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Diagnostic Imaging Corner
Case Challenge
Michelle A Wessely (1)*, Timothy J Mick (2) James Brandt (3) and Anne-Claire
Cravageot (1)
(1) Department of Radiology, Institut Franco-Europeen de Chiropratique
2) Imaging Consultants/CDI
(3) Private practice, Coon Rapids Chiropractic Clinic
* Corresponding author Address: Institut Franco-Europeen de Chiropratique (IFEC), 24 Boulevard Paul Vaillant Couturier, 94200 Ivry Sur Seine Email: mwessely@ifec.net
Journal of the Academy of Chiropractic Orthopedists
December 2009, Volume 6, Issue 4
Received: December 2009
Accepted: December 2009
This article is available from: http://www.dcorthoacademy.com © 2009 Wessely et at. and the Academy of Chiropractic Orthopedists This is an Open Access article which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Case History
A 15 year old female presented to the emergency room having sustained a sprained ankle. Prior to her presentation, developed severe pain immediately along the anteromedial aspect of the right foot and presented with a painful limp, with limited active and passive range of motion, globally. The clinical examination revealed edema surrounding the medial and lateral malleoli, and a focal swelling anteromedial to the medial malleolus. Imaging was performed, presented in Figure 1.
Figure 1. Radiographs of the right ankle from 2006.
- What are the imaging findings?
- What is your clinical/imaging diagnosis?
Imaging observations
1) What are the imaging findings?
AP and lateral views of the right ankle demonstrate an abnormal ossific density superimposed over the anterior
process/facet of the calcaneus on the lateral view. On the AP view, the same osseous density is noted along the
medial aspect of the foot, adjacent to the navicular. There is no evidence of accompanying soft tissue swelling.
What is your clinical/imaging diagnosis?
Type 2 accessory navicular of the right foot.
Management
The patient was discharged from the emergency room with the clinical diagnosis of a sprain of the medial collateral ligaments of the right ankle. The treatment provided was to place the patient in a plaster cast with no weight-bearing for several weeks. The symptoms diminished, but never fully resolved, although the patient returned to normal activity.
Two years later, the patient continued to have pain, and noticed swelling around the anteromedial aspect of her foot (Figure 2).
Figure 2a. Clinical image of the medial aspect of the right foot, in which an elevated red region was noted by the patient and clinician, in conjunction with a palpable mass.
Figure 2b. The more recent radiographs of the ankle, from 2008 show the region of abnormality particularly well demonstrated on the lateral view (oval).
Figure 2c. On the lateral and medial oblique radiographs, the additional ossific density is more readily seen lying medial and slightly proximal to the navicular (arrows), with evidence of a well corticated surface apposing that of the parent navicular.
She also noticed that the pain was provoked by wearing particular shoes and it was impossible for her to wear high heels. Imaging was performed at this time, as part of the clinical work-up (Figures 3 and 4).
Figure 3. Radiographic imaging comparison of lateral ankle views performed in 2006 (left) and 2008 (right) where the osseous abnormality is demonstrated on both images.
Figure 4. Dorsoplantar view of the left foot of the same patient demonstrating a smaller ossific density medial to the navicular, a type 1 accessory navicular or true os tibiale externum. As is typically the case, this was an asymptomatic incidental finding.
The patient then consulted an orthopedic surgeon, who ordered MR imaging of the ankle (Figure 5).
Figure 5a
Figure 5b
Figure 5c
Figure 5. MR imaging of the right foot demonstrating the relationship between the accessory navicular (Figure 5a arrow) and the tibialis posterior tendon, seen in Figure 5a, a sagittal T1-weighted MR image of the right ankle, where a long low signal oblique structure, the tendon of tibialis posterior, extends proximally and slightly posteriorly from the os tibiale externum. In Figure 5b, fat suppressed T2 sagittal MR image of the right ankle, shows an irregular, low signal division between the accessory navicular and the parent navicular bone (arrow) which may represent a fibrous connection between the two structures. There is no evidence of fluid at this margin which suggests that there is no pseudoarticulation here, another potential cause of focal pain in these patients. In Figure 5c, a short axis MR image of the right ankle, also a fat suppressed T2 weighted image demonstrates the accessory navicular and the low signal fibers of the tibialis posterior tendon extending along its posterior margin (arrow).
A diagnosis was made of an accessory navicular with tendinopathy of the tibialis posterior tendon and the patient was offered surgery to remove the accessory navicular followed by physiotherapy. However, her sister was a chiropractic student and the patient elected to be treated with chiropractic management, consisting of adjusting the ankle, through regions of joint restriction, soft tissue work, especially to the tibialis posterior and evaluation and treatment to address abnormalities of lower limb kinematics. The patient was satisfied with the treatment, with a reduction in her pain and swelling.
Discussion
There are a number of accessory ossicles of the foot and ankle. The os tibiale externum and accessory navicular are examples of the more common accessory ossicles associated with the navicular. Other accessory ossicles about the foot and ankle include the os trigonum, os peroneum and os supranaviculare. The original description of accessory ossicles about the navicular was of the os tibiale externum was in 1605 by Bauhin, cited by Geist. (1,2) The os tibiale externum has been reported in 10 to 16% of the population or 2 9% of dry specimens and is bilateral in 50 to 90% of cases, typically developing during adolescence. It is slightly more common in woman. (3)
The os tibiale externum has been referred also to as an os naviculare secundarium or accessorium, cornuate navicular, prehallux and bifurcated hallux. (4) However only if the accessory ossicle is seen as a sesamoid bone within the tendon of tibialis posterior is the term os tibiale externum applied. Clinically it is located along the medial and posterior aspect of the navicular and the patient may have noticed that either unilaterally or bilaterally that there is a bump, or that a particular preference for shoes has been noted, based on the bony irregularity.
The navicular is the last ossification center of the tarsal bones to appear radiographically, visible at 3 to 5 years old, and fully ossifying by between the ages of 9 and 11 years old, usually about one year earlier in girls. (5) Accessory ossification centers may occur, but fuse by age 20. Therefore accessory ossicles about the navicular may be confidently diagnosed, radiographically, only after age 20. However if the patient is symptomatic prior to this age, examination via ultrasound or MR imaging may evaluate the non-ossified cartilaginous anlage of the os tibiale externum/accessory navicular and, importantly, the relation between the developing os tibiale externum/accessory navicular and the tibialis posterior tendon.
The accessory navicular may coalesce with the navicular via tissue that is fibrovascular or connective in origin. The accessory ossicles about the navicular have been classified into three variant forms:
- Type 1 The ossification center forms a small (typically around 2-3 mm) sesamoid bone within the tibialis posterior. This is considered the true os tibiale externum.
- Type 2 the ossification is larger (up to 9-12mm or more), just medial to the navicular bone and a fibrocartilaginous or hyaline synchondrosis connects it to the navicular. Most or all of the tibialis posterior tendon insertion is onto the separate type 2 ossicle and this form is the most frequently symptomatic. This form is termed the accessory navicular.
- Type 3 also known as the cornuate navicular, this is essentially a type 2 connected by an osseous bridge, never forming a separate bone and having the radiographic appearance of an unusually prominent navicular tubercle. Symptoms may occur related to an overlying bursitis or tendinitis and this type has been shown, in some cases, to undergo fracture or stress fracture, with non-union, yielding an apparent type 2 accessory navicular.
Clinically the type 2 accessory navicular may be associated with a painful flat foot. There is often a palpable bony irregularity or prominence over the anteromedial aspect of the midfoot, which has been described as being as large as the size of a walnut. (2)
Although relatively uncommon, the type 2 accessory navicular may fracture through the fibrocartilaginous union with the parent navicular, usually an avulsive injury with a violent muscle contraction of the tibialis posterior, rather than a direct trauma. (6) Alternatively repetitive traction may produce multiple microfractures with a forceful contraction of the tendon finally resulting in a sudden, separation, in a type of stress fracture. (7)
Conclusions:
An accesssory navicular represents one of several accessory ossicles found in the ankle and foot, which may be clinically relevant. The relationship between the accessory navicular and the tibialis posterior tendon is especially important due to the associated tendinopathy that may develop. The radiographic features of an accessory navicular include an osseous fragment situated medial to the navicular, around which soft tissue swelling and/or displacement may be noted. MR imaging is valuable in assessing associated tendon injury and potential disruption of the fibrocartilaginous union, as well as any abnormality from secondary effects on the biomechanics of the ankle and foot.
Clinical Pearls:
- Accessory ossicles associated with the navicular may be detectable, clinically, as a bump along the anteromedial aspect of the midfoot, which may or may not be painful.
- Patients with accessory ossicles associated with the navicular may present with a painful flat foot deformity and/or foot pronation.
- An accessory navicular is seen, radiographically, as an osseous density medial to the navicular which may be bilateral.
- The accessory navicular may be associated with tendinopathy of the tibalis posterior and symptoms may also arise from repetitive stresses or trauma disrupting the fibrocartilaginous union with the parent navicular.
Useful website
http://pramodrad.blogspot.com/2009/10/os-tibiale-externun-accessory-navicular.html
References
- Bauhin (1605) cited by Geist ES (1914) Supernumerary bones of the foot: A roentgen study of the feet of 100 normal individuals. American Journal of Orthopedic Surgery, 12, 403.
- Evans EL (1925) Bilateral os tibiale externum, with unilateral hypertrophy of the navicular. Section of Orthopedics, 33.
- Anderson T (1999) Archeological evidence for os tibiale. The Foot, 201-202.
- Lawson JP, Ogden JA, Sella E and Barwick KW (1984) The Painful Accessory Navicular. Skeletal Radiology, 12, 250-262.
- Lee CH and Peh WCG (2004) Young man with left foot pain. Asia Pacific Family Medicine, 3, 18-19.
- Pavlov H, Torg JS and Freiberger RH (1983) Tarsal navicular stress fractures: Radiographic evaluation. Radiology, 148, 641-645.
- Mikami M and Azuma H (1978) Fracture of the os tibiale externum. A case report. Journal of Bone and Joint Surgery, 556 557.