Achilles tendon, also know correctly as tendo calcaneus, Is the largest and strongest tendon in the human body.  This tendon is commonly involved in soft-tissue overuse injury – often painful and debilitating.

What does the Achilles Tendon do? During the gait cycle (particularly stance phase), the triceps Surea is at its peak activity Helps to prevent excessive pronation by assisting in controlling the rate of ankle dorsiflexion Provides plantarflexion for toe off, heel lift assisting in allowing the body to fall forward

Anatomy The tendon arises from the gastrocnemius/soleus complex forming the Achilles tendon which continues to track along the posterior of the leg. The plantaris, which is a small muscle which arises from the popliteal surface of the femur fuses medially to the Achilles tendon, which then inserts into the posterior aspect of the calcaneus.  There is a small bursae which separates the upper part of the surface of the calcaneus and the Achilles. The Achilles tendon is made up of endotendon and paratendon:

  • Endotendon is made up of different types of collagen fibres (specifically type I and III) and tightly packed proteins, enclosed is a sheath.
  • The presence of the Paratendon facilitates the tendon’s ability to glide. The paradenton is a double-layered sheath of synovial cells.

Terminology Achilles tendinopathy is a broad description affecting the tendon ranging from inflammation to injury.  However, you can break this down to 3 distinct categories:

  • Tendonosis – the most commonest injury is as a result of repetitive overuse and ends in tendon degeneration, clinical signs of inflammation are almost never present on histological examination.
  • Paratendonitis – is a condition of acute oedema and hyperaemia of the paratendon causing paratendon sheath to become thickened and to adhere to the underlying unaffected tendon. The oedema is accompanied by the infiltration of inflammatory cells within the sheath.
  • Paratendonitis may occur on its own or in combination with the degeneration of the tendon itself.

Tendon injuries can be both acute and chronic:

  • Acute injuries often occurs in individuals who may suddenly participate in rigorous exercise, with little or no warm up stretches – symptoms may be described as a sudden calf muscle pain. An audible snap would signal a rupture of the Achilles tendon and this may be accompanied by a loss of plantarflexion and this can be tested by performing the Thompson squeeze test. However, most injuries are attributed to overuse/abnormal stress leading to micro trauma resulting in the breakdown of the tendon tissues.
  • Micro traumas creates microscopic tears within the tendon which are repaired by collegen type III. This is a major collagen specific to healing tendon injuries which produces a temporary bond between the damaged tendon fibres. In time, normally this type of immature collagen is replaced by type I collagen which has similar organised fibres to that of normal tendon tissue. However, with repetitive injury this collagen type III is not replaced with collagen type I and instead remains inflamed and continues to be a weak structure. If trauma continues to be faster than the healing rate, then tendon degeneration may occur and if left untreated may result in partial or total tendon rupture.
  • Due to the relatively poor blood supply proximal (approx 2-7cm) to the insertion of the tendon there tends to be a greater incidence of micro traumas and degeneration/rupture.

In chronic overuse injuries there may be many intrinsic and extrinsic factors which can result in tendon injury.

Intrinsic factors

  • Age – due to the natural aging process some literature suggests there is less type I collagen (more resilient) than type III, leaving the tendons more susceptible to injury. However, there is no conclusive research evidence.
  • Biomechanics – Malalignment of the lower limb. The Achilles tendon inserts medially to the STJoint axis creating a supinatory force. Any excessive/prolonged pronation will result in eccentric strain on the Achilles tendon. The pronation causes internal tibial rotation drawing the tendon medially, which if there is a rapid compensatory resupination of the STJ, a whipping force takes place on the tendon causing microtears. With such forces taking place, the vascular status becomes further impaired. Overtime, this may lead to degeneration etc.of the tendon. Common conditions occurring in the feet include: rearfoot varus, forefoot varus, post tibial weakness, ligament laxity, LLDiscrepancy.
  • Tight muscles – If the triceps surea muscles are tight they may limit ankle dorsiflexion placing excessive strain on the Achilles specifically during midstance.
  • Foot type – If the individual has a particularly rigid cavoid foot, there will be a lack of shock absorption and instability of the ankle joint causing stress on the tendon.

Extrinsic factors

  • Incorrect training – excessive distance running, increased duration/intensity, persistent angled camber or hard surfaces can all contribute towards tendon injury. Whilst running forces equivalent to 3 x of body weight will transmit through our foot and Achilles tendon. Incorrect training may take into account incorrect/poor stretching exercises which also can result in tendon injury.
  • Incorrect footwear – poor footwear which include inflexible soles, poor support, lack of shock absorption, excessively worn or basically poor fitting can also contribute to development of tendon injury.

Clinical Presentation Tendonosis is usually asymptomatic on its own.  With combined with paratendonitis the patient will experience pain.  The pain may be brought on rising from rest, starting exercise; however, as the condition worsens the individual will experience pain throughout exercise.

During the acute phase, there will be reduced ankle dorsiflexion due to oedema being present and crepitus felt within the tendon.  Crepitus can be felt during palpation of the tendon described as sponginess like wet leather.

The condition becomes chronic when the injury progresses and the crepitus reduces and is replaced with a nodular swelling signifying tendonosis.  Identifying the location of the swelling can prove to be difficult but the following tests can help:  Dorsiflex/plantarflex the foot and see if the swelling stays fixed to the reference of the malleoli.  This confirms as to whether the swelling is contained indicating paratendonitis.  However, if the swelling moves, this is an indication of tendinosis.

Approximately 30% of Achilles tendon injuries are asymptomatic.  The test for this is the Thompsons squeeze test.  With the patient lying prone or kneeling on a chair, the calf muscles are squeezed and if plantarflexion is absent, then this is indicative of tendon rupture.  If  in doubt, then an ultrasonography, MRI, is diagnostic for soft-tissue injuries.  Tendon rupture requires immediate surgical referral.

Treatment This includes – alleviation of the symptoms and secondly, prevention of reoccurrence.

  • Identifying the causative factor can be simply rectifying training regimes (e.g. intensity and duration of exercises), changing footwear. Rehabilitation management may involve both modified exercise regimes to maintain cardiovascular activity e.g. may take the form of swimming, cycling (saddle height to be correct height avoiding excessive ankle dorsiflexion).
  • If excessive pronation, supination, biomechanical pathology is the causative factor to injury, then it may be necessary for orthotics to be utilised in order to prevent overloading of the tendon. Heel raises are a very simple and effective treatment in helping relief symptoms, however, these can only be used for the short-term otherwise they can in the long-term shorten the Achilles tendon.
  • Other treatment may include ultrasound, which may help promote local healing by stimulating collagen synthesis.
  • NSAIDs is commonly prescribed, however, if the individual has tendonosis which is not an inflammatory condition, it would stand to reason that NSAIDs would have very little effect except for its analgesic effects.
  • Steroid injections can be controversial because it may lead to further degeneration or increase the risk of rupture of the tendon.

Conservative treatment is usually effective in the management of degeneration or inflammatory cases of tendon injury, however, if symptoms do not improve, then surgery may have to be considered.   Surgery may include removing degenerative nodules and fibrotic adhesions, the aim is to initiate the healing process by restoring vascularity, and stimulate viable cells.

Rehabilitation In the painful acute stage, stretching is not recommended.  But once the pain has subsided, then stretching and strengthening exercises are recommended for rehabilitation of tendon pathologies.  Strong calf muscles will help reduce risk of tendon injury by easing stress load on the Achilles.

Achilles tendon-stretching – this exercise requires the patient to stand forward towards the wall, placing one leg behind the other (keep back straight).  The patient is to lean into the facing wall with the front knee flexed and the back leg fully stretched  behind (both feet firmly on the ground).  Hold this position for 10 seconds (repeat 10-20 times, 3 times daily).  Repeat the exercise, but with the back knee slightly bent.  Another exercise involves standing on the edge of the step, plantarflexing the ankle, raising the heel and lift the leg.   Then the leg is slowly lowered to the level of the step with the heel further dropping very slowly below the level of the step.  These exercises are a gradual process and should not be hurried.  As rehabilitation continues the individual may progress with the addition of using hand weights or even back packs.  However, when planning an exercise regime, the health professional may have to take into consideration the age and mobility/flexibility of the patient.

Referenced: Peter Burbridge (2008) Clinical presentation, diagnosis, treatment and rehabilitation of Achilles Tendon injury – Podiatry Now, Vol. 11, Issue 11.