Normograde and Retrograde Pinning of the Distal Fragment in Humeral Fractures of the Dog.

OBJECTIVE:
To determine if normograde and retrograde pinning of the distal humeral fragment, to maximize pin purchase in this fragment, would damage vital structures in and around the elbow and shoulder joints in dogs.
STUDY DESIGN:
Anatomic study.
SAMPLE POPULATION:
Cadaveric dogs (n = 12; 12 thoracic limb pairs).
METHODS:
Twelve thoracic limb pairs were harvested from cross-breed dogs and 1 thoracic limb from each pair was allocated to 1 of 3 groups. A transverse osteotomy was created at the junction of the middle and distal thirds in the diaphyseal fracture group (n = 8) and proximal to the supracondylar foramen in the metaphyseal fracture group (n = 8). The humeri in the normograde group (n = 8) were left intact. In all specimens in the distal and supracondylar fracture groups, retrograde pinning of the distal fragment was performed with the elbow flexed. The pins were driven into the medial epicondyle until they exited the skin caudal to the elbow. Dissection of the soft tissues around the exit tract of the pin was performed. The fracture was then reduced and the pin was advanced until it exited the proximal humeral fragment. In the specimens in the normograde group, pinning was initiated on the distal aspect of the medial epicondyle. The pin was directed parallel to the caudal aspect of the medial epicondyle and driven proximally into the humerus until it exited the proximal humerus.
RESULTS:
Pins exiting the distal aspect of the medial epicondyle passed through muscle origins in 7 specimens in the diaphyseal osteotomy group and in all 8 specimens in the metaphyseal group. The ulnar nerve was entrapped in 1 specimen in the metaphyseal osteotomy group; however, it was not entrapped in any of the specimens in the diaphyseal osteotomy group. The articular cartilage of the trochlea was damaged in 2 specimens in each of the retrograde pinned groups. There was no damage to articular or periarticular structures by pins exiting the proximal humerus.
CONCLUSION:
Retrograde pinning of the distal fragment in humeral fractures in the dog may damage the articular cartilage and cannot be recommended.