TENSILE MATERIAL PROPERTIES OF THE GLENOID LABRUM

Abstract

The aim of this work was to define the tensile material properties of the glenoid labrum. Previous SEM studies of the labrum have observed three definitive layers, with a densely packed circumferentially orientated collagen core layer. The glenoid labrum from ten cadaveric shoulders were dissected out and divided into eight equal sections. Each section was cut to produce specimens from the core layer using a microtome and a specifically designed cryo-clamp resulting in uniform specimens with dimensions of 1mm x 1mm x 8mm. All of the tensile testing was performed within a controlled-environment unit of 38°C and 100% relative humidity. Each specimen was precycled to a quasi-static state to alleviate the effects of deep-freezing, prior to final testing. The elastic modulus was calculated for each specimen before and after a 5-minute period of stress relaxation and before failure initiation. The mean age of the specimens was 61 years (range 47–70). Load to failure was 2.7N (1.0–7.0). The mean modulus was 10.2MPa (3.0–22.3) before stress relaxation, 18.0MPa (5.8–36.7) immediately after stress relaxation and 22.3MPa (8.4–66.4) before failure initiation. The 1 and 2 o’clock specimens had lower moduli than the 4 and 5 o’clock specimens (p=0.01). These results can aid in explaining the differing pathologies encountered around the circumference of the labrum. The high moduli at the 4 and 5 o’clock positions may reflect the ability of this portion of the labrum to accommodate forces and thus resist anteroinferior subluxation. The lower moduli at the 1 and 2 o’clock positions suggest that this portion of the labrum is less apt to accommodate tension; this might explain the higher incidence of labral foramen observed in this area and the anatomical variant of the Buford complex.