Preventing Posterior Interosseous Nerve Injury during a Distal Biceps Tendon Repair, an Anatomic Study Comparing EDC and ECU Muscle Splitting Approaches.

Abstract

Background: Dorsal forearm approaches are commonly used to repair both partial and complete distal biceps tendon tears. Either the extensor digitorum communis (EDC) or extensor carpi ulnaris (ECU) and the supinator muscles are longitudinally split to expose the radial tuberosity (RT). Despite the known risk of posterior interosseous nerve (PIN) injury, there is little information on the safety of each approach. The purpose of this study was to define the location of the PIN relative to the radial tuberosity (RT) through both EDC and ECU muscle splitting approaches. Additionally, we aimed to find a reliable method to preoperatively locate the PIN, by using a novel line from the olecranon-to-radial styloid (ORS).

Methods: EDC and ECU muscle splitting approaches were performed on 20 cadaveric specimens, and RT-to-PIN lengths were measured in forearm supination, neutral, and pronation. Additional measurements were made from the olecranon to the point of PIN intersection along the ORS line and to the RT. After RT-to-PIN measurements, the coronal dissection plane for each approach was replicated with strings, and the EDC muscle was reflected to determine if the PIN or its branches crossed either approach lines.

Results: The ECU, versus EDC, approach resulted in longer mean distances between the RT and PIN (≥11mm; p<0.001). In both approaches, the PIN was farthest from the RT in pronation and closest in supination (p<0.001). The minimal distance from RT-to-PIN when using an ECU muscle splitting approach with the forearm in pronation was 21mm. The PIN crossed the midline of the radial shaft and approach line with an EDC approach; whereas only the ECU motor branch transversed the radial shaft and approach line in an ECU approach. The PIN intersected the ORS line at 35% of its total length. The RT was located 61±5mm from the tip of the olecranon.

Conclusion: The ECU, versus EDC, muscle splitting approach is less likely to endanger the PIN and/or its branches because the RT-to-PIN length was ≥11mm longer in all three forearm positions (p<0.001). Additionally, the PIN crossed the midline of the radial shaft and its approach line using an EDC approach, while only the ECU motor branch transversed the radial shaft and its approach line with an ECU approach. The PIN was located ≥21mm distal to the RT using an ECU muscle splitting approach in forearm pronation. The ORS line and olecranon are useful landmarks to locate the PIN and RT, respectively.