The Biomechanical Effectiveness of Classic and Congruent Arc Latarjet Procedures

INTRODUCTION: The Latarjet procedure is commonly used to treat glenoid bone loss due to recurrent instability and dislocation. In this procedure, the coracoid process is osteotomized from its native position and fixed to the anterior glenoid at the site of bone loss. As a result, the coracoid acts as an extension of the glenoid face, thus restoring the glenoid articulating surface and increasing stability of the glenohumeral joint. There are two methods of performing this procedure, the originally described technique, termed the “Classic Latarjet” and the “Congruent Arc” modification of the original technique. These methods differ in their orientation of the coracoid bone graft with respect to the glenoid. The Classic method affixes the coracoid so that its lateral edge becomes part of the glenoid face, while the Congruent method uses the inferior coracoid surface as part of the glenoid face. The objective of this study was to evaluate and compare the strength of these two Latarjet constructs by quantifying load transfer and graft displacement. METHODS: Eight fresh-frozen cadaveric shoulders (four pairs) were subjected to a compressive loading protocol using a testing machine (Instron, MA) (Figure 1). Specimens were tested in their intact condition and following Latarjet reconstruction of a simulated anterior glenoid defect measuring 25% of the glenoid width. The Classic Latarjet and Congruent Arc Latarjet were randomized for each shoulder pair. With the humerus in a static position of 30° abduction, the glenoid was subjected to a cyclic compressive load of 100 cycles at a frequency of 1 Hz, directed 30° anterior and applied on the glenoid rim. Cyclic loading followed a staircase pattern with magnitudes of 50, 100, 150 and 200N. Following sub-failure testing, the load was increased until the graft displaced 10 mm, which was recognized as failure.