As most SIB readers will be aware, the Achilles tendon is the largest tendon in the human body and is very vulnerable to injury, probably because of its limited blood supply and the variety of forces to which it is subjected during activity (“Common Conditions of the Achilles Tendon”, American Family Physician, Vol. 65(9), pp. 1805-1810, 2002.) Achilles-tendon maladies may account for 5-10% of all athletic injuries, and they are a major problem in almost every sport. Strangely enough, however, the exact mechanism which produces the debilitating pain of chronic Achilles tendinosis has remained unknown (see also SIB issue 19). Researchers have shown, though, that neovascularisation – the growth of many new blood vessels into damaged areas – is present in the painful Achilles tendons of individuals with chronic Achilles tendinosis, but not in pain-free, normal tendons. As a result, researchers at the University of Umea in Sweden hypothesised that such ingrowing blood vessels – and perhaps the nerves which accompanied them – were the true source of pain in tendinosis. The Umea group decided to test their hypothesis by sclerosing (hardening and closing) the invasive blood vessels in the Achilles tendons of 10 patients (eight walkers, one runner, and one golfer) suffering from painful, chronic, Achilles tendinosis (“Ultrasound Guided Sclerosis of Neovessels in Painful Chronic Achilles Tendinosis: Pilot Study of a New Treatment”, British Journal of Sports Medicine, Vol. 36, pp. 173-175, 2002). The average duration of symptoms in this group was 17 months.
The sclerosing chemical of choice used by the Swedish scientists was polidocanol (5 mg/ml), which has long been used in sports medicine as a local anaesthetic. Color Doppler (an ultrasound technique) was utilised to make the diagnosis of neovascularisation and to identify the entrance of the new blood vessels into the Achilles tendon. The polidocanol injections were accomplished dynamically, with ultrasound used to guide the needle to a spot close to the blood vessels. Enough polidocanol was injected to ensure that all blood vessels were closed, and all individuals were allowed to resume their normal activities on the day after treatment. During a three- to six-week follow-up period, the subjects were re-examined, and injections were repeated in case neovascularisation had returned until there was no detectable ingrowth of blood vessels in painful areas.
To assess pain levels, the Swedes used a visual analogue scale (VAS), and subjects recorded the amount of pain they experienced during activity. On the VAS, a total lack of pain is recorded as zero, while maximal-possible pain is scored as 100. Before the polidocanol injections, the average VAS rating among the Achilles-tendinosis sufferers was 74 (range 39-89), but after six months the mean VAS score dropped to a puny 8.4 (range 0-29) in eight individuals who were satisfied with their treatment (these individuals were able to return to their full, desired schedules of activity). Just two of the 10 subjects reported a lack of relief, and – interestingly enough – neovascularisation had returned in this pair during the six-month follow-up period (neovascularisation was not present in the eight happy patients). Average VAS score for the hurting duo was 71.
Another key finding was that Achilles-tendon pain disappeared immediately after the polidocanol injections, probably because polidocanol can act as an anaesthetic. Since the injections were made at the sites of neovascularisation, there is an implication that the neovascularised area is indeed the source of pain in Achilles tendinosis. Pain returned after six hours, as the anaesthetic effect subsided, but then steadily diminished during follow-up for eight of the subjects. While this research seems to indicate that the sclerotisation of neovascular structures in the Achilles tendons of individuals with Achilles tendinosis can provide a powerful pain-relieving effect and can help such individuals return to athletic activity, certain cautions are in order. First of all, the Swedish work is simply a pilot study; there was no control group, and the Achilles-tendinosis victims were not blinded to what they perceived as a new treatment.
There is also some concern that the blood vessels which were obliterated by polidocanol might have had a beneficial effect over the long term, perhaps by bringing nutrients necessary for healing to the degenerated areas of the Achilles tendons. Thus, although pain was diminished, long-term healing might have been compromised. This possibly negative scenario is relieved somewhat, however, when one realises that the individuals in the study had suffered from Achilles-tendon problems for an average of 17 months. One would think that this extended time period would be long enough for healing to begin, yet the individuals were often close to maxing out their VAS.
Is polidocanol treatment more effective than strengthening exercises for the Achilles tendon and its associated muscles? In the Swedish study, seven of the 10 subjects had completed calf-muscle training, with little positive effect (there was no description of the specific exercise programme utilised, however). In other research, calf-muscle training has been very effective, as long as the work has been eccentric in nature (providing elongation of the calf muscles as they are simultaneously attempting to shorten).
For example, in a separate study carried out at the University Hospital of Northern Sweden, researchers found that 12 weeks of heavy-load eccentric-calf-muscle training had a very positive effect on Achilles tendinosis (“Heavy-Load Eccentric Calf Muscle Training for the Treatment of Chronic Achilles Tendinosis”, The American Journal of Sports Medicine, Vol. 26, pp. 360-366, 1998). In this investigation, 15 athletes (12 men and three women) with a long duration of symptoms (18 months) of Achilles tendinosis were unable to engage in their normal running training because of tendinosis-related pain. The athletes had tried conventional treatments (rest, non-steroidal anti-inflammatory medications, changes of shoes, orthoses, physical therapy, and ordinary training programmes), to no avail. These 15 athletes were matched with a group of 15 similar athletes (11 men and four women) with the same diagnosis who underwent Achilles-tendon surgery instead of the heavy-duty eccentric training. All 30 individuals had the typical signs and symptoms of Achilles tendinosis, including thickened Achilles tendons, irregular tendon structure, disarray of the protein fibres within the tendon, separated tendon fibres, stiffness, and pain during running.
Two eccentric workouts were performed per day, seven days a week, for 12 weeks. Each workout consisted of three sets of 15 repetitions for two key exercises (to be described in a moment). Normal running training was permitted if it could be completed with only mild discomfort and no significant pain. The exercises proceeded as follows:
The athletes stood on their forefeet only (on both feet) close to the edge of a step, with the non-injured leg providing the force needed to rise up onto the forefeet. The non-injured leg was then lifted off the step, so that full body weight was supported only by the forefoot of the leg with the hurting Achilles tendon; the heel of the hurt leg was then slowly lowered until it came into position well behind and below the edge of the step (basically, the ankle moved from plantar flexion to dorsiflexion as the heel went down). This provided a strong eccentric contraction for the calf muscles attached to the damaged Achilles tendon, since they were contracting actively to slow the descent of the heel and yet were elongating as the heel dropped downward. No subsequent concentric loading of the calf muscles associated with the hurt Achilles tendon was carried out; the non-injured leg was used to provide the force necessary to return to the starting position.
For the first exercise (the first three sets of 15 reps), the injured leg was kept straight at the knee; during the second exercise (the next three sets of 15 reps), the injured leg was bent at the knee to activate the soleus muscle, which lies beneath the main calf muscle, the gastrocnemius. Possibly because there were just two exercises in the workout and because the exercises were straightforward to carry out, there were no drop-outs during the training period; all 15 athletes completed the 12-week programme.
An especially positive feature of this eccentric training was that it was progressive. When the athletes could perform the eccentric, loading exercise without experiencing pain or discomfort, they increased the load by adding weight placed in a backpack. If very high weights were needed, the athletes used a weight machine to increase the eccentric strain.
As it turned out, the eccentric training produced dramatically positive effects on both concentric and eccentric calf-muscle strength. Before the eccentric training was begun, the injured-side calf muscles had significantly lower concentric plantar-flexion strengths at 90º and 225º per second (12 and 18%, respectively) and significantly reduced eccentric plantar flexion strength (11%), compared with the non-injured-side calf muscles. After 12 weeks of training, however, the eccentric plantar-flexion strength and also the concentric plantar-flexion strengths at both speeds had improved considerably, and the there were no differences in strength between injured and non-injured sides. In contrast, the 15 athletes who underwent surgery were unable to bring their injured-side strength up to par with the injured side through the utilisation of conventional calf-muscle exercises and physical therapy, even after double the time period (24 weeks). Scores on the VAS were similarly positive. In the group which undertook eccentric calf-muscle training, the average VAS score was 81 before the 12-week training programme commenced but plummeted to a miserly 4.8 after the 12 weeks of daily work. All 15 individuals were able to resume their normal running training in a pain-free manner after 12 weeks of training. In the control group (consisting of the individuals who underwent surgery), VAS scores dropped from 72 to 21 over 24 weeks, but, as mentioned, strength in the injured-Achilles leg remained sub-par.
Other studies have suggested that eccentric muscle strength training works well for the rehabilitation of tendon injuries (“Eccentric Exercise in Chronic Tendinitis”, Clinical Orthopaedics, Vol. 208, pp. 65-68, 1986).The mechanism underlying this beneficial effect is uncertain, with one theory suggesting that the stretching of the muscle-tendon unit which takes place during eccentric activity actually permanently elongates the muscle and tendon, leading to less strain per unit length of muscle and tendon during ankle-joint motion. Another possibility is that the eccentric loading induces a special kind of “remodelling” within the muscle-tendon unit, including hypertrophic changes in the muscle and tendon. Long-term ultrasound examinations of athletes undergoing eccentric training should help resolve this issue. The eccentric calf-muscle training is safe: no new injuries occurred during the 12-week period. The training is also inexpensive: only a step and a backpack with a few weights are usually needed, although some individuals will certainly graduate to using a weight machine in a gym. In addition, once the 12-week training period is over, just small amounts of further training seem to be required to keep the problematic Achilles tendon healthy; in this study, just one to two eccentric workouts per week kept the formerly injured Achilles tendons happy.
How should chronic Achilles tendinosis be treated? Athletes with Achilles tendinosis should definitely try a heavy-load eccentric training programme similar to the one described in the University Hospital of Northern Sweden study. Note, though, that the 10 individuals with unresponsive Achilles tendinosis in the University of Umea investigation had already undergone strength training for their Achilles tendons, with little positive effect (their training was not heavily eccentric, however). At any rate, it is likely that eccentric strengthening programmes will not be successful in all cases. In situations when they fail, the new treatment – sclerosis of neovessels with polidocanol – appears to be very promising.