American Association for Hand Surgery
Theme: Beyond Innovation

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The Naked Capitellum: A Surgeon's Guide to Intra-Operative Identification of Posterolateral Rotatory Instability
Michael S Guss, MD1; Lindsay K Hess, BS1; Mark E. Baratz, MD2
1University of Pittsburgh, Pittsburgh, PA, 2Hand and Upper Extremity Surgery, University of Pittsburgh Medical Center, Washington, PA

Introduction: This study's aim was to provide an easy and reproducible way for surgeons to intra-operatively assess the status of the lateral ulnar collateral ligament (LUCL) origin and determine if there is posterolateral rotatory instability (PLRI) despite an intact common extensor origin. We hypothesized that we could recreate clinically relevant disruption of lateral supporting structures and illustrate progressive posterolateral instability of the elbow.

Methods: Using eight human cadaveric upper extremities the radiocapitellar joint was approached through an extensor-splitting approach. The lateral capsule posterior to the mid-axis of the radiocapitellar joint contains the LUCL. The relationship of the lateral capsule to the articular surface of the capitellum was noted. Next, the lateral capsule and extensor origin were sequentially sectioned. The posterior and lateral translation of the radial head (RH) relative to the capitellum was measured at 4 stages of sectioning: intact, release of capsule to the lateral epicondyle, release of posterior capsular insertion and release of the common extensor origin. All measurements were made with a digital caliper.
Results: Average specimen age was 78.9 years and five were male. Average RH and capitellum diameters were 23.8 mm and 22.9 mm respectively. In each specimen the lateral capsule originated within 1-2 mm of capitellar articular surface. Lateral capsular sectioning to the six-0'Clock position directly posterior to the lateral epicondyle created an unstable elbow with posterior and lateral RH translation. With sequential sectioning of the posterior capsular insertion there was a significant additional RH translation, posteriorly (p<0.05). With release of the capsule and extensor origin the elbow was grossly unstable. (Figure 3). Statistics were performed using a one-way ANOVA with "interval capsular sectioning" as the factor and individual as a random effect followed by a post-hoc Tukey HSD correction for multiple comparisons with alpha = 0.05.

Discussion: The elbow's lateral capsule and LUCL complex plays an important role in preventing PLRI. The lateral capsule normally originates within 1-2 mm of the capitellar artiicular margin. Progressively larger degrees of elbow laxity are associated with further peel-back of the capsule despite an intact extensor origin.
Clinical Relevance: If the surgeon extends the elbow and retracts the intact extensor origin and does not see capsule on the capitellum ("naked capitellum sign"), then the capsule has been disrupted from the articular margin and there is a high probability that PLRI exists. In this event, the capsuloligamentous complex must then be repaired.

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