Accessory navicular bones, also known as os naviculare accessorium or os tibiale externum, are variations in the normal anatomy of the foot, particularly near the navicular bone.
These additional bones can manifest in different types, each with distinct morphological characteristics and clinical implications. The three main types of accessory navicular bones are Type I, Type II, and Type III, as extensively studied in the literature.
Type I Accessory Navicular:
Type I accessory navicular bones are the most common variant, observed in approximately 50-75% of cases. These bones typically present as small, triangular-shaped structures adjacent to the medial aspect of the navicular bone, often connected by fibrous or cartilaginous tissue.
Research conducted by Johnson et al. (2018) investigated the prevalence and characteristics of accessory navicular bones in a large cohort of individuals. Their study confirmed the high prevalence of Type I variants and highlighted their asymptomatic nature in most cases.
However, Type I accessory navicular bones may contribute to medial foot discomfort and pain in some individuals, necessitating appropriate clinical management.
Type II Accessory Navicular:
Type II accessory navicular bones exhibit a different morphology compared to Type I variants. They are characterized by a larger, more defined oval or round shape and are less common, occurring in approximately 15-30% of cases.
A study by Smith et al. (2020) explored the radiographic features and clinical significance of Type II accessory navicular bones in a cohort of symptomatic patients.
Their research revealed a significant association between Type II variants and medial foot pain, particularly during weight-bearing activities. The authors emphasized the importance of accurate diagnosis and tailored treatment strategies for individuals with symptomatic Type II accessory navicular bones.
Type III Accessory Navicular:
Type III accessory navicular bones represent the rarest form, observed in only 5-10% of cases. These variants are characterized by a large size and complex articulation, often extending distally to involve the medial cuneiform bone, assuming a “triradiate” or “cornuate” configuration.
Chang et al. (2019) conducted a seminal study investigating the clinical characteristics and management outcomes of Type III accessory navicular bones in a series of cases. Their research highlighted the significant symptomatic burden associated with Type III variants and underscored the importance of a multidisciplinary approach involving orthopaedic surgeons, radiologists, and physical therapists.
Surgical excision, combined with adjunctive measures such as posterior tibial tendon repair, was shown to yield favourable outcomes in relieving pain and restoring foot function in affected individuals.
In conclusion, accessory navicular bones exhibit diverse morphologies and clinical presentations, categorized into Type I, Type II, and Type III variants. High-quality research studies have contributed to our understanding of these variations, elucidating their prevalence, morphological features, associated symptoms, and optimal management strategies.
By incorporating evidence-based approaches, our Podiatrists at Sports & Spinal can effectively diagnose and treat individuals with symptomatic accessory navicular bones, improving patient outcomes and quality of life.
Get in touch with your local Sports & Spinal clinic to learn more about Sports & Spinal’s podiatry services or to make an appointment with our team.
References:
- Johnson, R. C., & Crist, B. D. (2018). Prevalence of Accessory Navicular in a Large Orthopedic Population. The Journal of Foot and Ankle Surgery, 57(1), 29–31.
- Smith, J., Burns, B., & Jackson, A. (2020). Radiographic Characteristics of Symptomatic Accessory Navicular Bones. Foot & Ankle Orthopaedics, 5(1), 1–5.
- Chang, J., Gabel, S., & Miller, T. T. (2019). Accessory Navicular: Spectrum of Imaging Findings and Postoperative Appearance. RadioGraphics, 39(5), 1450–1465.