Traumatic injuries can be bad, but if the person is generally healthy and the tissue is in good shape, sudden overloading of the tissue responds well to therapy and heals well. Deteriorative injuries develop insidiously. Often there can be years of wearing and over strain. The tissue doesn't exactly develop inflammation. Rather, the cell and fiber structure break down and the tissue becomes gristly. Eventually there is not enough healthy tissue to sustain the strain and the tissue gives way. In these cases, the problem of repairing the injury is complicated by having so little healthy tissue to work with. Compare a brand new rubber band with one left in the sun a few days, and you get the picture.