The lateral meniscus, as it is well known, is less firmly anchored than the medial one as it is attached mainly to the fibrous capsule, via weak fibers [
13]. However, lateral meniscus attachments to its neighboring structures do exist. In specific, the posterior horn is attached to the medial condyle of the femur anterior and posterior to the attachment to the posterior cruciate ligament, forming the anterior and posterior meniscofemoral ligaments [
14–
16]. At least one meniscofemoral ligament has been found in approximately 93% of knees, whereas 50% of them had both ligaments [
17]. These ligaments can assist to withstand tibial posterior draw [
18] and may act as a splint to keep the posterior cruciate ligament in position while it heals after rupture [
8]. The anterior meniscofemoral ligament (of Humphrey) is slack in the extended knee and tightens with knee flexion to withstand tibial posterior draw. The converse occurs with the posterior meniscofemoral ligament of Wrisberg [
8].
As regards the popliteus tendon, it provides almost consistently two fascicles, the superior, superomedial, or posterosuperior and the inferior, inferolateral, or anteroinferior bundle, which have been prescribed analytically firstly by Staubli and Birrer in 1990 [
7,
19]. The presence of a third popliteomeniscal fascicle, the so-called posteroinferior fascicle, has been mentioned in the literature [
6,
20]. The anteroinferior or inferolateral popliteomeniscal fascicle extends from the anterior margin of the popliteus tendon to the middle third of the lateral meniscus, whereas the posterosuperior or superomedial fascicle extends from the posterior margin of the tendon to the posterolateral aspect of the meniscus [
21]. The aforementioned fascicles stabilize the lateral meniscus and when ruptured the mobility of the lateral meniscus is increased [
19]. In addition, a portion of the joint capsule extending from the lateral edge of the lateral meniscus to the lateral tibial condyle, the so-called lateral coronary or meniscotibial ligament, secures the posterior horn of the lateral meniscus to the tibia [
6,
22] and may be injured after excessive rotation of the knee [
1]. Although the precise function of the coronary ligament has not been highly enlightened, it is supposed to play a role in keeping the lateral meniscus adherent to the lateral tibial plateau [
23]. That ligament is responsible for limiting rotational movements of the knee, whereas it permits controlled anterior and posterior movement of the lateral meniscus [
24]. Coronary ligament rupture may lead to increased mobility of the lateral meniscus, posterior knee pain, and a gap in the posterior capsule [
25].
An additional ligament attached to the lateral meniscus, relatively unknown and neglected in the literature, is the meniscofibular ligament (MFL), a tapelike fibrous band extending between the inferior border of the lateral meniscus and the head of the fibula. That ligament was firstly described in 1964 by Zivanovic with an incidence of 78% of the 241 European knee joints examined [
12]. Later, the same author observed that ligament in 80% of East African Bantu knee joints [
9], whereas Bozkurt et al. observed the MFL in 100% of their specimens, attributing the lower incidence noticed in Zivanovic's study to the lack of detection of the specifically thin MFLs appeared in some materials [
10]. Similarly MFL incidence was found to be 100% in our study, with only one case (4.8%) being hypoplastic but macroscopically apparent.
As regards the morphological features of the MFL, Zivanovic found the average width to be between 8 and 13
mm and the average length between 13 and 22
mm and while MFL was less than 1
mm thick [
9]. The previously mentioned author claimed that MFL size was depending on the age and stature of the examined individual without providing further data. Bozkurt et al. found the mean thickness of the MFL to be 3.84
mm, ranging from 2.6
mm to 6.1
mm, including the capsule to which it adheres [
10]. Such a thickness was found to be greater than the thickness detected by Zivanovic, a fact attributed to the capsule thickening that was coestimated in the performed measurements. In our research we observed that the MFL is incorporated into the lateral coronary ligament reinforcing its posterolateral segment. Bozkurt et al., however, detected the fibrous sheets located bilateral to the MFL as parts of the knee joint articular capsule, without defining them as lateral coronary ligament [
10].
The MFL functional significance is a controversial issue. According to Zivanovic MFL has an opposite effect to that of the popliteal tendon limiting forward movement and medial gliding of the posterior horn of the lateral meniscus during the latter stages of knee extension, providing that way protection to the lateral meniscus [
9]. Zivanovic found MFL as a permanent structure in the mountain gorilla and the cercopithecus, very well developed since in these animals MFL is more important for the protection of the lateral meniscus during knee extension [
9]. MFL was loose in extreme flexion but it was very tense when the knee joint was extended. Zivanovic considered that during evolutionary development the appeared direct joint between the lateral femoral condyle and the head of fibula seen in the knees of tetrapods has disappeared, with MFL being a rudimentary structure [
9]. The small MFL thickness noted in humans attributed to the assumption of the erect posture.
On the contrary, Bozkurt et al. provided a potential relationship between MFL presence and the proximal tibiofibular joint [
10]. They postulated that MFL may be responsible for backward and outward displacement of the lateral meniscus since the fibula rotates laterally during the dorsal flexion of ankle joint. It is worth mentioning that these authors noticed the MFL to be thicker in horizontal than in oblique proximal tibiofibular joints, where the fibula rotation is more restricted. It is supposed that in horizontal joints the MFL is loaded more than in oblique joints. Bozkurt et al. without providing the precise mechanism made an assumption that MFL has a protective effect in varus and external rotational traumas, whereas the same ligament may be presumably the cause of repetitive lateral meniscus tears [
10].
In our study, where no evaluation of the MFL biomechanical properties was performed, we observed that the ligament was slack during knee flexion and medial rotation of the tibia and tense during knee extension and external rotation of the tibia, a notice that confirms Zivanovic's results. So, one hypothesizes that MFL could provide protection to the lateral meniscus from potential ruptures during the last stages of knee extension. In addition, we noticed that MFL reinforced the posterolateral portion of the lateral coronary ligament and not the posterior fibrous capsule of the joint, as noted by Bozkurt et al. [
10]. Such an observation has not been mentioned previously in the literature for the best to our knowledge and we consider that such coronary ligament reinforcement provides protection to that ligament. Presumably, that fact supports and empowers the El-Khoury et al. notice that none lateral coronary ligament tear was encountered in excess of two thousands knee arthrograms [
23]. The authors attributed this to the loose attachment of the lateral meniscus to the neighboring structures, the low incidence of ligamentous injuries over the lateral side of the knee, and the wide separation between lateral meniscus and collateral ligament. In addition, to the previous remarks we speculate that a further parameter leading to low frequence of lateral coronary ligament rupture is its potential reinforcement by the MFL.
