FHL Tendinopathy

Flexor Hallucis Longus (FHL) Tendinopathy

Article by Z.Russell, N.Stewart

What is FHL Tendinopathy?

FHL Tendinopathy is when pain emanates from the collagen fibres that compose the Flexor Hallucis Longus (FHL) tendon. Tendinopathy can occur at three locations along the length of the FHL tendon, including:

  1. The back of the ankle
  2. Under your mid-foot
  3. Under the base of your big toe

What is FHL Tenosynovitis?

FHL Tenosynovitis is inflammation or swelling that occurs to the sheath through which the FHL tendon passes. Often the terms FHL tendinopathy and tenosynovitis are used interchangeably, and the two conditions often occur together.

What are Tendons?

Tendons are the tough fibres that connect muscle to bone. Most tendon injuries occur near joints, such as the shoulder, elbow, knee, ankle and foot. A tendon injury may seem to happen suddenly, but usually, it results from many tiny tears to the tendon that have occurred over time.

Who Suffers from FHL Tendinopathy or Tenosynovitis?

FHL Tendinopathy and Tenosynovitis occurs most commonly in several athletic populations where training programs involve excessive, repetitive or prolonged loading of the FHL tendon. These populations include:

  • Athletes of all ages who participate in activities requiring large amounts of forefoot push-off including: running, jumping, hopping and rising onto the toes, e.g. ballet dancers, long-distance runners, soccer players, ice skaters, divers and gymnasts.
  • The general population, who have recently returned to physical activity involving large amounts of forefoot push-off
  • Workers in standing based roles. These may include correctional or security officers, nurses and hospitality staff.

What are the Signs and Symptoms of FHL Tendinopathy or Tenosynovitis?

FHL Tendinopathy and Tenosynovitis often present with a gradual onset of pain. They are less likely to occur with acute trauma, such as changing the type or quantity of activity in a training program involving forefoot push-off.

Symptoms of FHL Tendinopathy and Tenosynovitis as a result of gradual onset include:

  • Pain in the form of a dull ache that worsens to sharp pain with forefoot activity pushes off, including walking, running, jumping, hopping, rising onto the toes, demi-pointe work and pointe work.
  • Pain along the length of the FHL tendon. Pain can occur in several locations, including:
    • the back or inside of the ankle,
    • underneath the arch of the foot,
    • underneath the base of the big toe.
  • Swelling in the rear/inside of the ankle.
  • Occasional clicking at the back or inside of the ankle.
  • Pain with movement of the big toe.
  • Potential locking or catching of the big toe if left untreated.

FHL Tendinopathy and Tenosynovitis are rarely present due to acute trauma. In these sporadic cases, the symptoms are similar to those of FHL Tendinopathy and Tenosynovitis resulting from overuse. However, the injury mechanism will be different and is usually the result of a direct, blunt knock to the back of the ankle.

(Brukner & Khan, 2006; Howell, 2015; Mak & Assai, 2016; Michelson & Dunn, 2005; Peters, 2015)

Why Does FHL Tendinopathy or Tenosynovitis Occur?

The FHL muscle design is to assist with the movement of the ankle, foot and big toe. The FHL muscle’s role is to allow the foot to point at the ankle and the big toe and let the heel roll in at the heel inwards. This function enables us to perform activities such as: running, jumping, hopping and rising onto the toes.

The FHL tendon, like any other tendon in the body, becomes accustomed to a certain amount of loading to assist with movement. However, when overloading over a short period without time to adjust, or if an insult occurs to the FHL tendon that lowers its ability to tolerate load without adequate time to heal, the FHL tendon can become overused. Overuse results in damage to the collagen fibres, which make up the tendon. This damage leads to the tendon being unable to perform its role, which leads to further changes in the tendon’s structure, ultimately leading to pain and dysfunction.

What are the Risk Factors of FHL Tendinopathy and or Tenosynovitis?

Many factors can contribute to FHL tendinopathy and tenosynovitis, including:

Intrinsic Factors

  • Poor Foot Control
  • Poor Ankle Control
  • Tight or weak musculature in the foot and leg
  • Incorrect Training Technique
  • Previous Injury

Extrinsic Factors

  • Training Activities
  • Recent Change to Training Program
  • Training Environment
  • Amount of Training
  • Training Equipment
  • The fit of shoes if required
  • Fatigue
  • Inadequate Warm Up and Cool Down

How is FHL Tendinopathy or Tenosynovitis Diagnosed?

Several strategies can diagnose FHL Tendinopathy and Tenosynovitis correctly. Your physiotherapist will usually ask you some questions regarding your injury and perform several physical tests. Imaging is another option that your healthcare practitioner can also use to diagnose FHL Tendinopathy and Tenosynovitis.

Physiotherapist / GP Outcome Measures

  • Pain Description
  • Pain Location
  • History of Injury
  • Activity Levels / Changes
  • Pain Provocation
  • Functional Activities
  • Specific Muscle Tests


  • Ultrasound
  • MRI

Treatment for FHL Tendinopathy and Tenosynovitis


Exercise is vital in managing FHL Tendinopathy and Tenosynovitis to enable the FHL tendon to adopt a new activity level without increased pain, inflammation or further tendon degeneration. As you recover, your physiotherapist will help you progress your exercise program through several phases based on your stage of recovery. This progression usually occurs by utilising a traffic light system based on the loading your FHL tendon can tolerate enabling a safe return to activity. Your physio will progress you based upon your physiotherapist’s professional assessment.

Load Management, Activity Modification and Activity Prioritisation

Optimising your FHL tendon’s recovery is crucial to participate in training and everyday activities with tendinopathy limitations. As a result, you may need to temporarily modify your training activities or decrease the number of training sessions. All training sessions and actions should not aggravate your pain during and after training 24 to 48 hours.

Stretches, Massage, Foam Rollers and Trigger Balls

Massage, foam rolling, or a trigger ball can be used on your calves, back of the ankle, and under the foot to assist with recovery by lengthening tight muscles and decreasing the FHL tendon’s tension.

You can also perform stretches as long as the stretch is felt across the muscle belly of the FHL (deep leg), rather than at the FHL tendon at the back of the ankle, under the arch of the foot or at the base of the big toe.

Transverse Frictions & Ultrasound

Transverse friction or tendon massage and ultrasound can assist in healing FHL Tendinopathy and Tenosynovitis, as long as the individual tolerates the technique. This occurs through the increased circulation to the damaged area.

Adjacent Joints & Lower Limb Biomechanics

Your physiotherapist will ensure that your surrounding joints and muscles move and activate appropriately to prevent the FHL from overworking and overloading the FHL tendon. Areas where biomechanics are fundamental in FHL Tendinopathy and Tenosynovitis cases, include the ankle, foot, and toes.

Medications / Pharmacology

You can use NSAIDs, corticosteroids, and other pain and anti-inflammatory medications in conjunction with physiotherapy to help recover FHL Tendinopathy and Tenosynovitis by helping to settle pain inflammation locally. Your physiotherapist may refer you to a GP or sports doctor to discuss what medications are required in your management of FHL Tendinopathy and Tenosynovitis.


Splinting is not always required to treat FHL Tendinopathy and Tenosynovitis and is generally only utilised in advanced cases.


In advanced FHL Tendinopathy and Tenosynovitis, surgery can be utilised as a last resort following the failure of conservative treatment strategies to reduce the tendon’s constriction. If surgery is required, physiotherapy is usually followed to assist with rehabilitation and return to regular activity.

How is Your Treatment Rehabilitation Monitored?

Your physiotherapist will work with you to regularly assess your ability level as you progress through your rehabilitation program. This occurs through the retesting of some outcome measures to determine your progress. Your physiotherapist can even work with your support team (family, boss, coach, teachers etc.) to assist with your recovery and eventual return to your regular activities.