The Relationship Between the Distal Tibial Fibular Syndesmosis and the Varus Deformity in Patients With Varus Ankle Osteoarthritis

BACKGROUND: The impact of varus ankle osteoarthritis (OA) on the distal tibial fibular syndesmosis is poorly described. This study aimed to investigate the possible relationship between the condition of the distal tibial fibular syndesmosis and the degree of the varus deformity using weightbearing simulated computed tomography (CT), in patients with varus ankle OA. METHODS: This retrospective comparative study included 155 varus ankles, divided into 4 Takakura-Tanaka groups (stage 2, 3a, 3b, and 4). A control group comprised 35 ankles without prior ankle disorders. The angles between the tibial shaft and the articular surface of the tibial plafond on the anteroposterior view (TAS), and articular surfaces of the tibial plafond and talar dome (TTW) were measured from weightbearing ankle radiographs. The varus angle of the ankle (VA) was defined as 90 – TAS + TTW. On the CT axial view, 1 cm proximal to the tibial plafond, the area of the syndesmosis (“CT-area”) and the distance between the fibula and the tibia (CT-FCS) were measured. RESULTS: The CT area in stages 2, 3a, 3b, 4, and control group were 99, 79, 77, 103, and 97 mm(2), respectively. The CT-FCS were 3.5, 3.1, 2.9, 4.3, and 3.9 mm, respectively. In all 155 OA ankles, CT area and CT-FCS were negatively correlated with the VA (correlation coefficient r = –0.38, P < .01; and r = 0.38, P < .01, respectively). Both CT area and CT-FCS were significantly smaller in stages 3a and 3b than in the control group (P < .01). CONCLUSION: There may be a relationship between the narrowing of the syndesmosis and the varus deformity in patients with varus ankle OA, especially in stages 3a and 3b. CLINICAL RELEVANCE: Clinicians should be aware of the impact of varus ankle arthritis on the distal tibial fibular syndesmosis when operatively treating varus ankle OA. For some patients, the isolated treatment for the tibiotalar joint may be insufficient, and treatment for the syndesmosis as well as tibiotalar joint may be needed. LEVEL OF EVIDENCE: Level III, retrospective case control study.