Accessory Navicular Bone
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Also known as Prehallux, Os Tibiale Externum and Navicular Secundum.
An accessory navicular bone is an accessory bone of the foot that occasionally develops abnormally causing a plantar medial enlargement of the navicular. The accssory navicular bone presents as a sesamoid in the posterior tibial tendon, in articulation with the navicular or as an enlargment of the navicular.
The Geist classification divides these into three types:
Type II: consists of an accessory bone, upto 1.2cm in diameter, in which a synchondrosis exist between it and the navicular.
Type III: is the fused accessory navicular to the navicular resulting in large cornuate navicular.
Clinically Relevant Anatomy
Navicular (boat shaped) is an intermediate tarsal bone on the medial side of the foot. It is located on the medial side of the foot, and articulates proximally with the talus. Distally it articulates with the three cuneiform bones. In some cases it articulates laterally with the cuboid. The tibialis posterior inserts to the os naviculare. The tibialis posterior muscle also contracts to produce inversion of the foot and assists in the plantar flexion of the foot at the ankle. Tibialis posterior also has a major role in supporting the medial arch of the foot.  This supports is compromised by abnormal insertion of the tendon into the accessory navicular bone when present.  This lead to loss of suspension of tibialis posterior tendon and may cause peroneal spastic pes planus or simple pes planus. But, yet a cause and effect relationship between the accessory navicular and pes planus is doubtful and is yet unproved clearly.
The presence of accessory navicular 2 or 3 is also a cause of PTT tendinopathy as the insertion of PTT on accessory navicular leads to its proximal insertion (dashed line). Here by the leverage of malleolus on the PTT is reduced and therefore stress on the tendon increase. 
There also occurs calcaneal pitch angle lowering in patients with with symptomatic accessory navicular than in normal subjects.
- an accessory navicular bone is present in ~10% of the population
- first appears in adolescence. In children its incidence is 4-21% of the population.
- more common in female patients
- reported prevalence of bilaterality is ~70% (range 50-90%)
People who have an accessory navicular often are unaware of the condition if it causes no problems. However, some people with this extra bone develop a painful condition known as accessory navicular syndrome when the bone and/or posterior tibial tendon are aggravated. This can result from any of the following:
- Trauma, as in a foot or ankle sprain
- Chronic irritation from shoes or other footwear rubbing against the extra bone
- Excessive activity or overuse
- Typical young female (10-20 years of age) complaining of mid food/arch pain which may be insidious or post trauma.
- Difficulty with footwears.
- Prominent navicular
- Tenderness over the prominence
- Pain over the posterior tibialis tendon from a tendinitis and tightness of the tendo-achillis in long standing cases.
- Often pes planus.
- Inflamed bursa
- Stress fracture.
- Medial tuberosity fracture 
- Cartilage forming bone Tumor
- Kohler’s disease. 
- Routine standing AP and lateral view are enough to look for accessory navicular but in some cases oblique view is also obtained in order to completely define the abnormality of navicular. Bilateral films may be indicated as there occurs high incidence of symmetrical abnormalities.
- On lateral weight bearing/standing film, the talonavicular cuneiform first metatarsal dorsal lalignment should be clearfully examined. “Sag” at this joint indicates structural integrity of the area.
- MRI or CT is indicated (very rare) in order to exclude tumor, fracture of medial tubersity, bone marrow edema.
AP Veiw' Lateral Veiw 'Oblique Veiw
add links to outcome measures here (also see Outcome Measures Database)
Patient with accessory navicular may present with complex pain patterns requiring thorough examination.  The examination importantly includes
- Differentiation of navicular prominence from talar head prominence in flat foot deformity by inverting and everting through the subtalar joint with a thumb over the bony prominence.
- Recognition of the loss of structural integrity of the longitudinal arch is important because this component of the deformity will not be corrected by surgical treatment if required. 
- Thought examination of gait.
- Physical therapy
- Medications. Oral nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, may be prescribed. In some cases, oral or injected steroid medications may be used in combination with immobilization to reduce pain and inflammation. 
SURGICAL: Depending upon the severity the non operative or conservative treatment should be maintained for at least 4- 6 months before any surgical intervention.
There are 2 surgeries that can be performed depending upon the condition and symptoms
FIRST is simple surgical excision. In this generally the accessory navicular along with its prominence is removed. In this procedure, skin incision is made dorsally to the prominence of accessory navicular. Bone is removed to the point where the medial foot has no bony prominence over the navicular, between the head of the talus and first cuneiform. Symptoms are relieved in 90% of cases.
SECOND is Kindler procedure. In this the ossicle and navicular prominence is excised as in simple excision but along with the posterior tibial tendon advancement. Posterior tibial tendon is split and advanced along the medial side of foot to provide support to longitudinal arch.
After surgery 4 week short leg cast, well moulded into the arch with the foot plantigrade is applied. Partial weight bearing till the 8th week and later full weight bearing is allowed.. When the cast is being removed can start building up the ROM to counter atrophy and other physical therapy treatment which include stretching and strengthening exercises. 
Occasionally, a limited fusion of the cuneiform metatarsal or talonavicular joints also was recommended. The rationale and efficacy of this operation have been questioned.
Arthrodesis may be a reasonable treatment option in selected cases of patients with symptomatic recalcitrant Type II accessory naviculars that are large enough to accept small fragment screws.
Physical Therapy Management
If the accessory navicular bone becomes problematic physical therapy may be prescribed.
This will include use of therapeutic modalities which relieves pain include ultrasonic therapy, TENS, massage, ROM exercises and treatments to strengthen the intrinsic foot muscles and lateral thigh rotators muscles and decrease inflammation. Often is the accessory navicular bone linked to Posterior tibial dysfunction to a pes planus. To adjust the arch of the foot, orthotic devices may be used.
- Well padded shoe orthotic should be worn for arch support. This decrease direct pressure over the navicular.
- Stretching of pernoneal and posterior tibialis along with strengthening exericises.
- Strengthening the intrinsic foot muscles and lateral thigh rotators muscles and decrease inflammation.
- Activity modification, such as limiting or stopping any strenuous activities that cause the Accessory Navicular bone to become symptomatic can be used for initial treatment.
- Gait training and Balance exercise for proper normal gait when required.
Some examples of basic and functional posterior tibialis strengthening:
Foot health facts: http://www.footphysicians.com
Clinical Bottom Line
Usaully the type I accessory navicular is rarely associated with symptoms and if the symptoms appears then it respond well to the conservative/ physical therapy managment. Patients with Type II accessory navicular are at the risk for disruption either from traction injury or shear forces in the region and and mostly the onset is insidious or post trauma. It fails to respond to conservative treatment when severe and fusion of the accessory navicular to the navicular may successfully relieve pain without disrupting the tibialis posterior tendon insertion.
Type III when symptomatic then excising the accessory navicular rather than excising navicular beak is more helpful.
Recent Related Research (from Pubmed)
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- ↑ 1.0 1.1 Raymond T., Morrissy and Stuart L.Weinstein .Lovell, Winter’s Padiatric Orthopaedics. United States: Lippincot William’s Wilkin Publication, 2005.
- ↑ D.Richard, V.Wayne, M. Adam,Gray’s Anatomy for Students. Spain: Elsevier Publishers, 2005
- ↑ Golano P., ‘The anatomy of the navicular and periarticular structures.’ Foot Ankle Clinics, 2004, March, vol. 9, p. 1-23.
- ↑ Kiter E., Erdan N., Karatosun V., Gunall I., ‘Tibialis posterior tendon abnormalities in feet with accessory navicular bone and flatfoot’. Acta orthopaedica Scandinavia, 1999, December, vol. 70, p. 618-621
- ↑ 5.0 5.1 Kulkarni. G.S. Textbook of orthopedics and trauma.India: Jaypee Brother Publication, 1999
- ↑ 6.0 6.1 6.2 Kidner FC. The prehallux (accessory scaphoid) in its relation to flat-foot. J Bone Joint Surg 1929 : II : 831
- ↑ Kidner FC. Pre-hallux in relation to flatfoot. JAMA 1933; 101: 1539-42.
- ↑ 8.0 8.1 8.2 8.3 A. Bernaerts, F.M. Vanhoenacker, S. Van de Perre, A.M. De Schepper, P.M. Parizel1 Accessory navicular bone: Not Such a normal variant. JBR–BTR, 2004, 87 (5) page 250-252
- ↑ Prichausuk S, Sinphurmsukskul O: Kinder Procedure for symptomatic accessory navicular and its relation to pes planus, Foot Ankle 16:500,1995
- ↑ Harris RI. Army foot survey: an investigation of foot ailments in Canadian soldiers. National Research Council of Canada, 1947
- ↑ Shands AR Jr, Wentz IJ. Congenital anomalies, accessory bones and osteochondritis in the feet of 850 children. Surg.Clin.North Am 1953:97:1643-1666
- ↑ Geist ES. The accessory scaphoid bone. J Bone Joint Surg Am 1925; 7:570
- ↑ Jamshid Tehranzadeh; Musculoskeletal Imaging; page 680; Ed.2009
- ↑ Helen Carty, Donald Shaw, Francis Brunelle, Brain Kendall; Imaging in Children; Churchill Livingston publication. Vol.2; pg no.866.
- ↑ Ray S, Goldberg VM. Surgical treatment of the accessory navicular. Clin. Orthop 1983;177: 61-66.
- ↑ Sullivan JA, Miller WA. The relationship of the accessory navicular to the development of the flat foot. ClinOrthop 1979; 144: 233-237.
- ↑ 17.0 17.1 17.2 S.TerryCanale, James S. Beaty,Campbell Operative Orthopaedics. United States: Mosby Publication.2008
- ↑ Macnicol M. F., Voutsinass, ‘Surgical treatment of the symptomatic accessory navicular’, The Journal of Bone and Joint Surgery, 1984, vol. 66, p. 218-226.
- ↑ Kulkarni. G.S. Textbook of orthopedics and trauma.India: Jaypee Brother Publication, 1999.</ref><ref name="7">Kidner FC. The prehallux (accessory scaphoid) in its relation to flat-foot. J Bone Joint Surg 1929 : II : 831
- ↑ Leonard Z. C., Fortin P. T., ‘Adolescent accessory navicular bone’ Foot Ankle Clinics, 2010, vol. 15, p. 337-347.
- ↑ Scott AT.,Sabesan VJ, Saluta JR, Wilson MA, Easley ME.Fusion versus excision of the symptomatic Type II accessory navicular: a prospective study.Foot Ankle Int. 2009 Jan;30(1):10-5
- ↑ ShaychiITA. Tibialis Posterior Basic Strengthening. Available from: http://www.youtube.com/watch?v=zmh1FisBeeM [last accessed 24/11/12]
- ↑ ShaychiITA. Tibialis Posterior Basic Multiplanar Strengthening. Available from: http://www.youtube.com/watch?v=qv76eBxGQXI [last accessed 01/12/12]
- ↑ ShaychiITA. Tibialis Posterior Functional Strengthening: Full Body Weight Maintaining Supination. Available from: http://www.youtube.com/watch?v=1C_C5N9reB8[last accessed 01/12/12]|}
- ↑ ShaychiITA. Tibialis Posterior Functional Strengthening: Maintain Arch with Compass Squats. Available from: http://www.youtube.com/watch?v=TdHgyFZbOPk[last accessed 24/11/12]|}
- ↑ Chung JW, Chu IT.,Outcome of fusion of a painful accessory navicular to the primary navicular. Foot Ankle Int. 2009 Feb;30(2):106-9.