With marathon season quickly approaching, many runners' training plans are now starting to increase in intensity, and peroneal tendinopathy is a key topic to be aware of.

What is peroneal tendinopathy?

The peroneal muscles are located on the outside of the lower leg and ankle. These two muscles — the peroneus longus and peroneus brevis — function to evert the foot (turn the sole of the foot outward). They also weakly assist in plantarflexion (pointing the foot away). This means that when weight-bearing, they are always working to control and stabilize the position of our feet.

The peroneal muscles attach to the fibula head (just below the outer knee) and the upper third of the fibula itself. They travel down the lateral leg and the tendons begin just above the level of the lateral malleolus (outer ankle bone). The tendons then pass behind and below the malleolus.

The peroneus brevis tendon attaches to the base of the fifth metatarsal (on the outer foot). The peroneus longus tendon continues under the sole of the foot, inserting into the medial cuneiform and first metatarsal.

Tendinopathy is a term used to cover myriad overuse/degenerative tendon conditions such as tendinitis, tendinosis, tenovaginitis and tenosynovitis. It is nearly impossible to distinguish these particular tendon conditions without detailed scanning and potentially even biopsies — and in reality, the exact pathology matters little. Therefore, the term tendinopathy is used to cover all possibilities.

What are the symptoms?

• Pain on the outer ankle/foot — anywhere between the area behind the ankle bone, to the brevis attachment on the fifth metatarsal
• Pain with running — can be from the outset, come on mid-run or maybe not until after finishing
• Pain that becomes gradually worse and more long-lasting if ignored
• Pain with inverting or everting the foot (turning it in or out)
• Tenderness when pressing along the length of the tendons
• Mild swelling may be visible
• A feeling of instability around the ankle when weight-bearing

What causes it?

Peroneal tendinopathy is a classic overuse injury. It occurs with a gradual onset due to repeated excessive use of the tendon, overstretching of the tendon or possibly friction to the tendon from the surrounding bony structures.

There is no sudden moment of injury, such as with an ankle sprain where the tendons can be torn. However, previous ankle sprains that involved damage to the peroneal tendons can increase the risk of future tendinopathy.

Running is one of the most common ways to develop peroneal tendinopathy. Other weight-bearing activities, such as walking or sports involving running and jumping, can also trigger peroneal tendon issues.

You are particularly susceptible if you ...

• are rapidly increasing your mileage
• run on your forefoot
• have started running up hills
• are wearing inadequate footwear
• rapidly or excessively overpronate at the foot
• run on the outside of your foot
• have poor lower limb biomechanics

How is it treated?

The most important factor in peroneal tendinopathy treatment is that it needs catching quickly to avoid irreparable damage to the tendon. As soon as you feel pain in the lateral ankle/foot, stop your training, rest and seek professional advice.

The longer you continue to train on it, the more damage you are doing. Eventually, the structure of the tendon changes irreversibly, and this leads to weakness and a peroneal tendon dysfunction, which could reduce your foot's ability to roll in and flatten, resulting in a pes cavus or high-arched foot type.

Initial treatment is aimed at reducing the pain, inflammation and swelling (if present). This can be achieved with rest, anti-inflammatory medications and ice. A physical therapist may recommend certain footwear or strap your foot to reduce the use of the tendon. They may also use other therapies such as ultrasound or laser to reduce the inflammation. A topical ibuprofen gel can be applied to the area.

Once pain has eased, the next stage of treatment should be to address the cause of the condition. The cause of your particular case of peroneal tendinopathy could be very different from a fellow sufferer. Therefore, it is important that a physical therapist performs a thorough assessment and together you consider all the potential causes in relation to your own case.

Without establishing and addressing the causative factors, it is most likely that a return to running will only result in a return of your symptoms.

The assessment

This may require long conversations with your physical therapist about your training history and current program to determine whether this could be the cause. Increasing mileage too quickly is a common mistake that results in stresses on the tendon, which it is not yet strong enough to withstand.

Adding in hill training either in excess or too regularly can also be a culprit. This is due to the change in gait while running uphill to a forefoot strike, which generally makes the ankle less stable and so requires more work from the stabilizing peroneals.

Your physical therapist should also perform a thorough assessment to determine any biomechanical causes. The range of motion of the ankle, knee and hip should be tested, as should the strength of the muscles in this area. The PT should look at the foot for positions such as forefoot varus, which can contribute to the condition. It is also helpful to see the running shoes you have been wearing so that wear patterns can be identified.

Observing movement patterns using squat and lunge exercises can be helpful to identify any muscle imbalance issues. A common pattern is to see the knees fall in during a squat, which indicates weak hip abductors, or the inability to achieve a full depth of squat, which can be due to tight calf muscles.

Once you can comfortably run for a few minutes, the PT should observe your running gait. Ideally, you should be videoed and analyzed to pick up issues such as excessive pronation, point of foot contact, hip adduction, anterior pelvic tilt, contralateral pelvic dip, etc.

Common muscular dysfunctions and biomechanical causes

In order to understand the causes in detail, you need to understand the role of the muscle.

The peroneals act concentrically to evert the foot, i.e. the muscle shortens to twist the foot so that the sole is pointing outward (sometimes inaccurately known as pronation). The muscles also act eccentrically to decelerate the opposite motion, i.e. they lengthen under tension to slow rapid inversion (turning the sole inward — also sometimes inaccurately known as supination).

Therefore, peroneal tendinopathies are particularly common in those who run more on the outside of their feet — "supinators" — as the peroneals work hard to repeatedly, rapidly and forcefully evert the foot to bring the forefoot into contact with the ground. Thankfully, this is far less common than those whose foot collapses inward — "pronators."

Another factor along these lines that may contribute to the development of the injury is running on crowned or cambered roads. Running along the edge of a road, especially on smaller countryside roads often means that the road will be "cambered," i.e. it slopes down toward the outside. This in itself requires extra work from the peroneals as they fight to pull the inner foot down toward the road surface.

Running on uneven surfaces such as trails and footpaths also provides extra work for the peroneal muscles and tendons. As mentioned above, the peroneals are active stabilizers of the foot and work hard on uneven or slippery surfaces to ensure we stay upright and don't roll the ankle.

As is often the case in ankle and foot injuries, tight calf muscles can also play a part. If the gastrocnemius and/or soleus are tight, this reduces the available range of ankle dorsiflexion (pulling the foot up). When walking and running, the body often compensates for this by increasing pronation (overworking the peroneals) so that the overall stance isn’t shortened. So, stretching the calf muscles can help.

But the bigger question is, why are the calves tight in the first place? My go-to test if I find tight calves in runners is for glute max function. Weakness or even inhibition here (which is common — especially in those with an otherwise sedentary lifestyle) means the calves work overtime to propel the body forward, resulting in fatigue and tension.

Conclusion

Peroneal tendinopathy can be a difficult condition to treat. This is mostly due to the challenging and so often incomplete task of determining the cause of the condition.

While easing the initial pain can usually be achieved with rest, a return to running will typically result in a flare-up of symptoms. The causative factor(s) must be identified and corrected in order to prevent continued tendon stress.