Glenoid cartilage mechanical properties decrease after rotator cuff tears in a rat model

Abstract

Rotator cuff repairs are commonly performed to reduce pain and restore function. Tears are also treated successfully without surgical intervention; however, the effect that a torn tendon has on the glenohumeral cartilage remains unknown. Clinically, a correlation between massive rotator cuff tears and glenohumeral arthritis has often been observed. This may be due to a disruption in the balance of forces at the shoulder, resulting in migration of the humeral head and subsequently, abnormal loading of the glenoid. Our lab previously demonstrated changes in ambulation and intact tendon mechanical properties following supraspinatus and infraspinatus rotator cuff tendon tears in a rat model. Therefore, the purpose of this study was to investigate the effects of supraspinatus and infraspinatus rotator cuff tears on the glenoid cartilage. Nine rats underwent unilateral detachment of the supraspinatus and infraspinatus tendons and were sacrificed after 4 weeks. Cartilage thickness significantly decreased in the antero-inferior region of injured shoulders. In addition, equilibrium elastic modulus significantly decreased in the center, antero-superior, antero-inferior, and superior regions. These results suggest that altered loading after rotator cuff injury may lead to damage to the joint with significant pain and dysfunction. Clinically, understanding the mechanical processes involved with joint damage will allow physicians to better advise patients.

Figure 1

Coronal view of a representative B-mode image slice of the central portion of the glenoid. The top and bottom surfaces, cartilage and bone, respectively, were each selected to segment the articulating surface.

Figure 2

Figure 2A: Sagittal view of a representative cartilage thickness map determined by ultrasound and divided into six regions (center (C), antero-superior (AS), antero-inferior (AI), postero-superior (PS), postero-inferior (PI), and superior (S)). Figure 2B: Saggital view of a representative image of the rat glenoid, highlighting the six locations for mechanical indentation testing. Cartilage thickness was calculated at each location using ultrasound.

Figure 2

Figure 2A: Sagittal view of a representative cartilage thickness map determined by ultrasound and divided into six regions (center (C), antero-superior (AS), antero-inferior (AI), postero-superior (PS), postero-inferior (PI), and superior (S)). Figure 2B: Saggital view of a representative image of the rat glenoid, highlighting the six locations for mechanical indentation testing. Cartilage thickness was calculated at each location using ultrasound.

Figure 3

Rotator cuff tears resulted in cartilage thinning in the antero-inferior (AI) region of the glenoid (median±IQR) (*p<0.05).

Figure 4

Rotator cuff tears resulted in decreased modulus in the center (C), antero-superior (AS), antero-inferior (AI), and superior (S) regions of the glenoid (mean±SD) (*p<0.05).