accessory navicular is an accessory ossicle of the foot which is located on the medial side of foot, proximal to the navicular and in continuity with the tibialis posterior tendon;
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The accessory navicular is an anatomic variant that occurs in approximately 10% of individuals. It is characterized by an accessory ossification center adjacent to the navicular at the site of the tibialis posterior tendon attachment. It is frequently associated with pes planus and can occasionally be symptomatic.
There are 3 types...

Core Curriculum
Objectives
1. Describe the clinical symptoms associated with accessory
2. Discuss imaging studies useful for the evaluation of accessory navicular
3. Discuss treatment of accessory navicular

Matthew B Dobbs, MD and Tim Walton, RN, BSN Iowa Orthop J. 2004; 24: 84–85.
The accessory navicular bone is one of the most symptomatic bones of the foot. Although it has been reported to be present in various members of the same family, there is a lack of knowledge about...

Surgical Pearls: How To Conquer The Accessory Navicular Bone - By Richard T. Braver, DPM
the Modified Kidner procedure is one of the most reliable operations for reducing arch pain associated with an accessory navicular bone (a.k.a. os tibial externum). You can also use this procedure to treat a prominence at the...

The accessory navicular is occasionally the source of pain and local tenderness over the instep. If conservative measures fail, surgical treatment may be required and the results of 62 operations to one or both feet in 47 patients are reported. Twenty-six patients were treated by the Kidner operation, in which...

The authors describe a spectrum of accessory ossicle and sesamoid pathology and suggest appropriate imaging modalities. While they are considered to be normal anatomic variants, accessory ossicle and sesamoid bones may help to identify the source of patient symptomatology. The recognition of key imaging findings can help radiologists determine whether...

Korean J Radiology 2004: 5; 274 Choi et al
The MR imaging findings are a persistent edema pattern in the accessory navicular bone and within the synchondrosis indicating osteonecrosis, inflammation and destruction of the cartilage cap. Posterior tibial tendon dysfunction was clinically evident in most patients.

In Accessory Ossicles and Sesamoid Bones: Spectrum of Pathology and Imaging Evaluation Dr. Kalantari; Dr. Seeger; Dr. Chow; Dr. Motamedi Appl Radiol. 2007;36(10):28-37.

Wheeless' Textbook of Orthopaedics

Not such a normal variant JBR-BTR 2004 87(5)

Ankleandfoot site includes the following topics: - Accessory Bones - Achilles tendinosis - Ankle Varus - Ankle Valgus - AVN - Navicular - AVN - Talus - Bipartate Cuneiform - Calcific Achilles - Charcot arthropathy - Hallux Limitus - Hallux Rigidus - Hallux Valgus - Juvenile Hallux Valgus - Juvenile Hallux Varus - Peroneal Tendon
Podiatry Education site

This chapter on normal variations of the pediatric foot discusses accessory navicular. Os trigonum will be discussed at a later date.