An analytical solution for the stress field along compressive regions of tendon and its role on proteoglycan synthesis

Tendon to bone insertion site injuries are a leading cause of discomfort and disability in both young and, particularly, elderly populations. Surgical tendon reattachment procedures carry failure rates as high as 94% for massive rotator cuff tears [1]. The transfer of load from tendon to bone is governed by the mechanical properties of the tendon to bone insertion site [7], but scar tissue at the healing tendon to bone insertion has properties that are not optimized for load transfer [2,3]. Studies of rotator cuff healing in rats show an absence of fibrocartilage in the scar tissue formed at the healing insertion site [2,3]: the absence of proteoglycans in this scar tissue may result in poor resistance to compression. Proteoglycan synthesis appears to correlate with the presence of a compressive stress environment, such as the compressive radial stresses in wrap-around tendons like those in the hand and foot [4,5]. The present paper describes an exact linear elasticity solution that offers some insight into the specific nature of the compressive mechanical environment needed for proteoglycan synthesis. We address the physiologic question: what is the nature of the stress field at tendon locations where proteoglycan synthesis is observed? The elasticity solution leads us to hypothesize that only a single compressive principal stress component is needed to induce fibroblasts to synthesize proteoglycans.