The thickest and the strongest tendon in our body is the tendon of the calf muscles of the leg also known as the “Achilles tendon”.
As shown in Fig 1, the calf muscles of the leg include the gastrocnemius and the soleus muscles that tapers and merges with a tough connective tissue of the Achilles’ tendon. The Achilles tendon then inserts into the heel bone (calcaneus). Functions of the Achilles Tendon
- Downward Movement of the foot: When the calf muscles contracts and pulls the Achilles tendon it causes the foot to push downward. This contraction enables: gait, standing on the toes, running, and jumping.
- Bending the knee: The gastrocnemius muscle helps in bending the knee (flexion) during walking and running.
- Transferring body weight: With each step of walking each of the Achilles tendon help to distribute the person’s body weight. Depending upon the speed, stride, terrain and additional weight being carried or pushed, each Achilles tendon may be subjected to approximately 3-12 times a person’s body weight.
- Ankle stability: Along with the other muscles of the leg the Achilles tendon contributes to the stability of the ankle joint.
What surrounds the Achilles tendon? The Achilles tendon is protected by the Achilles tendon sheath and bursae. The sheath is the covering of the tendon that protects the tendon from friction and allows smooth movements. Similarly, the bursae around the Achilles is a thin fluid-filled sac that help to reduce friction between tendon and other tissue areas of the heel.
As shown in Fig 2, there are two bursae present at the heel. One of the bursae is present in between the surface of the tendon and the surface of the calcaneus at the distal attachment of the Achilles tendon. It is called the “retrocalcaneal bursa”. The other bursa is present between the calcaneum and the skin and is called as the “subcutaneous calcaneal bursa”.
Brief History on Achilles tendon injuries
Because of the Greek Achilles legend, the Achilles heel is known as a vulnerable part for injury. Hippocrates described that “this tendon if bruised or cut causes the most acute fevers, induces choking, deranges the mind and at length brings death”. It was first reported that a ruptured tendon was to be wrapped with bandages dipped in wine and spices. Since then the cause and treatment of Achilles tendon injuries have brought growing interests among many researchers.
What causes an Achilles tendon injury?
- Overuse injuries
This is mostly sports related and is due to overuse of the calf muscles causing an injury to the Achilles tendon. Overdoing or rapid action of the calf muscles or resuming too quickly after a layoff can stress the Achilles tendon. For example, while running or walking faster, up and down on steeper hills or stairs more powerful movements such as lunges, jumps, or push off.
- Misalignment and muscle imbalances
Short or tight Achilles tendons or calf muscles, unequal leg length, over or under arched foot, disproportionally weak calf muscles.
- Improper Footwear
- Side effects of certain medications
Medications (Quinolone / Fluoroquinolone and Cortisone) can weaken the Achilles tendon and this may lead to an injury. Cortisone shots in or near the Achilles tendon may reduce pain in the Achilles tendon, but the weakness in the tendons persists which can an injury during activities.
- Accidental trauma
- Inflammatory conditions
Achilles injury may occur in relation to inflammatory illnesses, such as ankylosing spondylitis, reactive arthritis, gout or rheumatoid arthritis.
Individuals with a genetic predisposition like hypermobile people are reported to be more at risk of developing Achilles tendon problems. This is because they have excessive laxity in ankle joints that lead to the wear and tear of the Achilles tendon.
Achilles tendon injuries
As shown in Fig 3, different types of Injuries to the tendon can occur along different locations of the tendon.
Musculotendinous junction: This explains the junction between the calf muscle and the Achilles tendon.
Mid portion of the tendon: This explains an injury midway between the top and bottom of the Achilles tendon.
Insertional Achilles tendon injury is an injury at the bottom of the Achilles tendon, where the Achilles tendon connects with (inserts into) the heel bone.
Non-insertional Achilles tendon injury means an injury to any part of the Achilles tendon except at the Achilles tendon – heel bone connection.
Types of Achilles injuries
The spectrum of Achilles injuries ranges from an acute inflammatory irritation to severe cases of rupture of the tendon as shown in Fig 4. The types of condition may co-exist depending on the severity of the injury.
Tendonitis and tenosynovitis
Achilles tendonitis is an acute inflammation of the Achilles tendon as shown in Fig 5. Tenosynovitis is an inflammatory condition of the Achilles tendon sheath, rather than an inflammation in the Achilles tendon itself.
Achilles Tendinosis (Tendinopathy): This is the degeneration and micro tears of the Achilles tendon that occurs over time due to overuse of an already inflamed and weak tendon (Refer Fig 6).
Both Achilles tendonitis and tenosynovitis can occur in parallel with, or lead to Achilles tendinosis.
Tendon Ruptures (Partial or complete tendon tear) Achilles tendon rupture is often described as an abrupt break with instantaneous pain that is felt in the foot or heel area. It occurs rapidly while performing activity like running or standing on the toes, which generates intense force on the tendon, leading to partial or complete rupture as shown in Fig 7.
What can happen if you have an Achilles tendon injury?
- Pain and tenderness along the Achilles tendon and at the back of the heel that worsens with activity.
- Thickening of the tendon
- Bone spur formation at the insert of the tendon
- Bruising and Swelling around the tendon area.
- Fibrosis and scarring may be seen in Achilles Tenosynovitis and tendinosis.
- Restriction of Achilles tendon’s motion within the Achilles tendon sheath.
- Bursitis: Inflammation of the bursas around the Achilles tendons.
- Snapping or popping noise can indicate a tendon rupture.
- Difficulty in moving the foot or pointing your toes (in complete tears of the tendon)
- A limp may be seen on weight bearing immediately after an Achilles tendon rupture
- Ankle instability
- Nerve or blood vessel damage: Signs include numbness, tingling, pins-and-needles sensation in your foot and bruised skin.
How is an Achilles tendon injury diagnosed? An initial examination of the ankle can help differentiate a tendon rupture from other types of injury. When an Achilles tendon rupture occurs, it will not be possible for the individual to stand on toes as shown in Fig 8.
An MRI or X-ray investigation can also be taken to further confirm the severity of the injury and differentiate the type of injury to the tendon. For example, an MRI scan of a ruptured Achilles tendon is shown in Fig 9.
When to seek expert care?
If you felt a sharp pain like a direct hit to the Achilles tendon or if you heard a distinct snap at your Achilles tendon, it calls for a medical emergency. If you have just begun with pain in the back of heels with swelling or discomfort in the Achilles tendon, it would be wise to seek expert assessment and treatment care. What may seem like a mild inflammation may lead to degeneration and rupture. Thus, an initial treatment for tendonitis will not only reduce problems of the tendon but will restore its strength and function which is important to prevent worsening and recurrence of the condition.