Achilles tendon

The Achilles tendon is the largest and strongest tendon in the human body, connecting the calf muscles to the calcaneus. It plays a critical role in locomotion, allowing plantarflexion of the foot and efficient energy transfer during walking, running, and jumping. Due to its high functional demands, it is prone to various injuries and degenerative changes.

Introduction

The Achilles tendon, also known as the calcaneal tendon, links the gastrocnemius and soleus muscles to the posterior surface of the calcaneus. It is essential for normal gait mechanics, enabling push-off during the stance phase of walking and running. Its structural properties allow it to withstand significant tensile forces, but overuse or trauma can lead to tendinopathy or rupture.

Anatomy

Gross Anatomy

The Achilles tendon originates from the convergence of the gastrocnemius and soleus muscles and inserts onto the posterior aspect of the calcaneus. It lies posterior to the ankle joint and is enveloped by the paratenon, a thin connective tissue layer that facilitates gliding.

Structure

• Composed primarily of type I collagen fibers arranged in parallel bundles.
• Length ranges from approximately 15 to 20 cm in adults.
• The tendon exhibits a twisted configuration, allowing it to absorb and transmit forces efficiently.

Blood Supply

• Proximal and distal portions receive blood from the musculotendinous junction and calcaneal insertion, respectively.
• The mid-portion, approximately 2–6 cm above the insertion, is a watershed zone with relatively poor vascularity and is more susceptible to injury.

Nerve Supply

• Innervated by branches of the tibial nerve.
• Contains proprioceptive fibers that contribute to balance and coordinated movement.

Physiology

Function

The Achilles tendon enables plantarflexion of the foot at the ankle joint, allowing push-off during walking, running, and jumping. It transmits forces generated by the gastrocnemius and soleus muscles to the calcaneus, facilitating forward propulsion and maintaining postural stability.

Biomechanics

• The tendon can withstand tensile forces up to 6–8 times body weight during activities such as running and jumping.
• Acts as a spring, storing elastic energy during the stance phase and releasing it during push-off, increasing locomotor efficiency.
• Absorbs shock and distributes load across the ankle and foot.

Adaptation

• Responds to repetitive loading through collagen remodeling, increasing tensile strength and thickness.
• Overuse or excessive strain without adequate recovery can lead to microtears and degenerative changes.

Pathology

Tendinopathy

• Chronic degeneration of the tendon due to overuse, often without significant inflammation.
• Commonly affects the mid-portion of the tendon, particularly the hypovascular zone.

Tendon Rupture

• Acute rupture usually occurs during sudden acceleration or jumping activities.
• Can be partial or complete, resulting in significant loss of plantarflexion strength and impaired gait.

Insertional Disorders

• Retrocalcaneal bursitis: inflammation of the bursa between the tendon and calcaneus.
• Haglund’s deformity: bony prominence at the posterior calcaneus causing mechanical irritation of the tendon.

Other Conditions

• Tendonitis: acute inflammatory response, often from repetitive microtrauma.
• Calcific tendinopathy: deposition of calcium within the tendon fibers.
• Paratenonitis: inflammation of the paratenon, the connective tissue surrounding the tendon.

Clinical Presentation

Symptoms

• Pain and tenderness along the posterior aspect of the heel, particularly during activity.
• Swelling or thickening of the tendon.
• Stiffness, especially in the morning or after periods of inactivity.
• Functional limitations such as difficulty walking, running, or performing plantarflexion movements.

Physical Examination

• Palpation reveals tenderness, nodularity, or crepitus along the tendon.
• Thompson test: absence of plantarflexion when the calf is squeezed indicates rupture.
• Assessment of ankle range of motion and calf muscle strength.
• Observation for asymmetry or deformity at the insertional region.

Red Flags

• Sudden, severe pain with a popping sensation suggesting acute rupture.
• Inability to stand on tiptoe or perform plantarflexion against resistance.
• Signs of infection such as redness, warmth, or systemic symptoms if post-surgical or traumatic.

Diagnostic Evaluation

Imaging

• Ultrasound: useful for assessing tendon integrity, tears, and tendinopathy.
• MRI: detailed visualization of tendon structure, partial or complete ruptures, and associated soft tissue changes.
• X-ray: primarily to identify calcific deposits, bony deformities, or Haglund’s deformity.

Laboratory Tests

• Generally not required unless systemic inflammatory or metabolic disorders are suspected.
• Inflammatory markers or metabolic panels may be indicated in atypical presentations.

Treatment

Conservative Management

• Rest and activity modification to reduce stress on the tendon.
• Physical therapy focusing on stretching, strengthening, and eccentric loading exercises.
• Use of orthoses, heel lifts, or supportive footwear to offload the tendon.

Pharmacologic Treatment

• Nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief.
• Corticosteroid injections may be used cautiously for localized inflammation, with awareness of rupture risk.

Surgical Management

• Tendon repair for acute complete ruptures.
• Debridement and repair for chronic tendinopathy unresponsive to conservative measures.
• Reconstruction techniques for severe degeneration or complex tears.

Rehabilitation

Post-Conservative Therapy

• Gradual progressive loading of the tendon using eccentric exercises.
• Strengthening of the gastrocnemius-soleus complex and surrounding musculature.
• Balance and proprioception training to prevent recurrence.

Post-Surgical Rehabilitation

• Initial immobilization period in a cast or boot to protect tendon repair.
• Progressive weight-bearing and range-of-motion exercises as healing permits.
• Return-to-sport protocols tailored to the individual, typically after 4–6 months.

Complications

• Re-rupture of the tendon, particularly after premature return to activity or inadequate healing.
• Chronic pain, stiffness, or reduced range of motion following injury or surgery.
• Infection, particularly after surgical intervention.
• Tendon elongation or weakness leading to impaired plantarflexion and altered gait mechanics.
• Adhesion formation between the tendon and surrounding tissues, limiting mobility.

Prevention

• Gradual increase in activity intensity to allow tendon adaptation.
• Regular stretching and strengthening exercises targeting the calf muscles and Achilles tendon.
• Use of appropriate footwear that provides heel support and cushioning.
• Avoidance of repetitive overuse, especially on hard or uneven surfaces.
• Education on early recognition of tendon pain and timely intervention to prevent progression to chronic injury.

Prognosis

The prognosis of Achilles tendon injuries depends on the type and severity of the condition, as well as the timeliness and adequacy of treatment. Most patients recover fully with conservative or surgical management, although recovery timelines may vary.

• Partial tears and mild tendinopathy generally respond well to conservative treatment with full functional recovery.
• Complete ruptures require surgical repair for optimal strength and function, with a return to pre-injury activity typically within 4–6 months.
• Chronic or recurrent injuries may result in persistent stiffness, weakness, or reduced athletic performance.
• Early diagnosis and adherence to rehabilitation protocols significantly improve outcomes.

References

1. Magnusson SP, Kjaer M. The impact of loading, unloading, and aging on the human tendon. J Physiol. 2003;546(Pt 1):271-281.
2. Riley G. The pathogenesis of tendinopathy. A molecular perspective. Rheumatology (Oxford). 2004;43(2):131-142.
3. Clancy WG Jr. Achilles tendon disorders. Curr Opin Orthop. 1996;7:45-52.
4. Maffulli N, Kader D. Tendinopathy of tendo Achillis. J Bone Joint Surg Br. 2002;84(1):1-8.
5. Longo UG, Ronga M, Maffulli N. Achilles tendinopathy. Sports Med Arthrosc. 2009;17(2):112-126.
6. Leppilahti J, Orava S. Total rupture of Achilles tendon. Sports Med. 1998;25(4):79-100.
7. Alfredson H, Lorentzon R. Chronic Achilles tendinosis: recommendations for treatment and rehabilitation. Sports Med. 2000;29(2):135-146.
8. Khan KM, Cook JL, Bonar F, et al. Histopathology of common tendinopathies. Sports Med. 1999;27(6):393-408.
9. Maffulli N, Longo UG, Gougoulias N, et al. Achilles tendon ruptures. Lancet. 2011;377(9779):612-625.
10. Becher C, Faulhammer P, Mauch F, et al. Management of Achilles tendon injuries. Dtsch Arztebl Int. 2017;114(39):655-662.