From a clinical point of view, the frozen shoulder occurs in two stages: inflammatory and fibrous and contracted. Both inflammation and fibrosis are mediated by inflammatory cells such as cytokines, growth factors and immune cells such as macrophages, mast cells and T and B lymphocytes. From the inflammatory phase in which pain is predominant and in which neoangiogenesis and neurogenesis are found, a gradual transition to the fibrotic phase is agreed with differentiation of fibroblasts into myofibroblasts and imbalance of the turnover of the cellular matrix with production of type III collagen. This process begins in the rotator interval extended in the subsequent phases to the entire capsule. The inflammatory phase will result in pain for the patient, while the fibrosis and contracture phase will result in stiffness.