BIOMECHANICAL EVALUATION OF FIXED-ANGLE SCREW PLATE CONSTRUCT VS. DUAL PLATE CONSTRUCT
FOR BICONDYLAR TIBIAL PLATEAU FRACTURES
*Higgins, TF; *Klatt, J; **Droge, J; +**Bachus, KN
*University of Utah, Department of Orthopedics, Salt Lake City, UT
+**Orthopaedic Bioengineering Research Laboratory, University of Utah School of Medicine, Salt Lake City, UT
INTRODUCTION:
Open reduction internal fixation has been an accepted standard of
treatment for displaced intra-articular tibial plateau fractures. As
always, osteosynthesis is a balancing act between rigid fixation and
preservation of a biologically friendly local environment by
minimizing periosteal stripping. This has been particularly
troublesome in bicondylar tibial plateau fractures, where stability has
demanded fixation of both columns of the tibial metaphysis. The
evolution of fixed-angle plating devices has given surgeons the ability
to achieve more rigid constructs without enlarging the plate footprint
on the soft tissues and bone and without stripping the opposite cortex.
What remains unclear at this time is whether or not unilateral plating
with a fixed-angled plate and screw system provides equivalent
stability to a dual plating construct.
Figure 1: Tibial osteotomy showing medial, lateral, and main bone
segments. Also shown are guide wires used in inserting screws.
Lateral
Segment
Medial
Segment
HYPOTHESIS:
Fixed angle plating (FAPTP) construct will prove to be more rigid
and provide greater stability than a traditional dual plating (DP)
constructs in a cadaveric bicondylar tibial plateau fracture model.
METHODS:
Eight human matched pair tibial cadaveric specimens were prepared
for study. DEXA studies were used to evaluate bone density. This data
provides a range of densities for the study group to assess the possible
effect of bone quality on fixation. All donor demographics were
recorded. Osteotomies were performed on each specimen to simulate
an unstable bicondylar tibial plateau fracture with metaphyseal
comminution (Figure 1). All specimen pairs were randomly assigned
to have the left specimen be fixed with either DP or FAPTP (Figure 2).
Specimens labeled DP were fixed with a low profile 4.5mm proximal
tibial plate laterally and a five hole one-third tubular plate along the
medial cortex. The specimens labeled FAPTP were fixed with a
4.5mm fixed- angle proximal tibial plate. The contralateral tibia
received the alternate treatment. Infra-red diodes for tracking on the
Optotrak system were placed on the tibial shaft as well as the medial
and lateral plateau fragments. The specimens were potted and
mounted on the Instron. After axial preload, an axial compressive load
of 100 N was applied at a rate of 100 N/second. Fracture fragment
displacement from initial position to preload and from preload to max
load was measured continuously via optical transducers.
The specimens were then subjected to an axial cyclic loading of
1000 N for 104 cycles to approximate loading in the initial healing
period. After cyclic loading, the specimens are again statically loaded.
Plateau fragment displacement was measured from initial position to
preload and from preload to max load (1000 N at 100 N/second).
Lastly, the constructs were axially loaded to failure. The specimens
were ramp loaded from a preload of 100 N at a rate of 100 N/second
and maximum compressive load to failure was recorded.
Load displacement curves and fracture displacement in axial
loading were acquired from the data to determine the stability of the
construct before and after cycling. Data analysis utilized paired t-test
for statistical evaluation. Analysis was based on fragment
displacement over cyclic load and load to ultimate failure, as well as
bone quality. All potential axes of displacement were assessed for both
the medial and lateral plateau fragments after pre-loading, post cyclic
loading, and total subsidence.
Main
Segment
Figure 2: Specimen Setup with FAP and DP constructs.
FAP
Lateral
DP
Lateral
CONCLUSIONS:
In a biomechanical cadaveric model simulating bicondylar tibial
plateau fractures, statistically significant differences could only be
detected in post cyclic loading displacements, with no significant
difference in total subsidence.
Clinically, these results suggest that even in poor quality bone,
fixed-angle screw-plate constructs may provide comparable fixation to
dual plate constructs. This may allow adequate fixation of unstable
bicondylar tibial plateau fractures without the soft tissue stripping
associated with instrumenting the medial cortex.
ACKNOWLEDGEMENTS:
The authors would like to acknowledge funding from the National
Science Foundation, funding and implants from Synthes, and the
Department of Orthopaedics, University of Utah School of Medicine.
RESULTS:
After pre-loading axial displacement was 2.17mm for FAPTP vs.
1.33mm for DP (SD1.40 v. 0.34, 95%CI 0.97 v. 0.24, p=0.12). Postcycling axial displacement was 1.26mm for FAPTP vs. 0.79 mm for
DP (SD 0.58 v. 0.23, 95%CI 0.40 v. 0.16, p=0.05). Total subsidence
was 3.19mm for FAPTP vs. 2.58mm for DP (SD 1.30 v. 0.84, 95%CI
0.90 v. 0.58, p=0.48). Regression analysis of DEXA vs. displacement
and fixation type yielded no significant advantage for either fixation in
lesser quality bone.
50th Annual Meeting of the Orthopaedic Research Society
Poster No: 0442