Orthopedics > Orthopedic Topics > Trauma > Tibia and Fibula > Tibia Fibula Fracture Abstracts > Biomechanical Stability Provided by Oblique Screws in Intramedullary

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Biomechanical Stability Provided by Oblique Screws in Intramedullary

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Location: http://www.hwbf.org/ota/am/ota02/otapo/OTP02001.htm

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.

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Added: Thu Nov 03 2005