Figure 1. Anteroposterior radiograph of left ankle.
Figure 2. Lateral view of ankle.
A 31-year-old woman presents with left ankle pain following a fall 2 days ago. She slipped on ice and her ankle twisted. On physical examination of the ankle, the patient has moderate swelling over the lateral distal fibula and medial ankle. She has tenderness to palpation over the lateral ankle and medial deltoid ligament. Radiographs are ordered (Figures 1 and 2).
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Knowing how to differentiate between stable and unstable ankle fractures is critical in determining which injuries would do better with surgical treatment. Ankle stability is provided by the bones of the ankle and the surrounding ligament structures. The lateral ligaments include the anterior talofibular (ATFL), calcaneofibular (CFL) and posterior talofibular (PTFL).1 The medial side of the ankle is stabilized by the deltoid ligament and the syndesmosis between the fibula and tibia is stabilized by the anterior and posterior inferior tibiofibular ligaments (AITFL and PITFL) and the interosseus ligament.1
Fracture patterns help dictate if a fracture is stable and if ligament structures have been injured. For instance, the more proximal that a fibular fracture occurs the more likely it is unstable. Medial-sided deltoid tenderness on physical examination was once thought to indicate an unstable injury, however, tenderness may indicate a superficial deltoid injury only and the stronger deep fibers may remain intact. A complete deltoid rupture will show medial clear space widening and lateral talar shift on mortise view radiography indicating an unstable injury.1,2
If a complete deltoid injury is suspected (high fibular fracture, syndesmosis tenderness, normal initial radiograph) a weight-bearing radiograph can be obtained 7 to 10 days after the injury to stress the joint. Magnetic resonance imaging (MRI) has not been shown to reliably or accurately determine a partial vs complete deltoid rupture and is not recommended for ankle fractures.2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Lampridis V, Gougoulias N, Sakellariou A. Stability in ankle fractures: diagnosis and treatment. EFORT Open Rev. 2018;3(5):294-303. doi:10.1302/2058-5241.3.170057
2. Nortunen S, Lepojärvi S, Savola O, et al. Stability assessment of the ankle mortise in supination-external rotation-type ankle fractures: lack of additional diagnostic value of MRI. J Bone Joint Surg Am. 2014;96(22):1855-1862. doi:10.2106/JBJS.M.01533