It’s Quite Humerus

The purpose of this study was to determine the optimal pin size that can be inserted into the medial epicondyle during open and percutaneous normograde pinning of the distal humerus in dogs. Forelimb pairs from 16 cadaver dogs were separated for either percutaneous or open pinning, then divided into 3 groups based on intramedullary (IM) pin diameter relative to medullary canal diameter: 25% to 35%, 36% to 45%, or 46% to 55%. Normograde insertion of pins into the medial epicondyle was performed, with pins aimed to exit at the lateral aspect of the major tuberculum. Pin tracts were dissected, and damage to the soft tissue, bony structures, and entry/exit points was assessed. There were no differences in any outcomes between open and percutaneous techniques. Cortical bone damage was more frequent in the 46% to 55% group. The authors conclude that pins 36% to 45% of the diameter of the humeral medullary canal at the distal 80th percentile of humeral length can be inserted with an optimal exit point and minimal damage to the cortex of the medial epicondyle.

IM pins, commonly applied in humeral fractures, provide good bending stability. Although I usually place these pins normograde from the proximal fragment, normograde placement from the distal fragment would be beneficial in some distal humeral fractures to increase bone purchase in the distal fragment. IM pins are frequently applied in combination with other stabilization techniques (eg, plates, external skeletal fixation), especially in comminuted fractures; the recommended size in this situation is around 30% to 40% of the medullary cavity. This would be a size range commonly used when applying IM pins in the humerus, and this study confirms these pins can be safely placed with minimal damage to bone when placed normograde from the distal fragment. However, when using larger pins or using IM pins in combination with cerclage wires for some diaphyseal humeral fractures, other pin placement methods (ie, normograde from the proximal fragment) would be more suitable.—Pilar Lafuente, DVM, PhD, DACVS-SA, DECVS, DACVSMR

This capsule is part of the WSAVA Global Edition of Clinician's Brief.