Fracture Motion in Distal Tibial Rodding: Effect of
Obliquity, Load, and Locking Screw Pattern
Chaiyos Chaichankul MD*, Chaisiri Chaichankul MD**
Affiliation :
* Department of Orthopedics, Veterans General Hospital, Bangkok, Thailand
** Department of Orthopaedics, Phramongkutklao Hospital and College of Medicine, Bangkok, Thailand
Objective : To conduct a biomechanical study on composite synthetic tibia bone models under physiologic torsional loading
conditions to evaluate the relationship between fracture obliquity and locking screws configuration of distal metaphyseal
tibial fracture model fixed by intramedullary (IM) nail fixation.
Material and Method: The biomechanics of six different locking screws configurations in an IM nail used to fix various
distal metaphyseal tibial fracture obliquities were evaluated. The Sawbones were osteotomized following reaming of
the medullary canal 2 mm over the respective nail diameter. Specimens were tested in internal and external rotation at
0.25 degrees/second to 7 Nm followed by a hold at 7 Nm for two seconds. The testing was conducted under two compressive
loading conditions, 20 N and 500 N, to determine if a constant compressive load affects interfragmentary motion during
torsion. The influence of screw configurations on construct stability was investigated at fracture obliquities ranging from
0° to 60° including a spiral obliquity (spiral configuration and obliquity of 45° by definition).
Results : During both internal and external rotation, significant differences were observed in interfragmentary motion
between the two compressive loading levels (20 N and 500 N). For internal rotation testing, there are significant differences
in interfragmentary displacement for fracture obliquities less than or equal to 40° when the degree of interlocking is
diminished. For obliquities between 0° and 30°, which could be classified as a transverse and short oblique fracture pattern,
significant rotatory changes become present as the degree of interlocking is decreased. Similar results are found in external
rotation, however, stability appears to be compromised with obliquities of 50° or less.
Conclusion : Our study examined interfragmentary motion during pure compressive loading to determine the optimal
interlocking pattern for distal metaphyseal fractures of various obliquities. The appropriate fixation configuration should
be selected to apply adequate fracture stabilization for all physiologic loading modalities. Although increasing fracture
obliquities provide increased stability during torsional loading, stability is adversely affected for increasing fracture obliquity
at greater than 30° and certainly by 40° of fracture obliquity during pure compression. The data confirmed that not just the
interlocking pattern but also the fracture configuration and compressive load level contribute to overall construct stability
when physiologic torsional loads were applied. Interfragmentary displacement was significantly increased, in compression
loading mode, when a progressive fracture obliquity degree was tested.
Keywords : Distal metaphyseal tibial fracture, Intramedullary nail, Biomechanic, Proximal interlocking screw, Distal
interlocking screw, Fracture obliquity, Screw configuration
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