30 - Orthotic Scanning Flashcards
Goals of orthotic scanning
- Review the literature to determine evidence based medicine (EBM) criteria for foot imaging
- Evaluate current foot imaging techniques to determine if EBM criteria met
- Review and recommend digital foot scanners based on their ability to meet the EBM criteria for capturing foot images
Questions to ask
Not a lot of great research on this topic
- What do I need to capture to make a clinically effective foot orthosis?
- Will a particular digital imager capture this information?
- Can you achieve optimum clinical outcomes?
Casting vs scanning time and cost
- Casting takes more time (3 weeks), scanning is a quick procedure (10 days)
- The cost of staff and your own time is greater for casting
EBM casting criteria KNOW THIS
1 The foot image must be captured in a NWB, STJ neutral position**
#2 The posterior heel must be captured to allow frontal plane correction of the orthosis o FF:RF balancing
#3 The foot image must obtain a precise 3D representation of the foot’s plantar aspect o So you can get an orthotic that will have full contact with the arch
o The first MPJ is a ginglymoid arthrodial (hinge then sliding joint)
o In order for the sliding motion to occur, the first metatarsal must be PLANTARFLEXED
o If this is not plantarflexed, you will get first MPJ jamming and pain
Comparison of NWB plaster vs SWB foam (simulated WB)
NWB plaster casting was superior to foam box SWB casting
o SWB casting resulted in artificial varus
o NOT an appropriate way to cast for a functional orthotic
NWB casting
o Good agreement with the clinically measured FF:RF
o SWB Foam impressions had poor FF:RF agreement and the SWB foot resulted in an artificial increase in varus
Effect of Forefoot and Rearfoot Wedging on Plantar Fascial Strain
- 6 degree wedges (medial and lateral, forefoot and rearfoot)
- Plantar fascial strain measured with transducer
Plantar fascia strain
- Decreased with lateral forefoot wedge
- Increased with medial forefoot wedge
- Rearfoot wedges had no significant effect
- The most effective way to decrease strain on the plantar fascia is to evert the forefoot
3D representation of the foot
The foot image must capture a precise 3D representation of the plantar aspect of the foot
- Total contact, rigid orthoses decrease metatarsal head force most effectively
- Orthoses that conform closely to the arch reduce plantar fascial tension
Orthotic arch contour and plantar fascial strain
Orthotic arch contour and plantar fascial strain
- Measured tension in plantar aponeurosis via strain gauge
- Compared five orthoses and shoe only
Studies support total contact orthoses for the following conditions
o Plantar fasciitis o Metatarsalgia o Neuroma o Diabetic ulcerations o Functional hallux limitus o Tarsal Tunnel Syndrome
Why first ray should be plantarflexed during casting
Decreased 1st MPJ dorsiflexion resulted when 1st ray plantarflexion was limited.
When the first ray was allowed to plantarflex there was an increase in available first MPJ dorsiflexion
Rearfoot Eversion and Hallux Dorsiflexion
o Eversion of the Rearfoot will lower the maximal hallux dorsiflexion
o If we don’t get the hindfoot orthotic right, it can drive an abnormal forefoot
o If we cause a rearfoot eversion, it will lead to pathologic hallux dorsiflexion and there will be decreased motion (limitus) and possibly pain in the first MPJ
Techniques that do NOT meet EBM criteria
- Contact Digitation
- Footprints
- White Light Scanners
Contact digitation
o Does not capture Posterior Heel
o SWB leads to dorsiflexion of 1st ray
o NOT adequate for a functional orthotic
Footprints
Footprints CANNOT predict arch height (this is what the good feet store does)
o Hawes, 1992: Measurements obtained from the footprints were invalid as a basis for predicting or categorizing arch height.
o Chu, 1995: 49% of arch height variance can be explained by digital footprints
o McPoil, 2006: Plantar surface contact area can explain only 27% of medial longitudinal arch height
