COF Orthotic Fitting Principles 3 — Questions and Answers
Question 1: When fitting a knee-ankle-foot orthosis (KAFO), the knee joint should typically be set to which position for a patient with quadriceps weakness?
- 5 degrees of flexion to reduce energy cost
- Full extension (0 degrees) to provide stability during stance (Correct answer)
- 10 degrees hyperextension to lock passively
- 15 degrees flexion to promote gait pattern
Correct answer: Full extension (0 degrees) to provide stability during stance
Setting the knee joint at 0 degrees (full extension) provides a stable base for stance phase when quadriceps are too weak to prevent knee buckling.
Question 2: A patient with drop foot requires an AFO. Which AFO design preserves the most sagittal-plane motion while still preventing foot drop?
- Solid ankle AFO with anterior shell
- Hinged AFO with a dorsiflexion assist spring (Correct answer)
- Posterior leaf spring AFO
- Ground-reaction AFO with solid ankle
Correct answer: Hinged AFO with a dorsiflexion assist spring
A hinged AFO with dorsiflexion assist spring allows plantarflexion during loading response while providing active assistance into dorsiflexion during swing phase.
Question 3: In orthotic fitting, what does the term 'trim line' refer to?
- The final edge cut of the thermoplastic orthosis that determines its borders and flexibility (Correct answer)
- The measurement from heel to first metatarsal head
- The line drawn on the patient's skin during casting
- The boundary of the shoe's last pattern
Correct answer: The final edge cut of the thermoplastic orthosis that determines its borders and flexibility
The trim line is the edge of the thermoplastic material after cutting, and its location determines the rigidity, flexibility, and anatomical coverage of the orthosis.
Question 4: Which material property is most important when selecting thermoplastic for a pediatric AFO that will undergo frequent adjustments?
- High rigidity for maximum support
- Reheating and reshaping capability (thermoplasticity) with low creep (Correct answer)
- Maximum thinness for cosmetic appearance
- High coefficient of friction on the inner surface
Correct answer: Reheating and reshaping capability (thermoplasticity) with low creep
Pediatric orthotics require frequent modifications as the child grows, so materials that can be reheated and reshaped without losing structural integrity are preferred.
Question 5: A patient is fitted with a cervical orthosis. Which design provides the GREATEST restriction of cervical flexion and extension?
- Soft foam collar
- Philadelphia collar
- Halo vest orthosis (Correct answer)
- Miami J collar
Correct answer: Halo vest orthosis
The halo vest orthosis is the most rigid cervical immobilization device, providing approximately 94% restriction of flexion/extension compared to soft collars' ~26%.
Question 6: During gait analysis for orthotic prescription, 'calcaneal eversion' during midstance is best corrected with which device feature?
- Forefoot valgus post
- Rearfoot varus wedge or medial heel skive (Correct answer)
- Metatarsal dome
- Toe spreader
Correct answer: Rearfoot varus wedge or medial heel skive
A rearfoot varus wedge or medial heel skive tilts the calcaneus toward inversion, directly correcting excessive eversion during the midstance phase of gait.
Question 7: When evaluating orthotic fit, 'pistoning' in an AFO refers to what problem?
- The ankle joint axis is misaligned with the anatomical axis
- The orthosis moves up and down on the limb during gait due to improper suspension (Correct answer)
- The trim line is cutting into the malleoli
- The calf band is applying excessive pressure
Correct answer: The orthosis moves up and down on the limb during gait due to improper suspension
Pistoning describes vertical movement of the AFO on the limb during walking, indicating inadequate suspension from the shoe or insufficient proximal containment.
COF Orthotic Fitting Principles 3
When fitting a knee-ankle-foot orthosis (KAFO), the knee joint should typically be set to which position for a patient with quadriceps weakness?