Biomechanics & Radiology

Question 1

role of pretibial muscles at contact period of gait

(TA, EDL, EHL)

Answer 1

1. decelerate ankle plantarflexion
2. decelerate pronation & provide even weight-bearing from lateral to medial side of foot
3. provide unstable midtarsal joint for shock absorption and adaptation (mobile adaptor)
4. absorb impact loads from the floor

*TA muscle generates the largest torque around the ankle joint → followed by EDL and EHL

Question 2

time constant T2

define

Answer 2

• describes how quickly the transverse magnetization decays over time;
• reflects the tendency of different protons (which are usually aligned together after a 90-degree pulse) to precess quickly out-of-sync with each other

Question 3

dephasing

Answer 3

process of protons falling out-of-sync with each other at different rates

Question 4

time constant T1

define

Answer 4

how soon the protons realign w/ the static magnetic field (B0) following a radio frequency excitation pulse

Question 5

characteristic radiographic finding of

bipartite medial cuneiform

Answer 5

the transverse joint space has to be identified in the center of the medial cuneiform, with the joint space incomplete from dorsal to plantar

bipartition can be partial or complete;

complete → divided into dorsal and upper segments (referred to as os cuneiform dorsale and os cuneiform plantare; plantar segment is usually larger)

Question 6

Isherwood projections

use and views

Answer 6

to provide complete view of STJ

• medial oblique axial view → visualizes middle & posterior facets
• lateral oblique axial view → visualizes posterior facet in profile
• oblique plantardorsal view → visualizes anterior facet of the STJ

Question 7

coleman block:

if varus foot assumes more rectus hindfoot when first ray is offloaded →

Answer 7

this result demonstrates forefoot contribution in the varus hindfoot deformity

sx: lateral ankle stabilization combined w/ a dorsiflexory wedge osteotomy of the 1st metatarsal

Question 8

coleman block:

if varus foot remains in varus hindfoot when first ray is offloaded →

Answer 8

indicates varus position is fixed in the rearfoot itself

sx: lateralizing calcaneal osteotomy (e.g. Dwyer) or lateral displacement osteotomy is indicated

Question 9

radiographic signs of bone graft failure

Answer 9

• graft or fixation movement
• dissolution of the graft
• sclerosis

Question 10

radiographic signs of progressing graft to host integration

Answer 10

• gradual blurring of cortical margins
• crossing of trabecular patterns across graft-bone junction

Clinical signs of healing include decreased edema, decreased pain, no evidence of instability

Question 11

radiodensity of bone graft

Answer 11

• cancellous bone grafts should initially appear more radiolucent
• cortical bone grafts appear more radiodense

Question 12

“bone within bone”

appearance (dysplasia)

Answer 12

OSTEOPETROSIS

aka Albers-Schonberg disease

Question 13

“bone islands”

multiple well-defined sclerotic lesion in bone

Answer 13

Osteopoikilosis

Question 14

“candle wax”

appearance with sclerosis in the periphery

Answer 14

Melorheostosis

Question 15

“linear bands of sclerosis w/in bone”

Answer 15

Osteopatha striata

Question 16

central ray location during

NWB Medial Oblique View of Ankle

Answer 16

central ray should be directed vertically between the malleoli; malleoli should be parallel to image receptor

patient’s foot and leg should be medially rotated ~15-20 degrees to demonstrate ankle mortise, and 40 degrees to demonstrate bony structure

Question 17

acroosteolysis

definition

Answer 17

• resorption of the distal phalangeal tufts
  
  • (acro- ‘tip’, osteo- ‘bone’, lysis- ‘destruction/loss’)
• may have the appearance of a cone as the tip is whittled down and resorbed → in severe cases, the phalanges may be completely destroyed

Question 18

acroosteolysis

associated conditions

Answer 18

• scleroderma
• hyperparathyroidism
• psoriatic arthritis

Question 19

acromegaly

radiographic findings

Answer 19

results from excess growth hormone in adults

Radiographic findings:

• soft tissue and osseous structures growing larger in size
• increased width of the heel pad, enlarged metatarsal heads and shafts, and spur formation is commonly seen
• growth and widening of the distal phalangeal tufts

Question 20

average base of gait

Answer 20

2-4 inches

(in order for the lateral shift of the body to be properly accepted by the limb)

defined as the horizontal distance from one heel-strike to the next heel-strike