Arthroscopically measured syndesmotic stability after screw vs. suture button fixation in a cadaveric model.

BACKGROUND: Appropriate management of ankle syndesmotic instability is needed to prevent the development of complications. Previous biomechanical studies have evaluated movement of the fibula after screw or suture button fixations with different results, most likely being caused by variations in experimental setups that did not mirror the in vivo clinical setting. This study aimed to arthroscopically compare in a cadaveric model the stability of syndesmotic fixation with either a suture button or syndesmotic screw.

METHODS: Eight fresh matched pairs of human ankle cadaver specimens (above knee) underwent arthroscopic assessment with (1) intact ligaments, (2) after complete disruption, and (3) after repair with either a quadracortical syndesmotic screw or suture button construct. In every stage, four loading conditions were considered under 100N of direct force: 1) unstressed, 2) lateral hook test, 3) anterior to posterior (AP) translation test, and 4) posterior to anterior (PA) translation test. Coronal plane tibiofibular diastasis, as well as sagittal plane tibiofibular translation, were arthroscopically measured.

RESULTS: Coronal plane anterior and posterior tibiofibular diastasis and sagittal plane tibiofibular translation were measured using probes of increasing diameters. Following screw fixation, syndesmotic stability was similar to the uninjured syndesmosis in the coronal plane (anterior, median 0.0mm [IQR 0.0-0.3] vs. 0.3mm [IQR 0.2-0.3]; p=0.57; posterior, median 0.1mm [IQR 0.0-0.4] vs. 0.2mm [IQR 0.1-0.3]; p=1.0) but more rigid in the sagittal plane (median 0.0mm [IQR 0.0-0.1] vs. 1.0mm [IQR 0.4-1.5]; p=0.012). Repairing the unstable syndesmosis with a suture button construct resulted in coronal plane stability similar to the uninjured syndesmosis (anterior, median 0.2mm [IQR 0.1-0.3] vs. 0.2mm [IQR 0.1-0.3]; p=0.48; posterior, median 0.2mm [IQR 0.1-0.3] vs. 0.3mm [IQR 0.1-0.5]; p=0.44). However, sagittal plane fibular motion remained unstable as compared to the uninjured syndesmosis (median 2.2mm [IQR 1.6-2.6] vs. 0.8mm [IQR 0.4-1.3]; p=0.012).

CONCLUSION: Current fixation methods for syndesmotic disruption maintain coronal plane fibular stability. Screw and suture button constructs, however, respectively resulted in greater or insufficient constraint to fibular motion in the sagittal plane as compared to the intact syndesmotic ligament. These findings suggest that neither traditional screw nor suture button fixations optimally stabilize the syndesmosis, which may have implications for postoperative care and clinical outcomes.