Key Clinical Formulas & Scores
K0: Does not have ability or potential to transfer or ambulate — prosthesis does not improve quality of life
K1: Ability to use prosthesis for transfers or level surfaces at fixed cadence — household ambulator
K2: Ability to traverse low-level environmental barriers (curbs, uneven surfaces) — limited community ambulator
K3: Ability to traverse most environmental barriers — variable cadence community ambulator
K4: Ability to exceed basic ambulation skills — high impact/variable demand — child, active adult, athlete
Determines Medicare coverage for prosthetic components
Residual limb volume changes: morning (smaller) to afternoon (larger)
Shrinker sock: reduces edema, shapes limb post-amputation
Adjustable socket systems: accommodate volume fluctuations
Target: maintain total contact, even pressure distribution, no pistoning
Pistoning: limb moves within socket → skin breakdown, poor control
Transfemoral (above-knee): 65-80% increased energy cost of walking
Transtibial (below-knee): 25-40% increased energy cost
Bilateral transtibial: 50-70% increased
Bilateral transfemoral: 120-150%
Normal walking: ~4.5 METs. High amputees may require wheelchair for energy conservation
Correlates with K-level assignment and prosthetic component selection
Hip hiking: abduction contracture, short prosthesis, weak hip abductors
Circumduction: long prosthesis, abduction contracture, weak hip flexion
Lateral trunk bend: short prosthesis, inadequate suspension, poor fit
Foot slap: weak dorsiflexion, loose plantar flexion bumper
Vaulting: long prosthesis, inadequate knee flexion, poor suspension
Asymmetric step length: hip flexion contracture, pain, inadequate knee control
PTB (Patellar Tendon-Bearing): pressure concentrated on patellar tendon, medial flare, popliteal fossa. Traditional transtibial design
TSB (Total Surface Bearing): pressure distributed over entire residual limb surface. Requires accurate volumetric assessment
Sub-ischial socket: encompasses ischial seat — improves suspension and weight-bearing
Vacuum suspension: air evacuation improves suspension, proprioception, volume management
Core Concepts
Levels of Lower Limb Amputation
Partial foot: transmetatarsal (Chopart), Lisfranc — preserves ankle, best function. Transtibial (below-knee): preserves knee — better energy efficiency, most common. Knee disarticulation (through-knee): long lever arm, good for bilateral amputees and children. Transfemoral (above-knee): highest energy cost. Hip disarticulation and hemipelvectomy: most extensive, highest prosthetic challenge. Amputation level determined by vascular viability, infection control, rehabilitation potential, and patient goals.
Prosthetic Components — Lower Limb
Suspension: pin/lock (mechanical), suction/vacuum, lanyard, sleeve. Knee joints: single-axis (locked — high stability, low function), polycentric (multi-axis — natural gait, stable stance), microprocessor-controlled (MPK — C-Leg, Rheo Knee — adaptive resistance, stumble recovery, safest). Feet: SACH (solid ankle cushion heel — basic), dynamic response (energy-storing — Flex-Foot — running, active users), microprocessor-controlled (Proprio Foot — adaptive terrain). Selection based on K-level, activity demands, cognitive ability, balance, and patient goals.
Orthotics — Principles and Applications
Lower limb: AFO (ankle-foot orthosis) — foot drop (stroke, CP), KAFO (knee-ankle-foot) — knee instability, HKAFO (hip-knee-ankle-foot) — scoliosis, paraplegia. Spinal: TLSO (thoracolumbosacral) — scoliosis, spinal fractures. Upper limb: WHO (wrist-hand) — wrist drop, resting hand splints. Orthotic principles: three-point pressure systems, total contact, offloading, control of motion, assistance of motion. Materials: thermoplastic, carbon fiber, 3D-printed custom devices. Gait analysis with orthotic tuning improves outcomes.
Clinical Case Studies
Case 1: Traumatic Transtibial Amputation
Patient: 28-year-old male, motorcycle accident, traumatic left transtial amputation (BKA), 6 weeks post-op. Residual limb well-healed, volume stable. Previously active (construction worker, recreational runner). Vascularly intact, good range of motion at hip and knee. K-level assessment: K3 potential (community ambulator, motivated, young).
Prosthetic Plan: Socket: TSB sub-ischial design with vacuum suspension. Knee: MPK (microprocessor-controlled) for community ambulation and safety. Foot: energy-storing (carbon fiber) for active lifestyle. Components selected for K3 level with goal of returning to work. Rehabilitation: 4-6 weeks gait training (parallel bars → assistive devices → independence), stairs, uneven terrain, community reintegration. Prosthetic training: donning/doffing, skin care, residual limb maintenance, activity progression.
Case 2: Diabetic Transfemoral Amputation with Poor Rehabilitation Potential
Patient: 68-year-old male, diabetic with PVD, right transfemoral amputation (AKA), diabetes type 2 × 20 years, retinopathy, nephropathy (CKD 3), BMI 32, poor balance, uses wheelchair full-time. K-level: K1 (household ambulator) or K2 (limited community). Cognitive impairment (mild dementia). Limited social support.
Prosthetic Plan: Socket: ischial containment with pin/lock suspension (simple, reliable, cost-effective). Knee: polycentric with stance-phase control and manual lock for safety. Foot: SACH or single-axis (stable, predictable, low maintenance). Rehabilitation: focus on transfers, short-distance household ambulation, wheelchair mobility as primary means of mobility. Goals: improve quality of life, reduce caregiver burden, prevent contractures. Palliative approach if rehabilitation prognosis poor. Medicare coverage: components justified by functional potential (K1-K2).
Case 3: Orthotic Management of Stroke with Foot Drop
Patient: 72-year-old male, left-sided hemiparesis 6 months post-ischemic stroke, foot drop (weak dorsiflexors, MMT 2/5), spasticity MAS grade 1+ in plantarflexors. Falls × 2 in past month due to tripping on affected side. Goals: safer gait, prevent falls, improve walking speed.
Orthotic Plan: Custom molded AFO (ankle-foot orthosis) — posterior leaf spring design for dorsiflexion assistance during swing, free dorsiflexion during stance, controls plantarflexion spasticity. Alternatively: hinged AFO for more active patients. Gait training with orthotic: PT focusing on heel strike, weight acceptance, step length symmetry. Goal: prevent contracture, improve gait kinematics, reduce fall risk. Monitor for skin breakdown (stroke patients have sensory deficits). Reassess as neurological recovery occurs (6-12 months).
Practice Questions
A: K3 — community ambulator who can traverse most environmental barriers. K3 patients qualify for more advanced components (MPK, dynamic response feet) than K1-K2.
A: Vacuum suspension creates negative pressure between socket and liner, improving suspension (eliminating pistoning), enhancing proprioception, managing limb volume fluctuations, and improving gait symmetry and energy efficiency.
A: Hip hiking indicates compensatory for prosthesis that is too long or inadequate knee flexion during swing phase. Other causes: abduction contracture, weak hip abductors. Check prosthetic length and knee unit function.
A: MPK provides adaptive resistance based on real-time gait analysis, offering stumble recovery, variable cadence walking, and safest gait for K3 ambulators. Particularly valuable for uneven terrain, stairs, and community ambulation.
A: Custom molded posterior leaf spring AFO. Provides dorsiflexion assist during swing phase, controls plantarflexion spasticity, prevents contracture. Alternative: hinged AFO for more active patients. Off-the-shelf prefabricated AFOs may be used temporarily.