Upper and Lower Limb Prosthesis Fabrication and Alignment
Scope
Component selection, fabrication sequence, and bench, static and dynamic alignment for upper and lower limb prostheses.
Lower limb
- Transtibial: PTB, TSB and KBM designs; suspension by pin/lanyard, suction, sleeve or corset. Set the foot with 5–7° toe-out and slight socket flexion at bench alignment.
- Transfemoral: quadrilateral or ischial containment socket; knee units (single-axis, polycentric, microprocessor); feet (SACH, energy-storing).
- Alignment sequence: bench → static (patient standing, check ground reaction force) → dynamic (gait observation). Adjust one variable at a time and re-check.
Upper limb
Body-powered systems use a harness and Bowden cable; myoelectric systems use surface electrodes and a battery. Transradial socket length is usually about 50% of forearm length; terminal devices include hooks, hands and task-specific tools.
Worked example
A transfemoral prosthesis is bench-aligned with 5° socket flexion and 7° toe-out. On walking, the patient shows early knee flexion and a forward trunk lean. The foot is found set at 15° toe-out. The excessive toe-out moves the ground reaction force behind the knee and reduces stance stability. Correct the foot to 7°, re-check bench alignment, then retest dynamically.
Traps
Changing several alignment variables at once; confusing bench and dynamic alignment; over-flexing the socket to hide a contracture; forgetting to check suspension before gait; fitting an upper-limb device without testing control-site reach.