The Relationship of the Posterior Interosseous Nerve to the Supinator Muscle in the Dorsal Approach to the Proximal Radius: A Descriptive and Quantitative Anatomic Study of Filipino Cadavers

Leslie M. Reyes,1 Phillip Anthony B. Kho2 and Edward H.M. Wang2

1Department of Anatomy, College of Medicine, University of the Philippines Manila
2Department of Orthopedics, College of Medicine and
Philippine General Hospital, University of the Philippines Manila

Background and Objective. The posterior interosseous nerve (PIN) is vulnerable to injury in the dorsal approach to the proximal radius. The goal of this study is to describe the quantitative relationship of the PIN to the supinator muscle in the context of anatomic landmarks. Knowledge of superficial landmarks related to the PIN would hopefully minimize iatrogenic injury to the posterior interosseous nerve.

Methods. 12 cadavers (22 forearms) were dissected and analyzed. The length of the supinator muscle was determined. The oblique distances of the PIN entry and exit points to the proximal and distal borders of the supinator muscle as well as their perpendicular distances to the lateral epicondyle-Lister’s tubercle (LE-LT) reference line were measured and recorded. The number of PIN branches inside the supinator substance was recorded. Mean and median values were determined and subjected to statistical analysis.

Results. Mean supinator length was 5 centimeters. Ninety-one percent of the cadaveric forearms had PIN branches inside the supinator muscle substance. Twelve of the 22 forearms (55%) had 2 branches. The mean oblique distances of the PIN from the lateral epicondyle to the entry and exit points in the proximal and distal borders of the supinator muscle was 3.52 and 7.31 centimeters, respectively. The mean perpendicular distances of the PIN from LE-LT reference line to the entry and exit points in the proximal and distal borders of the supinator muscle was 1.13 and 1.26 centimeters, respectively. An imaginary danger-zone 4 centimeters wide overlying the LE-LT reference line depicts the possible area where the PIN and its branches may most likely be located.

Conclusion. The dorsal approach to the proximal radius may allow a safe exposure without causing iatrogenic injury to the posterior interosseous nerve through the use of superficial anatomic landmarks and reference lines in combination with mean measurements from our study.

Key Words: Posterior interosseous nerve (PIN), supinator muscle, Lateral epicondyle - Lister's tubercle (LE-LT) reference line, Thompson dorsal approach, proximal radial fracture, safe zones