What pin size does each SK™ ESF Clamp support?

Are through-and-through (full) pins no longer utilized?

I never utilize large ESF pins - only small and medium. Why should I consider the large SK™ ESF System?

Tell me more about the economics of simple SK™ frames.

Why are carbon fiber rods and titanium rods choices with the small SK™ ESF System?

Why are carbon fiber and aluminum rods available for large SK™ ESF System?

How are various SK™ rods cut to length?

Which rod should be used to construct contoured rod frames?

Which size SK™ ESF components should be used on a given patient?

Is ever increasing stability necessary?

Tell me more about staged disassembly and rod downsizing?

The small SK™ clamp is designed to utilize 2.0mm to 4.0mm pin shanks in positive or negative thread pin designs. This means that 2.0mm shank, small, small-plus, and medium INTERFACE™ half-pins and CENTERFACE™ full-pins in standard thread versions can be utilized directly through the clamp. Medium, positive thread pins in cancellous versions (3/16” thread diameter) will not pass directly through the small SK™ clamp, but the shank can be effectively gripped. Cancellous pins are usually placed as one of the original pins in the frame and the clamp applied to the pin; therefore, use of medium cancellous pins is simple. The small SK™ clamp can grip pins with 4mm shanks; however, as a practical matter, pins that large belong on a larger clamp and rod.

The large SK™ clamp is designed to handle 3.0mm shank, medium, medium-plus, and large ESF pins, both positive and negative thread pin designs. These sizes of INTERFACE™ and CENTERFACE™ fixation pins can be applied directly through the clamp bolt, with the exception of the large cancellous version of positive thread pins - which are usually placed prior to application of clamp and rod. The maximum pin shank that can be held by and passed directly through the large SK™ clamp bolt is 3/16” (4.8mm). Human pins in the range of 3.0mm to 4.5mm can also be utilized.
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Are through-and-through (full) pins no longer utilized?
While dependency on full-pins is greatly reduced, they can occasionally be assets in challenging clinical cases, especially when combined with a strategy for staged disassembly. A review of mechanical testing confirms that simplified full-pin frames (only one full-pin per major fragment) are very powerful with the SK™ ESF System. These frames are readily applied to the tibia. In addition, the distal humeral condyle remains a location in which full-pins are frequently used. Due to the anatomy of the radius, full-pins are rarely recommended regardless of the ESF device utilized. Type 1-b frames are a very powerful alternative to multiple full-pin frames, providing potential for increased pin number in short fragments while utilizing safe pin corridors. Sales of full-pins to users of the SK™ ESF System have decreased significantly, while sales of half-pins have increased. This altered use ratio is supported by mechanical testing and practical results. With any ESF device, mechanical demands for stability must be weighed, and the fixation must be customized to the patient based on a fracture patient assessment, so across-the-board frame recommendations are not a reality. Patients with injuries to multiple limbs or other complicating factors will require increased (initial) frame rigidity.


I never utilize large ESF pins - only small and medium. Why should I consider the large SK™ ESF System?
Frame simplification results in reduced surgery time and hardware cost. The medium 1/8” (3.2mm) pin has certainly been the workhorse over a variety of different patient sizes and readily functions with small and large SK™ ESF clamps. While the medium KE device is capable of supporting fracture healing in large and giant breeds, the resulting frames are typically very complex and hardware-intensive. While any device can be pushed to support larger patients, it is easier, quicker, and less expensive to construct a simpler frame of stronger components. This is especially true with fractures of the humerus and femur where Type I-b, Type II, and Type III frames are not possible. Staged disassembly or rod downsizing can address potential concerns about excess frame stability.


Tell me more about the economics of simple SK™ frames.
Full-pins cost more than half-pins and require a clamp on each end. For example, a 6 pin, Type II ESF frame will require 12 clamps and two rods, while an 8 pin, Type I-b frame will require only 8 clamps and two rods. An even larger rod device might function in the same case as a 6 pin, Type I-a frame requiring only 6 clamps and a single rod. The 8 pin, Type 1-b frame will be easy to destabilize to a 4 pin, Type I-a if desired, and the large SK™ Type I-a frame can be easily downsized to a small SK™ rod and clamps if desired. The lack of need for aiming devices, torque wrenches, and rod augmentation further reduces cost of ownership and use of the SK™ ESF System.
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Why are carbon fiber rods and titanium rods choices with the small SK™ ESF System?
The 6.3mm carbon fiber rod is about the strength of the medium KE rod, and the 6.3mm titanium rod is just less than twice the strength of the medium KE rod. Since either rod is much stronger than the small KE rod, the lightweight, radiolucent carbon rod is virtually always used when pin choices are 2.0mm shank, small, or small-plus diameters. When medium pins are selected, less challenging, lighter weight patients may utilize carbon rods. On lower limbs, Type I-b or Type II minimal frames will extend the upper weight range for carbon rods. For larger patients with medium pins, the added strength of titanium rods is advantageous, especially if attempting to simplify frames or in most fractures involving the humerus or femur. At some point, more complex frames need to be built or large SK™ ESF rods should be utilized. Both carbon and titanium rods are in the small SK™ starter kit, but customers usually re-order their ultimate preference. Differences in strength can be utilized as part of a plan for staged disassembly or rod downsizing.


Why are carbon fiber and aluminum rods available for the large SK™ ESF System?
For the most part, aluminum rods are merely a back-up material for large SK™ rods in the unlikely event that carbon material is temporarily unavailable. Due to the 9.5mm diameter, both are much stronger than corresponding medium and even large KE rods and can serve to simplify the ESF method quite well. Down-staging from 9.5mm carbon to 9.5mm aluminum in the large SK™ is not typical and less likely to be beneficial as compared to downsizing to a small SK™ rod.


How are various SK™ rods cut to length?
Carbon fiber rods are not to be cut with bolt cutters or pin cutters; however, they can readily be sawed with a fine-toothed hacksaw blade or an abrasive disc on a Dremel tool. Carbon fiber dust is potentially dangerous, so it is recommended that a damp paper towel be laid over the cutting area to capture any dust. Small SK™ titanium rods can be cut with a large bolt cutter, but tend to develop a significant burr that must be smoothed with a file or sanding material. Large SK™ aluminum rods can be cut with a large bolt cutter or hacksaw. All SK™ ESF System connecting rods are stocked in length increments of 50mm. The variety of lengths available should greatly reduce the need for cutting rods.
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Which rod should be used to construct contoured rod frames?
The mini SK™ 3.2mm (1/8”) stainless steel rod is the same rod as the small KE system and is easy to contour. The small SK™ 6.3mm titanium external rod is the only rod other than the mini stainless steel rod that can be bent for this purpose. It is quite difficult to bend and is best bent prior to sterilization using a vise and two hand chucks. Plate benders can also be utilized. Readily constructed ring/SK™ hybrid frames, stable double clamps, and other alternatives to rod bending usually result in fixation superior to contoured rod frames. A different strategy must be used with large IMEX™ SK™ clamps because carbon fiber composite rods cannot be contoured. Two different techniques have been successfully used for spanning joints with all sizes of SK™ frames:

1. Single clamps and stainless steel rods (size medium KE rods) are used to articulate two of the large carbon fiber rods at the desired angle. A short articulation is placed where the rods converge (near the joint being immobilized) and a long articulation is placed at opposite ends of the rods.

2. Modified single clamps can be constructed to form an adjustable articulation that is quite secure. The SK™ single clamp body is comprised of two different parts (see page 1 for SK™ ESF clamp design): a B-1 body part that is placed on the side closest to the pin-gripping portion of the primary bolt with a threaded hole for the secondary bolt, and a B-2 body part that is placed on the opposite side with a smooth hole for the secondary bolt. Modified clamps for transarticular articulations are built with two B-2 body parts, two primary (pin-gripping) bolts, and two nuts. The articulation is built with two of these modified clamps and two short pieces of medium size KE rod. The angle of this articulation is adjustable, and can be used to the surgeon’s advantage when a transarticular fixator is employed in the management of Achilles tendon repairs.
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Which Size SK™ ESF components should be used on a give patient?
This is the most frequently asked question regarding any ESF device. Bone size should be examined to determine appropriate pin diameter, and pin diameter should be approximately 25% of bone diameter. Pin choice is then considered with the overall clinical demands of the patient, other injuries, and many other factors to determine not only device size, but the overall frame geometry. As previously discussed, undersized devices can be constructed to have great strength, but often become cumbersome and expensive. The better alternative is to increase inherent device strength to maintain a simpler, less expensive frame construct. For a highly comminuted, unstable fracture in a medium/large dog, large SK™ frame components and medium INTERFACE™ and CENTERFACE™ pins might be used to construct the initial frame. At six or so weeks after surgery, when staged disassembly is appropriate, small SK™ components can be substituted for large SK™ components as ONE method of reducing the support provided by the frame. In addition to removing frame elements (i.e. conversion of a Type II or a Type I-b to a Type I-a), carbon fiber composite rods can be substituted for titanium rods as part of the staged disassembly of a small SK™ fixator. If one considers only Type I-a frames, the following very general guidelines can serve as a starting point:

If one begins with a simple Type I-a frame, the previously listed options for staged disassembly are not applicable; however, two alternate strategies can be utilized. If reduction in pin number might jeopardize adequate pin bone interfaces, substituting a smaller, more flexible external rod for a larger, stronger one becomes a very attractive option to decrease the stiffness of a Type I frame (e.g. removal of large SK™ clamps and a 9.5mm carbon fiber composite rod and replacing them with small SK™ clamps and a 6.3mm titanium rod). While not truly a disassembly, rod downsizing does achieve the purpose of transferring a greater percentage of the load-bearing forces back to the bone and across the healing callus. A variation of this concept when utilizing the small SK™ device with 6.3mm titanium rods, is to replace the titanium rod with the less rigid carbon fiber composite rod of the same diameter. While not “downsizing” the connecting rod, this method does achieve a similar planned decrease in rigidity and might be useful in dogs when initial construction utilized medium fixation pins.

Since each SK™ clamp is designed to grip a wide range of pin diameters, and there is an overlap zone between the different sizes of fixation pins gripped by the different SK™ clamp sizes, it is frequently possible to construct the initial fixator with the larger clamps and rods and replace these components at about six weeks with those one size smaller. This wide range of pin shank diameters that can effectively be gripped with the SK™ clamp makes utilization of “overlapping pin zones” with the SK™ device particularly beneficial. Not all fixator frames will require staged disassembly. In particular, young patients tend to produce bony callus rapidly and need or benefit less often from staged disassembly. All patients will benefit from early fracture stability which promotes fracture zone debridement, revascularization, and early callus formation. Only after these stages occur will the potential benefits of decreased rigidity become pertinent. With several options for converting more complex frames to less complex frames, or downstaging larger, stronger rods to smaller, less rigid ones, it is prudent to initially use the stronger choice with a staged exit strategy available. In skeletally mature canine patients, the optimal time period for initiating staged disassembly appears to be at about 6 weeks after surgery.

Pin Size versus SK™ Clamp Size
This chart indicates what pins can be utilized using through-the-clamp application methods with the corresponding SK™ ESF clamp.

Staged Disassembly Strategies Relative to Size of Pins Used to Build SK™ Fixator
This chart indicates what pins are conducive to staged frame downsizing when utilizing small or large SK™ ESF frames for initial construction. When performing this type of destabilization, pins are already in place when clamps and rods are exchanged. Since positive thread pins do not need to pass through the clamp, the range of pins amenable to this form of staged disassembly is greater than that of initial frame construction.




Diagrams 1 and 2 borrowed with permission from: Toombs, J. P. Update on the SK™ External Fixation System: Components, Instrumentation, and Application Techniques. In Proceedings of the 2nd Korean External Skeletal Fixation Course. 2004:22-55.

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