Introduction

Peroneal tendonitis is the inflammation of the peroneal tendons that are located in the outer part of the lower leg. It is characterised by pain in the hindfoot and lateral ankle, and instability of the foot and ankle.¹ It usually occurs when the tendons are chronically overloaded due to the ankle instability, malalignment (misalignment of the bones, muscles and tendons) of the peroneal tunnel. It is essential to treat the condition and its causes promptly, so as to stop its progression into chronic peroneal disorders.²

Anatomy and Function of Peroneal Tendons

The peroneal tendons extend from the peroneal longus and peroneus brevis muscles, located in the leg’s lateral compartment. The tendons pass through the common peroneal synovial sheath and are innervated by the peroneal nerve. The main function of peroneal tendon is the hind foot eversion (turning outside) and also to assist in plantar flexion of the ankle. The peroneal muscles are the first to respond to rapid inversion of the ankle, playing a vital role in  stabilizing the foot and lateral ankle. Delayed peroneal activation in that case has been suggested as a contributing factor for functional instability of foot following lateral ankle sprain.³

Biomechanical role of peroneal tendons⁴

Peroneus Longus Tendon (PLT)

• Sustain the lateral longitudinal arch of the foot and 
• Maintains the integrity of transverse foot arch
• Helps plantar flexion of ankle¹
• Eversion (turning inside out or outward) of the ankle / hindfoot¹

The contraction of the PLT⁴

• Reduces stiffness of foot
• Enhance energy storage in foot and 
• Helps stabilize the first ray (big toe joint) 

While walking, peroneal muscles contribute to stability of the foot from lateral to medial side, and prevent inversion of the ankle. The peroneal muscles are more active during the mid-stance phase of walking, when the body is supported with one leg and the foot is flat.⁵ Abnormal peroneal longus activity can lead to loss of plantar arch or flat foot, which can shift more stress to peroneal tendon.⁵

The peroneal longus locks and ensures structural stability of the first metatarsocuneiform joint when the foot bears whole body weight.⁶

Causes of Peroneal Tendonitis³

The cause of peroneal tendonitis includes both inherent and external factors

Inherent factors

• Anatomical Factors
• Biomechanical misalignments

External factors

• Prolonged repetitive athletic activities
• Ankle inversion injuries
• Chronic lateral ankle instability
• Cavovarus hindfoot alignment
• Improper footwear 
• Excessive training load

Symptoms¹

• Swelling and pain on the lateral side of the ankle that occurs over time
• Fluid build up in the tendon sheath associated with crepitus
• Pain on palpation along the course of peroneal tendons, behind  and below the fibular head
• foot and ankle instability

How foot structure influence load on PLT⁶

Feet is generally classified into three types. These are the common variations seen in foot structure of the general population which explain the configuration of medial longitudinal arch.

• Planus - low arch
• Rectus - a moderate arch
• Cavus - high arch

The function of the peroneal tendon varies according to the type of foot.

Planus

Individuals with planus foot type have reduced peroneal function which can increase the movement of the first ray  (big toe joint) and result in restricted dorsiflexion of first metatarsophalangeal joint during walking. It is characterized by impaired hindfoot eversion, lateral ankle pain and swelling, functional ankle instability, and reduced dorsiflexion.⁶

Pes Cavus

Pes cavus is a condition that is characterized by the  elevation of the longitudinal arch of the foot or high arched foot. It leads to abnormal positioning of the foot ⁷ and cause overload on peroneal.⁴

High arched feet are more stiff with reduced shock absorption.⁸ Which raises the chance of injuries to the ankle, bones (tibia / femur) and to the lateral aspect of the leg.⁸

Hindfoot varus

Generally during walking, peroneal longus plantar flex the first ray causing hindfoot varus. Having an already existing hindfoot varus can subject the peroneals to more force during walking and predispose it to inflammation, subluxation and possible tears.^1,3 Peroneal weakness can also result in hindfoot varus.³

Adult acquired flatfoot deformity (AAFD)

In flatfoot condition, 

• The first tarsometatarsal joint height is reduced which decreases the plantar flexion ability of peroneal longus tendon, and changes its pull towards outward (valgus) direction⁴
• The dorsiflexion instability of big toe joint and loss of lateral column height further increase the  load on the peroneal tendon causing tendinopathy⁴
• This compensatory shift places more tension on to the peroneus longus tendon to maintain the foot shape as there is a weakening of the spring ligament and plantar fascia in AAFD which leads to collapse of the arch⁴
• PLT overload can be covered by pain from other tendons (Tibialis posterior) or valgus impingement pain⁴

EMG studies have shown elevated peroneus longus activity in individuals with flatfoot, whereas peroneus brevis showed reduced activity which highlights its role as an evertor that may actually worsen the flatfoot condition.⁴

Evaluation

X-ray

The basic imaging test that should be performed in suspected peroneal disorder is X-ray of the ankle joint. 

• Take weight bearing X-ray
• Take the following views of ankle 
• AP view (anteroposterior)
• Lateral ankle view
• Take the following views of foot
• AP 
• Lateral
• Oblique - for detecting midfoot fracture and evaluating foot alignment

Ultrasound

To evaluate the tendon in motion¹

MRI 

For  high resolution view of tendon¹

Treatment

Non-surgical 

• Rest
• Immobilization - ankle cast¹
• Controlled ankle motion boot ¹

Rest and reduced activity helps to:⁹

• Decrease the load on the affected tendon
• Stop further tendon damage
• Decrease pain
• Promote the healing of tendon
• Ice - helps in relieving pain and inflammation⁹
• NSAIDS (Nonsteroidal anti-inflammatory drugs) - Both systemic and NSAIDs help in relieving tendinopathy pain¹
• Modification of shoe wear
• Use of lateral heel wedge helps to unload the force on peroneal tendons¹
• Orthotics and braces - are safe and widely used⁹
• Help to unload the tendon
• Protect tendon during activity
• Correct biomechanical issues like pes planus or cavus
• Physical Therapy¹⁰
• Ankle range of motion exercises
• Peroneal strengthening exercise
• Proper warm-up
• Proprioception

Once pain has subsided, physical therapy that includes strengthening and stretching exercise should be considered.⁹

Surgical¹

Hindfoot varus - Hindfoot osteotomy should be performed to minimise tension on the peroneus longus.

Summary

Careful history taking, thorough clinical examination including the assessment of foot type, correct use of imaging technique should be used for proper diagnosis of peroneal tendon pathology as it is usually missed during evaluation. The treatment of peroneal tendon disorders should include the correction of the foot structure.³ If the diagnosis and treatment is not prompt, the pathology can aggravate into a chronic condition which cannot be managed with supportive or non-invasive treatment and surgery becomes essential.¹¹