Orthopedic Traumatology by Manish K. Sethi William T. Obremskey & A. Alex Jahangir

Author:Manish K. Sethi, William T. Obremskey & A. Alex Jahangir
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Fixation

For optimal treatment of vertical femoral neck fractures, fixation must be able to resist the high shear forces across the fracture with hip motion, weight-bearing, and muscle tone. Several fracture fixation constructs have been recommended for vertical femoral neck fractures; although, none of these constructs have been found to optimally resist the shearing forces across the hip with this fracture pattern. Shortening with resultant malunion and loss of fixation and nonunion have been common problems. Three parallel, cannulated lag screws placed along the axis of the femoral neck have been frequently described [19]. These screws , however, while optimally applied perpendicular to most femoral neck fractures (e.g., Pauwels’ type I), are applied obliquely in relation to more vertically oriented factures (e.g., Pauwels’ II and III); thus instability vs. shearing is possible. Also, the mechanical advantage of placing a screw along the shaft-neck’s inferior cortex or “calcar” as in repairing a typical osteoporotic neck fracture is lost, as this part of the fracture is attached to the head fragment in the vertical fracture pattern (Fig. 17.1a–c) [12]. Clinical failure rates using parallel screws appear greater than the SHS in a number of studies and have been shown to have the worst performance compared to other methods in mechanical testing using a “younger” fracture model [14, 15]. Other authors have recommended a nonparallel screw configuration, where two of the three screws are placed in typical orientation, but the third screw is modified to be placed more horizontally into the head or neck, more perpendicular to the vertical fracture line. This may allow a true lag effect compressing the major fragments across the vertical fracture to gain stability and possibly control shearing better than an all parallel screw construct. While never proven in a comparative clinical series, applying screws in the latter, nonparallel configuration has performed significantly better in several mechanical testing studies using a vertical neck fracture model [14, 15].

The sliding hip screw (SHS) has a reasonably successful record for typical hip fractures. It is a fixed-angled device so that it may provide increased resistance to varus collapse compared to parallel screws while also allowing compression along the axis of the femoral neck. For most femoral neck fractures, this is approximately parallel to the femoral neck axis. Unfortunately, in the vertical pattern, the SHS can also induce shearing forces with axial compression, but this may be better tolerated than with cannulated screws as the device includes a fixed angle design. As such, the SHS used alone may facilitate shortening, and it also lacks rotational control. This implant showed improved mechanical testing strength similar to the nonparallel screw construct previously described and better than three parallel screws in a vertical fracture model. Some clinicians have added a long parallel screw superior to the SHS lag screw for anti-rotation and intramedullary buttress effect (Fig. 17.2b), which seems to have improved failure rates but have still failed with varus collapse in 10% of cases.

Fig. 17.2(a) The reduced femoral neck fracture is provisionally held with a pointed clamp, provisional K-wires, and a medial buttress plate.

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