Abstract
Study Design:
Single‐blind, randomized, clinical trial.
Background:
The effect of eccentric training for mid‐portion Achilles tendinopathy is well documented; however, its effect on insertional Achilles tendinopathy is inconclusive. The primary purpose of this study was to investigate the effect of eccentric training on pain and function for individuals with insertional Achilles tendinopathy.
Methods:
All patients received a 12‐week conventional strengthening protocol. Patients who were randomly assigned to the experimental group received additional eccentric exercises. Patients completed the Short Form‐36 Health and Bodily Pain Surveys, the Foot and Ankle Outcomes Questionnaire, and the Visual Analog Scale at initial evaluation, after 6 weeks of therapy, and at 12 weeks after therapy.
Results:
Thirty‐six patients (20 control and 16 experimental; average age 54 years; 72% women) completed the study. Both groups experienced statistically significant decreases in pain and improvements in function. No statistically significant differences were noted between the groups for any of the outcome measures.
Conclusion:
Conventional physical therapy consisting of gastrocnemius, soleus and hamstring stretches, ice massage on the Achilles tendon, and use of heel lifts and night splints with or without eccentric training is effective for treating insertional Achilles tendinopathy.
Level of Evidence:
Level 2
Keywords: Achilles tendinopathy, eccentric training, posterior heel pain
INTRODUCTION
Achilles tendinopathy is a prevalent overuse injury that usually presents between the ages of 30 and 60 years.1 In recent years, eccentric training has gained popularity as an effective intervention for Achilles tendinopathy.2‐7 However, clinical outcomes are reported to be more effective in persons with mid‐portion Achilles tendinopathy and less effective with insertional tendinopathy.8,9 Physical therapy and other conservative interventions for this condition have included activity modification (rest or cross training, such as cycling instead of running), cryotherapy, ultrasound, calf stretches, heel lifts, orthotics, and nonsteroidal anti‐inflammatory drugs (NSAIDs).10‐12 Prolonged stretching, in particular, has been found to decrease heel pain.13 There are surgical options, but they are costly and generally involve a lengthy recovery.3,14‐16
Although Achilles tendinopathy is common in athletes, particularly runners, the authors' clinical practice has noted a high incidence of insertional Achilles tendinopathy among patients with diverse levels of activity. Researchers have reported that eccentric training is less effective among persons with high body mass index (BMI), sedentary lifestyle, or female sex.9,17 The primary purpose of this study was to investigate the effect of eccentric training on pain and function for individuals with insertional Achilles tendinopathy. It was hypothesized that the addition of eccentric training to a conventional physical therapy program would be more effective than conventional physical therapy alone in regards to pain and function. A secondary purpose was to determine if BMI, activity level, and baseline dorsiflexion range of motion and gastrocnemius/soleus strength had any effect on results.
METHODS
Institutional Review Board Approval and Informed Consent
The institutional review board (IRB) of the University of Tennessee School of Medicine approved the study and experimental protocol. Informed consent was obtained from all patients before the study, and their rights were protected.
Study Design
This was a prospective, single‐blind, randomized study.
Inclusion and exclusion criteria
The sample population included patients who were referred for conventional physical therapy treatment for insertional Achilles tendinopathy that was diagnosed by orthopaedic foot and ankle surgeons per history and physical findings. Physical findings of Achilles tendinopathy included swelling, pain at the insertion of the Achilles tendon, and start‐up pain (pain upon first arising). Inclusion criteria were (1) symptoms present for at least 3 months and (2) age of at least 18 years. Patients were excluded if they had rheumatoid arthritis, generalized polyarthritis, Reiter syndrome, bleeding disorders, severe endocrine disease, tumor, local infection, advanced peripheral vascular disease, or if they were pregnant. In addition, they were not eligible for enrollment if they had previous Achilles tendon surgery, ankle arthrodesis, hindfoot fracture, or leg‐length discrepancy of more than one‐half inch. If a patient had symptoms in both Achilles tendons, only the tendon that the patient considered worse at the initial visit was followed in the study.
Randomization
In the physical therapy department, patients were randomly assigned to either a conventional physical therapy (control) protocol or conventional therapy with eccentric strengthening (experimental) protocol. The computer generated randomized identification numbers following a 4:4 assignment so that for every four patients randomized at each location, two would be in each group. A statistician not involved in patient care or data procurement randomized the assignments into envelopes with an identification number labeled on the outside, leaving the physical therapists blinded to the assignment. When a patient came for the initial physical therapy appointment, the physical therapist pulled an envelope with the next identification number to assign a protocol.
Intervention
All patients were seen for four visits: initial evaluation, 1 week later (week 2), week 4, and week 6 but were instructed to follow the home exercise program for a total of 12 weeks. The control protocol consisted of gastrocnemius, soleus, and hamstring stretches, ice massage on the Achilles tendon twice a day (5‐10 minutes), use of bilateral heel lifts, and a resting night splint. Patients were instructed to perform each stretch for three repetitions (30 seconds) twice daily (Figure 1 A‐D).13,18,19 The heel lifts were adjustable, starting at 3/8” and lowered 1/8” every 2 weeks until ultimately no heel lift remained.
Figure 1.
Conventional stretches for insertional Achilles tendinopathy. (A) Gastrocnemius stretch. With the knee straight and heel on the floor (involved foot back), the patient leans forward. (B) Soleus stretch. With the knee bent and the heel on the floor (involved foot back) the patient leans forward. (C) Hamstring and gastrocnemius stretch. Lying supine, the hands (or a towel) are placed around the posterior aspect of the knee. The knee is slowly straightened until a stretch is felt. Then, keeping this position the foot is pulled toward the face. (D) Sitting in an upright position with the involved knee straight, a towel is placed around the ball of the foot. Using both hands, the patient pulls the towel, bending the foot toward the face.
The patients in the experimental group followed everything in the control protocol with the addition of two eccentric strengthening exercises. In the first exercise, the patient stood bearing weight on the involved foot in plantarflexion with the knee slightly bent (Figure 2A); the patient then slowly lowered the heel into dorsiflexion to a count of five (Figure 2B). The other leg could be used to assist the patient in returning to plantarflexion. In the second exercise, the patient stood bearing weight on the involved foot in plantarflexion but with the knee straight on the stance leg. Again, the patient lowered the heel to a count of five into dorsiflexion (Figure 2C). If too weak to hold the single leg in plantarflexion, the patient stood with the heel off a step as high as possible (which might be neutral) and slowly lowered the heel to a count of five. Patients were instructed to perform both exercises in two sets of 15 repetitions, twice daily. The patients were instructed to add a weighted backpack if the exercises became easy to perform. This protocol was used to accommodate the tolerance level of patients with various levels of activity, including those participating in recreational sports or those who performed manual labor. No medication was prescribed for any patient.
Figure 2.
Eccentric training exercises. (A) First exercise. The patient stands bearing weight on the involved foot in plantarflexion and the knee slightly bent and slowly lowers the heel into dorsiflexion to a count of five (B). (C) Second exercise. The patient stands bearing weight on the involved foot in plantarflexion with the knee straight and lowers the heel to a count of five.
Data collection
Data were collected at four clinic locations of a private orthopaedic practice with physical therapists administering the intervention and physicians collecting most of the data. Trained foot and ankle orthopaedic surgeons blinded to which protocol was being followed made the initial diagnosis and collected the outcome measures at baseline, 6 weeks, and 12 weeks. Baseline data included age, sex, race, body mass index (BMI), presence or absence of calcification, symptoms, and activity levels. Physical therapists recorded ankle range of motion and gastrocnemius and soleus strength at baseline. Subsequent measurements were taken at weeks 4 and 6. A standardized protocol based on Norkin and White's20 was reviewed at group meetings and used for body position, goniometer placement, and manual muscle testing.
Outcome measures
Patients completed several standardized instruments at initial evaluation, and at 6 and 12 weeks in the physician's office. These included the following:
(1) Short Form Health Survey (SF‐36) and the SF‐36 Bodily Pain subscale, which are designed to measure general health status in a variety of circumstances. They have a high level of internal consistency with correlation coefficients higher than acceptable levels across medical conditions (minimally clinical important difference [MCID] is 5).21,22,23,24
(2) Foot and Ankle Outcomes Questionnaire (FAOQ), which uses 25 questions to determine pain and stability of the foot and ankle during various activities, the degree to which the foot and ankle interfere with normal work and daily life, and general stiffness and swelling. The FAOQ has been found to be useful in evaluating foot and ankle outcomes, with good internal consistency, retest reliability, and moderate to strong correlation with physician ratings and the SF‐36.21
(3) Visual Analog Scale (VAS) for pain consists of a 100 mm line, demarcated in 10‐mm intervals, on which the patient records pain with 0 as no pain and 100 as pain so severe you would be in the emergency room. It has been validated by previous research and found to detect MCID in pain (absolute change between 20 and 30 mm on the 100 mm VAS and a 33% decrease of pain is associated with pain relief15,33).25,26,27
Statistical Analysis
Data were entered in Excel and analyzed using SAS 9.2. The outcome measures had excellent internal consistency. Cronbach alpha for the FAOQ was 0.93 and for the SF‐36, 0.90. The SF‐36 Bodily Pain subscale had moderate reliability, with an alpha value of 0.75. This strong internal consistency is good for this small sample size and suggests that the data may not be as limited as the small number suggests. The Mann‐Whitney U test was used to compare the outcome measures between the control group and the experimental group. The Wilcoxon U test compared outcomes to baseline for patients within the protocol.28 Chi‐square tests and Mann‐Whitney tests were used to check for unintentional biases in completion of study and assignment of protocol. Spearman's rank correlations were used to assess correlations between interval‐level data (e.g., BMI) with the outcome ordinal scales. The t‐test and the Wilcoxon signed‐rank test were used, respectively, to compare baseline and final range of motion and strength data.28 Statistical significance was set at an alpha level of p<0.05. Intention to treat analysis was used to assess the effect of incomplete protocols on primary outcomes.29
RESULTS
Baseline data
Recruitment and follow‐up were conducted between February 2007 and October 2010. The majority of patients were middle age, overweight women who had insertional Achilles tendon pain and a slight decrease in dorsiflexion range of motion and gastrocnemius strength. Most patients had attempted other treatments before participation in this study (Figure 3). Thirty‐six of 58 patients met inclusion criteria and adhered to one of the two protocols as instructed: 16 in the experimental group (11 women and five men; average age 51.7 years) and 20 in the control group (15 women and five men; average age 55.3 years) (Table 1). The average body mass index (BMI) was 37.6 in the experimental group and 32.7 in the control group; although not reaching a statistically significant difference between groups, analysis of BMI indicates that the sample population tended to be overweight if not obese (Table 1). Twenty‐seven patients (87%) had calcification in the tendon and three had bilateral symptoms (Table 2). Activity levels at baseline varied, but more patients in the conventional group reported higher activity levels than those reported by the experimental group (Table 2).
Figure 3.
Previous treatments for Achilles tendinopathy, reported by patients.
Table 1.
Patient demographics
| Experimental Group | Control Group | Total | |
|---|---|---|---|
| Number of patients | 16 | 20 | 36 |
| Sex | |||
| Male (%) | 5 (31.5) | 5 (25.0) | 10(27.8) |
| Female (%) | 11 (68.8) | 15 (75.0) | 26(72.2) |
| Mean age (SD) | 51.5 (7.5)yrs. | 55.3 (10.2)yrs. | 53.6 (9.2)yrs. |
| Race | |||
| Caucasian (%) | 12 (75.0) | 16 (80.0) | 28 (77.8) |
| African‐American (%) | 4 (25.0) | 4 (20.0) | 8 (22.2) |
| Mean body mass index (SD) | 37.6 (7.5) | 32.7 (6.5) | 34.9 (6.8) |
Table 2.
Patient baseline data
| Experimental Group | Control Group | Total | |
|---|---|---|---|
| Activity level prior to injury* (missing data = 4) | |||
| Sedentary (%) | 1 (7.7) | 0 (0.0) | 1 (3.1) |
| Mod active (%) | 5 (38.5) | 8 (42.1) | 13 (40.6) |
| Active (%) | 5 (38.5) | 10 (52.6) | 15 (46.9) |
| Very active (%) | 2 (15.4) | 1 (5.3) | 3 (9.4) |
| Current activity level* (missing data = 5) | |||
| Sedentary (%) | 6 (46.2) | 4 (22.2) | 10 (32.3 |
| Mod active (%) | 3 (23.1) | 10 (55.6) | 13 (41.9) |
| Active (%) | 3 (23.1) | 3 (16.7) | 6 (19.4) |
| Very active (%) | 1 (7.7) | 1 (5.6) | 2 (6.5) |
| Mean duration (months) of symptoms (SD)** | 18.5 (30.1) | 18.3 (31.4) | 18.4 (30.7) |
| Calcification in tendon (missing data = 5) | 11 (73.3) | 16 (100.0) | 27 (87.1) |
| Symptoms bilaterally (%) | 3 (18.8) | 0 (0.0) | 3 (8.3) |
| Ankle dorsiflexion involved side‐degrees mean (SD) | 7.7 (3.8) | 9.0 (4.3) | 8.5 (4.1) |
| MMT gastrocnemius involved side‐mean (SD) grade | 4.6 (0.8) | 4.6 (1.3) | 4.6 (1.1) |
sum percent > 100% due to rounding error
Note: The large standard deviations are due to three patients who had symptoms ≥ 120 months.
Note: Activity levels were self‐reported by patients. Sedentary = desk job, no regular exercise; moderately active = desk job and regular exercise; active = manual labor and regular exercise or recreational sports; very active = heavy work activity, regular exercise and competitive sports. MMT, manual muscle test.
Patients in both groups had mildly decreased ankle dorsiflexion and plantarflexion both on the involved and noninvolved sides at baseline. Although not statistically significant, the experimental group had less active dorsiflexion on the involved side compared with the control group (Table 2). Some gastrocnemius weakness was noted in both groups on the involved side (Table 2).
Outcomes
Overall, patients in both protocols significantly improved both in pain and function according to VAS, SF‐36 (Bodily Pain), SF‐36, and FAOQ, and the mean improvement also was statistically significant using these outcome measures (Table 3). The mean change of the SF‐36 was 10 (MCID 529,32) and on VAS it was 20 mm or 41.3% (MCID 20‐30 mm and 33% decrease15,33).
Table 3.
Comparison of outcomes in pain and function at 12 weeks with baseline
| Experimental Group | Control Group | |||||
|---|---|---|---|---|---|---|
| Outcome measure | Mean change | p value | 95% confidence interval | Mean change | p value | 95% confidence interval |
| VAS | −2.19 | < 0.001 | −2.98/−1.43 | −2.08 | <0.001 | −3.58/−0.58 |
| SF‐36 (Bodily Pain) | 16.22 | 0.016 | 5.0/27.4 | 16.40 | 0.026 | 3.7/29.0 |
| SF‐36 | 9.78 | 0.125 | −1.63/21.19 | 10.27 | 0.035 | 0.34/20.20 |
| FAOQ | −0.73 | 0.002 | −2.11/−1.05 | −0.758 | 0.0002 | −1.09/0.43 |
VAS= visual analog scale; SF‐36= Short Form‐36; FAOQ= Foot and Ankle Outcomes Questionnaire.
Note: Improvement in status is indicated by a negative change for the VAS and FAOQ, with a larger negative number indicating a bigger improvement. A positive change for the SF‐36 indicates improvement in status, with a larger positive change indicating better improvement in health.
No statistically significant differences were found in outcomes between patients in the two groups (Table 4). Although both groups experienced positive change, the conventional protocol group's change was statistically significant in all outcome measures (VAS, SF36 [Bodily Pain], SF‐36, and FAOQ), whereas the experimental group's change was significant in the VAS, SF‐36 (Bodily Pain), and FAOQ, but not the SF‐36 (see Table 3).
Table 4.
Comparison of outcomes between protocols
| Scale (12 weeks) | Experimental Group Mean (SD) | Control Group Mean (SD) | Test Utilized p values |
|---|---|---|---|
| VAS | 2.43 (1.99) | 1.50 (2.16) | MW=2.30, p=0.129 |
| SF‐36 | 70.00 (15.95) | 70.50 (19.97) | MW=0.07, p=0.789 |
| SF‐36 (Bodily Pain) | 72.44 (11.49) | 61.82 (27.15) | MW=0.08, p=0.778 |
| FAOQ | 0.78 (0.58) | 0.74 (0.75) | MW=0.54, p=0.464 |
VAS= visual analog scale; SF‐36= Short Form‐36; FAOQ= Foot and Ankle Outcomes Questionnaire, MW= Mann‐Whitney test
No statistically significant differences were found in outcomes by age, race, BMI, duration of symptoms, or prior activity level for either group. However, women improved more than men as measured by the VAS, and this was statistically significant (p = 0.033) regardless of treatment protocol.
Patients in both protocols had significantly improved ankle dorsiflexion range of motion and gastrocnemius manual muscle strength test at final follow‐up (Table 5). Better ankle dorsiflexion range and gastrocnemius strength at baseline were moderately correlated with significantly larger improvements in VAS (Spearman's rho [rs] =0.370, p = 0.048 and rs= 0.396, p = 0.0368, respectively). Better gastrocnemius strength at baseline showed moderate (statistically significant) correlation with improved FAOQ scores (rs = 0.5181, p = 0.005).
Table 5.
Changes in mean ankle range of motion and strength (of involved side)
| Measurement | Protocol | Baseline(1st visit physical therapy) | Last visit physical therapy (6 weeks) | Test Utilized, p value |
|---|---|---|---|---|
| AROM ankle dorsiflexion, reported in degrees (SD) | Experimental | 2.42 (4.68) | 7.67 (3.80) | t = −6.72, p > 0.0001 |
| Control | 0.89 (5.97) | 9.00 (4.27) | t=−5.27, p = 0.0002 | |
| Manual Muscle Test of gastrocnemius, reported as grade out of 5 (SD) | Experimental | 4.31 (0.94) | 4.64 (0.81) | S=27.5, p=0.002 |
| Control | 3.49 (1.61) | 4.56 (1.25) | S=4.5, p=0.012 |
AROM= ankle range of motion, t= t‐test, S= Wilcoxon‐signed rank test
Complications
One patient required physical therapy for knee pain that occurred after eccentric training. One patient who was removed from the study had a partial Achilles tendon rupture that occurred from activity not associated with the study. Because this complication occurred shortly after enrollment, the patient's participation in the study was not a factor. No other complications were noted.
Check for Biases and Effects
Statistical analyses indicated no bias in the assignment of protocol by age (Mann‐Whitney U=1.0, p=0.293), sex (Chi‐square = 0.04, p = 0.841), duration of symptoms (Mann‐Whitney U = 0.005, p =0.94), or activity level prior to injury. Patients assigned to the experimental group had a higher mean BMI (BMI=37) than those in the traditional protocol (BMI=32), but the difference was not statistically significant (Mann‐Whitney U = 3.24, p = 0.072). Because some heavier patients had difficulty performing the eccentric strengthening exercise and others reported doing better at 6 weeks and did not return at 12 weeks, an intention to treat analysis was performed and demonstrated no effects of incomplete follow‐through on outcome. An exercise diary was provided for each patient. Most participants had received other treatments prior to this study implying that the success was related to their compliance.
DISCUSSION
Eccentric training has been identified as an important part of clinical rehabilitation of chronic tendinopathy, particularly of the Achilles tendon at the midportion.7,9,26,30,31 Eccentric training also has been found to be more effective than concentric strengthening for Achilles tendinosis located 2‐6 cm from its insertion.4 The hypothesis that the addition of eccentric training to a conventional physical therapy program would be more effective than conventional physical therapy alone in the treatment of insertional Achilles tendinopathy was not supported by this research. This study found that patients with insertional Achilles tendinopathy experienced significant improvements with conventional physical therapy, with or without eccentric training. Improvement was noted in 86.7% of patients on the VAS, 84.2% on the SF‐36, 73.7% on the SF‐36 bodily pain subscale, and 93.3% on the FAOQ. The mean amount of improvement in pain and function also was considered clinically significant in the VAS, SF‐36, and FAOQ. A change of 5 on the SF‐36 has been shown to be a clinically significant improvement; the mean change of the SF‐36 was 10 in this study.29,32 According to Jensen, Chen, and Brugger, and absolute change between 20 and 30 mm on the 100 mm VAS scale and a 33% decrease of pain on the VAS is associated with pain relief.15,33 The mean change in the current study was 20 mm with a mean percentage change of 41.3%, which indicates that the decrease in pain was clinically significant. Better baseline ankle dorsiflexion range and gastrocnemius strength significantly correlated with larger improvements in both groups. It is interesting to note that patients in the control group also experienced statistically significant improvements in gastrocnemius strength even though their protocol did not include strengthening.
The findings in this study differ from those of Fahlström et al9 as well as those noted in the review by Alfredson and Cook8; both of those reports noted that only about a third of patients with symptoms at the insertion responded to treatment within 3 months. In contrast, all patients in this study improved in at least one outcome measure. It is important to note that the percentages of improvement in this study did not measure the same thing as the aforementioned articles. This study measured any improvement along a scale, whereas their articles noted the percentage of patients with functional improvement who were able to return to their previous levels of activity. Alfredson's and Cook's8 review and algorithm referred to a more athletic population than we had in this study, and this may account for the differences in results.
While the outcomes in the current study were better for insertional Achilles tendinopathy than reported in previous studies investigating eccentric strengthening, it is unknown if eccentric training made the difference.9,34,35 The interventions used in the control group have been supported by previous research for mid‐portion Achilles tendinopathy, including the use of insoles or heel lifts2 and Achilles stretches.13,35 The night splint has not been found to have additional benefit when added to eccentric strengthening.36 An airheel brace (a light weight compression brace with interconnected aircells under the arch of the foot and the back of the Achilles tendon to reduce strain), which was not used in this study, also has been found to be beneficial.37 Most of these patients (75%) had used at least one of these treatments before the study, suggesting that a combination of interventions may be required for effective treatment, as proposed by Angermann and Hovgaard.38
Unlike previous research that suggests patients with a higher BMI have worse outcomes,9 this was not so in this study, although obese patients were clinically observed to have more problems performing the eccentric exercises. Patients who reported having osteoarthritis also complained of knee discomfort during eccentric exercises with the knee flexed, and one patient required treatment for his knee after performing the eccentric strengthening protocol. Performing eccentric exercises only with the knee extended (see Figure 2C) or a simple prolonged eccentric stretch as described by Verrall et al34 may be an appropriate modification for patients with osteoarthritis. Recently, Stevens and Tan39 reported that a “6‐week do‐as‐tolerated” program of eccentric exercise was as effective but with less discomfort in the process as the recommended 180‐repetition exercise program for midportion Achilles tendinopathy. Their program may facilitate strengthening without knee discomfort, which could be appropriate for patients who report osteoarthritis or who are obese and who had trouble executing the eccentric strengthening exercise in the current protocol.
Previous authors have reported that eccentric strengthening is not particularly effective in a non‐athletic population;17 however, the subjects in the current study demonstrated no correlation between activity level and outcomes regardless of eccentric training. In addition, women who have been noted previously to have the same or poorer outcomes than men with eccentric training,12,31 reported more improvement in pain than men in all outcome measurements in the current study, and this difference reached a statistically significant difference on the VAS (U=4.65, p=0.033). Further study would be necessary to determine the reason for this finding.
The patient population in this study differed from the population most often described with chronic Achilles tendinopathy, namely middle‐aged, mostly male, recreational athletes. The patients in this study were overwhelmingly women (72%), with varied activity levels. The prevalence of obesity in this study population suggests that this was not a highly athletic population, which raises the question of whether the demographics and the causal factors are the same among persons for mid‐portion Achilles tendinopathy as for those with insertional Achilles tendinopathy.
This study has several limitations, including low patient numbers, short follow‐up (larger improvements may have been noted at a later point), and that patients performed the physical therapy protocol at home without supervision. In addition, patients did not progress beyond their body weight during the eccentric protocol. Also, no reliable information regarding the patient's use of over‐the‐counter medications was available, except that they were prescribed none. Having Achilles tendinopathy bilaterally could influence the outcome, but the sample size with this condition (N=3) was too small for meaningful exploration.
CONCLUSIONS
The results of this study showed that conventional physical therapy with or without eccentric strengthening was effective in the treatment of insertional Achilles tendinopathy in a population with varied activity levels. No statistically significant difference was noted in outcomes between the control group and the experimental group, as they both demonstrated statistically significant improvements. Better ankle range of motion and gastrocnemius strength at baseline correlated with significantly larger improvements. This study suggests that patients with diverse activity levels with insertional Achilles tendinopathy can improve significantly with an appropriate combination of stretches, heel lifts, night splint, and cryotherapy.
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