Flat ACL anatomy: fact no fiction.

Abstract

just posterior to the ACL insertion in the area intercondylaris anterior. No bundles have been drawn. At the beginning of the “modern” era of ACL surgery, such small details may not have played an important role for the orthopaedic society. Surgeons in their nature were fascinated by solving exciting technical issues like open and arthroscopic approach, transtibial and single-incision technique, bone tunnel placement and graft choice. So our ancestor’s art was forgotten. In 1938 Ivar Palmer was the first to describe bundles of the ACL and to perform an ACL reconstruction using a “double-bundle” technique [17]. Later Girgis et al. [8] divided the ACL into two functional parts: a smaller anteromedial band and a larger posterolateral band. This description was then used as a basis to understand the function of the different fascicles of the ACL [4, 18]. Whereas some authors found three anatomical bundles [2, 14], others only described a single flat continuum of fascicles without any bundle structure [3, 16, 26]. Inspired by anatomical reports, the ACL “doublebundle” reconstruction was refined by innovative surgeons like Mott [12], Zaricznyj [28] and Muneta et al. [13]. The last 10 years experienced a “double-bundle boom” which was driven by many surgeons and scientists around the globe [1, 5–7, 15, 20, 21, 27]. In an intension to better understand the ACL and to optimize surgical results, the anatomy and surgery was revisited. There was a strong interest to investigate the “double-bundle” structure with its anteromedial (AM) and posterolateral (PL) bundles and its insertion sites to support the surgical double-bundle concept. More than 600 articles have been published in PubMed related to the topic in recent years. Simultaneously in 2006, the flat midsubstance and flat femoral ACL insertion was described by Mochizuki et al. [11]: “The configuration of the natural ACL midsubstance is not oval, but rather flat, looking like ‘lasagne’ about 15 mm in length and about 5 mm in width after removal of the surface In 1836 Wilhelm and Eduard Weber published their detailed work on the anatomy and physiology of the lower extremity (Fig. 1) [25]. The anterior cruciate ligament (ACL) was shown to be flat in extension, twisted in flexion and aligned with the posterior femoral cortex. Nearly 100 years later (but also 100 years ago!), exactly in 1921 two French anatomists named Testut and Jacob described the flat ACL midsubstance and the close relationship between the anterior horn of the lateral meniscus and the tibial ACL insertion (Fig. 2) [24]. They beautifully showed that the bony insertion of the anterior root of the lateral meniscus was