Percutaneous ultrasonic debridement of tendinopathy—a pilot Achilles rabbit model
© Kamineni et al.; licensee BioMed Central. 2015
Received: 16 December 2014
Accepted: 22 April 2015
Published: 20 May 2015
Tendinopathy is a common clinical pathology, with mixed treatment results, especially when chronic. In this study, we examine the effects of an ultrasonic debridement modality in a rabbit tendinopathy model.
We asked four questions: 1) Was it possible to create and visualize with ultrasound a tendinopathy lesion in a rabbit Achilles tendon? 2) Was it possible to guide a 19-gauge ultrasonic probe into the tendinopathy lesion? 3) Following ultrasonic treatment, was tendinopathy debris histologically present? and 4) Was the collagen profile qualitatively and quantitatively normalized following treatment?
Skeletally mature female New Zealand white rabbits (n = 12) were injected with, ultrasonography localization, 0.150 ml of collagenase into the Achilles tendon. The collagenase-induced Achilles tendinopathy (3 weeks) was treated with percutaneous ultrasonic debridement. The tendons were harvested, at 3 weeks after treatment, and were subjected to histological assessment (modified Movin score) and biochemical analysis (collagen isoform content).
Histopathological examination revealed that all tendons injected with collagenase showed areas of hypercellularity and focal areas of tendon disorganization and degeneration. The treated tendons had lower (improved) histopathological scores than injured tendons (P < 0.001). Western blot analysis showed that ultrasonic therapy restored, within statistical limits, collagen type I, III, and X expressions in a treated tendon, to qualitative and semi-quantitative levels of a normal tendon.
We were successfully able to create a collagenase-injected tendinopathy lesion in a rabbit Achilles tendon and visualize the lesion with an ultrasound probe. A 19-gauge ultrasonic probe was inserted into the tendinopathic lesion under direct ultrasound guidance, and minimal tendinopathic debris remained after treatment. The treated tendon demonstrated a normalized qualitative and semi-quantitative collagen profile and improved histological appearance in the short term. This technique demonstrates scientific merit with respect to the minimally invasive treatment of tendinopathy and warrants further studies.
Recalcitrant tendinopathy has evaded consistent non-operative treatment since the tendinopathic debris remains in situ, to some extent, with non-operative approaches. This percutaneous emulsification/evacuation approach, under direct ultrasound visualization, has the potential to cure recalcitrant tendinopathies without open surgery, which would benefit the patient and result in significant healthcare cost reductions.
KeywordsTendinopathy Animal model Ultrasonic treatment Collagen Histology Collagenase
Tendinopathy is a widespread cause of morbidity affecting virtually all joints. Although the etiology is imperfectly understood, the path physiology is one of the degeneration and necrosis at the pathological site . There are several treatment modalities currently used in clinical practice, including physical therapy, non-steroidal anti-inflammatories, and injections of corticosteroid and platelet-rich plasma (PRP) [2–4]. However, no universally accepted treatment is known to be completely safe and effective with a high degree of predictability.
In clinical situations, magnetic resonance imaging (MRI) and ultrasound scanning are commonly utilized to provide fine internal architectural details of symptomatic tendons, for diagnosis and evaluation of treatment . Typically, ultrasound imaging of tendons has recently become a first-line investigation as it is widely available, relatively inexpensive, and is easy to use. In order to understand tendon biology and mechanics in normal and injury situations, a mouse model is commonly used [6, 7]. However, the use of diagnostic and localizing ultrasonography is less straightforward with mice than with a larger animal model, and hence, we chose a validated Achilles tendinopathy rabbit model [8, 9]. Furthermore, our choice of treatment is based on the previously published clinical use of ultrasonic energy to treat lateral epicondylitis .
The primary aim of this study was to characterize the mechanism by which ultrasonic emulsification and aspiration mechanistically produces its effect in a collagen degradation model. Our pilot study aims were to create a collagen degradation/tendinopathy rabbit model from literature data, treat the lesion using an ultrasonic aspiration probe, and analyze the results with histology and semi-quantification of the collagen profile. This study is the first step in characterizing the usefulness of ultrasonic treatment in tendinopathies, in a limited pilot form.
Materials and methods
Scheme of injection regimen and treatment with Tenex probe in rabbits
Injected for (weeks)
Treated (weeks) retrieved [weeks]
Scoring of histological sections to assess cellularity, vascularity, and collagen fiber organization
Presence of flattened cells in a linear pattern between fibers
Some rounded cells present, slight increase in cellularity
Many rounded cells present, obvious increase in cellularity
Mostly rounded cells present, much higher numbers
Presence of some vascular bundles parallel to collagen fibers
Slight increase in number of vascular bundles
Increased number of vascular bundles
Large increase in number of vascular bundles
Parallel collagen fibers of similar widths
Some loss of fiber organization, some loss of linearity
Moderate loss of fiber organization, few linear regions
Total loss of organization, no linear fibers
Tendons used for protein analysis were immediately stored in dry ice and subsequently in a −80° freezer. The tissue was homogenized using a 15-fold excess of extraction buffer (20 mM Tris, pH 7.4, 150 mM NaCl, 1 mM EDTA, 2 % SDS) and protease inhibitor cocktail (COMPLETE, Roche). The homogenate was centrifuged at 13,200 rpm for 30 min, and the supernatant was collected at −80 °C (Thermo Scientific Forma, −86 °C ULT Freezer, USA). Total protein concentration in the samples was determined using the BCA protein assay kit (Pierce, Thermo Scientific, USA).
Western blot analysis
Protein levels for collagen types I, III, and X were assessed using western blot techniques. Aliquots of the protein samples were then boiled for 5 min in SDS sample buffer with 2-mercaptoethanol (Bio-Rad) as a reducing agent, and 10 μg of protein per lane was electrophoretically resolved on a 7 % SDS-PAGE and transferred to a nitrocellulose membrane (Pall, East Hill) using a semi-dry transfer cell apparatus (Trans-Blot SD, Bio-Rad, USA). Immunoblotting was done with anti-collagens I, III, and X antibodies (Abcam and Novus Biologicals, USA), used at 8 ng/ml for collagen I, 4 μg/ml for collagen III, and 500 ng/ml for collagen X. Calnexin in each sample was probed with rabbit anti-calnexin polyclonal antibody (2 μg/ml; Abcam, USA) as a loading control. Goat anti-rabbit IgG-perixodase (GE Healthcare, Piscataway, NJ, USA) was used as the secondary antibody at 1:8000 dilutions with ECL as the detection system (Fischer Scientific, USA). For each independent sample, immunoblotting was done in triplicate. For semi-quantification of western blot signals, the densities of specific antibodies and calnexin were measured with Image J (NIH, USA). The same-sized square was drawn around each band to measure the density, and background level near the band was subtracted from it. The levels of collagen subtype (I, III, and X) were normalized against calnexin levels.
The ratios of treated to non-treated tendons were calculated for comparison. Student t test was used for statistical analysis. The contralateral Achilles tendons of the same rabbit were compared using Microsoft Excel (Microsoft Corporation, Seattle, WA, USA). Significance was set at a P value less than 0.05. We treated the Movin score as a continuous variable and used the Mann-Whitney U test. The assessments were descriptive and not analyzed statistically.
Hematoxylin and eosin staining
Summary of pathologic scores of the control, injured, and treated tendons
Assessment of each variable
Fiber arrangement: In the control tendons, the fibers were linear and parallel to each other, while collagenase-treated tendons showed complete disruption of linear fiber architecture. The fiber orientation of the ultrasonic-treated tendons was heterogeneous, since the normal peripheral fibers appeared ordered and linear, while the newly laid down fibers from the evacuation cavity were less ordered. The median for the control tendons was 0, injured tendons was 3 (group I), and for the ultrasonic-treated tendons was 1.5 (group II).
The randomly assigned four quadrants chosen for fiber orientation were analyzed for cellularity. Cellularity, based on nuclear staining, was observed to be dramatically increased (3/3) in the collagenase-treated group and increased (2/3) in the ultrasonic-treated group and normal in the controls (0/3).
Vascular bundles usually run parallel alongside the collagen fibers. The number of these vascular bundles increased with degeneration of the tendon. The median for the control tendon was 0, for the injured tendons was 3, and for the treated tendons was 1.5.
Western blot analyses
Our results corroborate the use of collagenase to effectively induce a tendinopathic lesion in the Achilles tendon of rabbits, although we wholly understand that there are several other models that produce more physiological tendinopathies. This finding agrees with other studies on tissue repair in the rabbit and with reports on the treatment of tendinopathy [8, 20, 22]. To our knowledge, a study applying ultrasonic therapy to animal model-based tendinopathic tissues has not been reported previously.
The Movin scoring system was used to classify the histopathological findings of the tendinopathy . The assessment system used was semi-quantitative. We are conscious of the limitations of this assessment system, as we categorized in four classes (from 0, normal, to 3, markedly abnormal); a qualitative evaluation of several aspects of the histopathological appearance of the tendon section was examined. It is likely that the fully automated image analysis systems used in other fields of musculoskeletal medicine will be useful in this field in the future and thus allow a more objective quantification of the abnormal appearance of tendinopathic tendons. The Movin score is based on semi-quantitative criteria to assess the changes associated with the process of tendinopathy on a four-point scale ranging from 0 to 3 . This scale was originally developed for the Achilles tendon (Movin) and the patellar tendon, and to assess the degree of tendinopathy in the rotator cuff and the long head of the biceps tendon [23–26]. In this study, we used a modified Movin score, which describes the tendinopathy of the Achilles tendon.
Fibroblasts were well aligned within the tightly packed and longitudinally arranged collagen fibrils in the normal tendon (Fig. 3a). Six weeks after collagenase injection, the tendons showed more immature fibroblast and mononuclear cell infiltration and a significantly disorganized pattern of collagen fibers. The ultrasonic-treated group at 3 weeks demonstrated a greater amount of mature and immature fibroblasts, less mononuclear cell infiltration, and a better-aligned pattern of collagen fibers, indicating that the tissue was regenerating (Fig. 3c).
The tendons themselves are composed of longitudinally arranged bundles of fibers; blood supply to tendons is poor compared to muscles and other tissues [27, 28]. The neovascularization, histologically demonstrated, leads to an improved blood supply and certainly plays a role in the tissue regeneration.
In this study, there were differences seen between the control, injured, and treated groups, in vascularity, collagen density, and collagen fiber organization (Fig. 3), results of which are in agreement with previous published studies [29, 30].
In accordance with other studies, the proportion of type III collagen was increased in specimens of ruptured Achilles tendon . Type III collagen is a major fibril collagen in compliant tissues such as skin and blood vessels and is normally only found in small quantities of normal tendons . Maffulli et al. reported greater amounts of type III collagen in ruptured and tendinopathic Achilles tendons compared to normal human Achilles tendons . The results from this current study are twofold, in that a massive increase in collagen II following collagenase treatment may demonstrate a greater fragment availability for western blot analysis, while a true up-regulation of 25 % was present at 3 weeks after ultrasonic treatment. The latter result corroborates those previous studies, reinforcing the role of collagen III as an important early stabilizer of a repairing/regenerating tendon [25–27].
Recently, some researchers have mentioned the abundance and ratio of type I and type III collagens [34, 35]. The change of the collagens I to III ratio after administration of reagents and after tendon rupture was highlighted. Thomopoulos et al. studied, a canine model, the effects of exogenous basic fibroblast growth factor on intra-synovial flexor tendon healing . Tendons that were treated with basic fibroblast growth factor had a lower ratio of type I collagen to type III collagen from DNA concentration. This indicated increased scar formation due to the growth factor. Otoshi et al. studied the process of tendon regeneration in an Achilles tendon resection rat model as a model for hamstring regeneration after harvesting for anterior cruciate ligament reconstruction . Using immunohistochemistry, the type I–type III collagen ratio in the regenerate tendon was significantly decreased in the early phase but gradually increased with time. The increase in type III collagen expression would have an influence on the inferior mechanical properties of the immature regenerate tendon. In our study, based on the percentage increase from a control starting point, there was a relative up-regulation of collagen III (25 %) compared to collagen I (16 %), further demonstrating an immature collagen ratio for the regenerating tendon.
In this study, it is interesting to note that collagen X is expressed and mildly up-regulated in the 3-week regenerating tendon. There might be morphological changes similar to tendon insertion, spur formation, intra-tendinous calcification, and fibro-cartilaginous zone [36, 37]. We hypothesized that this cartilage-specific collagen would be similar between the groups, but in the collagenase-treated group, the expression of type X collagen was significantly decreased, as compared to the treated groups. This effect may result from the non-specific collagenase destruction of this protein or a secondary loss due to collagen I disintegration.
Several limitations are recognized with this current study. Although validated, the collagenase-induced tendinopathy model may not truly represent an in-vivo chronic tendinopathy, with several other mechanically induced tendinopathy models available, and as mentioned previously. However, we recognize that all such models have limitations. Secondly, the follow-up time frame after treatment was insufficient to demonstrate a full restoration of the tendon, which will be the subject of future, longer term studies, as well as investigating the effect in different models of tendinopathy. Group 0 consisted of two specimens (to confirm the development of a tendinopathic lesion) compared to four specimens in groups I + II, and while this should be noted, future studies will aim to have equal numbers in all groups. Finally, our power analysis indicated that we needed four specimens per experimental group, but since there was a learning curve involved in the use of the ultrasonic probe, we decided to double the number in group II. This can be viewed as a deviation from an experimental protocol, and future experiments should utilize the same specimen numbers in all groups.
Two major effects of ultrasonic emulsification and evacuation treatment of a tendinopathic lesion have been identified. Firstly, the treatment results in the removal of pathological degenerate tendon material leaving a debris-free space that becomes filled with cells involved in tendon regeneration. Secondly, the qualitative collagen profile of the tendon is returned to a more normal state. Longer term studies are required to better elucidate the potential for complete tendon healing.
- Maffulli N, Barrass V, Ewen SW. Light microscopic histology of Achilles tendon ruptures. A comparison with unruptured tendons. Am J Sports Med. 2000;28(6):857–63.PubMedGoogle Scholar
- van der Plas A, de Jonge S, de Vos RJ, van der Heide HJ, Verhaar JA, Weir A, et al. A 5-year follow-up study of Alfredson’s heel-drop exercise programme in chronic midportion Achilles tendinopathy. Br J Sports Med. 2012;46(3):214–8.View ArticlePubMed CentralPubMedGoogle Scholar
- Magra M, Maffulli N. Nonsteroidal anti-inflammatory drugs in tendinopathy: friend or foe. Clin J Sport Med. 2006;16(1):1–3.View ArticlePubMedGoogle Scholar
- Del Buono A, Papalia R, Denaro V, Maccauro G, Maffulli N. Platelet rich plasma and tendinopathy: state of the art. Int J Immunopathol Pharmacol. 2011;24(1 Suppl 2):79–83.PubMedGoogle Scholar
- Bodner G, Rudisch A, Gabl M, Judmaier W, Springer P, Klauser A. Diagnosis of digital flexor tendon annular pulley disruption: comparison of high frequency ultrasound and MRI. Ultraschall Med. 1999;20(4):131–6.View ArticlePubMedGoogle Scholar
- Pirog KA, Jaka O, Katakura Y, Meadows RS, Kadler KE, Boot-Handford RP, et al. A mouse model offers novel insights into the myopathy and tendinopathy often associated with pseudoachondroplasia and multiple epiphyseal dysplasia. Hum Mol Genet. 2010;19(1):52–64.View ArticlePubMed CentralPubMedGoogle Scholar
- Oliva F, Zocchi L, Codispoti A, Candi E, Celi M, Melino G, et al. Transglutaminases expression in human supraspinatus tendon ruptures and in mouse tendons. Biochem Biophys Res Commun. 2009;379(4):887–91.View ArticlePubMedGoogle Scholar
- Chang KV, Wu CH, Ding YH, Shen HY, Wang TG, Chen WS. Application of contrast-enhanced sonography with time-intensity curve analysis to explore hypervascularity in Achilles tendinopathy by using a rabbit model. J Ultrasound Med. 2012;31(5):737–46.PubMedGoogle Scholar
- Chen J, Yu Q, Wu B, Lin Z, Pavlos NJ, Xu J, et al. Autologous tenocyte therapy for experimental Achilles tendinopathy in a rabbit model. Tissue Eng Part A. 2011;17(15–16):2037–48.View ArticlePubMedGoogle Scholar
- Koh JS, Mohan PC, Howe TS, Lee BP, Chia SL, Yang Z, et al. Fasciotomy and surgical tenotomy for recalcitrant lateral elbow tendinopathy: early clinical experience with a novel device for minimally invasive percutaneous micro resection. Am J Sports Med. 2013;41(3):636–44.View ArticlePubMedGoogle Scholar
- Nakama LH, King KB, Abrahamsson S, Rempel DM. Evidence of tendon micro tears due to cyclical loading in an in vivo tendinopathy model. J Orthop Res. 2005;23(5):1199–205.View ArticlePubMedGoogle Scholar
- Maganaris CN, Narici MV, Almekinders LC, Maffulli N. Biomechanics and path physiology of overuse tendon injuries: ideas on insertional tendinopathy. Sports Med. 2004;34(14):1005–17.View ArticlePubMedGoogle Scholar
- Cook JL, Khan KM, Maffulli N, Purdam C. Overuse tendinosis, not tendinitis part 2: applying the new approach to patellar tendinopathy. Physician Sports Med. 2000;28(6):31–46.Google Scholar
- Sullo A, Maffulli N, Capasso G, Testa V. The effects of prolonged peritendinous administration of PGE1 to the rat Achilles tendon: a possible animal model of chronic Achilles tendinopathy. J Orthop Sci. 2001;6(4):349–57.View ArticlePubMedGoogle Scholar
- Dahlgren LA, van der Meulen MC, Bertram JE, Starrak GS, Nixon AJ. Insulin-like growth factor-I improves cellular and molecular aspects of healing in a collagenase-induced model of flexor tendinitis. J Orthop Res. 2002;20(5):910–9.View ArticlePubMedGoogle Scholar
- Doherty GP, Koike Y, Uhthoff HK, Lecompte M, Trudel G. Comparative anatomy of rabbit and human Achilles tendons with magnetic resonance and ultrasound imaging. Comp Med. 2006;56(1):68–74.PubMedGoogle Scholar
- Leadbetter WB. Cell-matrix response in tendon injury. Clin Sports Med. 1992;11(3):533–78.PubMedGoogle Scholar
- Khan KM, Cook JL, Bonar F, Harcourt P, Astrom M. Histopathology of common tendinopathies. Update Implications Clin Manag Sports Med. 1999;27(6):393–408.Google Scholar
- Williams IF, McCullagh KG, Goodship AE, Silver IA. Studies on the pathogenesis of equine tendonitis following collagenase injury. Res Vet Sci. 1984;36(3):326–38.PubMedGoogle Scholar
- Hsu RW, Hsu WH, Tai CL, Lee KF. Effect of hyperbaric oxygen therapy on patellar tendinopathy in a rabbit model. J Trauma. 2004;57(5):1060–4.View ArticlePubMedGoogle Scholar
- Maffulli N, Longo UG, Franceschi F, Rabitti C, Denaro V. Movin and Bonar scores assess the same characteristics of tendon histology. Clin Orthop Relat Res. 2008;466(7):1605–11.View ArticlePubMed CentralPubMedGoogle Scholar
- Chen YJ, Wang CJ, Yang KD, Kuo YR, Huang HC, Huang YT, et al. Extracorporeal shock waves promote healing of collagenase-induced Achilles tendinitis and increase TGF-beta1 and IGF-I expression. J Orthop Res. 2004;22(4):854–61.View ArticlePubMedGoogle Scholar
- Movin T, Gad A, Reinholt FP, Rolf C. Tendon pathology in long-standing achillodynia. Biopsy findings in 40 patients. Acta Orthop Scand. 1997;68(2):170–5.View ArticlePubMedGoogle Scholar
- Maffulli N, Testa V, Capasso G, Ewen SW, Sullo A, Benazzo F, et al. Similar histopathological picture in males with Achilles and patellar tendinopathy. Med Sci Sports Exerc. 2004;36(9):1470–5.View ArticlePubMedGoogle Scholar
- Longo UG, Franceschi F, Ruzzini L, Rabitti C, Morini S, Maffulli N, et al. Histopathology of the supraspinatus tendon in rotator cuff tears. Am J Sports Med. 2008;36(3):533–8.View ArticlePubMedGoogle Scholar
- Longo UG, Franceschi F, Ruzzini L, Rabitti C, Morini S, Maffulli N, et al. Characteristics at haematoxylin and eosin staining of ruptures of the long head of the biceps tendon. Brit J Sport Med. 2009;43(8):603–7.View ArticleGoogle Scholar
- Williams JG. Achilles tendon lesions in sport. Sports Med. 1993;16(3):216–20.View ArticlePubMedGoogle Scholar
- Williams JG. Achilles tendon lesions in sport. Sports Med. 1986;3(2):114–35.View ArticlePubMedGoogle Scholar
- Sasaki N, Shukunami N, Matsushima N, Izumi Y. Time-resolved X-ray diffraction from tendon collagen during creep using synchrotron radiation. J Biomech. 1999;32(3):285–92.View ArticlePubMedGoogle Scholar
- Dowling BA, Dart AJ. Mechanical and functional properties of the equine superficial digital flexor tendon. Vet J. 2005;170(2):184–92.View ArticlePubMedGoogle Scholar
- Jozsa L, Balint BJ, Reffy A, Demel Z. Fine structural alterations of collagen fibers in degenerative tendinopathy. Arch Orthop Trauma Surg. 1984;103(1):47–51.View ArticlePubMedGoogle Scholar
- Ayad S, Boot-Handford R, Humphries MJ, Kadler KE, Shuttleworth A. Collagen type III, in the extracellular matrix facts book: Elsevier Inc. Secondth ed. 1998. p. 51–3. ISBN: 978-0-12-068911-8.Google Scholar
- Maffulli N, Ewen SWB, Waterston SW, Reaper J, Barrass V. Tenocytes from ruptured and tendinopathic Achilles tendons produce greater quantities of type III collagen than tenocytes from normal Achilles tendons—an in vitro model of human tendon heating. Am J Sports Med. 2000;28(4):499–505.PubMedGoogle Scholar
- Otoshi K, Kikuchi S, Ohi G, Numazaki H, Sekiguchi M, Konno S. The process of tendon regeneration in an Achilles tendon resection rat model as a model for hamstring regeneration after harvesting for anterior cruciate ligament reconstruction. Arthrosc-J Arthrosc Relat Surg. 2011;27(2):218–27.View ArticleGoogle Scholar
- Thomopoulos S, Kim HM, Das R, Silva MJ, Sakiyama-Elbert S, Amiel D, et al. The effects of exogenous basic fibroblast growth factor on intrasynovial flexor tendon healing in a canine model. J Bone Joint Surg Am. 2010;92(13):2285–93.View ArticlePubMed CentralPubMedGoogle Scholar
- Fiamengo SA, Warren RF, Marshall JL, Vigorita VT, Hersh A. Posterior heel pain associated with a calcaneal step and Achilles tendon calcification. Clin Orthop Relat Res. 1982;167:203–11.PubMedGoogle Scholar
- Rufai A, Ralphs JR, Benjamin M. Structure and histopathology of the insertional region of the human Achilles tendon. J Orthop Res. 1995;13(4):585–93.View ArticlePubMedGoogle Scholar
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