Lower extremity ossicles

Question 1

Define accessory ossicles?

Answer 1

• Secondary ossification centres that remain separated from the normal bone

Question 2

Define sesmoids?

Answer 2

• Bones that are incorporated into tendons and move with normal and abnormal tendons

Question 3

Name the most common ossicles?

Answer 3

• Os trigonum
• Accessory navicular ( os tibiale externum)
• Os intermetatarseum

Question 4

Name most common sesmoids?

Answer 4

• Os peroneum- in peroneus longus
• Hallux sesmoids- located in flexor hallucis brevis

Question 5

What is this?

Answer 5

• OS trigonium
• Semoid bone representing the separated POSTERIOR TUBERCLE OF TALUS
• Usually asymptomatic but symptomatic -> os trigonium syndrome

Question 6

Describe the epidemiology of Os trigonum?

Answer 6

• 10-25 % of population have os trigonium
• Commonly symptomatic in BALLET dancers due to EXTREME PLANTAR FLEXION

Question 7

Describe the pathophysiology of OS trigonium?

Answer 7

• Repetitive microfracture- may present as Stress FRACTURE
• Acute forced plantarflexion may present as acute fracture- downhill running, kicking or dancing

Question 8

Name associated conditions of OS trigonium?

Answer 8

• FHL Tenosynovitis or entrapement

Question 9

Describe the osteology of os trigonium?

Answer 9

• Secondary ossification centre forms posterior to talus between 8-13 years
• Normally fuses with talus within 1 year
• If ossicles fail to fuse, it articulates with talus thru synchondrosis
• Os lies LATERAL to FHL, TIBIAL nerve, PTT, POST tibial artery

Question 10

Describe the symptoms of os trigonium?

Answer 10

Symptoms

• Pain en pointe position

O/E

• Posterior lateral ankle pain with passive ankle flexion
• may have swelling & tenderness over FHL is associated with FHL tendonitis

Question 11

What investigations are useful in Os trigonium?

Answer 11

• Xrays
  
  • lateral with foot in planar flexion
  • show os trogonium impinging between posterior malleolus and calcaneal tuberosity
• MRI
  
  • show os trigonium adn associated inflammationadn oedema in FHL tendon

Question 12

What is the Differential dx of Os trigonium ?

Answer 12

• Posterior process of talus fracture - Shepherd’s fracture- see pic
• FHL & Post tibial tendonitis- produce medial ankle pain and tenderness.

Question 13

What is the Tx of Os trigonium?

Answer 13

• Non operative
  
  • NSAIDS, rest, immobilisation, restricted WB
• Operative
  
  • Surgical excision
  • if non op fails
  • through an OPEN LATERAL APPROACH or POST ANKLE ARTHROSCOPY- 80% gd to excellent results at 2-5 yr mark

Question 14

What is this?

Answer 14

• Os Subfibulare
• small piece of bone adjacent to inferior fibula

Question 15

What is the epidemiology and pathoanatomy of Os Subfibulare?

Answer 15

• 1-2% of population
• May represent Avulsion fx of ATFL that secondarily ossifies
• Accessory ossification centre

Question 16

What are the symptoms and signs of Os Subfibulare?

Answer 16

Symptoms

• May be asyptomatic
• Ankle pain ( symptomatic os subfibulare)
• Assoc with chronic ankle instability- present with recurrent ankle sprains

Signs

• Focal tendermess & swelling at site of ossicle
• Laxity with anterior draw & inversion/eversion stress test

Question 17

What imaging is helpful in Os Subfibulare?

Answer 17

• xrays
  
  • standard ankle series- WB AP, Lateral , Mortise
  • varus stress view
  • See accessory ossicle
  • Talar tilt on varus stress view- see pic
    
    • suggest ankle instability
    • increased separation of os fragment from fibular tip

Question 18

What is DDX of Os Subfibulare?

Answer 18

• Acute lateral malleolus avulsion fracture ( by ATFL)

Question 19

What is the Tx of Os Subfibulare?

Answer 19

• Non operative
  
  • NSAIDs, Rest, Immobilisation, restricted WB
  • intial tx for symptomatic os fibulare
• Operative
  
  • Surgical exicision
  • failed non operative treatment

Question 20

What is this?

Answer 20

• Os Peroneum
• Sesmoid bone found within PERONEUS LONGUS tendon near the base of the 5th MT
• May represent avulsion/rupture of peroneus longus

Question 21

What is the epidemiology of Os peroneum?

Answer 21

• Incidence 9-20%
• Bilateral 60%
• Bipartite 30%

Question 22

Describe the pathophysiology of injury/fracture?

Answer 22

• Direct Trauma
• Indirect Trauma- Sudden inversion/eversion
  
  • assoc with peroneus longus tendon rupture

Question 23

What investigations are useful in DDx of Os peroneum?

Answer 23

• Xrays
  
  • normal os peroneum
  • acute os peroneum fracture
  • peroneus longus rupture
• MRI
  
  • Normal os peroneum
  • Acute os peroneum fracture
  • peroneus longus rupture- see pic

Question 24

What is the DDX of Os peroneum?

Answer 24

• Painful os Vesalianum- see pic
• Biparite os peroneum

Question 25

Describe the Tx of OS peroneum?

Answer 25

* Non operative * **NSAIDS, Rest, immobilisation, restricted weightbearing** * inital Tx for painful os peroneum syndrome * minimally displaced os peroneum fractures * Operative * **Surgical Excision** * Painful os peroneum syndrome w consx tx * os peroneum fracture w displaced fragments * **Surgical excision w repair of Peroneus Longus Tendon or tenodesis to Peroneus Brevis**

Question 26

What is this?

Answer 26

* **Accessory NAVICULAR** * Normal variant in **12% population** * Majority pts are **asymptomatic** * More common in **females**

Question 27

What is the pathoanatomy of accessory navicular?

Answer 27

* Occurs as a **PLANTAR ENLARGEMENT of navicular bone** * Navicular ossifies at age 3 in girls, 5 in boys * **Accessory navicular doesn't ossify until 8 years** * exists as **secondary bone** or **complete ossified extension to navicular**

Question 28

What is the classification ot the accessory navicular?

Answer 28

* Radiograph * TYPE 1= Sesmoid bone in substance of TIBIALIS POST tendon- see pic * TYPE 2= Separate accessory bone attached to native navicular via **synchondrosis** * Type 3= Complete bony enlargement

Question 29

What are the symptoms and signs of accessory navicular?

Answer 29

* Symptoms * **Medial Arch pain is worse w OVERUSE** * due to repetitive microfracture at the synchondrosis or from inflammation of the posterior tibialis tendon insertion * O/E * **Tender at medial and plantar** aspect of **navicular** bone

Question 30

Describe the imaging useful for Dx?

Answer 30

* Xrays * Ap, Lat, obliques * best seen on **EXTERNAL OBLIQUE** * **bony enlargement or accessory bone** * **​MRI** * **​Helps delinate insertion of tibialis posterior tendon**

Question 31

What is the TX of accessory navicular?

Answer 31

* Non operative * **Activity restriction, shoe modification and non- narcotic analgesia** * use of arch supports/pads over bony prominences * UCBL orthosis may invert heel during walking and decrease symptoms * nearly all children & adolsecents who have symptomatic accessory tarsal navicular bone become asymptomatic when they reach skeletal maturity * **Short period pf cast immobilisation** * **Operative** * **Excision of accesory navicular** * failed consc tx

Question 32

Describe the technique for surgical excision of accessory navicular?

Answer 32

* **Bone needs to be resected flush with MEDIAL CUNEIFORM** * most common cause of persistent symtpoms post surgery is **INADEQUATE BONE RESECTION** * other pts may have persistent pain from **SCAR TISSUE** or other causes * May need to **SPLIT the posterior tibialis** tendon in order to excise the navicular * **Re- routing the posterior tibialis will NOT CORRECT FLAT FOOT DEFORMITY** * **CALCANEUS OSTEOTOMY if flatfoot correction is needed.**