The Journal of Bone and Joint Surgery, Vol 73, Issue 3 347-351, Copyright © 1991 by Journal of Bone and Joint Surgery, Inc
The joint-contact area of the ankle. The contribution of the posterior malleolus
VW Macko, LS Matthews, P Zwirkoski and SA Goldstein
Biomechanics, Trauma, and Sports Medicine Laboratory, University of Michigan, Ann Arbor 48109.
Eight ankles from fresh cadavera were tested under simulated clinical
conditions to determine the effect of increasing the size of the posterior
malleolar fracture on the contact area of the ankle joint and on the
distribution of joint pressure. The surface area of contact decreased with
increased size of the posterior malleolar fragment. However, the documented
changes were smaller than expected on the basis of the findings of Ramsey
and Hamilton; they reported a 42 per cent reduction in contact area with
only a one-millimeter lateral shift of the talus, which clinically would be
associated with a similar one-millimeter shift of the distal tibial
fragment. In addition, clinical experience has shown a high rate of
post-traumatic degenerative arthritis associated with an inadequately
reduced one-half-size posterior fragment. There were considerable changes
in the load-distribution patterns, with increased confluence and
concentration of loads as the size of the fragment was increased. In
plantar flexion, many specimens had three separate areas of contact between
the tibia and the talus. With increased size of the posterior fragment, the
three areas of contact always joined to become one. Similarly, for all
positions of the ankle, increased size of the posterior fragment caused
decreases in the contact area. The maximum loss of contact area was 35 per
cent for specimens with one-half-size fractures that were tested in the
neutral position.
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