Print

Ankle

July 2012 - Donna Magid, M.D., M.Ed.

Ankle for Pragmatists

“Hinge or ginglymus” joint—not really; subtle complex motions w/ flex/extension

Motions:

  • Plantar/dorsiflexion = foot on ankle
  • Inversion/eversion= (NWBg, plantar plane rotating in/out)
  • Supination/pronation = (WBg, resting weight on lateral/medial foot i.e., sole turns in/out) Adduction=supination, abduction=pronation, off-ground

Ring of bone and ligaments

Fx/trauma may disrupt in two sites:

  • E.g., bimalleolar; one malleolus and one ligament
  • Ligamentous disruption: inferred by changed bony relationships
  • Ligamentous damage may require surgery
  • Widened tib-fib space mortice, medial malleolus injury: suspect forces diverted cephalad, up intrasseous membrane, r/o PROX fibula fx (1ce called Maisonneuve injury)

AP image - alignment, articular surfaces, soft tissue clues

  • Soft tissue symmetric in thickness, radiodensity, preservation of fascial planes.

Mortise or internal-oblique - shows mortise: 3-4 mm wide, symmetric/parallel margins

  • Mortice asymmetry (even 1 mm widening is significant)    

Lateral - tibio-talar smooth, symmetric, joint effusion (‘dumbbell’)

  • Pre-Achilles or Kagar triangle (fat) should be sharply defined
  • Gastroc tendon integrity from muscle to calc. insertion; non-bulbous
  • Subtalar joint, anterior process calcaneus
  • Most common “Miss” zones: MT bases (5th), Gastroc tendon, anterior process/other calc. fxs (on lateral), Posterior lip tibia (tiny fractures over overlooked), Talar dome osteochondral (OCD) injury (tiny rounded subchondral defect talar dome’corners’ ; from angled impact of ‘corner’ against tibia during ankle injury

Stress images (by HO): test ligamentous integrity via varus/valgus force during radiography

  • Clinical exam often ’worse’ than non-stressed radiograph (ie near-normal XR)

 

FRACTURES

  • 2nd most commonly requested Emed image (CS 1st); 11% community EMed visits= ‘ankle’
  • 90% of Emed ankle visits get radiographed
  • 15% Emed ankles “serious” (need rigid immobilization)


OTTAWA RULES: XR only the more serious/less stable injuries

  • “Point tender over either malleolus (distal 6cm tib,fib)”
  • “Inability to bear weight immediately after trauma,” or
  • “Inability to take 4 steps in EMed”

Initial study 1992 (Canada) claimed “100% sensitive, 22% specific” (proved optimistic).  Decreased number of ordered radiographs by 28%.

2003: not as precise as initially claimed but about “93% sensitive, 6-11% specific.” Decreased ordered radiographs by 16% i.e. still significant impact. Can’t follow strictly; still ‘over-order’ JHH: Medical-legal inhibition, poor historians. Variable experience, nonspecialists and house officers

  • Hx of mech injury helpful but rarely accurate (<15% pts. Reliable reporters?)            
  • Fx pattern reveals mechanisms

Classification systems complex and confusing, neither reproducible nor prognostic

  • Lauge Hansen—describes mechanism/pattern of injury
  • Weber AO—too simple but (mis) used; developed for ORIF choices

Fracturing Forces:

  • "Pushed off" → oblique fracture
  • “Pulled off" (tension) transverse fracture
  • Torque or twist spiral or oblique

NOT SIMPLE!! MANY VARIBLES!! (Foot position relative to ankle, pt. weight, momentum (eg walk vs. run), velocity/magnitude, age, bone quality (e.g. osteoporosis, pre-existing stress risers), surface (eg grass vs. concrete….)

EXAMINE PT: point-tenderness often more convincing than radiograph. “Normal Ankle’ often attached to abnormal midfoot or distal lower leg (i.e. misordered—both pts, and docs can be a little vague on where or what ‘ankle’ really is).

ADVISE F/U 10-14 days: in face of significant soft tx swelling, joint effusion, subtle trabecular change, or other reason to be suspicious

 

References:

  1. Stiell IG, Greenberg GH, McKnight RD etal. A study to develop clinical decision rules for the use of radiography in acute ankle injuries. Ann Emergency Med 1992; 21 (4): 384—90.
  2. Bachmann LM, Kolb E, Koller MT, Steurer J, ter Riet G. Accuracy of Ottawa ankle rules to exclude   fractures of the ankle and mid-foot: a systematic review. BMJ 2003;326:417.

 

July 2012 - Donna Magid, M.D., M.Ed.