OTA 2004 Posters
Risk of Injury to Anterior Neurovascular Structures during Tension Band Wiring of Olecranon Fractures:
A Magnetic Resonance Imaging Analysis
Purpose: Tension band wiring (TBW) remains the most accepted form of surgical treatment for displaced olecranon fractures. Modifications have been made to the tension band construct to improve on stability and limit proximal migration of the wires. One such accepted modification is to place the Kirschner wires (K-wires) obliquely into the anterior ulnar cortex distal to the coronoid process for bicortical purchase. Concern has been raised, however, as to risk of injury to adjacent neurovascular structures in the proximal forearm by the penetrating wires (Schatzker J: Fractures of the Olecranon, in Schatzker J and Tile M (eds): The Rationale of Operative Fracture Care. Berlin, Germany, Springer-Verlag, 1987, p. 93). This study investigated the proximity of adjacent neurovascular structures to the anterior cortex of the proximal ulna through MRI to assess potential iatrogenic risk with pin penetration.
Methods: After obtaining our Institutional Review Board's exempt status, a medical archive retrieval database was searched for MRI scans of elbows in subjects over 18 years of age performed over a five-year period. Only scans read as normal and without pathologic conditions of any kind were included in the study group. Forty-seven scans met inclusion criteria for the study. The images were transferred to an IMPAX (Agfa Gevaert Group) system enhanced by MUSICA (multi-scale image contrast amplification) and analyzed with direct measurement software included in the ADC (Agfa Diagnostic Center). A musculoskeletal radiologist recorded the measurements from each subject. Measurements were taken for both distance and angular direction from a reference point on the anterior ulnar cortex, which was 1.5 cm distal to the tip of the coronoid process at the mid-sagittal point of the ulna. Measurements were made for the ulnar nerve (UN) and artery (UA), the median nerve (MN) and artery (MA), the posterior interosseous nerve (PIN), the radial artery (RA) and the superficial radial nerve (SRN). The anterior interosseous nerve and artery could not be visualized consistently and were not included. Distance from the reference point to a specific neurovascular structure was measured in millimeters. The angular measurement was recorded in degrees along the axial plane of the MRI image at the reference point. An anteriorly directed mid-sagittal line was set as the zero mark for angular measurements. Angles in an ulnar direction were listed as negative and in a radial direction as positive for recording purposes only. Univariate statistical analysis was performed with use of the SAS system.
Results: The UN was located 87.3° (± 25.4°) ulnar and 14.3 mm (± 3.4) away from the reference point. The MN was located 13.3° (± 17.5°) ulnar and 16.1 mm (± 5.7) away from the reference point. The UA was located 4.2° (± 12.0°) radial and 17.8 mm (± 3.9) away from the reference point. The RA was located 8.8° (± 9.6°) radial and 32.3 mm (± 5.5) away from the reference point. The SRN was located 19.8° (± 10.7°) radial and 29.7 mm (± 3.9) away from the reference point. The PIN was 41.7° (± 13.7°) degrees radial and 28.0 mm (± 5.2) away from the reference point.
Conclusions/Significance: During tension band wire fixation of olecranon fractures, placement of K-wires into the anterior ulnar cortex affords greater stability and helps prevent proximal wire migration. The possibility of iatrogenic injury to neurovascular structures adjacent to the anterior proximal ulnar cortex exists with such placement. We describe the anatomic proximity of the various neurovascular structures relative to a specific reference point on the anterior ulnar cortex. Such information guides the orthopaedic surgeon in safe placement of oblique K-wires during TBW. Within a reasonable arc for K-wire placement of 45° in either direction, the median nerve and ulnar artery are at greatest risk when the anterior ulnar cortex is penetrated at a point 1.5 cm distal to the coronoid. Even with consideration of anatomical variation, both of these structures were still beyond 10 mm from the anterior surface of the ulna. On the basis of these findings, the risk of injury to neurovascular structures when K-wires are anchored into the anterior ulnar cortex during TBW of olecranon fractures appears small. Protrusion of the K-wire tips beyond the anterior ulnar