OTA 2006 Posters
Scientific Poster #87 Basic Science
Locked versus Conventional Plating in a Bridge Plate Model
Robert T. Sullivan, Major, USAF, MC (a-Synthes);
Meredith Warner, Major, USAF, MC (*);
Patrick S. Brannan, Captain, USAF, MC (*);
Tristan Lai, Second Lieutenant, USAF (*);
Mark S. Richardson, Colonel, USAF, MC (*);
Wilford Hall Medical Center, San Antonio, Texas, USA
Purpose: Our purpose is to compare the initial fixation stability
of locking compression plates (LCPs) in several modes of fixation, over
a fracture gap, to that of limited contact dynamic compression (LCDC) plating.
Methods: Third generation composite bone humeri were used in order
to eliminate experimental variability. Narrow, 4.5, 10-hole LCDC plates
were anchored to composite humeri using 4.5-mm cortical screws in the neutral
position, with 8 cortices of fixation per fragment. Narrow 4.5, 10-hole
LCPs were anchored to the composite humeri using 4.0-mm locking screws with
4 cortices of fixation per fragment, varying the number and disposition
of screws between 4 separate constructs. Working length remained constant
for all constructs. LCP and LCDC constructs were tested under axial and
torsional loading within the elastic range. Force and displacement histories
yielded axial and torsional rigidities. Each group consisted of 7 identical
constructs. A one-way ANOVA with 6 groups of 7 constructs each was performed.
Results: All LCP constructs had higher mean values for axial rigidity
(range, 483-687 N/mm) than the LCDC constructs (403 N/mm). Two of 4 locked
fixation constructs had significantly greater axial stiffness than the LCDC
plating (687 N/mm, 607 N/mm vs. 403 N/mm, P <0.05). Locked plates
with bicortical fixation furthest from the osteotomy site had the highest
measured axial rigidity. The LCDC construct had a higher mean torsional
stiffness than all of the LCP constructs. The difference was significant
for only two LCP constructs. The number of screws per fracture fragment
for the LCP constructs did not correlate with torsional rigidity.
Conclusions: Locked plating offers greater axial stability than conventional
plating in a bridge plate construct when plate and working length are controlled.
Bicortical fixation furthest from the fracture site enhanced the axial stability
of the LCP constructs. Locked plating with only 4 cortices of fixation per
fragment did not confer more torsional stability than the LCDC plating.
Torsional stability is dependent upon the number of cortices engaged and
not the number of screws. Where torsional loading predominates, we recommend
bicortical fixation for a locking construct. Unicortical fixation is advised
only when limited by anatomic constraints or adjacent to an intramedullary
implant.
If noted, the author indicates something of value received.
The codes are identified as a-research or institutional support; b-miscellaneous
funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts
disclosed, and *disclosure not available at time of printing.
·
The FDA has not cleared this drug and/or medical device for the use
described in this presentation (i.e., the drug or medical device is being
discussed for an "off label" use). · · FDA
information not available at time of printing.