Clinical History
A 48-year-old female patient was admitted to our hospital due to persistent pain located at the medial side of her left knee, during the past month. Clinically, a tear of the medial meniscus was suspected and an MRI of her left knee was requested.
Imaging Findings
An MRI of the left knee was performed on a Philips Gyroscan NT 1.5 Tesla scanner, and consisted of an axial proton density fat suppressed sequence, a sagittal dual (PD, T2) spin echo sequence, a coronal T1 spin echo sequence, and a coronal proton density fat suppressed sequence. Chondromalacia of the medial femoral and tibial condyles and subchondral bone marrow oedema in the medial portion of the tibial epiphysis were found, and attributed to osteoarthritic changes (Fig. 3). There was a small amount of fluid in the joint. A torn posterior horn of the medial meniscus that was partially folded posteriorly was depicted (Fig. 2-3). There was a chord-like linear structure, in the midline above the intercondylar eminence, connecting the anterior horn of the medial meniscus with the posterior horn of the lateral meniscus. This was interpreted as a medial oblique meniscomeniscal ligament, with no relationship to the torn meniscus (Fig. 2-3).
Discussion
In the medical literature, different types of meniscomeniscal ligaments have been described [1–4]. The most common type is the anterior transverse ligament which is present in about half the examined knees [1]. It connects the frontal horns of the menisci. The posterior transverse ligament is not common, and has a reported frequency of 1%–4% [1]. It connects the posterior horns of the menisci. The oblique meniscomeniscal ligaments, occur in less than 1% of the examined knees [1-3]. The medial oblique meniscomeniscal ligament connects the anterior horn of the medial meniscus with the posterior horn of the lateral meniscus, and the lateral meniscomeniscal ligament connects the anterior horn of the lateral meniscus with the posterior horn of the medial meniscus. The most recently discovered type is the unilateral meniscomeniscal ligament connecting the anterior and posterior horn of the meniscus. It is called medial unilateral meniscomeniscal ligament when connecting the horns of the medial meniscus and lateral unilateral meniscomeniscal ligament when connecting the horns of the lateral meniscus [4].
The anterior transverse ligament has been described as a potential pitfall mimicking an anterior horn meniscal tear [3]. The oblique meniscomeniscal ligament and the unilateral meniscomeniscal ligament may mimic a bucket-handle type of a meniscus tear, or even a tear of the anterior or posterior cruciate ligament, because of its oblique course between the cruciate ligaments [2, 3].
In our case, we could not find any relationship between the flap of the meniscal tear and the chord-like structure above the intercondylar notch. We did verify that it was arising from the anterior horn of the medial meniscus and crossing over the intercondylar notch inserting into the posterior horn of the lateral meniscus, so we correctly interpreted it as a medial oblique meniscomeniscal ligament. The findings were verified by the subsequent arthroscopy.
Differential Diagnosis List
Medial oblique meniscomeniscal ligament, bucket–handle tear of medial meniscus.
Meniscal tear (especially bucket-handle type)
Tear of the anterior cruciate ligament
Final Diagnosis
Medial oblique meniscomeniscal ligament, bucket–handle tear of medial meniscus.
