Arthroscopic Quantification of Syndesmotic Instability in a Cadaveric Model Ross Feller, M.D., Todd Borenstein, M.D., Amanda J. Fantry, M.D., Roy Bradley Kellum, M.D., Jason T. Machan, Ph.D., Florian Nickisch, M.D., and Brad Blankenhorn, M.D. Purpose: To investigate whether arthroscopy or stress radiography can identify instability resulting from single-ligament injury of the ankle syndesmosis and to determine whether either modality is capable of differentiating between various levels of ligament injury. Methods: Syndesmotic/deltoid ligament sectioning was performed in 10 cadaver legs. Arthroscopic evaluation and fluoroscopic stress testing were completed after each sectioning. In group 1 (n ¼ 5), sectioning began with anteroinferior tibiofibular ligament (AITFL), then interosseous membrane (IOM), posteroinferior tibiofibular ligament (PITFL), and deltoid. In group 2 (n ¼ 5), this order was reversed. Measurements were made by determining the largest-sized probe that would fit in the anterior and posterior syndesmosis. Radiographic parameters included tibiofibular overlap/clear space and medial clear space. Results: No radiographic measurement proved useful in distinguishing between intact and transected AITFL. Anterior probe (AP) size reached significance when distinguishing between intact and AITFL-transected specimens (P < .0001). AP detected significant differences comparing single with 2-, 3-, and 4-ligament (AITFL, IOM, PITFL, deltoid) disruptions (P ¼ .05, <.0001, and <.0001, respectively). Significant differences were observed between 2- and 3/4-ligament (P ¼ .02) transections. Posterior probe (PP) size detected sig- nificant differences between intact and single-, double-, triple-, and complete ligament transections (P values .0006, <.0001, <.0001, <.001, respectively). PP detected significant differences between single- and double-, triple-, and complete ligament transection models (P ¼ .0075, .0010, and .0010, respectively). PP distinguished between 2- and 3/4- ligament (P ¼ .03) transections. Conclusions: Stress radiography did not distinguish between intact and single-ligament disruption, and was unreliable in distinguishing between sequential transection models. Arthroscopy significantly predicted isolated disruption of the AITFL or deltoid ligaments. Also, probing was able to differentiate between most patterns of ligament injury, including sequential transections. Clinical Relevance: These data can aid surgeons during arthroscopy of the ankle when attempting to correlate intraoperative syndesmotic evaluation findings with the extent of ligament injury. I njury to the syndesmosis is common and occurs in up to 11% of all ankle injuries. 1 These injuries can be purely ligamentous or may be associated with fractures, and they can be categorized by the Lauge-Hansen classification system. 2,3 Injury to the syndesmotic liga- ments may cause instability of the ankle, leading to changes in tibiotalar contact area and increased contact pressures. 4,5 Therefore, accurate diagnosis is essential to proper treatment and preventing long-term ankle dysfunction. Ankle arthroscopy is becoming increasingly used for both diagnosis and treatment of syndesmotic injuries. It has been shown to have the highest sensitivity and specificity and often can diagnose injuries previously missed on standard and stress radiographs. 6,7 Although parameters for arthroscopic diagnosis have been defined, including disruption of the deep portion of the posterior tibiofibular ligament, rupture of the inteross- eous ligament with a syndesmotic gap >2 mm, and a chondral fracture of the posterolateral portion of the tibial plafond, these parameters have not been quanti- fied. 8 Specifically, the authors were unable to identify From the Department of Orthopaedic Surgery, The Warren Alpert School of Medicine at Brown University, Rhode Island Hospital (R.F., T.B., A.J.F., J.T.M., B.B.), Providence, Rhode Island; Capital Orthopedic and Sports Medicine (R.B.K.), Flowood, Mississippi; and Department of Orthopaedics, University of Utah (F.N.), Salt Lake City, Utah, U.S.A. The authors report the following potential conflicts of interest or sources of funding: F.N. receives consultancy fees and royalties from Smith & Nephew and has stock/stock options in Connextions, First Ray, Surgical Frontiers, and Mortise Medical. Received October 26, 2015; accepted November 3, 2016. Address correspondence to Amanda J. Fantry, M.D., The Warren Alpert School of Medicine at Brown University, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, U.S.A. E-mail: amanda.fantry@gmail.com Ó 2016 by the Arthroscopy Association of North America 0749-8063/15986/$36.00 http://dx.doi.org/10.1016/j.arthro.2016.11.008 436 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 2 (February), 2017: pp 436-444