Updated: 5/19/2018

Lower Extremity Os

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https://upload.orthobullets.com/topic/7049/images/diagram all ossicles of foot.jpg
https://upload.orthobullets.com/topic/7049/images/lateral xr os trigonum.jpg
https://upload.orthobullets.com/topic/7049/images/os trigonum mri.jpg
https://upload.orthobullets.com/topic/7049/images/posterior process fracture.jpg
https://upload.orthobullets.com/topic/7049/images/xray - lateral - wheeless_moved.jpg
Introduction
  • Up to 40 accessory ossicles and multiple sesamoids have been described in the foot and ankle
  • Definition
    • accessory ossicles
      • are secondary ossification centers that remain separated from the normal bone
    • sesamoids
      • are bones that are incorporated into tendons and move with normal and abnormal tendon motion
  • Most common ossicles
    • os trigonum
    • accessory navicular (os tibiale externum)
    • os intermetatarseum
  • Most common sesamoids
    • os peroneum
      • located in the peroneus longus tendon
    • hallux sesamoids
      • located in the flexor hallucis brevis tendon at the base of the 1st metatarsal head
Classification
 
 Accessory Ossicles and Sesamoids of the Foot and Ankle
Accessory bone Prevalence Clinical significance Differential Diagnosis
Image
Os trigonum 10-25% Posterior ankle impingement, FHL entrapment Shepherd's fracture

Type II accessory navicular 2-12% Posterior tibial tendon dysfunction Navicular tuberosity avulsion frx, type I accessory navicular
Os subfibulare 2% Painful os subfibulare  Lateral malleolus avulsion frx  
Os peroneum 9-20% Painful os peroneum, fracture, diastasis Painful os vesalianum, bipartite os peroneum  
Os vesalianum 2% Painful os vesalianum Avulsion frx of the 5th metatarsal base  
Hallux sesamoids ~100% Fracture, stress fracture Bipartite tibial sesamoid
 
Os Trigonum
  • Definition
    • accessory ossicle representing the separated posterolateral tubercle of the talus 
    • usually asymptomatic, but can become symptomatic and cause os trigonum syndrome
  • Epidemiology
    • incidence
      • 10-25% of the population have os trigonum
      • commonly symptomatic in ballet dancers due to extreme plantar flexion ("en pointe" toe position)
  • Pathophysiology of os trigonum syndrome
    • repetitive microtrauma (ankle plantarflexion)
      • may present as a stress fracture
    • acute forced plantarflexion
      • may present as an acute fracture
  • Associated conditions
    • FHL tenosynovitis or entrapment 
  • Anatomy
    • osteology
      • the secondary ossification center forms posterior to the talus between 8-13yrs
      • normally fuses with talus within 1yr
      • if the ossicle fails to fuse, it articulates with the talus through a synchondrosis
      • the os lies lateral to FHL, tibial nerve, PTT, and posterior tibial artery 
  • Presentation
    • symptoms
      • pain in "en pointe" position
    • physical exam
      • posterolateral ankle pain with passive ankle plantar flexion
        • differentiate from FHL tendinitis where ankle pain is posteromedial and there may be triggering
      • may have swelling and tenderness over FHL if associated with FHL tendinitis
  • Imaging
    • radiographs
      • recommended views
        • lateral radiograph with foot in plantar flexion
      • findings
        • shows os trigonum impinged between posterior tibial malleolus and calcaneal tuberosity  
        • os trigonum can be round, oval or triangular and of variable size
    • MRI
      • findings
        • shows os trigonum and associated inflammation and edema in FHL tendon   
  • Differential diagnosis
    • fracture of the posterior process of the talus (Shepherd's fracture)  
    • FHL and posterior tibialis tendinitis 
      • produce posterior medial ankle pain and tenderness
  • Treatment
    • nonoperative
      • NSAIDS, rest, immobilization, restricted weightbearing
    • operative
      • surgical excision  
        • indications
          • if nonoperative management fails 
        • techniques
          • through open lateral approach or posterior ankle arthroscopy  
Os Tibiale Externum (Accessory navicular)
  • See Accessory Navicular 
Os Subfibulare
  • Definition
    • small piece of bone adjacent to inferior fibula
  • Epidemiology
    • incidence
      • 1-2% of population
  • Pathoanatomy
    • may represent avulsion fx of ATFL that secondarily ossifies
    • or accessory ossification center  
  • Presentation
    • symptoms
      • may be asymptomatic
      • may have ankle pain (symptomatic os subfibulare)
      • may be associated with chronic ankle instability and present with recurrent ankle sprains
    • signs
      • focal tenderness and swelling at the site of the ossicle
      • laxity with anterior drawer and inversion/eversion stress testing
  • Imaging
    • radiographs
      • recommended views
        • standard ankle series (weightbearing AP, lateral, mortise)
        • varus stress view
      • findings
        • accessory ossicle
        • talar tilt on varus stress view 
          • suggesting ankle instability  
          • increased separation of os fragment from fibula tip   
  • Differential diagnosis
    • acute lateral malleolus avulsion fracture (by the ATFL) 
  • Treatment
    • nonoperative
      • NSAIDS, rest, immobilization, restricted weightbearing
        • indications
          • initial treatment for symptomatic os subfibulare
    • operative
      • surgical excision
        • indications
          • failed nonoperative management
Os Peroneum
  • Definition
    • sesamoid bone found within the peroneus longus tendon near the base of the 5th MT
    • may represent avulsion or rupture of peroneus longus  
  • Epidemiology
    • incidence
      • 9-20% of adults
      • bilateral in 60%
      • bipartite in 30%  
  • Pathophysiology of injury or fracture  
    • direct trauma
    • indirect trauma (sudden inversion and supination)
      • associated with peroneus longus tendon rupture
  • Imaging
    • radiographs
      • findings
        • normal os peroneum  
        • acute os peroneum fracture  
        • peroneus longus rupture  
    • MRI
      • findings
        • normal os peroneum  
        • acute os peroneum fracture  
        • peroneus longus rupture  
  • Differential diagnosis
    • painful os vesalianum  
    • bipartite os peroneum 
  • Treatment
    • nonoperative
      • NSAIDS, rest, immobilization, restricted weightbearing
        • indications
          • initial treatment for painful os peroneum syndrome 
          • minimally displaced os peroneum fractures
    • operative
      • surgical excision
        • indications
          • painful os peroneum syndrome (with minimal tendon involvement) refractory to conservative treatment
          • os peroneum fracture with displaced fragments
      • surgical excision and repair of peroneus longus tendon or tenodesis to peroneus brevis
        • indications
          • os peroneum associated with peroneus longus tendon rupture
Hallux Sesamoids
  • See Sesamoid Injuries of the Hallux  
 

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(OBQ11.253) A 17-year-old ballet dancer presents with 5 months of pain in the posterior aspect of the right lower extremity that is exacerbated with the ballet position shown in Figure A. Her symptoms returned with ballet activity following a 1 month course of full rest, nonsteroidal anti-inflammatory medication, and physical therapy. On physical examination she has no tenderness at the insertion of the achilles tendon at the calcaneus. Radiographs are shown in Figure B and a MRI is shown in Figures C-E. Which of the following options is the most appropriate next step in treatment? Review Topic

QID: 3676
FIGURES:
1

Referral to an orthopaedic oncologist for biopsy and staging

1%

(13/2069)

2

Arthroscopic Haglund deformity excision and debridement of achilles tendon

5%

(110/2069)

3

Open os naviculare excision

3%

(55/2069)

4

Arthroscopic os trigonum excision

89%

(1843/2069)

5

Posterior tibial tendon debridement

2%

(39/2069)

ML 1

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