The human foot is a marvel of biomechanical engineering, composed of
twenty-six bones, thirty-three joints, and more than a hundred muscles, tendons,
and ligaments working in concert to support the body’s weight and propel it
forward. Yet within this precisely orchestrated architecture, anatomical
variations are surprisingly common. One of the most frequently encountered is
the accessory navicular, an extra ossicle (small bone) located on the medial aspect
of the foot near the navicular bone. Estimated to occur in approximately ten to
fourteen percent of the general population, it is most often an incidental finding
– a harmless quirk of development. In a smaller subset of individuals, however, it
becomes a significant source of medial foot pain, altered gait, and functional
disability. Understanding the anatomy, classification, biomechanical
implications, and treatment options of the accessory navicular is essential for any
clinician working with foot and ankle conditions.
Anatomy and Embryology
The navicular is a tarsal bone situated on the medial column of the foot,
articulating with the talus proximally and the three cuneiform bones distally. It
serves as the keystone of the medial longitudinal arch and is the primary
attachment site for the tibialis posterior tendon, one of the most important
dynamic stabilisers of that arch. The accessory navicular arises from a secondary
ossification centre that fails to fuse with the main navicular during skeletal
development. In most people, this centre either never appears or fuses
seamlessly during adolescence. In those who retain it, the result is a distinct bony
prominence on the medial and plantar aspect of the navicular.
Three subtypes have been described in the literature, most commonly
attributed to Geist (1914) and later refined by others. Type I, also called an os
tibiale externum, is a small sesamoid bone embedded entirely within the tibialis
posterior tendon and is generally asymptomatic. Type II is the most clinically
relevant: a larger ossicle connected to the navicular by a fibrocartilaginous
synchondrosis. Because the tibialis posterior tendon inserts partly onto this
accessory bone, mechanical forces across the junction can produce microtrauma,
inflammation, and pain. Type III represents a fused or partially fused accessory
navicular, creating a prominent ‘cornuate’ navicular with an enlarged medial
tuberosity. Although structurally fused, this type can still produce symptoms due
to its bony prominence and its effect on tendon mechanics.
Clinical Presentation
Accessory navicular syndrome – the symptomatic form of the condition –
most commonly presents in adolescence, coinciding with a period of rapid
growth and increased physical activity. It is somewhat more prevalent in females
than males, and a bilateral presentation is found in up to fifty percent of cases.
The hallmark symptom is medial foot pain, typically localised to the bony
prominence on the inner border of the midfoot. The area is often tender to
direct palpation, and the prominence itself may be visibly or palpably enlarged,
causing irritation from footwear. Activity-related pain – particularly running,
jumping, or prolonged standing – is a consistent complaint.
A key associated finding is pes planus, or flatfoot deformity. Because the
accessory navicular disrupts the normal insertion mechanics of the tibialis
posterior tendon, the dynamic support of the medial longitudinal arch is
compromised. Patients may consequently develop or worsen a pre-existing
flatfoot, contributing to broader biomechanical consequences such as hindfoot
valgus, forefoot abduction, and altered lower limb alignment. These secondary
changes can themselves become sources of pain and dysfunction if left
unaddressed.
Diagnosis
Diagnosis is primarily clinical but is confirmed radiographically.
Weight-bearing plain radiographs of the foot, including anteroposterior, lateral,
and oblique views, will typically demonstrate the accessory ossicle. The oblique
view is particularly valuable for visualising the synchondrosis in Type II cases.
Where plain films are inconclusive or when the extent of soft tissue involvement
needs assessment, magnetic resonance imaging (MRI) is the modality of choice.
MRI can identify bone marrow oedema at the synchondrosis – a reliable
indicator of active inflammation and the likely source of pain. Technetium bone
scanning has also been used to demonstrate increased uptake at the accessory
navicular site, confirming its symptomatic status.
Conservative Management
The vast majority of patients with symptomatic accessory navicular respond
well to non-operative treatment, and conservative management should always be
the first line of care. Rest from aggravating activities, non-steroidal
anti-inflammatory medications, and ice application form the cornerstone of
initial management. Immobilisation in a below-knee cast or a removable walking
boot for four to six weeks is highly effective in acute or severe flares, allowing the
inflamed synchondrosis to settle.
Once the acute phase has resolved, custom orthotic devices are the most
important tool for long-term symptom control. A well-fitted medial arch
support offloads the navicular prominence, reduces stress at the synchondrosis,
and helps correct the biomechanical consequences of the associated flatfoot
deformity. Footwear modification – favouring supportive, wide-toed shoes that
avoid direct pressure over the prominence – is equally important. Physiotherapy
targeting tibialis posterior strengthening, calf flexibility, and intrinsic foot muscle
activation is valuable in rebuilding dynamic arch support. Corticosteroid
injection into the synchondrosis can provide medium-term relief in refractory
cases, though its use is generally reserved for adults given the potential effects on
developing tissue in younger patients.
Surgical Management
When conservative measures fail after a sustained trial of at least three to six
months, surgical intervention is considered. The most widely performed
procedure is the Kidner operation, first described in 1929, which involves
excision of the accessory navicular and re-routing of the tibialis posterior tendon
to a more plantar and distal position on the native navicular. This re-attachment
is intended to improve the tendon’s mechanical advantage in supporting the
medial arch. Long-term outcomes following the Kidner procedure are generally
favourable, with the majority of patients reporting significant pain relief and
return to normal activities.
More recently, some surgeons have advocated for simple excision of the
ossicle without tendon re-routing, particularly in Type I cases or where the
tendon insertion is largely intact on the native navicular. Arthroscopic or
minimally invasive techniques for accessory navicular excision have also been
described, offering the potential advantages of smaller incisions, reduced soft
tissue disruption, and faster recovery. In cases with significant associated flatfoot
deformity, additional procedures to reconstruct the medial arch – such as
calcaneal osteotomy or medial column stabilisation – may be undertaken
concurrently.
The accessory navicular is a common anatomical variant that, in a
meaningful minority of individuals, evolves into a painful and functionally
limiting condition. Its close relationship with the tibialis posterior tendon and the
medial longitudinal arch means that its consequences can extend well beyond
simple bony prominences. A thorough understanding of its subtypes, clinical
presentation, and pathomechanics enables accurate diagnosis and the selection
of appropriate management strategies. With a well-structured conservative
programme, most patients achieve satisfactory outcomes without the need for
surgery. For those who do require operative intervention, modern techniques
offer reliable and durable relief. The accessory navicular is a reminder that even
the smallest structural variations in the foot can have outsized functional
consequences – and that attentive, individualised care makes all the difference.