What Is Iselin Disease?

Iselin disease — also called fifth metatarsal apophysitis — is an overuse condition affecting the growth plate (apophysis) at the base of the fifth metatarsal bone in the outer midfoot. Like Sever’s disease (calcaneal apophysitis), Iselin disease occurs in actively growing children and adolescents when the peroneus brevis tendon pulls excessively on the developing growth plate, causing inflammation and pain.

Iselin disease typically affects children between ages 8 and 13, with boys slightly more commonly affected than girls. It is most prevalent in children involved in running sports, particularly soccer, basketball, and track and field — sports that demand repetitive lateral foot loading and explosive movements that stress the peroneus brevis insertion at the fifth metatarsal base.

Why the 5th Metatarsal Base?

The peroneus brevis muscle runs along the outside of the lower leg and inserts via its tendon at the styloid process (bony prominence) at the base of the fifth metatarsal. This insertion coincides with the location of the apophysis (secondary ossification center) in growing children. During growth spurts, the apophysis represents a relatively weak point in the bone structure — the traction applied by the peroneus brevis during plantarflexion, inversion, and pushing off is transmitted directly to this growth plate, causing repetitive microtrauma and inflammation.

Symptoms

The hallmark of Iselin disease is pain at the outer (lateral) base of the foot — specifically at the prominence where the fifth metatarsal meets the midfoot. Symptoms include:

• Localized tenderness at the fifth metatarsal base that is exquisitely tender to palpation
• Swelling over the lateral midfoot
• Pain that worsens with running, cutting, jumping, and push-off activities
• Pain that improves with rest
• Possible mild limp during or after athletic activity

Symptoms typically worsen during periods of rapid growth and high athletic activity, and improve during rest periods.

Critical Differentiation: Iselin Disease vs Jones Fracture vs Avulsion Fracture

The outer midfoot location of Iselin disease pain creates important diagnostic overlap with two other fifth metatarsal conditions that must be distinguished because their management differs significantly:

Jones fracture is a stress fracture at the proximal diaphysis of the fifth metatarsal, approximately 1.5-2 cm distal to the metatarsal base. Jones fractures have a high non-union rate and often require surgical fixation in athletes. They occur more commonly in adults and adolescents who have completed skeletal growth.

Avulsion fracture occurs when the peroneus brevis tendon abruptly pulls off a piece of bone at its attachment during an inversion ankle sprain. Avulsion fractures are acute injuries (sudden onset with a specific traumatic event) rather than gradual-onset overuse conditions.

Iselin disease is distinguished from these by the patient’s age (skeletally immature child), gradual onset, X-ray appearance (irregular or fragmented apophysis rather than a discrete fracture line), and clinical context (overuse pattern without acute traumatic event).

X-rays including specific views of the fifth metatarsal base are essential. The apophysis in Iselin disease appears on X-ray as a longitudinally oriented secondary ossification center parallel to the metatarsal shaft — distinct from the transverse orientation of an acute fracture fragment. MRI can characterize marrow edema and apophyseal inflammation when the diagnosis remains uncertain.

Treatment

Treatment of Iselin disease is conservative and follows principles similar to Sever’s disease management:

Activity modification: Temporary reduction in high-impact and lateral-loading activities during flares. Most children can continue participation with load modification rather than complete rest.

Lateral wedge orthotic or padding: A small lateral wedge under the forefoot and fifth metatarsal base reduces peroneus brevis traction by slightly everting the foot during stance. Custom orthotics provide optimized support for the individual foot structure.

Immobilization: Severe or persistent cases may benefit from a walking boot for 3-4 weeks to rest the apophysis from traction forces during recovery.

Stretching: Peroneal muscle stretching and calf flexibility exercises reduce traction forces at the fifth metatarsal insertion.

Shoe modification: Ensuring adequate lateral forefoot support in athletic footwear, and avoiding shoes with narrow or tapered toe boxes that compress the lateral forefoot.

Surgery is essentially never indicated for Iselin disease — the apophysis fuses with skeletal maturity, permanently resolving the condition. Recurrent symptoms during subsequent growth spurts respond to the same treatment approach.

When to See a Podiatrist

Any child with outer foot pain that has persisted more than 1-2 weeks, is limiting sports participation, or causes limping deserves prompt podiatric evaluation. Distinguishing Iselin disease from a Jones fracture or avulsion fracture requires clinical expertise and appropriate imaging interpretation. Contact Balance Foot & Ankle at (810) 206-1402 or book online at our Howell or Bloomfield Township offices.

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Dr. Tom Biernacki, DPM

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Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.