BR Biomechanics

Question 1

What is normal ankle joint motion during gait?

Answer 1

The ankle is slightly dorsiflexed at heel contact
Plantarflexes to achieve ground contact
Dorsiflexes as the tibia moves over the foot
Plantarflexes during the propulsion
Dorsiflexes during the swing phase

Question 2

What is ankle equinus?

Answer 2

Sagittal plane deformity with less than 10 degrees of dorsiflexion available.

May be osseous or muscular

Question 3

What are the causes of ankle equinus?

Answer 3

Osseus 
Morphology of the articular surface
Muscular
Spastic paralysis (Cerebral palsy or CVA)
Tonic spasm
Weak dorsiflexors
Tight hamsrings
Prolonged bedrest

Question 4

What happens in the uncompensated equinus?

Answer 4

The heel cannot touch the ground resulting in a bouncy gait.
There is excessive weightbearing on the forefoot leading to forefoot callouses.

Hamstrings will contract

Proximal compensations include genu recurvatum
Abducted or adducted angle of gait
Knee flexion/hip flexion

Question 5

What is the axis of the subtalar joint?

Answer 5

16 degrees from the sagital plane

42 degrees from the transverse plane

Question 6

Describe the longitudinal and oblique axis of the mid tarsal joint

Answer 6

The longitudinal axis is 15 degrees from the transverse plane and 9 degrees from the sagittal plane.

The oblique axis is 52 degrees from the transverse and 57 degrees from the sagittal plane.

Question 7

Describe the axis of motion of the ankle joint

Answer 7

The axis roughly aligns the tips of the malleoli approximately 8 degrees to the transverse plane.

The motion is mainly dorsiflexion with small amounts of abduction and plantarflexion with small amounts of adduction.

Question 8

What is the functional importance of ankle dorsiflexion?

Answer 8

10 degrees of dorsiflexion is required for normal gait.
Dorsiflexion is necessary to enable ground clearance during the swing phase of gait and to enable to tibia to move over the supporting foot during stance phase of gait.
The ankle joint acts as a sagittal plane pivot.

Question 9

Why is ankle plantarflexion so important?

Answer 9

Plantarflexion is important for generating power for active propulsion .

Question 10

What is the normal range of passive ankle dorsiflexion and plantarflexion?

Answer 10

The normal range of passive ankle dorsiflexion is about 20 degrees and the normal range of passive plantarflexion is 50 degrees.

Question 11

What is the motion of the longitudinal axis of the midtarsal joint?

Answer 11

The motion is pronation/supination, predominantly in the frontal plane.

Question 12

What is the motion of the oblique axis of the midtarsal joint?

Answer 12

The motion is pronation/supination, predominantly in the sagittal and transverse plane.

Question 13

Which axis’ are different between the STJ and MTJ?

Answer 13

The longitudinal axis’ of both have opposite motions.

Question 14

What muscle causes supination of the long axis in the MTJ

Answer 14

The tibialis anterior will allow for supination of the MTJ

Question 15

What muscle will cause pronation of the oblique axis of the midtarsal joint?

Answer 15

The peroneus longus!!!
Causes pronation (stability) of the oblique axis of the MTJ.

Ground reactive forces will also cause pronation of the MTJ oblique axis.

Question 16

How does the STJ effect the MTJ?

Answer 16

when the stj is in pronation it unlocks the MTJ to allow for more accomodative motion.

Subtalar joint supination locks the MTJ allowing for a rigid lever.

Question 17

What exactly is the first ray and what is its axis?

Answer 17

It is the first met and medial cuneiform.

the axis of the first ray is 45 degrees to the frontal and sagital planes. (equal motion in both planes)

Question 18

What is the motion of the first ray?

Answer 18

Dorsiflexion and inversion

Plantarflexion and eversion

Question 19

What are the main muscles acting on the first ray?

Answer 19

Tibialis anterior and peroneus longus

Question 20

What can produce a plantarflexed first ray?

Answer 20

Weak gastroc (Foot will go into a rearfoot calcaneus position and the first ray will plantarflex to reach the ground)

Hypertonicity of the peroneus longus; weak tibialis anterior; cavus foot type.

Question 21

What is the acetablumum talus?

Answer 21

The anterior and middle facets of the talus and where it articulates with the navicular.

Question 22

What is the passive range of motion of the STJ?

Answer 22

Average range of motion is about 20-30 degrees of inversion

5-10 degrees of eversion.

However ranges have been cited as anywhere between 10-65 degrees of total range of motion in studies.

Question 23

What is the cause of a dorsiflexed first ray?

Answer 23

Metatarsus primus elevatus may be congenital or aquired.

Caused by hypertonicity of the tibialis anterior muscle or weakness of the peroneus longus muscle.

May be associated with forfoot supinatus, dorsal jamming of the first MPJ and commonly associated with hallux rigidus and limitus.

Question 24

What happens in uncompensated rearfoot varus according to root biomechanics?

Answer 24

The foot strikes the ground in an inverted position

Inadequate shock absorption occurs from the STJ

There is lateral instability

An aquired plantarflexed first ray may develop