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Effect of Distal Humeral Varus Deformity on Strain in the Lateral Ulnar Collateral Ligament and Ulnohumeral Joint Stability

Beuerlein, Murray J. MSc; Reid, Jeffrey T. MD; Schemitsch, Emil H. MD, FRCS(C); McKee, Michael D. MD, FRCS(C)

Journal of Bone & Joint Surgery - American Volume: October 2004 - Volume 86 - Issue 10 - p 2235–2242
Scientific Articles

Background: Recent reports have implicated cubitus varus deformity as a risk factor for the development of late posterolateral rotatory instability of the elbow. The purpose of this study was to determine the biomechanical relationship between cubitus varus and strain in the lateral ulnar collateral ligament and subluxation of the ulnohumeral joint as it relates to posterolateral rotatory instability.

Methods: Eleven fresh-frozen cadaveric elbow joints were mounted in an apparatus that allowed active elbow motion. Supracondylar osteotomies were performed to create cubitus varus deformities of 0° to 30° in 5° increments. Each elbow was loaded with a supination moment of 1.2 Nm and a resistive triceps extension force. Strain in the lateral ulnar collateral ligament and widening of the ulnohumeral joint were measured at each position of varus, and the resulting strain and joint-widening values were averaged.

Results: Strain in the lateral ulnar collateral ligament was found to increase as the cubitus varus deformity increased. Likewise, the ulnohumeral joint space was seen to progressively widen with increasing cubitus varus. Strain was significantly increased at 30° of varus deformity (p = 0.03), and widening of the ulnohumeral joint space was significantly increased at 25° of varus deformity (p = 0.004). When differences in the size of the cadaveric specimens were accounted for in an analysis of covariance, ligament strain was significantly increased at 25° of varus (p = 0.005) and widening of the ulnohumeral joint space, at 20° (p = 0.01).

Conclusions: Cubitus varus deformity of the elbow increases strain in the lateral ulnar collateral ligament, with a corresponding increase in ulnohumeral joint-opening consistent with the posterolateral rotatory instability of the elbow seen clinically.

Clinical Relevance: The results of this study are consistent with the clinical findings of posterolateral rotatory instability of the elbow following long-standing cubitus varus and support the clinical concept that increased strain in the lateral ulnar collateral ligament with this deformity may eventually lead to overt posterolateral rotatory instability of the elbow. We believe that these findings have implications for the etiology, prevention, and treatment of posterolateral rotatory instability of the elbow following cubitus varus deformity.

1 Upper Extremity Reconstructive Service (M.J.B., J.T.R., and M.D. McK.) and Division of Orthopaedics (E.H.S.), St. Michael's Hospital and the University of Toronto, 55 Queen Street East, Suite 800, Toronto, ON M5C 1R6, Canada. E-mail address for M.D. McKee: mckee@the-wire.com

Copyright 2004 by The Journal of Bone and Joint Surgery, Incorporated
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