Determining the force required in arthroscopic evaluation to assess the stability of syndesmotic ankle injury: a cadaveric study

Introduction The diagnosis of isolated distal tibiofibular syndesmotic ankle instability proves to be a challenge. Although diagnostic imaging has added value, it is limited in the detection of distal syndesmotic ankle instability. The gold standard remains intraoperative testing through arthroscopic probing while externally stressing the ankle in a sagittal direction. However, no validated arthroscopic guidelines have been established to distinguish a stable from an unstable syndesmotic ankle joint. This cadaveric study presents anatomical and biomechanical data that can help surgeons correctly identify isolated distal syndesmotic ankle instability. Objective The purpose of this study is to quantify the necessary forces applied during ankle arthroscopy to evaluate syndesmotic instability in freshly frozen cadaveric ankles. Methods A total of 16 fresh frozen cadaveric (age 58–74 years) ankles were included in the study. A dynamometer was used to measure the force necessary for the shaver tip to be inserted into the distal tibiofibular joint with the ankle in a neutral position. Measurements were performed first with the syndesmosis intact, and again following progressive transection of the syndesmotic ligaments, along with distal fixation. Results Significant differences were noted in the mean force required between the anterior inferior tibiofibular ligament (AITFL)+interosseous ligament (IOL) and no ligament cut methods (p<0.001 between the AITFL+IOL and AITFL cut (p<0.001; 95% CI 44.80 to 50.70), and between the AITFL+IOL and AITFL+IOL+ PITFL cut (p<0.001). There were also significant differences in the necessary mean forces applied between the one-SB and two-SB methods (p<0.001), between the one-SB and one-screw methods (p=0.010), between the one-SB and two-screw methods (p=0.01), between the two-SB and two-screw methods (p=0.003) and between the one-screw and two-screw methods (p<0.001). Significant differences were found between the AITFL+IOL cut and the one-SB (p<0.001), the two-SB (p<0.001), the one-screw (p<0.001) and the two-screw (p<0.001) methods. Conclusions This cadaveric study provides biomechanical data that can assist the surgeon in the arthroscopic evaluation of syndesmotic injuries. The data from this study need to be clinically correlated to ultimately assist in improving the outcome of patients with syndesmotic ankle injuries. Our study offers to bridge the gap to the development of arthroscopic tools that can identify the need for surgical fixation to the syndesmosis based on the laxity of specific ankle ligaments that contribute to subtle instability. Level of evidence Level V cadaveric study.