Orthopaedic Surgery - Achilles Tendinitis

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Basics

Achilles tendinitis is a common overuse disorder involving the Achilles tendon and the surrounding soft tissues. It represents a spectrum of conditions that may affect the tendon itself, the paratenon surrounding it, and the retrocalcaneal bursa.

The clinical spectrum ranges from acute painful inflammation of the Achilles tendon and its surrounding sheath to chronic degenerative tendinosis, partial tearing, or eventual tendon rupture.

Several related terms are commonly used. Retrocalcaneal bursitis refers to inflammation of the retrocalcaneal bursa without primary involvement of the Achilles tendon. Paratenonitis describes inflammation of the paratenon surrounding the tendon. Achilles tendinitis refers to acute inflammatory changes within the tendon, frequently associated with inflammation of the paratenon. Tendinosis describes chronic degeneration of the tendon substance with structural deterioration rather than predominantly acute inflammation.

Achilles tendon disorders are also described according to their location. Noninsertional disease usually occurs several centimeters proximal to the attachment of the tendon to the calcaneus, whereas insertional disease occurs directly at the posterior calcaneal attachment.

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General Prevention

Prevention focuses primarily on avoiding excessive or abrupt mechanical loading of the Achilles tendon. Repetitive uphill running should be limited, particularly when an athlete is not adequately conditioned.

Training errors should also be avoided. Running distance, speed, or intensity should be increased gradually rather than suddenly, because rapid increases in mileage are an important contributor to Achilles tendon overload.

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Epidemiology

Achilles tendinopathy is particularly common among recreational and competitive athletes, especially distance runners. It is also frequently encountered in physically active middle-aged adults.

The apparent male-to-female distribution generally reflects the proportion of men and women participating in the relevant sporting activity rather than a marked biological sex difference.

Chronic degenerative Achilles tendinosis can also occur in middle-aged and elderly patients who do not regularly participate in sports. Therefore, although athletic overuse is an important cause, Achilles tendon degeneration is not restricted to athletes.

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Incidence

Achilles tendon disorders have been reported in approximately 6% of runners, emphasizing the close relationship between repetitive running activity and tendon overload.

The typical area of tenderness in noninsertional Achilles tendinitis is located above the heel, usually involving a relatively broad region of the tendon.

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Risk Factors

Several systemic and local factors increase the likelihood of developing Achilles tendon disease. A prominent posterosuperior calcaneal tuberosity, commonly referred to as a Haglund prominence or Haglund process, may increase mechanical irritation around the insertion of the tendon.

Systemic conditions associated with microvascular impairment may predispose the tendon to degeneration. These include diabetes mellitus, systemic lupus erythematosus, rheumatoid disease, and other connective-tissue disorders.

Patients with chronic renal disease who undergo hemodialysis or peritoneal dialysis may also have increased susceptibility to Achilles tendon abnormalities.

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Pathophysiology

The Achilles tendon is composed predominantly of type I collagen, which accounts for approximately 95% of its collagen content. At rest, the collagen fibers have a characteristic wavy arrangement that allows the tendon to elongate and absorb force during activity.

The tendon is surrounded throughout most of its length by a thin, gliding paratenon. This tissue functions as an elastic sleeve that allows the tendon to move freely relative to surrounding structures.

Blood supply to the Achilles tendon is provided by intrinsic vessels originating from the musculotendinous and osteotendinous junctions, together with an extrinsic vascular supply derived from the paratenon.

A relatively hypovascular region exists approximately 2–6 cm proximal to the calcaneal insertion. This region corresponds closely with the common site of noninsertional Achilles tendinopathy and rupture.

True chronic inflammatory changes involving the tendon and paratenon are relatively uncommon. By contrast, tendinosis, characterized by chronic mucoid degeneration and disruption of the normal collagen architecture, is considerably more common.

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Etiology

Training errors account for a substantial proportion of cases, with approximately 60–80% related to inappropriate changes in physical activity. A sudden increase in running distance or intensity, a change in footwear, or a change in the training surface may overload the tendon.

Running on hills, rough ground, or uneven terrain increases the mechanical demand on the Achilles tendon. Improper footwear can further alter lower-limb mechanics and increase tendon stress.

Adverse environmental conditions such as snow, ice, or cold weather may also contribute by changing running mechanics or reducing tissue flexibility.

Biomechanical abnormalities anywhere along the kinetic chain, extending from the lumbar spine to the foot, may increase Achilles loading. Examples include excessive pronation, pes cavus, and leg-length discrepancy.

Insufficient preparation before exercise is another contributing factor. Repeatedly performing vigorous activity after an inadequate, shortened, or absent warm-up and stretching period may predispose the tendon to injury.

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Associated Conditions

An important associated condition is Achilles tendon rupture. Chronic tendon degeneration may progressively weaken the tendon and increase the risk of partial or complete rupture.

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Diagnosis

Signs and Symptoms

Patients usually describe a gradually increasing area of pain, swelling, and warmth along the course of the Achilles tendon. Symptoms may occur anywhere from the musculotendinous junction to the calcaneal insertion.

The most common location of pain is approximately 3–5 cm proximal to the tendon insertion on the calcaneus.

Repetitive microtrauma, such as continued running, often worsens the symptoms. An acute increase in force, such as a single powerful jump, may also produce sudden deterioration in a previously symptomatic tendon.

Pain typically improves to some degree with rest, although chronic cases may remain symptomatic during routine daily activities.

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Physical Examination

The ankle should be assessed for pain during dorsiflexion, as stretching the Achilles tendon may reproduce symptoms.

The entire tendon should be palpated carefully to identify the precise site of tenderness. In severe inflammatory cases, the tendon sheath may feel thickened or swollen, and crepitus may be present during ankle movement.

The examiner should also assess for nodular thickening or focal swelling within the tendon, which may indicate chronic tendinosis.

A Thompson test should be performed whenever tendon rupture is a concern. Failure of plantarflexion during calf compression suggests disruption of the Achilles tendon.

Swelling, warmth, or a boggy sensation immediately anterior to the insertion of the tendon is more suggestive of retrocalcaneal bursitis.

A single-limb heel-rise test is useful for evaluating Achilles tendon function and strength.

The remainder of the lower limb should also be assessed for structural abnormalities that may contribute to tendon overload. These include pes cavus, leg-length discrepancy, scoliosis, and equinus deformity.

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Laboratory Tests

Routine laboratory investigations are generally unnecessary in uncomplicated Achilles tendinopathy.

Laboratory evaluation may be appropriate when the history or clinical examination raises suspicion of an underlying inflammatory arthritis, systemic connective-tissue disorder, or another systemic inflammatory condition.

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Imaging

Plain Radiographs

Weight-bearing radiographs of the foot are useful when insertional disease or associated bony abnormalities are suspected. Standard views include anteroposterior, lateral, and oblique radiographs.

Radiographs should be examined for a prominent posterosuperior calcaneal tuberosity consistent with a Haglund deformity.

Other findings may include calcaneal insertional spurring and calcification within the Achilles tendon, the latter being associated with chronic degenerative tendinosis.

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MRI

Magnetic resonance imaging is particularly useful when the clinical findings suggest significant tendinosis, partial tearing, or tendon rupture.

A normal Achilles tendon demonstrates homogeneous low signal intensity on all MRI sequences. Its anterior surface is normally flat or slightly concave, and the tendon typically has a crescent-shaped appearance proximally and an ovoid configuration at its insertion onto the calcaneus.

Normal Achilles tendon thickness is generally less than 8 mm.

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MRI Findings in Acute Paratenonitis

In acute paratenonitis, MRI may demonstrate loss of the normal sharp interface between the Achilles tendon and the pre-Achilles fat.

T2-weighted imaging may reveal increased signal intensity surrounding the tendon and extending into the pre-Achilles fat, representing edema and inflammation. The tendon substance itself usually remains relatively low in signal intensity.

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MRI Findings in Chronic Achilles Tendinopathy

Chronic Achilles tendinopathy is commonly associated with tendon thickening. The tendon may measure more than 8 mm in thickness and may appear enlarged or fusiform.

The normally concave anterior tendon margin may become flattened or convex.

On T1-weighted MRI sequences, chronic degeneration may produce heterogeneous areas of increased signal within the tendon substance, reflecting structural disorganization.

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MRI Findings in Achilles Tendon Rupture

Achilles tendon rupture most commonly occurs approximately 3–5 cm proximal to the calcaneal insertion.

A partial tendon rupture typically produces focal areas of increased signal intensity within the tendon on T2-weighted sequences while preserving at least some continuity of the tendon fibers.

A complete rupture demonstrates complete loss of tendon continuity, with separation of the torn ends and a fluid-filled or high-signal gap on T2-weighted imaging.

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Ultrasound

Ultrasound is another useful method for assessing the Achilles tendon, although diagnostic accuracy is strongly influenced by the skill and experience of the examiner.

Ultrasound may demonstrate fluid surrounding the tendon, adhesions involving the peritendinous tissues, abnormal tendon thickening, degenerative changes, and partial or complete tendon tears.

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Differential Diagnosis

Conditions that may mimic Achilles tendinitis include precalcaneal bursitis, retrocalcaneal bursitis, peroneal tendinitis or tendon rupture, posterior tibialis tendinitis or rupture, and inflammatory arthritis.

A partial or complete Achilles tendon rupture must always be considered, particularly in patients with sudden functional deterioration. Rupture may represent the terminal stage of a chronically degenerative Achilles tendon.

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Treatment

General Measures

Treatment is usually conservative during the early and acute stages. Initial measures include rest, ice, NSAIDs, heel lifts, footwear modification, and correction of associated biomechanical abnormalities with appropriate orthoses.

Activities that aggravate symptoms should be temporarily reduced or modified. Gentle Achilles tendon stretching can be introduced as symptoms permit.

A carefully performed injection into the retrocalcaneal bursa may sometimes be considered when bursitis is the predominant pathology.

Patients who remain symptomatic despite these measures may benefit from temporary immobilization in a walking boot or cast.

Corticosteroid injection directly into or around the Achilles tendon is generally avoided because corticosteroids may weaken tendon tissue and increase the risk of subsequent rupture.

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Physical Therapy

Physical therapy plays an important role in rehabilitation. During appropriate phases of healing, modalities such as therapeutic ultrasound, phonophoresis, and iontophoresis may be used as adjunctive treatments.

Short-term use of a heel wedge can reduce tension across the Achilles tendon and may help during the painful stage.

As symptoms improve, rehabilitation should progressively focus on restoring flexibility, strength, endurance, and lower-limb conditioning.

Eccentric loading exercises are particularly important in the rehabilitation of chronic Achilles tendinopathy and are commonly incorporated into structured strengthening programs.

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Medication

First-line pharmacological treatment generally consists of nonsteroidal anti-inflammatory drugs for symptomatic pain relief during painful or inflammatory episodes.

Other simple analgesics may also be used when required.

Medication should be regarded as an adjunct to activity modification and rehabilitation rather than as definitive treatment for chronic degenerative tendinosis.

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Surgical Management

Surgical intervention may be considered when symptoms remain significant despite approximately 3–6 months of appropriate nonoperative treatment.

The surgical approach depends on the underlying pathological process.

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Surgery for Paratenonitis

Persistent symptomatic paratenonitis may be treated by surgical release or removal of diseased paratenon tissue.

This is commonly performed through a longitudinal medial incision, allowing the surgeon to release adhesions and excise chronically inflamed or fibrotic tissue surrounding the tendon.

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Surgery for Achilles Tendinosis

Chronic Achilles tendinosis may require intratendinous debridement, in which abnormal degenerative portions of the tendon are excised while preserving healthy tendon fibers.

When insertional pathology is present, surgery may also include a retrocalcaneal bursectomy and removal of a prominent Haglund exostosis.

Extensive tendon degeneration may leave insufficient healthy Achilles tendon for reliable repair. In these situations, reconstruction may require augmentation with another tendon.

Possible options include augmentation with the plantaris tendon or tendon transfer using the flexor hallucis longus tendon.

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Follow-Up

Patients should be reviewed periodically during treatment to assess pain, tendon tenderness, strength, range of motion, and functional recovery.

Return to running or sporting activity should be gradual. Full activity is generally resumed only after symptoms have settled and appropriate flexibility, strength, and endurance have been restored.

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Prognosis

The overall prognosis for Achilles tendinopathy is generally favorable, particularly when biomechanical factors and training errors are corrected.

However, recovery may be prolonged, especially in patients with chronic tendinosis. Improvement may occur gradually rather than immediately, and rehabilitation frequently requires sustained modification of activity together with a progressive strengthening program.

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Complications

Chronic degeneration may progressively weaken the Achilles tendon and ultimately result in partial or complete rupture with loss of normal function.

Persistent pain, recurrent tendinopathy, residual weakness, and incomplete recovery may occur in severe disease.

Surgical treatment also carries the possibility of unsatisfactory healing or treatment failure, particularly in patients with extensive degenerative tendon involvement.

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Patient Monitoring

Routine follow-up is recommended until symptoms have resolved and the patient has regained adequate strength and function.

Monitoring should include assessment of pain, swelling, tendon integrity, ankle motion, calf strength, heel-rise ability, and tolerance of progressively increasing physical activity.