Iselin’s disease is a relatively uncommon but clinically significant condition affecting the apophysis — the secondary ossification centre — at the base of the fifth metatarsal bone in the foot. Named after the German physician Hans Felix Iselin, who first described it in 1912, the condition is classified as an osteochondrosis, a group of disorders characterised by disruption to the normal process of bone development at sites of growth cartilage. While it often goes unrecognised or is mistaken for other lateral foot pathologies, a sound understanding of its anatomy, pathophysiology, clinical features, and management is essential for anyone treating young active patients presenting with outer foot pain.
Anatomy and Pathophysiology
The fifth metatarsal is the outermost long bone of the foot, running from the midfoot to the base of the little toe. At its proximal end — the styloid process — sits the apophysis, a secondary ossification centre that typically appears between the ages of eight and twelve in girls and nine and fourteen in boys. This apophysis serves as the attachment site for the peroneus brevis tendon, a powerful muscle that runs along the outer aspect of the lower leg and plays a critical role in foot eversion and lateral ankle stability. The Achilles tendon’s lateral fibres, via the plantar fascia, also contribute traction forces to this region.
The apophysis is vulnerable during the adolescent growth period because it has not yet fused with the main body of the metatarsal. The junction between the apophysis and the diaphysis is composed of cartilage, a mechanically weaker interface than mature bone. Repeated traction forces from the peroneus brevis tendon — particularly during running, jumping, and cutting movements — can cause microvascular disruption, impaired ossification, and ultimately a degree of avascular change at the apophysis. This process mirrors the pathophysiology seen in other osteochondroses such as Osgood-Schlatter disease at the tibial tubercle or Sever’s disease at the calcaneal apophysis.
Epidemiology
Iselin’s disease primarily affects children and adolescents, with the peak incidence corresponding to the period of rapid skeletal growth and coinciding with the most active years of youth sport participation. It is seen more frequently in active young people who participate in sports involving repetitive loading of the foot — sports such as football, gymnastics, basketball, and dance are particularly implicated. Girls tend to develop the condition slightly earlier than boys, which correlates with the earlier timing of their growth spurts.
Despite being a well-established entity, Iselin’s disease is thought to be significantly underdiagnosed in clinical practice. Its presentation is often confused with lateral ankle sprains, fractures of the fifth metatarsal, or simple soft tissue contusions. Clinicians unfamiliar with the condition may not consider it in the differential diagnosis, and even when imaging is obtained, the normal apophysis can be mistaken for a fracture by practitioners unaware of normal paediatric foot radiographic anatomy.
Clinical Presentation
The hallmark of Iselin’s disease is lateral foot pain localised to the base of the fifth metatarsal. Patients typically present with a gradual onset of pain that is exacerbated by physical activity and relieved by rest, though acute flares following specific sporting incidents are also reported. The pain may be accompanied by localised swelling and tenderness on direct palpation of the styloid process. In some cases, a visible or palpable bony prominence may be noted at the site.
On clinical examination, tenderness is reproducible at the base of the fifth metatarsal, and pain may be provoked by resisted eversion of the foot, which stresses the peroneus brevis tendon and its insertion. Passive inversion of the foot can also reproduce symptoms by stretching the same tendon under load. Gait may be antalgic, with the patient unloading the lateral border of the foot.
Diagnosis
Diagnosis is primarily clinical, supported by plain radiography. X-rays of the foot, including anteroposterior, lateral, and oblique views, should be obtained to assess the apophysis. In Iselin’s disease, the apophysis may appear irregular, sclerotic, or fragmented compared to the normal side, though these findings can be subtle. Importantly, the orientation of the normal apophysis at the fifth metatarsal runs parallel to the long axis of the bone, which helps distinguish it from an avulsion fracture, which typically runs perpendicular.
Comparison with the asymptomatic contralateral foot can be diagnostically useful, as can comparison with standard developmental atlases of paediatric foot ossification. In cases of diagnostic uncertainty, magnetic resonance imaging (MRI) provides superior soft tissue and marrow characterisation, potentially demonstrating bone marrow oedema at the apophysis consistent with active osteochondrosis. Ultrasound can also be a useful adjunct, particularly to assess the integrity of the peroneus brevis tendon insertion.
Management
The mainstay of treatment for Iselin’s disease is conservative, and the prognosis with appropriate management is generally excellent. Activity modification is the central pillar of initial management — reducing or temporarily ceasing the provocative sporting activity allows the apophysis to recover from repetitive stress and permits normal ossification to proceed. Complete immobilisation is rarely necessary, but in cases of significant pain, a period of protected weight-bearing with a walking boot or short-leg cast may be appropriate for two to four weeks.
Analgesia with non-steroidal anti-inflammatory drugs can help manage acute pain and local inflammation. Physiotherapy plays an important supporting role, addressing any biomechanical contributors such as tight peroneal muscles, limited ankle dorsiflexion, or altered foot mechanics. Stretching of the peroneal musculature and gradual progressive loading of the lateral foot as symptoms allow are key components of rehabilitation. Orthotic devices, such as lateral wedge insoles, can reduce the mechanical load on the peroneus brevis insertion and may assist in both symptom management and return to sport.
Return to sport should be guided by resolution of symptoms and restoration of pain-free function rather than a fixed timeline. Most patients recover fully within a few weeks to several months, and long-term sequelae are uncommon.
Iselin’s disease, though relatively rare and often overlooked, represents an important cause of lateral foot pain in the adolescent athlete. Its recognition requires familiarity with normal paediatric foot development and awareness of the clinical context in which it arises. With accurate diagnosis and appropriate conservative management, the vast majority of young patients can expect complete resolution of symptoms and a successful return to sport. As youth athletic participation continues to grow, so too does the importance of identifying and correctly managing conditions like Iselin’s disease that, if missed, can unnecessarily sideline young athletes.