What articulations comprise the ankle joint complex?
Talocrural joints 1.Distal tibia – talus 2.Medial malleolus – talus 3.Lateral malleolus – talus 4.Distal tibia – distal fibula (distal tibiofibular joint) Collectively allow dorsiflexion and plantarflexion Subtalar joints 5.Talus – Calcaneus Contributes to inversion and eversion Hence the talus & calcaneus are key to ankle function 1 2 3 4 5
AP Radiograph Adequacy –Fibula & tibia above talus –Open medial clear space > 10 mm
Lateral Radiograph Adequacy –Malleoli superimposed –Joint space cleary visible w/o overlap Look for signs of ankle effusion –Lucency anterior or posterior to joint capsule
Mortise View Evaluates articular surface Technique –Leg is internally rotated 15 – 20 o –X-ray beam perpendicular to intermalleolar line Adequacy –No overlap of talar dome & joint space –Med. & lat. clear spaces open Articular surfaces should be parallel throughout i.e. uniform joint width Should see mild (>1 mm) overlap of tibia & fibula Medial clear space should not exceed 4 mm Lateral clear space should not exceed 5.5 mm medial clear space lateral clear space (< 5.5 mm) >1 mm
Talus anatomy What is the risk with talar neck fractures? Why? Avascular necrosis –Most of the vascular supply to body via neck Neck Talar dome or trochlea Midfoot (Chopart joint) Subtalar joint Body Head
Talar fractures Minor talar fractures –Chip and avulsion fractures of neck,head, and body. –Usually same mechanism as ankle sprains Talar neck fractures –50% of major talar injuries. –extreme dorsiflexion force (aviator’s astralagus) –Frequent associated fractures –Hawkins classification Talar body fractures –23% of all talar fractures (including minor fractures) –Major talar body fractures are uncommon usually axial loading (e.g. falls) Talar head fractures –Uncommon (5-10%) –compressive force transmitted up through the talonavicular joint applied on a plantarflexed foot
Hawkins Classification of Talar Neck Fractures Type 1: = nondisplaced; Type 2: subtalar subluxation Type 3: dislocation of the talar body (50% open #’s) Type 4: dislocation of the talar body & distraction of the talonavicular joint. –Fracture type influences management & prognosis
Calcaneal anatomy Posterior tuberosity Anterior process apex of posterior facet Sustenaculum tali Lateral malleolus
Axial (Harris) View Sustenaculum tali Lateral malleolus Posterior tuberosity
Bohlers Angle apex of posterior facet Posterior tuberosity apex of anterior process
Calcaneus Fractures Classification –Compression #’s –Posterior tuberosity #’s –Anterior process #’s –Sustenaculum tali #’s High energy mechanism associated injuries –20% will have vertebral fractures
Key Concepts Plain films tend to underestimate hindfoot fractures –often require CT or MRI for better evaluation Calcaneal fractures are –frequently bilateral –associated with other injuries Abnormal Bohlers angle may be only clue Talus fractures are at risk for AVN
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