2018 - Donna Magid, M.D., M.Ed.
Ankle for Pragmatists
“Hinge or ginglymus” joint—not really; subtle complex motions w/ flex/extension
Motions: descriptions confusing
- Plantar/dorsiflexion = foot on ankle, in sagittal or cephalo-caudal plane
- Inversion/eversion= (NWBg, plantar plane rotating imedially/laterally)
- Supination/pronation = (WBg, resting weight on lateral/medial foot i.e., sole turns in/out) Adduction=supination, abduction=pronation, foot off-ground
“Ring” of bone and ligaments--no interlocking bony stability.Ligamentous injuries without fractures may still require surgery. 'Ring' concept means fx/trauma may disrupt in two sites. eg:
- Bimalleolar fxs, or one malleolus and one ligament , or two ligaments
- Ligamentous disruption: inferred by changed bony relationships
- Widened tib-fib space, asymmetry mortise, medial malleolus injury: suspect forces diverted cephalad, up intrasseous membrane,therefore r/o PROX fibula fx (aka Maisonneuve injury)
AP image - alignment, articular surfaces, soft tissue clues
- Soft tissue over malleoli symmetric in thickness, radiodensity (obesity is radiolucent, swelling/edema more radiodense), 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. Narrowing can be cartilage loss.)
Lateral - tibio-talar smooth parallel 'C', symmetric, r/o joint effusion (‘dumbbell’, density just anterior and/or posterior to tib-talar joint)
- Pre-Achilles clear space or Kagar triangle (fat) should be sharply defined anterior to Achilles margin; induration or increased density posteriorly raises issues with the tendon, more anteriorly, with the joint-- specify.
- Gastroc (Achilles-- I no longer fight this DWG name) tendon integrity from muscle to calc. insertion; non-bulbous, well-defined margins, uniform caliber, no bulbous changes. Calcifications within the tendon (vs. insertion enthesophathies) reflect chronic process.
- Subtalar (talo-calcaneal) joint, anterior process calcaneus. Stieda process or os trigonum at posterior margin posterior subtalar joint-- large ones contribute to impingement/symptoms, as you will learn at MR.
- Most common “Miss” zones: 5th MT bases, Gastroc/Achilles tendon, anterior process/other calc. fxs (on lateral), posterior tibial lip tibia (tiny fractures, '3rd malleolus', over overlooked), Talar dome osteochondral (OCD) injury (tiny rounded subchondral defect talar dome’corners’ ; from angled impact of talar ‘corner’ against tibia during ankle injury. Mortise asymmetry.
Stress images (by HO with 'lead' glove!!): test ligamentous integrity/mortise stability via varus/valgus force during radiography
- Clinical exam often ’worse’ than non-stressed radiograph (ie near-normal XR while examiner can detect instability)
- 2nd most commonly requested Emed image (C spine 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’ JHM: Medical-legal inhibition, poor historians. Variable experience, nonspecialists and house officers.
- Hx of mech injury helpful but rarely accurate (<15% pts. are reliable reporters)
- Fx pattern often suggests/reveals mechanisms
Classification systems complex and confusing, neither reproducible nor prognostic-- DO NOT use.
- Lauge Hansen—describes mechanism/pattern of injury
- Weber AO—too simple but (mis) used; developed for ORIF choices
- "Pushed off" → oblique fracture (eg fibula in eversion)
- “Pulled off" (tension) → transverse fracture (eg fibula in inversion)
- 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 or patient report of area of interest. “Unremarkable Ankle’ radiograph (again, do NOT say 'NORMAL" or "NO EVIDENCE OF") 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 the ‘ankle’ really is).
ADVISE F/U 10-14 days if clinically indicated: 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.
2018 - Donna Magid, M.D., M.Ed.