56 - Biomechanics of Digital Deformities Flashcards
1
Q
Hammer toe
A
- “A deformity in which the proximal phalanx of one of the smaller toes is bent upward or is dorsiflexed at the metatarsal-phalangeal joint, and the middle and distal phalanges are sharply bent downward, so that they form a more acute angle with the proximal phalanx” Schuster 1927
2
Q
Etiology of digital deformities
A
- Congenital or acquired
- Neuromuscular disorders: CMT = multiple clawtoes, peripheral neurologic disorders (cavus foot)
- Biomechanical dysfunction: MOST COMMON, static vs. dynamic etiologies (3)***
3
Q
Anatomic-Biomechanical review
A
- Stabilization of the lesser toes against the ground at the MTPJ’s provided mainly by FDL and FDB
- Dorsiflexion at the lesser MTPJ’s is accomplished by the EDL through the EXTENSOR SLING which supports the proximal aspect of the proximal phalanx
- Dorsiflexion of the middle and distal phalanges is mediated through the EXTENSOR WING controlled primarily by the lumbricals
4
Q
Long and short extensor tendons
A
- Held in place by 2 fibrous sheaths: Extensor hood
- Proximal part: EXTENSOR SLING
o Fibers encircle and attach to the plantar plate - INTEROSSEOUS muscles contribute to the sling
- Distal part: EXTENSOR WING
o Formed by expansions of the LUMBRICALS -
**KNOW THE ANATOMY **
o Know this diagram (color coded on slides) - THESE RELATIONSHIPS ARE IMPORTANT
5
Q
Long and short flexors
A
- Insert into the base of the middle and distal phalanges respectively
- Stance phase muscles
- Plantarflexory force to the MTPJ (non-weight-bearing),
but DORSIFLEX MTPJ in weight bearing - Plantarflex and stabilize digits during stance phase of gait
6
Q
Interossei muscles
A
- Seven muscles arising from metatarsal shafts, 4 dorsal and 3 plantar interossei***
- Pass above the deep transverse metatarsal ligament but below the transverse axis of the MTPJ and insert into the base of the proximal phalanx.
- STANCE PHASE MUSCLES
- Stabilize in the TRANSVERSE plane and PLANTARFLEX the MTPJ
- Balances the reverse buckling effect of the FLEXORS during stance phase of gait
7
Q
Lumbricals
A
- Four muscles arise from the FDL tendons
- Course beneath the deep transverse intermetatarsal ligament
- Insert medially into the base of the proximal phalanx and extensor hood
- Plantarflex and adduct the MTPJs and dorsiflex the IPJs
- Balance the effect of the long extensors and passive pull of the long flexors during swing phase of gait
- SWING PHASE MUSCLES
- This means that when the extensors are unopposed by the flexors, they will be contracted at the IPJ because of the lumbricals – they will passively oppose the long extensors
8
Q
Pathologic anatomy – Biomechanics
A
Static
o Associated with HAV
o Confining shoe gear
Dynamic MAJORITY OF DIGITAL DEFORMITIES YOU WILL SEE
o Flexor stabilization
o Flexor substitution
o Extensor substitution
You will be asked this on rotation – Should be able to rattle these off***
9
Q
Flexor stabilization
A
- Pronated foot
- Late stance phase of gait
- ***FDL & FDB have gained MECHANICAL ADVANTAGE over the interossei muscles
- Often an adductovarus rotation of the 5th digit due to weakness of the quadratus plantae
- Most common type*
10
Q
Mechanism of flexor stabilization
A
- Flexible pes valgus deformity with excessive STJ pronation
- Causes an unlocked/hypermobile MTJ: forefoot hypermobility – the body does NOT like a relaxed and unstable forefoot – The result is that the flexors compensate by…
- Flexors fire EARLIER and LONGER to try to stabilize osseous structures
- Ineffective at controlling the forefoot structures
- Flexors effectively overpower the interosseous muscles
- The response by the body is callus formation… When the toe is contracted up, the metatarsal plantarflexes, putting excess pressure under the metatarsal heads, leading to callus formation
11
Q
Flexor stabilization: Quadratus plantae weakness
A
- Excessive STJ pronation
- Forefoot abduction
- Changes the lateral vector force of the QP
- More medial pull by the FDL creates an adducto
varus rotation of the 5th digit (maybe 4th as well)
12
Q
Peripheral neuropathy
A
- In flexor stabilization, peripheral neuropathy leads to a loss of intrinsic power
- Keep in mind that in diabetic patients, neuropathy affects the foot and later on the leg
- You may see a loss of power to the intrinsics that can lead to a hammertoe deformity in these patients
13
Q
Flexor substitution
A
- Supinated foot
- Late stance phase of gait
- Flexors have gained advantage over the interossei
- Straight contracture of all lesser toes
- Due to weak triceps surae (gastroc soleus complex)
- This means that if someone ruptures an Achilles tendon or other surgical procedure to the Achilles, they may have hammertoes form several years down the road
- Deep posterior + lateral leg muscles try to substitute
- Least common type
14
Q
Flexor substitution: Deep posterior muscle group
A
- Tibialis posterior: primary decelerator of pronation & supinator of the rearfoot
- FHL & FDL also have axis of SUPINATION around the STJ
- Due to a weak triceps surae, these muscles fire earlier and longer
- Cause STJ SUPINATION – Results in contraction of the digits
- You will NOT see this in a pronated foot type – KNOW THIS***
15
Q
Flexor substitution biomechanics
A
- Peroneus longus: plantarflexes 1st ray – Also causes STJ supination (why?)
- High arched, late stance supinated foot with contracture of the toes results
- The deep flexors attempt to substitute for the weak triceps surae will not create heel lift
- Flexors overpower the interossei and cause hammertoe deformities
