Development and validation of a novel approach for quantifying dimensions of the lateral ligaments in human ankle dissections

The lateral ankle ligaments, composed of the anterior talofibular (ATFL), calcaneofibular (CFL), and posterior talofibular ligaments (PTFL) are frequently subject to injury. While conservative and surgical treatment methods have had some positive outcomes, high rates of re-injury, chronic ankle instability, and pain remain, prompting the investigation of tissue-engineered applications in the treatment of lateral ligament injuries. In order for tissue-engineered construct design to be undertaken, a complete understanding of the native anatomy of the lateral ankle ligaments must be obtained. To date, substantial data exist on the anatomical structure of the lateral ankle ligaments, particularly surrounding their dimensions throughout movements of the ankle complex. Despite this, current literature does not consider the dynamic nature of the lateral ankle ligaments when assessing true ligament length nor the ability of ligaments to stretch and recoil throughout joint movement. Existing methodologies for measuring the lateral ankle ligaments commonly use instruments with limited flexibility and simply measure the distance between attachment points, not accounting for any degree of relaxation within the ligament. Therefore, this study aims to establish a new methodology that considers the curvatures and form of the lateral ankle ligaments throughout all movements of the ankle complex. Cadaveric dissection was performed on 21 ankles to fully expose the lateral ankle ligaments. The full length of the ATFL, CFL, and PTFL was measured following a newly developed 'String for Dynamic Tissue' (SDT) method. Flax-coated wax string was aligned and moulded to the surface and curves of each ligament from the most proximal attachment point to the most distal attachment point, along the same plane and cut to size. Measurements for each ligament were assessed throughout all degrees of movement of the ankle complex: plantarflexion, dorsiflexion, inversion, eversion, and neutral. A digital calliper was used to measure the exact string length, representing both the relaxed and taut ligament's full ligament length. Across all samples, the full length of the ATFL ranged between 21.20 and 33.80 mm (n = 20) throughout all movements of the ankle complex. Measurements of the CFL ranged between 28.66 and 44.44 mm (n = 21), while full-length measurements of the PTFL ranged from 27.90 to 39.80 mm (n = 21). Ligament dimensions of the relaxed ligament were greater when compared to the current literature, while dimensions of the taut ligament closely resembled data currently available. The SDT method not only enables accurate measurement and assessment of non-linear structures but also highlights the importance of considering complete structural form, emphasizing the need to move beyond merely measuring the linear distance between two points. This method will have multiple applications within the anatomical and biomechanical fields and across a range of tissue types and locations.