Anatomic study of an anterior portal for percutaneous internal fixation of capitellum fractures.

Abstract

Fractures of the capitellum are uncommon and difficult to treat surgically. Capitellar open reduction-internal fixation uses a lateral open approach with posterior-to-anterior or anterior-to-posterior screw fixation. We investigated the use of an anterior portal for placement of anterior-to-posterior screw fixation through cadaveric measurement of the anatomic relationships from an anteriorly to posteriorly placed Kirschner wire (K-wire) to anterior elbow structures and calculated the percentage of articular surface accessed from the anterior portal. Eight fresh-frozen cadaveric elbows without radiographic or cutaneous evidence of prior trauma or surgery were used for this study. An arthroscopic proximal anteromedial portal was cannulized, and the radiocapitellar joint was evaluated. A single 1-cm portal was placed 1 cm distal to the elbow flexion crease and based lateral to the biceps tendon. The location of the portal was confirmed with a spinal needle, and blunt dissection with a hemostat was performed down to capsular tissue and for arthrotomy. A spinal needle sheath was threaded over a blunt switching stick and served as a cannula for placement of a 0.062 K-wire. Articular mapping was performed with cartilage scraping by the K-wire; the K-wire was then placed at the perceived center along the proximal-to-distal and radial-to-ulnar axis of the capitellum. Fluoroscopic confirmation of the wire's location was performed. Under loupe magnification, anatomic dissection was performed and the shortest distance measurements were recorded with digital calipers from the K-wire to the dissected structures. Capitellar articular measurements were recorded, in addition to the articular area defined by the K-wire. Data analysis was performed, and the average distance and standard deviation (in millimeters) were calculated. For structures that were pierced by or touching the K-wire, the distance was recorded as 0.1 mm. The average distance from the K-wire to the radial, lateral antebrachial cutaneous, and median nerves was 1.8 mm, 11.5 mm, and 28.0 mm, respectively. The average distance from the median cubital vein and biceps tendon was 3.7 mm and 13.4 mm, respectively. The pin track pierced the brachioradialis and supinator muscles in all but 1 specimen. The average capitellar articular surface marked was 39.1% of the calculated articular footprint of the capitellum. The anterior portal to the capitellum is directly adjacent to the radial nerve and lateral antebrachial cutaneous nerve, where each is susceptible to injury. We recommend blunt dissection and insertion of a cannula to allow drilling and placement of internal fixation in a relatively safe manner with respect to neurovascular structures.