PO-04 · Transtibial Prosthetics

Transtibial Prosthetics. Part of the Prosthetics & Orthotics series of the Reflex PM&R Board Review podcast. Audio corrections: (1) In the audio: and also the popliteal fossa in the back, the massive gastrocnemius and soleus bulk, and the anteromedial tibial surface. — Correct: The fifth pressure-tolerant area is the lateral shaft of the fibula, not the anteromedial tibial surface. The medial tibial *shaft*, unlike the flare, is subcutaneous and belongs with the relief areas. (2) In the audio: The patient causes for this same deviation are a hip flexion contracture or weak quadriceps. — Correct: For excessive knee flexion (drop-off) the patient cause to look for is a knee flexion contracture, which this chapter calls the most common post-amputation complication, together with weak quadriceps. Hip flexion contracture is the patient cause of a *short prosthetic step*, which the episode states correctly a few lines later. (3) In the audio: it gives near zero pistoning. To be specific with the numbers, elevated vacuum allows only 1.3 centimeters of pistoning compared to 1.8 centimeters for passive suction. — Correct: The numbers are right; the word around them is wrong. 1.3 cm and 1.8 cm are real published figures, but they are total axial bone-socket displacement measured under digital video fluoroscopy across loading from zero to full body weight, not gait pistoning. 1.3 cm is more than a finger's breadth and is not near zero, and the advantage arose almost entirely during initial loading. Gait pistoning by motion capture is an order of magnitude smaller, roughly 1 to 6 millimeters. (4) In the audio: elevated vacuum ... pin lock produces the most pistoning. — Correct: Pin lock is not established as the worst of the three. No study has compared elevated vacuum, passive suction and pin lock in a single protocol, and the one study using the same fluoroscopic paradigm found pin lock numerically better than a suction sleeve, not worse (18.24 mm vs 21.42 mm total axial displacement, p = 0.21). The three-way ranking is an inference stitched across incompatible measurement methods. (5) In the audio: 78% of patients report some blister formation with elevated vacuum. — Correct: The 78% figure is a survey of practitioners, not of patients. A practitioner reporting that they have seen blistering is a different quantity from a patient reporting that they blistered. (6) In the audio: that metabolic demand jumps to 60 to 70 percent more energy — Correct: Traumatic transfemoral is 55 to 65 percent, as oxygen cost per unit distance at self-selected speed. Primary values cluster 49 to 65 percent; 60 to 70 sits above that range and could not be verified as a Waters 1976 value. The transtibial figure it is contrasted with, 10 to 25 percent, is unchanged. The written chapter is correct. Full correction register: https://www.reflexpmr.com/errata. The full companion chapter and a linked board-style Q-bank set for this topic are at https://www.reflexpmr.com/read/PO-04.