|ECR 2013 / C-0904|
|Accesory ossicles and sesamoid bones of the foot. Review of the anatomy and clinical relevance|
|This poster was previously presented in Spanish at the 2012 Congreso Nacional SERAM (Granada)|
Normal variants are commonly found in foot. Fig. 1, 2 and 3.
- Accessory center of ossification: Variant center of ossification associated with a bone.
- Sesamoid: Ossicle arising witihin a tendon.
ACCESSORY CENTERS OF OSSIFICATION:
- Os supranaviculare, also called os talonaviculare dorsale or Pirie bone: dorsal, proximal margin of navicular.
- Accessory navicular, also called os tibiale externum: ossicle at median eminence of navicular. Fig 4-13.
Type 1: Sesamoid in tibialis posterior tendon.
Type 2: Accessory center of ossification joined to navicular by synchondrosis. Most frecuent.
Type 3 (also called cornuate): Enlarged media eminence of navicular.
- Os intercuneiform: dorsal aspect foot, between 1st and 2nd cuneiforms
- Cuboides secondarium (secondary cuboid): Proximal medial aspect of cuboid, between cuboid and navicular.
- Pars peronea metatarsalis primi: Plantar aspect foot, between base 1st metatarsal and 1st cuneiform.
- Os vesalianum: Base 5th metatarsal.
- Os intermetatarseum: Dorsal, between 1st and 2nd metatarsals.
- Os calcaneus secondarius: Dorsal, adjacent to anterior process calcaneus.
- Os trigonum: Posterior region of talus, is present in 10% of the population.
In some circunstances is possible to develop the syndrome of os trigonum, that is caused by trauma or repeated stress (excessive subtalar pronation with talar adduction, plantar flexion) that occurs in the case of athletes and ballet dancers. Fig 26, 27 and 31.
In the case of fusion with talus is known like trigonal process or process of Stieda. Fig. 28, 29 and 30.
- Os sustentaculi, is a rare accessory ossicle located posterior sustentaculum tali, joined to calcaneus by a fibrocartilaginous tissue.
- Os peroneale (also called os peroneum): Sesamoid within peroneus longus muscle, seen adjacent to lateral margin of cuboid. Fig 14-17.
- Sesamoids of great toe.
- Medial (tibial) sesamoid: Beneath metatarsal head, within flexor digitorum brevis and abductor hallucis.
- Lateral (fibular) sesamoid: Beneat metatarsal head, with flexor digitorum brevis and adductor hallucis. Fig. 18 and 19.
- 30% bipartite or multipartite (may not be symmetric on contralateral foot)
- Interphalangeal sesamoid: At interphalangeal joint, within flexor hallucis longus tendon. Fig. 22
- Sesamoids of 2nd -5th toes.
- Variably present
- May be at metatarsophalangeal or interphalangeal joints.
- May have both medial and lateral sesamoids at 5th metatarsophalangeal joint. Fig. 20 and 21.
MISCELLANEOUS NORMAL BONY VARIANTS.
- Intermetatarsal joint of 1st and 2nd digits
- Articular facet between bases of 1st and 2nd metatarsals variably present.
- Position of 2nd tarsometarsal joint
- Always proximal to 1st tarsometatarsal joint.
- May be proximal to or in same plane as 3rd metarsal joint
- Failure of segmentation: middle and distal phalanges of 5th toe commonly fail to segment.
- Quadratus plantae: May be absent
- Opponens digiti minimi: Variably present muscle slip of flexor digiti minimi
- Peroneus tertius: absent in 10% of population
HOW TO DIFFERENTIATE BETWEEN FRACTURES AND ACCESSORY OSSICLES
We use different image techniques like digital radiography, CT an MR to distinguish between accessory ossicles and fractures.
- Jagged fracture plane.
- Acude angle at fracture margin.
- Nonsclerotic margin (if acute)
- Bone marrow edema on MR
Accessory ossicle/ bipartite ossicle characteristics
- Smooth, rounded margins
- Obtuse angle at margin between ossicles
- Surrounded by cortex
- Bone marrow edema sometimes present on MR if injured
- Accessory centers may be symptomatic, due to injury of synchondrosis between ossicle an parent bone. If symptomatic, edema will be seen on MR, centered on synchondrosis.
- Another important point to consider is that normal variants may not be billaterally symmetric.
Is an inflammatory condition of sesamoid bones caused for repetitive injury in the plantar aspect toe. Findings in MR reveal an edema in the bone marrow (intensity decrease on T1 and hyperintensity on T2). The affectation of both sesamoid bones guide to diagnostic of sesamoiditis. Reactive changes in soft tissue include tendinitis, synovitis and bursitis. Differential diagnostic is necessary in the mayority of cases. Fig 23, 24,25, 38 and 39.
Congenital tarsal coalition is an entity that sometimes mislead to inappropiate conclusions in young people who refer pain in ankle and toe.
It represents the anormal fusion between two or more bone tarsals and is a frecuent cause of pain in ankle and toe. The two most common types are the calcaneonavicular and talocalcaneal coalition. There are other bone coalition combinations possible but they are very rare. The coalitions may be fibrous, osseous and cartilaginous.
Calcaneonavicular coalitions are easily detected by simple radiography in oblique proyection while the rest of tarsal coalitions require studies of CT an MR, that give us detailed information. Fig 40-44
OS SUBPERONEAL AND OS SUBTIBIAL
Another accessory bones to consider are os subperoneal and os subtibial.
Fig 32- 35.
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