Peripheral Talus Fractures
Talus has 7 articular surfaces and it is divided into the head, neck, and body, and 2 processes, the posterior process and the lateral process.
The posterior process is further subdivided in to posterolateral and posteromedial tubercles. Fractures of the lateral process and the posterior process are considered to be peripheral talar fractures.
Fractures of the talus comprise 3.4% of foot and ankle fractures and 0.32% of all fractures in the human body. They are uncommon and frequently missed due to difficulty in visualising them on plain radiographs and low level of suspicion.
Delayed diagnosis and treatment can potentially lead to poor outcome leading to long-term pain, disability, non-union and degenerative changes. Factors that can affect the outcomes of these fractures are the extent of initial articular damage, the accuracy of the reduction and the subtalar joint stability.
Fractures of the Lateral Process of the Talus
Lateral process fractures of the talus are traditionally misdiagnosed as ankle sprains and the missed or untreated injuries can potentially lead to persistent symptoms.
Anatomy
The lateral process of the talus has a large base that articulates with the fibula dorsolaterally, and contributes to maintain the ankle mortise. It forms the lateral portion of the subtalar joint articulating with posterior facet of the calcaneum inferomedially. The lateral talocalcaneal ligament originates from the tip of this process.
Incidence
In a review of 1500 ankles injuries only 0.86% were found to be the lateral process fractures. Their incidence among the general population is unknown; however these are seen frequently in snowboarding-related injuries, hence also known as snowboarder’s fractures. In one large series 2.3% of all snowboarding injuries were lateral process fractures, whilst some other studies have reported their incidence up to 6.3%.
Mechanism
Lateral process fractures are usually a result of high-energy injuries. The causative injuries include snowboarding injuries, falls from heights, road traffic accidents, direct trauma and football and rugby injuries.
The suggested mechanism is thought to be a consequence of forced dorsiflexion and inversion of fixed pronated foot. This results in a lateral shift of the talar head, an upward shift of the lateral process of the talus on the posterior articular surface of the calcaneus and loss of congruity of the posterior articulation.
Boon et al., in their cadaveric study, proposed that some degree of external rotation is also required to produce this type of injury. Funk et al., in another cadaveric study, suggested that a combined eversion and dorsiflexion might also play an important role resulting in these fractures.
Clinical Presentation
Clinically, up to 40-50% of the lateral process fractures can be missed due to similar presentation as ankle sprains even in the absence of distracting injuries. A history of an ‘ankle sprain’ and the presence of associated acute localized tenderness, swelling, and haematoma around the tip of the lateral malleolus and painful range of motion should raise the suspicion of a lateral process fracture.
Imaging
Plain radiographs of the ankle in anteroposterior, lateral and mortise views should be performed routinely. A lateral process fracture is best seen on a mortise view or Brodens view but the chip fractures are best seen on the lateral view just above the Angle of Gissane.
Presence of posterior subtalar effusion is highly suggestive of an occult lateral process fracture. A lateral radiograph with dorsiflexion and inversion of the ankle may assist in better visualization of the fracture fragment. CT is considered to be the gold standard in cases of a high index of suspicion based on their injury mechanism and clinical appearance.
Classification
Hawkins described three different patterns in his series of lateral process fractures.
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Simple fractures – extending from the talofibular articular surface to the posterior talocalcaneal articular surface of the subtalar joint.
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Comminuted fractures – involving both the articular surfaces and the entire lateral process.
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Chip fractures – arising from the anterior and inferior portion of the posterior articular process involving only the subtalar joint and not extending into the talofibular articulation.
Boack described a modified classification system that can be applied to the fractures of either the lateral or the posterior processes [5]. This classification includes four types of fractures, each type subdivided according to severity of bony injury, degree of chondral lesion and ligamentous stability. Based on their description, lateral and posterior process fractures are classified into the following 4 types:
Type 1 - a small chip or avulsion fracture (< 0.5 cm):
1a - Small (extra-articular) fragment of the lateral process of the talus
1b - Small fragment of the isolated medial tubercle of the posterior process
1c - Small (intra-articular) fragment of the lateral process of the talus
Type 2 - an intermediate fragment (0.5–1.0 cm) with some displacement:
2a - Extends into the subtalar joint but not to the talofibular joint
2b - Isolated fracture of the entire lateral tubercle of posterior process
Type 3 - a large fracture fragment (> 1 cm) with associated damage to both the ankle and the subtalar joints:
3a - Single large fragment of the lateral process extending from the talofibular articular surface to the posterior facet of the subtalar joint
3b - Comminuted fracture of the entire lateral process
3c - Fracture of the entire posterior process of the talus
Type 4 - a severe form of fracture of either of the processes and associated instability or dislocation of the subtalar joint.
Management
The literature lacks a consensus on the optimum management of the lateral process fractures, however the management is aimed at restoring the anatomy of the talus and the articular surfaces.
Appropriate management depends on the size, location, and displacement of the fragment, the degree of articular cartilage damage and instability of the subtalar joint. When these fractures were described in the initial reports, plaster cast immobilisation was considered an adequate treatment. However long-term follow-up in the largest individual series of 13 reported cases treated non-operatively showed that six months after sustaining the injury nearly 50% of patients had symptoms severe enough to warrant subsequent surgical intervention.
Management according to Hawkins classification
In cases of Hawkins type I fractures, previous reports have shown that those who were treated with ORIF had better outcome than those treated non-operatively and had minimal or no symptoms on subsequent follow-up. It has also been reported that the patients with type I fractures treated conservatively had 38% incidence of moderate or severe symptoms, of these 47% requiring subsequent surgery, most commonly requiring subtalar arthrodesis (25%). Missed or untreated fractures for more than two weeks after sustaining injury have been associated with poor outcome with long-term and persistent pain despite of undergoing subsequent surgery with up to 20% potentially requiring a subtalar fusion.
In Hawkins type II fractures, an arthroscopic assessment is recommended and depending on the chondral damage and size of the comminuted fragments, arthroscopic debridement is considered most suitable treatment option. Missed or untreated fractures or type II fractures treated with plaster cast have been reported to result in poor functional outcome requiring subtalar fusion .
Hawkins type III fractures have been shown to have good outcome with non-operative treatment with plaster cast immobilisation.
Management according to Boack’s classification
Boack recommended that type 1a fractures with an extra-articular or undisplaced small avulsion fragment are better to be treated with a below-knee plaster cast and partial weight bearing for a period of six weeks.
All displaced fractures involving the articular surface are recommended to be treated surgically in order to reduce the risk of long-term degenerative changes. Even the cases with a minimally displaced fragments (Boack type 1c) can potentially lead to significant symptoms. These types of fractures are recommended to be treated with subtalar arthroscopy and excision, because the loose fragments may damage the articular surface. There have been no reports of instability of the subtalar or the ankle joints following the excision of these fragments.
In Boack type 2 fractures, an arthroscopic assessment is recommended and depending on the chondral damage and size of the comminuted fragments, arthroscopic debridement or arthroscopic-assisted reduction and internal fixation is preferred.
In Boack type 3a fractures, the single large displaced fragment is best managed by arthroscopic or open reduction and anatomical fixation with headless compression screw. Type 3b fractures require ORIF or excision of the comminuted fragments.
In cases of an associated subtalar dislocation, up to 50% patients may have an additional osteochondral injury. In these cases, an emergency management is recommended to relocate the subtalar joint, arthroscopic assessment to visualise the articular surface and to excise any loose fragments to prevent subsequent problems.
Complications and Outcome
Timely diagnosis and management of these fractures have been emphasised to prevent long-term complications. Suboptimal management is associated with pain and functional problems due to delayed healing, nonunion, degenerative changes and impingement. Patients with an associated subtalar dislocation have been reported to have the worst outcomes.
Non-operative treatment has been reported to result in good outcome in up to 60% cases, however, a good outcome has been reported in all early and aggressively treated cases. Severe degenerative subtalar joint changes have been reported to occur in 10–15% of the patients requiring subsequent subtalar arthrodesis.
Non-union has been reported to occur in 60% cases managed non-operatively, compared to 5% cases following an early surgical intervention. Overall, non-union can result in poor outcomes in 50-70% cases. Further complications include an exostosis of the lateral process during bony healing resulting in impingement against the calcaneus or the fibula.
Fractures of the Posterior Process of the Talus
Anatomy
The posterior process of the talus comprises medial and lateral tubercles, bearing the groove for the flexor hallucis longus tendon. The lateral tubercle, known as Stieda’s process, projects more posteriorly than medially. The lateral tubercle provides attachments to the posterior talocalcaneal and posterior talofibular ligaments.
The medial tubercle is usually smaller but variable in size. It provides attachment to the posterior third of the deltoid ligament superiorly and the medial limb of the bifurcate talocalcaneal ligament inferiorly. The undersurface of the combined tubercles articulates with 25% of the posterior facet of the calcaneum.
Fractures of the Posterolateral Process (Shepherd’s fracture)
Fractures of the posterolateral process can potentially be mistaken as os trigonum, which is the posterior process arising from a secondary ossification failed to fuse with the body of the talus. An os trigonum appears rounded, corticated and is found in 7-10% of normal population.
It can also fracture and cause difficulty in diagnosis but a CT or an MRI scan can aid in differentiating the two conditions. Fractures of the lateral tubercle of the posterior process are known as Shepherd’s fracture and may be similar to ankle sprains in presentation, but may demonstrate posterolateral tenderness with pain both on movement of the subtalar joint and on passive movement of FHL tendon.
Fractures of the Postermedial Process (Cedell’s fracture)
Cedell first described the fractures of the medial part of the posterior process of the talus. These can be misdiagnosed as ankle sprains if not included in the differential diagnosis of posteromedial ankle pain. The fractures of the entire posterior process of the talus are very rare. There are only a few reported cases of the entire process fractures.
Mechanism
The causative injuries are similar to lateral process fractures. Two mechanisms have been postulated, forced hyperplantarflexion and inversion causing direct compression of the posterior talus between the posterior tibial rim and the dorsal rim of the posterior facet of the calcaneum and the second assumption is that the posterior talofibular ligament causes an avulsion fracture of the lateral tubercle during hyperdorsiflexion and inversion motion.
Cedell described the posteromedial tubercle fracture as an avulsion injury resulting from forced pronation and dorsiflexion of the foot. Other proposed mechanisms include direct trauma to the posteromedial facet, impingement of the sustentaculum tali in supination, and forced dorsiflexion in cases of high-energy trauma.
Clinical Presentation
The patients usually present with swelling and pain in the hindfoot area. The posterior talar impingement test is positive with an increasing pain associated with active movements of the toe flexors or passive extension of the big toe.
Imaging
Plain radiographs of the ankle (AP, mortise and lateral views) are routinely obtained, however the radiological features of minimal cortical breach and subtle lucency are not always easily identified. Broden view may aid in the assessment of subtalar joint involvement. It is taken by internally rotating the foot 45° while the beam is centered on the subtalar joint and angulated cephalad at a range between 10° and 40° from vertical.
Ebraheim et al. have suggested that two oblique views at 45° and 70° of external rotation may be helpful if the standard radiographs are inconclusive. Up to 40% of these fractures may be missed on initial presentation on plain radiographs. A high index of suspicion should be kept based on specific injury mechanisms and an urgent CT scan should be performed in order to identify the fracture, to assess the size, displacement, and extent of the fracture fragmentation, or to differentiate the presence of accessory ossicles from acute fractures. These fractures may be associated with subtalar dislocations and may have osteochondral injuries in up to 50% cases involving subtalar dislocations
Classification
Boack’s described his classification for the lateral process as well as for posterior process of the talus as described in detail previously.
Management
The principles of management are the same as per lateral process fractures. Undisplaced fractures can be managed in a plaster cast for 6-8 weeks but surgical treatment is recommended either in the form of open reduction and internal fixation or excision of the fracture fragments, depending on their size, in order to minimise long-term pain.
Surgical approach
ORIF of the posterior process fractures can be performed through a posterolateral or a posteromedial approach, depending on the location of the displaced fragments. Posteromedial approach involves a curved incision halfway between the medial malleolus and the margin of the Achilles tendon. The neurovascular bundle is mobilised for adequate access to the fracture fragments. Fracture fragments can be fixed using lag screws (1.5, 2.0, or 2.7 mm). Posterolateral approach involves a longitudinal incision between the lateral border of the fibula and the Achilles tendon. The fracture fragment is identified and fixed using the same techniques. It is essential to assess the stability of the subtalar joint and address it as needed to prevent long-term problems.
Complications and Outcome
Intra-articular fractures of the entire posterior process have been associated with a poor outcome due to the higher incidence of mal-union and early degenerative changes. In conservatively treated cases, up to one third may develop avascular necrosis. Up to 75% of the patients initially treated conservatively may subsequently require excision of the fragments in case of posteromedial tubercle fractures.
Displaced fractures, depending upon their size, can either be excised or fixed with small screws. In cases of non-union, mal-union or exostosis resulting in impingement, excision of the fragments should be considered to eliminate the symptoms. In cases of significant and symptomatic subtalar joint arthritis, an arthrodesis may be required.
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