Objective: To study the location and characterization of the safe zone with respect to bony landmarks on volar surface of proximal ulna for the protrusion of various ulnar fixations.
Material and Method: The present study was done on 39 upper extremities from 20 embalmed human, adult cadavers. The average ages of the cadavers were 67.28 + 10.96 years (range from 40 to 82 years), 10 females, and 29 males. The safe zone dimensions, both in coronal and sagittal planes, were measured.
Results: The distance between median nerve and volar surface of proximal ulna in sagittal plane at 2 cm and 4 cm distal to tip of coronoid process were 0.99 + 0.15 cm (range from 0.76-1.32 cm) and 0.85 + 0.17 cm (range from 0.64-1.75 cm), respectively. The distances between the lateral border of the proximal ulna and medial border of the median nerve in coronal plane at 2 cm and 4 cm distal to the tip of the coronoid process were 0.95 + 0.19 cm (range from 0.66-1.36 cm) and 0.82 + 0.14 cm (range from 0.52-1.14 cm), respectively.
Conclusion: Based on the present results, if intra medullary screws or K-wire fixations were used, it should theoretically be long enough to reach their proximal ulna in order to bite into the cortical bone, but should not be so long as to cut out into its lateral part and, in the sagittal plane, the protrusion should not be longer than 0.92 cm. Orthopedic surgeons must remain vigilant with regard to any types of fixation in the upper extremity because the risk of neurovascular injury is high.

Keywords: Proximal ulna, Safe zone, Fixation, Anatomical