Normal Tendon and Ligament Healing

To understand prolotherapy, a knowledge of the pathology of sprain or strain and the normal healing process is necessary. Sprains (ligaments) and strains (tendons) become chronic when healing does not result in sufficient tensile strength or tightness.14,50 This condition also is termed connective tissue insufficiency (CTI), in which the structure is either too loose or has insufficient tensile strength.33 Load bearing in CTI stimulates pain mechanoreceptors.33 Biedert et al. reported that “as long as connective tissue remains functionally insufficient, the pain mechanoreceptors can continue to malfunction.”4 Recent studies show that in chronic pain of softtissue origin the pathologic lesion is degenerative rather than inflammatory.3,33 Therefore, tendinosis is a more appropriate description of this tissue state than tendinitis.3,33 Abnormal ligaments and tendons relate directly to myofascial pain because mechanoreceptors also trigger twitch contractions,4 which may explain the taut bands observed in myofascial pain. Individual fiber bundles correspond to tight portions of the muscle belly. Significant sprain or strain results in cell damage, which in turn triggers an inflammatory healing cascade and the appearance of monocytes within hours, fibroblast proliferation and migration within 48 hours, procollagen deposition within one week, and maturation of procollagen to collagen by 8 weeks.6 In the maturation phase water is lost, causing constriction of the tendon and tightening and allowing for both thickening and tightening of weak or loose ligament, tendon, or joint capsules. After injury, growth factors are elevated enough to stimulate growth only for a matter of days. Thereafter, healing is dependent on maturation of immature repair tissue. If laxity or tensile strength deficit is not corrected sufficiently to stop pain mechanoreceptor stimulation, a chronic sprain or strain results. Without further stimulation by growth factors, sufficient repair cannot take place. In repetitive trauma, each individual trauma may be insufficient to provide a proliferation stimulus, so that even minor injury may be enough to accumulate damage to the point of initiating chronic pain. Prolotherapy raises the level of growth factors to resume or initiate a repair sequence that has prematurely aborted or never started. Cells in the area of exposure, such as chondrocytes or osteocytes in osteoarthritis (OA), also can be expected to respond if the growth factors are those that proliferate such cells.