an 18-year - old male visited our hospital complaining of right knee pain that had lasted for 7 months .
the patient was 182.1-cm tall and weighed 103.4 kg ( 228 lb ) and was a wrestler who had been active in athletics for over 10 years . on physical examination , the joint was negative for locking , snapping , and giving way and showed a normal range of motion ; however , he had been experiencing a catching sensation for 1 year .
dull pain was localized on the anterolateral side of the right knee , and there was tenderness in the same region .
1 ) . given the patient 's physique , athletic activity ( wrestling ) , and the size of the phlm tear , we thought that the radial tear of the phlm would become further aggravated and may cause additional injuries to surrounding cartilages , and decided to perform an arthroscopic examination .
arthroscopy showed two ligament structures that arose from the anterior horn of the medial meniscus ( ahmm ) and ahlm , respectively and were attached to the intercondylar notch of the lateral condyle of the femur .
these two ligaments were combined together , extended superiorly , ran parallel to the acl , and then inserted into the intercondylar notch in the 12 o'clock direction ( fig .
describing this combined ligament separately , the anteromedial mfl , which started from the ahmm , appeared to have the typical pattern that surgeons can occasionally observe4 ) ( fig .
2b ) , and the anterolateral mfl , which had never been found or reported , started from the ahlm , ran parallel to the acl , and inserted into the superior portion of the intercondylar notch anterior to the acl ( fig . 2c ) . because the ahlm was not attached to the tibia , hypermobility occurred and led to degeneration of the ahlm .
in addition , an outerbridge grade ii cartilage injury was visible on the anterior portion of the tibial plateau ( fig .
a fibrous structure assumed to be the anterolateral mfl and the anteromedial mfl were identified ( fig .
4 ) . although the characteristics of the patient 's pain were inconsistent with phlm radial tears , such an injury can completely disable the load - bearing function of the meniscus and thus result in an articular cartilage injury , wear , and degeneration .
thus , an arthroscopic partial meniscectomy for the radial tear of the phlm was performed . at 1-year short - term outpatient follow - up ,
appropriate anatomic placement of the tibial meniscus attachment is necessary to preserve critical knee joint functions7 ) .
the anteromedial mfl that is an anomaly of the ahmm has been descried by some authors8 ) and they have contended that ahmm hypermobility can lead to wear and subsequent degenerative changes9 ) .
however , there has been only 1 reported case of anterolateral mfl that was found in a patient with congenital absence of the acl , indicating how extremely rare the anomaly is6 ) . on review of the present case 's mri , ligamentous structures were identified anterolateral to the normal acl , which demonstrated low signal intensity on sagittal t1- and t2-weighted mri images ( fig .
4 ) . because the signal intensities were similar to those of normal ligaments around the knee , we suspected it could be the anterolateral mfl that had been observed during arthroscopy .
we discovered the lateral meniscus ( lm ) that had a normal tibial attachment of the phlm but the ahlm lacked the tibial attachment that otherwise ran parallel to the acl and inserted into the superior portion of the intercondylar notch anterior to the acl .
the present case also showed ahlm hypermobility , resulting in early meniscal degeneration at age 18 and an injury to the surrounding articular cartilage ( fig .
3 ) . since there had been no reports of this type of anomaly , we decided to administer rehabilitative treatments ( e.g. , strengthening exercises and activity modifications ) in the outpatient clinic .
furthermore , the concomitant presence of anteromedial and anterolateral mfls that were combined as a single structure is a new anatomical anomaly that has never been described in the literature .
the patient had been previously diagnosed with a radial tear of the lm in the contralateral knee and had undergone a partial menisectomy 10 months earlier performed by the same surgeon .
no ligament abnormalities were observed in that knee on arthroscopy or mri , indicating that it was a unilateral anomaly .
the present case report is significant in that it is the first description of an anterolateral mfl .
orthopedic surgeons should be aware of this anatomical anomaly , and future description of more cases would add to our knowledge regarding anomalous meniscus insertion .
 anatomical variations of the meniscus are a common anomaly that knee surgeons frequently encounter . 
 however , anomalies of the anterior horn of the lateral meniscus ( ahlm ) are extremely rare . in this report 
 , we present a newly discovered anomaly of the ahml : an anterolateral meniscofemoral ligament is described with clinical features and radiographic and arthroscopic findings . 
Case Report
Discussion