Symptomatic Accessory Navicular Bones It is Not

Only Type II Bariteau, Jason 1; Chamieh, Jad 1; Banerjee, Sima 1; Robertson, Douglas 1,2;

Harmouche, Elie 1; Labib, Sameh 1; Terk, Michael 1

1. Emory Spine and Orthopaedic Center, Atlanta, GA 30329

2. Georgia Institute of Technology and Emory University, Department of Biomedical Engineering, Atlanta, GA

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Symptomatic Accessory Navicular Bones It is Not Only Type II

Jason Bariteau

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Background

Accessory navicular bone found medial to the tarsal navicular bone’s posteromedial tuberosity

4-21 % incidence

More common in females (up to 80% of symptomatic patients)

50-90% bilateral

Associated with focal medial foot pain and pes planus

Three types

Type I: 2-3 mm sesamoid bone within the distal portion of the posterior tibial tendon (PTT)

Type II: triangular ossicle 8mm to 12mm in size connected to the navicular bone by a synchondrosis with fibers of the PTT inserting onto the accessory ossicle

Type III: bony union between the navicular bone and the ossicle producing a prominent navicular tuberosity

Aims Conventional thought is that type II may be symptomatic and type I and III are

basically asymptomatic

No prior studies reported the MRI finding of PTT sheath fluid as fluid may indicate PTT dysfunction

We hypothesize that types I and III may also lead to significant clinical and radiologic consequences

Aims

Study all three accessory navicular bone types

Associate bone type with

Localized pain

Pes planus

Bone marrow reactive change

PTT sheath fluid

Methods 309 individuals with accessory navicular bones identified from 2 institutions

Clinical symptoms and MRI findings analyzed

Those with spring ligament injury were omitted

Pertinent medical history retrieved

Pes planus measured from weight-bearing lateral foot radiographs

Ossicle size determined for type classification

Studies reviewed by two experienced musculoskeletal radiologists

Recorded spring ligament injury

Categorized the accessory navicular type

Recorded the presence of bone marrow reactive change (BMRC)

Noted location of PTT insertions

Determined presence of posterior tibial tendon (PTT) sheath fluid

Methods Information from medical charts

collected on

Onset and duration of symptoms

Location and intensity of pain (score 1-10, 10 being highest)

Difficulty with ambulation

Foot wear and conservative treatment

Surgical treatment

Only those with medial or medial dorsum foot pain were considered having a painful navicular bone

Pearson’s chi square test used for type comparisons in

Pain

Pes planus

BMRC

PTT sheath fluid

Age (below 50 years, 50 and above)

Binary logistic regression model adjusted for

Age

Gender

Type

Results 184 females

Mean age 46.7 years ±16.8

Range 5-96

125 males

Mean age 48 years ±14.6

Range 8-86

Type distribution

27.5% type I

57% type II

15.5% type III

Reason for presentation

Trauma 52%

58% sprain, inversion or twisting mechanism

26% repetitive trauma from athletic activities

10% had various mechanisms of injury

5% lacked sufficient data

Pain 43%, mean score 6.23 ± 2.2 out of 10

29% medial foot

20% lateral ankle

18.5% lateral foot

18% heel

4% lacked data

Results

Type I Type II Type III

Pain 25% 50% 8%

BMRC 9% 48% 6%

Pes Planus 32% 38% 8%

PTT Sheath Fluid 33% 42% 6%

No statistical differences between

Bone type and gender (p’s>0.5)

Bone type and the two age groups (p’s>0.9)

Two age groups with regards to

Pain

Pes planus

BMRC

PTT fluid

Only gender difference with PTT fluid, twice as frequent in females (p=0.023)

Table 1. Characteristics distribution among types

Results Type I vs Type II

9.2 [CI: 4 – 20] adjusted odds (ORadj) of BMRC in type II, p<0.0001

Pain, pes planus, PTT sheath fluid similar

Type I vs Type III

2 [CI: 1.1 – 3.5] ORadj of pain in type I, p=0.02

2.4 [CI: 1.4 – 4] ORadj of pes planus in type I, p=0.002

3 [CI: 1.6 – 5.6] ORadj of PTT sheath fluid in type I, p=0.001

BMRC similar

Type II vs Type III

6.6 [CI: 2 – 19] ORadj of pain in type II, p=0.001

13.9 [CI: 4 – 46] ORadj of BMRC in type II, p<0.0001

6.7 [CI: 2 – 19.5] ORadj of pes planus in type II, p=0.001

11.5 [CI: 3 – 39] ORadj of PTT sheath fluid in type II, p<0.0001

Discussion Highest prevalence of pain, pes planus, bone marrow reactive change, and

PTT sheath fluid in type II accessory navicular bones

MRI-detected bone marrow reactive change most prominent adjacent to the synchondrosis

Fair prevalence of pes planus in Types I and II accessory navicular bone types, 32% and 38%

PTT inserted into the proximal ossicle for all accessory navicular bone types

Type I and type II accessory navicular bones are actually similar with regards to pain, pes planus, and PTT fluid

BMRC greater in type II, explained by the type I ossicle’s small size making BMRC more difficult to visualize

Higher prevalence of pain, pes planus and PTT sheath fluid in type I bones over type III

Discussion Type II and III accessory navicular bones are different for all our assessments

Conforms to conventional thought as type III bones are expected to be fairly asymptomatic and type II to be the most symptomatic

Presence of PTT sheath fluid only significant difference between genders

Purely statistical significance, unlikely any clinical implication

No role for age group in all our assessments

Limitations

Retrospective design

Lack of surgical or histological correlation

All subjects did have foot pain, albeit in other locations, or they would not have had an MRI

Imaging screening of the population to identify individuals with accessory navicular bones with would be too costly

Conclusion

The results described here challenge the conventional thought that type I accessory navicular bones are mostly asymptomatic

No statistical difference in the prevalence of pain, pes planus, and PTT sheath fluid between type I and II bones

Our outcomes corroborate conventional thought that type II bones are the most symptomatic and type III bones relatively asymptomatic

In future work we plan to evaluate the effect of clinical interventions on the symptoms and findings of symptomatic accessory navicular bones

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