What role for eccentric exercises in conservative treatment of achilles tendinopathy

The authors seek answers to clinical questions regarding the optimal program of eccentric exercises: Does type of tendinopathy predict success? What modifications to exercise duration and repetitions make sense? What is the likelihood of long-term pain relief afforded by such a program of exercise?

By Jonathan L. Hook, DPM, MHA, and Curt Martini, DPM

Pain in the Achilles tendon is common among athletes, recreational exercisers, and inactive people alike. Achilles tendinopathy, a noninflammatory cause of pain in this tendon, affects approximately 7% to 9% of runners but also affects participants in other sports and nonathletes.^1,2

Maffulli and coworkers describe the clinical presentation of Achilles tendinopathy as a triad of pain, diffuse or localized swelling, and impaired performance of the Achilles tendon³; histologic examination of the Achilles tendon insertion demonstrates necrosis and mucoid degeneration, rather than inflammatory infiltrate.⁴ This absence of an inflammatory component defines the condition as tendinopathy.

We further subclassify Achilles tendinopathy as midsubstance (also midportion) Achilles tendinopathy, insertional Achilles tendino­pathy, and acute or chronic paratendinopathy.

Midsubstance Achilles tendinopathy represents approximately 55% to 65% of Achilles tendon injuries.⁵ This type, which occurs 2 to 6 cm from the insertion of the Achilles tendon, has the classic presentation of pain, swelling, and impaired performance⁶ owing to the region’s zone of hypovascularity.

Insertional Achilles tendinopathy presents as pain and stiffness at the posterior aspect of the calcaneus⁶ and accounts for approximately 20% to 25% of Achilles tendon injuries.⁵

Both acute and chronic paratendinopathy will have edema and hyperemia around the midportion of the tendon, while the pain of chronic paratendinopathy is exercise induced.⁶

A diagnosis of Achilles tendinopathy can be made clinically, based on pain with walking, running, or stairclimbing and physical examination findings that include pain on palpation to the Achilles tendon either proximal to or at the insertion; difficulty performing double heel raise; and decreased strength with plantar flexion typically due to guarding. Imaging studies with ultrasound and magnetic resonance imaging can confirm the diagnosis of Achilles tendinopathy, but imaging is not required to make the diagnosis.

Risk factors

Intrinsic risk factors for Achilles tendinopathy include age between 30 and 55 years, male sex, obesity, exercise-induced hyperthermia, presence of systemic disease (eg, diabetes mellitus, rheumatoid arthritis, Ehlers-Danlos syndrome), reduced tendon flexibility/ankle-joint range of motion, reduced blood supply, and prior injury to the area.⁷ Other intrinsic factors include abnormal subtalar-joint range of motion, increased foot pronation, decreased ankle-plantar flexion strength, and abnormal tendon structure.¹ Extrinsic factors for Achilles tendinopathy tend to cause acute injury; these extrinsic factors include training errors, faulty equipment, improper shoes, overuse, surface on which the athlete is training, and use of quinolones or corticosteroids.⁷

An overview of treatments

Conservative treatment generally is recommended as the initial strategy, regardless of the type or etiology of the patient’s Achilles tendinopathy. Several conservative modalities have better evidence than others to support their use, but we know of no high-quality head-to-head studies that compare the effectiveness of the various conservative treatment regimens described here. We review these modalities briefly to put in context the evidence regarding a program of eccentric exercise.

Initial treatment may include a combination of rest, pain medication, stretching, strength training, heel lift, footwear change, and correction of malalignment.⁸ Custom foot orthoses to control rearfoot motion have minimal effect when used as the only treatment modality^9,10; taping and use of heel lifts also have limited evidence of efficacy.¹ Stretching exercises may be helpful for patients who have limited dorsiflexion at the ankle joint.¹

Platelet-rich plasma also has been used recently, but compelling evidence to support its use is lacking. Corticosteroids are associated with an increased risk of tendon rupture and have minimal effect on Achilles tendinopathy.¹¹ Use of extracorporeal shock-wave therapy (ESWT) as monotherapy and in combination with other modalities has, however, recently been shown to benefit patients.¹²

Surgery is typically reserved for patients whose symptoms do not resolve with 3 to 6 months of conservative treatment; choice of procedure depends on both the amount of tendon involved and location of tendinopathy. Open surgery with debridement of adhesions and nonviable tendon may be effective for midsubstance tendinopathy; Rolf and Movin reported improvement in symptoms in 86% of patients after undergoing surgical debridement, with a complication rate of 13%.¹³

Augmentation is the procedure of choice in cases that require more than 50% debridement. Options include the use of the flexor hallucis longus tendon, owing to its good power; it is also an in-phase transfer and has a similar line of pull to the Achilles tendon.¹⁴ Researchers reported improvement in American Orthopaedic Foot & Ankle Society ankle-hindfoot scale from 41.7 to 90.1 following flexor hallucis longus tendon transfer performed on 29 tendons.¹⁵ Although the patient undergoing this procedure will lose plantar flexion at the hallux interphalangeal joint, it typically has no effect on gait and requires no modification of activity. The proximity of the flexor hallucis longus muscle belly to the hypovascular zone of the Achilles tendon allows for increased vascularity and postoperative healing. Tendons less commonly used for augmentation are the flexor digitorum longus, peroneus longus, peroneus brevis, and posterior tibialis tendon.¹⁴

Surgical treatment options for insertional Achilles tendinopathy include debridement and augmentation procedures described for midsubstance tendinopathy, along with resection of retrocalcaneal exostosis and removal of the retrocalcaneal bursa.¹⁶

Do eccentric exercises work?

A program of eccentric exercise for treatment of Achilles tendinopathy was first described by Alfredson and coworkers in 1998.¹⁷ A control group (n=15) underwent classical treatment and surgery, while an experimental group (n=15) was assigned to an exercise program performed twice daily (180 repetitions/day) every day for 12 weeks. Patients began with the ankle in plantar-flexed position and lowered the heel in relation to the forefoot, which eccentrically loaded the gastrocnemius and soleus muscle complex. The unaffected limb was then used to return to the start position to prevent concentric loading (Figure 1). Once pain had improved, patients would perform the same exercise with weight added.

Patients who underwent the exercise program had significant improvement in pain (visual analogue scale [VAS]) and strength of the affected tendons, and no statistically significant difference in outcomes was found between patients in the experimental-exercise group compared with those in the surgical group.

A multicenter study that compared short-term results of eccentric- vs concentric-exercise–training programs for treatment of chronic midsubstance Achilles tendinopathy found that 82% of patients undergoing an eccentric-exercise program were able to return to their preinjury activity level, compared with 36% of patients who underwent a concentric-exercise program.¹⁸ Although only 22 patients were included in each study group, the results suggest a significant difference between the 2 treatment programs for chronic midsubstance Achilles tendinopathy.

The mechanism by which an eccentric-exercise program exerts an effect on Achilles tendinopathy remains poorly understood, although 1 study demonstrated increased type 1 collagen associated with an eccentric-exercise program in diseased tendons. This finding supports the observation that diseased tendons are caused by chronic overuse that exceeds the repair capabilities of tissue and that an eccentric-exercise program allows for increased production of type 1 collagen that may assist the diseased tendon to achieve homeostasis.¹⁹

Other proposed mechanisms include²⁰:

• Structural tendon adaptation
• Tendon-length change
• Neurovascular ingrowth
• Neurochemical alterations
• Fluid movement
• Neuromuscular adaptations

Studies provide insight on modifications

Stevens and Tan sought to evaluate the effect of modifying the number of repetitions in the Alfredson eccentric-exercise program, with 28 patients in 2 groups: 1 performing the daily regimen of 180 repetitions (n=15) and the other group performing the exercises as tolerated (n=13). At 6 weeks, researchers noted significant improve­- ment in Victorian Institute of Sports Assessment-Achilles (VISA-A) questionnaire for both groups and in VAS pain scores for patients in the do-as-tolerated group.²¹ This study, however lacked sufficient follow-up to compare rates of recurrence between the do-as-tolerated and the 180 repetitions/day groups.

Another study sought to examine additional modifications to the Alfredson eccentric-exercise program: 6 weeks’ duration versus 12 weeks and stretches maintained for at least 15 seconds, compared with 10 seconds.²² The study included 190 patients: 168 with midsubstance Achilles tendinopathy and 22 with insertional Achilles tendinopathy. Researchers found that 86% of patients with midsubstance Achilles tendinopathy and 80% of those with insertional Achilles tendinopathy reported significant relief from pain.

The long run?

How durable are the effects of an eccentric-exercise regimen for Achilles tendinopathy? A randomized controlled study compared an eccentric-exercise group of 22 patients with a control group (n=18) who performed both concentric and eccentric exercises at a lower load than the experimental group, to determine effectiveness of the 12-week program at 1 year. Patients were evaluated at intervals of 6 weeks, 3 months, 6 months, and 1 year after initiating treatment.²³

No significant difference between the 2 groups was found at any of the evaluations, although significant overall improvement was noted in the eccentric-exercise group. This cohort of patients had better outcomes with respect to plantar flexion, reduced pain on palpation, asymptomatic periods, and reduced tendon swelling. In addition, more patients in the eccentric-exercise group felt they had fully recovered and had returned to regular activity levels. ²³

Although the effectiveness of the eccentric-exercise program was demonstrated at 1 year, it did not suggest longer-term benefit. For this, van der Plas and coworkers evaluated 70 tendons from 58 patients that had undergone the Alfredson eccentric-exercise program 5 years prior. Using the VISA-A questionnaire and pain status, the researchers determined that 58 tendons had an improvement in their VISA-A score from 49.2 to 83.6 after initial treatment and 83.4 at the 5-year mark. The researchers reported that 39% of patients were pain free and 48% had mild pain for which they received alternative treatments.²⁴ Thus, while supporting the use of Alfredson’s eccentric-exercise program for pain relief and as a good initial treatment modality, the study results demonstrated that approximately half of patients who undergo the treatment regimen will require further treatment with an additional modality or may continue to experience pain long term.

Evidence suggests that eccentric exercises may be more beneficial when used in combination with other modalities, specifically ESWT. Rompe and coworkers assigned 68 patients equally into 2 groups: 1 received only eccentric exercises, and the other group received eccentric-exercise program and ESWT.²⁵ At 4 months, 56% of patients in the eccentric-exercise–only group had significant improvement in symptoms, and 82% of patients in the combination therapy group with ESWT had significant improvement in symptoms.

Of benefit to all types, equally?

Does an eccentric-exercise program benefit 1 type of Achilles tendinopathy more so than another type? Of 101 cases of midsubstance chronic Achilles tendinopathy treated with an eccentric-exercise program, 89% of tendons had significant improvement, with patients reporting satisfactory results and return to preinjury activity levels. In this same study, the authors also examined the protocol’s effectiveness on insertional Achilles tendinopathy. In this cohort, only 32% had an improvement in VAS pain score and were satisfied with treatment.²⁶ This disparity between improvement for midsubstance compared with insertional Achilles tendinopathy is likely due to compression of the retrocalcaneal bursa. During the ankle dorsiflexion phase of the eccentric-exercise program, the bursa is pressed against the anterior surface of the Achilles tendon, resulting in increased tension at the insertion point.

Following the results of this study, Jonsson and coworkers sought to determine whether modifying the eccentric-exercise training program to prevent loading into dorsiflexion could better help patients who had insertional Achilles tendinopathy.²⁷ To accomplish this, patients performed the exercises on the floor, rather than on a step.  The researchers reported that 67% of patients in the modified-exercise group had less pain compared with 32% of subjects reporting improvement after undergoing the original eccentric-exercise program.

Additional research has demonstrated that eccentric exercises do not have the same effect for insertional Achilles tendinopathy compared with midsubstance Achilles tendinopathy. Kedia and coworkers conducted a single-blinded, randomized, controlled trial to determine whether the addition of eccentric exercises to a conventional training program significantly reduced pain.²⁸ Their finding? A program consisting of gastrocnemius, soleus, and hamstring stretching; ice massage on the Achilles tendon; heel lift; and night splints was as effective for insertional Achilles tendinopathy with or without a program of eccentric exercises.

In the clinic

The cause of the patient’s tendinopathy and its clinical presentation will inform management, which may include addressing any extrinsic factors causing pain, such as reducing the amount of training, modifying footwear or recommending a change in the training surface. Intrinsic modifications include use of custom orthoses to modify rearfoot alignment, improving range of motion at the ankle joint, strengthening the Achilles tendon, and controlling any systemic disease.

Strong evidence supports the use of an eccentric-exercise program, particularly for midsubstance Achilles tendinopathy, and greater efficacy may be realized when used in conjunction with another treatment modality, such as ESWT. Insertional Achilles tendinopathy, however, does not respond as well to eccentric exercises as does the midsubstance type. In these cases, the exercises must be modified to eliminate the dorsiflexion-loading phase, which will, in turn, relieve compression—and tension of the retrocalcaneal bursa—on the insertion of the Achilles tendon.

Alternatively, eccentric exercises can be used in conjunction with a stretching and strengthening program with regular icing for pain relief. There has also been improvement to insertional Achilles tendin­opathy when combining the modi­- fied heel-drop exercise with other types of therapy such as ESWT.

The continually demonstrated effectiveness of an eccentric-exercise program for Achilles tendinopathy, taken together with its low cost and low risk to the patient, position it high among first-line treatments for Achilles tendinopathy.

Dr. Hook practices at Midland Orthopedic Associates and is affiliated with the Podiatric Medicine and Surgery Residency Program at Mercy Hospital and Medical Center in Chicago. Dr. Martini is a first-year resident at Mercy Hospital and Medical Center in Chicago.