Achilles Tendinopathy Mid-Portion

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Achilles Tendinopathy (Mid-Portion)

Clinical Anatomy

Achilles tendinopathy represents a prevalent and challenging condition frequently encountered in clinical practice, particularly among athletes and physically active individuals.

The Achilles tendon is the largest and strongest tendon in the human body, formed by the convergence of the gastrocnemius and soleus muscles. It inserts onto the posterior aspect of the calcaneus and plays a crucial role in plantarflexion of the ankle, which is essential for activities such as walking, running, and jumping.

The tendon is composed of dense, parallel primarily type I collagen fibres, which confer tensile strength. It is enveloped by its paratenon, the loose connective tissue sheath that facilitates its smooth gliding. The Achilles tendon is relatively avascular, especially in its mid-portion, which makes it more susceptible to degenerative change and impairs healing.

Insertional and Mid-portion Tendinopathies

Anatomically, the Achilles tendon can be divided into two regions: insertional and mid-portion. Insertional Achilles tendinopathy affects the tendon near the attachment site, at the transition zone between the Achilles tendon and the calcaneus (less than 2 cm from its insertion). Mid-portion tendinopathy occurs in the relatively hypovascular zone of the tendon (more than 2 cm away from its insertion).

Pathophysiology of Achilles Tendinopathy

Achilles tendinopathy (as with all tendinopathies) is a degenerative rather than inflammatory condition. The pathophysiology involves a complex interplay of mechanical overload, cellular responses, and extracellular matrix changes, leading to chronic tendon degeneration.

Mechanical Overload and Microtrauma

• Repetitive loading and excessive tensile stress in running and jumping cause micro trauma to tendon collagen fibers, leading to a failed healing response and inadequate tendon matrix repair

Degenerative Changes (Tendinosis)

• Tendinosis is marked by non-inflammatory tendon degeneration, with collagen fiber disorganization, increased ground substance, and mucoid degeneration. Histologically, it shows collagen disruption, hypercellularity with fibroblasts and myofibroblasts, neovascularization, and a lack of inflammatory cells.

Neovascularisation and Nerve Infiltration

• Neovascularisation, accompanied by sensory nerve ingrowth, occurs in response to tendon degeneration and is linked to increased pain perception in tendinopathy.

Extracellular Matrix Remodeling

• Upregulation of matrix metalloproteinases (MMPs) and other degradative enzymes leads to extracellular matrix breakdown, altering tendon structure and impairing mechanical properties.

Inflammatory Mediators

• Though primarily degenerative, tendinopathy shows evidence of low-grade chronic inflammation, with inflammatory mediators like cytokines, prostaglandins, and substance P contributing to pain and matrix degradation.

Aetiology of Achilles Tendinopathy

Achilles tendinopathy is a multifactorial condition influenced by a combination of intrinsic and extrinsic aetiological factors. Understanding these factors is crucial for effective prevention, diagnosis, and treatment.

Intrinsic Factors

• Age – Tendinopathy is more common over age 30 due to age-related decreases in collagen synthesis, tendon elasticity, and vascularity, increasing susceptibility to degeneration
• Gender – Males are more frequently affected than females, likely due to higher activity levels involving repetitive tendon loading and possible hormonal influences on tendon structure.
• Genetic Predisposition – Genetic factors, including polymorphisms in collagen and MMP-related genes, can affect tendon structure and metabolism, increasing tendinopathy risk.
• Biomechanical Abnormalities – Abnormal foot mechanics, leg length discrepancies, and poor limb alignment can disrupt load distribution across the Achilles tendon, increasing the risk of tendinopathy.
• Comorbidities – Obesity, diabetes, hypertension, and hyperlipidemia increase the risk of tendinopathy by impacting tendon metabolism, blood supply, and tissue health.

Extrinsic Factors

• Training Errors – Sudden increases in training intensity, volume, or frequency without proper rest, along with inadequate warm-up and recovery, can overload tendons, causing microtrauma and degeneration.
• Footwear – Inappropriate footwear, including high heels, can alter biomechanics, increase Achilles tendon stress, and raise the risk of tendinopathy.
• Surface Conditions – Running or training on hard, uneven, or sloped surfaces increases tendon load and risk of injury.
• Occupational Activities – Occupations requiring prolonged standing, walking, or heavy lifting increase stress on the Achilles tendon and risk of tendinopathy.

Differential Diagnosis

The differential diagnosis includes the following:

• Achilles Paratendinopathy
• Achilles Tendon Rupture
• Retrocalcaneal Bursitis
• Insertional Calcific Tendinitis
• Haglund’s Deformity
• Posterior Ankle Impingement Syndrome

• Pain near the tendon’s attachment to the calcaneus (in insertional tendinopathy) or 2–6 cm above the attachment (in mid-portion tendinopathy).
• Pain is often described as aching, sharp, or burning.
  
• Pain worsens with activities like sprinting, hill running, or jumping, especially during or after exercise, and improves with rest.
• Muscle tightness in the gastrocnemius-soleus complex.
• Morning stiffness in the affected tendon area, especially upon waking, which gradually eases with activity.

• The affected Achilles tendon may appear thicker compared to the unaffected side.
• Swelling may occur around the Achilles tendon, especially in the acute phase.
• The range of motion in the ankle joint may be limited.
• Passive dorsiflexion (stretching) and active plantarflexion (contracting) may cause pain.
• Insertional tendinopathy shows tenderness near the tendon’s attachment to the calcaneus, while mid-portion tendinopathy presents tenderness 2–6 cm above the attachment.
• A creaking or grating sensation (crepitus) over the tendon during ankle movement may indicate paratendinopathy.
• Positive Arc test.
• Positive Royal London Hospital test.
• Negative Thompson and Matles tests.

• Plain Radiography – Achilles tendinopathy is primarily a clinical diagnosis, and imaging is generally unnecessary unless there is a need to rule out other conditions, such as a stress fracture or tendon rupture. Plain radiographs are typically not helpful in assessing Achilles tendon pathology but may reveal a heel spur or bony prominence (Haglund’s deformity), which are both associated with tendinopathy and calcaneal bursitis.
• Ultrasound and MRI – Ultrasound can detect enthesopathy or avulsion injuries at the distal portion of the tendon. MRI provides more detailed anatomical information and is more accurate in identifying partial Achilles tendon tears. In cases of tendinopathy, MRI may show an increased T2-weighted signal within the tendon or an increased tendon diameter.

The following are examples of red flags for patients presenting with ankle pain:

• A history of significant injury
• Severe pain
• Unrelenting pain
• Nocturnal pain
• Unexplained weight loss
• Fever
• Deformity
• Significant swelling
• Presence of tingling, numbness, burning, or other neurological impairment
• Significant loss of range of motion
• Severe tenderness on palpation or severe pain with any examination procedure

If any red flags are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Differentiating Achilles Conditions

Distinguishing between Achilles tendinopathy, Achilles rupture, retrocalcaneal bursitis, and paratendinopathy (paratenonitis) is essential for accurate diagnosis and effective treatment. Each condition affects the Achilles region differently, with unique clinical presentations that can guide diagnosis. Understanding key signs and symptoms, such as pain location, onset, and functional limitations, can help clinicians differentiate between these common causes of pain in the Achilles region.

Achilles Tendinopathy

• Pain Location: Pain is usually felt along the mid-portion of the Achilles tendon or near its insertion on the heel.
• Pain Characteristics: Gradual onset of pain, often dull or achy, which can progress to sharper pain with activity.
• Aggravating Activities: Pain worsens with running, jumping, or climbing stairs, particularly in the morning or after rest.
• Swelling and Thickening: The tendon may feel thickened or swollen.
• Pain on Palpation: Tenderness along the tendon, especially when squeezed.
• Positive Tests: Arc and Royal London Hospital tests.

Achilles Rupture

• Pain Location: Pain along the Achilles tendon region.
• Pain Characteristics: Immediate sharp or intense pain, often described as feeling like a “kick” in the back of the leg, accompanied by a snapping or popping sensation.
• Functional Limitation: Inability to push off when walking or standing on the ball of the affected foot.
• Visible Defect: A gap or indentation may be felt or seen along the tendon.
• Positive Tests: Thompson and Matles Tests.

Retrocalcaneal Bursitis

• Pain Location: Pain is localized just above the heel, deep to the Achilles tendon.
• Pain Characteristics: Dull, aching pain accompanied by swelling, warmth, and tenderness of the bursa.
• Aggravating Activities: Pain worsens with walking uphill or climbing stairs, and footwear pressure.
• Swelling: Swelling may be visible in the area just above the heel. Pain increases when the area on both sides of the Achilles tendon (just above the heel) is compressed.

Paratendinopathy (Paratenonitis)

• Pain Location: Pain is along the Achilles tendon, often spreading up and down the tendon rather than localized.
• Pain Characteristics: Acute, burning pain.
• Swelling and Redness: The tendon may appear swollen, with warmth and redness along its length.
• Aggravating Activities: Pain with activity, especially repetitive movements like running and sometimes even at rest.
• Crepitus: Palpable or audible crepitus when the tendon is moved, indicating inflammation of the tendon sheath (paratenon).

Myofascial Pain Syndrome Causing Posterior Ankle and Heel Pain

In patients presenting with posterior ankle and heel pain, a complete clinical examination should include an evaluation for myofascial pain syndrome as either the primary cause of the pain or as a concomitant condition. The trigger points associated with myofascial pain syndromes may be located anywhere within a muscle and its fascia. Therefore, the entire muscle should be examined thoroughly. However, based on our clinical experience, the common locations for trigger points for myofascial pain syndromes that produce posterior ankle and heel pain are presented below. The primary muscles to evaluate include the tibialis posterior and soleus (distal trigger point).

Alfredson Protocol for Achilles Tendinopathy 

The Alfredson Protocol is a specific rehabilitation program designed to treat Achilles tendinopathy through targeted eccentric exercises. Developed by Dr. Håkan Alfredson, this protocol involves performing controlled, slow, eccentric (lengthening) contractions of the calf muscles to stimulate tendon healing, reduce pain, and strengthen the Achilles tendon. This method has been widely used and supported by research for its effectiveness in managing chronic Achilles tendinopathy. The protocol includes “Straight-Knee Heel Drop” and “Bent-Knee Heel Drop.” For detailed instructions, please refer to the Patient Exercise Sheet PDF on this webpage.