Supplementary Medial Locking Plate Fixation Of Ludloff Osteotomy versus Sole Lag Screw Fixation: A Biomechanical evaluation

Background: The Ludloff oblique osteotomy is inherently
unstable, which might lead to delayed union and loss of correction.
Supplementary fixation to two lag screw fixation has been proposed. The
hypothesis is that the osteotomy fixation constructs supplemented by a
mini locking plate provide greater resistance to osteotomy gaping and
loss of angular correction in response to cyclic loading.
Methods: Twenty fourth generation composite 1st metatarsals were used and
underwent a Ludloff osteotomy. They were divided in two fixation groups:
two lag screws (Group A), and with a supplementary mini locking plate
(Group B). Specimens were subjected to either monotonic loading up to
failure or to fatigue (cyclic) tests and tracked using an optical system
for 3D Digital Image Correlation.
Findings: The osteotomy gap increased in size under maximum loading and
was significantly greater in Group A throughout the test. This increase
was observed very early in the loading process (within the first 1000
cycles). The most important finding though, was that with the specimens
completely unloaded the residual gap increase was significantly greater
in Group A after only 5000 cycles of loading up to the completion of the
test. The lateral angle change under maximum loading was also
significantly greater in Group A throughout the test, with that increase
observed early in the loading process (5000 cycles). With the specimens
completely unloaded the residual lateral angle change was also
significantly greater in Group A at the completion of the test.
Interpretation: Supplementary fixation with a mini locking plate of the
Ludloff osteotomy provided greater resistance to osteotomy gaping and
loss of angular correction compared to sole lag screws, in response to
cyclic loading.