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#4 Surg > 50 - Biomechanics of Hallux Abducto Valgus > Flashcards

50 - Biomechanics of Hallux Abducto Valgus Flashcards

1
Q

Abduction and adduction of interossei

A
  • Abduction and adduction of the lesser toes caused by the interossei- utilizes the 2nd toe (metatarsal) as the midline reference point
  • So, abduction is movement away from the 2nd toe and adduction is movement towards the 2nd toe
  • Plantar interossei adduct
  • Dorsal interossei abduct
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2
Q

Abduction and adduction of lumbricals

A
  • Adduction of the lesser toes caused by pull of the lumbricals utilizes the midline of the body as the reference point
  • So, adduction of all toes will be towards the midline of the body
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3
Q

Abduction and adduction of hallux

A
  • The actions of abduction and adduction of the great toe utilize the midline of the body
  • So, abduction of the great toe means that the hallux moves away from the midline of the body [towards the 2nd toe (caused by pull of the adductor hallucis)], and adduction means towards the midline of the body [away from the 2nd toe (caused by pull of the abductor hallucis)]
  • The names of abductor hallucis and adductor hallucis utilize the 2nd toe as the midline
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4
Q

Definition of HAV

A
  • Prominence of the medial aspect of the 1st metatarsal head secondary to medial deviation of the 1st metatarsal shaft and lateral deviation of the great toe (toward the second toe)
  • The vast majority of the bony prominence you see is normal bone
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5
Q

Etiology of HAV

A
  • CURRENTLY the primary etiology is STJ pronation
  • Calcaneocuboid and talonavicular joints assume
    a more parallel relationship which allows more
    movement in the forefoot so it can
    dorsiflex and invert on the rearfoot
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6
Q

Diagram of pronation, neutral and supination

A
  • On the left (pronation) you can see that the parallel relationship of the talus and calcaneus allows for increased motion in the forefoot – this motion will be dorsiflexion and inversion
  • Inversion of the forefoot is consistent with supination, which is the unstable position of the foot
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7
Q

Prolonged pronation

A
  • If pronation is prolonged, resupination is delayed during midstance and propulsion (resupination normally starts at 25% of the stance phase)
  • Foot is unstable and becomes hypermobile (especially the first metatarsal and first ray)
  • As the arch lowers with pronation and cuboid dorsiflexes the cuboid is on the same plane as 1st metatarsal, or even lower than the 1st metatarsal
  • Peroneus longus loses the pulley action of the cuboid and begins to lose its ability to plantarflex the 1st metatarsal, so the 1st metatarsal is then able to dorsiflex
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8
Q

Diagram of pronation

A
  • Note the difference between the normal position of the calcaneus and cuboid and the pronated position – by the cuboid dorsiflexing, you lose some of the pulley effect of the peroneus longus
  • When the cuboid is dorsiflexed, the peroneus longus tendon therefore is functionally weaker
  • The image on the right is just showing that the result of this is the 1st metatarsal dorsiflexing
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9
Q

Where does hypermobility really exist? Roling paper

A

Roling et al, Biomechanics of the first ray. Part IV: the effect of selected medial column arthrodeses. A three-dimensional kinematic analysis in a cadaver model. J Foot Ankle Surg. 2002
o Selective arthrodeses on 6 specimens to determine location of medial column hypermobility - Talonavicular joint (9%), naviculocuneiform joint (50%), first MCJ (41%)
o SUMMARY: Found that the most hypermobility was at the NAVICULOCUNEIFORM joint, not the 1st metatarsal cuneiform joint, which is what the traditional theory has been

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10
Q

Where does hypermobility really exist? Faber paper

A

Faber FW, et al. Mobility of the first tarsometatarsal joint in relation to hallux valgus deformity: anatomical and biomechanical aspects. Foot Ankle Int.
o Cadaveric study in hallux valgus feet
o First MCJ contributed 57%, the talonavicular joint contributed 8% and the naviculocuneiform joint contributed 35% of medial column motion
o SUMMARY: found that the 1st metatarsal cuneiform joint did contribute the most motion in the first ray, but naviculocuneiform contributed a significant amount (35%)

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11
Q

Hypermobility raises the question…

A
  • Is a Lapidus procedure (fusion of 1st metatarsal-cuneiform joint) the right procedure to correct a bunion with hypermobility of the 1st ray?
  • Hypermobility at the naviculocuneiform still remains – not addressed with a Lapidus
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12
Q

Raises another question…

A
  • Does hypermobility even exist?

- Courtesy of Dr. Thomas Roukis, DPM at ACFAS meeting, Austin, TX, 2016.

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13
Q

Technical definition of hypermobility

A 
Technical definition (applies to children) 
o	“Increased range of motion of joints, joint laxity occurring normally in young children or as a result of disease”
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14
Q

Biomechanical definition of hypermobility

A

o “Abnormal motion of bone caused by un-resisted forces at a time when the joint should remain stable”

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15
Q

DPM definition of hypermobility

A

o Quasi-scientific by using 10 mm as normal range with 5mm dorsal and 5mm plantar
o Half of the papers show that when the 1st ray dorsiflexes, it inverts (prevailing theory)
o Half of the papers show that when the 1st ray dorsiflexes, it everts (he believes this)
o Total range of motion averages from 4.5° for the navicular-cuneiform-1st metatarsal joint, 3.5° for the 1st metatarsal-cuneiform joint, and 10° for the 1st ray

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16
Q

What have studies shown in terms of hypermobility?

A

Coughlin M and Jones C. JBJS Am, 89:1887,2007
o “1st ray mobility was routinely reduced to a normal level without need for a Lapidus”
o “Plantar gapping is not a reliable radiographic indicator of sagittal plane 1st ray hypermobility”

Faber study – 2004
o “Theory that HAV and hypermobile 1st ray should be managed with Lapidus was not supported”
o “Presence or absence of 1st ray hypermobility makes no difference to the outcomes.”

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17
Q

1st ray hypermobility conclusion

A
  • To date, little has been proven regarding 1st ray hypermobility and its role in 1st ray pathology is not supported
  • However, the prevailing theory is that it does play a significant role in bunion development
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18
Q

Plantarflexion

A
  • Plantarflexion of the 1st ray is needed to stabilize it against the ground and allow the great toe to dorsiflex 65° (in propulsion, knee is flexed 45° and ankle is dorsiflexed 20°) to keep the hallux on the ground
  • The first 30° of hallux dorsiflexion comes purely from the MPJ (shape of the joint passively allows this first 30°)
  • To obtain 65°, the 1st ray plantarflexes which shifts the transverse axis of the 1st MPJ more proximally over the sesamoids – that allows the remaining 35° to occur
19
Q

Rate of bunion development depends upon…

A 
o	1. Extent of abnormal STJ pronation
o	2. Degree of calcaneal eversion
o	3. Amount of forefoot adductus
o	4. Extent of 1st MPJ inflammation
o	5. Angle and base of gait, stride length
o	6. Type of footgear (tight shoes)
20
Q

1st metatarsal in stage 1 bunion

A

ACTUALLY, the 1st metatarsal dorsiflexes and inverts ( everts?) away from a stable proximal phalanx
o Roukis TS and Landsman AS. Hypermobility of the first ray: a critical review of the literature. J Foot Ank Surg 2003; 42 (6):377-390.
o Dayton P, Kauwe M, Feilmeier M. Is our current paradigm for evaluation and management of the bunion deformity flawed? A discussion of procedure philosophy relative to anatomy. J Foot Ank Surg 2015; 54: 102-111.

21
Q

1st ray orientation

A
  • 1st ray axis is oriented from medial/proximal/dorsal to lateral/distal/plantar
  • So, as the 1st metatarsal dorsiflexes, it inverts (everts?)
  • There is evidence that the 1st ray everts instead of inverts, which is the traditional though
22
Q

1st ray motion

A
  • As this occurs, the hallux is held to the ground by muscle power
  • Hallux is everting and plantarflexing in relationship to the inversion (eversion?) and dorsiflexion of the 1st metatarsal, as well as, abducting (subluxing
    laterally) due to adduction of the 1st metatarsal
  • EHB pulls laterally
23
Q

Sesamoid displacement

A
  • Minor degree of lateral sesamoid displacement (?)
  • Quantification of Rotational Correction Achieved During
    Modified Lapidus Arthrodesis with Frontal Plane Correction; Dayton et al.
  • Correcting the eversion (by inverting) of the 1st metatarsal, realigns the sesamoids
  • Tension develops on medial side of 1st MPJ, and compression on lateral side (medial sesamoidal ligaments stretch, lateral ligaments tighten)
24
Q

Stage 2 bunion

A
  • Characterized by a true abduction deformity of hallux, with hallux pressing against second toe
  • Now the hallux is actually starting to move
25
Q

EHL and FHL in stage 2 bunion

A
  • Long axis of 1st metatarsal moves more medially which causes bowstringing of EHL and FHL tendons, as they move further away from the axis of motion
  • Leads to further lateral displacement of sesamoids
  • Or do they appear laterally displaced due to the valgus rotation of the 1st metatarsal? (Dayton)
26
Q

Abductor hallucis in stage 2 bunion

A
  • Abductor hallucis loses its medial stabilizing force as the 1st metatarsal dorsiflexes
27
Q

Effects of stage 2 bunion

A
  • This more plantar orientation prevents it from balancing the abductory force of adductor hallucis
  • FHB now contributes to lateral abductory force, as the sesamoids “drift” more laterally
  • This drift is actually being accomplished in this stage by some active pull of the tendons
  • Joint space widens and first signs of lateral joint deviation may be noted (however, most joint changes occur in Stage 3)
  • If the bunion progresses at a steady rate, bony adaptation maintains symmetric joint margins
  • If it progress rapidly, unequal joint margins are noted
28
Q

Stage 3 bunion

A
  • Characterized by increase in the intermetatarsal angle and widening of the foot
29
Q

Longitudinal axis of 1st metatarsal in stage 3 bunion

A
  • Moves more medially and becomes oriented from proximal/lateral/plantar to distal/medial/dorsal
  • 1st metatarsal is dorsiflexed and adducted
30
Q

Transverse axis of motion of 1st MPJ in stage 3 bunion

A
  • No longer level with the transverse plane and orients from proximal/lateral/dorsal to distal/medial/plantar
31
Q

Sesamoids in stage 3 bunion

A
  • Sesamoids appear to move more laterally-actually, are held stable by the adductor hallucis, and once again, it is the 1st metatarsal that moves
  • NOTE: Crista becomes eroded as the tibial
    sesamoid moves laterally beneath it
32
Q

Extrinsic and intrinsic muscles in stage 3 bunion

A
  • Extrinsic and intrinsic muscles increase their deforming forces from Stage 2
  • Intrinsic muscles tend to only stabilize the medial aspect of hallux during propulsion, thereby increasing its frontal plane valgus rotation
33
Q

Stage 4 bunion

A
  • Characterized by subluxation or dislocation of the 1st MPJ
  • 2nd toe can no longer act as a buttress for the great toe, and the hallux either underrides or overrides the 2nd toe
  • Orthotics may slow down the progression of the HAV and are most effective in the early stages
  • From Stage 3 on, orthotics useless (opinion)
34
Q

QUESTION

Hallux Abducto valgus means that the great toe…..
o Moves towards the second toe
o Moves away from the second toe

A

Moves towards the second toe

35
Q

The 1st dorsal interossei causes __________ of the 2nd toe
o Adduction
o Abduction

A

Abduction

36
Q 
The 1st lumbrical causes\_\_\_\_\_\_\_\_\_
o	Abduction of the 1st toe
o	Adduction of the 1st toe
o	Abduction of the 2nd toe
o	Adduction of the 2nd toe
A

Adduction of the 2nd toe

37
Q
  • Why is STJ pronation the most significant cause of bunions?
    o The cuboid becomes more dorsiflexed
    o The peroneus brevis gains a functional advantage
    o The 1st ray becomes dorsally hypermobile
    o The MTJ becomes stable
A

1 and 3

  • The cuboid becomes more dorsiflexed
  • The 1st ray becomes dorsally hypermobile
38
Q

Is a Lapidus procedure the correct choice for a hypermobile 1st ray?
o Yes
o No

A
  • Answer: The predominant opinion would be yes, but there is some evidence that it doesn’t
  • The hypermobility could be addressed regardless of the procedure you chose
39
Q

To obtain the full 65° of hallux dorsiflexion_________
o The first metatarsal must plantarflex
o The transverse axis of the 1st MPJ must move distally
o A portion of dorsiflexion must be passive due to normal gait

A

Answer: 1, 3
o The first metatarsal must plantarflex
o A portion of dorsiflexion must be passive due to normal gait

40
Q

As the first metatarsal dorsiflexes, it also__________
o Inverts
o Everts

A

Answer: On the boards = invert, the current theory is = everts

41
Q

Most of the mal-positioning of the sesamoids in HAV is due to active lateral movement of the sesamoids.
o Yes
o No

A

No

42
Q

The EHL, FHL, and FHB tendons contribute to HAV deformity. They are activated by:____
o The great toe abducting
o The great toe adducting
o The long axis of the 1st metatarsal moving laterally
o The long axis of the 1st metatarsal moving medially

A

The long axis of the 1st metatarsal moving medially

43
Q

As the first metatarsal dorsiflexes, the abductor hallucis muscle_________
o Falls below the axis of the 1st MPJ and increases its activity
o Falls below the axis of the 1st MPJ and decreases its activity
o Falls above the level of the 1st MPJ axis and increases its activity
o Falls above the level of the 1st MPJ axis and decreases its activity

A

Falls below the axis of the 1st MPJ and decreases its activity

#4 Surg (14 decks)

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