Sesamoid Disorders

 

Anatomy and Biomechanics

  • Sesamoids sit underneath the head of the 1st metatarsal within the tendons of the Flexor Hallucis Brevis
  • Each sesamoid can take up to 300% body weight during push-off
  • Important role in the dynamic function of 1st MTPJ
  • Pain underneath the 1st MT head can be due to:
    • fracture
      • acute
      • delayed- or non-union
    • chondromalacia
    • osteonecrosis
    • sesamoiditis
  • Risk factors causing increased plantar 1st MT pressure:
    • high-heeled shoes
    • dance
    • sports
    • anatomical factors
      • cavovarus foot shape
      • ankle equinus
      • absent crista
      • MT rotation

“Sesamoiditis” is a generic term for numerous conditions resulting in pain around the sesamoid(s)

 

Clinical Assessment

History

  • Insidious onset of pain
  • Usually unilateral
  • Plantar location
  • Exacerbated by certain shoes

Examination

  • Direct tenderness under sesamoid (most commonly medial)
  • Pain on resisted plantarflexion
  • Reduced range of movement
  • Reduced plantarflexion power
  • Plantar bursa
  • Important to assess:
    • foot shape: plantar-flexed 1st ray
    • sensory function to exclude digital nerve entrapment

Imaging

X-ray:

  • Weight-bearing views essential
  • AP/lateral/oblique and sesamoid skyline
  • Can be difficult to differentiate fracture from bipartite sesamoid (especially when delayed):
    • acute fractures have sharp margins
    • biparite edges are more rounded

CT:

  • More sensitive and specific for identifying fractures
  • Can also identify periostitis, callus formation and articular irregularity

MRI:

  • Sensitive for fractures and stress response (marrow oedema)
  • Osteoarthritis

 

Fractures

Cause

  • Forced dorsiflexion
  • Direct impact / crush

Treatment

  • Non-operative:
    • Minimally or undisplaced fractures:
      • non WB cast with toeplate for 6 weeks
      • then walking boot for 6 weeks
      • stiff-soled shoe / orthotic
  • Surgery indicated in:
    • displaced fractures
    • symptomatic delayed / non-union
    • options:
      • internal fixation with tiny screw(s)
      • bone grafting of non-union +/- internal fixation
      • partial sesamoidectomy for progressive diastasis of fracture or bipartite sesamoid
      • complete sesamoidectomy for refractory cases or AVN

 

Intractable plantar keratosis

  • Often associated with the tibial sesamoid
  • Can be caused by an osseous deformity of the sesamoid
  • Must be distinguished from a more diffuse keratosis beneath a plantarflexed first ray (e.g. cavus)
  • Plantar shaving of the sesamoid is an option when conservative treatment fails

 

Sesamoidectomy

Indications

  • Failure of conservative treatment
  • Sesamoid confirmed as pain source

Outcomes

  • The literature lacks sufficient information regarding post-operative results
  • Small series have reported up to 50% relief of pain and return to normal activities

Considerations

  • Maintain the integrity of the remaining intrinsic muscles and capsule to maintain 1st MTP joint stability and function
  • Avoid resection of both sesamoids unless necessary
  • Plantar digital nerves at risk
  • Late varus / valgus deformity may occur
  • Plantar scars can be problematic – avoid WB area

Approaches

  • Medial sesamoid via plantar medial incision
  • Lateral sesamoid via curved plantar incision lateral to WB area
    • Dorsolateral approach also described to reduce risk to digital nerve

 

 

References

Aquino M, DeVincentis A, Keating S. Tibial sesamoid planing procedure: an appraisal of 26 feet. J. Foot Surg., 23:226–230, 1984

Anderson R, McBryde A. Autogenous Bone Grafting of Hallux Sesamoid Nonunions. Foot & Ankle International. 1997;18(5):293-296. doi:10.1177/107110079701800509

Biedert R, Hintermann B. Stress Fractures of the Medial Great Toe Sesamoids in Athletes. Foot & Ankle International. 2003;24(2):137-141. doi:10.1177/107110070302400207

Cohen B. Hallux Sesamoid Disorders. Foot and Ankle Clinics.2009 Mar;14 (1): 91–104

Coughlin M. Sesamoids and Accessory Bones of the Foot. Mann’s Surgery of the Foot and Ankle 10th ED, Chapter 11, 434-461