|Classification and external resources|
Tendinosis, sometimes called chronic tendinitis, tendinosus, chronic tendinopathy, or chronic tendon injury, is damage to a tendon at a cellular level (the suffix "osis" implies a pathology of chronic degeneration without inflammation). It is thought to be caused by microtears in the connective tissue in and around the tendon, leading to an increase in tendon repair cells. This may lead to reduced tensile strength, thus increasing the chance of tendon rupture. Tendinosis is often misdiagnosed as tendinitis due to the limited understanding of tendinopathies by the medical community. Classical characteristics of "tendinosis" include degenerative changes in the collagenous matrix, hypercellularity, hypervascularity, and a lack of inflammatory cells which has challenged the original misnomer "tendinitis".
Swelling in a region of micro damage or partial tear may be detected visually or by touch. Increased water content and disorganized collagen matrix in tendon lesions may be detected by ultrasonography or magnetic resonance imaging.
Symptoms can vary from an ache or pain and stiffness to the local area of the tendon, or a burning that surrounds the whole joint around the inflamed tendon. With this condition, the pain is usually worse during and after activity, and the tendon and joint area can become stiffer the following day as swelling impinges on the movement of the tendon. Many patients report stressful situations in their life in correlation with the beginnings of pain, which may contribute to the symptoms.
Tendons are very slow to heal if injured. Partial tears heal by the rapid production of disorganized type-III collagen, which is weaker than normal tendon. Recurrence of injury in the damaged region of tendon is common.
Physical therapy, rest, and gradual return to the activity in which tendinosis was experienced is a common therapy. There is evidence to suggest that tendinosis is not an inflammatory disorder; anti-inflammatory drugs are not an effective treatment, and inflammation is not the cause of this type of tendon dysfunction. There is a variety of treatment options, but more research is necessary to determine their effectiveness. Initial recovery is usually within 2 to 3 months, and full recovery usually within 3 to 6 months. About 80% of patients will fully recover within 12 months. If the conservative therapy doesn't work, then surgery can be an option. This surgery consists of the excision of abnormal tissue. Time required to recover from surgery is about 4 to 6 months.
On-going research into new treatments
Both eccentric loading and extracorporeal shockwave therapy are currently being researched as possible treatments for tendinosis. One study found both modalities to be equally effective in treating tendinosis of the Achilles tendon and more effective than a 'wait and see' approach. Other treatments for which research is on-going includes vitamin E, vitamin B6, nitric oxide, and stem cell injections.
Vitamin E has been found to increase the activity of fibroblasts, leading to increased collagen fibrils and synthesis, which seems to speed up the regeneration and increase the regenerative capacity of tendons.
Nitric oxide (NO) also appears to play a role in tendon healing and inhibition of its synthesis impairs tendon healing. The use of a nitric oxide delivery system (glyceryl trinitrate patches) applied over the area of maximal tenderness was tested in three clinical trials for the treatment of tendinopathies and was found to significantly reduce pain and increase range of motion and strength.
Soft tissue mobilization
Augmented Soft Tissue Mobilization (ASTM) is a form of manual therapy that has been shown in studies on rats to speed the healing of tendons by increasing fibroblast activity. One case study showed ASTM resulting in full recovery in the case of an athlete suffering from chronic ankle pain and fibrosis, after an unsuccessful course of surgery and conventional physical therapy.
Perhaps the most promising avenue of therapy is indicated in a line of research finding dramatic rates of recovery including complete remodeling of chronically damaged tendon tissue with eccentric loading.
The use of an inflatable brace (AirHeel) was shown to be as effective as eccentric loading in the treatment of chronic Achilles tendinopathy. Both modalities produced significant reduction in pain scores, but their combination was no more effective than either treatment alone.
Shock-wave therapy (SWT) may be effective in treating calcific tendinosis in both humans and rats. In rat subjects, SWT increased levels of healing hormones and proteins leading to increased cell proliferation and tissue regeneration in tendons. Another study found no evidence that SWT was useful in treating chronic pain in the Achilles tendon.
The future of non-surgical care for tendinosis is likely bioengineering. Ligament reconstruction is possible using mesenchymal stem cells and a silk scaffold. These same stem cells were capable of seeding repair of damaged animal tendons. Autologous tenocyte implantation is currently being tested for tendinosis. There is a large randomized, double-blind, placebo controlled trial being conducted in the Netherlands to test the safety and efficacy of tenocyte therapy. Results from the trial are expected by April 2013.
In other animals
Mesenchymal stem cells, derived from a horse's bone marrow or fat, are currently being used for tendon repair in horses.  Bowed tendon is a horseman's term for tendinitis (inflammation) and tendinosis (degeneration), most commonly seen in the superficial digital flexor tendon (SDFT) in the front leg.
- Murrell GA (December 2002). "Understanding tendinopathies". Br J Sports Med 36 (6): 392–3. doi:10.1136/bjsm.36.6.392. PMC 1724561. PMID 12453831.
- Fu SC, Rolf C, Cheuk YC, Lui PP, Chan KM (2010). "Deciphering the pathogenesis of tendinopathy: a three-stages process.". Sports Med Arthrosc Rehabil Ther Technol 2: 30. doi:10.1186/1758-2555-2-30. PMC 3006368. PMID 21144004.
- Khan, K.M.; Cook, J.L., Kannus, P., Maffulli, N., Bonar, S.F. (2002-03-16). "Time to abandon the "tendinitis" myth : Painful, overuse tendon conditions have a non-inflammatory pathology". British Medical Journal 324 (7338): 626–7. doi:10.1136/bmj.324.7338.626. PMC 1122566. PMID 11895810. Retrieved 2007-04-02.
- Marsolais D, Duchesne E, Côté CH, Frenette J. (2007). "Inflammatory cells do not decrease the ultimate tensile strength of intact tendons in vivo and in vitro: protective role of mechanical loading". J Appl Physiol 102 (1): 3–4. doi:10.1152/japplphysiol.00162.2006. PMID 16916923.
- Wilson, J.J.; Best, T.M. (2005). "Common overuse tendon problems: A review and recommendations for treatment" (PDF). American Family Physician (American Academy of Family Physicians.) 72 (5): 811–8. PMID 16156339. Archived from the original on 2007-09-29. Retrieved 2007-04-02.
- David J. Magee, James E. Zachazewski, William S. Quillen Pathology and intervention in musculoskeletal rehabilitation
- Rompe JD, Nafe B, Furia JP, Maffulli N (2007). "Eccentric loading, shock-wave treatment, or a wait-and-see policy for tendinopathy of the main body of tendo Achillis: a randomized controlled trial". Am J Sports Med 3 (35): 374–83. doi:10.1177/0363546506295940. PMID 17244902.
- Gonzalez, Santander R; Plasencia Arriba MA, Martinez Cuadrado G, Gonzalez-Santander Martinez M & Monteagudo de la Rosa M. (1996). "Effects of "in situ" vitamin E on fibroblast differentiation and on collagen fibril development in the regenerating tendon". The International Journal of Developmental Biology (University Of The Basque Country Press) 1 (Supplemental): 181–2. PMID 9087752.
- Plasencia., M.A.; Ortiz C., Vazquez B., San Roman J., Lopez-Bravo A., Lopez-Alonso A. (1999). "Resorbable polyacrylic hydrogels derived from vitamin E and their application in the healing of tendons". Journal of Materials Science. Materials in Medicine (Kluwer Academic Publishers) 10 (10/11): 641–8. doi:10.1023/A:1008991825657. PMID 15347979.
- Xia, W.; Szomor Z., Wang Y. & Murrell G.A. (2006). "Nitric oxide enhances collagen synthesis in cultured human tendon cells". Journal of Orthopaedic Research (Wiley) 24 (2): 159–72. doi:10.1002/jor.20060. PMID 16435353.
- Darmani, H.; Crossan J.C. & Curtis A. (2004). "Single dose of inducible nitric oxide synthase inhibitor induces prolonged inflammatory cell accumulation and fibrosis around injured tendon and synovium". Mediators of Inflammation (Hindawi Pub. Corp.) 13 (3): 157–64. doi:10.1080/09511920410001713556. PMC 1781556. PMID 15223606.
- Murrell GA. (2007). "Using nitric oxide to treat tendinopathy". Br J Sports Med 41 (4): 227–31. doi:10.1136/bjsm.2006.034447. PMC 2658939. PMID 17289859.
- Craig J. Davidson et. al., "Rat tendon morphologic and functional changes resulting from soft tissue mobilization", Medicine & Science in Sports & Exercise, Mar. 1997, Vol. 29, No. 3, pp. 313-319.
- Gale M. Gehlsen, "Fibroblast responses to variation in soft tissue mobilization pressure", Medicine & Science in Sports & Exercise, Apr. 1999, Vol. 31, No. 4, pp. 531-535.
- Thomas J. Melham et. al., "Chronic ankle pain and fibrosis successfully treated with a new noninvasive augmented soft tissue mobilization technique (ASTM): a case report", Medicine & Science in Sports & Exercise, Jun. 1998, Vol. 30, No. 6, pp. 801-804.
- Alfredson Tom , MD, Håkan; Pietilä, T., Jonsson, P. & Lorentzon, R. (1998). "Heavy-Load Eccentric Calf Muscle Training For the Treatment of Chronic Achilles Tendinosis". The American Journal of Sports Medicine (American Orthopaedic Society for Sports Medicine) 26 (3): 360–6. PMID 9617396. Retrieved 2007-04-02.
- Mafi, N.; Lorentzon R. & Alfredson H. (2001). "Superior short-term results with eccentric calf muscle training compared to concentric training in a randomized prospective multicenter study on patients with chronic Achilles tendinosis". Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA (Springer International) 9 (1): 42–7. doi:10.1007/s001670000148. PMID 11269583.
- Fahlstrom ., M.; Jonsson P., Lorentzon R. & Alfredson H. (2003). "Chronic Achilles tendon pain treated with eccentric calf-muscle training". Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA (Springer International) 11 (5): 327–33. doi:10.1007/s00167-003-0418-z. PMID 12942235.
- Roos, E.M.; Engstrom M., Lagerquist A. & Soderberg B. (2004). "Clinical improvement after 6 weeks of eccentric exercise in patients with mid-portion Achilles tendinopathy -- a randomized trial with 1-year follow-up". Scandinavian Journal of Medicine & Science in Sports (Munksgaard International Publishers) 14 (5): 286–95. doi:10.1111/j.1600-0838.2004.378.x. PMID 15387802.
- Öhberg, L.; Lorentzon R. & Alfredson H. (2004). "Eccentric training in patients with chronic Achilles tendinosis: normalised tendon structure and decreased thickness at follow up". British Journal of Sports Medicine (BMJ Publishing Group Ltd.) 38 (1): 8–11. doi:10.1136/bjsm.2001.000284. PMC 1724744. PMID 14751936.
- Jonsson, P.; Alfredson H. (2005). "Superior results with eccentric compared to concentric quadriceps training in patients with jumper's knee: a prospective randomised study". British journal of sports medicine (BMJ Publishing Group) 39 (11): 847–50. doi:10.1136/bjsm.2005.018630. PMC 1725058. PMID 16244196.
- Rees, J.D.; Wilson A.M. & Wolman R.L. (2006). "Current concepts in the management of tendon disorders". Rheumatology (Oxford University Press) 45 (5): 508–21. doi:10.1093/rheumatology/kel046. PMID 16490749.
- Petersen W, Welp R, Rosenbaum D (June 14, 2007). "Chronic Achilles Tendinopathy: A Prospective Randomized Study Comparing the Therapeutic Effect of Eccentric Training, the AirHeel Brace, and a Combination of Both". Am J Sports Med 35 (10): 1659–67. doi:10.1177/0363546507303558. PMID 17569792.
- Cacchio A, Paoloni M, Barile A, Don R, de Paulis F, Calvisi V, Ranavolo A, Frascarelli M, Santilli V, Spacca G (2006). "Effectiveness of radial shock-wave therapy for calcific tendinosis of the shoulder: single-blind, randomized clinical study". Phys Ther 5 (86): 672–82. PMID 16649891.
- Chen YJ, Wang CJ, Yang KD, Kuo YR, Huang HC, Huang YT, Sun YC, Wang FS (2004). "Extracorporeal shock waves promote healing of collagenase-induced Achilles tendinosis and increase TGF-beta1 and IGF-I expression". J Orthop Res 22 (4): 854–61. doi:10.1016/j.orthres.2003.10.013. PMID 15183445.
- Costa ML, Shepstone L, Donell ST, Thomas TL (2005). "Shock wave therapy for chronic Achilles tendon pain: a randomized placebo-controlled trial". Clin Orthop Relat Res 440: 199–204. doi:10.1097/01.blo.0000180451.03425.48. PMID 16239807.
- Fan H, Liu H, Wong EJ, Toh SL, Goh JC (August 2008). "In vivo study of anterior cruciate ligament regeneration using mesenchymal stem cells and silk scaffold". Biomaterials 29 (23): 3324–37. doi:10.1016/j.biomaterials.2008.04.012. PMID 18462787.
- Long JH, Qi M, Huang XY, Lei SR, Ren LC (June 2005). "[Repair of rabbit tendon by autologous bone marrow mesenchymal stem cells]". Zhonghua Shao Shang Za Zhi (in Chinese) 21 (3): 210–2. PMID 15996290.
- Koch TG, Berg LC, Betts DH (2009). "Current and future regenerative medicine - principles, concepts, and therapeutic use of stem cell therapy and tissue engineering in equine medicine.". Can Vet J 50 (2): 155–65. PMC 2629419. PMID 19412395.