52: Biomechanics of Tailor's Bunion - Bennett Flashcards
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
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.
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)
The 5th ray axis is _________ to the MTJ oblique axis
parallel
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
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
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
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
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
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
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.
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.
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
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)
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
