Lesser Digits

Question 1

Which of the following are current aetiologies for digital deformity:

1. Extensor stabilisation
2. Extensor substitution
3. Flexor stabilisation
4. Flexor substitution

Answer 1

1. Flexor stabilisation
2. Extensor substitution
3. Flexor substitution

Question 2

What are the differences between flexible, semi-rigid, and rigid claw toe deformities?

Answer 2

Flexible - reducible when NWB and WB
Semi-rigid - reducible when NWB only
Rigid - not reducible

Question 3

Explain the flexor stabilisation aetiology

Answer 3

1. 0 Occurs in pes planovalgus deformity with excessive subtalar joint pronation, which unlocks the midtarsal joint and leads to hypermobility of the forefoot
2. 1 The flexors fire earlier and stay contracted for longer in an attempt to stabilise the forefoot.
3. With subtalar joint pronation, the abduction of the forefoot relative to the rearfoot creates a more medial pull from the FDL, leading to adductovarus rotation of the fifth toe
4. Peripheral neuropathy can lead to loss of power from the small intrinsic muscles and give mechanical advantage to the flexors (which originate more proximal).

Question 4

Explain the flexor substitution aetiology

Answer 4

1. Least common
2. Occurs in supinated feet when the deep posterior muscles (FHL and FDL) try to substitute for a weak triceps surae by firing earlier and for longer than usual, causing contraction of digits

Question 5

Explain the extensor substitution aetiology

Answer 5

Extensors overpower/gain mechanical advantage over interossei from:

1. Pes cavus: due to increased forefoot declination which extends the distance course of EDL, creating a passive pull (tendons don’t lengthen) and dorsiflexing MTPJs
2. Ankle equinus: anterior muscle group fires earlier and for longer in an attempt to increase ankle d/flexion
3. Neuromuscular disease: loss of function/weakness of lumbricals and/or spasticity of EDL

Question 6

What’s the origin, insertion and function of the lumbricals?

Answer 6

Origin - tendons of flexor digitorum longus
Insertion - dorsal surface of proximal phalanges (2-4) and expansions of the tendons of EDL
Action - flexes the MTP joints and extends PIP joints