The History
of SK™ ESF Technology
The SK™ ESF System is designed to simplify the application and management
of external skeletal fixators. The SK™ ESF clamp supports use of
positive thread pins directly through the primary clamp bolt, allows the
surgeon to
easily add a fixation clamp after the fact as needed, and provides the
freedom to utilize a great variety of fixation pin diameters and styles.
In addition,
the SK™ ESF System supports sleeved pre-drilling and targeting of
fixation pins. Traditional KE frames and new KE-like frames typically depend
on complex
frame geometries, connecting rod augmentation, and/or multiple full-pins
to achieve adequate frame strength. In contrast, the SK™ ESF System
features dramatically improved connecting rods that make use of simpler
frames a clinical reality. The SK™ ESF System dramatically changed
standard concepts of veterinary ESF by placing less emphasis on full-pins
and
frame complexity while promoting biological technique and safe pin corridor
philosophy to reduce patient
morbidity. By-products of simple frame constructs include: economy of hardware,
economy of operative time, and economy of required instrumentation. IMEX™ offers
the SK™ ESF System in three sizes: mini,
small, and large.
Review of SK™ ESF Clamp Design
The user-friendly design of the SK™ single clamp allows for pre-drilling
as well as placement of positive thread pins through the pin-gripping clamp
bolt. This eliminates the difficulty historically associated with the use
of positive profile threaded pins. The gripping mechanism of the SK™ ESF
clamp allows a variety of different pin sizes and types to be utilized at
the surgeon’s discretion. The split nature of the SK™ clamp allows
quick and easy addition or removal of a clamp without requiring frame
disassembly. Simple wrenches are the only required
instrumentation; however, optional drill sleeves are available to simplify
pre-drilling.
The aluminum clamp body is comprised of two different parts
(B-1 and B-2). Each has a pair of holes, the lower one to receive the primary
pin-gripping bolt (pb) and the upper one to receive the secondary bolt
(sb). None of these holes have threads except for the secondary bolt hole
in B-1 body part.
After each use, a clamp may be disassembled for proper
cleaning. The B-1 and B-2 body parts must not be interchanged when the clamp
is reassembled
for another use, or it will not work properly. Proper assembly of the clamp
is shown in the photo at right.
The large rod-gripping channel (R) is in the
center of the clamp. The primary pin-gripping bolt (pb) has a washer with
a slot or meniscus (arrow)
which enables a wide range of pin diameters to be securely gripped by the
clamp. The clamp is tightened by the secondary bolt and by a nut (n) on
the primary pin-gripping bolt.
The secondary bolt should be viewed as a
second pair of hands to be utilized to position and hold clamps in place
while aiming drill bits, drilling, and
placing pins. When one becomes comfortable utilizing the secondary bolt as
an assistant it becomes very easy to reduce fractures and apply frames. The
secondary bolt converts an empty clamp into both a drill guide and a targeting
device. While the mechanical properties of the SK™ ESF System allow
minimal use of full-pins, they can be easily targeted without additional
expensive instrumentation.
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Review of SK™ ESF Mechanics
The most powerful way to simplify the ESF method lies in mechanical frame
improvements that are not dependent on full-pins or complex frame geometries.
In this respect, the SK™ ESF System is designed to be dramatically
different from the KE and new KE-like systems that utilize traditional 1/8” and
3/16” connecting rods.
Mechanical testing of KE frames reveals that
the connecting rod is the “weak
link” of simple fixator frames. In retrospect, the choice of KE rods
historically utilized was, and still is, poorly matched to veterinary pin
diameters and patient demands, dictating that veterinary surgeons
utilize complex ESF frames. By eliminating the weak link of simple frames,
the SK™ ESF
System provides a simple but powerful
alternative to complex frame geometry.
Simple frames, the ability of clamps
to effectively grip a wide range of different pin diameters, and the need
for minimal instrumentation make the
SK™ ESF System the most economical ESF choice. Reduced use of
full-pins minimizes pin tracts and related morbidity while simplifying staged
disassembly and postoperative care. Most importantly, use of half-pins instead
of full-pins encourages and facilitates optimal pin centering and use of
safe pin corridors.
Isolated connecting rod testing does not tell the entire
story. Actual testing of ESF frame models confirms that frame simplification
can be accomplished
by incorporating strong connecting rods.
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Review of SK™ ESF Mechanics
Typical ESF frames were constructed of large SK™ components with medium
pins and medium KE components with medium pins. By comparing frames with
equivalent geometries and identical pins, the actual impact of the connecting
rod on mechanical performance can be seen (Bronson, D.G., Ross, J.D., Welch,
R.D., Proceedings
of Veterinary Orthopaedic Society Annual Meeting, 1999). Recently published
mechanical testing of currently
available veterinary ESF devices confirms the ability of larger diameter
connecting rods to allow clinical use of
simpler frame geometries (White, D.T., Bronson, D.G., Welch, R.D.: A Mechanical
Comparison of Veterinary External Skeletal Fixation Systems. Vet Surg 32:507-514,
2003).
The goal of the SK™ ESF System is not to generate ever-increasing
frame stiffness, but to achieve clinically appropriate strength while using
simple, patient friendly frames.
Axial
Compression
The large SK™ Type l-a frame exceeds the strength of the KE Type l-a,
KE Type l-b and the modified Type II KE (one full-pin per fragment and the
balance
half-pins). The large SK™ Type I-b
provides 60% of the axial strength and stiffness of the most complex KE frame
(Type lll).
Cranio-Caudal
Bending
The large SK™ Type l-a frame exceeds all KE frames except the Type
lll.
Medio-Lateral
Bending
Comparable Type l-a and l-b frames have an approximate fourfold increase
in strength when constructed utilizing the large SK™ rods.
