Sesamoids

Anatomy

 

3 Sesamoids may be present in great toe

- 2 almost always present on plantar aspect of MTPJ

- 1 may be present on plantar aspect of IPJ

 

MTPJ sesamoids most important

- embedded in FHB tendons

- held together by intersesamoid ligament & plantar plate

- each side of crista / inter-sesamoid ridge

- articulate with plantar facets of 1st MT

 

Tibial usually larger than fibula

 

Tibial more impacted in weight bearing than fibula

- higher incidence traumatic injury to tibial

 

Insertions

- FHB

- Adductor hallucis

- Abductor hallucis

- Plantar plate

- Intersesamoid Ligament

- Plantar aponeurosis

 

Orientation

- Proximal to MT head in stance

- Pulled under MT head with DF / toe off

 

Ossification

- between 7-10 years

- often multiple centers 

- may result in bipartite / tripartite appearance

 

Bipartite

- fibular rare

- tibial bipartite in ~ 10% 

- bilateral in ~ 25% of these

- congenital absence - one or both

 

Bipartite Sesamoid

 

Blood Supply

 

Type A 50% medial plantar artery and plantar arch

Type B 25% plantar arch

Type C 25% medial plantar artery

 

Increased risk of AVN if only single vessel into sesamoid

- which is seen in Type C more commonly than B

 

Functions

- absorb weight bearing pressure

- reduce friction

- protect tendons

- act as fulcrum to inc mechanical force of FHB

- Sesamoids and Collats provide medial / lateral stability of 1st MTPJ

 

History

 

Do not always present with symptoms directly referable to sesamoids

- generalized pain around Hallux

- pain after sudden pop or snap after running

 

Pain as hallux extends in terminal part of stance phase

 

Neuralgic symptoms or numbness if digital nerve compressed 

 

Examination

 

Local tenderness

Decreased strength on PF

Pain on passive DF

Loss of active & passive DF

 

Cavus foot

- plantar flexed 1st ray 

- excess axial load on sesamoid

 

Imaging

 

Standard lateral not very useful

- AP, medial oblique, lat oblique, axial

 

Bone scan 

 

Projection important to differentiate sesamoids from MTPJ

- may be obscured by AP scan

- PA or oblique with Collimation useful for DDx

- caution with increased uptake in ~25% of asymptomatic patients

- marked difference to contralateral side significant

 

MRI 

 

Useful for Osteomyelitis

 

CT 

 

Useful for post-traumatic changes 

- compared with contralateral side

 

Conditions

 

1.  Fracture

 

Difficult to differentiate from symptomatic multipartite sesamoid

- especially if fracture through bipartite 

- comparison X-ray with contralateral foot 

- MRI & bone scan with pin hole collimation useful

 

 Fractured SesamoidSesamoid Fracture CT

 

Non operative management

- initial treatment

- orthosis / dancer's pad / cast / MT bar

- especially stress fracture

 

Surgery

- excision of most comminuted fragment or entire sesamoid

- preferred over bone graft in most cases

- consider graft for athletes

 

2.  Osteochondritis

 

Infrequent

- osteonecrosis with regeneration & calcification may be present

- may be enlarged / deformed / sclerotic with mottling / fragmentation

 

3.  Infection

 

Rare except diabetic neuropathy

- Pseudomonas relatively common 

 

4.  Sesamoiditis

 

Repetitive trauma especially teens / young adults

- Inflammation & bursal thickening may be present

 

5.  Osteoarthritis

 

May be in conjunction with MTPJ OA / RA / Gout

 

Management

 

Stiff soled or rocker bottom shoe + MT pad

 

Sesamoidectomy

- may decreases pain

- Don't remove both

- leads to clawing of hallux

 

6.  Intractable Plantar Keratoses

 

Usually caused by

- sesamoid with plantar located osseous prominence

- plantarflexed first metatarsus / cavus

 

Management

 

Intractable lesions

- sesamoid shaving or resection

- avoid shaving if 1st MT is plantarflexed

- consider basilar dorsiflexion osteotomy

 

7.  Nerve Impingement

 

Impingement of medial branch plantar digital nerve on medial sesamoid

 

Sesamoidectomy

 

Principles

 

1.  Never excise both 

- high incidence of Hallux Valgus or Cock Up deformity

2.  Never make incision directly over sesamoid

3.  Always repair adductor if excising lateral sesamoid

 

Produce mechanical defect in FHB unit

- can excise up to 2/3 of either without disturbing ligamentous attachments

- may relieve pain without disrupting FHB mechanism

 

Tibial 

 

Tibial sesamoid excision

- 3cm plantar medial incision

- Medial branch plantar digital nerve identified & retracted

- Locate sesamoid by palpation

- Flex hallux 20-30o & retract FHL

- Incise inter-sesamoid ligament & pull sesamoid medial

- Shell out from capsule & plantar plate with knife

- Imbricate capsule

 

Tibial sesamoid shaving

- Plantar medial approach

- Excise plantar 1/2 with microsagittal saw

- Smooth with rongeur

 

Fibular

 

Approach

- either dorsal or plantar approach

- dorsal demanding due to depth

- plantar - NV bundle & FHL to negotiate  

 

Dorsal incision 

- from 2-3 cm proximal to web space

- Identify & protect branch SPN

- Interval between Adductor Hallucis & joint capsule opened

- Tendon of Add Hallucis reflected from lateral sesamoid

- Grasp sesamoid & divide inter-sesamoid ligament

- Release proximal & distal & excise

- repair adductor

- Close skin 

 

Plantar incision

- Flex hallux

- 4cm incision between MT 1 & 2

- Retract NV bundle either lateral or medial

- Locate FHL & open pulley over it

- Flex hallux to relax FHL & retract medially

- Divide inter-sesamoid ligament

- Excise proximally & distally

- Reattach cuff of FHB

- Consider oblique wire across MTPJ

 

Complications

 

Cock up toe

Hallux valgus or varus

Nerve injury

Fat pad disruption

Painful plantar scar if plantar incision