Prosthetics: Principles, Components, and Fitting Concepts
Core concepts
Prosthetic care begins with the residual limb, not the device. Candidates must understand residual limb assessment (length, shape, volume stability, skin integrity, sensation, and bony prominences), socket design (patellar-tendon-bearing for transtibial, ischial containment for transfemoral), suspension mechanisms (suction, pin/lanyard, sleeve, belt, anatomic), and the prosthetic foot/ankle and knee componentry that match the patient's K-level (activity potential). Know the difference between endoskeletal (modular pylon) and exoskeletal (hard shell) construction, and why alignment (bench, static, dynamic) is a process rather than a one-time event.
Traps to watch
Questions often test whether you recognize volume fluctuation as the leading cause of fit failure, not component choice. Another common trap is confusing K-level with age or diagnosis: a fit 70-year-old can be a K3 while a young patient may be K1. Distinguish prosthetic knee stances: stance-control and microprocessor knees address different problems than mechanical friction knees. Watch for questions on skin breakdown causes (shear vs pressure vs friction) and on when a new socket is indicated versus a liner or sock-ply adjustment.
Worked example / rule of thumb
A transtibial patient reports the limb "pistons" during walking and skin redness at the distal tibia. Rule of thumb: excessive pistoning plus distal pressure points to insufficient suspension and/or a socket that has become too large as volume decreased. First step is to check suspension and add sock ply or adjust the liner; only if fit cannot be restored is a new socket justified. Remember: assess limb, then suspension, then alignment, then components.
Exam focus
Expect terminology questions on socket types, suspension, and component categories, plus scenario items asking for the most appropriate next action.