Orthopedic Plates: Designs & Application

Orthopedic bone plates are developed in many different designs, most of which may be used to serve in different biochemical functions, depending upon how the surgeon applies the plate.

The orthopedic surgeon, not the designer of the plate, determines how a plate will function and how it will be applied.

This is a main element of preoperative planning. Any plate can be used to provide any of the five main functions of a plate. However, the design and application of the plate must consider the biomechanical environment. Therefore, a thin, one-third tubular plate is an excellent choice to protect fixation of a lag screw of the lateral malleolus but is mostly not strong enough to act as a bridging plate for a multi-fragmentary fracture at the same site.

This article will discuss the design and application of the various plates available and help guide the surgeon in selecting the accurate plate during preoperative planning.

Limited-contact dynamic compression plate (LC-DCP)

The limited-contact dynamic compression plate (LC-DCP) was introduced by Perren in 1990 and has become the gold standard for fixation of plate. The plate is available in two sizes, 3.5 and 4.5 mm, which is determined by the thread diameter of the cortex screws used together with the bone plate (an orthopedic implant, available with the orthopedic implant distributors). The screw hole design allows for axial compression by eccentric insertion of bone screw.

The plate may function in five different methods:

• Compression
• Protection
• Buttress
• Tension band
• Bridging

The LC-DCP is available in either titanium or stainless steel.

Its structured undersurface allows limited contact between bone and plate, and there is an even distribution of holes along the plate.

Design

Several changes in design have improved the LC-DCP compared with earlier designs (for example, DCP)

• The area of bone-plate contact (the plate footprint) is greatly reduced in the LC-DCP. There is less impairment of the capillary network of the periosteum, which results in a relative improvement of cortical perfusion.

This reduces bone reabsorption underneath the orthopedic plate. In addition, the structured geometry of the undersurface of the plate results in even distribution of stiffness, making contouring easier, and reducing the likelihood of bends in the plate being concentrated. In bridging method, this distribution of stiffness results in a gentle elastic deformation of the entire plate without stress concentration at one screw hole. The cross section of the plate is of a trapezoidal shape, so the bony ridges, which form along the edges of the plate, tend to be thicker and flatter, rendering them less prone to damage during plate removal.

In the DCP the area at the plate holes is less stiff than the part between them. During bending the plate tends to bend only in the areas of the hole.
The LC-DCP has an even stiffness without the risk of buckling at the holes of screw. The screw holes in the LC-DCP are best described as a part of an inclined and angled cylinder. Like a ball, the screw head slides down the inclined shoulder of the cylinder.

Dynamic compression principle:

The holes of the plate are shaped like a transverse and inclined cylinder. Like a ball, the screw head slides down the inclined cylinder.
The horizontal movement of the head, as it impacts against the angled side of the hole, results in movement of the plate and fragment of fracture already attached to the plate by the first screw. This leads to compression of the fracture.