Dancer's Tendonitis

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Original Editor - Puja Gaikwad

Top Contributors - Puja Gaikwad, Vidya Acharya, Wanda van Niekerk and Kim Jackson  

Introduction

The ankle is a crucial joint to acknowledge in the context of dance injuries because it is the connection between the leg and the foot that establishes lower limb stability. It is one of the most commonly injured body areas in dance. Incidences of injury to the ankle-foot complex scale from 27% to 49% of total injuries in ballet, modern, flamenco, and tap dancers. Dancer’s tendonitis is also referred to as Flexor Hallucis Longus tendonitis which is an overuse injury in which repetitive Plantarflexion and Dorsiflexion (pointing and flexing) of the foot results in inflammation of the FHL tendon.

In dancers, injury to the FHL is usually provoked by the recurrent movement caused by changing position from a plié position to a relevé position. (Plié is a French term meaning to bend, relevé, is a ballet term meaning “raised.” The term relevé explains the action when a dancer rises up on their toes). This movement of action produces a force that is ten times the dancer's body weight.

The Flexor Hallucis Longus (FHL) has been also called as the ‘Achilles of the foot’ due to its unique role controlling midfoot pronation and supination, and its physiological and mechanical properties, which permit it to act as a powerful convertor of force from the rear foot all the way through to the big toe. Due to its anatomical arrangement and its unique actions, it is a muscle-tendon unit that can often become injured in athletic populations. This is often called the ‘dancers tendonitis’ because it is so prevalent in classic ballet dancers. However, it's going to affect any sport which requires repetitive push-off and extreme plantarflexion such as swimmers, sprinters, footballers, and gymnasts.

Relevant Anatomy and Biomechanics

The FHL arises from the posterior and distal two-thirds of the fibula, the interosseous membrane of the limb and to the intermuscular septa. It's distal and lateral to the muscle belly of the flexor digitorum longus (FDL) and deep to the soleus and gastrocnemius. It is pennate in shape and therefore the fibres of the muscle continue and converge on its tendon because it crosses the posterior surface of the lower tibia. The FHL tendon then passes posterior to the talus and deep to the medial retinacular structures at the posteromedial ankle. It is surrounded within a synovial sheath and passes through a fibro-osseous tunnel between the medial retinaculum and therefore the lateral tubercles of the talus. Because it turns to course towards the arch, it sits below the sustentaculum tali, which forms a horizontal sheath of bone on the Calcaneus. The FHL is, therefore a part of the tarsal tunnel, and within the tunnel, it lies posterior to the neurovascular bundle. As the tendon of FHL moves through the arch of the foot, it crosses over the FDL tendon to lie on top of it. This is termed as the ‘knot of Henry’. At this level, the FHL is dorsal to the medial edge of the plantar fascia. This tendon continues to extend between the two Sesamoid bones of the first Metatarsophalangeal (MTP) joint where it is covered by the intersesamoid ligament and inserts at the base of the distal phalanx of the great toe. The FHL therefore, associates with three retinacular structures (at the tarsal tunnel, Knot of Henry and inter-sesamoid ligament) and this has implications for generating abnormal compression and stress on the tendon that can lead to an injury.

Injury to FHL occurs when the dancer is not fulfiling the natural requirements of movement through the joints. For instance,  when executing relevé it creates sickling and unstable foot positions because their forefoot is not strong enough and the limb external rotation and hip joint muscular support are not synchronous with the heel raises. In contrast, when executing plié, the result of poor control of weakened foot muscles is due to strain on the passive supporting structures, like the plantar ligaments, ankle joint capsules, and plantar fascia, etc. This result in faulty bone alignment, increased bone load, and risk of overuse syndromes in different tissues. Both these manoeuvers put tremendous strain on the ankles and feet because the bones are loaded in weight-bearing and the soft tissues must tether the bones sufficiently to control their positions and minimize the occurrence of injury.

Causes

While the accurate cause of FHL injury is debated, it is thought that constriction occurs at the fibro-osseous tunnel in the posterior ankle in and around the tarsal tunnel or the Knot of Henry in the midfoot or intersesamoid ligament. This pseudo- entrapment generates repetitive microtrauma, usually occurs due to gradual wear and tear associated with overuse. Although irritation may happen at the knot of Henry and within the sesamoids of the great toe, the most commonly irritated location is deep to the flexor retinaculum, where the tendon lies within the fibro-osseous tunnel.

Recurrent irritation of the tendon’s sheath can lead to hypertrophy of the tendon within this tunnel. Thickening or fibrosis may impede the normal gliding of the tendon, thus creating pain and movement restrictions. Increased pain and decreased use can cause weakness of the tendon and muscle. Adhesions and the development of calcific nodules can follow.

When the foot is fully plantarflexed, the relative inconsistency among the FHL and the fibro-osseous tunnel exists. This might cause abnormal stresses and resultant tenosynovitis to the FHL tendon. Injury at the level of the talus may also occur due to an abrupt change in direction of the tendon at this level. Other likely causes can relate to a low-lying FHL muscle belly or an accessory FDL. Immunohistochemical studies on cadaveric tendons have recognised avascular zones where the tendon wraps around the talus and where the tendon intersects the first metatarsal head. This can all be combined by the high tensile loads imposed on the FHL tendon as a dancer/ athlete jumps and lands and absorbs shock through the foot and thus FHL tendon.

Dancer’s tendonitis is more common in female ballet dancers who spend plenty of time en pointe or demi-pointe. FHL tendonitis can occur as a primary condition, or as a secondary condition of os trigonum impingement syndrome. Failure to accurately treat inflammation may result in a nodule (obstruction of the fibrous tunnel the tendon runs through) or partial or complete tear of the tendon.

Dancers are exposed to a wide range of risk factors for this kind of injury. The most common issues that cause injuries are:

• Type of dance and frequency of classes, rehearsals, and performances
• Duration of training
• Environmental conditions like hard floors and cold studios etc.
• Equipment used, especially shoes
• Individual dancer's body alignment
• Prior history of injury
• Nutritional deficiencies

Clinical Signs and Symptoms

Subjective Assessment

Injury to the FHL tendon is typically characterised by pain situated posterior and inferior to the medial malleolus, which gets worse by jumping and landing or going from demi-pointe to full pointe. Demi-pointe position in ballet is when the dancer is on the balls of their feet, referred to as half-point and Full Point (en pointe position) is when the dancer has a completely extended vertical foot). In dancers, the FHL tendon is typically compressed while performing a relevé position and is overstretched while performing a plié position. In such cases, the dancer will feel pain around the posteromedial ankle when performing the plié. This can also be incorporated with a sensation of crepitus in the tendon and triggering of the great toe depending on the severity of the tendon injury. Triggering can also involve an inability to relax the toe after full plantar flexion when pointing the foot, resulting in a locking sensation of the great toe. That is also usually painful because as a result, when it begins to fray, the tendon gets swollen, irritated, and inflamed, their fluid accumulates around that area, and the patient experiences swelling and pain.

Objective Assessment

Clinical examination of the foot and ankle in a dancer with a suspected FHL injury involves specific attention to four regions of the foot and ankle:

• Posterior ankle
• sustentaculum tali
• Plantar midfoot
• The level of the sesamoids

The ankle and great toe are held in either a neutral or dorsiflexed position to put the FHL under tension. Proximally, the muscle and the musculotendinous junction are palpated just posterior and lateral to the posterior tibial tendon. Medially and inferior to the sustentaculum tali, the FHL is often palpated as it passes through the fibro-osseous tunnel. At the plantar surface, the FHL can be found just plantar to the navicular and medial cuneiform bone, and it can often be palpated as it traverses the knot of Henry. Distally, the FHL is palpated while it travels between the sesamoids.

There will also be pain with resisted flexion of the IP joint. Great toe triggering can be felt with active or passive motion with no tenderness at the level of the first metatarsal head. Resistance to the FHL could also be painful. Often, one can best elicit pain by placing the ankle in the plantar flexion and pressing on the FHL tendon area while moving the great toe into a forced dorsiflexion position. This will result in pain and tenderness at the point of manual compression in the posterior ankle region. Symptoms can be further provoked with ankle inversion. It can decrease the dimension of the tarsal tunnel causing more compression or irritation to the FHL tendon.

Positive Tomasen test: This test assesses the influence of the FHL on first MTP motion. This test is performed by assessing first MTP motion in both positions that is, in maximal plantarflexion and moderate dorsiflexion of the ankle. To perform the test accurately, the first metatarsal head should be stabilised to avoid compensatory first metatarsal head plantar flexion. A positive test consists of discomfort or reduced first MTP joint extension by 20 degrees with ankle dorsiflexion. When you allow the patient to release the foot and to now plantarflex and point the foot, then they will have a better range of motion of the big toe. So this occurs because when putting the foot into dorsiflexion, it makes that tendon taut.

Diagnostic Procedures

X-Rays will not provide an accurate diagnosis of FHL injuries. Nevertheless, X-Rays are good for ruling out fractures that can cause an impingement of the FHL tendon (calcaneus, distal medial malleolus, or os trigonum). A comprehensive patient history, followed by a full physical examination is usually critical for accurately diagnosing this condition. On the other hand, in some cases, MRI is required to evaluate tears in the FHL tendon and any sources of impingement of the FHL. One of the best diagnostic examinations for FHL tendonitis condition is dynamic ultrasound. This allows real-time testing of the FHL tendon while it goes through a range of motion. Ultrasound often can be the option for the diagnosis of stenosis or impingement of a low-lying muscle. Often, one can combine ultrasound with MRI to check for os trigonum problems or posterior ankle impingement.

Resources

https://www.arthritis-health.com/video/flexor-hallucis-longus-fhl-tendinitis-video