Accessory navicular is an important cause of medial foot pain. Magnetic resonance imaging [MRI] is useful in evaluating the cause of foot pain. This article describes the MRI findings in a symptomatic case of type 2 accessory navicular bone.
A 46 year old female presented with long standing history of left foot pain, localised to the medial aspect. It was constant but aggravated by physical activity. There was no history of preceding trauma. Clinical examination revealed tenderness over the medial aspect of the foot with mild soft tissue swelling. She did not have any other systemic findings. Laboratory investigations were within normal limits.
She underwent MRI of the left foot on a 3Tesla MR scanner using a dedicated single channel transmitter receiver quadrature extremity coil. Images were obtained in the axial, coronal and sagittal planes, using spin echo [SE] T1 and fat saturated proton density [PD] weighted sequences; using frequency selective chemical presaturation technique. Post contrast fat saturated SE T1 images were also obtained after intravenous administration of 10ml of gadodiamide [0.5mmol/ml].
The examination revealed a type 2 accessory navicular bone measuring 10x9mm, located immediately posterior to the navicular tuberosity. An ill defined synchondrosis was noted between it and the navicular [Figure1]. No marrow continuity was seen between the two bones. This accessory bone depicted an area of T1 hypointensity [Figure 1] and T2 hyperintensity [Figure 2] consistent with marrow oedema. Enhancement was noted in this area on administration of contrast [Figure 3 and Figure 4]. The overlying soft tissue also depicted oedema. The tendon sheath of tibialis posterior passing posterior to this bone had mild fluid within it with normal tendon morphology [Figure 5 and Figure 6]
The accessory navicular is a commonly occurring accessory ossicle of the foot, being present in 4-14% of the population [1, 2]. In most instances, it causes no symptoms [3]. There are three subtypes of accessory navicular [5]. Type 1 is a true sesamoid fully incorporated within the distal posterior tibialis tendon. Type 2 is described as a larger ossicle, triangular or heart shaped upto 12mm in size. It is considered as a secondary centre of ossification in the cartilaginous analge of navicular [5] with a cartilaginous or fibrocartilaginous synchondrosis between it and the main bone. It accounts for about 50% of all accessory navicular bones [6]. Type 3 is considered to be a prominent navicular tuberosity representing a completely fused type 2 accessory navicular [6].
Accessory navicular causing medial foot pain is almost always the type 2 [6], typically occurring in a female patient in the second decade [5].
The cause of pain in a symptomatic type 2 accessory navicular is thought to be repetitive tension and shearing stress, across the synchondrosis as a result of the pull of the tibialis posterior tendon [7]. Histological studies of resected type 2 accessory navicular bone have shown reactive new bone formation and granulation tissue at the bone-cartilage interface of the synchondrosis [5, 7] and in some cases chronic osteonecrosis [4]. Associated inflammation of the overlying soft tissues has also been described [8].
MRI is of value in demonstrating both bone marrow and soft tissue oedema [8] which in a symptomatic patient represents the cause for pain. The marrow oedema represents either osteonecrosis or bone remodelling due to shear stress [4].
Plain radiographic evaluation of the cause for pain is limited by its inability to depict soft tissue or bone oedema. Bone scintigraphy has a high sensitivity but lacks specificity [3].
In conclusion, accessory navicular is a common asymptomatic normal variant. Recognition of bone marrow oedema pattern on MRI within it helps to identify it as the cause of pain in a symptomatic patient.
Type 2 accessory navicular bone
1. MRI sequences show an additional small bone at the medial navicular tuberosity of the foot, presenting a triangular or heart-shaped form near the tarsometatarsal joint surface of the medial navicular.
2. This accessory bone is connected to the main navicular via cartilage or fibrocartilage, with a visible signal transition zone at the interface.
3. On T2-weighted and fat-suppressed sequences, there is marked hyperintensity between the accessory bone and the adjacent navicular, suggesting bone marrow edema or an inflammatory response.
4. Localized hyperintensity is also noted in the nearby soft tissue (especially around the tibialis posterior tendon insertion and surrounding tissue), indicating soft tissue inflammation or fluid accumulation.
5. No obvious fracture signs are seen in the main navicular itself, but mild cortical irregularities and signal changes may reflect chronic stress or secondary bone reactions.
1. Symptomatic Accessory Navicular (Type 2)
The accessory navicular is one of the common accessory ossicles. In particular, Type 2 typically appears with cartilage or fibrocartilage between the accessory bone and the navicular. Repetitive traction from the tibialis posterior tendon often leads to localized stress. MRI findings of significant bone marrow and soft tissue edema are consistent with chronic irritation or inflammation as the clinical source of pain.
2. Tibialis Posterior Tendinitis/Tendinopathy at the Insertion
Some patients may also present with tibialis posterior tendinitis, whose clinical symptoms overlap with those of an accessory navicular. If there is inflammation or degenerative changes within the tendon sheath, high signal intensity can appear on MRI and may contribute to increased pain.
3. Other Tarsal Conditions (e.g., Tarsal Coalition)
Although less common in this case, hidden coalitions or inflammation of tarsal joints can also cause foot pain. Further evaluation using three-dimensional reconstruction or CT is needed to rule these out.
Considering the patient is a 35-year-old female with medial foot pain and MRI findings showing conspicuous bone marrow edema and soft tissue inflammation at the accessory navicular and the adjacent navicular side, the presentation is most consistent with a Symptomatic Type 2 Accessory Navicular. This type is prone to chronic inflammation and localized pain due to repeated traction; therefore, it is considered the most likely diagnosis in this case.
1. Conservative Treatment
• Bracing and Arch Support: Use shoe inserts with medial arch support or custom orthotics to reduce localized stress over the navicular tuberosity.
• Physical Therapy: This includes local heat therapy, ultrasound treatment, and manual massage, aiming to alleviate soft tissue inflammation and pain.
• Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Can be taken orally or applied externally to reduce local pain and inflammation.
• If pain is severe or persistent, local injection under medical guidance can be considered, although caution is advised.
2. Surgical Indications
• No significant improvement after prolonged conservative management (typically 3–6 months).
• Severe pain affecting daily activities or work, after excluding other relevant conditions.
• Common procedures include excision of the accessory navicular, reshaping of the navicular prominence, and repair or reconstruction of the tibialis posterior tendon insertion.
3. Rehabilitation Plan and Exercise Prescription
Following the FITT-VP principle step by step:
• F (Frequency): Engage in ankle stability training 2–3 times per week, supplemented by low-intensity aerobic exercises such as swimming or cycling on other days.
• I (Intensity): Start with an intensity that does not provoke notable pain, then gradually increase loading or resistance as recovery progresses.
• T (Time): Begin with 20–30 minutes per session, and gradually extend to 30–45 minutes depending on tolerance.
• T (Type): Focus on strengthening the tibialis posterior, fibular muscles, and intrinsic foot muscles (e.g., inversion/eversion against resistance, foot core strengthening), along with flexibility exercises (stretching the arch, Achilles tendon, etc.).
• V (Volume): Adjust the total volume based on pain and fatigue levels, limiting any increase to no more than 10% of the total volume each time.
• P (Progression): Once pain is under control and the current training volume is well tolerated, gradually increase weight-bearing, repetitions, or resistance.
Sample Exercises:
• Ankle Active Movements: Plantar flexion, dorsiflexion, inversion, and eversion, 10–15 reps each, 1–2 sets.
• Foot Intrinsic Muscle Strengthening: Seated toe exercises (picking up towels or small objects) for 10–15 reps, 2–3 sets.
• Resistance Band Exercises: Use a resistance band for ankle inversion, hold for 5 seconds, repeat 10–12 times, 2–3 sets.
• Progressive Weight-Bearing: Once pain is controlled, transition to standing balance or single-leg stance exercises to improve ankle stability.
Safety Precautions
• If any movement causes pronounced pain, increased swelling, or other discomfort, rest immediately and consider reducing the intensity or frequency of training.
• Avoid excessive loading, as chronic stress may aggravate the local condition.
Disclaimer: This report is solely a reference analysis based on current imaging and patient history. It should not replace an in-person consultation or the professional opinion of a qualified physician. Specific diagnosis and treatment must be conducted under professional medical guidance, taking into account the actual clinical situation.
Type 2 accessory navicular bone
