tendency for operative Rx in more severely injured ankles
Anatomical & Biomechanical considerations
articulations of 3 bones: distal tibia, distal fibula & talus
major articulation between dome of the talus & tibial plafond - forms a congruent saddle shaped joint
talus has a medial facet (articulates with medial malleolus) & a lateral facet (articulates with lateral malleolus)
80 to 90% of the load is transmitted thro the plafond to the dome of the talus
with varus or valgus stress 20% transmitted thro the medial facet & 10% thro the lateral facet
normally the 17% of the load is transmitted proximally thro the fibula
Ligaments
the distal tib & fib are bound by the anterior & posterior tibio-fibular ligs & the syndesmosis
laterally the fibula is attached to the hindfoot by 3 ligs:
anterior talo-fibular lig
calcaneofibular lig
posterior talo-fibular lig
medially the ankle is stabilized by the deltoid lig which has 2 parts:
superficial part - fans onto the neck of the talus - resists eversion &
deep part - inserts onto the medial part of the talus - resists external rotation of the talus
plantar flexion is a combination of sliding & rolling
ROM with axial loading is 30° of dorsiflexion & 45° of plantar flexion
motion of the talus in dorsi & plantar flexion causes motion of the fibula
new studies show that the primary stabilizer of the ankle is on the MEDIAL side of the joint & that the major instability is EXTERNAL ROTATION of the talus, not lateral shift (which is a two dimensional X Ray illusion)
during peak loading the ankle joint carries 4X’s the body weight
Goals of Treatment
most scientific studies do not show that operative Rx gives better clinical results
2 indications for surgery
static incongruity = step off in the weight bearing part of the articular surface (pilon fracture’s)
dynamic incongruity or instability = abnormal talar tracking
operative Rx results in an anatomical reduction more frequently
incidence of infection with ORIF - 1 to 4%
Classification
2 purposes of a classification
determine the most appropriate treatment
prognosticate
2 widely used classifications
Lauge-Hansen
based on fracture patterns in cadavers
2 part nomenclature
the 1st word = the position of the foot at the time of injury: supination or pronation
the 2nd word = direction of deforming force: rotation (ER or IR) or translation (abd or add)
Concept:
supination puts the lateral structures under tension
pronation puts the medial structures under tension
Supination ER fracture
Injury begins anteriorly & progresses around the ankle - stage 1 to 4
1 = injury to anterior tib-fib lig
2 = lateral malleolus
3 = posterior capsule or posterior malleolus
4 = medial malleolus or deltoid lig
Pronation ER fracture
injury begins medially & ends posteriorly (also 1 to 4)
Supination abduction fracture
initial injury is to the lateral malleolus followed by a medial fracture or lig injury
Pronation abduction fracture
initial injury is 1st medial then lateral
complicated & difficult to apply
was designed as a guide for the Rx of closed unstable fractures
Weber Classification
3 Types
A, B & C
further subdivided into types 1, 2 & 3
popular system because it is easy to apply
type B fractures account for 80-90% of all ankle fractures
Diagnosis
History, mechanism of injury
twisting force
Clinical
open or closed
ST damage
localize tenderness
X-Rays
AP, lateral & mortise view (= true AP of the ankle joint)
1. isolated fractures of the lateral malleolus
85% of these fracture have NO injury to the medial side
1mm lateral shift of the talus decreases the contact area of the tib-talar joint by 42% (Ramsey & Hamilton)
recent studies - displacement of the fibula does not cause talar shift in isolated lateral malleolus fracture
operative Rx DOES NOT give better clinical results than conservative Rx
no dynamic instability without a medial injury - operative Rx not justified
