Effect of an Anterior Glenoid Defect on Anterior Shoulder Stability

Abstract

Background There have been few biomechanical studies to clarify which size of a glenoid defect is critical. However, those studies have assumed that the defect occurred anteroinferiorly. Recent studies have reported that the defect is located anteriorly rather than anteroinferiorly. Therefore, the effect of the anterior, not anteroinferior, glenoid defect on shoulder stability needs to be investigated. Hypothesis The anterior glenoid defect would have a similar effect on anterior shoulder stability as that of the anteroinferior glenoid defect. Study Design Controlled laboratory study. Methods Eight fresh-frozen cadaveric shoulders were used (mean age, 74 years). The specimen was attached to a shoulder-testing device with the arm in abduction and external rotation. An osseous defect was created stepwise with a 2-mm increment of the defect width. The stability ratio was used to evaluate joint stability. With a 50-N axial force, the translational force applied to the humeral head was measured by a force transducer. Results The stability ratio without a defect (32% ± 6%) significantly decreased after creating a 6-mm defect (17% ± 5%; P = .0001), which was equivalent to 20% of the glenoid length. Conclusion An osseous defect at 3 o'clock with a width that was equal to or greater than 20% of the glenoid length significantly decreased anterior stability. Clinical Relevance The results suggest that reconstruction of the glenoid concavity might be necessary in shoulders with an anterior glenoid defect of at least 20% of the glenoid length.