Normograde Pinning for Feline Humeral Fractures

Humeral fractures in cats commonly occur in the distal diaphysis. Extreme care must be taken when directing an IM pin through the distal humerus; incorrectly placed pins can result in poor stabilization of the distal fragment and/or cause serious damage to periarticular structures of the elbow. This study evaluated normograde and retrograde introduction of IM pins. Twenty-four thoracic cat cadaver limbs were allocated to 1 of 3 groups: in group 1, diaphyseal osteotomies were created in the humerus; in group 2, metaphyseal osteotomies were created in limbs; in group 3, the humerus was left intact. In groups 1 and 2 (retrograde technique), a 1.5-mm IM pin was introduced via the fracture site, directed toward the medial epicondyle, and driven distally until exiting the skin caudal to the flexed elbow. The pin was then retracted until it was even with the fracture line and the fracture was reduced. The pin was advanced until it exited the proximal humerus. In group 3 (normograde technique), a 1-mm guide hole was predrilled into the medial epicondyle and a 1.5-mm IM pin advanced through the guide hole until it exited the proximal humerus. Normograde pinning spared muscles, nerves, and articular cartilage from damage; retrograde technique was associated with a high incidence of damage to vital structures of the elbow. Normograde IM pinning of the distal fragment in humeral fractures can be safe in cats, but retrograde pinning is not recommended.

CommentaryDistal humeral fractures are more challenging when working with small feline bones. During retrograde 1.6-mm pin placement (from the fracture site to the medial epicondyle), 7 out of 16 pins damaged the joint surface, 2 went through the ulnar nerve, and 13 damaged the flexor muscles. Normograde placement was accomplished by drilling a pilot hole from the medial epicondyle area into the medullary canal and then sliding a beveled pin proximally by hand. This method avoided any damage to the elbow joint or surrounding important structures and exited the humerus in the greater tubercle cranial to the shoulder joint.

The results affirmed the difficulty in safely placing an IM pin starting at the fracture. There is simply not enough room in the medial epicondyle of the cat for the pin to exit without risk of complication.—Jonathan Miller, DVM, MS, DACVS

SourceNormograde and retrograde pinning of the distal fragment in feline humeral fractures. Cohen L, Israeli I, Levi S, et al. VET SURG 41:604-610, 2012.