What is the diagnosis?

Fracture of the lateral tubercle of the posterior process of the talus with minimal displacement. This is known as Shepherd’s fracture [1,2].

Image 2. Talus is viewed superiorly. Courtesy of Life in the fast lane, www.litfl.com [2].

• Pearl: A fracture isolated to the medial tubercle is “Cedell’s fracture” [1,2].

What is the mechanism of injury?

Shepherd’s fracture is usually caused by inversion and forced hyperplantarflexion of the ankle. The fracture may result from compression on the posterior talar process from other structures occupying the posterior ankle joint space [1,2].

Alternatively, inversion and hyperdorsiflexion may cause a Shepherd’s fracture as an avulsion injury to the bone resulting from the stress applied to the posterior talofibular ligament [1].

What physical exam findings are expected?

Signs and symptoms are similar to an ankle sprain (which is often associated with the bony injury or mistaken as the only injury). Physical exam demonstrates diffuse ankle swelling and pain localized to the posterolateral region on palpation and with passive movement of the ankle joint. Flexor hallucis longus (FHL) tendon runs in the groove between the medial and lateral tubercles of the posterior talar process (Image 2), thus pain with passive big toe flexion or standing on tiptoe may also be painful in the setting of this injury. Posterior ankle impingement test (also known as the heel thrust test) may be positive as well [1].

• Pearl: Up to 40% to 50% of posterior talar process fractures are missed due to similarity in presentation to ankle sprain, even in the absence of additional, distracting injuries [1].

• Pearl: Shepherd’s fracture missed from mistaking the finding for an os trigonum which can be found in 7-10% of normal population [1,2].

• Pearl: Stieda’s process is another normal variant structure. Note that a Stieda’s process is a protuberant tubercle of the posterior talar process whereas an os trigonum is an accessory bone in the posterior joint space due to failed fusion of a secondary ossification center. Fracture of a Stieda’s process may actually be a Shepherd’s or Cedell’s fracture [3,4].

Image 3. Schematic diagram of possible causes of posterior ankle impingement. Note FHL tendon shown in the groove between medial and lateral tubercles of the posterior talar process [4]. Origin: Case courtesy of Flores DV, Department of Radiology, Makati Medical Center, Makati City, Philippines. www.eurorad.org, case 13747

Which imaging modalities can be used?

Obtain anteroposterior, lateral (best to visualize chip fracture), and mortise (best to visualize lateral process fracture) plain film views. A posterior subtalar effusion demonstrated on plain film is highly suggestive of a lateral process fracture. Due to very poor sensitivity and high rates of missed injury, a CT is the gold standard and should be obtained in cases of high clinical suspicion or classic mechanism of injury [1,2].

What is the management in the ED?

Patients with minimal displacement can be managed conservatively with placement of a short leg U-Splint (Stirrup Splint) with a posterior slab. In general, most patients can be placed in a splint with outpatient referral for surgical consideration. See table 1 below for additional information.

Table 1. Management of talar process fractures based on Boack classification system applicable to lateral and posterior process injuries, table courtesy of EFORT open reviews [1,2].

When do you consult Orthopedics?

Complex fractures (intra-articular, significantly displaced, multifragmentary, associated dislocation, etc.) may require surgical management thus necessitating Orthopedics consultation for determination of need for urgent or emergent open reduction and internal fixation. Surgical management may be indicated to prevent or later treat to reduce or eliminate symptoms of adverse outcomes such as non-union, malunion, or early degenerative changes [1].

• Pearl: Up to ⅓ of conservatively managed cases may develop avascular necrosis, so despite being relatively uncommon injuries overall, it is important to maintain high clinical suspicion for posterior talar process fractures. Missed or delayed diagnosis and inadequately treated fractures are more likely to result in significant disability and cause long-term problems [1].