The String of Pearls (SOP) System

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The String of Pearls (SOP) System

Malcolm G. Ness

11.1 Introduction

The string of pearls (SOP) is a veterinary locking plate system developed specifically for veterinary use [1, 2]. Since its inception in 2006, SOP has been used in well over 100,000 clinical cases, thoroughly evaluated, and reported in many clinical research presentations and papers published internationally in the peer‐reviewed veterinary literature. The system was designed by a small group of veterinary surgeons and engineers to address the problems and limitations they had encountered using first‐generation locking systems.

11.2 Description of the System

The SOP system is manufactured in three sizes, 2.0, 2.7, and 3.5 mm (corresponding to the cortical bone screw size) and available in surgical stainless steel (316 LVM) or titanium alloy (Ti‐6Al‐4 V) [4].

The “plates” have a circular cross‐section with a repeating pattern of cylindrical “internodes” and spheroid “pearls.” Each pearl is threaded in the base to accept a standard cortical bone screw, with a proximal aperture just wide enough to accept the screw’s head. The screwhead impinges within the pearl, producing an interference fit – a secondary lock between the plate and screw (Figure 11.1).

Image described by caption and surrounding text.

Figure 11.1 Cut‐away section of a 3.5 string of pearls (SOP) plate, with screw in situ. The base is threaded to accept a standard cortical bone screw and the inner surface of the pearl features a small ridge – the aperture reduces from 6.00 to 5.85 mm diameter – against which the 6.00 mm screwhead will impinge and lock.

Size‐specific bending irons are used. The “bending end” imparts four‐point bending and a “twisting end” twists the plate evenly along the length of the internode [24].

Specific drill guides position the drilled hole central and perpendicular to the pearl. Finally, small, reusable screw‐like “bending tees” placed into each pearl preserve the locking function despite contouring.

11.3 Design Features of the SOP Locking Plate System

Specific design features of the SOP system include the following:

  1. The SOP is slightly stiffer and stronger than the corresponding standard 2.0, 2.7, and 3.5 self‐compressing plates [1].
  2. The design of the four‐point bending irons minimizes the inevitable weakening that follows the bending or twisting of any metallic implant [2, 4].
  3. The SOP plate’s circular cross‐section facilitates complex contouring of the implant [5, 6].
  4. The locking function is preserved without compromise following bending and/or twisting of the plate.
  5. There is a secure double‐locking mechanism – a conventional “thread‐in‐thread” feature and a second interference fit between screwhead and pearl.
  6. Screw holes are not weak points – empty screw holes can be left over a fracture or elsewhere, according exclusively to clinical need [7].
  7. SOP has a relatively consistent stiffness profile, which mitigates damaging stress concentration under bending loads and optimizes the biomechanical environment at the fracture site [8].
  8. The plates can be cut to any length and without compromising locking function using only the bending irons.
  9. The SOP system utilizes standard cortical bone screws.

11.4 Perceived Limitations/Controversies

11.4.1 Screws Cannot Be Angled through the SOP Plate

While the design of the SOP precludes the use of angled screws, the SOP plate is easily and precisely contoured, allowing screws to be effectively directed into underlying bone without compromise (Figures 11.2 and 11.3).

Image described by caption.

Figure 11.2 Cranio‐caudal radiographs of a Y‐T fracture of the distal humerus of a 36 kg Labrador retriever fixed with two string of pearls (SOP) plates (one 3.5 and one 2.7) and 11 screws.

Image described by caption.

Figure 11.3

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Jun 13, 2021 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on The String of Pearls (SOP) System

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