Achilles Tendinitis: Symptoms, Types, Causes and Treatment

Achilles tendinitis is a common condition that affects people of all activity levels, from elite athletes to those who enjoy occasional walks. The Achilles tendon, connecting the calf muscles to the heel bone, is the largest and strongest tendon in the human body. Despite its strength, it is highly susceptible to overuse injuries, particularly in those who engage in repetitive activities like running or jumping. Understanding the symptoms, types, causes, and available treatments for Achilles tendinitis can help individuals recognize the condition early and pursue effective management strategies.

Symptoms of Achilles Tendinitis

Achilles tendinitis can manifest in a variety of ways, often starting subtly before progressing to more significant discomfort. Recognizing these symptoms early can lead to quicker interventions and better outcomes.

Primary Symptom	Description	Associated Features	Source(s)
Pain	Aching or burning sensation in the back of the heel or lower calf, especially after activity	May worsen with prolonged activity or after periods of rest	1, 5, 9
Stiffness	Morning stiffness or after inactivity, improves with movement	Often most noticeable during first steps in the morning	1, 6
Swelling	Localized swelling over the tendon	Can be accompanied by warmth or thickening	5, 9
Reduced Strength	Decreased muscle power in the affected leg	Difficulty with activities such as pushing off or climbing stairs	1, 5

Table 1: Key Symptoms

Pain: Location and Characteristics

Pain is the hallmark symptom of Achilles tendinitis. It is typically localized at the back of the heel or just above it, often described as a dull ache, sharp pain, or burning sensation. For many, pain is worse after periods of activity (such as running) or after rest, such as first thing in the morning. The area may also be tender to the touch. In more advanced cases, pain may persist even during rest or at night 1, 5, 9.

Stiffness and Swelling

Morning stiffness is a frequent complaint, often easing as the tendon "warms up" with movement. Swelling and thickening along the tendon can develop, sometimes with visible nodules or bumps. The swelling may be accompanied by a sensation of warmth over the affected area 1, 5, 9.

Reduced Strength and Function

As the condition progresses, people may notice a reduction in calf muscle strength. This can make activities that require pushing off with the foot, like climbing stairs or running, noticeably harder. There may also be a sense of instability or weakness in the ankle 1, 5.

Other Associated Symptoms

• Crepitus: A crackling or creaking sensation may be felt when moving the tendon.
• Limited Range of Motion: Difficulty flexing the foot upwards (dorsiflexion) due to pain or stiffness.
• Functional Impairment: Difficulty participating in sports or even daily activities if the condition becomes chronic 1, 5.

Types of Achilles Tendinitis

Not all Achilles injuries are the same. The type and location of the problem often guide the approach to treatment. Understanding the differences between the main types is crucial for proper management.

Type	Location	Key Features	Source(s)
Insertional	Where tendon attaches to heel (calcaneus)	Pain at tendon-bone junction, often with swelling and possible bone spurs	5, 6, 9
Noninsertional	2–6 cm above heel insertion	Pain in mid-portion, thickening, nodules, more common in younger, active people	5, 6, 9, 11
Paratenonitis	Sheath surrounding tendon	Diffuse pain, swelling, sometimes crepitus, may occur with or without tendinopathy	4, 9, 13
Tendinosis	Within the tendon substance	Degenerative changes without true inflammation, chronic pain	5, 9, 7

Table 2: Types of Achilles Tendinitis

Insertional vs. Noninsertional Tendinitis

Insertional Achilles tendinitis occurs where the tendon meets the heel bone (calcaneus). It often presents with pain directly at the back of the heel, and there may be associated swelling, bony enlargement, or even calcification. This type is more common in less active or older individuals but can affect anyone 5, 6, 9.

Noninsertional (midportion) Achilles tendinitis involves the section of the tendon located 2–6 centimeters above the heel bone. This is the most common type in runners and active individuals. Pain, swelling, and thickening are typically found in this area, and nodular changes can be felt along the tendon 5, 6, 9, 11.

Paratenonitis and Tendinosis

Paratenonitis refers to inflammation or irritation of the sheath (paratenon) surrounding the tendon, rather than the tendon itself. This form can produce more diffuse pain, swelling, and sometimes a crackling sensation (crepitus) with movement. It may occur alone or in conjunction with tendinopathy 4, 9, 13.

Tendinosis describes chronic degeneration within the tendon, marked by disorganized collagen fibers, increased cellularity, and neovascularization, but without significant inflammation. This is now considered the predominant process in chronic Achilles pain and is often why the term "tendinopathy" is preferred by many experts 5, 9, 7.

Other Related Disorders

• Partial Ruptures: Can occur alongside chronic tendinopathy, especially if the tendon is weakened 4, 11.
• Retrocalcaneal Bursitis: Inflammation of the bursa between the Achilles tendon and heel bone, sometimes coexisting with insertional tendinitis 4, 9.
• Tenosynovitis: Technically refers to inflammation of a true synovial sheath, which the Achilles doesn't have, but the term is sometimes used interchangeably 3.

Causes of Achilles Tendinitis

Achilles tendinitis does not usually occur in isolation; it is the result of multiple interacting factors. Some are intrinsic, relating to the individual, while others are extrinsic, related to environment or activity.

Cause Type	Example Factor	Description/Effect	Source(s)
Overuse	Excessive running or jumping	Repetitive loading exceeds tendon capacity, leading to microtrauma	2, 5, 7
Biomechanical	Flat feet (overpronation)	Alters tendon loading, increasing risk	2, 7
Muscular	Calf muscle weakness/tightness	Reduces shock absorption, increases strain on tendon	2, 5
Intrinsic	Age, sex, genetic predisposition	Reduced blood supply, tendon structure changes with age	7, 5
Extrinsic	Footwear, training errors, medications	Inappropriate shoes or sudden increases in activity	2, 7, 5

Table 3: Major Causes and Risk Factors

Overuse and Training Errors

The most common cause of Achilles tendinitis is repetitive overuse, particularly in runners and athletes. Overtraining—such as increasing running distance or intensity too rapidly—places excessive stress on the tendon. Activities involving frequent jumping or abrupt direction changes also increase risk 2, 5.

Biomechanical and Muscular Factors

Altered biomechanics, such as overpronation (excessive inward rolling of the foot) or flat feet, can cause abnormal forces and a "whipping" effect on the Achilles tendon. Muscle imbalances or insufficient calf muscle strength/flexibility further elevate the risk by reducing the ability of the lower leg to absorb impact 2, 5, 7.

Intrinsic Factors

• Age: Older adults have decreased tendon elasticity and blood flow, making tendons susceptible to injury and slower to heal 7, 5.
• Sex: Some studies suggest males may be at higher risk, possibly due to activity patterns 7.
• Genetics and Systemic Conditions: Certain genetic factors, systemic diseases (like rheumatoid arthritis), and anatomical variations contribute to risk 7.

Extrinsic Factors

• Footwear: Inadequate or worn-out shoes fail to provide necessary support and cushioning 2, 7.
• Training Surfaces: Hard or uneven surfaces increase impact forces through the tendon 2.
• Medications: Some drugs, including certain antibiotics (fluoroquinolones) and steroids, have been linked to tendon degeneration 7.

Pathophysiological Mechanisms

Recent research has shown that Achilles tendinitis is predominantly a degenerative process (tendinosis), rather than a purely inflammatory one. Microtrauma leads to failed healing responses, disorganized collagen, and increased neovascularization, which may perpetuate pain and dysfunction 5, 9, 7.

Treatment of Achilles Tendinitis

Effective management of Achilles tendinitis requires a multifaceted approach, tailored to the severity, duration, and type of injury. Most cases respond well to conservative (non-surgical) measures, while surgery is reserved for persistent or severe cases.

Approach	Description	Typical Use Case	Source(s)
Exercise Therapy	Structured calf muscle eccentric exercises, stretching	First-line for most cases	1, 12
Activity Modification	Rest, cross-training, gradual return	Acute or overuse injuries	1, 5
Medications	NSAIDs, pain relievers	Short-term symptom relief	5, 10
Physical Therapy	Manual therapy, modalities (e.g., ultrasound, laser)	Adjunct to exercise	1, 10
Orthotics	Heel lifts, supportive footwear	Address biomechanical issues	2, 6
Injections	Corticosteroids, platelet-rich plasma (PRP)	Selected refractory cases	12
Surgery	Debridement, tendon repair, paratenon release	Chronic/severe or failed conservative care	11, 13

Table 4: Treatment Modalities

Exercise-Based Therapy

Eccentric calf muscle exercises are the cornerstone of Achilles tendinitis treatment. These exercises, which involve lengthening the muscle-tendon unit under load, are strongly supported by clinical evidence and are often the first-line recommendation. They help stimulate tendon remodeling and improve function 1, 12.

• Programs usually span 6–12 weeks.
• Can be performed at home or under physical therapist supervision.

Activity Modification and Load Management

Reducing or temporarily halting activities that provoke symptoms (e.g., running, jumping) allows the tendon to recover. Cross-training with low-impact activities (like swimming or cycling) can help maintain fitness while minimizing tendon stress. A gradual return to activity is crucial to prevent recurrence 1, 5.

Medications and Modalities

Nonsteroidal anti-inflammatory drugs (NSAIDs) can provide short-term pain relief, although their role is limited in chronic, degenerative cases. Physical therapy modalities, such as low-level laser therapy (LLLT), have shown promise in reducing local inflammation and pain, particularly in acute presentations 10.

Orthotics and Footwear Adjustments

Correcting biomechanical issues with heel lifts, arch supports, or custom orthotics can offload the tendon and reduce pain. Proper footwear with good cushioning and support is also essential, especially for those with flat feet or overpronation 2, 6.

Injections

Various injections, including corticosteroids and platelet-rich plasma (PRP), are sometimes used for persistent cases, though evidence for their efficacy is mixed. These may help selected patients but are generally not first-line due to potential risks 12.

Surgical Intervention

Surgery is reserved for cases that do not respond to prolonged conservative management (typically >6 months). Surgical options include:

• Debridement: Removal of degenerated tendon tissue.
• Paratenon release: For cases involving sheath inflammation.
• Tendon repair/reconstruction: Especially in those with partial ruptures or severe degeneration.

Outcomes are generally favorable, especially in motivated athletes, but as with any surgery, there are risks of complications 11, 13.

Emerging and Adjunctive Treatments

• Shockwave therapy: May help stimulate healing in some cases.
• Night splints: Used as adjuncts, especially for insertional tendinopathy 12.
• Novel biologics and regenerative therapies: Under investigation but not yet standard care 5.

Conclusion

Achilles tendinitis is a multifactorial condition that, while common, can significantly impact quality of life and athletic performance. Early recognition and a tailored treatment plan are vital for optimal recovery.

Key Points:

• Symptoms often include pain, stiffness, swelling, and reduced strength, most commonly felt at the back of the heel or lower calf.
• There are several types, with insertional and noninsertional tendinitis being the most common. Understanding the type helps guide treatment.
• Causes are multifactorial, involving overuse, biomechanical abnormalities, muscle imbalances, age, and extrinsic factors like footwear and training methods.
• Treatment is typically conservative, focusing on exercise therapy, activity modification, and addressing underlying risk factors. Surgical options exist for chronic, refractory cases.

By understanding the complexity of Achilles tendinitis and the spectrum of management options, individuals can take informed steps toward recovery and prevention.