Imaging of Anatomical Variants Around the Knee

Abstract

Several anatomical variants have been described in the knee. These variants may involve intra- and extra-articular structures, such as menisci, ligaments, plicae, bony structures, muscles, and tendons. They have a variable prevalence, are generally asymptomatic, and are usually discovered incidentally in knee magnetic resonance imaging examinations. A thorough knowledge of these findings is essential to avoid overestimating and overinvestigating normal findings. This article reviews most anatomical variants around the knee, describing how to avoid misinterpretation.

Keywords

normal variant - meniscus - ligament - knee - magnetic resonance imaging

Publication History

Article published online:
03 April 2023

• References

• 1 Bellelli A, Silvestri E, Barile A. et al. Position paper on magnetic resonance imaging protocols in the musculoskeletal system (excluding the spine) by the Italian College of Musculoskeletal Radiology. Radiol Med (Torino) 2019; 124 (06) 522-538
• 2 Ariyachaipanich A, Bae WC, Statum S, Chung CB. Update on MRI pulse sequences for the knee: imaging of cartilage, meniscus, tendon, and hardware. Semin Musculoskelet Radiol 2017; 21 (02) 45-62
• 3 Tyler P, Datir A, Saifuddin A. Magnetic resonance imaging of anatomical variations in the knee. Part 1: ligamentous and musculotendinous. Skeletal Radiol 2010; 39 (12) 1161-1173
• 4 Saavedra M, Sepúlveda M, Jesús Tuca M, Birrer E. Discoid meniscus: current concepts. EFORT Open Rev 2020; 5 (07) 371-379
• 5 Chew FS. Medial meniscal flounce: demonstration on MR imaging of the knee. AJR Am J Roentgenol 1990; 155 (01) 199
• 6 Schnarkowski P, Tirman PFJ, Fuchigami KD, Crues JV, Butler MG, Genant HK. Meniscal ossicle: radiographic and MR imaging findings. Radiology 1995; 196 (01) 47-50
• 7 de Abreu MR, Chung CB, Trudell D, Resnick D. Anterior transverse ligament of the knee: MR imaging and anatomic study using clinical and cadaveric material with emphasis on its contribution to meniscal tears. Clin Imaging 2007; 31 (03) 194-201
• 8 Shankman S, Beltran J, Melamed E, Rosenberg ZS. Anterior horn of the lateral meniscus: another potential pitfall in MR imaging of the knee. Radiology 1997; 204 (01) 181-184
• 9 Mohankumar R, White LM, Naraghi A. Pitfalls and pearls in MRI of the knee. AJR Am J Roentgenol 2014; 203 (03) 516-530
• 10 Soejima T, Murakami H, Tanaka N, Nagata K. Anteromedial meniscofemoral ligament. Arthroscopy 2003; 19 (01) 90-95
• 11 Otsubo H, Shino K, Suzuki D. et al. The arrangement and the attachment areas of three ACL bundles. Knee Surg Sports Traumatol Arthrosc 2012; 20 (01) 127-134
• 12 Ergün S, Karahan M, Akgün U, Kocaoğlu B. A case of multiple congenital anomalies including agenesis of the anterior cruciate ligament [in Turkish]. Acta Orthop Traumatol Turc 2008; 42 (05) 373-376
• 13 Venkatanarasimha N, Kamath A, Mukherjee K, Kamath S. Potential pitfalls of a double PCL sign. Skeletal Radiol 2009; 38 (08) 735-739
• 14 Gupte CM, Smith A, McDermott ID, Bull AMJ, Thomas RD, Amis AA. Meniscofemoral ligaments revisited. Anatomical study, age correlation and clinical implications. J Bone Joint Surg Br 2002; 84 (06) 846-851
• 15 Weaver JK. Bipartite patellae as a cause of disability in the athlete. Am J Sports Med 1977; 5 (04) 137-143
• 16 Wibeeg G. Roentgenographs and anatomic studies on the femoropatellar joint: with special reference to chondromalacia patellae. Acta Orthop Scand 1941; 12: 319-410
• 17 Kazley JM, Banerjee S. Classifications in brief: The Dejour classification of trochlear dysplasia. Clin Orthop Relat Res 2019; 477 (10) 2380-2386
• 18 Liu YW, Skalski MR, Patel DB, White EA, Tomasian A, Matcuk Jr GR. The anterior knee: normal variants, common pathologies, and diagnostic pitfalls on MRI. Skeletal Radiol 2018; 47 (08) 1069-1086
• 19 Tyler P, Datir A, Saifuddin A. Magnetic resonance imaging of anatomical variations in the knee. Part 2: miscellaneous. Skeletal Radiol 2010; 39 (12) 1175-1186
• 20 Suh JS, Cho JH, Shin KH. et al. MR appearance of distal femoral cortical irregularity (cortical desmoid). J Comput Assist Tomogr 1996; 20 (02) 328-332
• 21 Boles CA, Martin DF. Synovial plicae in the knee. AJR Am J Roentgenol 2001; 177 (01) 221-227
• 22 Leal-Blanquet J, Ginés-Cespedosa A, Monllau JC. Bifurcated popliteus tendon: a descriptive arthroscopic study. Int Orthop 2009; 33 (06) 1633-1635
• 23 Doral MN, Atay AO, Bozkurt M, Ayvaz M, Tetik O, Leblebicioglu G. Three-bundle popliteus tendon: a nonsymptomatic anatomical variation. Knee 2006; 13 (04) 342-343
• 24 Duc SR, Wentz KU, Käch KP, Zollikofer CL. First report of an accessory popliteal muscle: detection with MRI. Skeletal Radiol 2004; 33 (07) 429-431
• 25 Koplas MC, Grooff P, Piraino D, Recht M. Third head of the gastrocnemius: an MR imaging study based on 1,039 consecutive knee examinations. Skeletal Radiol 2009; 38 (04) 349-354
• 26 Kurtys K, Gonera B, Olewnik Ł, Karauda P, Tubbs RS, Polguj M. Is the plantaris muscle the most undefined human skeletal muscle?. Anat Sci Int 2021; 96 (03) 471-477
• 27 Reid L, Mofidi A. Bilateral snapping biceps femoris tendon: a case report and review of the literature. Eur J Orthop Surg Traumatol 2019; 29 (05) 1081-1087
• 28 Beltran J, Matityahu A, Hwang K. et al. The distal semimembranosus complex: normal MR anatomy, variants, biomechanics and pathology. Skeletal Radiol 2003; 32 (08) 435-445
• 29 Kim J, Lee JH. A unique case of an accessory sartorius muscle. Surg Radiol Anat 2019; 41 (03) 323-325