The management of rotator cuff tears in the elderly

Validation of an empirical damage model for aging and in vivo injury of the murine patellar tendon

While useful models have been proposed to predict the mechanical impact of damage in tendon and other soft tissues, the applicability of these models for describing in vivo injury and age-related degeneration has not been investigated. Therefore, the objective of this study was to develop and validate a simple damage model to predict mechanical alterations in mouse patellar tendons after aging, injury, or healing. To characterize baseline properties, uninjured controls at age 150 days were cyclically loaded across three strain levels and five frequencies. For comparison, damage was induced in mature (120 day-old) mice through either injury or aging. Injured mice were sacrificed at three or six weeks after surgery, while aged mice were sacrificed at either 300 or 570 days old. Changes in mechanical properties (relative to baseline) in the three week post-injury group were assessed and used to develop an empirical damage model based on a simple damage parameter related to the equilibrium stress at a prescribed strain (6%). From the derived model, the viscoelastic properties of the 300 day-old, 570 day-old, and six week post-injury groups were accurately predicted. Across testing conditions, nearly all correlations between predicted and measured parameters were statistically significant and coefficients of determination ranged from R² = 0.25 to 0.97. Results suggest that the proposed damage model could exploit simple in vivo mechanical measurements to predict how an injured or aged tendon will respond to complex physiological loading regimens.

A review of shoulder replacement surgery

Shoulder replacement surgery is employed in the treatment of severe shoulder arthritis and following some proximal humeral fractures. Three different replacements are available: hemiarthroplasty (HAS), total shoulder replacement (TSR) and reverse shoulder replacement (RSR). HAS and TSR are indicated in patients with intact rotator cuffs and RSR for cuff deficient older patients. Outcomes are favourable, with the majority of patients having improvements in shoulder pain and function.