Alternatives In Fixation For Osteoporotic Bone

Start Page: 54
Davi Cross, DPM, and Lawrence A. DiDomenico, DPM, FACFAS

Emerging Insights On Locking Compression Plates And Polyaxial Locking Plates

The development of the locked internal fixator concept has provided surgeons with technological advances that can apply to the fixation of bone fragments in lower extremity trauma or reconstruction. Locking compression plates and polyaxial locking plates are two such advances. Although they differ from early generation locking systems, they both still promote less soft tissue and blood supply damage while ensuring more rapid and predictable fracture healing. Locking compression plates feature a combination of holes that can be conventional (the compression principle), locking (the internal fixator principle) or a combination of the two.21

   The polyaxial system also allows eccentric loading. This allows the foot and ankle surgeon to take advantage of many plating principles. Surgeons may use this system to facilitate conventional compression of a solid, reducible area of a fracture or osteotomy while reserving the opportunity to lock and bridge an area of significant bone grafting or comminution within the same plate.

   This “lag and lock” principle involves the combination of compressing the plate to bone while the locking screws are locked to the plate. Foot and ankle surgeons can use this principle in cases in which good bone quality and bicortical screw purchase coexist with diseased or osteoporotic bone. The locking compression plates can maintain both angular stability and interfragmentary compression within one plate.

   Polyaxial locking plates allow surgeons to apply the fixed angle concept in more than one axial relationship.22 Previous locking constructs limited the option for screw plate locking to one 90-degree option. The polyaxial concept opens the door for screw placements in upward of a 15-degree divergence in any one direction or plane. The advancement of the polyaxial concept makes it possible to introduce multiple locking screws with an independent axis of orientation. Studies have shown that surgeons can accomplish the polyaxial concept without compromising torque to failure or pullout strengths of the implant.23

What You Should Know About Screws And Other Fixation

Screw type can also affect fixation outcomes in osteoporotic bone. Cannulated screws offer the surgeon the advantage of precise anatomic placement but may possess decreased holding strength in comparison to non-cannulated screws.

   Ramaswamy and colleagues examined the holding power of four types of small fragment, cannulated screws in normal versus osteoporotic bone.24 Their study determined that the Barouk screw, which possesses more threads and a greater surface area, demonstrated a greater pullout and push out strength than the other types tested. Interestingly, the authors did find that the average pullout strength decreased by 4 to 30 percent in normal and osteoporotic bone after surgeons implanted the screws, removed them and then reinserted them.

   Researchers have discussed other methods of fixation in the literature for osteoporotic bone. For example, authors have described intramedullary nailing as a viable alternative for ankle fractures in bone with decreased density. This method offers the additional benefit of a minimal incision with decreased risk of soft tissue infection.2,25 Other authors have described the utilization of a nylon cavity plug in osteoporotic bone for instances in which the tapped thread in cortical bone has become stripped.25

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