The main finding of the preliminary study was that the FCAP could be feasibly and reliably ascertained under arthroscopy. The distance that based on this landmark measured at the lateral groove was varied from that from the conventional landmark at the anterolateral side. The distances from the FCAP to the ATFL footprint center and then to the CFL explicated the positional relationship between the FCAP and the ligament insertions.
Different operative procedures have been published to treat the chronic lateral ankle instability [7–10]. Currently, repair and reconstruction are the two preferred operative techniques: repair corresponds to a suturing of the torn lateral ligaments, while reconstruction refers to the replacement of the irreparable or chronically deficient lateral ligaments with other tissue . Thus, anchors or tunnels should be inserted or established on the fibula to fix the ligament or its substitutes. Shoji’s investigation  revealed that the nonanatomic tunnel position in ATFL repair resulted in significant inversion from 5° to 15° of dorsiflexion and significant internal rotation at neutral position. Besides, internal rotation laxity was significantly increased relative to the intact state in the nonanatomic repair. In addition, it has also been reported in a systematic review comparing the different operative techniques that anatomic stabilization techniques provided superior results in terms of functional outcome compared to non-anatomic techniques . Therefore, an anatomic ligament repair or reconstruction was the most popular and effective treatment to solve lateral ankle instability.
In both ligament repair and ligament reconstruction, it is crucial to accurately ascertain the ligamental attachment sites to achieve proper anchor insertion or tunnel creation at the distal fibula . Anterior fibular tubercle, fibular tip and fibular obscure tubercle were the most commonly used landmarks to describe the ATFL and CFL attachments, and to assist in positioning during ligament stabilization [14, 15]. However, these landmarks could only be recognized when performing open surgeries or radiographic perspectives . Teramoto et al.  performed a study to evaluate the relationship between the lateral malleolus view under ankle arthroscopy and the ATFL attachment site. They found that standard ankle arthroscopy portals might not allow for complete visualization of the tip of the lateral malleolus. Meanwhile, it might not be feasible to thoroughly observe the CFL attachment site [12, 13]. Therefore, it might still be a huge challenge to accurately confirm the ATFL attachment, as well as the further CFL attachment under arthroscopy, especially for junior surgeons without extensive experience for ankle arthroscopy.
The shape of the fibular articular surface is approximately triangular, with the anterior edge slopes from anterosuperior to posteroinferior direction. Meanwhile, the upper edge is connected to the anterior edge through a curved margin [16–18]. Thus, a process is formed in the junction of the anterosuperior curved edge and the anteroinferior oblique edge, which represents to the most anterior position of the articular surface. In the present study, both the experienced senior surgeon and the inexperienced junior resident have successfully marked the FCAP with a Kirschner wire without sufficient debridement under the arthroscopic image. This landmark was confirmed after open dissection, and the distance between the anatomic FCAP' and the marked FCAP varied from 1.23 mm to 1.52 mm, both of which were less than the deviation value of the marked ATFL insertion after establishing accessory portal and thorough dissection under arthroscopy (1.7–2.9 mm) . Therefore, it might be much easier and more accurate to ascertain the upper FCAP than the ATFL insertion at the lateral groove. Moreover, the deviation that performed by the junior resident showed no significant difference compared with that measured after the senior’s operation, and the ICC was more than 0.75, both indicating that the identification and marking manipulation of the FCAP under arthroscopy was reliable and repeatable. Consequently, it is reasonable to believe that the FCAP could be regarded as a landmark to assist in positioning the insertions of the lateral ligaments under arthroscopy, especially for junior surgeons who lack extensive experience.
To maximally simulate and restore the perspectives of the arthroscope, the ATFL and CFL footprint centers were ascertained at the lateral groove where the bone hole or tunnel was made to fix the ligament remnant or graft in arthroscopic surgeries. Compared to the distance that measured at the anterolateral side from the anterior fibular tubercle, the distance from the FCAP to the ATFL footprint center was slightly shorter. This phenomenon corresponded to the previous studies that showing the position of FCAP was lower than that of anterior fibular tubercle [16, 17]. The FCAP could be detected much easier than the anterior fibular tubercle under arthroscopy [12, 13], indicating the superiority of regarding the FCAP as a landmark. On the other hand, the distance from ATFL to CFL that measured at the anterolateral side or lateral groove was similar, which confirmed the internal consistency of the methods for ligament footprint discerning and distance measurements. Because the isolate ATFL repair was the most popular and commonly used method to treat lateral ankle instability under arthroscopy [6, 19], and the ATFL reconstruction or in combination with CFL reconstruction was considered in patients with poor ligament quality or severe instability [4, 19]. That meant the intervention of CFL was usually selectively performed followed the ATFL management. Thus, we intended to first ascertain the ATFL footprint center based on the FCAP, and then measured the ATFL-CFL distance so as to ascertain the latter’s position on the basis of the ATFL fibular insertion. Since the anterior fibular edge was a curved rather than a straight line , the direct linear measurement from the landmarks (whether the anterior fibular tubercle or the fibular tip) to the ligament insertions seemed to shorten the distances. Because the lateral malleolus can’t be completely exposed in arthroscopic surgeries, the sectional measurement for the distances from FCAP to ATFL, then to CFL on the lateral groove would be more helpful to accurately mark the native ligament insertions. Additionally, measuring the distance at the lateral groove would be closer to clinical practices because the hole or tunnel ready for ATFL (and CFL) stabilization was prepared at the lateral groove.
The clinical relevance of this study is that FCAP could be used as a landmark or a supplementary reference to position the lateral ligaments under arthroscopy, thus arthroscopic techniques of anatomic repair or reconstruction might be accurately developed or improved. However, this study just preliminarily verified the feasibility and reliability of ascertaining the FCAP under arthroscopy, and revealed the positional relationships between the landmark and the ligament insertions. These findings provided a possibility of using the FCAP as a landmark to label ligament insertions on the fibula. The actual maneuverability should be further confirmed in ankle specimens, and whether using the auxiliary landmark was better than using the traditional method also needs further exploration. Second, since it was not applicable to repeat the arthroscopic marking operations in a single specimen, we performed the ICC analysis in paired ankles of a cadaver to reduce variation between the specimen individuals as previously , the reliability and repeatability analysis might not be extremely rigorous. Moreover, twenty specimens may not be enough to represent the general population, especially with regard to the landmark labelling manipulation.