52: Biomechanics of Tailor's Bunion - Bennett Flashcards Preview

Surg+BioMech [all exams] > 52: Biomechanics of Tailor's Bunion - Bennett > Flashcards

Flashcards in 52: Biomechanics of Tailor's Bunion - Bennett Deck (15)
1

describe a tailor's bunion

  • An abnormally prominent 5th metatarsal head
  • Can be a dorsal, dorsal-lateral, or plantar-lateral bunion
  • Usually associated with an adductovarus deformity of the 5th toe
  • Shearing force of the shoe often causes an adventitious bursa overlying the bone

2

define tailor's bunion

Definition:  Symptomatic Prominence,  Hypertrophy, or Irritation Involving Bone or Soft Tissue About the Lateral or Dorsolateral Fifth Metatarsophalangeal Joint

The Deformity is a Mirror Image of HAV. 

The Fifth Toe is Usually in a Varus Angulation.

3

what is the axis of the 5th metatarsal?

  • Axis of motion of 5th ray lies 20° from transverse plane and 35° from sagittal plane
  • It runs from proximal-plantar-lateral to distal-dorsal-medial
  • Motion (supination and pronation) --> results in a small amount of abduction and adduction
  • There is about 10 degrees of tri-plane motion (mostly frontal plane inversion/eversion)

4

The 5th ray axis is _________  to the MTJ oblique axis

parallel

5

structural vs. functional etiologies of tailor's bunions

Structural

  • increased IM angle
  • bowing of the metatarsal
  • dumbbell shaped metatarsal head
  • Accessory ossicle
  • soft tissue hypertrophy

Functional

  • Uncompensated rearfoot varus
  • uncompensated forefoot varus
  • forefoot valgus foot types
  • Abnormal STJ pronation
  • Uncompensated or partially compensated RF varus
  • Uncompensated, partially compensated,  FF varus
  • Congenitally dorsiflexed or plantarflexed 5th ray deformity
  • Flexible FF valgus
  • Compensated gastroc-soleus equinus

6

how does STJ pronation contribute to tailor's bunion?

Abnormal STJ pronation by itself will not cause a tailor’s bunion; it must be present along with one of the other etiological factors

--->

Hypermobility of the 5th ray against fixed shoe pressure leads to a dorsiflexed, abducted, everted position

Due to the everted position, when viewed on an AP x-ray, the plantar concavity of the shaft becomes laterally positioned, making the shaft appear to be curved

The plantar condyles become laterally positioned and often are mistaken for an exostosis

7

IM angle of Fallat and Buckholz

and

Lateral deviation Angle

greater than 8.71 degrees FB and lateral deviation greater than 8 is associated with tailor's bunion

normal = 6.22-6.47 fallat buckholz

normal lateral deviation = 2.64-7.5

 

8

splayfoot deformity

  • An IM angle > 12° between the 1st and 2nd metatarsals, and an IM angle > 8° beween the 4th and 5th metatarsals
  • tailor's bunion can be assoc w/ splayfoot deformity

9

what soft tissue components contribute to varus deformity at 5th  met?

  • As the shaft everts, the abductor digiti quinti is placed more plantarly, so it loses its abductory force on the 5th toe, and the toe adducts and moves into varus
  • Adductovarus deformity of 5th toe may produce joint changes at the 5th MPJ

10

how do uncompensated and partially compensated varus deformities contribute to tailor's bunion?

Must occur in a fully pronated foot to cause a hypermobility of the 5th ray

5th metatarsal is forced into a dorsiflexed, abducted, and everted position by ground reaction forces

A varus foot will exist in a fully pronated foot when the total amount of degrees in varus exceed the amount of calcaneal eversion.

EX: 3 tibial varum, 10 calcaneal varus, STJ ROM 24. rearfoot varus = 13, STJ can evert max 8 degrees. --> 5 degrees rearfoot varus when max pronated

11

how does a plantarflexed 5th met contribute to tailor's bunion deformity?

  • The 5th metatarsal head either will not reach or will just reach the common transverse plane of the other meta-heads when the 5th ray is fully pronated to its maximum dorsiflexed position
  • Prominence of meta-head is lateral or plantar-lateral
  • Very unstable metatarsal when pronating
  • A normal 5th metatarsal declination angle is 10 degrees. This pathology is seen when > 10 degrees.

12

clinical s/s tailor's bunion

  • Hyperkeratosis is primarily identified on the lateral aspect of the 5th.
  • If the pronation and subluxation are not adequate to dorsiflex the 5th. Met head to the transverse plane, hyperkeratosis will be located plantar lateral.
  • Hyperkeratosis may be identified when fully pronated at the base of the 5th. Met.

13

how does a dorsiflexed 5th met contribute to tailor's bunion?

  • The shaft is neither everted nor abducted, so there is no curvature seen laterally on an AP x-ray of the foot
  • The prominence of the metahead is dorsally located

14

etiology of idiopathic tailor's bunion

  • etiology is the transverse head of the adductor hallucis inserts into the 3rd, 4th, and 5th mtpj and transverse ligament.
  • In a tailors bunion deformity the insertion into the 5th. is absent
  • This primarily causes increased abduction and instability (lack of adduction)

15

what type of orthotics would you use for tailor's bunion?

  • Because abnormal pronation alone is not a cause of tailor’s bunions, orthotic control may be unsuccessful in reducing progression of symptoms
    • uncompensated varus deformities
    • congenital fixed plane deformities
    • Orthotics may work with a flexible FF valgus foot type

Decks in Surg+BioMech [all exams] Class (68):