The PMTC was a primary stabilizer of the knee involved in both static and dynamic stabilization, providing external rotation stability, and with small but important primary stabilization roles in the case of internal rotation, varus angulation, and anterior translation [22, 23]. Despite its important function, it was believed that the anatomic descriptions of the PMTC are controversial due to its complex and variable anatomy [24]. Previous researches shows that PT was the key structure of the PMTC [22, 25]. In agreement with previous literature, the present study has found that the complexity of the anatomy of PMTC was due largely to the variable alignment of this structures. According to our findings, the popliteus muscle (PM) also plays asignificantly role in this complexity.
The PM originated at the posterior tibia and ended at the lateral femoral condyle. When the PM transversed the articular capsule at the level of the posterior edge of the tibial plateau, the dense muscular fascia originated from the PM, which inserted into the PCL and became part of the PCL. In addition, the tendon-muscle junction gave off a series of dense fibrous bundles to connect with the PCL, the PMFL, the lateral meniscus, and the articular capsule. In accordance with the present results, this study has important similarities and yet differences compared to previous reports.
Based on previous reports[19], in 42 knee joints, there was a connection between the PM and lateral meniscus, posteriorlateral articular capsule, posterior cruciate ligament. This was similar to the results. However, for posterior cruciate ligament, a total of 13 cases (P45 section 7 cases, 78%, gross anatomy 6 cases, 86%) were found to have a dense connection between the PT and the PCL, the total rate was 81% in this study. This was different from the findings by Feipel et al[19]. and Chuncharunee et al[18], their results were 5% and 0%. The knee joint is the largest and most complex joint of the musculoskeletal system. Hence, it is difficult to determine the boundary of soft tissue by the method of gross anatomy. However, the adjacent relationship between organizations could be revealed on the premise of retaining the original organizational structure by the P45 sheet plastination technique, because of the characteristics of its high-definition soft tissue display. The anatomical structure observed using P45 sheet plastination technique could make us more targeted in the process of gross anatomy. This reason might be responsible for the significant difference in the gross anatomical results of this study and previous studies[18, 19]. Therefore, through the combined method of P45 and gross anatomy, we identified that there were dense connections in the PMTC. Meanwhile, it was found for the first time that two kinds of ventral and dorsal fiber bundles were sent out during the popliteal tendon penetrated the articular capsule. One connected the lateral meniscus anteriorly and the other ascented and blended into the articular capsule. Demonstrated by P45 sheets, the fiber connection between popliteal muscle and posterior cruciate ligament was firstly described. The relationship between the PM and lateral meniscus enriched previous observation of Chuncharunee et al. [18], by revealing the details of the connection between the PM and lateral meniscus in the sagittal plane.
PLC injury is often associated with complex injury of the knee, clinically, concomitant injuries of posterolateral corner structures with a cruciate injury lead to an increased incidence of ACL and PCL reconstruction failures [5]. Thus, the operation should take one not only to reconstruct the cruciate ligament but also to reconstruct the PLC [26, 27]. Nowadays, anatomical reconstruction of the PLC is commonly performed in chronic PLC injuries. However, the guidelines for PLC reconstruction remain unclear, and several surgical techniques for PLC reconstruction have been suggested, such as open techniques with a large lateral incision and extensive soft tissue dissection, or arthroscopic assisted techniques [28]. Despite there are still many differences in the treatment of PLC injury, it is difficult to formulate a unified treatment strategy due to PMTC complex and variable anatomy [25, 29]. Many investigations using laboratory, radiographic, and surgical studies to define the anatomy and function of PMTC[25, 29, 30], aimed at better understand this complex area. These studies have found that the PT, which functions as the fifth major ligament of the knee, is the key structures of the PMTC[22]. The complexity of the anatomy of PMTC is due largely to the variable alignment of these structures[23, 24]. In this study, there were dense connections between the PM and the posterior cruciate ligament, the PMFL, the lateral meniscus, and the lateral articular capsule, in which dense fiber connections were concentrated in the tendon-muscle migration where the PT penetrates the AC. Whether this anatomical structure plays an important role in maintaining the stability of the knee joint coulcd be addressed in further study, and yet the existence of this connection should be paid a clinical attention.
In particular, there are studies indicating that those higher rates of cruciate graft failure were due to increased force transmitted through the cruciate ligaments if a concomitant posterolateral corner injury was not fixed alongside the cruciate injury [31]. Thus, hopefully, the anatomy about dense connections between the PM and the posterior cruciate ligament, could contribute to the resolution of the related clinical issues.