Current trends in tendinopathy: consensus of the ESSKA basic science committee. Part II: treatment options.

The treatment of painful chronic tendinopathy is challenging. Multiple non-invasive and tendon-invasive methods are used. When traditional non-invasive treatments fail, the injections of platelet-rich plasma autologous blood or cortisone have become increasingly favored. However, there is little scientific evidence from human studies supporting injection treatment. As the last resort, intra- or peritendinous open or endoscopic surgery are employed even though these also show varying results. This ESSKA basic science committee current concepts review follows the first part on the biology, biomechanics and anatomy of tendinopathies, to provide a comprehensive overview of the latest treatment options for tendinopathy as reported in the literature.

Apolipoprotein A1 distribution pattern in the human Achilles tendon.

Metabolic factors such as cholesterol appear to play an important role in the development of Achilles tendinopathy. There is, however, no morphologic proof explaining the link between high cholesterol and tendinopathy. As apolipoprotein A1 (Apo-A1) is essential for reverse cholesterol transport, it may be related to cholesterol overload in tendon. Nothing is known about Apo-A1 expression in tendon tissue. We examined the distribution of Apo-A1 protein in biopsies from normal and tendinopathy-affected human Achilles tendons, and APOA1 mRNA production from cultured human hamstring tenocytes. Specific immunoreactions for Apo-A1 were detected. The tenocytes showed specific Apo-A1 immunoreactions. These reactions were usually distinct in the tendinopathy specimens. While the tendinopathy specimens often showed granular/small deposit reactions, the slender tenocytes of control specimens did not show this pattern. The magnitude of Apo-A1 immunoreactivity was especially marked in the tendinopathy specimens, as there is a high number of tenocytes. Reactions were also seen in the walls of blood vessels located within the tendon tissue proper of both the normal and tendinopathy tendons and within the peritendinous/fatty tissue of the tendinopathy tendons. The reactions were predominantly in the form of deposit reactions within the smooth muscle layer of the vessel walls. Cultured hamstring tenocytes produced APOA1 mRNA. We demonstrated the presence of Apo-A1 in human tendon tissue. This suggests there may be a link between Achilles tendinopathy and cholesterol metabolism. We hypothesize that Apo-A1 may be important for tenocyte and blood vessel function within tendons.

Marked expression of TNF receptors in human peritendinous tissues including in nerve fascicles with axonal damage - Studies on tendinopathy and tennis elbow.

BACKGROUND: The peritendinous connective tissues can have importance in chronic tendon pain. Recently cytokine TNF-α has been suggested to be involved in tendinopathic processes. It is not known how TNF-α and its receptors TNFR1 and TNFR2 are expressed in peritendinous tissues. METHODS: The objective for this study was to immunohistochemically evaluate the expression patterns of these in the peritendinous tissue located between the plantaris and Achilles tendons and the one located superficially to the extensor origin at the elbow region for patients with tendinopathy/tennis elbow. RESULTS: The nerve fascicles were of two types, one type being homogenously stained for the nerve markers ßIII-tubulin and neurofilament and the other showing deficits for these suggesting features of axonal damage. Much more distinct TNFR1/TNFR2 immunoreactions were seen for the latter nerve fascicles. TNFR1 was seen in axons, TNFR2 mainly in Schwann cells. TNFR1 and particularly TNFR2 were seen in walls of parts of blood vessels. The dispersed cells showed frequently TNFR1 and TNFR2 immunoreactivity. DISCUSSION: These findings suggest that TNF-α can be related to degenerative events but also attempts for healing concerning the nerve structures. The marked expression of the TNF-α system in the peritendinous tissue suggests an impact of TNF-α in tendinopathy/tennis elbow.

Richly innervated soft tissues covering the superficial aspect of the extensor origin in patients with chronic painful tennis elbow - Implication for treatment?

BACKGROUND: Tennis elbow is difficult to treat. The results of surgical treatments are not convincing. Treatment studies on Achilles and patellar tendinopathy targeting the richly innervated and vascularized soft tissues outside the tendon have shown promising outcomes. The innervation patterns in the fibrous/fatty tissues superficially to the elbow extensor origin have not been clarified. METHODS: Nine tissue specimens from the fibrous/fatty tissue covering the extensor origin was taken from seven patients (mean age: 45 years) undergoing surgical treatment for chronic painful tennis elbow. The specimens were stained for morphology (haematoxylin and eosin, H and E) and immunohistochemically for general nerve marker protein gene product 9.5 (PGP 9.5) and markers for sympathetic (tyrosine hydroxylase, TH) and sensory nerve fibres (calcitonin gene-related peptide, CGRP). RESULTS: All specimens contained multiple blood vessels and nerve structures indicated by morphology and immunoreactions. There was a frequent occurrence of TH reactions, especially peri-vascularly, but also in nerve fascicles. Immunoreactions for CGRP were seen in nerve fascicles and isolated nerve fibres. CONCLUSION: The results provide new information on the innervation patterns of the superficial tissues of the extensor origin and their potential as source of tennis elbow pain. LEVEL OF EVIDENCE: IV.

Current trends in tendinopathy: consensus of the ESSKA basic science committee. Part I: biology, biomechanics, anatomy and an exercise-based approach.

Chronic tendinopathies represent a major problem in the clinical practice of sports orthopaedic surgeons, sports doctors and other health professionals involved in the treatment of athletes and patients that perform repetitive actions. The lack of consensus relative to the diagnostic tools and treatment modalities represents a management dilemma for these professionals. With this review, the purpose of the ESSKA Basic Science Committee is to establish guidelines for understanding, diagnosing and treating this complex pathology.

The plantaris tendon: a narrative review focusing on anatomical features and clinical importance.

In recent years, the plantaris tendon has been implicated in the development of chronic painful mid-portion Achilles tendinopathy. In some cases, a thickened plantaris tendon is closely associated with the Achilles tendon, and surgical excision of the plantaris tendon has been reported to be curative in patients who have not derived benefit following conservative treatment and surgical interventions. The aim of this review is to outline the basic aspects of, and the recent research findings, related to the plantaris tendon, covering anatomical and clinical studies including those dealing with histology, imaging and treatment. Cite this article: Bone Joint J 2016;98-B:1312-19.

Marked innervation but also signs of nerve degeneration in between the Achilles and plantaris tendons and presence of innervation within the plantaris tendon in midportion Achilles tendinopathy.

OBJECTIVES: The plantaris tendon is increasingly recognised as an important factor in midportion Achilles tendinopathy. Its innervation pattern is completely unknown. METHODS: Plantaris tendons (n=56) and associated peritendinous tissue from 46 patients with midportion Achilles tendinopathy and where the plantaris tendon was closely related to the Achilles tendon were evaluated. Morphological evaluations and stainings for nerve markers [general (PGP9.5), sensory (CGRP), sympathetic (TH)], glutamate NMDA receptor and Schwann cells (S-100ß) were made. RESULTS: A marked innervation, as evidenced by evaluation for PGP9.5 reactions, occurred in the peritendinous tissue located between the plantaris and Achilles tendons. It contained sensory and to some extent sympathetic and NMDAR1-positive axons. There was also an innervation in the zones of connective tissue within the plantaris tendons. Interestingly, some of the nerve fascicles showed a partial lack of axonal reactions. CONCLUSION: New information on the innervation patterns for the plantaris tendon in situations with midportion Achilles tendinopathy has here been obtained. The peritendinous tissue was found to be markedly innervated and there was also innervation within the plantaris tendon. Furthermore, axonal degeneration is likely to occur. Both features should be further taken into account when considering the relationship between the nervous system and tendinopathy.

Alpha-2 adrenergic stimulation triggers Achilles tenocyte hypercellularity: Comparison between two model systems.

The histopathology of tendons with painful tendinopathy is often tendinosis, a fibrosis-like condition of unclear pathogenesis characterized by tissue changes including hypercellularity. The primary tendon cells (tenocytes) have been shown to express adrenoreceptors (mainly alpha-2A) as well as markers of catecholamine production, particularly in tendinosis. It is known that adrenergic stimulation can induce proliferation in other cells. The present study investigated the effects of an exogenously administered alpha-2 adrenergic agonist in an established in vivo Achilles tendinosis model (rabbit) and also in an in vitro human tendon cell culture model. The catecholamine producing enzyme tyrosine hydroxylase and the alpha-2A-adrenoreceptor (α2A AR) were expressed by tenocytes, and alpha-2 adrenergic stimulation had a proliferative effect on these cells, in both models. The proliferation was inhibited by administration of an α2A AR antagonist, and the in vitro model further showed that the proliferative alpha-2A effect was mediated via a mitogenic cell signaling pathway involving phosphorylation of extracellular-signal-regulated kinases 1 and 2. The results indicate that catecholamines produced by tenocytes in tendinosis might contribute to the proliferative nature of the pathology through stimulation of the α2A AR, pointing to a novel target for future therapies. The study furthermore shows that animal models are not necessarily required for all aspects of this research.

Physical activity level in Achilles tendinosis is associated with blood levels of pain-related factors: a pilot study.

Physical activity affects the pain symptoms for Achilles tendinosis patients. Brain-derived neurotrophic factor (BDNF), tumor necrosis factor-alpha (TNF-α) and their receptors have been detected in human Achilles tendon. This pilot study aimed to compare serum BDNF and soluble tumor necrosis factor receptor I (sTNFRI) levels in Achilles tendinosis patients and healthy controls and to examine the influence of physical activity, and BMI and gender, on these levels. Physical activity was measured with a validated questionnaire, total physical activity being the parameter analyzed. Physical activity was strongly correlated with BDNF among tendinosis women [Spearman's rho (ρ)=0.90, P<0.01] but not among control women (ρ=-0.08, P=0.83), or among tendinosis and control men. Physical activity was significantly correlated with sTNFRI in the entire tendinosis group and among tendinosis men (ρ=0.65, P=0.01), but not in the entire control group or among control men (ρ=0.04, P=0.91). Thus, the physical activity pattern is related to the TNF and BDNF systems for tendinosis patients but not controls, the relationship being gender dependent. This is new information concerning the relationship between physical activity and Achilles tendinosis, which may be related to pain for the patients. This aspect should be further evaluated using larger patient materials.

Ultrasound and Doppler findings in the Achilles tendon among middle-aged recreational floor-ball players in direct relation to a match.

OBJECTIVE: In this study, structure, blood flow and thickness in the Achilles tendon related to tendon-loading activity were investigated. DESIGN: Examination by ultrasound (US) and colour Doppler (CD) immediately before and after 1 h of floor-ball matchplay. SETTING: Sports Medicine Unit, Umeå University, Sweden. PARTICIPANTS: 36 Achilles tendons in 18 middle-aged (mean 39 years) recreational male floor-ball players. MAIN OUTCOME MEASUREMENTS: Structure and high blood flow (HBF)/neovessels (NV) in the tendons were registered. Tendon thickness was measured 3 and 4.5 cm above the upper calcaneus and at the thickest part of the tendon. RESULTS: The US examination showed that 11/36 tendons (30.5%) in nine individuals had structural changes before and after the floor-ball match. In 7/36 tendons (five with structural changes), there were HBF/NV before, and after, the match. In six of these seven tendons, the blood flow was higher after than before the match. In three more tendons (two with structural changes), there were HBF/NV after, but not before, the match. After the match, mean tendon thickness had decreased significantly in both normal tendons and tendons with structural changes at the 3-cm level (6.0 (1.0) mm to 5.8 (0.9) mm; p<0.019), at the 4.5-cm level (5.7 (1.1) mm to 5.5 (1.0) mm; p<0.044), and at the thickest part (6.6 (1.1) mm to 6.3 (1.2) mm; p<0.000). CONCLUSIONS: In about 1/3 of the tendons, there were structural changes, about half of those tendons also had HBF/NV, which was higher after, than before, the match. Mean tendon thickness in both normal tendons and tendons with structural changes had decreased significantly after a 1-h floor-ball match.

A two-year sonographic follow-up after intratendinous injection therapy in patients with tennis elbow.

BACKGROUND: Tennis elbow is a tendinopathy affecting the upper extremity. Recent studies have shown high sensitivity for ultrasound (US) examination and high specificity for colour Doppler (CD) examination. There are no mid- or long-term follow-up investigations of the tendon structure and blood flow using these techniques. OBJECTIVE: To use US and CD to study structure and blood flow in the extensor origin in patients with tennis elbow treated with intratendinous injections. DESIGN: Follow-up study. SETTING: Sports Medicine Unit, Umeå University. PATIENTS: 25 patients (28 elbows), mean age 46 years (range 27-66), treated with intratendinous injections due to chronic pain from tennis elbow. METHOD: US and CD examination of the extensor origin was carried out at inclusion and at follow-up two years after intratendinous injection treatment with polidocanol and/or a local anaesthetic. MAIN OUTCOME MEASUREMENTS: US (structure) and CD (blood flow) findings. RESULTS: All patients had structural tendon changes and high blood flow at inclusion when given the injection treatment. At the two-year follow-up, structural tendon changes were seen in 20/28 elbows and high blood flow was seen in 4/28 elbows. The majority of patients with a good clinical result after treatment had no visible blood flow (17/20), but the structural changes showed no relation to a good result (13/20 remaining changes). CONCLUSIONS: Doppler findings, but not structure, might be related to the clinical result after intratendinous injection treatment of tennis elbow.

Presence of the neuropeptide Y1 receptor in tenocytes and blood vessel walls in the human Achilles tendon.

BACKGROUND: Questions remain concerning the mechanisms of the development of chronic pain and impaired function of tendons (tendinosis). Aspects known to occur are cell proliferation, angiogenesis and altered blood flow regulation. Neuropeptide Y (NPY) is widely distributed in the body and has powerful effects in relation to these processes. NPY has its effects via the G-protein-coupled Y receptors. There is no information concerning the presence or absence of NPY receptors in Achilles tendons or other tendons. OBJECTIVE: To clarify the expression patterns of the NPY receptors Y1 and Y2 in normal and tendinosis Achilles tendons of humans. METHODS: Immunohistochemical methods were used. Examination on NPY was carried out in parallel. RESULTS: The tenocytes showed strong immunoreactions for the Y1 receptor. The immunoreactions were more intense in the tenocytes of tendinosis tendons than in non-tendinosis tendons. The rounded/oval tenocytes typically seen in tendinosis tendons exhibited marked Y1 receptor reactions on their exterior. Pronounced Y1 reactions were seen in the smooth muscle of the arterioles of both tendinosis and non-tendinosis tendons. No reactions for the Y2 receptor were noted. NPY was detected in nerve fascicles and in perivascular innervation. CONCLUSIONS: This study shows that there is a morphological correlate for the occurrence of pronounced NPY effects via the Y1 receptor in both tenocytes, especially for tendinosis tendons, and blood vessel walls in the Achilles tendon. The findings are of particular interest as NPY is known to have proliferative, angiogenic and blood vessel-regulating effects. The effects of targeting the Y1 receptor in tendinosis is an interesting task to be evaluated further.

Immunohistochemical evidence of local production of catecholamines in cells of the muscle origins at the lateral and medial humeral epicondyles: of importance for the development of tennis and golfer's elbow?

BACKGROUND: Tennis elbow (TE) is a painful condition affecting the common extensor origin at the lateral humeral epicondyle. Colour Doppler examination has shown increased blood flow at this site and the sensory, and sympathetic innervation patterns have been delineated. However, it is not known whether there is local production of catecholamines and/or acetylcholine in this tissue, which is the case in patellar and Achilles tendinopathies. OBJECTIVE: To investigate the possible presence of local production of catecholamines and acetylcholine in non-neuronal cells (fibroblasts) in connective tissue at the muscle origin at the lateral humeral epicondyle in patients with TE. DESIGN: Immunohistochemical studies were performed on biopsies taken from the extensor origin in patients with TE and in pain-free controls. For reference purpose, biopsies from the flexor origin in patients with golfer's elbow (GE) were also studied. PATIENTS: Seven patients with TE and four patients with GE. Six healthy asymptomatic individuals served as controls. METHOD: Immunohistochemistry, using antibodies detecting synthesising enzymes for catecholamines (tyrosine hydroxylase; TH) and acetylcholine (choline acetyltransferase; ChAT). RESULTS: TH-like immunohistochemical reactions were seen in fibroblasts in four of the seven patients with TE and two of the four patients with GE. No such reactions were detected in controls (0/6). No ChAT reactions were seen in any of the investigated specimens. CONCLUSIONS: There is evidence of local, non-neuronal production of catecholamines, but not acetylcholine, in fibroblasts in the tissue at the muscle origin at the lateral and medial epicondyles in patients with TE and GE, respectively, which might have an influence on blood vessel regulation and pain mechanisms in these conditions.

No normalisation of the tendon structure and thickness after intratendinous surgery for chronic painful midportion Achilles tendinosis.

OBJECTIVE: To characterise Achilles tendon structure and thickness a minimum of 8 years after intratendinous surgery. MATERIAL AND METHODS: Fourteen patients (16 tendons; nine men and five women, mean age 43 years, range 27-55) surgically treated (intratendinous surgery) for chronic painful midportion Achilles tendinosis, were followed with clinical examination and grey-scale ultrasonography for a minimum of 8 years (range 8-16, mean 13). RESULTS: All patients were satisfied with the result of surgery and were active in Achilles tendon loading activities without restrictions. In all operated tendons, structural abnormalities remained and tendons remained thicker than normal tendons. CONCLUSIONS: Resection of tendinosis is associated with persistent structural abnormalities and thickening of the tendon 13 years after surgery, despite successful clinical outcomes.

Pain relief after intratendinous injections in patients with tennis elbow: results of a randomised study.

BACKGROUND: "Tennis elbow" is a difficult condition to treat. Ultrasonography (US) and colour Doppler (CD) guided injections with polidocanol targeting the area with increased blood flow in the extensor origin have shown promising clinical results. OBJECTIVE: To evaluate and compare effects of US and CD guided intratendinous injections with sclerosing polidocanol and a local anaesthetic (lidocaine + epinephrine), in patients with tennis elbow. DESIGN: Prospective, randomised, controlled, double-blind, crossover study. SETTING: Sports Medicine Unit, Umeå University. PATIENTS: 32 patients (36 elbows), age range 27 to 66 years, with a long duration of elbow pain diagnosed as tennis elbow, were included in the study. All patients were followed up 3 and 12 months after treatment. Two patients were excluded due to other interventions during the study. INTERVENTIONS: One US and CD guided injection with the sclerosing agent polidocanol (group 1) or the local anaesthetic lidocaine plus epinephrine (group 2). At the 3 month follow-up, additional injections with polidocanol were offered to both groups (crossover for group 2). MAIN OUTCOME MEASURES: Satisfaction with treatment (Yes/No), elbow pain during activity (visual analogue scale), and maximum voluntary grip strength. RESULTS: There were no significant (p<0.05) differences in the outcome between group 1 and group 2. In both groups, there was a significantly lower VAS at the 3-month and 12-month follow-ups, and grip strength was significantly higher at the 12-month follow-up. CONCLUSIONS: US and CD guided intratendinous injections gave pain relief in patients with tennis elbow. Polidocanol and lidocaine plus epinephrine injections gave similar results.

New regimen for eccentric calf-muscle training in patients with chronic insertional Achilles tendinopathy: results of a pilot study.

BACKGROUND: Chronic painful insertional Achilles tendinopathy is seen in both physically active and non-active individuals. Painful eccentric training, where the patients load the Achilles tendon into full dorsiflexion, has shown good results in patients with mid-portion Achilles tendinosis. However, only 32% of patients with insertional Achilles tendinopathy had good clinical results with that type of eccentric training regimen. AIM: To investigate whether a new model of painful eccentric training had an effect on chronic painful insertional Achilles tendinopathy. PATIENTS AND METHODS: 27 patients (12 men, 15 women, mean age 53 years) with a total of 34 painful Achilles tendons with a long duration of pain (mean 26 months), diagnosed as insertional Achilles tendinopathy, were included. The patients performed a new model of painful eccentric training regimen without loading into dorsiflexion. This was done as 3x15 reps, twice a day, 7 days/week, for 12 weeks. Pain during Achilles-tendon-loading activity (VAS) and patient's satisfaction (back to previous activity) were evaluated. RESULTS: At follow-up (mean 4 months) 18 patients (67%, 23/34 tendons) were satisfied and back to their previous tendon-loading activity. Their mean VAS had decreased from 69.9 (SD 18.9) to 21 (SD 20.6) (p<0.001). Nine patients (11 tendons) were not satisfied with the treatment, although their VAS was significantly reduced from 77.5 (8.6) to 58.1 (14.8) (p<0.01). CONCLUSION: In this short-term pilot study this new model of painful eccentric calf-muscle training showed promising clinical results in 67% of the patients.

Sclerosing polidocanol injections of small vessels to treat the chronic painful tendon.

The chronic painful tendon (tendinopathy, tendinosis) is generally considered difficult to treat, not seldom causing long-term disability and sometimes ending the sports or work carreér. Most common sites for tendinopathy are the Achilles-, patellar-, extensor carpi radialis brevis (ERCB)-, and supraspinatus tendons. The origin of pain has for many years been unknown, but recently, by using ultrasound (US) + colour Doppler (CD), immunohistochemical analyses of tendon biopsies, and diagnostic injections of local anaestesia, we found a close relationship between areas with vasculo-neural ingrowth and tendon pain. Sensory nerves (Substance-P-SP and Calcitonin Gene Related Peptide-CGRP) were found inside and outside the vascular wall. In following clinical studies we have demonstrated good short-and mid-term clinical results using treatment with US+CD-guided sclerosing polidocanol injections, targeting the area with neovessels outside the tendon. Two-year follow ups have showed remaining good clinical results, and sonographically signs of remodelling with a significantly thinner tendon with a more normal structure. Whether the effects of polidocanol are mediated through destruction of neovessels, activity on nerves or a combination, is under evaluation.

Current physical activity is related to bone mineral density in males but not in females.

The purpose of the present study was to investigate the association between high-, medium-, and low-impact physical activity in males and females at the time of peak bone mineral density in young adulthood. The cohort consisted of 62 male medical students (aged 28.1 +/- 3.9) and 62 female medical students (aged 25.1 +/- 3.9). The bone mineral density (aBMD, g/cm (2)) of the total body, femoral neck, and lumbar spine, and the bone mineral content (BMC, grams) and area (cm (2)) of the femoral neck and lumbar spine was measured using dual energy X-ray absorptiometry. Volumetric BMD (vBMD, mg/cm (3)) of the femoral neck and lumbar spine was estimated. The total amount of physical activity per week, which was recorded in a questionnaire, was divided into high-impact, medium-impact, and low-impact activity. In the male cohort, hours of high-impact physical activity per week was associated with aBMD and BMC of all sites (r=0.27 - 0.53, p<0.05) and bone area of the femoral neck (r=0.38, p<0.01). Total amount of physical activity per week was associated with aBMD of the total body and femoral neck, BMC of femoral neck and lumbar spine, femoral neck vBMD, and the lumbar spine area (p<0.05 for all). Using multiple linear regression, high-impact physical activity was independently associated with aBMD (beta=0.27, p<0.05) and BMC (beta=0.34, p<0.01) of the femoral neck. In the female cohort there was no association between amount or type of physical activity to aBMD, BMC, vBMD, or the bone area of any site. Instead body weight, lean body mass, or fat mass were significantly related to aBMD and all BMC sites in this group. The results of the present study suggest that present physical activity level has a stronger relation to different aspects of bone mass in the male compared to the female adult skeleton.

Superior results with eccentric compared to concentric quadriceps training in patients with jumper's knee: a prospective randomised study.

BACKGROUND: A recent study reported promising clinical results using eccentric quadriceps training on a decline board to treat jumper's knee (patellar tendinosis). METHODS: In this prospective study, athletes (mean age 25 years) with jumper's knee were randomised to treatment with either painful eccentric or painful concentric quadriceps training on a decline board. Fifteen exercises were repeated three times, twice daily, 7 days/week, for 12 weeks. All patients ceased sporting activities for the first 6 weeks. Age, height, weight, and duration of symptoms were similar between groups. Visual analogue scales (VAS; patient estimation of pain during exercise) and Victorian Institute of Sport Assessment (VISA) scores, before and after treatment, and patient satisfaction, were used for evaluation. RESULTS: In the eccentric group, for 9/10 tendons patients were satisfied with treatment, VAS decreased from 73 to 23 (p<0.005), and VISA score increased from 41 to 83 (p<0.005). In the concentric group, for 9/9 tendons patients were not satisfied, and there were no significant differences in VAS (from 74 to 68, p<0.34) and VISA score (from 41 to 37, p<0.34). At follow up (mean 32.6 months), patients in the eccentric group were still satisfied and sports active, but all patients in the concentric group had been treated surgically or by sclerosing injections. CONCLUSIONS: In conclusion, eccentric, but not concentric, quadriceps training on a decline board, seems to reduce pain in jumper's knee. The study aimed to include 20 patients in each group, but was stopped at the half time control because of poor results achieved in the concentric group.