July 2012 - Donna Magid, M.D., M.Ed.
Ankle for Pragmatists
“Hinge or ginglymus” joint—not really; subtle complex motions w/ flex/extension
- 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)
- 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
- "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
- 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.
- 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.