Distal Normograde Intramedullary Pin and Locking Plate Placement in the Canine Humerus: A Cadaveric Study

Abstract

Study DesignEx vivo anatomic study. Sample PopulationCanine cadavers (n=10 Greyhounds). MethodsAn anatomic landmark for pin insertion was identified based on three-dimensional reconstructions of previous elbow computed tomography studies and cadaveric dissection of the medial aspect of the humeral condyle. Bilateral distal normograde IM pin and LCP placement were performed and confirmed radiographically and by disarticulation and sagittal sectioning. ResultsThe anatomic landmark for pin insertion was consistently identified in each specimen using the technique described. Distal normograde insertion of a 3.5 mm IM pin was possible in Greyhound cadaveric humeri at the described location in conjunction with a 3.5 mm LCP with fixed angle, locked screws. A monocortical locking screw was required to avoid interference with the IM pin in 28 of 60 of the 3 proximal screw holes. No pin interference was encountered in any of the distal screw holes. ConclusionThe anatomic landmark and technique described in our study enabled repeatable successful placement Plate-rod constructs have also been reported for humeral fracture repair.[1, 9] Advantages over a bone plate alone include simplifying fracture reduction, maintaining spatial alignment, reducing plate strain across the fracture gap, and increasing the stiffness, load to failure, and fatigue life of the construct.[10-12] Current general recommendations for plate-rod constructs recommend the use of a pin that occupies 30-40% of the narrowest IM diameter. [10,12]

Biomechanical Comparison of External Fixation and Double Plating for Stabilization of a Canine Cadaveric Supracondylar Humeral Fracture Gap Model

“…A 3.2 mm Steinmann pin was placed in a normograde fashion from distal to proximal, starting in the fossa of origin of the deep and superficial flexor muscles, caudal and distal to the medial epicondyle. 19 The pin was driven with a surgical drill until it exited the proximal humerus in the region of the greater tubercle. The distal point was cut from the pin and the proximal end was grasped with the drill and withdrawn until 2 mm of the pin remained protruding distally.…”

“…[13][14][15][16][17] Normograde placement of an intramedullary pin in the humerus starting from the distal metaphysis allows maximal pin purchase within the distal fragment, which is useful for fixation of distal humeral fractures. 19 The mechanical properties of single versus double plating with String of Pearls locking plates in a canine distal humeral metaphyseal gap model are described. 20 The double-plate group consisted of caudomedial and caudolateral plates secured with short monocortical screws and was compared with a medial plate group with bicortical screws including a transcondylar screw.…”

“…20,21 The ESF-IMP construct combines the advantages demonstrated in both biomechanical and clinical studies of a type I-II external fixator with an intramedullary pin tie-in, with the intramedullary pin placed normograde from the distal metaphysis for maximal distal bone purchase. [12][13][14][15][16][17]19 The authors hypothesized the double-plate construct would be stiffer, stronger and more resistant to repeated loading than the external fixator construct when evaluated by simulated load bearing in a cadaveric model.…”