Achilles tendon ruptures: lessons from professional sport and what it means for you.

28 July

Achilles tendon ruptures are receiving quite some airtime in sports media at present, with seven players in the recent NBA season experiencing this injury.

The Achilles tendon is in fact the strongest tendon in the body, but it is also the most frequently ruptured.

But before we get into how and why this is so, let’s first dive into what a tendon is…

What is a tendon?

Tendons are strong, flexible tissue that occur at either end of a muscle, connecting it to a bone.

Tendons are very strong, allowing them to transmit large mechanical forces between muscles and bones.

In simple terms, tendons store and release energy like a spring.

They transfer the force of a muscle contraction to our skeletal system, while also absorbing external forces acting upon our body to prevent injury to the muscle.

Tendon anatomy and cell structure

Tendons are primarily made up of an extracellular matrix, and a small percentage of tenocytes (specialised tendon cells).

These tenocytes are mechanosensitive, which means they sense and respond to mechanical loading of the tendon, such as stretch (tension), compression and shear motion. Surrounding the tendon cells is the extracellular matrix (ECM).

*Pictured: examples of mechanical loading of the tendon.*

The ECM construction varies depending on the specific tendon but provides the tendon with mechanical strength, elasticity and the ability to transmit force.

The key components that make up the ECM are:

Collagen: provides tensile strength (a tendon’s ability to withstand pulling or stretching forces without breaking a part).
Proteoglycans and GAGS: help to regulate collagen fibril formation, which is essential for maintaining the mechanical properties and structural integrity of tendons.
Elastin: provides elasticity and recoil.
Glycoproteins: contribute to their structure and function.
Water: essential for viscoelastic properties (how the tendon’s mechanical behaviour changes depending on how quickly it is stretched or loaded).
Cells: mainly tenocytes that maintain and remodel the ECM.

In other words, the ECM is the architecture of the tendon that gives the tendon its physiological properties.

The tenocytes within the tendon cause remodelling of the ECM in response to the mechanical stresses acting upon it.

*Pictured: components of the Achilles tendon.*

What is the role of the Achilles tendon?

The Achilles (calcaneal)  tendon is a common tendon shared between the gastrocnemius and  the soleus muscles of the lower leg.

The gastrocnemius muscle (the outermost muscle) has two heads, the medial and lateral.

The gastrocnemius muscle originates above the knee and so contributes to both knee flexion and ankle (plantar) flexion.

The soleus sits deeper within the calf compared to the gastrocnemius muscle, but originates from beneath the knee and so only contributes to ankle flexion.

The Achilles tendon connects these two muscle groups (collectively known as the triceps surae) to the calcaneus – your heel bone.

Through the action of the triceps surae the Achilles tendon helps with plantar flexion of the foot.

Plantar flexion is the movement that points the toes downward, away from the shin. When we are upright, this enables our heel to lift from the ground as we push the ball of our foot into the ground.

In biomechanical terms, the ankle functions as a second-class lever, which results in efficient force transfer.

This action is very significant in human movement and propulsion, responsible for actions such as walking, running and even jumping.

The anatomy of the tendon provides for both elasticity (recoil) and shock-absorbance in the foot.

It is estimated that the peak force transmitted through the Achilles tendon in humans during running is 9 kN, which is equivalent to 12.5 times body weight.

Both the level of muscle contraction and the tendon’s relative size influence the mechanical forces on a tendon.

In general, the greater the cross-sectional area of a muscle, the higher force it can produce and the larger stress its tendon undergoes.

Different activities induce different levels of forces, even on the same tendon.

How Achilles tendons are injured

Normal Achilles tendons can withstand a load of 400kg. Therefore, many have hypothesised that to rupture this tendon either a huge force is required, or a degenerative process must be present to weaken the tendon at the time of rupture.

An Achilles tendon injury occurs when significant forces are translated through a malaligned tendon with a dorsiflexed foot (see picture below) and an extended knee.

This can be due to chronic degeneration of the tendon or a breakdown in the body’s natural protective signalling system that prevents muscles from over-contracting and damaging the tendon.

In other words, the basis for an Achilles tendon rupture is believed to be due to a combination of intra-tendon degeneration and mechanical stress.

Because the tendon runs from a very compliant tissue (muscle) to a ridged stiff tissue (bone), the role of the tendon (if the tendon is compromised) can be very difficult and result in strain at the site of merging tissues. 

According to Arner et al, 33% of people experience posterior ankle pain prior to rupture, which may indicate an active degenerative process and impending rupture.

This has been confirmed by the presence of chronic inflammatory cells and degenerative tissue on histopathological testing.

Over the past several decades, the incidence of Achilles tendon ruptures has increased, likely due to an increasing participation in team sport.

Roughly 60 - 75% of ruptures take place in sporting activities, including basketball and soccer, with the highest incidence found in men between 30 and 39 years, although the incidence is increasing in older age groups.

In the most recent NBA season, seven players experienced an Achilles rupture, the most high-profile being Tyrese Haliburton, which occurred in game 7 of the NBA finals.

In the video below you can see the shock of the rupture ripple up his calf muscle from the 0.33 seconds mark.

In comparison, between 1970 and 2019, only 47 Achilles tendon ruptures occurred during the basketball season, which is roughly a little over one per season.

This is likely due to overuse/increased player load, fatigue from extended seasons and the high-intensity nature of basketball.

One interesting trend is that historically these tendon ruptures are more likely to occur earlier in the season, which may indicate that it is a lack of offseason conditioning, combined with the ‘ramp up’ in the early months of the season, that leaves players vulnerable.

Understanding tendon capacity and how this applies to Achilles ruptures

Capacity is a tissue's ability to withstand load without incurring damage or dysfunction.

Injuries occur when the load placed on a tendon exceeds its capacity.

Each tendon in the body has a specific capacity, and every individual has a unique level of capacity for their tendons.

When appropriate loads are placed on them, they respond favourably. However, when they are exposed to abnormal loads, they are negatively affected.

Optimal, progressive loads result in an increase in tendon integrity. 

This process happens slowly, and if too much load is placed on a tendon too quickly, it becomes susceptible to injury.

There is now a tendon continuum model to understand the stages a tendon goes through under excessive loading:

Normal tendon
Reactive tendinopathy
Tendon disrepair (failed healing)
Degenerative tendinopathy
Tear/rupture

Tendons are also slow to heal after an injury.

Risk factors for Achilles tendon ruptures

There are several risk factors for the increased likelihood of Achilles tendon ruptures.

There are the associated factors from alcohol, antihypertensives, eye drops, diuretics, cocaine, marijuana, gout, diabetes, rheumatoid arthritis, hyperparathyroidism and SLE.

And there is also a higher risk factor of injury associated with steroid injections.

Steroid injections increase the risk of rupture as they can speed up the degenerative process through fibroblast suppression and growth inhibition.

Steroid injections are one of the most prominent comorbid risk factors and is well-recognised for its association with tendon injuries.

Other comorbidities include cardiac disease, diabetes mellitus and Achilles tendinopathy.

How Achilles tendon ruptures are diagnosed and treated

A diagnosis for Achilles tendon rupture can be established with a physical examination of weakness of plantar flexion, a palpable gap in tendon, and a positive squeeze test (the Thomson test).

Interestingly, due to the other muscles that contribute to plantar flexion (plantaris, tibialis posterior, flexor longus muscles, peroneal), a person may not initially realise they have completely ruptured their Achilles as they will still have some weight bearing capacity.

An MRI or ultrasound is only really required to confirm diagnosis or for surgical planning.

Conservative care

Conservative care - or a non-surgical approach – usually results in the foot placed in a cast or splint, held in plantar flexion.

The patient may then wear a boot for several weeks, with restriction to only low-impact exercises for the first 6 months.

High-impact exercises are added after this, and patients can then return to play as soon as they feel comfortable.

Conservative treatment for acute rupture by immobilisation in a cast and then a boot provides satisfactory results for healing an Achilles tendon rupture.

Complications of the conservative care method include re-ruptures and residual lengthening of the tendon, which may result in significant calf muscle weakness.

Functional bracing and modified post-operative mobilization (including daily active plantar flexion exercises) may stimulate tendon healing and reduce the potential rate of re-rupture.

Surgical care

Surgical care for Achilles tendon rupture involves undergoing surgery to restore the proper length, function and tensile strength of the tendon.

For the younger, more athletic patient, surgical repair should be considered.

Chronic or delayed ruptures of the Achilles tendon are best managed with tendon transfers, advancement flaps and/or free tendon grafts.

Surgical vs conservative care

Surgical versus conservative care for Achilles tendon ruptures is a hotly debated issue.

The outcome will depend on level of activity or competition, the patient’s age and other factors.

Non-operative treatments have shown a higher incidence of re-rupture when compared with operative management of the injury.

When non-operative treatment is chosen, early functional rehabilitation is paramount to regain strength and mobility.

Historically, conservative management has had higher rates of re-rupture and patient reported outcomes.

Patients were typically casted in plantarflexion for long periods, leading to significant muscle loss and typically longer recovery.

Yet the benefit of conservative care is that patients don’t have to go through the surgical process and can avoid surgical complications such as infection and sural nerve injury.

In recent years, the need for surgical management of Achilles tendon ruptures has been decreasing due to a better understanding of non-operative care.

The results of a meta-analysis of Achilles tendon rupture care demonstrate that conservative treatment should be considered at centers using functional rehabilitation.

In this setting, this resulted in re-rupture rates similar to those for surgical treatment while offering the advantage of a decrease in other complications.

Surgical repair may be preferred at centers that don’t employ early range-of-motion protocols as this may decrease the re-rupture risk in such patients.

Preventative care

Unfortunately, there is no definitive way to protect against Achilles rupture occurring as this injury is often the result of an unfortunate combination of excessive force and tendon degradation.

But it is generally advised to find the middle ground between excessive loading and insufficient loading to promote tendon health.

For the Achilles tendon, this will mean maintaining a certain level of exposure to hopping/jumping movements, without overdoing it.

It is better for these ballistic-type movements to take place in a controlled setting, rather than only on the sporting field.

It is also advisable to expose the tendon to heavy, slow loads (e.g. weighted calf raises).

Some other factors to consider include:

Be careful if you are over the age of 30.
Pay attention to ongoing issues such as heel pain.
Don’t return to play too quickly or aggressively after other lower limb injuries.
Be cautious with movements that involve landing in a position of ankle dorsiflexion and hip extension, and then taking off quickly (e.g. turning around on the running track at the gym).
Maintenance of a continual level of activity counteracts the structural changes within the musculotendinous unit induced by inactivity and ageing.
Physically inactive lifestyles lead to a decrease in tendon vascularisation.
Proper warm-up and stretching are essential for preventing musculotendinous injuries, but improper or excessive stretching or warming-up can predispose to these injuries.

A quick note on Achilles tendinopathies

Achilles tendinopathies - although also an Achilles injury – are generally more of a chronic issue that takes time to manage and become pain-free.

Achilles tendinopathies often occur with repetitive movements and activities.

While Achilles tendinopathies are not a pre-cursor to an Achilles rupture (unless quite advanced), they are a risk factor, so be mindful of that.

Conclusion

In conclusion, the Achilles tendon - while the strongest tendon in the human body - is uniquely vulnerable due to its role in transmitting immense forces during activities like running and jumping.

Ruptures often stem from a combination of chronic degenerative changes and sudden excessive loading, exacerbated by factors such as age, medication use or inadequate tendon conditioning.

When ruptures occur, non-operative treatment with early functional rehabilitation offers outcomes comparable to surgery, with the added benefit of fewer complications.

However, surgical repair may still be optimal for younger, athletic individuals or in settings without structured rehab programs.

Prevention remains the best strategy: smart, progressive loading of the tendon through controlled load exercises, consistent physical activity, and cautious management of overuse and risk factors is key.

Be aware of early warning signs, such as particularly heel pain, overuse or unsafe landing mechanics, as they can precede injury.

By blending informed prevention strategies, accurate early diagnosis and tailored rehabilitation plans, clinicians and athletes can effectively reduce the incidence and impact of Achilles tendon ruptures.

References:

Achilles tendonAchilles tendon rupture

Timothy Morris