Internal Fixation of a Complicated Mandibular Fracture in a Filly Using a String-of-Pearls Locking Plate Assisted by a 3D Printed Model

Objective The aim of this study was to describe the successful surgical treatment of a complicated mandibular fracture with a 3.5 mm string-of-pearls (SOP) locking plate in a 5-month-old Appaloosa filly presenting with neurological signs. Study Design This is a case report. Results The neurological signs were due to severe head trauma and stabilized with medical treatment. Financial concerns initially prevented advanced imaging; radiographs identified a mandibular symphysis fracture, a fracture of the left vertical ramus that originated at the junction between the horizontal and vertical ramus and extended toward the coronoid process and rostral maxillary fractures. Following intra-dental wiring of the symphysis fracture, a lateral malocclusion developed. Computed tomography additionally identified fractures of the right wing of the basisphenoid bone, right zygomatic arch, left paracondylar process and the lateral body of the mandible. The vertical ramus fracture was repaired utilizing a 20-hole 3.5 mm SOP plate contoured to the ventral aspect of the angle of the mandible. A scaled (1:4) three-dimensional printed model aided pre- and intra-operative surgical planning. The filly was comfortable and eating well at the 4-week recheck. Radiographs showed good callus formation at the maxilla, healing of the mandibular symphysis and ramus. Just prior to the 10-week recheck, the filly suffered severe enterocolitis and was euthanatized. Conclusion The locking function of the SOP plate provided adequate stability for the fracture to heal without the expense of locking screws. The three-dimensional printed model aided in navigation of the complex fracture without the availability of fluoroscopy.

Stiffness Comparisons of SOP Interlocking Plate Configurations in 3D Printed Canine Lumbosacral Vertebrae

There are no published biomechanical studies evaluating the effect of stabilization techniques on the stability of the 3D printed models of the canine lumbosacral junction. The purpose of the study was to quantify stiffness of String of Pearls (SOP) interl ocking plating system on the lumbosacral junction in dogs. Testing was performed on five canine lumbosacral junction 3D printed models. Four - point bending was applied and displacement along the ventral aspect of the lumbosacral junction measured. Stiffness of six stabilization techniques was tested:  Models with contiguous polymer reconstruction articular facets.  Models with two dorsal SOP plate each with two pedicle screws in L7, two sacral screws and contiguous polymer reconstruction articular facets.  Models with two SOP plates with two L7 pedicle screws, two sacral screws and disarticulated L7 - S1 articular facets.  Models with two SOP plates with only the caudal L7 pedicle screw and two sacral screws and disarticulated L7 - S1 articular facets.  Models wit h two SOP plates with only the cranial L7 pedicle screw, two sacral screws and disarticulated L7 - S1 articular facets.  Models with one SOP plate, with two pedicle screws in L7 and two sacral screws and disarticulated L7 - S1 articular facets. The greatest st iffness was obtained in models with contiguous polymer reconstruction articular facets stabilized by two SOP plates with two screws engaging the pedicle of L7 (90.13 ±11.16 N/mm). There was no difference in gap stiffness between models with two SOP plates and disarticulated articular facets (54.43 ± 6.25 N/mm), and models with two SOP plates and only a cranial L7 pedicle screw (42.01 ± 8.64 N/mm). The lowest stiffnesses was recorded in constructs with two SOP plates and a caudal L7 pedicle screw (26.38 ± 4. 56 N/mm) and one SOP plate (26.94 ±5.83 N/mm) and intact models, contiguous polymer reconstruction articular facets, with no stabilization technique applied to the lumbosacral junction (16.16 ± .89 N/mm). The study - demonstrated stiffness using a single cra nial pedicle screw in the pedicle of L7 was no different from models with two pedicle screws in L7. Contiguous polymer reconstruction articular facets had a constructive effect on overall stiffness of the lumbosacral junction.

A biomechanical comparison of unilateral and bilateral String-of-Pearls™ locking plates in a canine distal humeral metaphyseal gap model

SummaryObjective: To compare the in vitro biomechanical performance of two String-of-Pearls (SOP) plate constructs in a canine distal humeral metaphyseal gap model.Methods: Seven pairs of canine cadaveric humeri, including the elbow joints, were prepared. One group consisted of a unilateral medially placed SOP plate with bicortical screws (UNI). The second group consisted of bilateral caudo-medial and caudo-lateral SOP plates applied with monocortical screws (BI). A 2 cm ostectomy was performed immediately proximal to the supratrochlear foramen. Constructs were tested in torsion and axial compression.Results: The UNI constructs had significantly lower stiffness in torsion and axial compression than the BI group. However, UNI constructs had a significantly higher ultimate strength than BI constructs. All UNI constructs failed by bending of the transcondylar screw and SOP plate. All BI constructs failed by axial pullout of the distal most screws.Clinical significance: In stabilizing canine supracondylar humeral fractures as modeled here, both the UNI model and the BI model demonstrated biomechanical advantages. The incorporation of a transcondylar screw through the medial plate appears to be beneficial to construct strength.

The effect of bending and twisting on the stiffness and strength of the 3.5 SOP implant

SummaryLocking plates are becoming increasingly popular in veterinary orthopaedics. The SOP is a novel locking plate system, which can be contoured with 6° of freedom and which utilises standard bone screws. The purpose of this work was to investigate the mechanical consequences of contouring the 3.5 SOP plate to support the formulation of clinical guidelines. The implants were loaded in four point bending using an industry standard protocol. The uncontoured SOP was found to be significantly stiffer and stronger than the uncontoured 3.5 DCP. Bending, and to a lesser extent, twisting, diminished the SOP’s stiffness and strength but the contoured SOP remained at least as stiff and strong as the untouched DCP.