Talus - Posterior Process Etiology / Epidemiology / Natural History
May be caused by forceful plantar flexion of the ankle producing a nutcracker-like compression of the posterior process between the posterior malleolus and the calcaneus (Nasser S, Foot Ankle 1990;10:235)
Medial tubercle avulsion fractures may be caused by forced dorsiflexion and pronation
Lateral tubercle avulsion fractures may be caused by forced ankle inversion
The artery of the tarsal canal(posterior tibial artery) is the main blood supply to the body of the talus. It forms an anastomotic sling with the artery of the tarsal sinus (peroneal). Others=superior neck vessels from anterior tibial artery, Deltoid artery(post tibial) (Mulfinger JBJS 1970;52B:160).
60% covered with articular cartilage, no muscle originate from or insert into talus.
Lateral process: a wide, wedge-shaped prominence extending from the lateral aspect of the body of the talus; consists of two distinct articular facets: the dorsolateral and the inferomedial. The dorsolateral facet articulates with the distal fibula; the inferomedial facet forms the anterolateral portion of the subtalar joint. The lateral process is the site of insertion of the lateral talocalcaneal ligament.
Posterior process: composed of a medial and a lateral tubercle(Stieda’s process) which are separated by a groove within which lies the flexor hallucis longus tendon. The Y-shaped, bifurcate talocalcaneal ligament forms a roof over this grooveand inserts onto each tubercle. The posterior talofibular ligament inserts onto the lateral tubercle of the talus. The posterior talotibial portion of the deltoid ligament inserts onto the medial tubercle.
Os trigonum: located directly posterior to the lateral tubercle(Stieda's process). It is an accessory bone that arises from a secondary ossification center between the ages of 8 and 11 years. Generally fuses to the lateral tubercle within 1 year of its appearance. May persist as a separate ossicle, attached to the talus by a cartilaginous synchondrosis. (Grogan DP, JPO 1990;10:618)
Talus - Posterior Process Clinical Evaluation
Deep tenderness anterior to the Achilles tendon but posterior to the talus indicates posterior process fractures.
Tenderness over the posterolateral ankle, just medial to the peroneal tendons indicates fracture of the lateral tubercle of the posterior talar process and/or the os trigonum
Tenderness medially, just posterior to the medial malleolus indicates fracture of the medial tubercle of the posterior talar process.
Forced plantar flexion often causes posterior ankle pain in patients with posterior talar process or os trigonum fractures.(Paulos LE, AJSM 1983;11:439)
Resisted flexion of the great toe may cause pain as the flexor hallucis longus tendon slides past a medial or lateral tubercle fracture of the posterior talar process.
Talus - Posterior Process Xray
A/P, Lateral, and Mortise Ankle and A/P, Oblique, Lateralfoot xrays indicated
Large posterior process fractures are best seen on lateral view
Medial and lateral tubercle fractures are difficult to see on plan xray.
CT with 1mm cuts allows accurate assessment of hindfoot fractures and is indicated for patients with clinical suspision of a hindfoot fracture and negative xrays.
Talus - Posterior Process Classification / Treatment
Medial Tubercle, Acute Non-displaced (<1cm in size or <2mm displaced):short-leg, non-weight bearing cast for 6 weeks. Advance to wbat in removable cam-walker if asymptomatic at 6weeks. (Kim DH, Foot Ankle Int 2003;24:172)
Medial Tubercle, Noncomminuted, Displaced(>1cm in size or >2mm displaced): ORIF with small or mini-fragment screws or k-wires. Approached via a posteromedial incision, dissection between the flexor digitorum longus tendon anteriorly and the NV bundle posteriorly. Fractured tubercle is medial to the FHL tendon.
Lateral Tubercle, Acute Non-displaced(<1cm in size or <2mm displaced):short-leg, non-weight bearing cast for 6 weeks. Advance to wbat in removable cam-walker if asymptomatic at 6weeks.
Lateral Tubercle, Noncomminuted, Displaced(>1cm in size or >2mm displaced): ORIF with small or mini-fragment screws or k-wires. Posterolateral approach between the peroneal tendons and the Achilles tendon. Must identify and protect the sural nerve.
Complete posterior process Fx: generally displaced, ORIF indicated. Either a posteromedial or posterolateral approach. Posteromedial approach is between the flexor digitorum longus tendon anteriorly and the NV bundle posteriorly. Posterolateral approach is between the peroneal tendons and the Achilles tendon. Must identify and protect the sural nerve.
Chronic injuries generally have poor outcomes with non-surgical management and fragment excision for small non-articular fragments or ORIF for large articular fragments should be consider
Talus - Posterior Process Associated Injuries / Differential Diagnosis