Sat., 10/6/12 Upper Extremity Injuries, PAPER #81, 10:10 am OTA-2012
Radial Head Instability Following Malalignment of the Proximal Ulna: A Biomechanical Study
Emilie Sandman, MD1,2; Fanny Canet, Ing Jr, MScA1; Yvan Petit, PhD1,3;
G. Yves Laflamme, MD, FRCSC1; George S. Athwal, MD, FRCSC4;
Dominique M. Rouleau, MD, MSc, FRCSC1 ;
1Hôpital du Sacré-Coeur de Montréal, Montreal, Quebec, Canada;
2Université de Montréal, Montréal, Quebec, Canada;
3École de Technologie Supérieure, Montreal, Quebec, Canada;
4Hand and Upper Limb Center, St Joseph’s Health Care, University of Western Ontario,
Ontario, Canada
Purpose: Nonanatomic reconstruction of the elbow following a proximal ulna fracture/dislocation may lead to malunion, arthrosis, and instability. The proximal ulna has a sagittal plane bow, termed the proximal ulna dorsal angulation (PUDA), which measures between 0° and 14°. An understanding of the unique anatomy of the proximal ulna is important when treating complex injuries, such as Monteggia fracture/dislocations. Thus, the purpose of this study was to evaluate the magnitude of angular malalignment of the PUDA that would lead to radial head subluxation.
Methods: This biomechanical study was conducted on six fresh-frozen upper extremities. Testing was done on a validated motorized elbow movement simulator. An osteotomy, to simulate a proximal ulna fracture, was performed at the PUDA on each specimen. The osteotomy was stabilized with internal fixation at 5 angles (–10°, –5°, 0°, 5°, and 10°). Lateral elbow fluoroscopic images were taken in four elbow (maximal extension, 45°, 90°, maximal flexion) and three forearm (neutral, pronation, supination) positions during continuous elbow motion. The simulated fracture scenarios were done with an intact annular ligament and then, with annular ligament release. The displacement of the radial head was quantified with the radiocapitellar ratio (RCR), a previously validated measurement method. An RCR value of 100% represents a complete radial head dislocation. The relationships between radial head displacement and the degrees of malalignment of the proximal ulna, elbow, and forearm positions, and integrity of the annular ligament were assessed using an analysis of variance test.
Results: A significant triple interaction exists between elbow positions, angles of malalignment, and annular ligament integrity, when evaluating radial head instability with the RCR measurement (P <0.001). The greatest magnitudes of radial head subluxation were observed when the annular ligament was ruptured for all measurements (P <0.001), with a mean radial head displacement ranging from 4% posterior to 88% anterior. Significant differences were found between the different angles of internal fixation (P = 0.002). Anterior subluxation of the radial head progressively increased as malalignment was fixed into extension. Indeed, the mean radial head displacement was 61% when the elbow was in maximal flexion, fixed at 10° of extension, and the annular ligament ruptured. Conversely, posterior subluxation increased as malalignment progressed into flexion. Additionally, significant differences were shown for different elbow positions (P <0.001). Anterior subluxation of the radial head increased as the elbow joint was moved from extension to flexion, while posterior subluxation of the radial head decreased as the elbow joint progressed towards flexion. However, there were no differences observed for forearm positions (P = 0.4).
Conclusion: Our results demonstrate that malalignment of the proximal ulna leads to radial head instability. This is especially important, as fixation of the proximal ulna fractures are frequently done with straight plates that do not account for the normal anatomic bow, termed the PUDA. This malalignment may lead to abnormal tracking of the radial head, pain, restricted motion, and possibly secondary osteoarthritis. Malalignment of even 5° directly affects elbow biomechanics, especially with an associated annular ligament tear. Thus, this study demonstrates the importance of anatomic reconstruction of the proximal ulna, specifically recreation of each individual’s unique PUDA.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.