus; MRI, magnetic resonance imaging; PD-TSE-FS-COR, proton density-weighted fat suppression fast spin echo sequence, coronal view; T1-TSE-SAG, T1-weighted fast spin echo sequence, sagittal view; T2-TSE-FS-TRA, T2-weighted fat suppression fast spin echo sequence, transverse view; TGL, transverse geniculate ligament.)
Fig 5Observation of the location of TGL insertion into the medial and lateral meniscus on PD-TSE-FS-SAG MRI and simulation diagram. (A) Right knee. All TGLs inserted at the anterior superior edge of the anterior horn of the lateral meniscus. (B) Right knee. Connection point located at the front edge of the medial meniscus. (C) Left knee. Connection point located at the upper front edge of the medial meniscus. (D) Right knee. Connection point located at the upper edge of the medial meniscus. (E) Connection point located at the back upper edge of the medial meniscus. (F) Right knee. Connection point located at the back edge of the medial meniscus. (G) 1: Front edge; 2: Upper front edge; 3: Upper edge; 4: Back upper edge; 5: Back edge; only one type of TGL insertion into the anterior horn of the lateral meniscus. (MRI, magnetic resonance imaging; PD-TSE-FS-SAG, proton density-weighted fat suppression fast spin echo sequence, sagittal view; TGL, transverse geniculate ligament.)
Incidence of the Pseudotear Sign in the Anterior Horn of the Meniscus
In our study, there were 4 cases of the pseudotear sign in the anterior horn of the meniscus, accounting for 5.88% (4/68); the sign was in the anterior horn of the lateral meniscus in 3 cases (4.41%) (Fig 6 A-C ). T anterior horn of the medial meniscus in one case (1/68) (Fig 6D). The direction of the pseudotear sign of the anterior horn of the meniscus was from anteroinferior to posterosuperior.
Fig 6Pseudotear sign of the TGL in the anterior horn of the medial and lateral meniscus on PD-TSE-FS-SAG MRI. (A-C) Pseudotear sign of the TGL in the anterior horn of the lateral meniscus (A, left knee; B, right knee; C, right knee.). (D) Pseudotear sign of the TGL in the anterior horn of the medial meniscus (right knee). (LM, lateral meniscus; MM, medial meniscus; MRI, magnetic resonance imaging; PD-TSE-FS-SAG, proton density-weighted fat suppression fast spin echo sequence, sagittal view; PS, pseudotear sign; TGL, transverse geniculate ligament.)
The most important finding of this study is an improved understanding of TGL morphology. In this study, more than 6 cross-sectional shapes of the TGL were observed. On the sagittal plane, there is only one site for TGL insertion into the anterior horn of the lateral meniscus, whereas there are 5 types of TGL connection to the anterior horn of the medial meniscus. These features are of great significance for the accurate diagnosis of meniscal injury. True and false tears of the meniscus anterior horn can be distinguished effectively by observing the shape, position, and course direction of the TGL on continuous images on the sagittal and coronal planes to avoid misdiagnosis and unnecessary arthroscopic surgery.
Cause of the Pseudotear Sign in the Anterior Horn of the Meniscus
The meniscus showed a low signal on conventional MRI, as did the central tendon attachment of the ligament. The fat components in the middle of them showed a high signal on both T1-weighted imaging and T2-weighted imaging. The linear high signal between the 2 low-signal tissues was observed on the sagittal plane, which could easily be mistaken for a tear of the anterior horn of the meniscus. According to a study by Imhoff et al.,
the TGL is seen in association with a large branch of the lateral inferior geniculate artery and may be mistaken for a grade 3 signal intensity in the anterior horn of the lateral meniscus.
Identification of True and False Tears of the Meniscus Anterior Horn
(1) The meniscus was observed in continuous MRIs on the sagittal plane. Pseudotear of the meniscus is discontinuous and mostly occurs near the anterior horn of the meniscus, whereas the TGL can be displayed continuously on other sagittal planes. (2) The direction and position of the linear high signal were observed. A true tear of the meniscus is complex, and the position is not constant, whereas a pseudotear caused by the TGL is inclined from anteroinferior to posterosuperior and fixed at the anterior horn of the meniscus. (3) Observation of meniscus morphology. In the case of a true tear, the whole shape of the meniscus shows a high signal due to irregular fragmentation. However, in the case of a pseudotear of the anterior horn of the meniscus caused by the TGL, there is no abnormal fragmentation because the meniscus itself is smooth and maintains its regular "bow-tie" shape. (4) Differentiation of true and false tears on coronal MRI. A true tear of the meniscus will exhibit a high signal on both the sagittal and coronal planes, whereas a pseudotear will exhibit a high signal on the coronal plane.
Function of the TGL
The TGL is a normal anatomical structure connecting the anterior horn of the medial meniscus to that of the lateral meniscus. It helps to maintain the stability of the knee joint during movement and plays an important role in maintaining the stability of the anterior horn of the meniscus and preventing excessive rotation.
examined 6 cadaveric knee joints by MRI before and after cutting the TGL. This study found that there was a statistically significant difference in the movement deviation of the anterior and posterior horn of the medial meniscus before and after cutting the TGL under 30° of flexion of the knee joint. They believed that under little flexion of the knee joint, the anterior and posterior deviation of the TGL relative to the anterior horn of the medial meniscus significantly limited movement. de Abreu et al.
Anterior transverse ligament of the knee: MR imaging and anatomic study using clinical and cadaveric material with emphasis on its contribution to meniscal tears.
observed through arthroscopy that patients with TGL attachment to the medial meniscus were more likely to tear the medial meniscus than those without such TGL attachment (76.7% vs 16.7%). The results suggest that the TGL restricted the movement of the medial meniscus and increased the possibility of tearing of the medial meniscus. Some scholars think that the TGL will be placed under slight tension when the knee flexes, whereas transverse and rotational stresses will have no obvious influence on the ligament. If the ligament is removed, there is no obvious difference in the integrity of the knee joint; thus, the TGL plays only a very small role in the normal function of the knee.
Histology, Occurrence, and MRI Characteristics of the TGL
Investigations were carried out on 42 embryos of developmental stages 18-23 (44-56 postovulatory days) from the collection of the Department of Anatomy in Poznań. The cellular primordium of the TGL, connected to the medial and lateral meniscus, was clearly visible at stage 22. The primordium consisted of oval cells arranged into densely packed parallel strands. The cells were larger than those forming the menisci.
showed that the TGL was located behind the fat pad under the patella, manifesting as a thick band of connective tissue. On histologic sections, they found that the medial side of the TGL was a thick circular structure surrounded by loose connective tissue. Around the ligament, more blood vessels could be observed between the fiber bundles.
found 3 types of TGL connections at or near the front corner of the meniscus: in type I, the anterior horn of the medial meniscus was connected to the front edge of the lateral meniscus; in type II, the anterior horn of the medial meniscus was connected to the joint capsule adjacent to the lateral meniscus; in type III, the anterior capsule, but not the anterior horn, of the medial meniscus was connected to that of the lateral meniscus. These results are similar to those of Marcheix et al.
In our study, we found that the TGL originated from the anterior horn of the medial meniscus, with a starting point that could originate from multiple sites in the anterior horn. The TGL was observed to pass horizontally behind the fat pad under the patella, and the insertion point was fixed at the front upper edge of the upper corner of the lateral meniscus.
The incidence of the TGL reported by different research methods is quite different. Marcheix et al.
dissected 10 human cadavers and found the TGL in 9 of them, with an average length of 31.2 mm (25-45 mm) and an average distance between the TGL and the ACL of 12 mm (11-15 mm). In the same study, they found the TGL by MRI in 34 of 51 cases (82.9%), which is a greater rate than that in our study. In contrast, Erbagci et al.
conducted MRI of the knee in 100 healthy subjects (52 women, 48 men). The TGL was found in 19 female and 12 male subjects, for an incidence of 31%, which is lower than that in our study. We determined that the reason for the low occurrence of the TGL observed by MRI may be related to the scanning parameters selected. Due to the limited development of the TGL in some cases, the thickness of the MRI slice and the gap between slices may be too large, which may cause the target ligament to not be displayed. The TGL is a transverse elastic fiber tissue. In our study, we found that in addition to the flat shape, the cross-section also showed a variety of shapes, such as round, oval, and short rod-like shapes, which have rarely been mentioned in previous studies.
In this study, the average length, thickness, and width of the TGL was 38.75 ± 3.56 mm, 1.79 ± 0.60 mm, and 1.88 ± 0.35 mm, respectively, showing a difference from values previously reported in the literature.
Anterior transverse ligament of the knee: MR imaging and anatomic study using clinical and cadaveric material with emphasis on its contribution to meniscal tears.
One reason for this difference may be inconsistent research methods and measurement standards. It is also possible for a mucosal wrapping to be present on the surface of the TGL, yielding a gross anatomy larger than that measured on MRI.
The purpose of this study was to make comprehensive and systematic morphologic observations of the causes of the pseudotear sign in the meniscus and the related TGL through MRI to improve the anatomical understanding of the ligament and find an effective method to distinguish true and false tears of the anterior horn of the meniscus.
Limitations of This Study
Due to the limitations of the experimental conditions, there was no control of gross anatomy in this study. The measured data may be different from the autopsy data, but they are still valuable for deepening the understanding of the anatomy and morphology of the TGL and establishing a set of methods for identifying true and false tears of the anterior horn of the meniscus. In all, 101 knee joints examined by MRI were included in this study. The incidence of pseudotear of the meniscus caused by the TGL was 5.88%, which may be related to the small sample size. Data from multiple centers and larger samples would improve the reliability of the measurement results. After matching for sex and laterality, this group was still sufficient for statistical study. Finally, there was no biomechanical study of the target ligament in this study, but this study focused more on morphology; thus, this deficiency should have no significant impact on the purpose of this study.
Conclusions
In MRI examination of the knee, the anterior horn of the meniscus sometimes shows a pseudotear sign. According to the shape and route of the TGL on MRI and the direction and position of the pseudotear sign of the anterior horn of the meniscus, true and false tears of the anterior horn of the meniscus can be identified.
Acknowledgments
We are greatly thankful to the radiologist of our hospital for their contribution.
Quantifying quadriceps muscle strength in patients with ACL Injury, focal cartilage lesions, and degenerative meniscus tears: Differences and clinical implications.
Anterior transverse ligament of the knee: MR imaging and anatomic study using clinical and cadaveric material with emphasis on its contribution to meniscal tears.
The authors report that they have no conflicts of interest in the authorship and publication of this article. Full ICMJE author disclosure forms are available for this article online, as supplementary material.
Cheng-wei Kang, M.D., and Li-xue Wu, M.D., are co-first authors.
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