Description: OTA 2002 Posters OTA 2002 Posters Poster #1 Basic Science *Biomechanical Stability Provided by Oblique Screws in Intramedullary
Nailed Proximal Tibial Fractures Cari M. Whyne, PhD ( a-Zimmer, Inc. USA) ; G.
Yves LaFlamme, MD, FRCS(C); Daniela Heimlich, BS; Hans J. Kreder, MD, FRCS(C);
David J. Stephen, MD, FRCS(C); Sunnybrook & Women's College Health Science
Centre, Toronto, Ontario, Canada Purpose: Intramedullary nailing has become an increasingly attractive
treatment method for tibial fractures because of the ability to stabilize
the fracture while minimizing disruption of soft tissue and the periosteal
blood supply. However, proximal tibia fractures treated with traditional
intramedullary nailing have a high incidence of malunion. The purpose of
this study was to evaluate the mechanical stability of oblique screws in
supplementing intramedullary nail fixation of high proximal fractures. The
specific objectives were to compare the stability of the bone-nail construct
with two additional proximal oblique screws against both the traditional
nail construct (two transverse screws only) and tibial plating in the treatment
of short proximal tibial fractures. Methods: Ten paired fresh-frozen human cadaveric tibiae were tested.
One tibia of each pair was randomized to be instrumented with an intramedullary
nail (M/DN Zimmer), while the other was stabilized with a plate (Synthes
AO/ASIF 13-hole stainless steel). Specimens were tested in varus/valgus
and flexion/extension up to a maximum bending moment of 12 Nm at a displacement
rate of 0.5 mm/sec. Rotation of the tibia (torsion) was carried out up to
a torque of 7 Nm at an angular rate of 0.5°/sec. Specimens were tested
before (intact) and after a 2-cm gap osteotomy was performed 8 cm below
the tibial plateau. Testing of the nailed tibiae after osteotomy was initially
performed with four proximal screws (two transverse and two oblique, 4.5
mm in diameter), followed by testing with only two transverse screws in
the proximal fragment. Bone density (BD) was physically determined by removing
a core of trabecular bone from the distal end of each tibia subsequent to
testing. Displacement data in the three loading configurations were statistically
analyzed by using a repeated-measures analysis-of-variance design and linear
regression (SPSS/PC) to evaluate and compare the different constructs. Results: The maximum displacements in varus/valgus and flexion/extension
under bending moments of 12 Nm and maximum rotations under torsional loading
of 7 Nm were measured for the five constructs. Maximum Displacements of Tibia Under Loading (mean ± SD) Repair Construct Varus/Valgus (mm) Flexion/Extension (mm) Torsion (deg) Intact (with nail) 2.40 ± 1.9 2.47 ± 2.0 2.18 ± 0.6 Intact (with plate) 2.43 ± 1.3 2.71 ± 1.4 2.84 ± 1.8 Nail with 4 screws 7.25 ± 4.4 8.15 ± 6.1 13.80 ± 5.7 Nail with 2 screws 14.10 ± 11.2 15.35 ± 12.9 16.78 ± 5.3 Plate 6.76 ± 3.9 8.74 ± 4.0 12.11 ± 2.8 Intact versus Osteotomy: There was no difference between the nailed
intact tibia and the plated intact tibia in varus/valgus ( P = 0.936),
flexion/extension ( P = 0.486), and torsion ( P = 0.144). There
was, however, a significant reduction in stability between the intact tibiae
and all post-osteotomy tibiae ( P <0.01). Effect of Proximal Screws: When the results of the nailed constructs
with two and four screws were compared, the addition of the proximally placed
oblique screws increased the stability of the construct in varus/valgus
by 50% (6.8 mm, P <0.05) in flexion/extension by 47% (7.2 mm, P <0.05)
and in torsion by 18% (3.0°, P <0.05). Nail versus Plate Stability: In varus/valgus, flexion/extension,
and torsion there was no significant difference between the intramedullary
nail construct with four proximal screws and the plated construct (varus/valgus, P = 0.783; flexion/extension, P = 0.740; torsion, P = 0.239). The nail with two transverse screws exhibited a trend towards
lower stability than the plate by 52% in varus/valgus (7.3 mm, P = 0.084) and 43% in flexion/extension (6.6 mm, P = 0.133). In torsion,
the plate was more stable than the nail with two transverse screws by 30%
(5°, P = 0.002). BD and Stability: Trabecular bone density had a significant effect
in reducing stability ( P <0.05). Moderate correlations were found
between BD and stability in varus/valgus, flexion/extension, and torsion
for the nailed construct with four screws (R 2 = 0.47 to 0.52),
the nailed construct with two screws (R 2 = 0.20 to 0.40), and
the plated tibiae (R 2 = 0.15 to 0.62). Discussion/Conclusion: The results of this study of the fixation
of fractured proximal tibiae demonstrated a significant increase in stability
when two additional oblique screws were added to the two proximal parallel
screws of the bone-intramedullary nail construct in the medial/lateral and
anterior/posterior planes, and in torsion. In addition, intramedullary nailing
with the four-screw proximal configuration was found to provide comparable
stability to the plated constructs in varus/valgus and in flexion/extension,
with only slightly less stability in torsion. The stability of both the
plated and nailed constructs was reduced in tibiae with lower trabecular
densities. Clinically, the M/DN intramedullary nail with two added proximal
oblique screws may provide a stable, minimally invasive technique for repairing
high proximal tibia fractures. Acknowledgements: This project was supported by Zimmer Inc.
Previous