The knee joint is the largest synovial joint in the human body and is a complex hinge joint composed of multiple intracapsular and extracapsular structures that collectively provide stability while permitting a wide range of movements. The articular capsule, menisci, cruciate ligaments, collateral ligaments and posterior capsular structures contribute to maintaining the integrity of the joint and resisting the considerable biomechanical stresses encountered during weight bearing and locomotion.1 The posterior aspect of the knee is anatomically complex and contains several important stabilizing structures. Among these, the oblique popliteal ligament (OPL) is a prominent structure forming an important component of the posterior capsule of the knee. It has been described as the largest structure on the posterior aspect of the knee and is closely related to the semimembranosus tendon and the posterolateral structures. Because of its broad configuration and strategic location, the OPL may be involved in posterior knee injuries; however, injuries to this structure may not always be adequately recognized during surgical reconstruction.2-4 The OPL represents one of the important expansions associated with the semimembranosus muscle and forms part of the posterior anatomy of the knee. The semimembranosus tendon contributes to stabilization of the posterior capsule through its connection with the OPL. The ligament forms part of the floor of the popliteal fossa and courses obliquely from the medial side towards the lateral side. It has traditionally been regarded as an important restraint to knee hyperextension and therefore plays a major role in preventing genu recurvatum.5-12 The structural nature of the OPL has itself been a subject of anatomical debate. Although traditionally described as a ligament, its morphological characteristics have led to the suggestion that it may have a predominantly tendinous character. Benninger's anatomical observations and subsequent anatomical investigations have highlighted the close relationship between the OPL and the distal semimembranosus tendon. Furthermore, Hedderwick et al. described the OPL as a distinct expansion of the semimembranosus tendon and sheath, coursing superolaterally to the posterolateral joint capsule or fabella when present.13 The biomechanical significance of the OPL has been demonstrated experimentally. Morgan et al. studied fresh-frozen human knees by sequentially sectioning posterior and other stabilizing structures and found that sectioning of the OPL produced the greatest increase in knee hyperextension. The increase in hyperextension approached or exceeded that observed following sectioning of the anterior and posterior cruciate ligaments combined. These findings established the OPL as an important, and potentially primary, ligamentous restraint against knee hyperextension.3 A detailed understanding of the morphology and morphometry of the OPL can therefore provide a more accurate anatomical basis for understanding posterior knee stability. It may also assist orthopaedic surgeons and radiologists in recognizing anatomical variations, interpreting posterior knee pathology and planning surgical procedures involving the posteromedial and posterolateral regions of the knee. The existing inconsistencies in descriptions of the OPL, together with the limited morphometric data available, provide a rationale for further cadaveric investigation. Hence, the present cadaveric study on morphological and morphometric analysis of the oblique popliteal ligament of the knee joint was undertaken to document its morphological patterns and establish quantitative measurements of its dimensions and anatomical relationships. Such a systematic assessment may contribute to a better understanding of the normal anatomical variations of the OPL and provide useful anatomical information for clinical diagnosis, imaging interpretation, surgical reconstruction and avoidance of iatrogenic injury..

15 embalmed cadavers were selected from the cadavers allotted to 1styear MBBS students in the Department of Anatomy, L.L.R.M. Medical College, Meerut and 30 cadaveric knee joints of both genders were taken for the study. Study Method: Dissection method Study Design: Descriptive Observational Study Study Duration: 15 months Study Material: • 15 embalmed cadavers • Digital Vernier callipers • Paper pins/All pin • Complete dissection kit including scissors, scalpel and forceps etc. Inclusion Criteria: Only knees from cadavers with no of evidence meniscal tears, and meniscal implants were included in the study. Dissection procedure for the study of oblique popliteal ligament (OPL): For detailed study of Oblique popliteal ligament, knee joint was deeply dissected posteriorly. After cleaning the contents and boundaries of popliteal fossa, the two heads of gastrocnemius and plantaris were cut below the knee joint and reflected proximally. To get proper view of the floor of the popliteal fossa the tibial and common peroneal nerves, and the popliteal vessels were also removed. The oblique popliteal ligament was observed. The gross morphological features like its general shape (band like or cord like), number of bands and presence of any extensions were observed. Subsequently, morphometry of the OPL was performed using digital Vernier callipers accurate to 0.1 mm. Following parameters were included in the study of oblique popliteal ligament: a. Mediolateral length of OPL (length of upper margin): measured between semimembranosus (SM) tendon and medial border of lateral femoral condyle. b. Mediolateral length of OPL (length of lower margin): measured between SM tendon and lateral head of gastrocnemius. c. Width at medial attachment of OPL: d. width of SM expansion e. width of attachment to medial femoral condyle. f. Width at lateral attachment of OPL. g. Position of neurovascular hilum: relative to lateral border of SM tendon. Statistical analysis: Data so collected was tabulated in an excel sheet, under the guidance of statistician. The means and standard deviations of the measurements per group were used for statistical analysis (SPSS 22.00 for windows; SPSS inc, Chicago, USA). Difference between two groups was determined using t test and the level of significance was set at p < 0.05.

The present observational study was conducted in Department of Anatomy, L.L.R.M. Medical College, Meerut, U.P. among 30 cadaveric adult human knee joints. The aim of the study was to analyse the incidence of various shapes in oblique popliteal ligament and measurements of the different parts of oblique popliteal ligament (distance, thickness and width). The morphological types of the OPL were categorized into four types. Type 1 was seen in 9 (30%) specimens, in which the OPL was mainly band like, with the medial attachment at the SM tendon only and lateral attachment at the lateral head of the gastrocnemius and medial border of the lateral femoral condyle. Type 2 was found in 13 (43.3%) specimens, it was also like a band, with a broad medial attachment to both the SM tendon and medial femoral condyle. The lateral attachment was similar to type 1. Type 3 OPL was found in 4(13.3%) specimens and was cord like, with medial attachment to the SM tendon and lateral attachment to the medial border of the lateral femoral condyle. Type 4 was found in 4(13.3%) specimen. In this type, the OPL was fanning out from a narrow medial attachment to its lateral attachment to the lateral femoral condyle and lateral head of the gastrocnemius (table 1). Table 1: Shape of OPL Shape N % Type 1 (band like) 9 30.0 Type 2 (band like) 13 43.3 Type 3 (cord-like) 4 13.3 Type 4 (fanning-out) 4 13.3 Total 30 100.0 In oblique popliteal ligament; mean length of upper and lower margin was 24.17mm and 30.56mm with minimum and maximum of 19.48mm, 31.89mm and 19.85mm, 37.87mm respectively (table 2). Table 2: Length of OPL at its upper and lower margin Variables Minimum Maximum Mean SD Upper margin 19.48 31.89 24.17 4.34 Lower margin 19.85 37.87 30.56 4.71 In oblique popliteal ligament; mean width at medial attachment including SM Expansion, at attachment to medial femoral condyle and lateral attachment was 11.71±2.25mm, 15.28±3.61mm and 19.01±4.50mm respectively (table 3). Table 3: Width of OPL Variables Minimum Maximum Mean SD Width at Medial Attachment including SM expansion 8.10 18.23 11.71 2.25 Width at attachment to Medial Femoral Condyle 9.20 23.90 15.28 3.61 Width at Lateral Attachment 7.30 27.70 19.01 4.50 In oblique popliteal ligament; mean position of Neurovascular hilum (NVH) was 17.71mm with minimum and maximum of 11.43mm and 21.44mm respectively.

The oblique popliteal ligament (OPL), chief posterior support of the knee, is an extension of the semimembranosus (SM) tendon and runs supero-laterally to the lateral femoral condyle. Due to variations and immense functional value of OPL; the present study was conducted to analyse the incidence of various shapes in oblique popliteal ligament and measurements of the different parts of oblique popliteal ligament. In past, various studies have been performed on knee joint. But less or no attention to posterior aspect of knee joint was given, among of all posterior structures, oblique popliteal ligament is important structure in maintaining the stability of knee joint. In present study the morphology of oblique popliteal ligament is observed through detailed cadaveric dissection of knee joints. Wu XD et al classified the OPL into band-shaped, Y-shaped, Z-shaped, trident-shaped and complex-shaped configurations. In the present study, the OPL was classified into type 1, type 2, type 3 and type 4. Types 1 and 2 were band-shaped, type 3 cord like and type 4 fan-shaped.14 Shape viz. type 1, 2, 3 and 4 was reported in 30%, 43.3%, 13.3% and 13.3% of the oblique popliteal ligament. Mehta V et al in their study found that type 1, 2, 3 and 4 was present in 40%, 50%, 6.6% and 3.3% of specimens, respectively. This is approximately similar to the present study.15 In oblique popliteal ligament; mean length of upper and lower margin was 24.17mm and 30.56mm with minimum and maximum of 19.48mm, 31.89mm and 19.85mm, 37.87mm respectively. Mean width of OPL at its medial attachment including SM expansion, at attachment to the medial femoral condyle and lateral attachment was 11.71±2.25mm, 15.28±3.61mm and 19.01±4.50 mm respectively. In a study by Mehta V et al, the mean length (upper), length (lower), width of the SM tendon expansion, width at attachment to the medial femoral condyle and width at the lateral attachment were 33.4 mm, 38.41 mm, 8.58 mm, 12.46 mm and 21.42 mm, respectively.15 In the present study, the length of the lower and upper margin of the OPL was shorter than that reported by Hedderwick et al.13 Fam et al measured the length of the OPL along both its middle and upper and lower margins.4 The width of SM expansion recorded by Hedderwick et al was higher, whereas that recorded by Fam et al was lower as compared to the present study. In the present study, the width of the lateral attachment of the OPL was larger than that measured by Hedderwick et al. In the present study, the neurovascular hilum (NVH) was usually observed near the upper margin of the OPL, between its medial and lateral attachments, dividing the ligament into two bands. In Type 1 OPL, the NVH was located between the upper band and the main ligament, whereas in Type 3 it was positioned centrally within the main ligament and in Type 4 it was seen between the two upper bands. Our observations suggest that the variable morphological patterns of the OPL are primarily related to the position of the NVH, with changes in its location corresponding to the different shapes of the ligament. This finding is consistent with the observations of Mehta et al15, who also reported that the morphology of the OPL is closely associated with the position of the NVH. In our study, the mean distance of the NVH from the lateral border of the SM tendon was 11.43 mm. Fam et al dissected 11 knees to measure the anatomical structure and relationships of OPL.4 They confirmed the role of OPL in controlling the knee hyperextension due to soft tissue recurvatum. Hyperextension affects walking, especially on uneven surfaces. Morgan et al performed a study exploring the biomechanics of the knee joint, in which they sectioned the structures on the posterior aspect of the knee joint one by one, and they found that the maximum degree of hyperextension occurred when the OPL was cut.3 The OPL serves as the main structure that prevents genu recurvatum. Therefore, this study is an attempt to understand the contribution of OPL in stabilizing the posterior knee. Table 4: Summary of OPL measurements in the present study in comparison with those of previous studies. Parameters Present study Fam et al (2013)4 Hedderwick et al (2017)13 Mehta V et al (2022)15 Mean (mm) Length upper margin 24.17 33.6 34.6 33.4 Length of lower margin 30.56 43.6 38.41 Width of SM expansion 11.71 7.4 10.7 8.58 Width at lateral attachment 19.01 _ 17.4 21.42 Horizontal distance of NVH from SM tendon 17.71 _ 16.7 19.52 Limitations 1. Better results are expected by including more number of cadavers in the study. There was no parity in the number of male and female cadavers taken up for the study. 2. In addition to anatomy, radiological and arthroscopic evaluation of the meniscofemoral ligaments can give a better perspective and understanding about their occurrence and variations.

Variations can occur in the morphology and attachments of the oblique popliteal ligament (OPL). Posterior part of knee capsule is biomechanically supported by OPL and it may prevent hyperextension of knee joint. Anatomical variations of the OPL described in this study will help in better understanding in biomechanical role of OPL in supporting the posterior part of knee capsule especially in deranged functions due to knee injury. Additionally, by using this knowledge, knee surgeons can optimise the functional outcome of their procedures when operating on the posterior part of the knee. Thus, the practical application of anatomical knowledge of OPL will help in solving the clinical diagnosis or in devising a surgical solution of knee diseases it’s process & applied to patient care.

1. Standring S. Pelvic girdle and lower limb. In: Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. London: Churchill Livingstone Elsevier; 2016. p.1393-401. 2. LaPrade RF, Morgan PM, Wentorf FA, Johansen S, Engebretsen L. The anatomy of the posterior aspect of the knee: an anatomic study. J Bone Joint Surg Am. 2007;89(4):758-64. 3. Morgan PM, LaPrade RF, Wentorf FA, Cook JW, Bianco A. The role of the oblique popliteal ligament and other structures in preventing knee hyperextension. Am J Sports Med. 2010;38(3):550-7. 4. Fam LP, Fruheling VM, Pupim B, Ramos CH, de Moura MF, Namba M, et al. Oblique popliteal ligament–an anatomical study. Rev Bras Ortop (English Edition). 2013;48(5):402-5. 5. LaPrade RF, Engebretsen AH, Ly TV, Johansen S, Wentorf FA, Engebretsen L. The anatomy of the medial part of the knee. J Bone Joint Surg Am. 2007;89:2000-10. 6. Beltran J, Matityahu A, Hwang K, Jbara M, Maimon R, Padron M, et al. The distal semimembranosus complex: normal MR anatomy, variants, biomechanics, and pathology. Skeletal Radiol. 2003;32:435-45. 7. Robinson JR, Sanchez-Ballester J, Bull AMJ, Thomas R, Amis AA. The posteromedial corner revisited. J Bone Joint Surg. 2004;86:674-81. 8. Veltri DM, Deng XH, Torzilli PA, Warren RF, Maynard MJ. The role of the cruciate and posterolateral ligaments in stability of the knee: a biomechanical study. Am J Sports Med. 1995;23(4):436-43. 9. Shahane SA, Ibbotson C, Strachan R, Bickerstaff D. The popliteofibular ligament: an anatomical study of the posterolateral corner of the knee. J Bone Joint Surg Br. 1999;81(4):636-42. 10. Bejui J, Walch G, Gonon GP, et al. Anatomical and functional study on the musculus semimembranosus. Anat Clin. 1984;6:215-23. 11. Warren LF, Marshall JL. The supporting structures and layers on the medial side of the knee: an anatomical analysis. J Bone Joint Surg Am. 1979;61:56-62. 12. Loredo R, Hodler J, Pedowitz R, et al. Posteromedial corner of the knee: MR imaging with gross anatomic correlation. Skeletal Radiol. 1999;28:305-11. 13. Hedderwick M, Stringer MD, McRedmond L, Meikle GR, Woodley SJ. The oblique popliteal ligament: an anatomic and MRI investigation. Surg Radiol Anat. 2017;39:1017-27. 14. Wu XD, Yu JH, Zou T, Wang W, LaPrade RF, Huang W, Sun SQ. Anatomical characteristics and biomechanical properties of the oblique popliteal ligament. Scientific reports. 2017; 7(1): 42698. 15. Mehta V, Dawani P, Prabhat GO. Morphologic and Morphometric Evaluation of Oblique Popliteal Ligament–A Clinico-Anatomical Study. Maedica. 2022; 17(3): 641.