Biomechanics & Radiology Flashcards
role of pretibial muscles at contact period of gait
(TA, EDL, EHL)
- decelerate ankle plantarflexion
- decelerate pronation & provide even weight-bearing from lateral to medial side of foot
- provide unstable midtarsal joint for shock absorption and adaptation (mobile adaptor)
- absorb impact loads from the floor
*TA muscle generates the largest torque around the ankle joint → followed by EDL and EHL
time constant T2
define
- 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
dephasing
process of protons falling out-of-sync with each other at different rates
time constant T1
define
how soon the protons realign w/ the static magnetic field (B0) following a radio frequency excitation pulse
characteristic radiographic finding of
bipartite medial cuneiform
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)
Isherwood projections
use and views
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
coleman block:
if varus foot assumes more rectus hindfoot when first ray is offloaded →
this result demonstrates forefoot contribution in the varus hindfoot deformity
sx: lateral ankle stabilization combined w/ a dorsiflexory wedge osteotomy of the 1st metatarsal
coleman block:
if varus foot remains in varus hindfoot when first ray is offloaded →
indicates varus position is fixed in the rearfoot itself
sx: lateralizing calcaneal osteotomy (e.g. Dwyer) or lateral displacement osteotomy is indicated
radiographic signs of bone graft failure
- graft or fixation movement
- dissolution of the graft
- sclerosis
radiographic signs of progressing graft to host integration
- 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
radiodensity of bone graft
- cancellous bone grafts should initially appear more radiolucent
- cortical bone grafts appear more radiodense
“bone within bone”
appearance (dysplasia)
OSTEOPETROSIS
aka Albers-Schonberg disease
“bone islands”
multiple well-defined sclerotic lesion in bone
Osteopoikilosis
“candle wax”
appearance with sclerosis in the periphery
Melorheostosis
“linear bands of sclerosis w/in bone”
Osteopatha striata
central ray location during
NWB Medial Oblique View of Ankle
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
acroosteolysis
definition
-
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
acroosteolysis
associated conditions
- scleroderma
- hyperparathyroidism
- psoriatic arthritis
acromegaly
radiographic findings
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
average base of gait
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
