MPT Gait and Prosthetics 2 — Questions and Answers
Question 1: Which phase of the gait cycle is typically reduced in stride length by a patient with significant hip flexion contracture?
- Terminal stance (Correct answer)
- Loading response
- Mid-swing
- Pre-swing
Correct answer: Terminal stance
Hip flexion contracture reduces hip extension in terminal stance, causing the patient to prematurely advance off the stance limb and shorten the step length of the contralateral limb.
In terminal stance, the hip normally extends to approximately 20 degrees behind the trunk. A hip flexion contracture limits this extension, causing the pelvis to anteriorly tilt and the lumbar spine to hyperlordose as a compensation. The patient effectively falls forward prematurely, reducing stride length. This pattern is commonly seen in patients with spastic cerebral palsy, prolonged bed rest, or hip arthroplasty. Thomas test quantifies hip flexor flexibility, guiding stretching and strengthening interventions.
Question 2: A vaulting gait deviation (rising on the toes of the sound limb during prosthetic swing) is caused by:
- Prosthetic foot toe break too rigid
- Prosthesis being too long (Correct answer)
- Excessive dorsiflexion of the prosthetic foot
- Socket volume loss
Correct answer: Prosthesis being too long
Vaulting occurs when the prosthesis is too long, requiring the patient to rise on the toes of the sound limb during prosthetic swing phase to allow the prosthetic foot to clear the ground.
Vaulting is a swing-phase deviation where the stance limb goes into plantar flexion to create ground clearance for a prosthesis that is too long or insufficiently flexed during swing. Causes include prosthesis that is truly too long, insufficient knee flexion in transfemoral prosthesis, or inadequate prosthetic foot dorsiflexion. Other compensations for inadequate clearance include hip hiking, circumduction, and trunk lean. PTs identify the root cause to recommend appropriate prosthetic modification or gait training.
Question 3: In normal gait, the center of mass reaches its highest point during which phase?
- Loading response
- Mid-stance (Correct answer)
- Pre-swing
- Mid-swing
Correct answer: Mid-stance
The center of mass reaches its highest vertical point during mid-stance (single-limb support), when the body vaults over the relatively straight stance limb like an inverted pendulum.
Normal gait uses an inverted pendulum mechanism during single support — kinetic energy converts to potential energy as the center of mass rises over the extended stance limb, then converts back during double support. The center of mass oscillates approximately 5 cm vertically and 5 cm laterally during normal gait. This energy exchange reduces metabolic cost. Pathological gaits increase center of mass displacement and metabolic cost. Understanding center of mass dynamics is essential for analyzing gait efficiency and designing rehabilitation programs.
Question 4: Which prosthetic foot design is best suited for a highly active K4-level transtibial amputee returning to running?
- SACH (solid ankle cushion heel) foot
- Single-axis foot
- Energy-storing and return carbon fiber foot (Correct answer)
- Multi-axial foot
Correct answer: Energy-storing and return carbon fiber foot
Carbon fiber energy-storing and return (ESR) feet are best suited for K4-level (high activity, sports) amputees. They store elastic energy during loading and return it during push-off, enabling running.
The K-level classification (K0-K4) guides prosthetic prescription. K4 patients (high activity, athletes) benefit from carbon fiber ESR feet that deflect under load and spring back during push-off. SACH feet are appropriate for K1 limited household ambulators. Single-axis feet help with uneven terrain for K2-K3 users. Multi-axial feet provide triplanar motion for active community ambulators. The NPTE tests K-level definitions and appropriate component selection.
Question 5: Scissor gait, characterized by the legs crossing the midline during swing, is most commonly associated with:
- Lower motor neuron lesion
- Cerebellar ataxia
- Spastic diplegic cerebral palsy (Correct answer)
- Peripheral neuropathy
Correct answer: Spastic diplegic cerebral palsy
Scissor gait is a hallmark of spastic diplegia (commonly seen in cerebral palsy) where bilateral hip adductor and flexor spasticity causes the legs to cross the midline during swing.
In spastic diplegic CP, bilateral hypertonicity of hip adductors (particularly adductor longus and brevis) causes the thighs to adduct and internally rotate during swing, with the feet crossing the midline. Associated findings include equinus foot posture (from gastrocnemius spasticity) and crouch gait. PT interventions include spasticity management (serial casting, orthotics, Botox referral), strengthening of antagonist muscles, and gait training. Scissor gait increases fall risk and energy expenditure.
Question 6: The push-off power generated during terminal stance and pre-swing is primarily produced by which muscle group?
- Quadriceps
- Hamstrings
- Plantar flexors (gastrocnemius and soleus) (Correct answer)
- Hip flexors
Correct answer: Plantar flexors (gastrocnemius and soleus)
The plantar flexors (gastrocnemius and soleus) generate the primary propulsive power burst during terminal stance and pre-swing, providing forward propulsion and contributing to swing initiation.
Biomechanical analyses using instrumented gait analysis show the plantar flexors generate the largest power burst of any muscle group during normal gait, peaking at approximately 3-4 W/kg at terminal stance and pre-swing. This propulsive burst accelerates the limb into swing and contributes to forward progression. Weakness of plantar flexors (as in Charcot-Marie-Tooth disease, post-stroke, or post-Achilles repair) significantly impairs gait speed and increases energy cost.
MPT Gait and Prosthetics 2
Which phase of the gait cycle is typically reduced in stride length by a patient with significant hip flexion contracture?