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R. Palmer1
1Colorado State University, Clinical Science, Fort Collins, USA ESF Nomenclature
The ESF System is comprised of many different types
of devices including linear, ring and acrylic ESF devices. Among the most popular of the current generation of linear devices is the IMEX SKÔdevice and it will be
the device used in our discussions and laboratories. Regardless of specific manufacturer, linear devices have 3 basic elements (Fig 1):
· 1.
· 2.
The frame classification described above fosters accurate communication between colleagues and also provides a basic sense of frame stiffness under axial loading (Type III > Type II > Type I).
Type 1b frames are sometimes applied for the purpose
of enhancing this multi-planar stiffness. Uniplanar frames are most able to resist bending forces that are applied
in the plane of the frame (versus those in the plane perpendicular to the frame). As an example, a frame occupying the medio-lateral plane is less able to resist bending forces in the cranio-caudal plane. Application of multi-planar frames, therefore, imparts better multi-planar stiffness. In theory, this is best accomplished by placing the frames 90°to one another. Clinical practicality, however, dictates that frames be applied as regional
soft tissue anatomy and bony cross-sectional structure warrant. As an example, Type Ib frames applied to the radius typically consist of a frame in the cranio-medial plane and a second frame in the cranio-lateral plane (Fig 3).
Type II frames are not as frequently employed as they once were. When the frames are comprised entirely
of full-pins, they are called “maximal” Type II frames. A “minimal” Type II frame is comprised of one full-pin in the proximal main fracture segment and one full-pin in the distal segment, and the remaining positions are filled in with half-pins.
ExFix Pins
Smooth (non-threaded) Steinmann pins were originally used with ESF, however, premature pin loosening was
a major problem and their use has been replaced by
use of various threaded pin designs. Positive- versus negative-thread profile, cortical versus cancellous thread form, length of the threaded portion, and pin size must all be considered for optimal pin selection for a given bony insertion site.
Thread profile.Negative profile threadsare cut into the pin at the expense of the core diameter. When threads are cut into the pin over its entire length, the pin loses its stiffness and is subject to bending or breakage. When threads are conventionally cut only into the end of the pin (end-threaded pin), the abrupt change in pin diameter is a “stress-concentrator”and these pins are predisposed to breakage at the junction of the threaded and non-threaded portions. Historically, SCATÔpins were designed such that threads engaged only the far-cortex of bone and the breakage-prone thread-shaft junction was located within the intramedullary canal, theoretically, protecting it from cyclic bending forces. In reality, these SCAT pins are seldom used with modern devices such as the IMEX SKÔdevice. The weaknesses of negative profile pins were initially overcome by introduction of fixation pins with a positive thread profile. Positive profile threads are raised above the
The connecting rod(s), fixation pins and clamps define an ESF frame(Figs 1 & 2). Frame configuration is described by the number of distinct sides of the limb from which it protrudes [“unilateral” or “bilateral”] as well as the number of planes it occupies [“uniplanar” or “biplanar”].
· Unilateral-uniplanar (Type 1a) framesprotrude from just 1 side of the limb and are restricted to one plane. Type Ia frames (Fig 2 – left) are formed by connecting 1 or more half-pins of each main fracture segment.
· Bilateral-uniplanar (Type II) framesprotrude from 2 distinct sides of the limb, but are restricted to just one plane (typically the medio-lateral plane). Type II frames (Fig 2, right) are formed by connecting 1 or more full-pins of each main fracture segment.
· Bilateral-biplanar (Type III) framesprotrude from 2 distinct sides of the limb and occupy 2 planes. Type III frames are formed when both a Type 1a and Type II frame are applied to a bone. These are seldom used with modern ESF devices.
· Unilateral-biplanar (Type Ib) framesoccupy 2 planes, but because these frames do not protrude from
2 distinctsides of the limb (180°to each other) they are thought of as “unilateral”. If the frame occupies more than 1 plane, but does not connect a full-pin
in the proximal segment to a full-pin in the distal segment, it is a Type 1b. Standard type Ib frames (Fig 3) are formed when two Type Ia frames are applied to a bone.
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  Fasteners (percutaneous fixation pins) Connecting rods
Linkage devices (clamps linking the fixation pins
· 3.
to the connecting rods)
Fixation pins are termed either half-or full-pins(Fig 2)
based upon how they are inserted.
· Half-pinspenetrate the near-skin surface and both the near- and far-cortex of bone.
· Full-pinspenetrate the near-skin surface, both cortical surfaces of the bone, and exit the far-skin surface of the limb.

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