Veterinary Screw Targeting Clamp (STC)
Fabrice Rossignol, Janik Gasiorowski, Kati Glass, Christopher Lischer, Michael Kowaleski, Jeffrey Watkins
Fig 1: Rendering showing the positioning of the Screw Targeting Clamp (STC) for management of a parasagittal fracture of the third phalanx. Angled outer sleeve allows secure placement of the STC on oblique bone contour. A targeted screw placement system permits improved accuracy of screw insertion when used in conjunction with intraoperative imaging. Improved accuracy of screw insertion gives more consistent, confident fracture repair, particularly through minimal invasive approaches and in challenging anatomical locations, such as distal phalanx and navicular bone fractures. It is also a safe and accurate placement of specific screws into subchondral bone cysts close to joint space.
The Screw Targeting Clamp (STC) developed by the AO Technical Commission's Foot and Ankle Expert Group has many useful features for veterinary use. However, available drill guides for the STC do not accommodate the screw sizes frequently used in large animal surgery. Therefore, large animal veterinary-specific sleeves were created for the existing STC to allow placement of 3.5−5.5 mm screws entirely through the STC maintaining alignment.
The Foot and Ankle Screw Targeting Clamp was designed to provide the ability to maintain compression and targeted screw insertion. When evaluated in equine bone, clamp bending was observed on application of the compression function. The aiming arm was modified to improve stiffness for use in equine bone, and sleeves were developed to accommodate the screw sizes used in equine surgery. Angled outer sleeves were designed to secure placement of the STC on oblique bone contour (Fig 1).
With its unique design, the STC will hold a bone fragment in reduction and applies a modest amount of interfragmentary compression to maintain stability of the fragments during the procedure. The STC can be associated with standard bone clamps placed adjacent to it if a stronger compression is needed. It also allows all processes necessary for insertion of a cortex screw in lag fashion to be completed through the clamp, from initial drilling to final screw tightening. Screw sizes supported include 3.5, 4.5, and 5.5 mm screws. An adjustable rail helps to ensure ideal screw placement.
Once the fracture is reduced, the STC is placed using imaging control to verify that the trajectory of drilling and screw placement is precise. With the provided insert sleeves, the screw hole is prepared, and the screw is placed while the STC remains in position to protect the adjacent tissues. The STC aids in retaining interfragmentary reduction throughout the entire process of positioning the cortex screw in lag fashion. Once the fracture is reduced and the clamp confirmed to be in the correct location, screw placement can be completed without further imaging.
Feedback from surgeons who tested the new Veterinary Screw Targeting Clamp stated that a more accurate placement of screws can be achieved, and that the system is more stable than the existing targeting clamp and standard drill guides.
Fig 2: Components of the Screw Targeting Clamp. 
Fig 3a-c: External surgical view of the positioning of the Screw Targeting Clamp (STC) for fracture fixation of a parasagittal fracture of the third phalanx. Note that the STC is maintained during the entire procedure from drilling to screw tightening. 
Fig 4a−e: Radiographic and image intensifier views of the procedure. 
Fig 5a−b: Control radiographs 3 months postoperatively indicating complete healing of the fracture. Veterinary Screw Targeting Clamp
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